Capacitive MEMS absolute pressure sensor using a modified commercial microfabrication process

Abstract

We present the design and fabrication of a capacitive absolute pressure sensor using a modified commercial microfabrication process. The pressure sensor is fabricated using MEMS Integrated Design for Inertial Sensors (MIDIS), a process recently developed by Teledyne DALSA Semiconductor Inc. (TDSI). The MIDIS process provides wafer-level vacuum encapsulation under a high vacuum pressure of 10 mtorr, which enables the absolute pressure measurement. We perform post-fabrication processing of the obtained devices from the foundry to create a thin single crystal silicon membrane and expose it to atmospheric pressure to serve as the sensing membrane for the pressure sensor. The proposed pressure device includes Through Silicon Vias (TSVs) suitable for flip-chip bonding with a signal conditioning integrated circuit. The presented sensor uses a deflectable large membrane with accurate controllable thickness and offers a high sensitivity of 16.5 fF/kPa with a good linearity over designed pressure range of 101---125 kPa. The operating pressure range can be modified by simply varying the physical dimensions of the sensing membrane. We demonstrate several prototype absolute capacitive pressure sensors with different membrane diameters ranging from 140 to 360 µm and thicknesses ranging from 1 to 10 µm with a fixed gap of 2 µm between the membrane and immovable electrode. The sensor calibration data is collected in a regulated pressure chamber using a reference commercial pressure sensor.