Microbolometers

Microbolometers are uncooled infrared detectors that measure thermal radiation by detecting the small temperature rise in a microfabricated absorber when it is exposed to IR light. Each pixel in a microbolometer array typically contains an IR-absorbing element mounted on a thin, thermally isolating membrane, with a thermistor or resistive element whose resistance changes as the pixel heats. A readout integrated circuit converts this resistance change into an electrical signal, producing a calibrated temperature map of the scene.

Common absorber materials include vanadium oxide (VOx) and doped amorphous silicon, though other materials are used in some designs. The spectral response of standard microbolometer cameras is largely in the long-wave infrared range (about 8–14 micrometers), which matches thermal emission from objects at or near room temperature. Arrays are manufactured using MEMS techniques and are integrated with CMOS readout circuits, enabling compact, low-cost imaging sensors.

Key performance characteristics are responsivity, noise-equivalent temperature difference (NETD), and the time constant. NETD indicates the smallest temperature difference detectable by the system. Microbolometers are designed for room-temperature operation, offering advantages in size, power consumption, cost, and ruggedness compared with cooled infrared detectors such as HgCdTe or InSb. Their limitations include lower intrinsic sensitivity and slower response relative to cooled technologies, as well as fixed-pattern noise that is mitigated through calibration and nonuniformity correction.

Applications include thermal imaging cameras for security and surveillance, automotive night vision, industrial inspection, firefighting, and medical or scientific thermography, where cost and robustness are important.