Frequency trimming of SAW devices

This paper describes a frequency trimming technique suitable for GHz band SAW devices. A frequency shift was obtained by forming grooves on the substrate surface using an RF reactive sputter etching technique. Because the center frequency of a SAW transducer in a GHz band is very sensitive to the groove depth, a precise control of the etched amount is necessary. A very low etching rate of less than 1 nm/min. has been realized by modification of a conventional RF diode sputter etching apparatus. The low etching rate made it possible to realize precise frequency trimming for GHz band filters. Frequency trimming of more than 1000 ppm was obtained without any remarkable characteristic changes