A Packaging Solution to Reduce Electrical Noise in MEMS Capacitive Elements Resulting from Environmental Mechanical Vibrations

摘要

Micromachined parallel plate capacitors are utilized as subcomponents in many different types of MEMS devices, including tunable RF and optical components, accelerometers and pressure sensors. In many of these types of devices, the separation distance between the capacitor electrodes can be altered either by the application of internal or external forces. Time varying relative motion of the electrodes results in the generation of electrical current in the capacitor circuit if charge is stored in the capacitor. This phenomenon has been exploited to measure the relative velocity between the two electrodes through detecting the current flowing out of the capacitor when a DC voltage is applied across it [1]. However, this phenomenon can be undesirable if the resulting current flowing out of the capacitor is a noise current in the overall electrical system. This phenomenon and the resulting intermodulation products have been well characterized when this even occurs due to two RF signals passing through a micromachined capacitor so that they cause relative motion between the electrodes due to the resulting electrostatic force between the electrodes [2]. Another case where this can occur is when the capacitor electrodes are forced into relative motion by an external event, such as mechanical vibrations present in the operating environment.