Research On 20 μm Microbolomer Structure Optimization And Performance

Microbolometer is one of uncooled infrared detectors, which attracts more and more attention from military and civilian than before by its low power consumption, portable, high-performance, low-cost. Nowadays, infrared detector is developing towards large scale, high-density, gazing intelligent infrared focal plane, which result in the pixel size become 15 μm×15μm compare to early 65 μm×65 μm or larger. what’s more, pixel structure is becoming more diversification, such as double umbrella-type structure, S-type structure and three layers, than the traditional single sacrifice Layer structure. However, it is restricted to foreign technology and equipment blockade, there is few paper reported about uncooled infrared detectors in domestic, which pixel size are 20 μm 20 μm or less. Furthermore, take into the process of condition of our experiment into consideration, so the pixel size researched are 20 μm×20 μm and the structures which are widely used in civilian and military are single layer L-type, double umbrella-type, double S-type.Intellisuite, which is a professional MEMS software, was used to build three-dimensional finite element analysis model for above structures. On this basis, the infrared absorption model of double umbrella-type, double S-type were set up by mathematical analysis software Matlab. we did optical performance simulation and calculation of device thermal conductivity for this three structures under high performance indicators, which thermal conductivity is 10-8 W/K order corresponding NETD Less than 50 mk and thermal time constant Less than 8 ms. We obtained excellent optical properties and much smaller device thermal conductivity by adjusting the thickness of thin film material and cavity height.Additionally, we did mechanical performance simulation for the three structures. By changing internal stress of each materials, thickness of each thin films and cavity height, we get smaller displacement and better mechanical properties. Moreover, the support Layers and passivation layers are the main stress Layers, which play major roles in mechanical property.Last but not least, we confirmed the three structures parameters based on the research of optical, mechanical properties and devices theoretical thermal conductivity. Then we did dynamic thermal finite element simulation to research device thermal properties, such time constant, device thermal conductance; However, the microbolometer is required to load bias current or voltage while working. Therefore, we firstly imitated the three structures working states and did dynamic thermoelectric coupling finite element simulation. on this basis, under high performance indicators, according to the relationship among of the bias current, effective thermal conductance and device thermal conductance, the range of current is got. Different current and the same amount of heat radiation were Loaded on the devices for dynamic thermoelectric coupling finite element simulation. Considering the thermal time constant, effective thermal conductance and power consumption, threshold voltage the optimal current can be drawn.