A model of metal film resistance bolometers based on the electro-thermal feedback effect

The detectivity of metal film resistance bolometers is modeled using one main operating parameter, the self-heating AT. The model comprises the electro-thermal coupling effect on sample impedance, responsivity and time constant. The main simplifications are a linear dependence of the electrical resistance on temperature and lumped thermal conductance G and heat capacity C. Furthermore current controlled operation and perfect absorption of the incident infrared (IR) radiation, eta = 1, are supposed. The contributions of phonon noise, Johnson noise, and current noise are taken into account. Because of their importance the consequences of temperature dependent resistance fluctuations are investigated in detail. Within this frame, the model yields realistic estimates of the achievable NEP and detectivity D* for a given bolometer design for a wide range of DeltaT. These properties are compared with the characteristics obtained for bolometers exhibiting a constant TCR, which are obtained using a corresponding model. Metal film resistance bolometers found to be immune against thermal runaway due to the electro-thermal feedback effect. The presented model simplifies significantly the competitive rating of diverse bolometer designs or competing technologies. (C) 2004 Elsevier B.V. All rights reserved.