Effect of stress on the pull-in voltage of membranes for MEMS application

In this work, the effect of process residual stress has been studied on three different designs of membranes for RF MEMS switch application. Expressions for the pull-in voltage of stressed membranes have been developed by simple modification of existing relation for unstressed membranes. To validate the results, gold membranes have been fabricated and released successfully using silicon dioxide as the sacrificial layer. The theoretical results show a very good match with experimental results. This expression allows the estimation of the pull-in voltage of stressed membranes without the need for numerical simulations. The stress in the membranes can also be extracted from pull-in voltage measurements. Our results show that high spring constant (K) structures are less prone to deflection and change in the pull-in voltage. Also, for a high stress value, the pull-in voltages of the structures become almost independent of the spring constant.