The research group of Professor Aimin Song of the School of Microelectronics proposed a new type of thin-film transistor with high performance. The result has been published in Proceedings of the National Academy of Sciences of the United States of America (PNAS, IF: 9.41) with title “Extremely high-gain source-gated transistors”. Prof. Song is the corresponding author and the co-first authors are Dr. Jiawei Zhang and Dr. Joshua Wilson from the University of Manchester. PhD candidate Yiming Wang, Dr. Mingsheng Xu, and Associate Prof. Qian Xin are the co-authors of this work.
Transistors are the bedrock of the recent technology revolutions that have shaped the modern world. To drive further advancement, new transistors must be designed to meet industry needs. One unconventional transistor design combines the thin-film transistor (TFT) with another fundamental component of electronics, the Schottky diode. The resulting advantages include high intrinsic gain, low-voltage saturation, insensitivity to channel length and semiconductor quality, and improved stability. Within the literature, such devices with common designs and characteristics are given various names, such as source-gated transistors (SGTs), Schottky barrier TFTs, and tunneling contact transistors. Under these different names, conflicting theories of device operation continue to be put forward. For example, the gate dependence of the current has been variously attributed to lowering of the source barrier height, increased tunneling current, and modulation of the effective source length. There are also differing claims about the effects of using a Schottky drain contact. Similarly, diode reverse current saturation, tunneling, and depletion of the semiconductor by the source have all been suggested as causes of current saturation.
Prof. Song proposed a new design rule of the SGTs using oxide semiconductors based on his recent discovery of the conduction mechanism in reverse-biased thin-film Schottky diodes (ACS Appl. Electron. Mater. 1, 8, 1570, 2019). The analytical theory was also presented and verified using simulation and experimental results. The oxide semiconductor SGTs with intrinsic gains consistently above 10,000 (peaking around 29,000) are demonstrated. Furthermore, the research group produces oxide semiconductor SGTs that are intrinsically impervious to NBITS. Moreover, these same devices show no indication of performance degradation down to channel lengths of 360 nm, one or two orders of magnitude smaller than typical IGZO TFTs. Finally, such design no longer restricts the channel layer to being a semiconductor as demonstrated by using a semimetal-like oxide, indium tin oxide (ITO).
In the past few years, Prof. Song and his research group has made a series of advances in the thin-film Schottky junctions, such as the analytical theory of the thin-film Schottky diode (ACS Appl. Electron. Mater. 1, 8, 1570, 2019), influences of inhomogeneities in the thin-film Schottky diodes (Applied Physics Letters, 111, 213503, 2017, IF:3.60), and flexible IGZO Schottky diodes with record operating frequency (Nature Communications, 6, 751, 2015, IF:12.12). This work was supported by the North-West Nanoscience Doctoral Training Center, the Engineering and Physical Sciences Research Council (EPSRC) Grants EP/N021258/1 and EP/G03737X/1, National Key Research and Development Program of China Grants 2016YFA0301200 and 2016YFA0201800, and National Natural Science Foundation of China Grants 11374185 and 11304180.
