A Slot-Structure MEMS Gyroscope Working at Atmosphere With Tunable Electrostatic Spring Constant

Abstract

This paper proposed a novel slot-structure z-axis gyroscope with a positive or negative electrostatic spring. The slot-structure gyroscope has in-plane drive and sense modes. Different from conventional comb finger structure, variable-area fixed out-of-plane electrodes under the proof-mass are used to excite the in-plane vibratory modes. To overcome the disadvantage that the resonant frequencies are unable to be adjusted through variable-area capacitors in the conventional slot-structure gyroscope, a variable-area capacitor with triangular shape fixed electrodes is designed to introduce the electrostatic tuning of the in-plane vibratory modes. A voltage difference Vt across the triangular fixed electrodes and movable electrodes produces a positive or negative electrostatic spring. The induced electrostatic spring constant is proportional to Vt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A prototype with a positive electrostatic spring is fabricated and tested. The difference of the nature frequencies of the drive mode and sense mode is about 13.5 Hz. A 15 V Vt makes the gyroscope perfect mode matching. The scale factor of the prototype is about 72 mV/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /s when Vt is 0 V and increases with Vt. It presents a scale factor of 320.6 mV/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /s and noise density of 11.63 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /h/vHz when mode matched. Interestingly, the bandwidth of the gyroscope only slightly decreased from the initial value of 7 Hz to 4.6 Hz when mode matched, possible reasons are discussed in this paper.