1. Introduction
Parylene is getting more and more popular for MEMS applications such as for valves, pumps, nozzles, flow sensors and even accelerometers [4]–[7]. Unlike the conventional silicon material, however, parylene has a significant plastic deformation even at room temperature if it is stressed over the yield point. It is therefore very important to measure the not-yet-known yield strength of thin-film parylene so that the operation limit of devices made of parylene can be predicted. For parylene membranes under uniform pressure loading, the total stress is the sum of the intrinsic stress and the loading stress, while intrinsic stress (caused mainly by thermal mismatch between the membrane and the substrate) usually dominates[8]. Although stress distribution models for zero-intrinsic-stress, large-deflection membrane under loadings are available[1], there is the lack of a simple analytical model to cover both the effects of large intrinsic stress and large deflection existent at the same time in membranes[9] [10]. Here we propose to use the membrane load-deflection method[11] to determine the plastic deformation onset pressure of thin-film parylene-c and we present a simple analytic modeling of it.