A low-pressure encapsulated deep reactive ion etched resonant pressure sensor electrically excited and detected using 'burst' technology

摘要

A purely silicon resonant pressure sensor fabricated using deep reactive ion etching (DRIE) and encapsulated at low pressure by two glass lids is presented. The sensor consists of a vibrating dual-diaphragm capsule suspended at four points in a fixed frame. The support beams an hollow and act as pressure inlet ports. As the ambient gas pressure changes, the resonator shape changes, thereby changing its resonance frequency. The sensor integrates corner holes and is encapsulated at low pressure to reduce squeezed-film damping effects between the resonating structure and the glass lid. The sensor is electrostatically excited into a balanced mode of oscillation and capacitively detected using a novel 'burst' technology. This technique is based on independently exciting the structure and detecting the resulting output frequency at separate periods in time. Several sizes and design variations of the sensor have been fabricated and evaluated. Measurements show the smallest structure (5 mm membrane diameter width) to have a Q factor of 14 000 after low-pressure encapsulation, pressure sensitivity of 15 ppm/mbar(-1) over the range 0.1-1500 mbar, and expected temperature sensitivity of -34 ppm degrees C-1. The structure had a resonance frequency of 35 078 Hz in atmospheric air pressure. If higher sensitivity is desired, a larger sensor can be chosen (140 ppm/mbar(-1) for a sensor with a 10 mm wide membrane), however, at the expense of a lower Q factor. [References: 15]