Development and Modeling of a Wafer-Level BCB Packaging Method for Capacitive RF MEMS Switches

This paper presents a novel wafer-level packaging method for shunt, capacitive RF MEMS switches using BCB as the adhesive interlayer. Fabrication and electrical characteristics of the proposed package were initially evaluated for 50 Omega CPW lines. Microwave measurements of these packaged test structures were fitted to a circuit model, which was later employed to optimize the package for RF MEMS switches. The proposed packaging method was next successfully integrated with an in-house RF MEMS fabrication process. Mechanical and microwave characteristics of these switches were investigated prior to and following the packaging process. Measured shear strength for five packaged switches averages to 18.3 MPa. MEMS bridges deflect by 71 nm on the average due to the packaging step. C-V measurements show 4.2 V average increase in pull-in voltages. Millimeter-wave measurements confirm the negligible effect of package on switch performance. Measured upstate return and insertion losses at 35 GHz read 28 and 0.4 dB, respectively. The downstate isolation attains 35 dB at 35 GHz for most of the packaged switches. Lifetime measurements of a packaged switch demonstrate 10.2 billion cycles without failure.