Micromachined water vapor sensors: a review of sensing technologies

The measurement of water vapor is important in many applications ranging from predicting changes in the weather to ensuring heating and cooling comfort in homes. In manufacturing, water vapor measurements help to control performance properties of engineered materials and optimize fuel efficiency in power generation. This paper presents a technology review of water vapor sensors and manufacturing techniques. Micromachining, more commonly known as MEMS or microelectromechanical systems, is an enabling technology based upon standard semiconductor manufacturing. MEMS technology makes possible solid-state sensors with greatly reduced power consumption and low operating voltage that are fully compatible with digital electronics and can be manufactured in high volumes at low cost. A water vapor microsensor just becomes another part on the circuit board. A "technology roadmap" for water vapor microsensors is defined where the sensing technologies have been organized into four major transduction schemes: capacitive, mass-sensitive, optical and resistive. Sensing element type, key geometric features and excitation scheme provides further classification. Operating principles and general performance characteristics are also presented.