Thermoelectric Devices: Influence of the Legs Geometry and Parasitic Contact Resistances on ZT

Abstract

In this chapter, the impact of the shape of thermoelectric legs and parasitic contact resistances from metal electrodes and device wiring on thermoelectric figure of merit ZT is addressed. First section deals with the influence of the legs geometry on ZT. The shape of the legs is crucial in the thermoelectric performance of the thermoelectric devices. Unlike to conventional geometry thermoelectric legs, non-constant cross-section legs could help by lowering the overall thermal conductance of the device so as to increase the temperature gradient along legs, hence harnessing the Thomson effect, which is generally neglected in constant square cross-section thermoelectric legs. The final section is devoted to the electrical contact engineering of the device. Parasitic contact and wiring resistances play an important role in the performance of the device because they increase the isothermal resistance of the device. As the isothermal resistance of the device increases, the ZT decreases.

Thermoelectric Modules: Key Issues in Architectural Design and Contact Optimization

“…[99][100] Here, the Thomson effect, i. e. Thomson coefficient, t T ð Þ ¼ TdS dT ( Seebeck coefficient varies at different points along the length of the thermoelements) is harnessed which is otherwise neglected in the conventional cuboidal structure. [86] Thus, the output power demonstrates ~70% augmentation in the pyramidal structure in comparison to the cuboidal geometry, proving the significance of the geometrical layout of the thermoelectric legs in the device functioning.…”

“…[97] Recently, a pyramidal shaped prototype thermoelectric generator was assembled by Mijangaos et al and found that pyramidal legs i. e. asymmetrical thermoelements lower the thermal conductance, in turn, enhances the temperature gradient, alongside the legs as shown in Figure 7. [86] Moreover, Sahin and Yilbis also carried out detailed analysis of the impact of the geometry of the thermoelements on the efficiency and output power of thermoelectric power generators. [98] It has been analysed that thermoelectric performance of the trapezoid legs i. e. where the cross-section varies linearly gives more output power density than conventional rectangular leg geometry.…”

“…In the second sawing process, the metallized wafers are slashed which form the thermoelectric legs. [85][86] 7. Incisioned legs are subsequently pulled out, located and then soldered to the ceramic plates which are pre-metalized using direct plate copper.…”

Materials and Devices for On-Chip and Off-Chip Peltier Cooling: A Review

“…In practice, typical figures may be higher, between 10 −7 and 10 −5 • cm 2 [111]. As an example of the influence of electrical contact resistivity, the optimal film thickness of a TFTEC changes from 20 μm [83], [112] for contact resistivity in the order of 10 −6 •cm 2 to <2 μm when the contact resistivity decreases to 10 −8 •cm 2 [7]. For a 100× 100 μm 2 Si/SiGe TEC, an increase in contact resistivity from 10 −9 to 10 −4 •cm 2 degrades performance by ∼85%, whereas the same device scaled to a 3000 × 3000 μm 2 area would face only a ∼5% degradation [111].…”

Optimization of Variable Cross-Sectional Area Thermoelectric Elements Through Multi-Method Thermal-Electric Coupled Modeling

“…al found that the power output of a TEG is maximized at a shorter leg length than that at which device efficiency is maximized [22]. Fabian-Mijanos and Alvarez-Quintana studied pyramidal-shaped semiconductor legs and found that maximum power output was almost two times greater than that of symmetric rectangular legs, which was accredited to the utilization of the Thomson effect [23]. While these works give insight on the effects of individual geometric parameters, the work presented herein eliminates the necessity for parametric studies by providing an algorithm that optimizes the semiconductor leg shape profile based on the realized temperature difference.…”