On the Anodization Trimming of Ti－Si0_2 Cermet Thin Film Resistors

The trimming of the resistance of thin film resistors has been carried out by cutting their size with mechanical cutter or laser beam. However, the cutting method generally introduces micro-cracking into the thin films. The cermet thin films consisting of Si0_2 and metal are deposited more thickl compared with metal thin film resistors, but are rather weak against mechanical and thermal shock. Therefore, we have investigated the trimming by changing the film thckiness by anodic oxidation for cermet thin film resistors. The Ti-Si0_2 cermet thin films were anodized for 30 minutes at several different anodizing voltages using filter papers, which were wetted with Dimethyl Sulfoxide-Phosphoric Acid （20％）solution, and sandwiched between the film and top cathode electrode. The films showed a wide resistance change by anodization, but the anodized film resistors were not so stable as expected. By an anodization with the voltage lower than 15 volts, the trimming of less than 5％ is possible and reproducible. The heat-treatment in air after anodization developed markedly the stability of resistance. The cermet thin films, heat-treated at 300℃ for 3 hrs. in air after anodization at 50 volts, showed fairly good stability and a resistance change of less than 1％ by a 1000-hour stability test at 125℃ in air. The films sputtered from a composite target with a 16％ SiO_2 area ratio provided the most stable cermet thin film resistors. It was found that the anodization?heat-treatment combination is the most valuable trimming method in order to realize the exact and stable Ti-SiO_2 cermet thin film resistors