Balanced-Bridge Method for the Characterization of Dielectric Charging in RF MEMS Cantilever Switches

This paper presents a balanced-bridge method for the characterization of dielectric charging effect in RF MEMS (radio frequency micro-electromechanical system) cantilever switches. The method measures the relative change of up-state capacitance caused by dielectric charging. Compared with previous methods, this approach employs simple and inexpensive test equipment. The test system consists of two symmetric capacitive switches, two adjustable resistors, a function generator, and a voltmeter. Measurement results indicate that it can achieve a resolution of 0.1 fF/Q. By this test system, the slight variation of up-state capacitance can be converted to the significant change of the resistance. Analysis of the experimental data shows that dielectric charging under the DC-voltage stress mainly occurs in the first 1200 seconds. The mechanisms resulting in capacitance variation can be divided into two groups: dielectric polarization and charge injection. Moreover, in contrast to the DC voltage, the RF signal does not have a significant influence on the charging process.