Study On The Preparation And Performance Of Inkjet-Printed NiO TFT

Metal oxide semiconductors thin film transistors(TFTs)have superior electrical performances,thermal stability,and excellent optical transparency in visible region.The p-type oxide TFT based on the solution process show wide application prospect in high-performance,low-cost organic light-emitting diodes and low-power complementary metal oxide semiconductor circuits.Inkjet printing(IJP)technology is currently one of the most competitive process technologies because of its feasibility in large area and direct patterning fabrications.In this paper,the active layer of p-type NiOx-TFT was fabricated by IJP technology.The morphology,structure,optical properties of NiOx thin film,as well as the electrical properties of TFT devices were investigated.The main research contents are as follows:Stable ink systems and the control methods of film uniformity were obtained through the study of the ink technology.Stable ink ejection was achieved by adjusting the drive voltage of piezoceramics.The uniformity of the thin film was optimized by controlling the substrate temperature and the viscosity of the ink.The results showed that an increase in substrate temperature enhanced the capillary flow to the edge of the ink droplets,thereby exacerbating the "coffee ring" phenomenon.This effects can be readily eliminated by simply modulating the ink viscosity.With the increase in ink viscosity,ring-like edges of the printed films gradually disappear to form uniform layers due to the inhibition of the outward diffusion of solute,while increasing the ink viscosity excessively resulted in the formation of dome-shaped films.The effects of annealing temperature on the morphology,structure,chemical composition and optical properties of NiOx thin films were systematically studied.The results showed that amorphous NiO.films were obtained at an annealing temperature below 280?.The crystallinity and surface roughness of the NiOx films increased at elevated annealing temperature.The films annealed at 180-380? exhibited high transmittance,and the transmittance decreased slightly with increasing annealing temperature.With the increase of annealing temperature,the band gap of NiOx films reduced and the concentration of nickel vacancies in the films decreased.The electrical properties of IJP NiOx-TFT devices were evaluated.First,the effects of the annealing temperature of the active layer on the electrical properties of the device were studied in a wide temperature window.The best performance of the device was achieved when annealed at 280?,On this basis,the impacts of different dielectric layers(SiO2,Al2O3,TiO2,etc.)on the device performance was also studied.The results showed that the high-k insulating layer was conducive to improving the device performance,while the excessively high interface polarity would confine the transport of carriers.Compared to SiO2 and TiO2 dielectric layers,the devices with Al2O3 films presented better performances.The optimum device performances were obtained for NiOx annealed at 280? on 50 nm-Al2O3 dielectric,with a mobility of 0.78 cm2V-1 s-1,threshold voltage-0.6V,subthreshold swing 1.37 V/dec,and current-switching ratio 5.30×104,respectively.Metal cation-doped NiOx-TFT devices were also fabricated by inkjet printing process.The effect of doping concentration on the device performance was studied.The results showed that copper doping increased the carrier transport path and thus improved device performances.For 3 mol%Cu-doped NiOx device,the mobility,threshold voltage,sub-threshold swing and current-switching ratio were 0.94 cm2V-1s-1,0.3 V,0.72 V/dec,and 6.70×104,respectively.