Radiation imaging with 2D a-Si sensor arrays

Radiation imaging with a large-area amorphous silicon (a-Si) sensor array is discussed. X-ray images approaching medical diagnostic quality were obtained by a 256×240 array of 0.45 mm pixel pitch with 40 ms exposure time. Low-flux γ-ray imaging was demonstrated by a 64×40 sensor array with a pixel pitch of 0.9 mm, operated at a low external bias with 20-s integration time. The signal readout process is modeled and compared with experiments. At low external bias, charge collection and retention characteristics were influenced by the additional sensor-bias created by the charge injection associated with the thin-film transistor operation. Charge retention in a sensor element was limited by the leakage through the sensor