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 are obtained by a 256 x 240 array of 0.45 mm pixel pitch with 40 ms exposure time. Low-flux gamma ray imaging is demonstrated by a 64 x 40 sensor array with pixel pitch of 0.9 mm, operated at a low external bias with 20 sec integration time. The signal readout process is modeled and compared with experiments. At low external bias, charge collection and retention characteristics are influenced by the additional sensor-bias created by the charge injection associated with the TFT operation. Charge retention in a sensor element is limited by the leakage through the sensor.