Effect of Excessive Bias Heating on a Titanium Microbolometer Infrared Detector

In a metal film infrared microbolometer, the responsivity is improved by high bias current to compensate for its low-temperature coefficient of resistance (TCR). However, what are the upper limits of this current without damaging the microbolometer element is not well understood. To study the effects of large bias current, we performed the destructive I-V measurements on an element of a 16 times 16 Ti-microbolometer array developed at our laboratory and report here the experimental observations of its electrical and physical damages. In this study, we performed the I-V measurements repeatedly on a microbolometer element and increased the final bias current in steps of 50 muA in each repetition. The effect of the heating due to I²R power dissipation has been analyzed at each step by monitoring I-V characteristics, specific detectivity and physical health. We report a significant decrease in the detectivity when bias stress is increased beyond 450 muA, which corresponds to the element temperature of 370degC. Further, we found that the resistance started decreasing, when the power dissipated and the element had increased to about 2.5 mW, resulting in a peaked I-V characteristics. This corresponds to the bias stresses more than 650 muA. Using a new I-V model, we extracted the temperature to be about 750degC at these peaks. A further increase in bias stress has resulted in the complete physical damage of the element.