Radio frequency (RF) microelectromechanical system (MEMS) switches have advantages over their solid-state counterparts. However, ohmic contact MEMS devices face several significant limitations, preventing entry into the mass market. These limitations are cost, reliability, packaging, and integration.
The device described in this work is an advancement of a low-cost, process-independent RF MEMS switch that shares all of that switch’s benefits, with new benefits described herein. This device is again based on a single crystal silicon mechanical structure, but incorporates a refractory metal contact, dry release, and improved RF design, along with mechanical changes for improved robustness and performance. The design can be adapted to both SOI (silicon on insulator) and bulk silicon CMOS (complementary metal-oxide semiconductor) processes. This device is also suitable for usage as a leakage control device or relay. Cost for typical RF MEMS devices is driven up by low yields and high production costs. RF MEMS fabrication typically relies on a separate, secondary fabrication process due to material and processing incompatibilities with modern CMOS processes. Because the secondary fabrication is not as well characterized or controlled, process variation in key mechanical properties of the device may be significantly affected, resulting in dramatic variation in device behavior outside of specified criteria. For the device presented here, utilizing the extremely well characterized CMOS fabrication processes, one can expect dramatic improvements in device yield and uniformity.
Reduction in packaging complexity and improved integration also follow closely from the proposed device. Current implementations of ohmic contact RF MEMS switches fall into the following primary categories: off-chip discrete component, bonded wafer, and above-wafer post-processing. In each, close proximity and direct integration of the MEMS device as a circuit component are inherently physically limited, and the RF performance benefits of the device are mitigated by packaging losses. By directly fabricating the RF MEMS device alongside the CMOS circuitry with a dry release process, a complete system or subsystem can minimize losses due to elimination or significant reduction in packaging complexity, vias, wirebonds, and interconnects. This in turn, directly enables much closer integration of the MEMS switch to the rest of the associated electronics.
This work was done by Adam Fruehling and Dimitrios Peroulis of Purdue University for Johnson Space Center. MSC-25475-1