Preparation of oxide semiconductor films via solution deposition method and investigation on the interfaces inside the films

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Zinc oxide films were fabricated using a sol, which was prepared from zinc acetate with additions of diethanolamine, and co-addition of monoethanolamine and acetoin. The prepared sol was 0.5 mol/L concentration. The co-added amounts of monoethanolamine and acetoin were equimolar and a half molar to zinc, respectively. The substrates used were heat resistant glass and silicon wafer with oxide layer of 130 nm thick. A non-ionic surfactant was used for coating on silicon wafer. Deposited films by a dip-coating procedure were heated at 600 to 900 to form oxide films. In order to investigate the thin film transistor, zirconia thin film was also deposited between the silicon wafer and zinc oxide layer.By rapid heat treatment, zinc oxide films were oriented with c-axis perpendicular to the substrate surface. The electrical resistivity of the films heated at 500-600℃ ranged 1 to 5 Ωcm, and became larger when heated higher temperature. The film of the lowest resistivity, had a carrier density of 10^<16> cm^3 and a mobility of 1-5 cm^2/Vs. The measurement of electrical conductivity of this film deposited on SiO_2/Si wafer revealed a considerable amount of leakage current through the insulating SiO_2 layer. This leakage was attributed to defects of the SiO2 layer. In order to passivate the SiO_2 layer, cover deposition with Ta_2O_5 or ZrO_2 was examined. The ZrO_2 film with smooth surface was obtained and the film prevented the leakage through the insulating layer. Thus manufactured multilayered film, ZnO/ZrO_2/SiO_2/Si, exhibited an excellent feature as a thin film transistor.