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Journal of ELECTRONIC MATERIALS, Vol. 42, No. 7, 2013
DOI: 10.1007/s11664-013-2505-3
2013 TMS
Thermal Conductivity Measurement Methods for SiGe Thermoelectric Materials
L. FERRE LLIN,1,5 A. SAMARELLI,1 Y. ZHANG,1 J.M.R. WEAVER,1P. DOBSON,1 S. CECCHI,2 D. CHRASTINA,2 G. ISELLA,2T. ETZELSTORFER,3 J. STANGL,3 E. MULLER GUBLER,4 and D. J. PAUL1
1.School of Engineering, University of Glasgow, Rankine Building, Oakeld Avenue, Glasgow G12 8LT, UK. 2.L-NESS, Politecnico di Milano, Como, Italy. 3.Johannes Kepler Universitt, Linz, Austria. 4.ETH Zurich, Zurich, Switzerland. 5.e-mail: [email protected]
A new technique to measure the thermal conductivity of thermoelectric materials at the microscale has been developed. The structure allows the electrical conductivity, thermal conductivity, and Seebeck coefcient to be measured on a single device. The thermal conductivity is particularly difcult to measure since it requires precise estimation of the heat ux injected into the material. The new technique is based on a differential method where the parasitic contributions of the supporting beams of a Hall bar are removed. The thermal measurements with integrated platinum thermometers on the device are cross-checked using thermal atomic force microscopy and validated by nite-element analysis simulations.
Key words: Silicon germanium, thermal conductivity, thermoelectrics, heterostructure, device fabrication
INTRODUCTION
The efciency of a thermoelectric material is evaluated by calculating the gure of merit ZT = a2rT/j, where a is the Seebeck coefcient, r is the electrical conductivity, T is the temperature, and j is the thermal conductivity. While great progress has been made in the design of engineered materials to enhance the ZT value, very few structures have been proposed to allow accurate characterization of all the parameters in ZT for a single structure. The electrical characterization of the structure is easily done using van der Pauw or Hall bar structures, where the latter is able to guarantee an accuracy in the measurement as good as 1% if the physical dimensions of the structure are chosen properly. For the estimation of the Seebeck coefcient and the thermal conductivity, an accurate temperature distribution across the structure under examination is required. Moreover, for the calculation of the thermal conductivity a precise value of the thermal ux is required.
One of the most popular techniques for the characterization of the thermal properties of materials is the 3x technique.1 In this method, temperature oscillations of a...