LiCoO2 thin films prepared by RF sputtered

Thin film processing is an important step in the fabrication of microbattery. In this research, the LiCoO2 thin films were deposited on Pt-coated silicon. Various parameters such as the different working pressures and the various ratio of Ar/O-2 gas flow of RF sputtering process were investigated. It was observed that after annealing at 600degreesC, the films consist of only LiCoO2 phase under the 20mTorr by RF sputtering process. In addition to LiCoO2 phase, a Co3O4 second phase was obtained when the sputtering was carried out at a higher or lower working pressure than 20mTorr. The as-deposited LiCoO2 films were annealed at different temperatures for crystallization. The crystallization of layered LiCoO2 was strongly affected by the annealing temperature. After annealing at 500 similar to 600degreesC, the LiCoO2 films exhibited (110) preferred orientation followed by two weak reflections (101) and (003). A strong (003) reflection was also detected in the films but only after annealing at 700-800degreesC. The extent of crystallization of the films increased with the increase of annealing temperature. The grain sizes of the crystalline LiCoO2 films annealed at 600degreesC and 700degreesC were 30nm and 40mn, respectively. The CV test shows two well-defined oxidation and reduction current peaks. Thus, the film deposited by RF sputtering was electrochemical active. The capacity for 0.7mum LiCoO2 thin film was about 50muAh/cm(2) mum.