Sensitivity tunable capacitive type micro accelerometer

In this paper, we present a novel sensitivity tunable capacitive type micro accelerometer which could adjust its sensitivity. The previous bulk-micromachined accelerometer is hard to make a pattern which is smaller than 1um with high aspect ratio because of ICP etching errors such as loading effect and footing. In this paper, by making movable ground electrodes which have MEMS actuators, we present a high sensitivity micro accelerometer with a narrow sensing gap under 1um using conventional bulk micromachining. Unlike previous capacitive type MEMS accelerometers which have anchored ground electrodes, the proposed micro accelerometer has movable ground electrodes. By simply applying DC bias to MEMS actuators, the ground electrodes are moved to the sensing electrodes. The fabricated sensing gap is 1.9um and it could be reduced to 0.8um according to the actuation voltage, VDD. The working sensitivity of the micro accelerometer is 0.410 pF/g at VDD=1.0 V, which is higher than 0.125 pF/g with no actuation, VDD=0 V.

I. Introduction

Recently, the accelerometers with high sensitivity and high resolution are needed in various applications such as microgravity sensing for geophysical survey and building safety management, inertial navigation system for automotive, and spacecraft guidance/stabilization. MEMS accelerometers for these applications have been researched due to low cost, mass production, small size and high performance. There are several types of sensing schemes for MEMS accelerometers such as piezo-resistive, resonant, tunneling-current, and capacitive. Among them, the capacitive sensing type has becoming more attractive and promising for high precision micro accelerometers due to its advantages such as high sensitivity, low noise, stable DC characteristics, low power dissipation, and low temperature sensitivity [1].