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  • 201.
    Lee, Hyung-Seok
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Domeij, Martin
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Allerstam, Fredrik
    Department of Microtechnology and Nanoscience, Chalmers University of Technology.
    Sveinbjörnsson, Einar Ö.
    Department of Microtechnology and Nanoscience, Chalmers University of TechnologyDepartment of Microtechnology and Nanoscience, Chalmers University of Technology.
    1200-V 5.2-m Omega center dot cm(2) 4H-SiC BJTs with a high common-emitter current gain2007In: IEEE Electron Device Letters, ISSN 0741-3106, E-ISSN 1558-0563, Vol. 28, no 11, p. 1007-1009Article in journal (Refereed)
    Abstract [en]

    This letter presents fabrication of a power 4H-SiC bipolar junction transistor (BJT) with a high open-base breakdown voltage BVCEO approximate to 1200 V, a low specific ON-resistance R-SP_ON approximate to 5.2 m Omega . cm(2), and a high common-emitter current. gain beta approximate to 60. The high gain of the BJT is attributed to reduced surface recombination that has been obtained using passivation by thermal silicon dioxide grown in nitrous oxide (N2O) ambient. Reference BJTs with passivation by conventional dry thermal oxidation show a clearly lower current gain and a more pronounced emitter-size effect. BJTs with junction termination by a guard-ring-assisted junction-termination extension (JTE) show about 400 V higher breakdown voltage compared with BJTs with a conventional JTE.

  • 202.
    Lee, Hyung-Seok
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Domeij, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Heinze, Birk
    Chemnitz University of Technology.
    Lutz, Josef
    Chemnitz University of Technology.
    Influence of the base contact on the electrical characteristics of SiC BJTs2007In: 19th International Symposium on Power Semiconductor Devices and ICs, ISPSD'07: Jeju Island; 27 May 2007 through 31 May 2007, 2007, p. 153-156Conference paper (Refereed)
    Abstract [en]

    In this paper, we have investigated how the specific on-resistance and common emitter current gain of SiC BJTs depend on the base contact resistance. The on-state characteristics of SiC BJTs were investigated before and after base contact annealing at different temperatures. The common emitter current gain and specific on-resistance was improved by 23 % and 300 % compared to the values of before base contact annealing, respectively. Large area SiC BJTs (active area 0.0324 cm(2)), have been measured up to 34 A collector current in pulsed mode showing a gain of 35, and a specific on-resistance of 2 8.79 m Omega center dot cm(2)

  • 203.
    Lee, Hyung-Seok
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Domeij, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lu, J
    Investigation of TiW contacts to 4H-SiC bipolar junction devices2006In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 527-529, p. 887-890Article in journal (Refereed)
    Abstract [en]

    One important challenge in SiC Bipolar Junction Transistor (BJT) fabrication is to form good ohmic contacts to both n-type and p-type SiC. In this paper, we have examined contact study in a SiC BJT process with sputter deposition of titanium tungsten contacts to both n-type and p-type regions followed by annealing at different temperatures between 750 T and 950 T. The contacts were characterized using linear transmission line method (LTLM) structures. To see the formation of compound phases, X-ray Diffraction (XRD) theta-2 theta scans were performed before and after annealing. The results indicate that 5 minutes annealing at 950 T of the n(+) contact is sufficient whereas the p(+) contacts remain non-ohmic after 30 minutes annealing. The n(+) emitter structure contact resistivity after 5 min annealing with 750 degrees C and 950 degrees C was 1.08 x 10(-3) Omega cm(2) and 4.08 x 10(-4) Omega cm(2), respectively. Small amorphous regions of silicon and carbon as well as titanium tungsten carbide regions were observed by high-resolution transmission electron microscopy (HRTEM), whereas less carbide formation and no amorphous regions were found in a sample with unsuccessful formation of TiW ohmic contacts.

  • 204.
    Lee, Hyung-Seok
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Domeij, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Sveinbjörnsson, Einar Ö.
    Department of Microtechnology and Nanoscience, Chalmers University of Technology.
    A comparative study of surface passivation on SiC BJTs with high current gain2007In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 556-557, p. 631-634Article in journal (Refereed)
    Abstract [en]

    The effect of the different types of passivation layers on the current gain of SiC BJTs has been investigated. Measurements have been compared for BJTs passivated with thermal SiO2, plasma deposited (PECVD) SiO2 and BJTs without passivation. The maximum DC current gain of BJTs with thermal SiO2 was about 62 at I-c=20 mA and V-ce=40 V. On the other hand, the BJTs with a passivation by PECVD SiO2 had a DC current gain of only 25. The surface recombination current was extracted from measurements with BJTs of different emitter widths. The surface recombination current of BJTs with a thermally grown oxide was about 25% lower than unpassivated BJTs and 65% lower than that of PECVD passivated BJTs.

  • 205.
    Lee, Hyung-Seok
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Koo, Sang-Mo
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Danielsson, Erik
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Domeij, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Simulation study of 4H-SiC junction-gated MOSFETs from 300 K to 773 K2004In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 457-460, p. 1437-1440Article in journal (Refereed)
    Abstract [en]

    The electrical characteristics of 4H-SiC junction gated MOSFETs (JMOSFETs) have been investigated by 2-dimensional device simulations. The results have been compared with measured data from 300 K to 573 K. and applied to predict the device performance up to 773 K. Simulation results predict a decrease of the saturation current to 7.5% of its room temperature value as the temperature increases from 300 K to 773 K. However, by applying a proper voltage on the top MOS gate, carrier accumulation can be used to compensate for the reduced mobility and a constant drain current can be maintained over the whole temperature range (300 K - 773 K), where the main deviations for different temperatures are at low drain voltages before the drain current saturates.

  • 206. Lee, S. -K
    et al.
    Danielsson, Erik
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Palmquist, J. -P
    Högberg, H.
    Jansson, U.
    The formation and characterization of epitaxial titanium carbide contacts to 4H-SiC2000In: Materials Research Society Symposium - Proceedings, San Francisco, CA, 2000, Vol. 622, p. T691-T696Conference paper (Refereed)
    Abstract [en]

    Epitaxial TiC Ohmic and Schottky contacts to 4H-SiC were formed by a new deposition method, UHV co-evaporation with Ti and C60, at low temperature (< 500°C). We achieved a contact resistivity of 2 × 10-5 Ωcm2 at 25°C for as deposited Ohmic contacts on Al ion implanted 4H-Silicon carbide. The rectifying behavior of TiC Schottky contacts was also investigated using I-V and C-V. The measured Schottky barrier height (SBH) was 1.26 eV for n-type and 1.65 eV for p-type 4H-SiC using C-V measurements for frequencies ranging from 1kHz to 1MHz. LEED, RBS, XPS, and XRD measurements were performed to analyze composition ratio, interface reaction, and structural properties of the TiC epitaxial layer.

