An Improved Micro-Fabrication Technique for Aluminum Electrode of Surface-Acoustic-Wave Transducers

The SILO (spacer-inserted lift-off) method, using a sputtered ZnO film as a spacer, was proposed and its usefulness in a micro-fabrication technique for making surface-acoustic-wave transducer aluminum electrodes was certified. This technique is based on the fact that the H3PO4 solution etching-rate on the ZnO film is much larger than that on an aluminum film. A precise ZnO film etching-rate measurement was demonstrated by an optical multiple reflection method, using a He–Ne laser beam. These techniques enabled fabricating an about 0.8 µm wide aluminum electrode without any damage. This electrode width corresponds to about 1 GHz fundamental frequency.