Study Of Indium Gallium Zinc Oxide Thin Film Transistors

Recently, with the development of large liquid crystal and organ-ic-light-emitting-diode displays, conventional silicon and organic TFTs cannot satisfy the requirements, transparent amorphous oxide semiconductors (TAOSs) represented by In-Ga-Zn-O (IGZO), which satisfy almost all the requirements, are expected to be the channel material of TFTs in next-generation flat-panel displays. Thin film transis-tors(TFTs) based on indium gallium zinc oxide as active layer were studied in this thesis. As a code part of the TFT, the characteristics of active layer, such as film quality, thick-ness, will strongly determine the performance of TFTs. In addition, annealing treatment is an important way to improve the performance of TFTs.Firstly, indium gallium zinc oxide (IGZO) thin films were deposited by magnetron sputtering and studied. X-ray photoelectron spectroscopy measurements were per-formed to find out the quantitative and qualitative chemical properties of the IGZO thin films. The atomic ratio of In:Ga:Zn of the IGZO thin films was consistent with the tar-get. It could be found that the introduction of O2 in the sputtering could inhibit oxygen vacancies. The result of XRD measurement indicated the structure of IGZO films depo-sited at lower substrate temperature (below 200℃) was amorphous. AFM results showed that the surface of IGZO films was smooth. IGZO thin films showed high opti-cal transmission in the visible region, the optical band gap was approximately 3.69eV and decreased with the substrate temperature improvement. Furthermore, we studied IGZO thin films deposited with different sputtering power (50W,100W), the results showed that the film deposited under 100W has a smoother surface and higher trans-mittance in the visible region.Secondly, on the basis of optimized sputtering parameters, IGZO-TFTs with dif-ferent IGZO thickness (40,60,80,120nm) were fabricated on SiO2/Si substrates using top contact configuration with bottom gate. The electrical properties of devices showed that TFTs with a 80nm thick active layer showed the best performance, such as field-effect mobility (0.113cm2/Vs), threshold voltage (-12.99V) and on/off-current ratio (2.56×102). All the devices operated in n-type depletion mode.Finally, in order to investigate the effect of annealing on the performance of IG-ZO-TFT, devices were annealed at different temperature (without annealed,200℃, 400℃) before the source and drain electrodes were deposited. The electrical properties of devices showed that the field-effect mobility of TFTs was increased after annealing treatment, but the threshold voltage exhibited small negative shifts. XRD results showed IGZO films annealed at 400℃began to crystallize and had a rougher surface according to the AFM measurement. It could be concluded that annealing at 200℃was more ef-fective than 400℃to improve the performance of IGZO-TFTs.