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  • 1.
    Ergül, Adem
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Fabrication and Characterization of Superconductive Coplanar Waveguide Resonators: Fabrication and Characterization of Superconductive Coplanar Waveguide Resonators2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The objective of this thesis is to evaluate a generic process for fabrication and characterization of the Superconductive coplanar waveguide (CPW) resonators. Superconductive CPW resonators with various lengths and shapes are designed to investigate their electrical and magnetic properties as well as resonance properties and sensitivities. In the first part of thesis, two different models are introduced in order to estimate the nonlinear kinetic inductance of a superconducting CPW resonator. The first model is based on Bean critical-state model and the second one is based on current dependence of London penetration depth. The existence of a shift in resonant frequency  of Superconductive CPW resonator caused by a non-linear kinetic inductance is also shown experimentally. Simulations were carried out to estimate the nonlinear kinetic inductance due to the self- induced magnetic field penetration.

    The rest of the thesis is concerned with development of very smooth Aluminum (Al) thin films with RMS (Root Mean Square) roughness 1~nm and CAD (Computer Aid Design) of superconductive CPW resonators. Experimental investigation of a generic fabrication technique for superconductive CPW resonator is carried out. Many resonators are fabricated with different design parameters, such as centerline or gap width, film thickness and gap capacitors length. The fabrication process is described in detail. Electron Beam Lithography is used to fabricate Nb and Al CPW resonators which are coupled to outer conductors via gap capacitors. We have fabricated GHz frequency CPW resonators with quality factors, Q up 5X10^5.

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  • 2.
    Ergül, Adem
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Nonlinear dynamics of Josephson Junction Chains and Superconducting Resonators2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents the results of the experimental studies on two kindof Superconducting circuits: one-dimensional Josephson junction chains andsuperconducting coplanar waveguide (CPW) resonators. One-dimensionalJosephson junction chains are constructed by connecting many Superconducting quantum interference devices (SQUIDs) in series. We have studied DC transport properties of the SQUID chains and model their nonlineardynamics with Thermally Activated Phase-Slips (TAPS). Experimental andsimulated results showed qualitative agreement revealing the existence of auniform phase-slipping and phase-sticking process which results in a voltage-independent current on the dissipative branch of the current-voltage char-acteristics (IVC). By modulating the effective Josephson coupling energy ofthe SQUIDs (EJ ) with an external magnetic field, we found that the ratio EJ /EC is a decisive factor in determining the qualitative shape of theIVC. A quantum phase transition between incoherent Quantum Phase Slip, QPS (supercurrent branch with a finite slope) to coherent QPS (IVC withwell-developed Coulomb blockade) via an intermediate state (supercurrentbranch with a remnant of Coulomb blockade) is observed as the EJ /EC ratio is tuned. This transition from incoherent QPS to the intermediate-statehappens around R0 ∼ RQ (RQ = h/4e^2 = 6.45kΩ). We also fabricated structured chains where a SQUID at the middle of the chain (central SQUID) has different junction size and loop area compared to other SQUIDs in the chain. Results showed that with these structured chains it is possible to localize andtune the amplitude of both TAPS and QPS at the central SQUID.

    The second part of the thesis describes the fabrication process and themeasurement results of superconducting CPW resonators. Resonators withdifferent design parameters were fabricated and measured. The transmissionspectra showed quality factors up to, Q ∼ 5 × 10^5 . We have observed bendingof the resonance curves to the lower frequencies due to existence of a nonlinear kinetic inductance. The origin of the nonlinear kinetic inductance isthe nonlinear relation between supercurrent density, Js, and superfluid veloc-ity, vs , of the charge carriers on the center line of the resonators. A simplemodel based on the Ginzburg-Landau theory is used in order to explain ob-served nonlinear kinetic inductance and estimates using this model showedgood agreement with the experimental results.

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  • 3.
    Ergül, Adem Björn
    KTH, School of Engineering Sciences (SCI), Applied Physics, Functional Materials, FNM. Jet Propulsion Laboratory, Caltech.
    Magnesium Diboride (MgB2) & Molybdenum Silicide (MoSi) Superconducting Nanowires2016Book (Other academic)
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  • 4.
    Ergül, Adem Björn
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Superconducting Nanowire Single-photon Detectors: WSi SNSPDs for Quantum Optics Applications2018Report (Other academic)
    Abstract [en]

    In this study we have developed a new fabrication technique for Tungsten Silicide (WSi) Superconducting Nanowire Single-Photon Detectors (SNSPD). These detectors arespecifically designed to interact with the photons in the infra-red region of theelectro magnetic spectrum. Fabrication process is described in great detail with the intention of giving the readers a broad view about the facts or aspects of various situations they might face in the clean room processes. Ultimate goal for the project is to integrate these high temperature SNSPD detectors with the photonic circuits.

