Structural Design And Performance Optimization Of Microbolometer Absorber

Uncooled infrared focal plane array detectors are widely used in military and civilian fields for their advantages of low power consumption,high performance and low cost.In recent years,infrared devices have been developing towards smaller pixel sizes and larger array scales,and its pixel size has approached the physical limit of infrared detection.Therefore,how to improve the micro-radiometric and thermal absorption performance of small pixels have become the key point to improving device performance..In order to improve the absorption performance of small-sized microbolometer structures in the long-wavelength infrared band,a three-dimensional infrared absorption simulation model was established by using CST STUDIO SUITE(CST)simulation software.Multiple single-layer and double-layer microbolometer structures with different micro-bridge structures and the pixel size of 12 μm×12 μm were designed,and infrared absorption simulations and related parameter optimizations were carried out.The effects of microbolometer cavity height,absorber layer thickness and silicon nitride film thickness on the absorption characteristics of microbolometer were investigated.The optimized single-layer and double-layer microbolometer structures were obtained which can achieve high absorption with an average absorption rate of 80% or more of infrared waves in the long-wave infrared band from 8 μm to 14 μm.To further enhance the absorption characteristics and broaden the absorption bandwidth,various absorber structures were designed,including metal arrays and aperture arrays with different arrays,sizes,shapes,and thicknesses.The absorber structures were combined with microbolometer structures and modeling simulations and optimization analyses were conducted.All the above structures achieve wideband high absorption of long-wave infrared waves,resulting in devices with an average absorption of 95% and an overall absorption greater than 90%.The absorption mechanism was analyzed by setting up a field monitor to observe the location of absorption in the absorbing structure.The infrared absorption characteristics of the device are calculated when the electromagnetic waves are incident at different angles and polarizations,and the angular sensitivity and polarization sensitivity of the absorbing structure coupled with the microbolometer structure are investigated.In addition,the effect of the aperture size and dual vacuum cavity height of the umbrella structure on the absorption characteristics of the structure in the 3 μm-14 μm wavelength range was also studied in the double-layer microbolometer structure.Finally,the impedance matching principle was used to verify the results of enhancing the structures infrared absorption characteristics and reducing heat capacity by impedance matching the four diffrent microbolometer structures with the free space.The device’s response to target radiation and detection performance were iproved,meeting the requirements for preparing large-scale,high-performance,fast response,and highabsorption microbolometers..In addition,the design method proposed in this paper can also predict the device performance quickly,accurately,and at low cost during the device design stage of microbolometer structural units,guide and support the device design process,shorten the development cycle,improve the design accuracy and efficiency,and provide a reliable reference for the subsequent actual device preparation and structural design.