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  • 1. Abdalla, M. A.
    et al.
    Frojdh, C.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A CMOS APS for dental X-ray imaging using scintillating sensors2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 460, no 1, p. 197-203Article in journal (Refereed)
    Abstract [en]

    In this paper we present an integrating CMOS Active Pixel Sensor (APS) circuit to be used with scintillator type X-ray sensors for intra oral dental X-ray imaging systems. Different pixel architectures were constructed to explore their performance characteristics and to study the feasibility of the development of such systems using the CMOS technology. A prototype 64 x 80 pixel array has been implemented in a CMOS 0.8 mum double poly n-well process with a pixel pitch of 50 mum. A spectral sensitivity measurement for the different pixels topologies, as well as measured X-ray direct absorption in the different APSs are presented. A measurement of the output signal showed a good linearity over a wide dynamic range. This chip showed that the very low sensitivity of the CMOS APSs to direct X-ray exposure adds a great advantage to the various CMOS advantages over CCD-based imaging systems,

  • 2. Abdalla, M. A.
    et al.
    Frojdh, C.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, no 1, p. 232-236Article in journal (Refereed)
    Abstract [en]

    We present in this paper an integrating CMOS Active Pixel Sensor (APS) circuit coated with scintillator type sensors for intra-oral dental X-ray imaging systems. The photosensing element in the pixel is formed by the p-diffusion on the n-well diode. The advantage of this photosensor is its very low direct absorption of X-rays compared to the other available photosensing elements in the CMOS pixel. The pixel features an integrating capacitor in the feedback loop of a preamplifier of a finite gain in order to increase the optical sensitivity. To verify the effectiveness of this in-pixel preamplification, a prototype 32 x 80 element CMOS active pixel array was implemented in a 0.8 mum CMOS double poly, n-well process with a pixel pitch of 50 mum. Measured results confirmed the improved optical sensitivity performance of the APS. Various measurements on device performance are presented.

  • 3. Aboelfotoh, M. O.
    et al.
    Frojdh, C.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schottky-barrier behavior of metals on n- and p-type 6H-SiC2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 7Article in journal (Refereed)
    Abstract [en]

    The Schottky-barrier height of a number of metals (Ti, Ni, Cu, and Au) on n- and p-type Si-terminated 6H-SiC has been measured in the temperature range 150-500 K. It is found that the barrier height to n-type 6H-SiC does not exhibit a temperature dependence, while for p-type 6H-SiC the change in the barrier height with temperature follows very closely the change in the indirect energy gap in 6H-SiC. These results are inconsistent with models of Schottky-barrier formation based on the concept of a charge neutrality level. Furthermore, the present results cannot be reconciled with a defect pinning mechanism, contrary to the conclusions of earlier studies on III-V compound semiconductors. We suggest that chemical bonding at the metal-semiconductor interface plays an important role in determining the Schottky-barrier height.

  • 4.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Galeckas, Augustinas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kleimann, P.
    LENAC, Université Claude Bernard Lyon-I, Villeurbanne.
    Fröjdh, C.
    Mitthögskolan, Department of Electronics.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Improvement of an X-ray imaging detector based on a scintillating guides screen2002In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 487, no 1-2, p. 129-135Article in journal (Refereed)
    Abstract [en]

    An X-ray imaging detector has been developed for dental applications. The principle of this detector is based on application of a silicon charge coupled device covered by a scintillating wave-guide screen. Previous studies of such a detector showed promising results concerning the spatial resolution but low performance in terms of signal to noise ratio (SNR) and sensitivity. Recent results confirm the wave-guiding properties of the matrix and show improvement of the detector in terms of response uniformity, sensitivity and SNR. The present study is focussed on the fabrication of the scintillating screen where the principal idea is to fill a matrix of Si pores with a CsI scintillator. The photoluminescence technique was used to prove the wave-guiding property of the matrix and to inspect the filling uniformity of the pores. The final detector was characterized by X-ray evaluation in terms of spatial resolution, light output and SNR. A sensor with a spatial resolution of 9 LP/mm and a SNR over 50 has been achieved using a standard dental X-ray source and doses in the order of those used at the moment by dentists (around 25 mR).

