Electronic Design

Low-Cost Production Of Broadband MEMS Switches Moves Closer To Realty

A surface-micromachined, all-metal wafer-bonding process has been used with high-resistivity silicon to develop an electrostatically actuated broadband microswitch with impressive performance characteristics for dc to RF applications. Device yields of 90% achieved at a commercial MEMS foundry make this process a potential low-cost method for manufacturing broadband MEMS switches for applications like cell phones and operation, the beam is deflected by applying about 80 V between the gate and source electrodes, which produces a contact force of 200 µN (Fig. 1). The contact material is a thin layer of platinum deposited on the underside of the beam and the drain. Wafer-level capping ensures a hermetic seal (Fig. 2).

Typically, each switch has eight contacts in parallel to yield total on-resistance of less than about 0.2 ‡ at dc and low frequencies. On-response time was measured at 5 µs. Lifetimes of more than 1010 cycles (using currents of 10 mA or less) have been achieved. The switch can handle up to 1 A and has a low insertion loss of just 0.3 dB at 2 GHz and 30 dB of isolation.

Prototypes are being made for the U.S. Air Force for an X-band, electronically steerable antenna array. Process and design modifications are also under way to optimize RF performance and contact resistance. A four-terminal device for better isolation is being investigated as well.

Contact Rick Morrison at (978) 562-3866, ext. 296, or [email protected].

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