Spark Plasma Sintering And Electrical Conductivity Of Antimony-doped Tin Oxide (ATO) Ceramic Targets

Antimony doped tin oxide (ATO) as a new kind of tranaparent conductive oxides, has many superior properties, such as wide band gap (3.6eV), high electrical conductivity, high transparency in visible light, good chemical stability, low cost and nontoxic, which can be applied in the solar cells, displays and other photoelectric devices. Magnetron sputtering is one of the most widely used methods in industry for coating large area substrates at a high rate with competitive costs. In order to get high quality ATO thin films, ATO ceramic targets with high density, electrical conductivity and purity used for sputtering are needed. But the densification of ATO ceramics is difficult due to the nondensifying mechanisms (surface diffusion and evaporation-condensation) related to the SnO2system and Sb addition. Added some sintering additives can enhance the density, but may deteriorate the purity and conductivity properties. In addition, the valence variation of Sb (Sb5+and Sb3+) results in the electrical conducitity of ATO ceramics uncontrollable. So, the aim of this research is to prepare the ATO ceramic targets wih high density and conductivity.Firstly, in order to solve the problems of low density of ATO ceramic targets, pure SnO2and ATO nanoparticles with20at.%Sb doping content are used as raw materials, and spark plasma sintering technology are used as sintering method in this paper. These techniques can enhance the density by improving the sintering activity, decrease the sintering temperature and restrain the evaporation of SnO2. The influence of SPS process parameters (sintering temperature, heating rate, pressure and holding time) and Sb doping content on the phase, density and microstructure of ATO ceramic targets is investigated. The optimum sintering process is achieved, when the sintering temperature is1000℃, heating rate is100℃/min, pressure is40MPa, and holding time is3min. And the density of all samples with different Sb doping contents is over94.5%at this process. When the Sb doping content is20at.%, the density of ATO ceramic targets is97.2%.Then, the SPS sintered ATO ceramic targets are post-anealed. The influence of post-annealing temperature and time on the phase, density and microstructure of ATO-12ceramic targets is studied. The results suggest that post-annealing has little influence on the phase and density of ATO ceramic targets.At last, the resistivity of all samples after SPS is above1×10-2Ω·cm. In order to descrease the resistivity of ATO ceramic targets, post-annealing process is introduced in this paper. Post-annealing can eliminate the oxygen vacancies and promote Sb3+oxidized to Sb5+. The influence of Sb5+/Sb3+ratio, density, Sb doping content and micro structure on the resisitivity, carrier concentration and hall mobility of ATO ceramic targets is studied, and the conducting mechanism of ATO ceramic targets is also discussed. The results show that post-annealing is effective for the increase of hall mobility and the decrease of resistivity. When the Sb doping content is12at.%, the resistivity of ATO ceramics post-annealed at800℃for100hours is decreased to a value of5×10-3Ω·cm. The conductivity of ATO ceramic targets is evaluated by the carrier concentration and mobility. It can be enhanced by the increase of carrier concentration and mobility.