An analytic model employing an elliptical surface area to determine the gaseous thermal conductance of uncooled VOx microbolometers

•An inaccurate assumption in the conventional model leads to a substantial error.•An elliptical surface area method is proposed.•The elliptical area model is simple to apply and relies on the membrane dimensions.•The elliptical area model provides results very close to FEM simulation results.•The use of surface profilometry confirms the deformation of the device membranes. This work presents a detailed overview of the analytic methods for calculating the beam and gaseous thermal conductance components associated with uncooled VOx microbolometers. The conventional method to calculate the gaseous component relies on the assumption that the entire plate is maintained at a uniform temperature, thus the surface area of the plate is used for the calculation. We have observed using an industry leading multiphysics simulator that this assumption is not strictly true for VOx microbolometers as the conduction pattern exhibits an elliptical shape. Based on this, we have developed and propose an analytic method that employs an elliptical surface area scaled appropriately with the device dimensions to obtain an estimate of the average temperature conduction pattern. Prototype devices were manufactured and experimentally characterised. The devices exhibit thermal conduction characteristics comparable to those in literature and industry, and we could achieve 0.5μW/K under vacuum conditions and 15μW/K at atmospheric pressure with a TCR of −1%/K. However, both simulated and experimental result sets of the gaseous thermal conductance exhibit large deviations from the conventional analytic method, on average approximately 40%. The proposed method reduces this average error significantly to less than 10% when compared to the simulated results.