A torsional sensor for MEMS-based RMS voltage measurements

J Dittmer,R Judaschke,S Büttgenbach

doi:10.5194/ars-6-31-2008

Abstract

Abstract. RF voltage measurement based on electrostatic RMS voltage-to-force conversion is an alternative method in comparison to the conventional thermal power dissipation method. It is based on a mechanical force induced by an RF voltage applied to a micro-mechanical system. For a theoretically adequate resolution and high precision measurements, the necessary geometrical dimensions of the sensor require the application of micro machining. In this contribution, the dependence between electrical and geometrical properties of different sensor designs is investigated. Based on these results, problems related to practical micro-machining and solutions with respect to possible sensor realizations are discussed. The evolution of different sensor generations is shown.

Highlights

RF voltage measurement based on electrostatic RMS voltage-to-force conversion can be performed by a mechanically tunable capacitor having one elastically suspended electrode plate
A mechanical force proportional to the square of its high frequency voltage is generated between the plates and the plate moves to the equilibrium position between spring counterforce and electrostatic force
Taking into account the necessary mechanical dimensions of a micro-machined sensor, several generations of devices have been developed. In this contribution we first discuss the theoretical basis for MEMS-based RF voltage measurement, with an emphasis on the design choices

Summary

Introduction

RF voltage measurement based on electrostatic RMS voltage-to-force conversion can be performed by a mechanically tunable capacitor having one elastically suspended electrode plate. A mechanical force proportional to the square of its high frequency voltage is generated between the plates and the plate moves to the equilibrium position between spring counterforce and electrostatic force. The position of the plate is measured using a second capacitor. Taking into account the necessary mechanical dimensions of a micro-machined sensor, several generations of devices have been developed. In this contribution we first discuss the theoretical basis for MEMS-based RF voltage measurement, with an emphasis on the design choices. We present an overview of first (Beissner et al, 2003), second (Dittmer et al, 2007a), and third. Similar devices have been developed by Bartek et al (2000) in bulk- and Fernandez et al (2003) in surface-micro machining technology

Theory

Devices

First generation

Second generation

Third generation

Conclusions