The Preparation And Study Of Indium Gallium Zinc Oxide And Indium Zinc Oxide Targets

At present,IGZO-TFT are expected to overcome the disadvantages of low carrier mobility and high energy consumption of silicon-based TFTs.Because the quality of IGZO target determines the performance of IGZO-TFT,the key to the successful application of IGZO is to prepare high-quality IGZO target.This paper aims to study IGZO target,firstly,nano-scale IGZO powders are prepared by multi-step coprecipitation method to enhance the sintering activity of powder and green compacts.Then green compacts are treated by cold sintering process（CSP）and dry pressing process（CP）,and master sintering curve（MSC）of InGaZnO₄is established for the sintering process of green compacts.Secondly,IGZO powders with different particle sizes are planetary ball milled to increase the density of green compact,InGaZnO₄target with high density and low shrinkage is successfully prepared.Non-isothermal sintering kinetic model is used to clarify the material diffusion mechanism of IGZO sintering process,the lattice distortion of ball milled powders is quantitatively analyzed by double Voigt function to analyse the mechanism of planetary ball milling enhancing the sintering performance of IGZO powders.Based on the mechanism,In₂Ga₂ZnO₇targets with uniform microstructure and IZO targets are prepared.Finally,the effects of annealing temperature on the photoelectric properties of IZO,IGZO and IZO/IGZO thin films are studied by DC magnetron sputtering.The main conclusions are as follows:（1）When the reaction temperature of multi-step coprecipitation method was about10℃,the stoichiometric ratio of precursor powder elements was closest to the theoretical atomic ratio of InGaZnO₄.CSP process promoted the material transportation and rearrangement between powder particles in the molding process.The densities of CSP compacts were higher than that of CP compacts under the same sintering conditions.When the CSP parameters were 200MPa and 180℃,and the treated green compact was sintered at 1200℃for 1h,the highest relative density of InGaZnO₄compacts was 99.30%.The results of MSC model showed that the activation energy Qa of CSP/PLS process and CP/PLS process were 489.7k J·mol^-1and 655.6k J·mol^-1,respectively.（2）The main factors affecting the dispersibility of mixed powders were the ball to material ratio and dispersant,the highest density of green compact was 67.14%.When the green compact was sintered at 1400℃for 150 min,the relative density of InGaZnO₄compact reached the highest of 99.50%,and the resistivity was 6.07×10^-3Ω·cm.The specific surface area,grain size and the lattice distortion of the powders are optimized with the increase of milling speed.The lattice distortion of the powders milled at 300rpm（IGZO-3）,200rpm（IGZO-2）were 1.62～2.85 times,2.01～10.27 times than that of powders milled at 100rpm（IGZO-1）,respectively.The densification rate and grain growth rate of InGaZnO₄increase with the increase of milling speed.The highest relative densities of IGZO-1,IGZO-2 and IGZO-3 compacts were 92.87%,98.72%and 99.12%,respectively.Grain boundary diffusion was the main mechanism of grain growth for InGaZnO₄,and the activation energies of grain growth for IGZO-1,IGZO-2 and IGZO-3compacts were 78.78,67.17 and 49.52k J·mol^-1,respectively.（3）After planetary ball milling of IGZO powders（In:Ga:Zn=2:2:1）and IZO-1（In₂O₃:ZnO=1:1）,IZO-2（In₂O₃:ZnO=1:3）,IZO-3（In₂O₃:ZnO=1:5）powders,due to the volatilization of In₂O₃in compact and the concentration gradient of In in the second phase,the diffusion of In leaded to the decomposition of In₂Ga₂ZnO₇and the segregation region increased with the sintering temperature increasing from 1250℃to 1500℃.Thus,the second phase in compact increased with the increase of sintering temperature and holding time.Single-phase In₂Ga₂ZnO₇compact was formed after holding at 1300℃for 8h,and the relative density reached 99.25%,resistivity was 3.17×10^-3Ω·cm.Under the same sintering conditions,IZO-1 owned the lowest resistivity,IZO-2 owned the largest grain size and IZO-3 owned the highest density.When the sintering temperature was 1500℃,the lowest resistivity of IZO-1 was 2.53×10^-3Ω·cm,the highest relative density of IZO-3was 99.25%.（4）After annealing at 200℃,400℃and 600℃,the visible light transmittance of IZO films was between 82%and 93%,and the band gap was between 2.79e V and 3.81e V.The lowest resistivity was 2.09Ω·cm when IZO-2 films annealed at 400℃.The maximum carrier concentration and mobility of IZO-1 films were 4.17×10¹⁷·cm^-3and15.34cm²·V^-1·S^-1when deposited at room temperature.Under the same conditions,the visible light transmittance of IGZO was 80%～89%,and the band gap was 3.54e V～3.82e V.The e lowest resistivity was 8.41×10^-2Ω·cm,the maximum carrier mobility was4.78cm²·V^-1·S^-1,and the maximum carrier concentration was 5.85×10¹⁹·cm^-3.The lowest resistivity of IZO/IGZO film was 4.36×10^-1Ω·cm,the maximum carrier concentration was2.42×10¹⁸·cm^-3,the maximum carrier mobility was 7.57cm²·V^-1·S^-1,which proved that the IZO/IGZO thin film retained the advantages of high carrier mobility of IZO films,low resistivity and high carrier concentration of IGZO films.