Temperature detection using micro plate vibrations

Pala, Sedat
This thesis presents the design, modelling, fabrication and characterization of a resonant MEMS plate temperature sensor. In the proposed application, temperature change is measured by tracking natural frequency shifts of a specific mode shape of the resonating micro plate. The design and modelling of the resonant MEMS plate temperature sensor are conducted for Chladni plate geometry that is square plate supported at the geometric center, having all edges free to move. Energy methods are utilized to solve the equation of motion of transversely vibrating Chladni plate structure to obtain the closed form equations for the mode shapes and respective natural frequencies with electrostatic softening effect. Thermo-electro-mechanical model is derived with the addition of thermal effect on top of the electromechanical solution. Finite Element (FE) simulations are conducted for each step of analytical model to verify the derived model. The designed sensors are fabricated using a silicon-on-glass (SOG) process. The fabricated temperature sensors are characterized with frequency response and system level temperature tests. The Q-factors of modes (1,1) and (2,0) - (0,2) are measured to be 14300 and 10700 at a vacuum pressure level of 20mTorr, respectively. The Laser Doppler Vibrometer (LDV) tests at vacuum level of 0.364mTorr verify the analytical model and FE simulations. In addition, effect of electrostatic softening is also tested for a proof mass voltage range of 0-40V, and corresponding frequency shift is measured to be 0-26Hz. System level temperature tests are done with a Phase Locked Loop (PLL) to track frequency drifts with changing temperature at vacuum level of 0.405mTorr. The scale factor of the fabricated sensor is obtained as 2.0214Hz/°C and 2.7211Hz/°C for mode shapes (1,1) and (2,0) - (0,2), respectively. The temperature equivalent frequency instabilities of the fabricated sensor are measured to be 0.3725mK for (1,1) mode shapes and 0.1499mK for (2,0) - (0,2) mode shape.  
Citation Formats
S. Pala, “Temperature detection using micro plate vibrations,” M.S. - Master of Science, Middle East Technical University, 2017.