Abstract
A novel resonant pressure sensor with an improved micromechanical double-ended tuning fork resonator packaged in dry air at atmospheric pressure is presented. The resonator is electrostatically driven and capacitively detected, and the sensor is designed to realize a low cost resonant pressure sensor with medium accuracy. Various damping mechanisms in a resonator that is vibrating at atmospheric pressure are analyzed in detail, and a formula is developed to predict the overall quality factor. A trade-off has been reached between the quality factor, stress sensitivity and drive capability of the resonator. Furthermore, differential sense elements and the method of electromechanical amplitude modulation are used for capacitive detection to obtain a large signal-to-noise ratio. The prototype sensor chip is successfully fabricated using a micromachining process based on a commercially available silicon-on-insulator wafer and is hermetically encapsulated in a custom 16-pin Kovar package. Preliminary measurements show that the fundamental frequency of the resonant pressure sensor is approximately 34.55 kHz with a pressure sensitivity of 20.77 Hz/kPa. Over the full scale pressure range of 100–400 kPa and the whole temperature range of −20–60 °C, high quality factors from 1,146 to 1,772 are obtained. The characterization of the prototype sensor reveals the feasibility of a resonant pressure sensor packaged at atmospheric pressure.
Highlights
Resonant pressure sensors have been widely used in the field of precision pressure measurement in recent years for their advantages in accuracy and long-term stability
The open loop frequency response characteristics of the resonant pressure sensor are tested by an electrical measurement system based on the Agilent 35670A dynamic signal analyzer, as illustrated in Preliminary measurements show that the resonant pressure sensor has a fundamental frequency of approximately 34.55 kHz at 20 °C and 100 kPa, which agrees well with the simulation
There are other influences which have corresponding negative impacts on the Q-factor, such as the notching effect at the bottom edges, sidewall microfabrication defects resulting from deep reactive ion etching (DRIE), small unbalanced oscillations due to the inevitable asymmetry of the electrostatically driven force and the microfabricated resonator structure, and a gas temperature rise owing to the heat produced by mechanical vibration
Summary
Sen Ren 1,2, Weizheng Yuan 1,2,*, Dayong Qiao 1,2, Jinjun Deng 1,2 and Xiaodong Sun 1,2. Shaanxi Province Key Laboratory of Micro and Nano Electro-Mechanical Systems, Northwestern Polytechnical University, Xi’an 710072, China. Received: 20 September 2013; in revised form: 19 November 2013 / Accepted: 28 November 2013 /
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