| 1. |
- Abdalla, Munir A, et al.
(author)
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A CMOS APS for dental X-ray imaging using scintillating sensors
- 2001
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In: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 460:1, s. 197-203
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Journal article (peer-reviewed)abstract
- 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,
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| 2. |
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| 3. |
- Abdalla, Munir A, et al.
(author)
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An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier
- 2001
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In: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 232-236
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
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| 5. |
- Aboelfotoh, M. O., et al.
(author)
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Schottky-barrier behavior of metals on n- and p-type 6H-SiC
- 2003
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:7, s. 075312-
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Badel, Xavier, et al.
(author)
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Improvement of an X-ray imaging detector based on a scintillating guides screen
- 2002
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In: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 487:1-2, s. 129-135
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Journal article (peer-reviewed)abstract
- 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).
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| 7. |
- Badel, Xavier, et al.
(author)
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Metallized and oxidized silicon macropore arrays filled with a scintillator for CCD-based X-ray imaging detectors
- 2004
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In: IEEE Transactions on Nuclear Science. - : IEEE. - 0018-9499 .- 1558-1578. ; 51:3, s. 1001-1005, s. 1006-1010
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
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| 9. |
- Bertilsson, Kent, et al.
(author)
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Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC
- 2001
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In: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:3-7, s. 1283-1286
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Journal article (peer-reviewed)abstract
- 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
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| 10. |
- Bertilsson, Kent, et al.
(author)
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Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector
- 2001
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In: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 183-187
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Journal article (peer-reviewed)abstract
- 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.
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