A MEMS (Micro-Electro-Mechanical System) microbolometer is a crucial component used in thermal imaging devices to detect and convert infrared (IR) radiation into electrical signals, which are then processed to create thermal images. Here's an overview of the operation of a MEMS microbolometer:
Bolometer Principle: A bolometer is a thermal sensor that operates based on the principle that the electrical resistance of certain materials changes when exposed to variations in temperature. In the case of a microbolometer, a tiny and sensitive thermally sensitive material is used as the sensing element.
Thermally Sensitive Material: The core component of a MEMS microbolometer is a thin film of thermally sensitive material. This material has a property that its electrical resistance changes with temperature. Typically, vanadium oxide (VOx) or amorphous silicon (a-Si) is used because of their suitable electrical and thermal properties.
Pixel Structure: A microbolometer array consists of numerous individual pixel elements, each containing a microbridge made of the thermally sensitive material. This microbridge acts as a miniature absorber of infrared radiation.
Absorption of Infrared Radiation: When the MEMS microbolometer is exposed to a scene, the incident infrared radiation is absorbed by the microbridge. The absorbed radiation causes a temperature rise in the microbridge, which in turn changes its electrical resistance.
Temperature Sensing and Readout: The change in electrical resistance of the microbridge is sensed using electronic circuits. These circuits are designed to measure the resistance changes with high precision. The temperature rise is directly proportional to the intensity of the incident infrared radiation.
Thermal Isolation: To ensure accurate temperature measurements, the microbridge is thermally isolated from its surroundings. This isolation prevents heat from dissipating quickly into the surrounding structure, allowing the microbridge to reach a stable temperature that corresponds to the incident infrared radiation.
Signal Processing: The resistance changes in the microbridges are converted into electrical signals, which are then processed by the device's electronics. These signals are amplified and digitized for further processing.
Image Formation: The processed signals from all the individual pixels are used to construct a thermal image of the scene. Each pixel's signal corresponds to the temperature of a specific point in the scene, and combining these signals creates a visual representation of the temperature distribution across the observed area.
Display and Visualization: The final thermal image is displayed on the device's screen, revealing the temperature variations and hot/cold spots within the scene. Warmer areas appear as brighter regions, while cooler areas appear darker.
MEMS microbolometers offer several advantages for thermal imaging applications, such as their small size, low power consumption, and compatibility with integrated circuit fabrication techniques, making them suitable for use in compact and portable thermal imaging devices.