The influence of residual stress and membrane thickness on the performance of Fe–Ni–Cr/Invar bimetal freestanding membrane for microdevices

Abstract

This study attempts to demonstrate that the 75Fe–22Ni–3Cr (FNC)/64Fe–36Ni (Invar) bimetal membrane seem to be a promising candidate for the fabrication of microelectromechanical system (MEMS) devices. The performance and mechanical properties of a series of freestanding membrane under mechanical and thermal load is presented. It is found that the residual stress level and membrane thickness play an important role on the membrane performance. For membrane with thickness of 1 μm and 1 mm in side length, a 164 MPa elevation in residual stress may result in 30% reduction in membrane deflection. The increase in membrane thickness increases both the flexural rigidity of the membrane and the effective current conduction cross-section. The decrease of the flexibility of the membrane results in a reduction in deflection of about 25% as thickness varies from 0.9 to 2.0 μm. Meanwhile, the Young’s modulus also decreases quickly as membrane thickness decreased by virtue of the grain size variation, approaching the value of the bulk material of 190 GPa at about 3.2 μm thick. On the other hand, the reduction in membrane resistance may reduce the heating power. As a result, the increase in membrane thickness from 2 to 3.2 μm cause a reduction in conversion efficiency factor (CEF) of 72% from 1027 to 743 μm/W.