Bulk Foil Pt-Rh Micro-relays for High Power RF and Other Applications.

Abstract

This work explores the potential of bulk foil metal alloys on micromachined relays for high power DC and RF applications. Platinum-rhodium (Pt-Rh) is of particular interest because it is both chemically inert and mechanically robust. The contributions include the investigation of design and manufacturing options, addressing issues such as the geometry of electrostatically actuated cantilevers, the integration of heat sinks, the integration of encapsulation, batch mode fabrication, and other aspects. In one part of the investigation, DC micro-relay test structures using Pt-Rh contacts were benchmarked against the ones using stainless steel (SS316L) contacts. Devices with 6.5 mm2 footprint were directly assembled on the printed circuit boards (PCB). Devices also included microfabricated on-device heat sinks subjected to a heat management using forced cooling to dissipate contact heat. Fabricated micro-relays exhibited 1.5 Ω and 1.25 Ω on-state resistances for SS316L and Pt-Rh contacts, respectively. In hot switching high power tests, Pt-Rh and SS316L micro-relays operated up to 1.8 A and 2.6 A, respectively. In another part of the investigation, RF micro-relays with Pt-Rh contacts were designed and fabricated. Test structures with 6.4 mm2 footprint had 90 V pull-in voltage. The micro-relays had down-state insertion loss and up-state isolation better than-0.2 dB and -25 dB up to 5 GHz, respectively. Unpackaged micro-relays exhibited RF power handling up to 18.5 W hot switching in ambient air. The third part of this investigation was directed at batch mode manufacturing and packaging of micro-relays directly on PCB substrates. For this, 4x1 device arrays were designed, fabricated, and encapsulated. Subsurface metal layers on the PCB were used to transfer the signal into and out of the sealed encapsulation. The footprint of packaged test structures was 8.4 mm2. The contact resistance and the pull-in voltage for the fabricated devices were 78 V and 1.1 Ω for an actuation voltage of 115 V, respectively. The packaged devices operated in atmospheric pressure nitrogen and exhibited down-state insertion loss and up-state isolation better than -0.25 dB, and -15 dB, respectively for up to 5 GHz. Packaged devices operated up to 20 W hot switching RF power.