Active Matrix a-Si:H Thin Film Transistors Back Plane with Light Shield Structure for Imager Application
Gwanghyeon Baek, Geonwook Yoo and Jerzy Kanicki
For high resolution imager application, photo-diode (PD) is proposed to be integrated on the top of a-Si:H TFT active matrix backplane. With this structure, fill factor of 80%, pixel pitch of 50x5 5µm2 and critical dimension of 5µm could be achieved. However, the light which is not absorbed by active region of photodiode penetrates into channel area of a-Si:H TFT and induces high leakage current. Consequently, photo-current generated by the PD smaller than Ioff vanishes and dynamic range of imager decreases. Before depositing a pixel electrode layer, metal layer of 200 nm thickness was sputtered and another layer of passivation was inserted between light shield and electrode layer. By implementing this light shield structure, light induced leakage current is successfully suppressed as shown in the figure below; (left) without and (right) with light shield structure. This work is supported by the DARPA/MTO HARDI program.
