A mechanical approach to overcome RF MEMS switch stiction problem

Abstract

MEMS switches provide high isolation when open and low insertion loss vhen closed. They also Iuve the advantages of low p o w r consumption. Thcrefore, RF MEMS switches are an attractive solution to switch antenna bands and transmit/rcceive switching for future multi-band. high bandwidth cell phones. However: Stiction is a major concern for resistive sn-itchcs with metal-to-mctal contact.An iterative-coupled electrostatic-structuml analysis is utilized to evaluate the effect of design parameters on restoring force of MEMS switches. Parameters including mctal thickness, diclcctric thickness. beam-to-ground gap height: metal and dielectric width. and cantilcvcr beam length can be evaluated. The clcctrostatic force is first calculated based on the clcctrical field component. A strnctural analysis is then performed to determine the cantilever beam deflection due to the electrostatic force. A unique integrated empiricalnumerical method is used to qualitativel?-dctcrminc the stiction force bascd on measured actuation \'ohages for real dcviccs. The analysis can provide quick evaluation and screenings of proposed designs to dctcnnine if their actuation voltage falls in the acceptable range. Simulation prediction agrees ver?. well with test measurements.Although increasing cantilever thickncss and shortening cantilever length both increasc restoring force, the actuation vollage will increase significantly as a result. The most favorable moditication is to increase the clcctrode area. A short and wide smctnre with a large area can increase rcstoring force while maintaining low actuation voltage. Compared to similar bi-layer designs, sandwich designs can be actuated at fulther reduced voltages without changing the beam restoring force. In addition, the sandwich structure:being thermal-stress-balanced, is less sensitive to temperature excursion. With the properly selected design parameters, the new designs will be able to achieve the break awav restoring force of the original design at much lower actuation voltages.Switches with good electrical as well as mechanical performances have been successfully fabricated.

Mechanically tri-stable, true single-pole-double-throw (SPDT) switches

“…Thus, unlike typical latching mechanisms in optical switches e.g., the interlocking hooks are not only utilized for mechanical bistability, but at the same time for creating the passive contact force between the switching contacts. This special concept of utilizing the actuators active and passive forces in the opposite way as in conventional switch designs, makes it very suitable for soft contact materials such as gold, being known for developing large adhesion forces between the touching switch contacts [29,30], but requiring only a small contact force for a low and stable contact resistance [31][32][33]. The forces of a bi-stable variant of the presented switch concept and its suitability for soft contact materials have been thoroughly investigated by the authors in an earlier study [13].…”

Design of Stictionfree - Lower Pull in Voltage RF MEMS Switch Using Varying Section Cantilever Beam

“…To overcome stiction large restoring force is essential, which can be achieved with larger values of cantilever width and thickness [3]. This in turn will tend to increase the pull-in voltage where as lower pull-in voltage is the main focus.…”