High Performance Amorphous Silicon Image Sensor for X-ray Diagnostic Medical Imaging Applications

Following our previous report concerning the development of a 127 μm resolution, 7.4 million pixel, 30 x 40 cm active area, flat panel amorphous Silicon (a-Si) x-ray image sensor, this paper describes enhancements in image sensor performance in the areas of image lag, linearity, sensitivity, and electronic noise. New process improvements in fabricating a-Si thin film transistor (TFT)/photodiode arrays have reduced first-frame image lag to less than 2%, and uniformity in photoresponse to < 5% over the entire 30 x 40 cm active area. Detailed analysis of image lag vs. time and x-ray dose will be discussed. An improved charge amplifier has been introduced to suppress image cross-talk artifacts caused by charge amplifier saturation, and system linearity has been optimized to eliminate banding effects among charge amplifiers. Preliminary sensitivity improvements through the deposition of CsI(Tl) directly on the arrays are reported, as well as overall imaging characteristics of this improved image sensor.