Tech Briefs

No significant deterioration of performance was found after >1011 switch cycles.

Life tests have demonstrated the longevity of an electrostatically actuated capacitive switch of a microelectromechanical systems (MEMS) type suitable for handling radio signals having frequencies of multiple gigahertz. The tests were performed to contribute to understanding of factors that affect the reliability of MEMS switches in general and of how improvements in designs and materials can increase operational lifetimes of MEMS capacitive switches. The tests were based partly on the concept that data obtained in monitoring both high-speed and low-speed switching characteristics provide valuable insight into quantifying the lifetime properties of the switches and enable estimation of switching lifetimes under a variety of operating conditions.

Figure 1. This MEMS Capacitive Switch was subjected to life tests in which the potentials shown in Figure 2 were measured.
The tests were performed on a stateof- the-art metal-dielectric-metal radiofrequency (RF) MEMS capacitive switch fabricated on a glass substrate (see Figure 1). The top switch electrode was a 0.3-μm thick flexible aluminum-alloy membrane that was suspended over an air gap and was electrically tied to DC and RF ground. The bottom switch electrode was composed of chromium/gold and served as the center conductor of a 50-Ω-impedance coplanar waveguide for the RF signal. Thick copper posts, approximately 3 μm tall, served as anchor points for the suspended membrane as well as RF-transmission-line conductors.

In the absence of applied electrostatic force, the membrane was normally suspended in air at a distance of 2.2 μm above the switch insulator, which was a dielectric layer on the lower switch electrode. Application of a control potential between 25 and 35 V to the bottom electrode produced electrostatic attraction that pulled the membrane into contact with the switch insulator, thus forming a 120-by-80-μm capacitor to shunt the RF signal to ground; this condition was the higher-capacitance or "on" switch state, characterized by a capacitance between 280 and 340 ff. When the control potential was removed, the membrane sprang back to its fully suspended position (the lower-capacitance or "off" switch state) wherein the capacitance was between 15 and 20 fF.