Dissertation Defense, Zhen Peng

Title: Dielectric Charging of RF MEMS Capacitive Switches




While RF (Radio frequency) MEMS (Microelectromechanical system) capacitive switches are poised to be an excellent alternative to RF switch technology, there are still reliability problems limiting the switch’s lifetime. In particular, dielectric charging is the most important reliability issue in RF MEMS capacitive switches.


In this work, a novel technique is used to separate the surface charging and bulk charging in the dielectrics of different types of RF MEMS capacitive switches under different electric field, humidity levels and packaging practices. The ambient humidity affects surface charging and discharging through enhanced surface conduction. By solving a coupled surface-bulk charge diffusion problem and by fitting the solution with measured discharging characteristics of a silicon-nitride dielectric, the surface and bulk diffusivities are determined to be on the order of 10−10 cm2/s and 10−14 cm2/s, respectively. On the other hand, after minimizing surface charging, remaining bulk charging can be modeled and characterized to predict its impact on switch lifetime. A high-cycle life test is demonstrated only limited in bulk charging. A bipolar charging model is also developed based on superposition of unipolar charging model; well predict the bulk charging behavior. Charge transport mechanism is also discussed by examining the steady-state current voltage characteristics for Al/SiO2/Cr Metal-insulator-metal capacitors under different bias and temperature conditions.

In this presentation, I will selectively summarize my research achievements on dielectric charging of RF MEMS Capacitive switches.

PhD Committee:

Prof.  James C.M. Hwang (Chairman and advisor, ECE, Lehigh)

Prof. Svetlana Tatic-Lucic (ECE, Lehigh)

Dr.  Chuck L. Goldsmith (MEMtronics)

Prof.  Richard P. Vinci (MSE, Lehigh)

Prof. Boon S. Ooi (ECE, Lehigh)

Prof. Richard Decker (ECE, Lehigh)