Characterization of current programmed amorphous silicon active pixel sensor readout circuit for dual mode diagnostic digital x-ray imaging

Abstract

A dual mode current-programmed, current-output active pixel sensor (DCAPS) in amorphous silicon (a-Si:H) technology is introduced for digital X-ray imaging, and in particular, for hybrid fluoroscopic and radiographic imagers. Here, each pixel includes an extra capacitor that selectively is coupled to the pixel capacitance to realize the dual mode behavior. Pixel structure, operation and characteristics are presented. The proposed DCAPS circuit was fabricated and assembled using an in-house bottom gate inverted staggered a-Si:H thin film transistor (TFT) process. Gain, lifetime, transient performance as well as noise analysis were carried out. The results are promising and demonstrate that the DCAPS enables dual mode X-ray imaging while compensating for the long term electrical and thermal stress related a-Si TFT threshold voltage (V t ) shift.