A Capacitive Silicon Microaccelerometer with Force-Balancing Electrodes

Abstract

A surface micromachined accelerometer, which senses an inertial motion with an area variation, has been developed. The accelerometer is designed as an interdigital rib structure that has a differential capacitor arrangement. The movable electrodes are mounted on a mass of 7 µm thick polysilicon and a pair of stationary electrodes is formed under the mass with a 1.5 µm gap. Both sides of the movable electrodes are fixed on the mass, and the stationary electrode is formed on the substrate without being suspended. As a result, the mechanical stress and the electrical pulling effects can be reduced in comparison to the comb-type capacitor arrangement. In order to improve the dynamic range and the linearity, a pair of comb-shaped force-balancing electrodes is placed on both sides of the mass. The force-balancing electrodes are fabricated on the same layer as the mass and anchored on a silicon substrate. In particular, differential feedback electrodes enable linear control of mass repositioning.

Electrodeposition of Gold Alloys and the Mechanical Properties

“…In recent years, microelectromechanical system (MEMS) capacitive accelerometers have been developed and used in a variety of consumer electronics for acceleration detection in a range of 1-5 G (1 G = 9.8 m/s 2 ) [1][2][3]. For applications in medical and health care fields, accurate sensing with sub-1 G detection is necessary to monitor hardly detectable body motions [4,5].…”

“…Combining Eqs. (2) and 4, the nucleation rate can be promoted by an increase in the current density, leading to electrodeposits having a finer-grained structure. In addition, electrodeposition can produce not only pure metals but also alloys with controlled compositions.…”

Suspension design analysis on the performance of MEMS area-changed lateral capacitive accelerometer

“…Capacitive-based accelerometers can be designed based on either the distance-changed or area-changed principle. Area-changed capacitive sensing principle is chosen to design the accelerometer in this study because of its inherent linearity [5,6].…”

Mechanical Sensitivity Enhancement of an Area-Changed Capacitive Accelerometer by Optimization of the Device Geometry

“…This in turn causes the differential capacitance to be very small which makes the design of the detection circuit difficult. For an area-changed capacitive accelerometer, the differential capacitance is shown to vary linearly with the overlapped area of the proof mass and the fixed electrodes underneath and independent of the air gap between the proof mass and the electrodes [6,7].…”