Study On Preparation And Mechanism Of ITO Ceramic Target With Controllable Grain Size

With the rapid development of the electronic information industry,the needs of the sputtering target were increasing.ITO materials have attracted domestic and international attention because of their excellent photoelectric properties and wide application prospects.To satisfy the needs of high-quality ITO targets,in this paper the nanometer indium oxide and tin oxide powders were taken as raw materials and the sand milling was used to get ITO slurry with high solid content and low viscosity.Then pressure slip casting was used to obtain high-density green compacts.Finally,the densification and fine-grained ITO ceramic targets were prepared by a two-step sintering method.We constructed the master sintering curve（MSC）of ITO targets through dilatometer data with heating rates of 1℃/min,3℃/min,5℃/min,and7℃/min,which describe the sintering behavior of ITO targets sintered in air and oxygen atmospheres and predict the apparent activation energy of densification Q_ssuccessfully.The brook dynamic model of grain growth was used to calculate the grain growth activation energy Q_t.The grain size controllable conditions and grain growth mechanism of ITO targets were systematically studied from kinetics.In this experiment,analysis of rheological properties of ITO slurry by laser particle size analyzer,viscosimeter,Zeta potential.XRD,SEM,XPS,four-probe,densitometer and other analysis methods were used to analyze the microstructure and properties of the ITO targets.The main research results are as follows:（1）The effects of pH,dispersant amount,solid content,and sand milling time on rheological properties of ITO slurry were studied.The results showed that the maximum absolute value of zeta potential is 55.9 m V and the slurry system is the most stable when the pH value is 10.The optimal ITO slurry,in which NH₄PAA dispersant content is 0.7 wt%and solid content is 75 wt%was obtained.The average particle size of ITO slurry decreases with the extension of the sand milling time from 10 minutes to70 minutes,and then increases due to huge surface energy caused by particle agglomeration.The minimum average particle size and viscosity of the slurry is 192nm and 90 m Pa·s(25℃,the shear rate is 1.98 S^-1)respectively when sand milling time is 50 min.（2）The effects of powder pretreatment（sand milling time）,sintering atmosphere（air and oxygen）,sintering temperature,holding time on density and grain size of ITO ceramic targets were studied in conventional sintering.The results showed that ITO slurry with a sand milling time only of 10 min can’t be used for the preparation of densified ceramic targets due to its large number of agglomerates.Oxygen atmosphere can inhibit the decomposition of indium tin oxide to promote the densification of ITO targets.The grain size increases with increasing sintering temperature and holding time.When the green ITO compacts which were prepared by slurry with sand milling time of 50 min were sintered at 1550℃ for 10 h,the ITO targets had excellent properties with an average grain size of 5.19μm,the densification of 99.1%,the resistivity of0.21 mΩ·cm respectively.（3）Study on the kinetic differences of ITO ceramic targets between the grain boundary diffusion and grain boundary migration was carried out.The experiment gives the predict that the apparent activation energy of densification Q_s is 510 k J/mol through building the MSC of ITO targets and the grain growth activation energy Q_t is730 k J/mol through the Brook dynamic model of grain growth.（4）The effects of T₁,T₂,t₂ on the grain size of ITO ceramic targets based on densification were studied in two-step sintering and compared with traditional sintering.The results showed that the two-step sintering process can inhibit the growth of ceramic grains.Under the same density conditions,the grain size of the ITO ceramic targets prepared by the two-step method is reduced by 0.8μm compared with the traditional sintering.When T₁is 1550℃,t₁ is 0.5 h,T₂is 1450℃,t₂ is 20 h,the average grain size of ITO targets is 3.80μm,the densification is 99.4%,the resistivity is 0.20 mΩ·cm,respectively.The"kinetic window"for reaching full density without grain growth of the ITO targets is determined by regulation of two-step sintering parameters（T₁,T₂,t₂）.