Process integration of a-Si:H Schottky diode and thin film transistor for low-energy X-ray imaging applications

In this paper, we discuss the various design and fabrication issues related to the process integration of a molybdenum/amorphous silicon (Mo/a-Si:H) Schottky diode and a thin film transistor (TFT), for realization of an X-ray pixel intended for large area and low energy imaging applications. Here, the Schottky diode serves as the sensor and the TFT as a switching element for charge readout. Different pixel configurations are fabricated and compared taking into consideration design aspects such as leakage current, process sequence in terms of mask count, fill factor, and mechanical integrity of various layers. Preliminary X-ray response measurements, over the range (40 - 115)kVp, yield a pixel sensitivity of (1-10) million electrons for a readout sampling period of 16.7 ms.