A Thermal Conductance Optimization and Measurement Approach for Uncooled Microbolometers

This paper introduces an optimization approach of thermal conductance for single level uncooled microbolometer detectors. An efficient detector design is required due to the limited availability of silicon area per pixel, i.e., the pixel pitch, and due to the capabilities of the fabrication line. The trade-offs between physical parameters are studied to attain the best performance, including the thermal conductance, the thermal time constant, the effective temperature coefficient of resistance (TCR), and the active area, where the main performance criterion has been selected as the Noise Equivalent Temperature Difference (NETD). A microbolometer pixel is modeled using theoretical formulations, and simulations are carried out using this model, and then, the accuracy of the model is verified by Finite Element Method (FEM) analysis. Consequently, optimum design parameters, such as the length of the support arms and the choice of interconnect metal can be extracted from the simulations for a defined process flow. Furthermore, a simple and reliable method for measuring the thermal conductance has been introduced. With this method, it is possible to accurately measure the thermal conductance in a large pixel temperature range, which is required especially for high thermal resistance microbolometers as they heat up rapidly in vacuum. The validity and accuracy of this method are also verified by comparing the simulation results with measurements performed on a single pixel microbolometer that is designed and fabricated based on the optimization approach outlined in this paper