New Type Of Double Micro Bolometer Structure Optimization Design

Owning to the advantages of high performance, low-cost and small volume,uncooled infrared microbolometers exhibit wide prospects in the applications ofmilitary and civilian. However, the optical absorption layer and the heat-sensitive layerin the traditional single sacrifice layer structure can not be changed separately, whichaffects the improving of the device performance. Recently, double sacrifice layersmicrobolometers were proposed. And these structures exhibit excellent capabilities.Although the performance of such two-layer microbolometers has been certified to beexcellent, rather rare results about their structures have been previously reported.Consequently, many of their advantages and disadvantages still remain unclear.By using the mathematical analysis software Matlab and finite element analysissoftware IntelliSuite, the properties of traditional I-type structure, L-type structure,S-type structure and umbrella-type structure were systematically simulated in this thesis.The results reveal that the new two-layer microbolometers exhibit better overallperformances. Among these two-layer structures, the temperature rise of the S-typemicrobridge is the highest. Unfortunately, the lengths of cantilever of S-typemicrobridge are too long, and the mechanical property of such structure is poor, whichlimits the practical application. On the contrast, the umbrella-type microbridge exhibitsbetter thermal properties and structural stability, and this structure is easy to befabricated. Therefore, the umbrella-type structure is more preferable.In addition, the thermal property of the U-type structure was optimized bychanging the thin film materials and cantilever frame. The simulated results shows thatwhen a SiO2film is utilized as the isolating and supporting material located at the lowerbridge plane, the temperature rise of the pixel is improved about27%, but thedeformation becomes3times higher than the original one. If the frame of the cantileverchanges from I-type to L-type, its temperature rise is increased for about57%, while itsdeformation is improved for about46%.In this thesis, the relationship between the film thickness and the two-layer U-typeproperties was also investigated. By comparing the simulation results, a group of optimized thickness parameters was also deduced, by which the temperature rise isincreased to115.3mK (76.97%enhanced) and the displacement is reduced to0.02008μm (32.1%reduced)Finally, the thermal uniformity of the heat-sensitive layer is improved by designingnew two-layer microbridges which specially contains metallic membrane and varioussupporting cylinders. Not only the stability is improved (the displacement is decreasedfor8.4%), but also the differentia of temperature in the heat-sensitive layer is decreasedfrom9.6mK to1.3mK. Therefore, compared with the U-type microbridges, ourstructures exhibit better mechanical stability and temperature uniformity.