A Micro Electro Mechanical System incorporates all of the essential components of a chemical detection system into a single micro-scale device. The actual MEMS sensing mechanism may range from 1 to 100 micrometers in size, allowing the size of the overall chemical detector to be quite small compared to most conventional detection systems.
Products utilize a sensor platform in which polymer-filled micro-machined capacitors (also referred to as chemi-capacitors) measure the dielectric constant of an array of selectively-absorbing materials. The interaction between target analyte and polymer modifies the dielectric properties of the polymer, resulting in a change in capacitance. Analyte selectivity is achieved by populating the array with different polymers that exhibit a variety of capacitive properties, which in theory results in a signature output pattern from the array. In reality, there is often not enough difference in capacitive property among the polymers to distinguish individual chemicals. Polymer films can also swell in high humidity and may suffer very long recovery times following an exposure event. Polymer film MEMS sensors tend to respond and recover faster to high vapor chemicals such as acetone and ethanol, while recovery times following exposure to low vapor pressures can be several minutes to hours.