Studies On Fabrication Processes And Properties Of CuO-TFT Using Magnetron Sputtering Method

Since the 21 st century,oxide thin film transistor technology has made great progress.Most of n-channel oxide TFTs have been investigated intensively and even applied to the actual LCD due to their high field-effect mobilities,high optical transparency in visual light range and the characteristic of low temperature preparation.However,the performance of p-type oxide semiconductor material lags far behind of n-type,which prevent the implementation of complementary metal oxide semiconductors based on oxide semiconductors,therefore,it is very necessary to study the p-type TFTs.For the preparation of p-TFTs with good performance.This article focuses on the study for the preparation technics using magnetron sputtering method and performance characterizations of CuO-TFTs,the main contents of the article are as follows:In this work,Cu disk is used as the sputtering target,the samples are deposited on glass substrates by rf-magnetron sputtering with different oxygen partial pressures and different annealing temperatures.And then respectively to study the variations of a series of performances as functions of oxygen partial pressures and annealing temperatures.XRD and XPS results show that the films prepared with the increase of Opps are gradually oxidized.The films prepared with 3% Opp was pure Cu₂ O,the films containe Cu when the Opp less than 3%,and the films transferred to CuO when the Opp more than 3%;The films prepared with higher annealing temperatures have better crystallization properties and bigger grain sizes;And the transmittance in the visible range of the films which thinner than 100 nm is above 70%.Moreover,optial band gaps width of the films under different preparation technics are between 1.9 V and 2.6 V.Hall results show that the carrier mobilities of the films prepared with the increase of Opp at room temperature are gradually increased.After annealing treatment,the carrier mobilities are increased evidently,the biggest can improve to 8.433 cm²/Vs,and the carrier concentrations can depress to 2.873 × 1013 cm^-3.By comparing the performance of the films under different preparation technics,the best deposition parameters of thin films were determined.The two best preparation conditions are as follows: a base pressure of 5 × 10^-7 mbar,a working pressure of 3 × 10^-3 mbar,a rf power of 60 W,the oxygen partial pressure of 3% and 7% respectively,and both annealed at 600? for 10 hours.Further,we fabricated S-BG thin film transistors with “Si-SiO₂-CuO-Al” structure,and the CuO films was prepared by the two deposition conditions above.The two TFTs show typical enhancement mode operation of p-channel transistor,have obvious saturability,and good VGS regulation performance.The active layer of the device with better performance was prepared at lower Opp of 3%.And it give an on-off ratio of 3.0 × 10²,field effect mobility of 0.32 cm²/Vs,threshold voltage of-9 V,subthreshold swing of 5.4 V/dec and Dit of 1.4 × 1012 cm^-2.However,the electrical performances of the two TFTs are not ideal,this probably because the existing of high density hole trap states at the interface layers between the active layers and dielectric layers.Then we compare the transfer curves obtained using a “double sweep” methodology,from the results,a hysteresis of ¹V is observed;Then compare the transfer curves of the fabricated CuO-TFTs measured after different durations of air exposure.It shows that curves slightly increases,and the threshold voltage represent a negative deviation.