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  • 5.
    Ergül, Adem
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Lidmar, Jack
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Johansson, Jan
    Azizoglu, Yagiz
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Schaeffer, David
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Localizing quantum phase slips in one-dimensional Josephson junction chains2013In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 15, p. 095014-Article in journal (Refereed)
    Abstract [en]

    We studied quantum phase-slip (QPS) phenomena in long one-dimensional Josephson junction series arrays with tunable Josephson coupling. These chains were fabricated with as many as 2888 junctions, where one sample had a separately tunable link in the middle of the chain. Measurements were made of the zero-bias resistance, R-0, as well as current-voltage characteristics (IVC). The finite R-0 is explained by QPS and shows an exponential dependence on root E-J/E-C with a distinct change in the exponent at R-0 = R-Q = h/4e(2). When R-0 > R-Q, the IVC clearly shows a remnant of the Coulomb blockade, which evolves to a zero-current state with a sharp critical voltage as E-J is tuned to a smaller value. The zero-current state below the critical voltage is due to coherent QPSs and we show that these are enhanced when the central link is weaker than all other links. Above the critical voltage, a negative, differential resistance is observed, which nearly restores the zero-current state.

  • 6.
    Ergül, Adem
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Schaeffer, David
    KTH.
    Lindblom, Magnus
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Lidmar, Jack
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Johansson, Jan
    Phase sticking in one-dimensional Josephson junction chains2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 10, p. 104501-Article in journal (Refereed)
    Abstract [en]

    We studied current-voltage characteristics of long one-dimensional Josephson junction chains with Josephson energy much larger than charging energy, E-J >> E-C. In this regime, typical I-V curves of the samples consist of a supercurrent-like branch at low-bias voltages followed by a voltage-independent chain current branch, I-chain at high bias. Our experiments showed that I-chain is not only voltage-independent but it is also practically temperature-independent up to T = 0.7T(C). We have successfully model the transport properties in these chains using a capacitively shunted junction model with nonlinear damping.

  • 7.
    Ergül, Adem
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Stockholm University, Sweden.
    Weissl, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Johansson, Jan
    Lidmar, Jack
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Spatial and temporal distribution of phase slips in Josephson junction chains2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 11447Article in journal (Refereed)
    Abstract [en]

    The Josephson effect, tunnelling of a supercurrent through a thin insulator layer between two superconducting islands, is a phenomena characterized by a spatially distributed phase of the superconducting condensate. In recent years, there has been a growing focus on Josephson junction devices particularly for the applications of quantum metrology and superconducting qubits. In this study, we report the development of Josephson junction circuit formed by serially connecting many Superconducting Quantum Interference Devices, SQUIDs. We present experimental measurements as well as numerical simulations of a phase-slip center, a SQUID with weaker junctions, embedded in a Josephson junction chain. The DC transport properties of the chain are the result of phase slips which we simulate using a classical model that includes linear external damping, terminating impedance, as well as internal nonlinear quasiparticle damping. We find good agreement between the simulated and the experimental current voltage characteristics. The simulations allow us to examine the spatial and temporal distribution of phase-slip events occurring across the chains and also the existence of travelling voltage pulses which reflect at the chain edges.

  • 8.
    Hamawandi, Bejan
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Noroozi, Mohammad
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Jayakumar, Ganesh
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ergül, Adem
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Zahmatkesh, Katayoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Radamson, Henry H.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Electrical properties of sub-100 nm SiGe nanowires2016In: Journal of semiconductors, Vol. 37, no 10Article in journal (Refereed)
    Abstract [en]

    In this study, the electrical properties of SiGe nanowires in terms of process and fabrication integrity, measurement reliability, width scaling, and doping levels were investigated. Nanowires were fabricated on SiGe-on oxide (SGOI) wafers with thickness of 52 nm and Ge content of 47%. The first group of SiGe wires was initially formed by using conventional I-line lithography and then their size was longitudinally reduced by cutting with a focused ion beam (FIB) to any desired nanometer range down to 60 nm. The other nanowires group was manufactured directly to a chosen nanometer level by using sidewall transfer lithography (STL). It has been shown that the FIB fabrication process allows manipulation of the line width and doping level of nanowires using Ga atoms. The resistance of wires thinned by FIB was 10 times lower than STL wires which shows the possible dependency of electrical behavior on fabrication method.

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    Abstract
  • 9.
    Noroozi, Mohammad
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ergül, Adem
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Abedin, Ahmed
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Toprak, Muhammet S
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Radamson, Henry
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Fabrications of size-controlled SiGe nanowires using I-line lithography and focused ion beam technique2014In: ECS Transactions, 2014, no 6, p. 167-174Conference paper (Refereed)
    Abstract [en]

    In this study, a novel method using Focus Ion Beam (FIB) technique was applied to scale down Si1-xGex wires (x=0.27-0.57) to 20 nm width. Originally, the wires were processed by using Iline lithography and dry etching of SiGe on oxide (SGOI) substrates. The SGOI wafers were processed through condensation method where a SiGe/Si layer was grown in the beginning on SOI wafers and oxidized at 850-1050 °C. The shape of the nanowires (NWs) during the successive FIB cutting was examined by scanning electron microscopy (SEM) and the carrier transport through the NWs was checked by resistivity measurements. The contact resistance was reduced by Ni-silicide prior to metallization. The fabricated NWs were also suspended by tilting FIB. The results present the limitations and challenges of FIB technique to create NWs for advanced sensors and transistors.

