microbolometer

Microbolometer is a type of uncooled infrared detector that converts incident infrared radiation into a change in electrical resistance. It typically consists of a microfabricated thermistor suspended on a thin membrane on a silicon readout substrate, forming a focal plane array that can image infrared scenes without cryogenic cooling. Microbolometers are designed to sense radiation in the long-wavelength infrared range, commonly around 8 to 14 micrometers.

How it works: Infrared photons are absorbed by the detector element, causing a small rise in its temperature. The temperature-dependent resistance of the thermistor changes in a detectable way, and a readout circuit converts this resistance change into an electrical signal. To maximize sensitivity, each pixel is thermally isolated by a low-thermal-conductance support, and often the pixel is optimized with an optical cavity and a black absorbing coating. Materials for the thermistor include vanadium oxide (VOx) or amorphous silicon (a-Si).

Manufacture and performance: Microbolometer FPAs are fabricated using MEMS processes on silicon substrates, with pixelated thermometer materials and integrated readout circuits (ROICs) either on the same chip or bonded to a separate chip. The devices are operated at near room temperature, allowing compact, low-cost cameras. Typical performance is described by NETD: the smallest detectable temperature difference; uncooled microbolometers aim for tens to hundreds of millikelvin under suitable conditions.

Applications and characteristics: Microbolometers are widely used in thermal imaging cameras for civilian and commercial use, in industrial inspection, firefighting, search and rescue, building diagnostics, and automotive night-vision sensors. Advantages include operation at ambient temperature, lower cost, and ruggedness; limitations include lower sensitivity and resolution compared with cooled infrared detectors and dependence on scene temperature and emissivity.