Transduction principles of a-Si:H Schottky diode X-ray image sensors

This paper reports on the operating principles, along with design and fabrication considerations, of a novel direct conversion X-ray image sensor based on Mo/a-Si:H Schottky diodes. The choice of Mo as a Schottky contact follows from its relatively low intrinsic mechanical stress, temperature stability, and relatively large X-ray absorption. Furthermore, it is compatible with the standard a Si:H thin film transistor (TFT) technology. Here, the TFTs are intended for use as switching elements in large area imaging applications. Results of X-ray sensitivity are presented for a broad range of X-ray energies (20-100 keV), along with the influence of various geometric and operating parameters on X-ray sensitivity. The detector shows a linear response with respect to the number of absorbed X-ray photons. Analysis shows that the detector sensitivity reaches its maximum for a Mo layer thickness of around 500 nm at 60 kVp. Measurements, performed in a medical environment, demonstrate the feasibility of the detector for large area medical imaging applications.