Solution-processed tin oxide thin film for normally-off hydrogen terminated diamond field effect transistor

The solution processed method has been wildly used in the thin film fabrication because of the advantages of low cost, high efficiency, large scale for production, and long-term stability. In this paper, a normally-off hydrogen-terminated diamond field-effect transistor (FET) has been realized by using a solution processed SnO2 (sp-SnO2) film as an insulator layer. X-ray photoelectron spectroscopy results demonstrated the stoichiometry of the sp-SnO2 film, which shows good insulator properties with leakage current density less than 2.1 × 10−5 A·cm−2 at gate voltages from −6.0 to 6.0 V. The drain–source current maximum, threshold voltage, extrinsic transconductance maximum, and effective mobility of the FET with a gate length of 10 μm are −17.6 mA·mm−1, −0.5 V, 5.7 mS·mm−1, and 41.3 cm2/V s, respectively. According to the capacitance voltage characteristic, the enhancement mode could be ascribed to the high positive fixed charge density in the sp-SnO2 film, which will repel the hole in the channel. This paper provides a simple method and a low temperature process to fabricate an insulator layer.