  • 10.
    Noroozi, Mohammad
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Jayakumar, Ganesh
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Lu, Jun
    Mensi, Mounir
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Hamawandi, Bejan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Zahmatkesh, Katayoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Tafti, Mohsen. Y
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Marcinkevičius, Saulius
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Hultman, Lars
    Ergül, Adem
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ikonic, Zoran
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Radamson, Henry H.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Significant Improvement of Thermoelectric Efficiency in SiGe NanowiresArticle in journal (Refereed)
    Abstract [en]

    The thermoelectric (TE) properties of SiGe nanowires (NWs) with width of 60 nm in a back-gate configuration have been studied experimentally and theoretically. The carrier transport in NWs was modified by biasing voltage to the gate for different temperatures. The original wafers were SiGe-on-oxide (SGOI), which were formed through condensation of SiGe on Si-on-oxide wafers (SOI).  The power factor of SiGe NWs was enhanced by a factor of >2 in comparison with SiGe bulk material over a temperature range of 273 K to 450 K. This enhancement is mainly attributed to the energy filtering of carriers in SiGe NWs which were introduced by the roughness in the shape of NWs, non-uniform SiGe composition and the induced defects during the manufacturing of SGOI wafers or processing of NWs. These defects create potential barriers which may significantly enhance the Seebeck coefficient, while the conductivity can be boosted by tuning the back-gate bias.

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    summary
  • 11.
    Noroozi, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Linköping University, Sverige.
    Jayakumar, Ganesh
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Zahmatkesh, Katayoun
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lu, J.
    Hultman, L.
    Mensi, Mounir
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Marcinkevicius, Saulius
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hamawandi, Bejan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Yakhshi Tafti, Mohsen
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ergül, Adem
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ikonic, Z.
    Toprak, Muhammet
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Radamson, Henry H.
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Unprecedented thermoelectric power factor in SiGe nanowires field-effect transistors2017In: ECS Journal of Solid State Science and Technology, ISSN 2162-8769, E-ISSN 2162-8777, Vol. 6, no 9, p. Q114-Q119Article in journal (Refereed)
    Abstract [en]

    In this work, a novel CMOS compatible process for Si-based materials has been presented to form SiGe nanowires (NWs) on SiGe On Insulator (SGOI) wafers with unprecedented thermoelectric (TE) power factor (PF). The TE properties of SiGe NWs were characterized in a back-gate configuration and a physical model was applied to explain the experimental data. The carrier transport in NWs was modified by biasing voltage to the gate at different temperatures. The PF of SiGe NWs was enhanced by a factor of >2 in comparison with bulk SiGe over the temperature range of 273 K to 450 K. This enhancement is mainly attributed to the energy filtering of carriers in SiGe NWs, which were introduced by imperfections and defects created during condensation process to form SiGe layer or in NWs during the processing of NWs.

  • 12.
    Tholén, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Ergül, Adem
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Doherty, Evelyn
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Weber, Frank
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Grégis, Fabien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Nonlinearities and parametric amplification in superconducting coplanar waveguide resonators2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 25, p. 253509-Article in journal (Refereed)
    Abstract [en]

    Experimental investigations of the nonlinear properties of superconducting niobium coplanarwaveguide resonators are reported. The nonlinearity due to a current dependent kinetic inductanceof the center conductor is strong enough to realize bifurcation of the nonlinear oscillator. Whendriven with two frequencies near the threshold for bifurcation, parametric amplification with a gainof +22.4 dB is observed.

  • 13.
    Tholén, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Ergül, Adem
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Schaeffer, David
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Gain, noise and intermod-ulation in a nonlinear superconducting resonatorManuscript (preprint) (Other academic)
  • 14.
    Tholén, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Ergül, Adem
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Stannigel, Kai
    Hutter, Carsten
    Haviland, David
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Parametric amplification with weak-link nonlinearity in superconducting microresonators2009In: Nobel Symposium 141: Qubits for Future Quantum Information; Gothenburg; 25 May 2009 through 28 May 2009, 2009Conference paper (Refereed)
    Abstract [en]

    Nonlinear kinetic inductance in a high Q superconducting coplanarwaveguide microresonator can cause a bifurcation of the resonance curve. Near thecritical pumping power and frequency for bifurcation, large parametric gain is observedfor signals in the frequency band near resonance. We show experimental results onsignal and intermodulation gain which are well described by a theory of the parametricamplification based on a Kerr nonlinearity. Phase dependent gain, or signal squeezing,is verified with a homodyne detection scheme.

1 - 14 of 14
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