Abstract
This paper presents a resonant pressure microsensor with the measurement range of 1 MPa suitable for the soaring demands of industrial gas pressure calibration equipment. The proposed microsensor consists of an SOI layer as a sensing element and a glass cap for vacuum packaging. The sensing elements include a pressure-sensitive diaphragm and two resonators embedded in the diaphragm by anchor structures. The resonators are excited by a convenient Lorentz force and detected by electromagnetic induction, which can maintain high signal outputs. In operation, the pressure under measurement bends the pressure-sensitive diaphragm of the microsensor, producing frequency shifts of the two underlining resonators. The microsensor structures were designed and optimized using finite element analyses and a 4” SOI wafer was employed in fabrications, which requires only one photolithographic step. Experimental results indicate that the Q-factors of the resonators are higher than 25,000 with a differential temperature sensitivity of 0.22 Hz/°C, pressure sensitivities of 6.6 Hz/kPa, and −6.5 Hz/kPa, which match the simulation results of differential temperature sensitivity of 0.2 Hz/°C and pressure sensitivities of ±6.5 Hz/kPa. In addition, characterizations based on a closed-loop manner indicate that the presented sensor demonstrates low fitting errors within 0.01% FS, high accuracy of 0.01% FS in the pressure range of 20 kPa to 1 MPa and temperature range of −55 to 85 °C, and the long-term stability within 0.01% FS in a 156-day period under the room temperature.
Highlights
Pressure microsensors are widely used in the fields of industrial metering, aerospace aviation, meteorology, medical, automobiles, and consumer electronics [1,2,3,4], which function according to several typical working principles, such as capacitive sensing [5,6], piezoresistive sensing [7,8], piezoelectric sensing [9,10], fiber optical sensing [11,12], and resonant sensing [13,14]
The resonant pressure microsensor was first introduced by Greenwood in 1984, and is based on electrostatic excitation/capacitive detection [17]
Du introduced a resonant pressure microsensor based on an electrostatic excitation/capacitive detection resonator which showed a pressure sensitivity of −8.7 Hz/kPa, a maximum error of 0.0310% FS under the pressure measurement range of 30to 190 kPa and temperature range of 30 to 70 ◦ C [21]
Summary
Pressure microsensors are widely used in the fields of industrial metering, aerospace aviation, meteorology, medical, automobiles, and consumer electronics [1,2,3,4], which function according to several typical working principles, such as capacitive sensing [5,6], piezoresistive sensing [7,8], piezoelectric sensing [9,10], fiber optical sensing [11,12], and resonant sensing [13,14]. Du introduced a resonant pressure microsensor based on an electrostatic excitation/capacitive detection resonator which showed a pressure sensitivity of −8.7 Hz/kPa, a maximum error of 0.0310% FS under the pressure measurement range of 30to 190 kPa and temperature range of 30 to 70 ◦ C [21]. Those developed sensors included only one resonator which might cause the output frequency strongly sensitive to temperature. The compromised pressure measurement range might result from the nonlinearity of frequency responses to the pressure under measurement To address these issues, this study presents a resonant pressure microsensor based on dual resonators using convenient magnetic excitation/magnetic detection. The resonant pressure microsensor was fabricated and experimental characterizations including open-loop tests, closed-loop tests, and long-term tests to validate the design
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