Design and implementation of a planar capacitive pressure sensor

Abstract

In this paper we present the implementation of a capacitive pressure sensor using interdigitated electrodes and a polymer cavity, the sensor functionality is based on the compression of a sealed cavity which changes the dielectric properties on top of two planar interdigitated electrodes (IDE). COMSOL was used to perform multiphysics simulations of the mechanical and electrical behavior of the sensor. The fabrication process of the sensor was made in tree steps: the interdigitated electrodes were fabricated using copper on a FR4 substrate, a sealed cavity of polydimethylsiloxane (PDMS) was built using FR4 molds, and finally the cavity and IDE were assembled with a thin layer of PDMS. The IDE electrodes are composed of 21 fingers and had a squared area of 11×11 mm, the PDMS cavity had an area of 11×11 mm with a height of 900 μm. A precision LCR meter (Agilent 4248A) was used to measure the capacitance variations caused by the pressure changes, the sensor was tested in the range of 0 to 40 psi and has a sensitivity of 3.35 fF/psi. Simulations were used to study the possibility of using functionalized polymers to increase the sensor sensitivity; the aim of this work is to present the design and fabrication process for a planar capacitive sensor, this design requires less fabrication steps than common micro-electromechanicals systems (MEMS) pressure sensors reducing the production costs of the pressure sensors, also allowing new types of integrations.