A wireless batch sealed absolute capacitive pressure sensor

Abstract

This paper reports the development of an absolute wireless pressure sensor that consists of a capacitive sensor and a gold-electroplated planar coil. Applied pressure deflects a 6 μm-thin silicon diaphragm, changing the capacitance formed between it and a metal electrode supported on a glass substrate. The resonant frequency of the LC circuit formed by the capacitor and the inductor changes as the capacitance changes; this change is sensed remotely through inductive coupling, eliminating the need for wire connection or implanted telemetry circuits. The sensor is fabricated using the dissolved-wafer process and utilizes a boron-doped silicon diaphragm supported on an insulating glass substrate. The complete sensor measures 2.6mm×1.6 mm in size and incorporates a 24-turns gold-electroplated coil that has a measured inductance of 1.2 μH. The sensor is designed to provide a resonant frequency change in the range 95–103 MHz for a pressure change in the range 0–50 mmHg with respect to ambient pressure, providing a pressure responsivity and sensitivity of 160 kHz/mmHg and 1553 ppm/mmHg, respectively. The measured pressure responsivity and sensitivity of the fabricated device are 120 kHz/mmHg and 1579 ppm/mmHg, respectively.