Warpage Study of Electrodeposited-Au Micro-Components with Ti/Au Multi-Layered Structures toward MEMS Applications

Abstract

Electrodeposited Au-based micro-electromechanical systems (MEMS) capacitive accelerometers with Ti/Au multi-layered structures are promising devices for detecting very low accelerations due to the high mass density of Au. On the other hand, the large difference in the coefficients of thermal expansion (CTE) between Ti and Au causes warpage in the electrodeposited-Au proof masses in MEMS capacitive accelerometers, which reduces the accuracy of the acceleration sensing. In this study, the warpage behavior of electrodeposited Au proof masses with Ti/Au structures is evaluated to clarify factors affecting their structural stability. Ti/Au multi-layered proof masses with four different multi-layered structures and seven different sizes are fabricated. The warpage of the proof mass is quantified by the height information determined by a 3D optical microscope. The 3D optical microscopy analyses show that the observed concave warpage is suppressed by increasing the layer number of Ti/Au layered structures in the proof mass. The warpage is also investigated by Finite Element Analysis (FEA) simulations. The experimental results are in good agreement with the FEA simulations.