Improvements to the electrothermal modelling of conventional and dual element microbolometers

Abstract

The thesis contributes to the understanding of the influence of detector material and geometry on heat flow in integrated microbolometer systems. Microbolometers are key technological components for a large range of thermal applications and well represented in the marketplace. Despite their ubiquity, their modelling is surprisingly inaccurate. The proposed models, covering different fabrication technologies and operating conditions, make major contributions to the predictability of the microbolometer performance with up to 40% improvements compared to conventional methods, in turn allowing for more complex bolometer concepts. In particular: i) A lumped description of the geometry assumes an ellipse rather than the conventional rectangular geometry, which closer resembles the simulated temperature distribution of the absorber. ii) The separation of the device geometry into separate lumped thermal elements, augmented by coupling coefficients, which link them together and better capture the thermal network and the modes of heat transfer among multiple resistive components sharing the microbolometer structure. iii) The entire bolometer is captured as a linear set of equations, which properly describes selfheating and the effective thermal impedance of the system. Based on the comprehensive comparison between conventional and proposed analytic models, a wide variety of finite element simulations and a number of careful experimental measurements, it is conclusively shown that the proposed models significantly outperform the conventional methods. Furthermore, the extended complex structure models accurately predict the simulated and measured device behaviour. The latter allows for the development of new integrated electrothermal systems with confidence.