An experimental investigation on viscoelastic behavior in tunable planar RF-MEMS resonators

In this paper, the viscoelastic behavior of a tunable RF-MEMS resonator and its impacts are studied by means of direct RF measurements for the first time. This tunable resonator consists of one lambda/2 coplanar waveguide (CPW) Resonator and two nanocrystalline-Ni RF-MEMS varactors. S-parameters of this tunable resonator have been measured for 80 hours under a bi-state bias condition of 0 and 40 V. It is demonstrated that the resonant frequency is shifted by 90 MHz and the varactor deformed by 0.12 ¹m over the 80 hour period. The gap of the loaded varactor is extracted from the measured S-parameters using finite-element analysis (FEA) tools. A generalized Voigt-Kelvin model is employed to verify the viscoelastic behavior of the resonator. The creep compliance extracted from the RF measurements is in excellent agreement with results in literature.