Low temperature thermoelectric coolers for infrared detectors

The solid state reliability and convenience of thermoelectric coolers make them an attractive solution to cooling detectors. We present evidence that the temperature difference of thermoelectric Bi2Te3 coolers can be increased by optimizing the device parameters. Computer modeling of multistage coolers was used to analyze the parametric effects on their performance. Experimental coolers were constructed on the basis of modeling results and tradeoffs between performance and size. A heat treatment was applied to the Bi2Te3 elements, reducing their resistivity to about 25% of that of untreated elements. The performance of radiation shielded coolers in vacuum was investigated, with the heat sink temperature maintained at 293 K. Without field enhancement, the temperature difference measured for a six-stage cooler was 137 K in presence of a thermal load of 10 mW. To compensate for the increase of the stage dimensions in seven-stage coolers, the thermal resistance of the stage surface was reduced by means of solder coating. For the best seven-stage device, a difference of 166 K could be achieved for a thermal load of 20 mW. For the parameter values used in the experiment, the cooldown time was typically 500 sec regardless of the supplied voltage. The measured ratio of temperatures of adjacent stages varied negligibly, indicating that the coefficient of performance of the studied cooler is close to the optimum value. The good agreement found between experimental and computer modeling data suggests that the developed model may be suited for further performance prediction.