Development of a Bi₂Te₃-based thermoelectric generator with high-aspect ratio, free-standing legs

Abstract

A bismuth telluride alloy-based thermoelectric generator with high-aspect ratio, free-standing legs was fabricated. Such legs are desirable for efficient generator performance from low-grade heat sources but are difficult to assemble because they are fragile and difficult to handle and position. Plunge and wire electro-discharge machining (EDM) were used to produce 150 lm  300 lm legs, approximately 6-mm long, with high fidelity. Removal of recast material from EDM was necessary for good adhesion of metallization, but sputter etching was found to deteriorate the mechanical strength of the contacts. A wet chemical cleaning process was developed instead that resulted in good adhesion under test conditions. Au was preferred for designs where interconnects could be patterned directly on the module. Module figure of merit (ZT) was 0.72, close to the 0.85 value expected from bulk material property measurements. Impedance spectroscopy and the Harman technique were shown to significantly underestimate module ZT in the present test configuration. Shear and fatigue testing were performed on arrays of high-aspect ratio legs. Legs survived over 10 4 cycles of shear loading at 90% of the load to failure.

Two-layer process for a micro thermoelectric cross-plane generator with electroplating and reflow soldering

“…generators where the heat flow is vertical as are the TCs, are preferred over other design options. At room temperature applications, Bi 2 Te 3 -based materials offer the greatest potential for thermoelectric applications [2] and are therefore widely used in a variety of generator applications [1,[3][4][5][6][7][8]. Among other options for processing the materials, electrochemical deposition has proven to be feasible [1,7] and allows the realization of thick layers of several hundred microns [9].…”

“…To assemble the generator with two materials, one option is to prepare the materials on different substrates and assemble them afterwards [3,6,8]. In this work, two different materials were electrochemically deposited on a single substrate similar to [1,7].…”

Spark plasma sintered bismuth telluride-based thermoelectric materials incorporating dispersed boron carbide

“…A key advantage of bismuth telluride based materials is that proven module manufacturing approaches are available, which lowers technical development risk. However, poor mechanical properties of directionally solidified material mean that modules with high aspect-ratio legs are difficult to manufacture [6] and the capacity to withstand loads in service is a concern. The aim of this paper is to investigate and develop novel bismuth telluride based thermoelectric materials with improved mechanical properties relative to conventional directionally solidified materials.…”

Energetics and diffusion of gold in bismuth telluride-based thermoelectric compounds

“…Au 9,10 . Au and Au/Ti layers [11][12][13] in particular have been found to form good electrical contacts with acceptable mechanical properties.…”