  • 207. Lee, S. K.
    et al.
    Koo, S. M.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Ohmic contact formation on inductively coupled plasma etched 4H-silicon carbide2002In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 31, no 5, p. 340-345Article in journal (Refereed)
    Abstract [en]

    We report on the investigation of ohmic contact formation using sputtered titanium-tungsten contacts on an inductively coupled plasma (ICP) etch-damaged 4H-SiC surface. Transfer length method (TLM) measurements were performed to characterize how ICP-etch damage affects the performance of ohmic contacts to silicon carbide. In order to recover etch damage, high-temperature oxidation (1250degreesC for 1 h) was evaluated for one of the samples. Some of the etch damage was recovered, but it did not fully recover the etch damage for the sample etched with medium platen power (60 W). From our TLM measurements, the specific contact resistance (rho(C) of sputtered titanium tungsten on highly doped n(+)-type 4H-SiC epilayers with a doping of 1.1 X 10(19) cm(-3) for the unetched reference sample, 30-W etched, and 60-W etched with and without sacrificial oxidation was as low as 3.8 X 10(-5) Omegacm(2), 3.3 X 10(-5) Omega cm(2), 2.3 X 10(-4) Omegacm(2), and 1.3 X 10(-3) Omegacm(2), respectively. We found that the low-power (30 W) ICP-etching process did not affect the formation of ohmic contacts, and we did not observe any difference between the unetched and the 30-W etched sample from our TLM measurements, having the same value of the rho(C). However, medium-platen-power (60 W) ICP etching showed significant influence on the ohmic contact formation. We found that the specific contact resistance is highly related to the surface roughness and quality of the metals, and the lower, specific contact resistance is due to the smoother and denser ohmic contacts.

  • 208. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Danielsson, E.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Palmquist, J. P.
    Hogberg, H.
    Jansson, U.
    Electrical characterization of TiC ohmic contacts to aluminum ion implanted 4H-silicon carbide2000In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 77, no 10, p. 1478-1480Article in journal (Refereed)
    Abstract [en]

    We report on the investigation of epitaxial TiC ohmic contacts to Al ion implanted 4H-SiC. TiC ohmic contacts were formed by coevaporation of Ti and C-60 at low temperature (< 500 degrees C). A sacrificial silicon nitride (Si3N4) layer was deposited on the silicon carbide substrate prior to Al implantation in order to reach a high Al dopant concentration at the surface while maintaining a low dose. The combination of epitaxially grown TiC and the silicon nitride layer resulted in a promising scheme to make low resistivity ohmic contacts. The lowest contact resistivity (rho(C)) and sheet resistance (R-s) of the implanted layer at 25 degrees C were as low as 2 x 10(-5) Ohm cm(2) and 0.6 k Ohm/square, respectively.

  • 209. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Microscopic mapping of specific contact resistances and long-term reliability tests on 4H-silicon carbide using sputtered titanium tungsten contacts for high temperature device applications2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, no 1, p. 253-260Article in journal (Refereed)
    Abstract [en]

    We report on the microscopic mapping of specific contact resistances (rho(c)) and long-term reliability tests using sputtered titanium tungsten (TiW) ohmic contacts to highly doped n-type epilayers of 4H-silicon carbide. The TiW ohmic contacts showed good uniformity with low contact resistivity of 3.3x10(-5) Omega cm(2). Microscopic mapping of the rho(c) showed that the rho(c) had a distribution that decreased from the center to the edge of the wafer. This distribution of the rho(c) is caused by variation of the doping concentration of the wafer. Sacrificial oxidation at high temperature partially recovered inductively coupled plasma etch damage. TiW contacts with platinum and gold capping layers have stable specific contact resistance at 500 and 600 degreesC in a vacuum chamber for 308 h.

  • 210. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schottky barrier height dependence on the metal work function for p-type 4H-silicon carbide2001In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 30, no 3, p. 242-246Article in journal (Refereed)
    Abstract [en]

    We investigated Schottky barrier diodes of several metals (Ti, Ni, and Au) having different metal work functions to p-type 4H-SiC (0001) using I-V and C-V characteristics. Contacts showed excellent Schottky behavior with stable ideality factors of 1.07, 1.23, and 1.06 for Ti, Ni, and Au, respectively, in the range of 24 degreesC to 300 degreesC. The measured Schottky barrier height (SBH) was 1.96, 1.41, and 1.42 eV for Ti, Ni, and Au, respectively, in the same temperature range from IV characteristics. Based on our measurements for p-type 4H-SiC, the SBH (phi (Bp)) and metal work functions (phi (m)) show a linear relationship of phi (Bp) = 4.58 - 0.61 phi (m) and phi (Bp) = 4.42 - 0.54(phim) for I-V and C-V characteristics at room temperature, respectively. We observed that the SBH strongly depends on the metal work function with a slope (S = phi (Bp)/phi (m)) of 0.58 even though the Fermi level is partially pinned. We found the sum of the SBH (phi (Bp) + phi (Bn) = E-g) at room temperature for nand p-type 4H-SiC to be 3.07 eV, 3.12 eV, and 3.21 eV for Ti, Ni, and Au, respectively, using I-V and C-V measurements, which are in reasonable accord with the Schottky-Mott limit.

  • 211. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schottky diode formation and characterization of titanium tungsten to n- and p-type 4H silicon carbide2000In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 87, no 11, p. 8039-8044Article in journal (Refereed)
    Abstract [en]

    Titanium tungsten (Ti0.58W0.42) Schottky contacts to both n- and p-type 4H silicon carbide were fabricated using sputtering. The n- as well as p-type Schottky contacts had excellent rectifying characteristics after vacuum annealing at 500 degrees C with a thermally stable ideality factor of 1.06 +/- 0.03 for n-type and 1.08 +/- 0.01 for p-type. The measured Schottky barrier height (SBH) was 1.22 +/- 0.03 eV for n-type and 1.93 +/- 0.01 eV for p-type in the range of 24-300 degrees C. Our results of Ti0.58W0.42 Schottky contacts to both n- and p-type can be explained perfectly by thermionic emission theory and also satisfy the Schottky-Mott model in contrast to earlier works. Capacitance-voltage measurements were also performed and the results were in good agreement with those of current-voltage measurements. In addition, the inhomogeneous behavior with higher ideality factor and lower SBH of p-type Ti0.58W0.42 contacts for as-deposited contacts is explained by using a model with contribution of recombination current originated by lattice defects to thermionic emission current.

