MEMS-based devices for RF applications: Switches and field probes

Two MEMS devices are developed and characterized for radio-frequency (RF) applications. The first device is a RF MEMS capacitive switch designed and fabricated with printed circuit processing techniques. The advantages of such fabrication technique allow for the ease of integration and batch fabrication with other RF components, which are very cost-effective. The key feature of this approach is the use of a flexible circuit film, Kapton-E polyimide film, as the movable switch membrane. Switches with top electrode area and gap height are 2 mm x 1 mm and 40 mum, respectively. Electro-mechanical model is established to evaluate different design configurations, and the modeling results are compared with mechanical displacements measured using an interferometer. In addition, a streamlined lifetime testing setup is developed to study the number of operations to failure. The switches reach up to 75 million cycles, with pull-down voltage ranging from 80 V to 120 V.;The second device is for imaging high-frequency (1-20 GHz) near-field microwaves; such a measurement is important to the detection of interference, short, circuits; or coupling of on-chip components. A process is developed to fabricate this MEMS-based cantilever probe by surface and bulk micromachining techniques with dielectric silicon nitride and silicon oxide materials on a silicon wafer. A patterned gold metallization at the tip of the cantilever provides a source of eddy current heating due to the high frequency magnetic field. This thermally absorbed power is converted to mechanical deflection by a trilayer cantilever system. Experimental characterization of the MEMS probes is performed to study the field sensitivity. The spatial resolution achieved is 5 micrometers. Analytical models and finite element models are developed to guide the design of the MEMS probes to yield the appropriate sensitivity. The analysis and experiment show that an asymmetrical tri-layered (nitride-oxide-nitride) structure is a better approach than a bimorph structure because it reduces the curvature associated with the thermal misfit strain developed during high temperature deposition. This probe demonstrates the first eddy current-based magnetic field imaging device with a patterned sensor on dielectric cantilever ever reported.