Signal, noise, and readout considerations in the development of amorphous silicon photodiode arrays for radiotherapy and diagnostic x-ray imaging

Recent advances in the fabrication of sensors and transistors from hydrogenated amorphous silicon are allowing the creation of flat panel, large area, radiation-damage-resistant arrays for radiotherapy and diagnostic imaging. A straightforward application of available a-Si:H technology involves the configuration of photodiode sensors coupled with field effect transistors into regular 2-dimensional pixel patterns. While the specifications of the array design must be tailored to the demands of the imaging application, the design is at the same time constrained by various array parameters. Considerations affecting choices for these parameters and how they relate to the signal, noise, and readout properties of radiotherapy arrays are presented and some initial data reported. Implications for a-Si:H diagnostic imagers are discussed.