6 mm microbolometers for uncooled thermal imaging
Besides nowadays challenges in contactless measurement of body temperature, the market for uncooled thermal imager continuously increased in the last years. The size of the camera core is a parameter, that needs to follow the miniaturization of the whole camera body. State-of-the-art value for pixel sizes of microbolometers in uncooled thermal imagers is 10 mm. Pushing the microbolometer size to the optical limit, Fraunhofer IMS provides a manufacturing process for FIR-imagers (uncooled thermal imagers) based on a scalable microbolometer technology. Taking this scalable technology as a basis, we are introducing a fully implemented uncooled thermal imager with 6 mm pixel size. The 6 mm microbolometers are made by Fraunhofer IMS's manufacturing technology for a thermal MEMS isolation realized by vertical nanotubes. Performance of the 6 mm microbolometers is estimated by a 17 mm digital readout integrated circuit in QVGA resolution. Responsivity and number of electrical defect pixels as well as NETD are determined by an electro-optical characterization based on a test setup with a black body at two different temperatures. NETD of the 6 µm microbolometers is estimated to be at 611 mK. Supporting the quantitative measurements, FIR test images will be presented to demonstrate the microbolometer's functionality in a fully implemented uncooled thermal imager. In summary, a fully implemented uncooled thermal imager with QVGA resolution based on a 6 mm nanotube-microbolometer detector is presented here. Compared with commercially available uncooled thermal imagers, the highly limited absorption area of our microbolometers with structure sizes below the target wavelength causes an accordingly higher NETD. Nevertheless, it can be stated that 6 mm pixel size still shows the capability of absorbing infrared radiation at wavelengths of approximately 10 mm in an uncooled thermal imager.
Michel, Marvin D.