  • 212. Lee, S. -K
    et al.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Titanium tungsten (TiW) for Ohmic contacts to n-and p-type 4H-SiC2001In: Materials Research Society Symposium - Proceedings, Boston, MA, 2001, Vol. 640, p. H7.2.1-H7.2.6Conference paper (Refereed)
    Abstract [en]

    In the present work, we investigated sputtered titanium tungsten (TiW) contacts for Ohmic contacts to both n- and p-type 4H-SiC with long-term stability under high temperature (500°C). Epitaxial layers with a doping concentration of 1.3×1019 and 6×1018 cm-3 were used. After high temperature annealing (&gt;950°C) sputtered TiW contacts showed Ohmic behavior with good uniform distribution of the specific contact resistance. We obtained an average specific contact resistance (ρc) of 4×10-5 Ωcm2 and 1.2-1.7×10-4 Ωcm2 for p- and n-type, respectively from linear TLM measurement. We also found some variation of the specific contact resistance and the sheet resistance from our TLM measurement for p-type contacts. We will discuss this behavior with the measurement of SIMS. Long-term stability with a top-cap layer is also discussed.

  • 213. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Aberg, I.
    Magnusson, M. H.
    Deppert, K.
    Wernersson, L. E.
    Samuelson, L.
    Litwin, A.
    Reduction of the Schottky barrier height on silicon carbide using Au nano-particles2002In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 46, no 9, p. 1433-1440Article in journal (Refereed)
    Abstract [en]

    By the incorporation of size-selected Au nano-particles in Ti Schottky contacts on silicon carbide, we could observe considerably lower the barrier height of the contacts. This result could be obtained for both n- and p-type Schottky contacts using current-voltage and capacitance voltage measurements. For n-type Schottky contacts, we observed reductions of 0.19-0.25 eV on 4H-SiC and 0.15-0.17 eV on 6H-SiC as compared with particle-free Ti Schottky contacts. For p-type SiC, the reduction was a little lower with 0.02-0.05 eV on 4H- and 0.10-0.13 eV on 6H-SiC. The reduction of the Schottky barrier height is explained using a model with enhanced electric field at the interface due to the small size of the circular patch and the large difference of the barrier height between Ti and Au.

  • 214. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Moon, B. M.
    Electrical characterization of titanium-based ohmic contacts to 4H-Silicon carbide for high-power and high-temperature operation2002In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 40, no 4, p. 572-576Article in journal (Refereed)
    Abstract [en]

    We report on titanium-based ohmic contacts (titanium carbide. titanium tungsten, and titanium) on both highly doped epilayers (n(+) and p(+)) and Al-ion-implanted layers. The TiC contact layer was epitaxially grown on epilayers as well as an Al-ion-implanted layers of 4H-SiC by co-evaporation Ti and C-60 under an ultra-high vacuum condition at low temperature (<500 degreesC). For comparison and long-term stability test, we also deposited TiW (weight ratio 30 : 710) ohmic contacts to p and n-type epilayers of 4H-SiC. The specific contact resistances (p(c)) were found to be as low as p- 5X10(-6), 2x10(-5), 2x10(-5), 3x10(-4), 4x10(-5), and 1X10(-4) Omegacm(2) for TiC contacts to n(+) epilayers, p(+) epilayers, and Al-ion-implanted layers, Ti contacts to p(+) epilayers, and TiW contacts to p(+) and to n(+) epilayers, respectively, by using linear transmission line method (TLM) measurements. During the long-term reliability tests in a vacuum chamber, we found that evaporated Au capping layers helped to keep the contacts from degrading.

  • 215. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Palmquist, J. P.
    Hogberg, H.
    Jansson, U.
    Low resistivity ohmic titanium carbide contacts to n- and p-type 4H-silicon carbide2000In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 44, no 7, p. 1179-1186Article in journal (Refereed)
    Abstract [en]

    Low resistivity Ohmic contacts of epitaxial titanium carbide to highly doped n- (1.3 x 10(19) cm(-3)) and p- (>10(20) cm(-3)) type epilayer on 4H-SiC were investigated. The titanium carbide contacts were epitaxially grown using coevaporation with an e-beam for Ti and a Knudsen cell for C-60 in a UHV system. A comparison of epitaxial evaporated Ti Ohmic contacts on p(+) epilayer of 4H-SiC is also given. The as-deposited TiC Ohmic contacts showed a good Ohmic behavior and the lowest contact resistivity (rho(C)) was 7.4 x 10(-7) Ohm cm(2) at 200 degrees C for n-type, and 1.1 x 10(-4) Ohm cm(2) at 25 degrees C for p-type contacts. Annealing at 950 degrees C did not improve the Ohmic contact to n-type 4H-SiC, but instead resulted in an increase in rho(C) to 4.01 x 10(-5) Ohm cm(2) at 25 degrees C. In contrast to n-type, after annealing at 950 degrees C the specific rho(C) for p-type SiC reached its lowest value of 1.9 x 10(-5) Ohm cm(2) at 300 degrees C. Our results indicate that co-evaporated TiC contacts to n- and p-type epilayers of 4H-SiC should not require a higher post-annealing temperature, contrary to earlier works. Material characteristics, utilizing X-ray diffraction, Low energy electron diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements are also discussed.

  • 216. Lee, S. K.
    et al.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Palmquist, J. P.
    Jansson, U.
    Low resistivity ohmic contacts on 4H-silicon carbide for high power and high temperature device applications2002In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 60, no 02-jan, p. 261-268Article in journal (Refereed)
    Abstract [en]

    We investigated titanium based ohmic contacts using co-evaporated epitaxial titanium carbide (TiC) on highly doped n(+)- and p(+)-type epilayers as well as Al ion implanted layers for high power and high temperature device application. Epitaxially grown TiC ohmic contacts on epilayers as well as Al implanted layers of 4H-SiC were formed by UHV co-evaporation with Ti and C-60 at low substrate temperature. The specific contact resistance (rho(C)) was as low as 5 x 10(-6), 2 x 10(-5), and 2 x 10(-5) Omegacm(2) for TiC contacts on n(+), on p(+) epilayer, and on Al implanted layer, respectively, using a linear TLM measurement. In addition to TiC, we also investigated TiW (weight ratio 30:70) ohmic contacts to p- and n-type 4H-SiC for the purpose of long-term reliability tests at high temperature. The average rho(C) of sputtered TiW contacts was 4 x 10(-5) for p(+) and n(+) epilayer. We also found that an evaporated top layer (Au or Pt) helps to protect from degradation of the contacts under long-term reliability tests with temperatures of up to 600degreesC in a vacuum chamber.

  • 217. Lee, S. -K
    et al.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Åberg, I.
    Magnusson, M. H.
    Deppert, K.
    Wernersson, L. -E
    Samuelson, L.
    Litwin, A.
    Reduction of the barrier height and enhancement of tunneling current of titanium contacts using embedded Au nano-particles on 4H and 6H silicon carbide2002In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 389-393, no 2, p. 937-940Article in journal (Refereed)
    Abstract [en]

    We have investigated the electrical characteristics of Ti Schottky contacts with embedded Au nano-particles on various types of epilayers of SiC (4H- and 6H-SiC). From our current-voltage (I-V) and capacitance-voltage (C-V) measurements, we observed that Ti Schottky contacts with embedded Au nano-particles had 0.19 eV (n-4H-SiC) and 0.15 eV (n-6H-SiC) lower barrier height than those of particle free Ti Schottky contacts. In order to understand this reduction of the Schottky barrier height (SBH) for Ti Schottky contacts with embedded Au nano-particles, it has been proposed that SBH lowering is caused by an enhanced electric field due to the small size of the Au nano-particles and the large SBH difference. We have also tested these contacts on highly doped n-and p-type SiC material to study ohmic contacts using linear TLM measurements.

