X-Ray Detection Using a Two-Transistor Active Pixel Sensor Array Coupled to an a-Se X-Ray Photoconductor

A direct-conversion X-ray sensor array using amorphous silicon (a-Si) thin-film transistor (TFT) based active pixel sensor (APS) readout circuit coupled with a stabilized amorphous selenium (a-Se) photoconductor for large-area digital imaging applications is presented. The pixel readout circuit employs a novel two-transistor (2T) active/passive pixel architecture that enables a compact pixel circuit for high-resolution sensor arrays with high large-area fabrication reliability. The X-ray detector consists of an in-house fabricated 150 mum pixel pitch 2-TFT pixel coated with an 80 mum thick a-Se photoconductor. A detector dark current of 110 pA/cm² at 10 V/mum electric field, and a controllable pixel conversion gain up to 8.4 nA/mR with a quantum efficiency of 60% was measured. Capabilities such as voltage programmable gain and dynamic range control, as well as nondestructive readout during X-ray exposure are demonstrated. The detector in this work represents a highly promising technology for high-resolution X-ray digital imaging, adaptable to a wide range of applications owing to its gain and dynamic range programmability.