Thermoelectric conversion structure and method of manufacturing same

#The present invention relates to a thermoelectric conversion structure and to a method of manufacturing such a structure. More specifically, the present invention relates to a thermoelectric conversion structure, used in an electricity generation element which uses differences in ambient temperature, and to a method of manufacturing such a structure.

#In recent years energetic research has been conducted on so-called energy harvesting techniques for recovering electric power from waste energy, such as vibrations and heat, which normally is merely dissipated. For example, utilization is anticipated in vibration-generated power, which can be used as a power source for automobile tire pressure gauges and ubiquitous sensor networks, for example. On the other hand, thermoelectric generated power is applied only in niche fields such as for example watches which utilize the temperature differences between the human body and the environment. One reason for this is the low performance of the thermoelectric conversion materials used in thermoelectric elements. The performance index (or figure of merit) of thermoelectric conversion materials is expressed by Z=S2/(ρ·κ)  equation (1)

#Here S is the Seebeck coefficient (μV/K), ρ is the resistivity (Ω-cm), and κ is the thermal conductivity (W/(m·K)). The units of the figure of merit Z are K−1, and as the efficiency of a thermoelectric element using a thermoelectric conversion material, often ZT, the product of the figure of merit and the usage temperature T (K), is used. The efficiency ZT of a conventional thermoelectric element using bulk material as the thermoelectric conversion material is approximately 1. It is thought that if a thermoelectric conversion material with efficiency ZT exceeding 3 could be fabricated, such a material could be substituted for compressors and other cooling systems used for example in refrigerators.

#FIG. 1 is a schematic cross-sectional view of the thermoelectric conversion element of an embodiment of the invention;

#FIG. 2 shows schematic side views of the crystal lattice with (210) face orientation in SrTiO3 single crystal or the cubic perovskite structure of the oxide additional layer of an embodiment of the invention, in which FIG. 2A is a side view seen from the in-plane [1-20] axis and FIG. 2B is a side view seen from the in-plane [001] axis;

#FIG. 3 is an AFM image of the surface of the (210) orientation of a SrTiO3 single crystal after annealing in air for 12 hours at 1180° C., in one embodiment of the invention;

#Below, embodiments of thermoelectric conversion structures using perovskite type manganese oxides of this invention are explained. In the following explanations, unless stated otherwise, portions or elements common to all the drawings are assigned common reference symbols. Further, in the drawings, elements of embodiments are not necessarily shown to scale.

#Below, an embodiment of a thermoelectric conversion material of this invention is explained based on the drawings. Here a SrTiO3 thermoelectric conversion structure is explained, in the surface of which is formed a concave-convex structure defined by the [001] axis and (100) plane of a (210) orientation SrTiO3 single crystal surface. In particular, the ease with which the thermoelectric conversion structure is formed with good reproducibility, having an electron spatial distribution with a quasi-one-dimensional structure fabricated using the concave-convex structure, is explained.

#First, the configuration of the thermoelectric conversion structure of this embodiment is explained. FIG. 1 is a schematic cross-sectional view showing the configuration of the thermoelectric conversion structure 100 of this embodiment. The thermoelectric conversion structure 100 comprises a single crystal 10. As explained below, the single crystal 10 comprises a single crystal of SrTiO3, in the surface of which is a microscopic concave-convex structure. A carrier doping structure 20 is formed so as to be in contact with the surface of this SrTiO3 single crystal. In FIG. 1, the vertical direction in the plane of the paper is perpendicular to the single crystal face, and the horizontal direction is parallel to the single crystal face. The single crystal 10 comprises a SrTiO3 single crystal thermoelectric conversion material.