Abstract
In this study, a novel method to assemble a micro-accelerometer by a flip chip bonding technique is proposed and demonstrated. Both the main two parts of the accelerometer, a double-ended tuning fork and a base-proof mass structure, are fabricated using a quartz wet etching process on Z cut quartz wafers with a thickness of 100 μm and 300 μm, respectively. The finite element method is used to simulate the vibration mode and optimize the sensing element structure. Taking advantage of self-alignment function of the flip chip bonding process, the two parts were precisely bonded at the desired joint position via AuSn solder. Experimental demonstrations were performed on a maximum scale of 4 × 8 mm2 chip, and high sensitivity up to 9.55 Hz/g with a DETF resonator and a Q value of 5000 in air was achieved.
Highlights
Resonator-based micro-accelerometers have drawn great attention due to their digital frequency output without the need of analog/digital conversion, which may induce additional errors [1,2,3,4,5]
The double-ended tuning fork (DETF) works in an anti-phase in-plane flexural mode and the two beams vibrate in the opposite direction, canceling the force and torque produced at the two joint roots
The proof mass structure is composed of a base and a proof mass, which are connected by a thinned flexure
Summary
Resonator-based micro-accelerometers have drawn great attention due to their digital frequency output without the need of analog/digital conversion, which may induce additional errors [1,2,3,4,5]. Most micro-resonant accelerometers are fabricated on silicon wafers, quartz-based vibrating beam accelerometers (QVBAs) have been studied for a long time owing to their simple structure, high frequency stability and so on [6]. The two ends of the quartz DETF are jointed on the base and proof mass surface, respectively This kind of sensor measures the acceleration information in a direction perpendicular to the proof mass surface, which is converted into so called inertial force. The development of quartz micromachining techniques makes it possible to fabricate the proof mass structure in a batch process on a thick quartz wafer, and the key feature is to make a flexure thin enough to transfer the inertial force produced by the proof mass to the DETF resonator. The AuSn alloy is demonstrated to be suitable for fluxless processes, which is very important for MEMS device long term performance [27]
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