SAW interferometers using micromachined silicon plates

A general purpose sensor structure has been invented that is based on the SAW propagation characteristics and the micromachining properties of silicon, single-crystal substrates. The two distinctive cavity shapes that are obtainable by micromachining a silicon die with a KOH etchant are used to define the beam paths needed to form a SAWI (Surface Acoustic Wave Interferometer). Design principles and fabrication procedures are described and results are presented. Devices with a silicon die size, 20 mm long and 10 mm wide, and with InterDigital Transducers (IDTs) using a 5 μm thick ZnO film and operating in the 60 to 100 MHz frequency range, have been built and tested. The ability of the basic structure to function as an interferometer has been demonstrated