Thin-film transistors (TFTs) are an important class of semiconductor devices, which have a wide range of application values ​​in flat panel displays, sensors and other fields. In recent years, wide-bandgap oxide semiconductors have attracted extensive research interests in the field of thin-film transistors due to their low-temperature film formation, high electron mobility, and transparency to visible light. Due to the weak capacitive coupling of the conventional SiO2 gate dielectric, the typical operating voltage of the current thin film transistor is generally greater than 10V, which greatly limits its application in the portable field. Studies have shown that ionic liquids and ionic gels (IonGels) have low-frequency electric double-layer capacitances as high as 10 μF/cm2. The researchers used this type of electric double layer gate dielectric to fabricate organic thin film transistors with an operating voltage of only 1.0V-2.0V. But so far, such gate dielectrics are rarely used in the development of inorganic oxide semiconductor transistor devices.
Beginning in 2009, Wan Qing's research group from Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences observed a huge electric double layer capacitance in a microporous film system composed of nano-SiO2 particles, and used the dielectric film as a gate dielectric to successfully develop a high-performance, Low-voltage transparent thin-film transistor with an operating voltage of less than 1.5V (Appl.Phys.Lett.95, 152114(2009); Appl. Phys. Lett.96, 043114(2010)). The paper was highlighted by NatureAsiaMaterials entitled transparent transistors: lowpower, high performance. On this basis, the research group successfully developed high-performance paper transistors on paper substrates using a full room temperature process, and achieved transistor enhancement and depletion regulation through oxygen pressure regulation technology (IEEE Trans. on Electron Devices. 57, 2258 (2010)). In addition, the research group also introduced Li, H plasma into the SiO2 nanoparticle film by simply soaking, which significantly enhanced the electric double layer capacitance of the gate dielectric. Then, an ultra-low voltage oxide electric double layer thin film transistor with vertical structure was successfully developed (IEEE Electron Device Letters, 31, 1263 (2010); Appl. Phys. Lett. 97, 052104 (2010)).
Recently, the research group has independently developed a self-assembly process. Using only one mask, the ITO channel and ITO source/drain electrodes are deposited on the electric double layer gate dielectric with one magnetron sputtering, and the transistor fabrication is completed. (IEEE Electron Device Letters. 31, 1137 (2010)). In addition, the research group should also use a single SnO2 nanowire as the transistor channel to successfully develop an ultra-low voltage, fully transparent nanowire electric double-layer transistor (Journal of Materials Chemistry, 20, 8010 (2010)).
The above-mentioned ultra-low voltage electric double-layer transistors based on oxide semiconductors have wide application value in the fields of low-cost, portable sensing and display devices.