  • 5.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kleimann, P
    Norlin, B
    Koskiahde, E
    Valpas, K
    Nenonen, S.
    Petersson, Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Frojdh, C
    Metallized and oxidized silicon macropore arrays filled with a scintillator for CCD-based X-ray imaging detectors2004In: 2003 IEEE NUCLEAR SCIENCE SYMPOSIUM, CONFERENCE RECORD, VOLS 1-5, 2004, p. 1006-1010Conference paper (Refereed)
    Abstract [en]

    Silicon Charge Coupled Devices (CCD) covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this work-, we fabricated such waveguides by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(TI). The resulting structures were observed using SEM and tested under X-ray exposure. The detector performances were also compared with simulations, indicating that the optimal pore depth for metallized macropore arrays is about 80 mum while it is around 350 mum for oxidized ones. This result, together with the roughness of the metal coating, explains why lower performances were measured experimentally with the metallized macropores. Indeed, our macropore arrays had depths in the range of 210-390 mum, which is favorable to oxidized structures.

  • 6.
    Badel, Xavier
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kleimann, P.
    LENAC, Univ.́ Claude Bernard Lyon-I, Villeurbanne.
    Norlin, B.
    Department of Information Technology, Mid-Sweden University, Sundsvall.
    Koskiahde, E.
    Metorex International Oy, Espoo.
    Valpas, K.
    Metorex International Oy, Espoo.
    Nenonen, S.
    Metorex International Oy, Espoo.
    Petersson, Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fröjdh, C.
    Department of Information Technology, Mid-Sweden University, Sundsvall.
    Metallized and oxidized silicon macropore arrays filled with a scintillator for CCD-based X-ray imaging detectors2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 3, p. 1001-1005Article in journal (Refereed)
    Abstract [en]

    Silicon charge-coupled devices (CCDs) covered with a scintillating film are now available on the market for use in digital medical imaging. However, these devices could still be improved in terms of sensitivity and especially spatial resolution by coating the CCD with an array of scintillating waveguides. In this paper, such waveguides were fabricated by first etching pores in silicon, then performing metallization or oxidation of the pore walls and finally filling the pores with CsI(TI). The resulting structures were observed using scanning electron microscopy and tested under X-ray exposure. Theoretical efficiencies of macropore arrays filled with CsI(TI) were also calculated, indicating that the optimal pore depth for metallized macropore arrays is about 80 mum while it is around 350 mum for oxidized ones. This result, together with the roughness of the metal coating, explains why lower SNR values were measured with the metallized macropores. Indeed, the macropore arrays had depths in the range of 210-390 mum, which is favorable to oxidized structures.

  • 7. Bertilsson, K.
    et al.
    Dubaric, E.
    Nilsson, H. E.
    Hjelm, M.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC2001In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 10, no 3-7, p. 1283-1286Article in journal (Refereed)
    Abstract [en]

    The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device.

  • 8. Bertilsson, K.
    et al.
    Dubaric, E.
    Thungstrom, G.
    Nilsson, H. E.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, no 1, p. 183-187Article in journal (Refereed)
    Abstract [en]

    A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.

  • 9. Bertilsson, K.
    et al.
    Nilsson, H. E.
    Hjelm, M.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kackell, P.
    Persson, Clas
    The effect of different transport models in simulation of high frequency 4H-SiC and 6H-SiC vertical MESFETs2001In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 45, no 5, p. 645-653Article in journal (Refereed)
    Abstract [en]

    A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations.

  • 10. Dubaric, E.
    et al.
    Frojdh, C.
    Nilsson, H. E.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Resolution and noise properties of scintillator coated X-ray detectors2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, no 1, p. 178-182Article in journal (Refereed)
    Abstract [en]

    The imaging properties of X-ray pixel detectors depend on the quantum efficiency of X-rays, the generated signal of each X-ray photon and the distribution of the generated signal between pixels. In a scintillator coated device the signal is generated both by X-ray photons captured in the scintillator and by X-ray photons captured directly in the semiconductor. The Signal-to-Noise Ratio in the image is then a function of the number of photons captured in each of these processes and the yield, in terms of electron-hole pairs produced in the semiconductor, of each process. The spatial resolution is primarily determined by the light spreading within the scintillator. In a pure semiconductor detector the signal is generated by one process only. The Signal-to-Noise Ratio in the image is proportional to the number of X-ray photons captured within the sensitive layer. The spatial resolution is affected by the initial charge cloud generated in the semiconductor and any diffusion of carriers between the point of interaction and the readout electrode. In this paper we discuss the theory underlying the imaging properties of scintillator coated X-ray imaging detectors. The model is verified by simulations using MCNP and by experimental results. The results from the two-layer detector are compared with those from a pure semiconductor X-ray detector.

