Authors: J. Dittmer, A. Dittmer, R. Judaschke, S. Büttgenbach
Affilation: Technische Universität Braunschweig, Germany
Pages: 521 - 524
Keywords: rf MEMS, design, modeling, electrostatic, torsional actuator, rms voltage
The optimization of design parameters and methods for electrostatic voltage sensors based on torsional actuators is presented. The analytical software model used for this optimization process is discussed and compared to measurement results. Voltage excitation leads to an electrostatic attractive force, inducing a deflection of the actuator which in turn is detected using capacitance measurement. The conventional measurement principle for RMS voltages is based on power dissipation by ohmic resistance. We look at devices with parallel plate capacitances in a rotational design, which allows direct, substitution and compensation measurement of RF voltages. An analytical and numerical model for this type of sensor is presented, focusing on absolute and relative sensitivity and precision for metrology purposes. The main design parameters are extracted from this model and variation of each is discussed. The influence of fabrication tolerances on the dimensions and subsequently on the measuring results is researched and an upper limit is given. Using this model, sensor designs are developed which fulfil the requirements for electrostatic voltage sensing for different sensitivity and range requirements. The final designs are checked against fabrication process limitations and an estimate of the maximum total error is given. The results of this work are verified with devices designed with this theoretical understanding and built in a micromechanical bulk silicon process.