Chemical Milling and Photochemical Milling

Abstract

Synonyms Electrostatic RF MEMS switches; Micromechanical switches; RF MEMS switches Definition Capacitive micro-electro-mechanical systems (MEMS) switches are a special type of micromachined switches that control radio frequency (RF) signal paths in microwave and millimeter-wave circuits through mechanical motion and contact. Overview Capacitive and direct current (dc)-contact MEMS switches are among the most important micromachined devices for high-frequency applications due to their near-ideal RF performance. Dc-contact switches function similarly to conventional relays: micromachined beams or plates move under the influence of an appropriately applied force (e.g., elec-trostatic force) to open or close a metal-to-metal contact. While micromachined beams or plates are also utilized in capacitive switches, these switches rely on metal-to-dielectric contacts to implement their on and off states. Capacitive switches are particularly attractive for demanding high-frequency communications, electronic warfare, and radar systems due to their ultralow loss (< 0.1-0.2 dB up to 40 GHz), high isolation (>20-50 dB for frequencies beyond 10 GHz), very high linearity (>66 dBm third-order intercept point), and near-zero power consumption ($tens of nJ per switching cycle and zero quiescent power for electrostatically actuated switches). When compared to solid-state switches, capacitive switches are relatively slow devices with speeds ranging in the tens to hundreds of microseconds range. This speed is primarily limited by switch inertia and squeeze film damping. Their relatively large lateral dimensions of tens or hundreds of mm allow capacitive switches to handle several hundred mW of RF power. Long-term operation, however, can only be achieved if they are hermetically sealed in order to avoid contamination-and humidity-induced failure. Hermetically sealed capacitive switches have successfully switched over B. Bhushan