Design, modeling and fabrication of a copper electroplated MEMS, membrane based electric field sensor

Abstract

A MEMS based electrostatic field sensor is presented which uses capacitive interrogation of an electrostatic force deflected microstructure. First the deflection of the sensor’s membrane which is caused by electrostatic force in the presence of electric field is calculated both by simulation and theoretical model and it has been shown that the results of the simulations have acceptable values compared to the theoretical ones. Simulation models have also been designed to improve the vibration of the membrane for measuring the ac electric fields. It has been shown that by adding perforations to the surface of the membrane, it is possible to reduce the air drag force effect on the membrane and still have similar electrostatic force on the membrane. Therefore, it is possible to reduce the damping due to air resistance in membrane movement when measuring ac fields. After successful modeling of the sensor structure, the fabrication process for the sensor has been designed. The electroplating process as the most important fabrication step has been studied in detail prior to starting the fabrication of sensor. The process parameters for electroplating process, such as current amplitudes, duty cycle and frequency have been optimized to get the lowest surface roughness to thickness ratio for the electroplated films. A lithography molding process was developed for the electroplating. Both dc and pulse plated films have been studied to show the role of pulse plating in improving the quality of the electroplated films. It was found during the release process that the electroplated copper interacted with sulfur during plasma etching of silicon. However, the result of the releasing process was very helpful to find the best recipe of releasing and they can be used in next projects.