Impact of Geometry on Thermoelastic Damping in Flexural Mode Resonators

In the design of Micro ElectroMechanical Systems (MEMS) such as micro-resonators, one of the major energy dissipation mechanisms to consider is Thermoelastic Damping (TED) .TED is an important issue in the development of MEMS based actuators, resonators, and filters when the microstructures are resonating under flexural mode of vibration.TED is induced by the irreversible heat dissipation during the coupling of heat transfer and strain rate in an oscillating system. The magnitude of the energy loss depends on the vibrational frequency and the thermal relaxation time constant of the structure. TED highly affects the Quality factor (Q Factor) and a high value of Q is always preferred for reliable operation. In this work, width dimensions on TED limited QFactor of simple fixed-fixed beam resonators in flexural mode are analyzed. It is found that depending on the resonance frequency of microstructures, different Q are obtained.The performance of such MEMS resonators is directly related to their thermoelastic quality factor which has to be predicted accurately. In this paper, the geometry dependence of the Q factor of MEMS resonators is analyzed. The methods to alleviate this energy loss is achieved by the proper geometric design of the resonator structures. The changes in the dimensions of the resonator highly affects its resonant frequencies and thus the Q factor. It is seen that at some particular width,there is a huge transition for Q value and it is proposed that this width is the critical width of the resonator. In this paper, the critical width of a Simple beam fixed-fixed type resonator corresponds to a value of 25µm and whenever this width is exceeded eigen frequencies of the resonator drastically falls and Q factor rapidly drops to a very low value. The geometric effects play an important role in limiting Q factor and by proper design of the dimensions of the resonator structures high Q is achieved. The effects of geometry on the energy dissipation induced by TED are investigated using COMSOL Multiphysics software. Index terms- Eigen frequency analysis, Flexural mode resonators, QFactor, Thermoelastic Damping