Design and characterization of a robust MEMS membrane under residual stress

MEMS membranes are utilized as both transmitter and receiver in acoustic and ultrasound applications. Their operating frequency ranges are determined by their resonance frequencies. Thus, the resonance frequency estimation is one of the most critical part of the membrane design. In this study, two perforated circular MEMS membranes are designed and fabricated with PolyMUMPs process. The radius values are chosen as 220 µm and 205 µm to get proper operation under residual stress since this stress might cause buckling of the membrane. Finite element methods (FEM) and optical measurements are performed to extract the resonance frequencies. For the fundamental mode, the FEM results deviate 5.5% and 6.7% from the experimental work. Also, critical stress parameters of the membranes are investigated with finite element analysis. 33.4% stress relaxation is achieved for the proposed perforated membranes. Furthermore, eight different circular membranes are simulated and compared with the analytical solutions. The minimum and maximum average errors are acquired as 0.5% and 3.3% for the fundamental mode. The electrical characterizations are carried out with the impedance analyzer and results are supported by FEM. Stress was successfully managed with the help of the perforation, as verified by the experimental work and simulations.