A microbolometer is a specific type of bolometer used as a detector in a thermal camera. Infrared radiation with wavelengths between 7.5–14 μm strikes the detector material, heating it, and thus changing its electrical resistance. This resistance change is measured and processed into temperatures which can be used to create an image. Unlike other types of infrared detecting equipment, microbolometers do not require cooling.
Theory of construction A microbolometer is an uncooled thermal sensor. High resolution thermal sensors require exotic and expensive cooling methods including stirling cycle coolers and liquid nitrogen coolers. These methods of cooling high resolution thermal imagers are expensive to operate and unwieldy to move. Also, high resolution thermal imagers require a cool down time in excess of 10 minutes before being usable.
A microbolometer consists of an array of pixels, each pixel being made up of several layers. The cross-sectional diagram shown in Figure 1 provides a generalized view of the pixel. Each company that manufactures microbolometers has their own unique procedure for producing them and they even use a variety of different IR absorbing materials. In this example the bottom layer consists of a silicon substrate and a readout integrated circuit (ROIC). Electrical contacts are deposited and then selectively etched away. A reflector, for example, a titanium mirror, is created beneath the IR absorbing material. Since some light is able to pass through the absorbing layer, the reflector redirects this light back up to ensure the greatest possible absorption, hence allowing a stronger signal to be produced. Next, a sacrificial layer is deposited so that later in the process a gap can be created to thermally isolate the IR absorbing material from the ROIC. A layer of absorbing material is then deposited and selectively etched so that the final contacts can be created. To create the final bridge like structure shown in Figure 1, the sacrificial layer is removed so that the absorbing material is suspended approximately 2 μm above the readout circuit. Because microbolometers do not undergo any cooling, the absorbing material must be thermally isolated from the bottom ROIC and the bridge like structure allows for this to occur. After the array of pixels is created the microbolometer is encapsulated under a vacuum to increase the longevity of the device. In some cases the entire fabrication process is done without breaking vacuum. The microbolometer array is commonly found in two sizes, 320×240 pixels or less expensive 160×120 pixels. Current technology has led to the production of devices with 640×480 or 1024x768 pixels. There has also been a decrease in the individual pixel dimensions that was typically 45 μm in older devices, decreased to 12 μm in the 2000s, and most recently 6 μm in 2025-manufactured microbolometers. As pixel dimensions decrease and the number of pixels per unit area of the array increases proportionally, an image with higher resolution is created, but with a higher NETD (noise equivalent temperature difference (differential)) due to smaller pixels being less sensitive to IR radiation.
Detecting material properties There is a wide variety of materials that are used for the detector element in microbolometers. A main factor in dictating how well the device will work is the device's responsivity. Responsivity is the ability of the device to convert the incoming radiation into an electrical signal. Detector material properties influence this value and thus several main material properties should be investigated: TCR, 1/f noise, and resistance. A microbolometer array imaging system(MAIS) has potential for medical applications to detect 1-5 Thz signals on the body’s surface created by a non-ionizing radiation generator as of 2025.
Temperature coefficient of resistance (TCR) The material used in the detector must demonstrate large changes in resistance as a result of minute changes in temperature. As the material is heated, due to the incoming infrared radiation, the resistance of the material decreases. This is related to the material's temperature coefficient of resistance (TCR) specifically its negative temperature coefficient. Industry currently manufactures microbolometers that contain materials with TCRs near −2%/K. Although many materials exist that have far higher TCRs, there are several other factors that need to be taken into consideration when producing optimized microbolometers.
1/f noise
1/f noise, like other noises, causes a disturbance that affects the signal and that may distort the information carried by the signal. Changes in temperature across the absorbing material are determined by changes in the bias current or voltage flowing through the detecting material. If the noise is large then small changes that occur may not be seen clearly and the device is useless. Using a detector material that has a minimum amount of 1/f noise allows for a clearer signal to be maintained between IR detection and the output that is displayed. Detector material must be tested to assure that this noise does not significantly interfere with signal.
Resistance Using a material that has low room temperature resistance is important for two reasons. First, lower resistance across the detecting material means less power will need to be used. Second, higher resistances comes with higher Johnson–Nyquist noise.
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