  • 218. Leerungnawarat, P.
    et al.
    Cho, H.
    Pearton, S. J.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Effect of UV light irradiation on SiC dry etch rates2000In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 29, no 3, p. 342-346Article in journal (Refereed)
    Abstract [en]

    Inductively Coupled Plasma etching of 4H-SiC under ultraviolet illumination was examined for SF6/Ar and Cl-2/Ar chemistries. Etch rate enhancements up to a factor of 8 were observed with UV light irradiation during Cl-2/Ar etching. The enhancement mechanism is related to photodesorption of SiClx and CClx species. Surface morphologies were unchanged as a result of the UV enhancement with Cl-2/Ar discharges. By contrast, there was no effect of UV irradiation on the SiC etch rates in SF6/Ar plasmas, but the surfaces were typically smoother than those obtained without the ultraviolet illumination. In the SF6/Ar chemistry the rate-limiting steps are either Si-C bond-breaking or supply of fluorine radicals to the surface, and not desorption of the SiFx and CFx etch products.

  • 219. Leerungnawarat, P.
    et al.
    Hays, D. C.
    Cho, H.
    Pearton, S. J.
    Strong, R. M.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Via-hole etching for SiC1999In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 17, p. 2050-2054Article in journal (Refereed)
    Abstract [en]

    Four different F2-based plasma chemistries for high-rate etching of SiC under inductively coupled plasma (ICP) conditions were examined. Much higher rates (up to 8000 #x2009; #xc5; #x2009;min-1) were achieved with NF3 and SF6 compared with BF3 and PF5, in good correlation with their bond energies and their dissociation efficiency in the ICP source. Three different materials (Al, Ni, and indium #x2013;tin oxide) were compared as possible masks during deep SiC etching for through-wafer via holes. Al appears to produce the best etch resistance, particularly when O2 is added to the plasma chemistry. With the correct choice of plasma chemistry and mask material, ICP etching appears to be capable of producing via holes in SiC substrates. #xa9; 1999 American Vacuum Society.

  • 220.
    Lemme, Max C.
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Vaziri, Sam
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Smith, Anderson D.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Li, Jiantong
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rodriguez, Saul
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Graphene for More Moore and More Than Moore applications2012In: IEEE Silicon Nanoelectronics Workshop, SNW, IEEE , 2012, p. 6243322-Conference paper (Refereed)
    Abstract [en]

    Graphene has caught the attention of the electronic device community as a potential future option for More Moore and More Than Moore devices and applications. This is owed to its remarkable material properties, which include ballistic conductance over several hundred nanometers or charge carrier mobilities of several 100.000 cm 2/Vs in pristine graphene. Furthermore, standard CMOS technology may be applied to graphene in order to make devices. Integrated graphene devices, however, are performance limited by scattering due to defects in the graphene and its dielectric environment [1, 2] and high contact resistance [3, 4]. In addition, graphene has no energy band gap (Figure 1) and hence graphene MOSFETs (GFETs) cannot be switched off, but instead show ambipolar behaviour [5]. This has steered interest away from logic to analog radio frequency (RF) applications [6, 7]. This talk will systematically compare the expected RF performance of realistic GFETs with current silicon CMOS technology [8]. GFETs slightly lag behind in maximum cut-off frequency F T,max (Figure 2) up to a carrier mobility of 3000 cm 2/Vs, where they can achieve similar RF performance as 65nm silicon FETs. While a strongly nonlinear voltage-dependent gate capacitance inherently limits performance, other parasitics such as contact resistance are expected to be optimized as GFET process technology improves.

  • 221.
    Lemme, Max C.
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Vaziri, Sam
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Smith, Anderson D.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Alternative graphene devices: Beyond field effect transistors2012In: Device Research Conference (DRC), 2012 70th Annual, IEEE , 2012, p. 24a-24bConference paper (Refereed)
    Abstract [en]

    The future manufacturability of graphene devices depends on the availability of large-scale graphene fabrication methods. While chemical vapor deposition and epitaxy from silicon carbide both promise scalability, they are not (yet) fully compatible with silicon technology. Direct growth of graphene on insulating substrates would be a major step, but is still at a very early stage [1]. This has implications on potential entry points of graphene as an add-on to mainstream silicon technology, which will be discussed in the talk.

  • 222.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Delekta, Szymon Sollami
    Zhang, Panpan
    Yang, Sheng
    Lohe, Martin R.
    Zhuang, Xiaodong
    Feng, Xinliang
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Electronics.
    Scalable Fabrication and Integration of Graphene Microsupercapacitors through Full Inkjet Printing2017In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 11, no 8, p. 8249-8256Article in journal (Refereed)
    Abstract [en]

    A simple full-inkjet-printing technique is developed for the scalable fabrication of graphene-based microsupercapacitors (MSCs) on various substrates. High-performance graphene inks are formulated by integrating the electrochemically exfoliated graphene with a solvent exchange technique to reliably print graphene interdigitated electrodes with tunable geometry and "thickness. Along with the printed polyelectrolyte, poly(4-styrenesulfonic acid), the fully printed graphene-based MSCs attain the highest areal capacitance of similar to 0.7 mF/cm(2), substantially advancing the state-of-art of all-solid-state MSCs with printed graphene electrodes. The full printing solution enables scalable fabrication of MSCs and effective connection of them in parallel and/or in series at various scales. Remarkably, more than 100 devices have been connected to form large-scale MSC arrays as power banks on both silicon wafers and Kapton. Without any extra protection or encapsulation, the MSC arrays can be reliably charged up to 12 V and retain the performance even 8 months after fabrication.

  • 223.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Lemme, Max C.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits. University of Siegen, Germany.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Inkjet Printing of 2D Layered Materials2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 16, p. 3427-3434Article in journal (Refereed)
    Abstract [en]

    Inkjet printing of 2D layered materials, such as graphene and MoS2, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation-assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials.

  • 224.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Mishukova, Viktoriia
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits. Univ Grenoble Alpes, France.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    All-solid-state micro-supercapacitors based on inkjet printed graphene electrodes2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 12, article id 123901Article in journal (Refereed)
    Abstract [en]

    The all-solid-state graphene-based in-plane micro-supercapacitors are fabricated simply through reliable inkjet printing of pristine graphene in interdigitated structure on silicon wafers to serve as both electrodes and current collectors, and a following drop casting of polymer electrolytes (polyvinyl alcohol/H3PO4). Benefiting from the printing processing, an attractive porous electrode microstructure with a large number of vertically orientated graphene flakes is observed. The devices exhibit commendable areal capacitance over 0.1 mF/cm(2) and a long cycle life of over 1000 times. The simple and scalable fabrication technique for efficient micro-supercapacitors is promising for on-chip energy storage applications in emerging electronics.

