Production trimming of SAW devices using CF4 chemistry and its effects on SAW characteristics

This paper presents a method of precise frequency trimming of Surface Acoustic Wave (SAW) devices using Reactive Ion Etching (RIE). The SAW devices are fabricated on quartz wafers and trimmed down in frequency by removing part of the quartz substrate between the electrodes, thus achieving the specified center frequency. A controlled frequency shift in the range of 10 kHz to 400 kHz is demonstrated. It has been observed that quartz etch rates of <100 Å/min. can be controlled, resulting in very low frequency shifts. Also, presealed hybrid and surface mount parts have been successfully trimmed to achieve a desired center frequency. Various parameters and test results are presented with no significant change in insertion loss or bandwidth observed. This method is simple and cost effective in high-volume SAW device production. Finally, a viable low-cost, high-volume production method of SAW device fabrication using this trimming process is demonstrated