  • 11. Kleimann, P.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Frojdh, C.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    An x-ray imaging pixel detector based on a scintillating guides screen2000In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 47, no 4, p. 1483-1486Article in journal (Refereed)
    Abstract [en]

    We have developed and preliminary tested a new digital X-ray imaging sensor based on a scintillating guide screen. The scintillating guides are used to channel the emitted visible light to the pixel detector. This enables us to avoid the well-known tradeoff between detection efficiency and spatial resolution which is encountered when a non-patterned scintillating layer is used on top of a CCD. A prototype has been fabricated using microtechnologies. The scintillator is CsI:T1 and the low-index cladding material used to channel the light is silicon dioxide. The performance of this prototype has been compared to that of a thick CsI single crystal. The results concerning the spatial resolution are quite promising and demonstrate a proof-of-principle. However, the performance in terms of signal to noise ratio and sensitivity have to be improved. These problems are currently addressed.

  • 12. Kleimann, P.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Frojdh, C.
    Petersson, C. Sture
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    An X-ray imaging pixel detector based on scintillator filled pores in a silicon matrix2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 460, no 1, p. 15-19Article in journal (Refereed)
    Abstract [en]

    An X-ray imaging pixel detector has been fabricated and preliminary testing has demonstrated a proof-of-principle. The detector is based on a conventional charge coupled detector (CCD)-imaging detector where a scintillator-filled silicon pore matrix provides enhanced X-ray sensitivity without sacrificing lateral resolution. The scintillator blocks inside the pores provide light guiding of the emitted Visible photons to increase the number of photons detected by the CCD element. Preliminary X-ray measurements demonstrate good lateral resolution although non-uniform filling of the pore matrix results in a pronounced fixed noise pattern. The detector has primary applications in dental imaging but would also be of importance in other imaging techniques where the X-ray absorption length exceeds lateral pixel size.

  • 13. Kok, A.
    et al.
    Kohout, Z.
    Hansen, T. -E
    Petersson, Sture
    KTH.
    Pospisil, S.
    Rokne, J.
    Slavicek, T.
    Soligard, S.
    Thungström, G.
    Vykydal, Z.
    Silicon sensors with pyramidal structures for neutron imaging2014In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, p. C04011-Article in journal (Refereed)
    Abstract [en]

    Neutron detection is a valuable tool in nuclear science research, homeland security, quality assurance in nuclear plants and medical applications. Recent developments and near future instrumentations in neutron imaging have a need for sensors with high spatial resolution, dynamic range, sensitivity and background discrimination. Silicon based neutron detectors can potentially fulfil these requirements. In this work, pad and pixel detectors with pyramidal micro-structures have been successfully fabricated that should have an improved detection efficiency when compared to conventional planar devices. Titanium di-boride (TiB2) and lithium fluoride (LiF) were deposited as the neutron converters. Excellent electrical performances were measured on both simple pad and pixel detectors. A selection of pad detectors was examined by alpha spectroscopy. Measurement with thermal neutrons from a 241Am-Be source shows an improvement in relative efficiency of up to 38% when compared to conventional planar devices.

  • 14. Petersson, Sture
    et al.
    Grishin, Alexander
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Tunable acoustic wave device2002Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention discloses a tunable acoustic wave device (100; 200) comprising a piezoelectric material (120; 220) with a tunable dielectric permittivity. The dielectric permittivity of the material is tuned by applying a tuning electric field (190), preferably a DC-bias field, low frequency AC field, pulsed electric field or AC electric field superimposed onto an electric field pulse, thereto. By tuning the dielectric permittivity, the operation characteristics of the device (100; 200), including the acoustic wave velocity in the material (120; 220) and the resonance frequency and bandwidth of the device (100; 200), may be tuned. The tuning electric field (190) may applied by superimposing it onto the input high frequency electric field signal of the device (100; 200) or by applying it over at least a portion of the piezoelectric material (120; 220). A piezoelectric material (120; 220) with a tunable dielectric permittivity can be found in ceramic crystalline superparaelectric materials, e.g. perovskite niobates-tantalates.

  • 15. Thungström, G.
    et al.
    Westerberg, L.
    Spohr, R.
    Petersson, Sture
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Fabrication and characterization of thin Delta E detectors for spectroscopic application2005In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 546, no 1-2, p. 312-318Article in journal (Refereed)
    Abstract [en]

    Ultra-thin Delta Edetectors for spectroscopic applications have been fabricated and characterized down to a thickness of 4.5 mu m. A common one-side mask aligner was used to fabricate the detectors. The detectors display low leakage current and the resulting capacitance is close to the detector window capacitance below a threshold voltage. The detector telescope needs to be slightly tilted to reduce the probability for channeling. However, even better control of the thickness uniformity is needed to improve the resolution in the Delta E-E detector telescope.

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