  • 225.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Naiini, Maziar M.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Vaziri, Sam
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Lemme, Max C.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits. University of Siegen, Germany.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Inkjet Printing of MoS22014In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 24, no 41, p. 6524-6531Article in journal (Refereed)
    Abstract [en]

    A simple and efficient inkjet printing technology is developed for molybdenum disulfide (MoS2), one of the most attractive two-dimensional layered materials. The technology effectively addresses critical issues associated with normal MoS2 liquid dispersions (such as incompatible rheology, low concentration, and solvent toxicity), and hence can directly and reliably write uniform patterns of high-quality (5-7 nm thick) MoS2 nanosheets at a resolution of tens of micrometers. The technology efficiency facilitates the integration of printed MoS2 patterns with other components (such as electrodes), and hence allows fabricating various functional devices, including thin film transistors, photoluminescence patterns, and photodetectors, in a simple, massive and cost-effective manner while retains the unique properties of MoS2. The technology has great potential in a variety of applications, such as photonics, optoelectronics, sensors, and energy storage.

  • 226.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ostling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Precise percolation thresholds of two-dimensional random systems comprising overlapping ellipses2016In: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, E-ISSN 1873-2119, Vol. 462, p. 940-950Article in journal (Refereed)
    Abstract [en]

    This work explores the percolation thresholds of continuum systems consisting of randomly-oriented overlapping ellipses. High-precision percolation thresholds for various homogeneous ellipse systems with different aspect ratios are obtained from extensive Monte Carlo simulations based on the incorporation of Vieillard-Baron's contact function of two identical ellipses with our efficient algorithm for continuum percolation. In addition, we generalize Vieillard-Baron's contact function from identical ellipses to unequal ellipses, and extend the Monte Carlo algorithm to heterogeneous ellipse systems where the ellipses have different dimensions and/or aspect ratios. Based on the concept of modified excluded area, a general law is verified for precise prediction of percolation threshold for many heterogeneous ellipse systems. In particular, the study of heterogeneous ellipse systems gains insight into the apparent percolation threshold symmetry observed earlier in systems comprising unequal circles (Consiglio et al., 2004).

  • 227.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ray, Biswajit
    Alam, Muhammad A.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Threshold of hierarchical percolating systems2012In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 85, no 2, p. 021109-Article in journal (Refereed)
    Abstract [en]

    Many modern nanostructured materials and doped polymers are morphologically too complex to be interpreted by classical percolation theory. Here, we develop the concept of a hierarchical percolating (percolation-within-percolation) system to describe such complex materials and illustrate how to generalize the conventional percolation to double-level percolation. Based on Monte Carlo simulations, we find that the double-level percolation threshold is close to, but definitely larger than, the product of the local percolation thresholds for the two enclosed single-level systems. The deviation may offer alternative insights into physics concerning infinite clusters and open up new research directions for percolation theory.

  • 228.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Unander, Tomas
    López Cabezas, Ana
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Shao, Botao
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Liu, Zhiying
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. Uppsala University, Sweden.
    Feng, Yi
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Forsberg, Esteban Bernales
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhang, Zhibin
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Jögi, Indrek
    Gao, Xindong
    Boman, Mats
    Zheng, Li-Rong
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Nilsson, Hans-Erik
    Zhang, Shi-Li
    KTH, School of Information and Communication Technology (ICT). Uppsala University, Sweden.
    Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 8, article id 084915Article in journal (Refereed)
    Abstract [en]

    The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel formation. The transistors are manufactured on oxidized silicon wafer and flexible plastic substrates at ambient conditions. For this purpose, ink-jet printing techniques are developed aiming at high-throughput production of SWCNT thin-film channels shaped in long strips. Stable SWCNT inks with proper fluidic characteristics are formulated by polymer addition. The present work unveils, through Monte Carlo simulation and in the light of heterogeneous percolation, the underlying physics of the superiority of long-strip channels for SWCNT TFTs. It further predicts the compatibility of such a channel structure with ink-jet printing taking into account the minimum dimensions achievable by commercially available printers. The printed devices exhibit improved electrical performance and scalability, compared to previously reported ink-jet printed SWCNT TFTs. The present work demonstrates that ink-jet printed SWCNT TFTs of long-strip channels are promising building blocks for flexible electronics.

  • 229.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Vaziri, Sam
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Lemme, Max C.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    A simple route towards high-concentration surfactant-free graphene dispersions2012In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 50, no 8, p. 3113-3116Article in journal (Refereed)
    Abstract [en]

    A simple solvent exchange method is introduced to prepare high-concentration and surfactant-free graphene liquid dispersion. Natural graphite flakes are first exfoliated into graphene in dimethylformamide (DMF). DMF is then exchanged by terpineol through distillation, relying on their large difference in boiling points. Graphene can then be concentrated thanks to the volume difference between DMF and terpineol. The concentrated graphene dispersions are used to fabricate transparent conductive thin films, which possess comparable properties to those prepared by more complex methods.

  • 230.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Vaziri, Sam
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Lemme, Max C.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Efficient inkjet printing of graphene2013In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 25, no 29, p. 3985-3992Article in journal (Refereed)
    Abstract [en]

    An efficient and mature inkjet printing technology is introduced for mass production of coffee-ring-free patterns of high-quality graphene at high resolution (unmarked scale bars are 100 μm). Typically, several passes of printing and a simple baking allow fabricating a variety of good-performance electronic devices, including transparent conductors, embedded resistors, thin film transistors, and micro-supercapacitors.

  • 231.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhang, Zhibin
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhang, Shi-Li
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Distinguishing self-gated rectification action from ordinary diode rectification in back-gated carbon nanotube devices2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 133111Article in journal (Refereed)
    Abstract [en]

    Self-gating leading to rectification action is frequently observed in two-terminal devices built from individual or networked single-walled carbon nanotubes (SWCNTs) on oxidized Si substrates. The current-voltage (I-V) curves of these SWCNT devices remain unaltered when switching the measurement probes. For ordinary diodes, the I-V curves are symmetric about the origin of the coordinates when exchanging the probes. Numerical simulations suggest that the self-gated rectification action should result from the floating semiconducting substrate which acts as a back gate. Self-gating effect is clearly not unique for SWCNT devices. As expected, it is absent for devices fabricated on insulating substrates.

