MEMS relays for make-break power switching applications : {111} silicon etched planar electrical contacts

Abstract

Relays and switches are of interest in applications such as test equipment, radar, communications, and power systems, amongst others. Unlike solid state switches, mechanical relays provide galvanic isolation across the power ports. This characteristic is important because, for safety reasons, electrical codes stipulate that loads in certain power applications must be disconnected by open gaps. This requirement imposes significant isolation, heat dissipation, tribology and reliability constraints on a relay.The objective of this research is to explore power handling by a MEMS device in a relay context. This work presents concepts, analytical performance models, fabrication processes and design rules for MEMS relays capable of hot-switching inductive loads in power applications. To this end, a horizontal-displacement, electrostaticallyactuated, MEMS relay for make-break power switching applications is presented. The MEMS-relays are etched in (100) Si through a combination of KOH etching, and DRIE, bonded to a glass substrate, and plated with a 10 /pm thick buffer film of either copper or nickel-cobalt, and a 1-2 [mu]m thick film of a platinum-family metal such as palladium, rhodium, and alloyed palladium (palladium-cobalt).The relays feature { 111}-plane silicon-etched electrical contacts. The { 111}-plane contacts provide travel of 30-80 [mu]m, which prevents arcing. Their oblique geometry introduces contact wipe, which is known to enhance the contact reliability. Further, the contact geometry allows for an enhanced metallization process which provides lower on-state contact resistance than traditional horizontal displacement Mems-relays. Experimental relays exhibit a best-case total on-state contact resistance of 130 m[omega], a response time of 750 [mu]s, a settling time of 3ms, electrical isolation in excess of 1 kV (tested to 997 V with available equipment), a hot switched current of 800 mA using resistive loads, and a hot switched current of 350 mA using a 1 mH inductive load. The relays have been hot-switched in excess of 10⁵ cycles without signs of performance degradation.