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Proceedings Paper

High-resolution high fill factor a-Si:H sensor arrays for medical imaging
Author(s): Jeffrey T. Rahn; Francesco Lemmi; Richard L. Weisfield; Rene Lujan; Ping Mei; Jeng-Ping Lu; Jackson Ho; Steve E. Ready; Raj B. Apte; Per Nylen; James B. Boyce; Robert A. Street
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Paper Abstract

We describe new amorphous silicon (a-Si:H) image sensor arrays which are the highest resolution imagers so far reported. The pixel sizes of 64 micrometer (resolution 8 lp/mm) and 75 micrometer (6.7 lp/mm) are made possible using a photodiode technology that enables high sensor fill factor even in very small pixels. This approach allows the a-Si:H imagers to satisfy high resolution requirements of digital mammography. Each array contains 512 X 512 pixels with matrix addressing provided by a-Si:H thin film transistors (TFT). The high fill factor structure contains a continuous a-Si:H photodiode layer grown on top of the TFT array, with contacts to each pixel through a patterned metal/n+ layer. X-ray detection is accomplished by use of a phosphor layer superimposed on the array. The continuous photodiode layer maximizes light absorption from the phosphor and provides high x-ray conversion efficiency. Since the photodiode forms a continuous layer, crosstalk between adjacent pixels due to the lack of isolation is a particular concern, and has been extensively studied. We find that the high fill factor structure can be made such that the lateral charge leakage is minimal in the dark or under moderate illumination, although small amount of charge spreading is observed under conditions of sensor saturation. The measured MTF for optical illumination exceeds 60% at the Nyquist frequency, even for long integration times.

Paper Details

Date Published: 28 May 1999
PDF: 8 pages
Proc. SPIE 3659, Medical Imaging 1999: Physics of Medical Imaging, (28 May 1999); doi: 10.1117/12.349529
Show Author Affiliations
Jeffrey T. Rahn, Xerox Palo Alto Research Ctr. (United States)
Francesco Lemmi, Xerox Palo Alto Research Ctr. (United States)
Richard L. Weisfield, dpiX, a Xerox New Enterprise Co. (United States)
Rene Lujan, dpiX, a Xerox New Enterprise Co. (United States)
Ping Mei, Xerox Palo Alto Research Ctr. (United States)
Jeng-Ping Lu, Xerox Palo Alto Research Ctr. (United States)
Jackson Ho, Xerox Palo Alto Research Ctr. (United States)
Steve E. Ready, Xerox Palo Alto Research Ctr. (United States)
Raj B. Apte, Xerox Palo Alto Research Ctr. (United States)
Per Nylen, Xerox Palo Alto Research Ctr. (United States)
James B. Boyce, Xerox Palo Alto Research Ctr. (United States)
Robert A. Street, Xerox Palo Alto Research Ctr. (United States)


Published in SPIE Proceedings Vol. 3659:
Medical Imaging 1999: Physics of Medical Imaging
John M. Boone; James T. Dobbins, Editor(s)

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