A passive mechanism for thermal stress regulation in micro-machined beam-type structures

Abstract

In this article, a passive mechanism for thermal stress regulation in micro-bridge structures is proposed. The mechanism is essentially a set of precisely designed parallel chevron beams that replace one of the fixed ends of the micro-bridge. The axial stress/force of the beam is determined by utilizing a sensing mechanism that makes use of two side-electrodes and the electromechanical buckling of the micro-bridge toward one of them. A combination of analytical and finite element methods has been employed for the modeling of the proposed mechanism. It has been demonstrated that the regulator mechanism has negligible dynamic effect on the sensing micro-beam. The model takes into account the effect of electric field fringes between the electrically charged bodies. It has been shown that there is a time delay between the moment that the pull-in occurs and the instant that the sensing beam rests on a side-electrode. The results of the modeling are verified by experiment on two devices fabricated using MetalMUMPs® fabrication technology. The thermal stress sensitivities of the devices are positive and their residual stresses are in excellent agreement.