Dual-gate photo thin-film transistor: a "smart" pixel for high- resolution and low-dose X-ray imaging

6th International Conference on Optical, Optoelectronic and Photonic Materials and Applications 2014

Wang, Kai^1,2 ; Ou, Hai^3 ; Chen, Jun^3

Sun Yat-sen University-Carnegie Mellon, University Joint Institute of Engineering, Sun Yat-sen University, Guangzhou

510275, China^1

Sun Yat-sen University-Carnegie Mellon, University Shunde International, Joint Research Institute, Foshan

528300, China^2

State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Province Key Laboratory of Display Material and Technology, School of Physics and Engineering, Sun Yat-sen University, Guangzhou

510275, China^3

关键词: Amorphous silicon flat-panel;    Amplification effects;    Flat panel detectors;    Fundamental building blocks;    Light-induced threshold;    Low-level light detections;    Photolithography process;    Sub-threshold regions;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/619/1/012023/pdf
DOI  :  10.1088/1742-6596/619/1/012023

来源: IOP

【 摘 要 】

Since its emergence a decade ago, amorphous silicon flat panel X-ray detector has established itself as a ubiquitous platform for an array of digital radiography modalities. The fundamental building block of a flat panel detector is called a pixel. In all current pixel architectures, sensing, storage, and readout are unanimously kept separate, inevitably compromising resolution by increasing pixel size. To address this issue, we hereby propose a "smart" pixel architecture where the aforementioned three components are combined in a single dual-gate photo thin-film transistor (TFT). In other words, the dual-gate photo TFT itself functions as a sensor, a storage capacitor, and a switch concurrently. Additionally, by harnessing the amplification effect of such a thin-film transistor, we for the first time created a single-transistor active pixel sensor. The proof-of-concept device had a W/L ratio of 250μm/20μm and was fabricated using a simple five-mask photolithography process, where a 130nm transparent ITO was used as the top photo gate, and a 200nm amorphous silicon as the absorbing channel layer. The preliminary results demonstrated that the photocurrent had been increased by four orders of magnitude due to light-induced threshold voltage shift in the sub-threshold region. The device sensitivity could be simply tuned by photo gate bias to specifically target low-level light detection. The dependence of threshold voltage on light illumination indicated that a dynamic range of at least 80dB could be achieved. The "smart" pixel technology holds tremendous promise for developing high-resolution and low-dose X-ray imaging and may potentially lower the cancer risk imposed by radiation, especially among paediatric patients.