University of Nebraska–Lincoln,
Keywords: MEMS, humidity
Summary:Accurate humidity measurement is essential in commercial and industrial applications such as HVAC systems and microelectronics manufacturing. Typical humidity sensors suffer from degradation over time, consume a relatively high amount of power, and have limited range. To overcome these problems, we present simulation and experimental investigations of the use of uncoated capacitive MEMS oscillators to measure humidity. This new sensor concept takes advantage of the MEMS oscillator’s thermo-electrical variations as the water content (humidity) of air changes. This research shows that water content of air increases the dielectric constant of air and changes the oscillator’s squeeze-film-air damping effect. This results in an overall increase in the oscillator amplitude and a shift in its primary resonance frequency and its subharmonic resonance frequency (twice the resonance frequency). The results of an extensive simulation for a capacitive MEMS oscillator, lumped in a spring-mass-damper model, will be used to calibrate the oscillator amplitude and frequency changes to humidity. Moreover, the simulation results will be compared to experimental data.