Design of Micro-Plates Subjected to Residual Stresses in MEMS Applications

Abstract

Micro-beams and micro-plates fabricated by deposition suffer from stiffening and curling, resulting from residual stresses initiated during fabrication. Stiffening and curling affect the performance of these micro-structures in MEMS applications. Reducing response time is also favourable in MEMS applications such as RF MEMS switches. Previous literature shows that it is challenging to reduce both phenomena simultaneously. This thesis proposes a new design concept aiming at reducing both stiffening and curling. In addition, reducing switching time is also taken into consideration. First, simplified model for a fixed-fixed beam is studied to examine the factors affecting stiffening, and curling. The analytical solution of the beam model depicts that stiffening can be decreased by increasing the ratio between the second moment of area of the beam cross-section and its cross-sectional area. In addition, increasing this ratio increases the critical buckling temperature. Thus, extending the operational temperature range of the MEMS device. This simple beam model cannot capture the plate effects. Thus, a Finite Element model is developed. The Finite Element model is verified with previous results in the literature. A preliminary parametric size optimization is done on three well-known configurations of flat micro-plates with fixed-fixed supports. The objective is to study the effect of in-plane (2D) structure enhancement in reducing stiffening, curling, and increasing the natural frequency. The higher is the natural frequency, the lower the switching time. For comparison purposes, same volume is set as a constraint for all three designs. Compared to conventional rectangular micro-plate, a reduction of 34% in stiffening for configuration 2, and 44% in curling for configuration 3 are achieved. configuration 1 showed the maximum fundamental natural frequency. Thus, it is predicted to have the lowest switching time. Moreover, configuration 2 showed the maximum critical buckling temperature. The effect of changing micro-plate material is also studied.