Stress bimorph MEMS switches and methods of making same

Abstract

A micro-electromechanical system (MEMS) switch formed on a substrate, the switch comprising a transmission line formed on the substrate, a substrate electrostatic plate formed on the substrate, and an actuating portion. The actuating portion comprises a cantilever anchor formed on the substrate and a cantilevered actuator arm extending from the cantilever anchor. Attraction of the actuator arm toward the substrate brings an electrical contact into engagement with the portions of the transmission line separated by a gap, thus bridging the transmission line gap and closing the circuit. In order to maximize electrical isolation between the transmission line and the electrical contact in an OFF-state while maintaining a low actuation voltage, the actuator arm is bent such that the minimum separation distance between the transmission line and the electrical contact is equal to or greater than the maximum separation distance between the substrate electrostatic plate and arm electrostatic plate.

Description

BACKGROUND [0001] 1. Field [0002] The present invention relates to micro-electromechanical systems (MEMS) and, in particular, to a micromachined electromechanical radio frequency (RF) switch that can preferably function over a range of signal frequencies from 0 Hz to approximately 100 GHz. [0003] 2. Description of Related Art [0004] MEMS (micro-electromechanical system) switches have a wide variety of uses in both military and commercial applications. For example, electrostatically actuated micro-electromechanical switches can conduct RF current in applications involving the use of antenna phase shifters, in the tuning of reconfigurable antenna elements, and in the fabrication of tunable filters. [0005] A representative example of a prior art MEMS switch is disclosed in Yao, U.S. Pat. No. 5,578,976, issued Nov. 26, 1996. Typically, this type of MEMS switch is fabricated on a semi-insulating substrate with a suspended micro-beam element as a cantilevered actuator arm. The cantilever ...

AI Technical Summary

Benefits of technology

The present invention relates to electromechanical switches that minimize the OFF-state capacitance of the switch without increasing the actuation voltage required to activate it. This is achieved by controlling the separation distance between the actuator arm and the substrate, which allows for a large separation between the transmission line and the substrate. The actuator arm is designed to bend away from the substrate when the switch is open, reducing the capacitance in the OFF state. The switches can be fabricated using standard integrated circuit fabrication processes. The technical effect of the invention is to provide a high-isolation switch with low OFF-state capacitance, suitable for high-frequency applications.

Problems solved by technology

Thus, the distance between the metal contact and the RF signal line when the RF MEMS switch is in the open position is limited to the distance between the cantilever actuator arm and the substrate along nearly the entire length of the cantilever actuator arm.

However, integrated RF MEMS switches are difficult to implement.

Due to the proximity of the electrical contact formed on the cantilever arm to the signal line formed on the substrate, these switches tend to exhibit poor electrical isolation at high frequencies.

These losses, which increase with signal frequency, limit the use of MEMS switches in high frequency applications.

However, in the MEMS switch described above, there is a design tradeoff between the OFF-state capacitance and the switch actuation voltage.

Another problem with the conventional cantilever switch described above stems from the methods used to manufacture the switch.

One problem with the use of this release process for a beam in relatively close proximity to the substrate is that surface tension forces exerted by the release agent tend to pull the beam toward the substrate as the device is immersed in and pulled out of the solutions.

The unbalanced residual stresses can be generated by manipulation of deposition process parameters during formation of the actuator arm structure.

Images