A comprehensive model for bolometer element and uncooled array design and imaging sensor performance prediction

This paper reports on a model developed to predict bolometer performance in its environment, where the environment consists of thermal, optical and electrical components. Two complementary methods were employed to predict performance. The first solves the heat balance equation for the bolometer in its circuit and its thermal environment with known values of heat capacitance, thermal conductance, absorptance, temperature coefficient of resistance and the user-defined bias current (either constant or pulsed). This iteration yields a bolometer temperature rise, and a corresponding change in resistance and voltage. This is the signal part of the equation. The second method is required to calculate the total bolometer noise. It uses equations derived from the literature to predict bolometer noise, response, NEP and NETD from first principles for the four types of noise generated in thermal detectors (thermal fluctuation noise, background fluctuation noise, johnson noise and 1/f noise). Thermal conductance and heat capacities are calculated using all the elements of the bolometer structure such as the silicon nitride structure, the VOx coating, and the nichrome electrical leads. Using a calculation of the full spectral irradiance on the bolometer from the scene and the dewar and a user-defined bolometer element spectral absorption, the model will accurately assess performance in any environment. The model also employs a 3-D noise model and provides synthetic images of PSF-blurred bar targets for NETD and WTD predictions.