High mobility, solution processed p-type TFTs employing NiOx semiconducting channels

Afouxenidis, Dimitrios and Milne, W.I. and Adamopoulos, George (2016) High mobility, solution processed p-type TFTs employing NiOx semiconducting channels. In: EMRS 2016 Spring Meeting, 2016-05-022016-05-06.

Abstract

Despite the tremendous potential of all oxide thin film transistors for application in large area microelectronics further advancements have been hampered by the lack of hole transporting oxides with similar or comparable transport characteristics to their n-type counterparts. Although there are a few studies reporting p-type doping of traditional n-type oxides, the subject still remains controversial and stable p-type material has not been reproducibly observed. Hence, alternative metal oxides that show intrinsic p-type characteristics are required especially for applications in CMOS (complementary metal oxide semiconductor). There has been some success with alternative materials such as Cu2O and SnOx and indeed p-type TFTs were reported[1]. However TFTs incorporating Cu2O as a semiconducting channel suffer from a very low field effect mobility (< 10-2 cm2 V-1 s-1) making it unsuitable for CMOS applications. Additionally, these TFTs show high off-state currents that indicate the presence of a large number of copper vacancy defect states that pin the Fermi Level in the device. Here we report the fabrication of hole-transporting NiOx-based TFTs. Nickel nitrate hexahydrate and erythritol solutions in ethanol (0.2 M) were spin coated onto fused silica, c-Si, spray coated Al2O3 gate dielectrics and glass and underwent thermal annealing at different temperatures in air. Analyses revealed that at the optimum annealing temperature of about 340 oC NiOx films (80 nm) with optical band gap of about 3.6 eV and overall transmittance in the visible spectrum in excess of 75 % were produced. X-ray diffraction showed both cubic and hexagonal NiOx polycrystalline material (average crystal size of 15 nm) embedded in a dominant amorphous matrix. TFTs employing thermal evaporated gold source and drain contacts exhibit excellent hole transport characteristics with negligible hysteresis, low operating voltages (-10 V), high hole mobility in the order of 10 cm2 V−1 s−1 and high current on/off ratio of about 10^4. [1] P. Pattanasattayavong, S. Thomas, G. Adamopoulos, M. A. McLachlan and T. D. Anthopoulos, p-channel thin-film transistors based on spray-coated Cu2O films, Appl. Phys. Lett, 102, 163505, 2013