Differential resistance methods for characterizing figure of merit of microcoolers
U. Ghoshal, K. Kolle, A. Miner
NanoCoolers Inc., Austin, TX 78746. USA.
One of the major difficulty in developing novel thin film thermoelectric materials and microcoolers lies in obtaining consistent and accurate measurement of their thermal and electrical properties. The efficiency and maximum temperature differential of thermoelectric coolers are directly dependent on the figure-of-merit ZT. ZT has been characterized by measuring the materials parameters, the power factor and thermal conductivity individually or by the transient measurement technique, often known as the ZT-meter or the Harman Technique. Microcoolers typically have transients in microsecond regimes, and the application of ZT-meter methods result in inherent electrical and thermal measurement errors that are difficult to quantify or suppress.
This paper presents an alternative purely electrical differential resistance method of characterizing ZT that exploits the dc and high-frequency thermoelectric cooling characteristics. We have applied these methods to a variety of thermoelectric coolers of different physical scales – from centimeters to microns – with consistent and accurate results. We will also describe the extensions of these methods for scanning tunneling microscopy.