Traditional electrostatic space accelerometers, whose proof-mass is usually made of platinum-rhodium alloy or gold coated titanium alloy, are mainly manufactured by accurate machining and grinding, and thus suffer from the problems associated with complicated machining processes, large size and meantime 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. Based on the MEMS technology, an electrostatically suspended micro-accelerometer (ESMA) has the merits of small size, low-power and low cost. Compared to conventional force-balanced micromachined accelerometers, which typically have a proof mass connected to the substrate by a mechanical spring system, the effective spring constant of the ESMA depends only on the levitation voltage of the system due to the electrostatic levitation of the proof mass [4,5].
By changing the bias voltage, the spring constant can be readily adjusted, thus the sensitivity and the bandwidth of the system can be tuned according to different sensor applications. Inhibitors,Modulators,Libraries Furthermore, six-axis accelerations, namely three linear accelerations and three angular accelerations, can be measured simultaneously by only one ESMA sensor, where uniform sensitivity in all degrees of freedom can be offered. This six-axis ESMA is very suitable to constitute a micro inertial measurement unit (MIMU), especially a gyroscope-free inertial measurement unit [6].
Although Inhibitors,Modulators,Libraries the ESMA has the potential to deliver navigation-grade performance, relatively little work has been done to realize it, due to the difficult techniques required, such as microfabrication, high vacuum packaging, detection and control of six degrees of freedom (6-DoF) of the proof mass. Among these techniques, one of the most challenging is microfabrication, because very small gap spacing, for electrostatic forces or torques generation and capacitive Inhibitors,Modulators,Libraries detection, should be formed between the proof mass and the stators. Using proprietary Ball semiconductor technology [7], a single crystal silicon spherical proof mass with 1 mm diameter has been commercially used as an electrostatically levitated 3-axis accelerometer [8], whose noise floor was reported Inhibitors,Modulators,Libraries about 40 ��g/Hz1/2 level.
For a flat disc-like proof mass mostly employed, the micromachined electrostatically suspended accelerometer, as well as rotational microgyroscope by rotating the AV-951 disc proof 17-DMAG Phase 2 mass at high speed, have been reported mainly in [4,5,9�C12]. Additionally a levitated rotational microgyro/accelerometer prototype with a flat ring-shaped silicon rotor has been successfully developed, whose noise floor of the tri-axis accelerometer was 20 ��g/Hz1/2 in 10 Hz bandwidth [12]. However, no six-axis ESMA employing MEMS technology with a square micro plate used as the proof mass has been reported so far.