Sensor Units to Measure Multi-Direction Seebeck Coefficient of Micro-Scale Film
Authors: Kim Yeongseok , Kang Sang-Woo , Kim Hyeong-U , Kim Taesung 
Published: February 2020

Since the discovery of the Seebeck effect in the early 19th century, which describes the electromotive force depending on the temperature gradient, thermoelectric (TE) materials have been studied in the research of the alternative energy source. Especially, high-efficiency TE materials are important for power generation device within 200 ~ 500 K temperature range because it has simple and reliable structure [1].

Inducing the nanotechnology to the synthesis of TE materials in the 1990s, TE materials have achieved lower thermal conductivity without reducing the electrical conductivity and it has improved thermoelectric figure of merit (ZT) dramatically [2]. It has been researched reduction of dimension like nanowire (1D) and superlattice (2D), or nanocomposition with nanoparticle embedded in particular to improve the ZT by inducing the phonon scatter at the interface between particle and grain boundary. Despite of the good performance of low dimension TE materials, commercial measuring equipment is not appropriate to measure the thermal properties of these materials. Consequently, various methods were suggested to evaluate the noble TE materials depending on the dimension of the materials [4 ~ 7]. Unlike the bulk materials, TE materials which have low dimension such as 2D, 1D and 0D, or which nanocomposition technique was induced, has different thermal properties of in- and cross-plane directions because of the anisotropic crystal structure and array of quantum dot [8]. So many research groups have developed various types of evaluation methods which were appropriate for their research results. These methods could measure the thermal properties in the only one direction between in- and cross-plane. And these methods were insufficient to have a standard traceability because those didn’t apply to other cases.

In this study, we developed a sensor unit which could measure the Seebeck coefficient in the in- and cross-plane directions. This sensor unit was designed to measure the TE sample generated by various deposition methods. Target sample was micro scale film type which was general results of nanocomposition and superlattice TE sample. In case of physical vapor method (PVD) such as sputtering and evaporation, we designed that TE material could be deposited on the sensor to evaluate the properties more exactly. While the commercial measuring equipment was difficult to measure the thermal properties in case of film type TE materials because the temperature gradient become smaller as film thickness thinner, we measured Seebeck coefficient of 1 ~ 100 ㎛ thickness TE sample. And we measured the coefficient at 300 ~ 500 K temperature range which TE material has merit compared to mechanical heat engines to retain the availability of the sensor. To confirm the validity of the sensor, we measured Bi-Te and silicon sample which have progressed preceding research from other research groups.

Reference

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