The impact of self-aligned amorphous Si thin film transistors on imager array applications

Laser processing allows the fabrication of self-aligned amorphous Si thin film transistors (a-Si:H TFTs). These devices have much smaller parasitic capacitance between gates and source/drain contacts and can have much shorter channel lengths compared to the conventional a-Si:H TFTs. We have fabricated matrix-addressed, optical imager arrays using these new a-Si:H TFTs as pixel switches. We also have demonstrated that four-phase dynamic shift registers using short channel a-Si:H TFTs can be operated at a clock speed of 400 kHz (less than 0.625 μs for each clock phase), indicating the possibility of integrating some of the peripheral circuits based on a-Si:H TFT technology. The advantages of using self-aligned a-Si TFTs as pixel switches in large-area, flat-panel imagers are discussed. Improved noise performance is expected for large area imager arrays.