  • 232.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhang, Zhibin
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhang, Shi-Li
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Improved electrical performance of carbon nanotube thin film transistors by utilizing composite networks2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 133103Article in journal (Refereed)
    Abstract [en]

    This work presents a simple scheme of using composite carbon nanotube networks (c-CNNs) to significantly improve the electrical performance of long-channel thin film transistors based on single-walled carbon nanotubes (SWCNTs). Such c-CNNs comprise two sets of SWCNTs. A primary set consists of dense arrays of perfectly aligned long SWCNTs along the transistor channel direction. A secondary set is composed of short SWCNTs either randomly orientated or perpendicularly aligned with respect to the channel. While retaining a high on/off current ratio, the drive current in such c-CNNs is much higher than that in currently studied systems with single CNNs or SWCNT arrays.

  • 233.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Conductivity scaling in supercritical percolation of nanoparticles: not a power law2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 8, p. 3424-3428Article in journal (Refereed)
    Abstract [en]

    The power-law behavior widely observed in supercritical percolation systems of conductive nanoparticles may merely be a phenomenological approximation to the true scaling law not yet discovered. In this work, we derive a comprehensive yet simple scaling law and verify its extensive applicability to various experimental and numerical systems. In contrast to the power law which lacks theoretical backing, the new scaling law is explanatory and predictive, and thereby helpful to gain more new insights into percolation systems of conductive nanoparticles.

  • 234.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Corrected finite-size scaling in percolation2012In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 86, no 4, p. 040105-Article in journal (Refereed)
    Abstract [en]

    This Rapid Communication proposes a comprehensive scaling theory for percolation, which clarifies the intrinsic nature of finite-size scaling and effectively addresses the finite-size effects. This theory applies to extensive systems, including especially the explosive percolation. It is suggested that explosive percolation shares the same scaling law as normal percolation, but may suffer from more severe finite-size effects. Remarkably, in contrast to previous studies, relying on the framework of our theory, the present Rapid Communication suggests that for all systems, the universal scaling functions do not depend on the boundary conditions.

  • 235.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Percolation thresholds of two-dimensional continuum systems of rectangles2013In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 88, no 1, p. 012101-Article in journal (Refereed)
    Abstract [en]

    The present paper introduces an efficient Monte Carlo algorithm for continuum percolation composed of randomly oriented rectangles. By conducting extensive simulations, we report high-precision percolation thresholds for a variety of homogeneous systems with different rectangle aspect ratios. This paper verifies and extends the excluded area theory. It is confirmed that percolation thresholds are dominated by the average excluded areas for both homogeneous and heterogeneous rectangle systems (except for some special heterogeneous systems where the rectangle lengths differ too much from one another). In terms of the excluded areas, generalized formulas are proposed to effectively predict precise percolation thresholds for all these rectangle systems. This paper is, therefore, helpful for both practical applications and theoretical studies concerning relevant systems.

  • 236.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Prevention of graphene restacking for performance boost of supercapacitors-a review2013In: Crystals, ISSN 2073-4352, Vol. 3, no 1, p. 163-190Article, review/survey (Refereed)
    Abstract [en]

    Graphene is a promising electrode material for supercapacitors mainly because of its large specific surface area and high conductivity. In practice, however, several fabrication issues need refinement. The restacking of graphene flakes upon being packed into supercapacitor electrodes has become a critical challenge in the full utilization of graphene's large specific surface area to further improve the device performance. In this review, a variety of recent techniques and strategies are overviewed for the prevention of graphene restacking. They have been classified into several categories to improve and facilitate the discussion on the underlying ideas. Based on the overview of the existing techniques, we discuss the trends of future research in the fields.

  • 237.
    Li, Jiantong
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Scalable Fabrication of 2D Semiconducting Crystals for Future Electronics2015In: ELECTRONICS, ISSN 2079-9292, Vol. 4, no 4, p. 1033-1061Article, review/survey (Refereed)
    Abstract [en]

    Two-dimensional (2D) layered materials are anticipated to be promising for future electronics. However, their electronic applications are severely restricted by the availability of such materials with high quality and at a large scale. In this review, we introduce systematically versatile scalable synthesis techniques in the literature for high-crystallinity large-area 2D semiconducting materials, especially transition metal dichalcogenides, and 2D material-based advanced structures, such as 2D alloys, 2D heterostructures and 2D material devices engineered at the wafer scale. Systematic comparison among different techniques is conducted with respect to device performance. The present status and the perspective for future electronics are discussed.

  • 238. Lindberg, AC
    et al.
    Hellberg, Per-Erik
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Mohadjeri, B
    Zhang, Shi-Li
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Influence of interface roughness on electrical properties of pMOSFETs with a Si/Si1-xGex channel2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, p. 22-25Conference paper (Refereed)
    Abstract [en]

    The effect of epitaxial growth induced surface roughness on the electrical properties of Si/Si1-xGex channel pMOSFETs was investigated. Grown by chemical vapour deposition for selective epitaxy, the surface of the channel region was considerably rougher for the channel structures with a buried Si1-xGex layer with x = 0.16-0.20 than for those with only Si. Although the increased surface roughness, determined by means of atomic force microscopy, resulted in a doubled interface charge density the density remained low at the mid-10(10) cm(-2) eV(-1) level. Furthermore, identical transconductance values were found for the MOSFETs with and without the Si1-xGex layer. Since the inversion charge was confined predominantly within the surface Si layer, the surface roughness apparently had little effect on the transconductance. However the subthreshold slope was found to increase from 78 mV/decade for the Si-only channel MOSFEF to 105 mV/decade for the Si/Si1-xGex channel MOSFETs.

  • 239. Linder, M.
    et al.
    Ingvarson, F.
    Jeppson, K. O.
    Grahn, J. V.
    Zhang, Shi-Li
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Extraction of emitter and base series resistances of bipolar transistors from a single DC measurement2000In: IEEE transactions on semiconductor manufacturing, ISSN 0894-6507, E-ISSN 1558-2345, Vol. 13, no 2, p. 119-126Article in journal (Refereed)
    Abstract [en]

    A new procedure for extracting the emitter and base series resistances of bipolar junction transistors is presented. The parameters are extracted from a single measurement in the forward active region on one transistor test structure with two separate base contacts, making it a simple and attractive tool for bipolar transistor characterization. The procedure comprises two methods for extracting the emitter resistance and two for extracting the base resistance. The choice of method is governed by the amount of current crowding or conductivity modulation present in the intrinsic base region. The new extraction procedure was successfully applied to transistors fabricated in an in-house double polysilicon bipolar transistor process and a commercial 0.8-mu m single polysilicon BiCMOS process. We found that the simulated and measured Gummel characteristics are in excellent agreement and the extracted series resistances agree well with those obtained by means of HF measurements. By adding external resistors to the emitter and base and then extracting the series resistances, me verified that the two base contact test structure offers a simple means of separating the influence of emitter and base series resistances on the transistor characteristics.

