Incorporation of the stress concentration slots into the flexures for a high-performance microaccelerometer

Abstract

Presented in this paper is a development of a high-performance piezoresistive microaccelerometer based on the slot etching in the quad flexures for the vibration detection of high speed spindle. The proposed structure consists of a proof mass supported by four thin flexures with slots etched in the middle. Boron diffused piezoresistors located near the stress concentration regions are used for sensing the localized stress resulting from the incorporation of the slots into the flexures. Theoretical analysis and finite element analysis show satisfactory results of an improved sensitivity and favorable natural frequency higher than 10 kHz, conforming to the initial design requirements. The microfabrication techniques are described to prototype the two accelerometer chips, one with slots and the other one without slots. The tested microaccelerometers with 3 V DC power supply show an average sensitivity of 0.424 mV/g normal to the proof mass plane, increased by 60.6% than the ones without slots. An average transverse sensitivity is found to be 9.2 μV/g along X axis and 14.2 μV/g along Y axis, either of which is less than 3.5% of prime-axis sensitivity. Concerning the resonant frequency, dynamic experiment shows about 12.46 kHz and is available for the proposed design with a tiny loss of 3.5% compared with the quad-beam design. When taking the product of sensitivity and natural frequency as judgment criteria, an inspiring increase by 28.6% of the figure of merit is accomplished for the proposed accelerometer. Overall, the findings of this study confirm the feasibility of incorporating slots into the conventional configurations to improve the sensor sensitivity while maintaining a comparatively high natural frequency.

Performance enhancement for piezoresistive microaccelerometer by geometrical design: a focused review

“…Various SCR forms have been implemented to amplify the sensing stress, including holes, grooves, slots, etc. (Wang et al, 2011;Joshi et al, 2007;Wahid et al, 2014;Zhao et al, 2012). Herein, the slotted-quad-beam structure reported by Zhao et al (2012) is taken as an example to verify the effectiveness of SCR.…”

Research on Micro-piezoresistive Accelerometer with Slotted Beams

“…(13) In 2012, Zhao et al successfully developed a piezoresistive accelerometer based on a slotted quad-beam structure, which consisted of a proof mass supported by four thin flexures with slots etched in the middle and had greater sensitivity than the traditional structure. (14) However, the above study did not deeply investigate the mechanism by which the slots affect the sensor performance, and the natural frequency of the sensor decreased after the slots were introduced. How to minimize this effect should be further studied.…”

An improved structural design for accelerometers based on slotted eight-beam structure

“…Its sensitivity was up to 5.189 mV/(Vg) (Wang et al, 2011). Zhao et al (2012) proposed a structure consisting of a proof mass supported by four thin flexures with slots etched in the middle; it has good frequency response and moderate measurement sensitivity. However, absence of theoretical analysis of the sensitivity and natural frequency made this interesting proposition not convincing enough.…”

“…The proposal has a sound effect, but the additional operations will lead to additional fabrication process, higher cost and even more possible interconnection failure in Wheatstone bridge. Zhao et al (2012) report a CB-membrane structure which can reduce the cross-axis sensitivity at the cost of a great loss in sensitivity. Meanwhile, the 0 per cent crossaxis sensitivity accelerometer based on PolyMUMPs process (Farahani et al, 2009) and the silicon-on-glass-based triaxle accelerometer (Hsu et al, 2010) are both capacitive ones, whose proposals cannot be directly applied in the piezoresistive sensors.…”