Dual-Gate Photosensitive a-Si:H Thin-Film Transistor With a $\pi $ -Shape Channel for Large-Area Imaging and Sensing

This letter reports on a photosensitive dual-gate amorphous silicon (a-Si:H) thin-film transistor (TFT) for low-level light detection. It differs from a conventional dual-gate TFT in that a 760-nm π -shape channel layer is implemented instead of a typically thin a-Si:H layer of 50 ~ 100 nm in the conventional TFTs. Not only such a device improves the photoabsorption, it also preserves the transfer characteristics of the TFT. Upon the low-level light exposure, the photosensitivity can be multiplied by operating the device in the subthreshold region. In addition, resetting the device can minimize the residual photocurrent and improves the photoresponse. The device can be, therefore, sensitive and fast enough to enable optical applications, such as low-dose indirect-conversion X-ray imaging and large-area document scanning.