Analysis of 320X240 uncooled microbolometer focal plane array ...

13then the transient term goes to zero with time and the periodic function is left. However,ifthen the transient term increases exponentially large until eventually the bolometeroverheats and bums up. Assuming that R I, is much greater than RB and thermalconductance stays about the same with change in temperature (1( ,K0), the unstable bumout condition is whena (7; — To ) > 1. (2.22)For metals, where a decreases with temperature (Equation 2.10), it does not meet thecondition in Equation 2.22, and self-burnout does not occur. However, in the case ofthermistor material, if the bias current is large enough, it will overheat and burnout. Theself burnout condition is given byThe value of )611;2 is about 0.04 for thermistor materials. If the bolometer is at anambient temperature of 300K, then the critical temperature for self-burnout is about325K [7].2.2.2 ResponsivityFrom the definition of temperature coefficient (Equation 2.8), the change in the bolometerresistance due to change in temperature by AT is