Research On Preparation And Performance Of Indium Tin Oxide Powders And Targets

Indium tin oxide（ITO）films have been applied in the fields of flat panel displays,solar cells and gas sensors,due to high optical transmittance,low resistivity,high infrared reflectance and ultraviolet absorptance.At present,the magnetron sputtering has been the mainstream preparation technology for ITO films,which utilizes ITO targets as raw material.Therefore,the high-quality ITO targets are the prerequisite for preparing ITO films with excellent performance.However,the independent research and development of domestic ITO targets start relatively late.Nowadays,China relies on imports of the upscale ITO targets from Japan and South Korea,and the performance of domestic targets still needs to be improved.The preparation of high-quality ITO targets is regarded as one of the"bottleneck"technologies that needs to tackle.On the other hand,the high-density ITO targets are prepared by pressureless sintering at high sintering temperature.That causes abnormal grain growth of ITO targets,and thus could influence the optoelectronic properties of ITO films.In view of the above two problems,this work optimized the preparation process of ITO targets based on pressureless sintering from the two processes of powder preparation and target sintering.And the sintering mechanism of ITO targets was revealed,providing theoretical and experimental guidance for the preparation of high-performance ITO targets.Firstly,the ITO powders with spherical and cubic shapes were prepared by polyacrylamide gel method and seed-assisted coprecipitation method.The effects of preparation process parameters on powder properties were systematically studied,and the different preparation mechanisms of ITO powders were analyzed.Secondly,the high-density and low-resistivity ITO targets were prepared using the prepared ITO submicro-cubes as the raw material.The effects of sintering additive content and sintering temperature on the microstructures and properties of ITO targets were discussed.The action mechanisms of sintering additives were clarified,and the grain growth activation energy of ITO targets was calculated.The main research works and results are as follows.1.The spherical ITO nanopowders were prepared by polyacrylamide gel method.The preparation process was optimized by single factor experiment and orthogonal experiment design.And the effects of molar ratio of monomer（AM）and crosslinker（MBAM）,In³⁺concentration,p H,calcination temperature and holding time on powder resistivity were systematically studied.The best preparation process combination was obtained:molar ratio of monomer and crosslinker was 25/6,In³⁺concentration was 0.3 mol/L,calcination temperature was 700°C and holding time was 9 h.The significance order of affecting ITO nanopowder resistivity was as follow:n（AM）/n（MBAM）>calcination temperature>In³⁺concentration>holding time.Under the optimum preparation process,a low-resistivity value of 0.161Ω·cm was achieved for nearly spherical-like c-ITO nanopowders with particle size distribution of34～54 nm.2.The ITO submicro-cubes were prepared by seed-assisted coprecipitation method.The preparation process was optimized by single factor experiment and orthogonal experiment design.And the effects of seed（indium tin hydroxide）content,In³⁺concentration,aging time,reaction temperature and calcination temperature on powder resistivity were systematically studied.The best preparation process combination was obtained:seed content was 6 wt%,In³⁺concentration was 0.06 mol/L,reaction temperature was 80°C and calcination temperature was 750°C.The significance order of affecting ITO submicro-cubes resistivity was as follow:calcination temperature>seed content>reaction temperature>In³⁺concentration.Under the optimum preparation process,the optimal powders with well dispersion were indexed to cubic phase In₂O₃,and presented a cubic shape with a size of nearly 500 nm and low resistivity of 0.814Ω·cm.3.The high-density and low-resistivity ITO targets were prepared with Bi₂O₃-CeO₂ sintering additives,using the prepared ITO submicro-cubes as raw materials.The effects of sintering additive content and sintering temperature on properties of ITO targets were studied.The results revealed that all ITO targets showed the cubic phase In₂O₃ and rhombohedral phase In₄Sn₃O₁₂.The appropriate Bi₂O₃ and CeO₂ additions decreased sintering temperature from1550 to 1500℃,and refined grain size from 4.19 to 3.65μm.Compared with the additive-free ITO targets(99.44%,2.56×10^-4Ω·cm),the ITO target with1.0 wt%Bi₂O₃-1.0 wt%CeO₂ showed the higher relative density of 99.57%and the lower resistivity of 1.82×10^-4Ω·cm.Moreover,the ITO target had the excellent mechanical properties,namely nanohardness,Young’s modulus and fracture toughness of 13.70 GPa,148.50 GPa and 1.60 MPa·m^1/2,and the grain growth kinetics was applied to calculate the grain growth activation energy of394.79 kJ/mol.4.The high-density and low-resistivity ITO targets were prepared with Sb₂O₃-CeO₂ sintering additives,using the prepared ITO submicro-cubes as raw materials.The effects of sintering additive content and sintering temperature on properties of ITO targets were studied.The results revealed that all ITO targets showed the cubic phase In₂O₃ and rhombohedral phase In₄Sn₃O₁₂.After adding an appropriate amount of Sb₂O₃ and CeO₂,Sb₂O₃ formed liquid phase to accelerate the mass transfer,decreasing sintering temperature from 1550 to1450℃.Meanwhile,Sb₂O₃ was converted into Sb₂O₄.Sb₂O₄ and CeO₂ of donor dopants could generate extra free electrons in the process of substituting In³⁺,reducing the resistivity of ITO targets.Compared with the additive-free ITO targets(99.44%,2.56×10^-4Ω·cm),the ITO target with 1.0 wt%Sb₂O₃-1.5 wt%CeO₂ showed the maximum relative density of 99.61%and the minimum resistivity of 1.71×10^-4Ω·cm.Moreover,the ITO target had the maximum nanohardness,Young’s modulus and fracture toughness of 14.95 GPa,216.53 GPa and 2.06 MPa·m^1/2,and the grain growth kinetics was applied to calculate the grain growth activation energy of 456.16 kJ/mol.