10 January 2003 Integrated x-ray and charged particle active pixel CMOS sensor arrays using an epitaxial silicon-sensitive region
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Integrated CMOS Active Pixel Sensor (APS) arrays have been fabricated and tested using X-ray and electron sources. The 128 by 128 pixel arrays, designed in a standard 0.25 micron process, use a ~10 micron epitaxial silicon layer as a deep detection region. The epitaxial layer has a much greater thickness than the surface features used by standard CMOS APS, leading to stronger signals and potentially better signal-to-noise ratio (SNR). On the other hand, minority carriers confined within the epitaxial region may diffuse to neighboring pixels, blur images and reduce peak signal intensity. But for low-rate, sparse-event images, centroid analysis of this diffusion may be used to increase position resolution. Careful trade-offs involving pixel size and sense-node area verses capacitance must be made to optimize overall performance. The prototype sensor arrays, therefore, include a range of different pixel designs, including different APS circuits and a range of different epitaxial layer contact structures. The fabricated arrays were tested with 1.5 GeV electrons and Fe-55 X-ray sources, yielding a measured noise of 13 electrons RMS and an SNR for single Fe-55 X-rays of greater than 38.
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Stuart Kleinfelder, Stuart Kleinfelder, Hans Bichsel, Hans Bichsel, Fred Bieser, Fred Bieser, Howard S. Matis, Howard S. Matis, Gulshan Rai, Gulshan Rai, Fabrice Retiere, Fabrice Retiere, Howard Wieman, Howard Wieman, Eugene Yamamoto, Eugene Yamamoto, } "Integrated x-ray and charged particle active pixel CMOS sensor arrays using an epitaxial silicon-sensitive region", Proc. SPIE 4784, X-Ray and Gamma-Ray Detectors and Applications IV, (10 January 2003); doi: 10.1117/12.450826; https://doi.org/10.1117/12.450826

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