Micromachined silicon resonant strain gauges fabricated using SOIwafer technology

The optimum mode of double-ended tuning-fork-style resonators is a lateral vibration in the plane of the wafer. Lateral vibrations are typically excited using the comb drive approach, but this requires modification to the resonator structure. This paper reports a simple method for exciting and detecting lateral vibrations without modifying the resonator, thereby enabling the optimum dynamically balanced structure to be used. This approach uses plane electrodes positioned parallel to the resonator's tines to excite the vibrations while the change in resistance along the length of the resonator enables the vibrations to be detected. Test devices have been fabricated in single-crystal silicon using the buried oxide in silicon-on-insulator wafers as a sacrificial layer. The resonators are 340-μm long, 3-μm thick with tines 2-μm wide. The gap between the tines and the electrode is 2 μm. Visual inspection in a scanning electron microscope and electrical tests have confirmed the validity of this approach