  • 240. Linder, M.
    et al.
    Ingvarson, F.
    Jeppson, K. O.
    Grahn, J. V.
    Zhang, Shi-Li
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    On DC modeling of the base resistance in bipolar transistors2000In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 44, no 8, p. 1411-1418Article in journal (Refereed)
    Abstract [en]

    The total base resistance R-BTot constitutes a crucial parameter in modeling bipolar transistors. The significant physical effects determining R-BTot are current crowding and conductivity modulation in the base, both causing reduction of R-BTot With increasing base current I-B. In this paper, it is shown that the reduction of R-BTot(I-B) With increasing I-B is directly related to the physical effect dominating in the base. A new model for R-BTot(I-B) is presented where a parameter alpha is introduced to account for the contributions of current crowding and conductivity modulation in the base. Theoretically, alpha is equal to 0.5 when conductivity modulation is dominant and close to 1.0 when current crowding is the most significant effect. This was verified by measurements and simulations using a distributed transistor model which accounts for the lateral distribution of the base current and the stored base charge. The model proposed for R-BTot(I-B) is very suitable for compact transistor modeling since it is given in a closed form expression handling both current crowding and conductivity modulation in the base. An accurate extraction procedure of the model parameters is also presented.

  • 241. Lindgren, A. C.
    et al.
    Chen, C.
    Zhang, Shi-Li
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zhang, Y.
    Zhu, D.
    Characterization of strained Si/Si1-xGex/Si heterostructures annealed in oxygen or argon2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 5, p. 2708-2712Article in journal (Refereed)
    Abstract [en]

    The strained Si/Si1-xGex/Si layer heterostructure heat treated from 700 degreesC to 950 degreesC in Ar (annealing) or O-2-C2H2Cl2 (oxidation) was characterized using high-resolution x-ray diffraction in combination with Rutherford backscattering. Only small changes to the structure are observed up to 800 degreesC, within the resolution limits of diffraction and backscattering. Severe strain relaxation occurs at 950 degreesC and the heterostructure tends to relax more during annealing in Ar than during oxidation in O-2-C2H2Cl2. The strain relaxation is mainly caused by interdiffusion of Si and Ge rather than formation of misfit dislocations. Diffusion of Si interstitials generated during oxidation into the heterostructure is suggested as the cause responsible for the less pronounced interdiffusion of Si and Ge in the oxidized samples.

  • 242.
    Litta, Eugenio Dentoni
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hellström, Per-Erik
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Integration of TmSiO/HfO2 Dielectric Stack in Sub-nm EOT High-k/Metal Gate CMOS Technology2015In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 62, no 3, p. 934-939Article in journal (Refereed)
    Abstract [en]

    Integration of a high-k interfacial layer (IL) is a promising technological solution to improve the scalability of high-k/metal gate CMOS technology. We have previously demonstrated a CMOS-compatible integration scheme for thulium silicate (TmSiO) IL and shown excellent characteristics in terms of equivalent oxide thickness (EOT), interface state density, channel mobility, and threshold voltage control. Here, we report on optimized annealing conditions leading to gate leakage current density comparable with state-of-the-art SiOx/HfO2 nFETs (0.7 A/cm(2) at 1 V gate bias) at sub-nm EOT (as low as 0.6 nm), with near-symmetric threshold voltages (0.5 V for nFETs and -0.4 V for pFETs). We demonstrate an excellent performance benefit of the TmSiO/HfO2 stack, i.e., improved channel mobility over SiOx/HfO2 dielectric stacks, demonstrating high-field electron and hole mobility of 230 and 70 cm(2)/Vs, respectively, after forming gas anneal at EOT = 0.8 nm. Finally, the reliability of the TmSiO/HfO2/TiN gate stack is investigated, demonstrating 10-year expected life-times for both oxide integrity and threshold voltage stability at an operating voltage of 0.9 V.

  • 243. Liu, C. W.
    et al.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hannon, J. B.
    New materials for post-Si computing2014In: MRS bulletin, ISSN 0883-7694, E-ISSN 1938-1425, Vol. 39, no 8, p. 658-662Article in journal (Refereed)
    Abstract [en]

    It is now widely recognized that continued performance gains in electronic computing will require new materials, both in the short and long term. In the short term, the silicon channel in transistors will be replaced by materials with higher mobility that are easier to "scale" (make thinner). In data storage, the goal is to have fast, non-volatile memory with a smaller cell size. In the long term, new architectures and new types of logic devices will be needed in order to further reduce power consumption. New materials cannot only boost performance, but can also add new functionalities, such as on-chip photonics, which can vastly improve interchip interconnects. The need for new materials is a big opportunity for materials research, but also a challenge. Replacement technologies must outperform conventional silicon technology, but also be compatible with the vast infrastructure of silicon manufacturing. Examples of some of the materials advances in the areas of computation, memory, and communication are given in this issue of MRS Bulletin

  • 244. Liu, W.
    et al.
    Danielsson, Erik
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Electro-Thermal Simulations and Measurement of Silicon Carbide Bipolar Transistors2003In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 433-436, p. 781-784Article in journal (Refereed)
    Abstract [en]

    Silicon carbide bipolar junction transistors were fabricated in the study reported here. Three-dimensional thermal simulations were conducted for the SiC BJTs using FEMLAB. Thermal images of a device under operation were also recorded using an infrared camera. Both the simulations and the measurement show a significant temperature increase in the vicinity of the device when operated at high power densities, thus causing the decrease in the DC current gain. The junction temperature extracted during self-heating was approximately 154 °C at a power dissipation of 5.5 W, using the assumption that the current gain only depends on the temperature. The simulation results show a junction temperature of 157 °C at the same power level. Long-term stability tests over 80 hours were also performed at elevated temperatures, and a 10% decrease in the current gain was observed.

  • 245.
    Liu, Wei
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zetterling, Carl Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Eriksson, J
    Rorsman, N
    Zirath, H
    High frequency measurements and simulations of SiC MESFETs up to 250 degrees C2004In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 457-460, p. 1209-1212Article in journal (Refereed)
    Abstract [en]

    4H-SiC metal-semiconductor field effect transistors (MESFETs) [1] were characterized at 25, 100, 150, 200, and 250 degreesC and two-dimensional electro-thermal simulations [2] were performed to examine the effects of elevated device operating temperature and self-heating on DC and RF performance of the MESFETs. The gate and drain characteristics (I-d-V-g & I-d-V-d) were measured at room and elevated temperatures. The threshold voltage decreased with temperature and drain voltage. The shift of the threshold voltage was more prominent at low temperatures (2 V from 25 to 100 degreesC) than at high temperatures (negligible shift above 150 degreesC). No short channel effects could be seen in drain characteristics due to the self-heating effects. The measured drain saturation current decreases with increase temperature. At lower gate and drain voltages the measured drain current at room temperature is smaller than the drain current at elevated temperatures. The threshold voltage shift and the lower drain current at room temperature are believed to be caused by the substrate traps, which induce extra charges at the channel-buffer interface acting as a backside gate. The current gain and power gain were measured as a function of frequency. Decrease of f(T) and f(max) with increase of temperature was observed for both measurements and simulations. Higher fT and f(max) were obtained from simulations than from the measurements. Traps and parasitics are believed to be the cause for the differences. A strong influence of contact resistance was seen on f(T) and f(max) in the HF simulations.

