A new approach to IR bimaterial detectors theory

In this paper we propose a new theoretical approach to the analysis of bimaterial infrared thermal detector (BMD) performance. In order to determine the basic parameters of a BMD—sensitivity, noise equivalent power, detectivity—we considered the BMD as a mechanical oscillating system and introduced an equivalent “thermomechanical” excitation force. This force is proportional with temperature changes and causes mechanical oscillations of the bimaterial cantilever. After identifying all of the relevant noise mechanisms (temperature fluctuations, Brownian motion), we solved the appropriate Langevin stochastic equation and obtained the mean square deflection of the bimaterial cantilever oscillator. This enabled us to determine all of the important BMD parameters. These parameters depend on the relevant thermal, mechanical and geometrical properties of the constituent parts of the detector and the chosen materials, as well as on the gas type and pressure inside the housing. Our analysis is focused on the study of pressure influence to the BMD performance. We showed that detectivity can approach the ideal value with pressure decrease if other bimaterial microcantilever parameters are properly chosen. Finally, we applied our theory on a BMD fabricated at ORNL.