Physics of microcontacts for MEMS relays.

摘要

The significant opportunities for MEMS switching devices have fueled interest in the government, industrial, and academic communities. Contemporary MEMS relays have made substantial improvements, but research into the limitations of the electrical contact itself has been neglected. To further this work, the author has performed a series of low-load experiments on different metals to determine contact performance characteristics. Contact force is applied and DC current load is passed through a contact, with resistance measured by a four-point-probe method. Contacts are made under both hot-switch and cold-switch conditions, varying applied force and current loads, as well as electrode morphology.; Two plated gold contact systems were explored in this work. The system of HRL Laboratories is an electroplated cathode mated to a hard sputtered anode under hot-switch conditions. Several hundred muN of force are required for stable resistance, and current loads of 100 mA can be switched with nominal damage. Thermal conduction and surface hardness are found to be critical parameters. In comparison, electroless plated gold showed low, stable contact resistance but higher thermal sensitivity and damage with force and current loading, attributed to material softness. Cold-switched electroless gold suffered from contact resistance instability with reduced damage.; Two sputtered rhenium film contact systems were explored. The first, a void-filled rhenium, demonstrated high variance to current loading. Overall resistance and its thermal sensitivity are high due to voiding of subsurface material. Initial strike instability is also high, but instability of the subsequent contact is low. The second film, a dense sputtered rhenium, performed with superior hot-switch characteristics. The high thermal conductance gave the best overall hot-switch performance, with cold-switching offering the lowest overall damage and highest resistance stability.; A MEMS relay was developed at HRL Laboratories based on the switching requirements obtained from the experiments on the sputtered to electroplated gold system. Contact performance is shown to be comparable to the initial experiment, with devices proven functional and within specification. The relay was shown to have comparable DC and RF power handling characteristics as limited by the contact constrictions.