Abstract
A micromachined electrostatically suspended six-axis accelerometer, with a square plate as proof mass housed by a top stator and bottom stator, is presented. The device structure and related techniques concerning its operating principles, such as calculation of capacitances and electrostatic forces/moments, detection and levitation control of the proof mass, acceleration measurement, and structural parameters design, are described. Hybrid MEMS manufacturing techniques, including surface micromachining fabrication of thin film electrodes and interconnections, integration fabrication of thick nickel structures about 500 μm using UV-LIGA by successful removal of SU-8 photoresist mold, DRIE of silicon proof mass in thickness of 450 μm, microassembly and solder bonding, were employed to fabricate this prototype microdevice. A levitation experiment system for the fabricated microaccelerometer chip is introduced, and levitation results show that fast initial levitation within 10 ms and stable full suspension of the proof mass have been successfully demonstrated.
Highlights
An electrostatically suspended accelerometer mainly comprises a mechanically free proof mass and stator electrodes, which maintain the mass suspension at its null position by capacitive position detection and electrostatic levitation control
A designed structure of a micromachined electrostatically suspended six-axis microaccelerometer, with a square plate as proof mass housed by top stator and bottom stator, was presented
A precision electrostatically suspended micro-accelerometer (ESMA) prototype chip was achieved using hybrid microfabrication techniques, that is, the top stator and the bottom stator were fabricated by surface micromachining and UV-LIGA
Summary
An electrostatically suspended accelerometer mainly comprises a mechanically free proof mass and stator electrodes, which maintain the mass suspension at its null position by capacitive position detection and electrostatic levitation control. The operation principle of this servo-controlled electrostatic accelerometer is based on the measurement of the electrostatic force necessary to maintain the proof-mass motionless with respect to the sensor cage [1]. The unique micro-gravity environment in space has brought this high-precision electrostatic accelerometer numerous space applications, such as the measurement of micro-gravity and non-gravitational weak forces induced by atmospheric drag, solar radiation pressure, and so on. Traditional electrostatic space accelerometers, whose proof-mass is usually made of platinumrhodium alloy or gold coated titanium alloy, are mainly manufactured by accurate machining and grinding, and suffer from the problems associated with complicated machining processes, large size and high cost, which limits their potential applications for micro platforms such as micro spacecraft, micro aerial vehicles, unmanned underwater vehicles, small long-range munitions, etc Electrostatic space accelerometers, with high resolutions ranging from pico-g to better than femto-g in the low frequency domain below 1 Hz, have been or will be used in many space scientific missions, such as CHAMP, GRACE and GOCE satellite projects for determination of the Earth’s gravity [1], the LISA mission satellites for the observation of the gravity waves [2], and the MICROSCOPE mission for orbit testing of the equivalence principle [3].
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