Stability conditions, nonlinear dynamics, and thermal runaway in microbolometers

The nonlinear dynamic behavior of microbolometers, operating at room temperature (300 K) under conditions of positive electrothermal feedback is investigated. An improved device model, based on the heat balance equation is developed. It takes into account the temperature dependence of the thermophysical parameters, such as thermal coupling coefficient between the sensor and its surroundings, and sensor heat capacity and its thermal resistance coefficient. Operational considerations for thermoresistive microbolometer with positive and negative temperature coefficient of resistance are discussed for both, constant current and constant voltage modes of operation. Analytical expressions are derived for predicting stable and unstable operation. Safety factors L-0, establishing the biasing conditions for stable device operation are proposed for the positive temperature coefficient of resistance and negative temperature coefficient of resistance type sensors. Limits for fast catastrophic destruction are provided, and the dynamic characteristics of the associated thermal runaway phenomenon is illustrated. This effect, as predicted by analysis and numerical simulation, was observed experimentally, confirming the validity of the proposed modeling approach for the microbolometer. (C) 2001 American Institute of Physics.