DESIGN, FABRICATION AND CHARACTERIZATION OF A CMOS-MEMS MASS-SENSITIVE RELATIVE HUMIDITY SENSOR

This research presents the design of CMOS-MEMS device with embedded
microheater operating at relatively elevated temperatures (40°C to 150°C) for the
purpose of relative humidity measurement. It is designed, simulated, fabricated and
characterized to resolve the problem of reversibility and stability. The sensing
principle is based on the change in amplitude of the CMOS-MEMS device due to
adsorption/absorption or desorption of humidity on the active material layer of
titanium dioxide (Ti02) deposited on the moving plate that results in changes in the
mass of the device. The CMOS-MEMS device is operated in the dynamic mode using
electrothermal actuation by applying an AC current through the embedded
microheater to produce vibrations. These vibrations induce stress at the anchor points
of the supporting beams resulting in change of the resistance of the piezoresistors
(PZR) which can be measured using a Wheatstone bridge arrangement.