  • 246.
    Liu, Wei
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Thermal-issues for design of high power SiC MESFETs2004In: PROCEEDINGS OF THE SIXTH IEEE CPMT CONFERENCE ON HIGH DENSITY MICROSYSTEM DESIGN AND PACKAGING AND COMPONENT FAILURE ANALYSIS (HDP'04), NEW YORK: IEEE , 2004, p. 331-335Conference paper (Refereed)
    Abstract [en]

    Silicon carbide (SiC) power MESFETs have found application in RF source and power amplifiers for wireless telecommunication systems, phased-array radar systems, and other applications. SiC MESFETs can handle much higher power than silicon and gallium arsenide power devices, due to its superior material properties, including high critical electrical field, high electron saturation velocity, and high thermal conductivity. Despite the high thermal conductivity of the material, SiC power devices may suffer from severe self-heating when operating at very high power levels. In this report, the effect of self-heating on DC performance of SiC MESFETs with 1, 2, and 3 gate fingers were studied through 2D electro-thermal simulations using ISE-TOAD. The reduction in drain current caused by self-heating was found to be more prominent for transistors with more fingers and it imposes a limitation on both the output power and the power density (in W/mm) of multi-fingered large area devices. Thermal simulations have been performed using FEMLAB to predict the junction temperature of a MESFET with 1.5 mm gate periphery and a power dissipation of 4.5 W. Three different finger layouts were examined in terms of junction temperature, yield, and the ease and cost for fabrication of the devices. Thermal simulations were also done for a larger area MESFET with a gate periphery of 12 mm and power dissipation as high as 36 W. Three different ways to place the unit cell were studied. The effect of the thermal resistance between the die backside and the environment on the junction temperature was analyzed. The thermal resistance of the die itself was deduced. It was found that the packaging thermal resistance is usually much larger than the die thermal resistance. A couple of useful ways to reduce the packaging thermal resistance and the self-heating are also discussed.

  • 247.
    Lobov, G. S.
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Marinins, A.
    KTH, School of Information and Communication Technology (ICT).
    Etcheverry, S.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT).
    Vasileva, Elena
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sugunan, A.
    Laurell, F.
    Thylén, Lars
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wosinski, L.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT).
    Toprak, M. S.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Direct birefringence and transmission modulation via dynamic alignment of P3HT nanofibers in an advanced opto-fluidic component2017In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, no 1, p. 52-61Article in journal (Refereed)
    Abstract [en]

    Poly-3-hexylthiophene (P3HT) nanofibers are semiconducting high-aspect ratio nanostructures with anisotropic absorption and birefringence properties found at different regions of the optical spectrum. In addition, P3HT nanofibers possess an ability to be aligned by an external electric field, while being dispersed in a liquid. In this manuscript we show that such collective ordering of nanofibers, similar to liquid crystal material, significantly changes the properties of transmitted light. With a specially fabricated opto-fluidic component, we monitored the phase and transmission modulation of light propagating through the solution of P3HT nanofibers, being placed in the electric field with strength up to 0.1 V/μm. This report describes a technique for light modulation, which can be implemented in optical fiber-based devices or on-chip integrated components.

  • 248.
    Lobov, Gleb S.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Marinins, Aleksandrs
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jiantong
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Thylen, Lars
    KTH, School of Biotechnology (BIO).
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Ostling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Size Impact of Ordered P3HT Nanofibers on Optical Anisotropy2016In: Macromolecular Chemistry and Physics, ISSN 1022-1352, E-ISSN 1521-3935, Vol. 217, no 9, p. 1089-1095Article in journal (Refereed)
    Abstract [en]

    Poly-3-hexylthiophene (P3HT) nanofibers are 1D crystalline structures with semiconductor properties. When P3HT nanofi bers are dispersed in nonconducting solvent, they react to external alternate electric field by aligning along the field lines. This can be used to create layers of ordered nanofi bers and is referred to as alternating current poling method. P3HT nanofi bers with three different size distributions are fabricated, using self-assembly mechanism in marginal solvents, and used for the alignment studies. Anisotropic absorption of oriented 2 mu m long nanofi bers exponentially increases with the magnitude of applied field to a certain asymptotic limit at 0.8 V mu m(-1), while 100-500 nm long nanofi bers respond to electric field negligibly. Effective optical birefringence of oriented 2 mu m long nanofi bers is calculated, based on the phase shift at 633 nm and the average layer thickness, to be 0.41. These results combined with further studies on real-time control over orientation of P3HT nanofi bers in liquid solution or host system are promising in terms of exploiting them in electroabsorptive and electrorefractive applications.

  • 249.
    Lobov, Gleb S.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jiantong
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Sugunan, A.
    Thylén, Lars
    KTH, School of Biotechnology (BIO). Hewlett-Packard Laboratories, United States.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT).
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Electric field induced optical anisotropy of P3HT nanofibers in a liquid solution2015In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 5, no 11, p. 2642-2647Article in journal (Refereed)
    Abstract [en]

    The nanofiber morphology of regioregular Poly-3- hexylthiophene (P3HT) is a 1D crystalline structure organized by π - π stacking of the backbone chains. In this study, we report the impact of electric field on the orientation and optical properties of P3HT nanofibers dispersed in liquid solution. We demonstrate that alternating electric field aligns nanofibers, whereas static electric field forces them to migrate towards the cathode. The alignment of nanofibers introduces anisotropic optical properties, which can be dynamically manipulated until the solvent has evaporated. Time resolved spectroscopic measurements revealed that the electro-optical response time decreases significantly with the magnitude of applied electric field. Thus, for electric field 1.3 V ·μm-1 the response time was measured as low as 20 ms, while for 0.65 V ·μm-1 it was 110-150 ms. Observed phenomenon is the first mention of P3HT supramolecules associated with electrooptical effect. Proposed method provides real time control over the orientation of nanofibers, which is a starting point for a novel practical implementation. With further development P3HT nanofibers can be used individually as an anisotropic solution or as an active component in a guest-host system.

  • 250.
    Lobov, Gleb S.
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT).
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jiantong
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Sugunan, A.
    Thylen, Lars
    KTH, School of Biotechnology (BIO).
    Wosinski, L.ech
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Fotonik och mikrovågsteknik, FMI.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Popov, Sergei Yu
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Electro-optical response of P3HT nanofibers in liquid solution2015In: Asia Communications and Photonics Conference, ACPC 2015, 2015Conference paper (Refereed)
    Abstract [en]

    AC electric poling introduces in P3HT nanofibers anisotropic electro-optical response and birefringence. Along with birefringence, such material exhibits strong amplitude modulation which makes it more efficient alternative to liquid crystals. © 2015 OSA.

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