A Numerical Study of an Amorphous Silicon Dual-Gate Photo Thin-Film Transistor for Low-Dose X-Ray Imaging

Abstract

The amorphous silicon flat panel X-ray detector (FPD) has gained significant adoption in digital radiography such as chest radiography due to its large size and superior performance. As a fundamental building block of a FPD, the pixel is composed of sensor, storage and readout units to collect charges and transfer them to external electronics. In all current pixel architectures, however, these three aforementioned components are unanimously separate. It would inevitably compromise spatial resolution due to increased pixel size. Thus, we propose a compact design of a “smart” pixel to combine sensor, storage and readout units into one single dual-gate photo thin-film transistor (TFT). Simulation results indicated that an implementation of a $\pi$ -shape channel structure would enhance photo absorption and preserve switching performance as well. The sensitivity of the device is dependent on the threshold voltage shift induced by light illumination, which in turn enlarges the photocurrent. A numerical study also showed a total noise of approximately ${\sim} {\hbox{700}}$ e and a dynamic range of 120 dB can be achieved, which potentially outperforms current available amorphous silicon passive pixel sensor. The “smart” pixel therefore holds a great promise for high-resolution and low-dose X-ray imaging, which may potentially reduce the cancer risk induced by X-ray radiation, especially for pediatric patients.