I will introduce the microbolometer specially focused on the MEMS approach.
There are two steps to infrared imaging : First , the thermal radiation of the scene must be focused onto a sensor to cause a physical effect, such as photoconductivity, which generally requires cooled devices, or a change in a physical property caused by an increase in temperature, as in bolometric devices. Second, the resulting physical effect must be read and displayed.
Cooled IR detectors really bean with the work by Lawson et al.,(1959) at the then Royal Signals and Radar Establishment in the United Kingdom, who identified mercury cadmium telluride(MCT) as an intrinsic semiconducting photoconductor that only required cooling to 77K. The French pursued a photovoltaic approach; however, the British and Honeywell in the United States initially developed mechanically scanned, hybridized linear arrays of MCT detectors cooled to 77K that operated in the photoconductive mode(Kruse, 1981). This first generation of imaging systems operating in the 8 to 12um range and, in the United States built from common module elements defined by the US Army Night Vision Laboratory, are today the mainstay of battlefield night-vision imaging systems.
The development of the technology of uncooled arrays really took off in the 1980’s, particularly in the United States where the US Army Night Vision Laboratories recognized the significance of low-cost, lightweight applications and jointly funded with the Defence Advanced Projects Agency(DARPA) the development of both ferroelectric and resistive arrays. These programs have culminated with arrays having resolutions of over 300 lines and NETDs as low as 0.04°C, which are now manufactured for military and civilian applications.
In this work we have fabricated a 50μm×50μm pixel structure bolometer. For the good Detectivity, both fill factor and thermal isolation are needed. But it is difficult to increase both fill factor and thermal isolation. Because these parameters are trade off. These depend on the structure. I will show you varies microbolometer structures and from that, I will give one solution to solve this problem.
