Mechanical Stress and Process Integration of Direct X-ray Detector and TFT in a-Si:H Technology

This paper presents an alternate strategy to reduce the mechanical stress issues pertinent to the process integration of molybdenum/hydrogenated amorphous silicon (Mo/a-Si:H) Schottky diodes and thin film transistors (TFTs), used as X-ray sensor pixels for medical imaging. The previous approach was to minimize the intrinsic stress in the Mo layer through appropriate process conditions and film thickness, but over narrow process latitude and with a compromise in X-ray sensitivity. Alternatively, the mechanical stress in Mo can be reduced by reducing and/or avoiding the extrinsic stress exerted on Mo by the underlying films through a different masking sequence in the fabrication. This modified process allows for a more flexible design of the Mo layer for enhanced X-ray sensitivity, while maintaining the mechanical integrity of the various layers. Also, the performance of the Schottky diode is improved, in terms of its forward current. The pixel shows good linearity in the X-ray response over the range of 40 ∼ 100 kV p .