| 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. |
- Abdalla, Munir A, et al.
(author)
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An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier
- 2001
-
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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Dubaric, Ervin, et al.
(author)
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Resolution and noise properties of scintillator coated X-ray detectors
- 2001
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In: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 178-182
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Journal article (peer-reviewed)abstract
- 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.
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