Technology and Investigation of Ohmic Contacts to Thermoelectric Materials

Abstract

Technology is developed, materials and regimes of the fabrication of ohmic contacts to the effective thermoelectric materials Bi2Te2.8Se0.2 (n-type) and Bi0.5Sb1.5Te3 (p-type) are determined. Ohmic contacts were obtained by the vacuum deposition of nickel. Factors determining adhesion strength and resistivity of fabricated contacts are determined. Process of surface preparation of the thermoelectric materials before the ohmic contact deposition is optimized during the technology development. The use of electrochemical polishing, ultrasound treatment, finish cleaning in toluene and isopropyl alcohol vapor, and annealing in vacuum allowed achieving stable results in the formation of contacts. It was shown that contacts fabricated using of electron-beam evaporation of nickel possess maximum adhesion strength of 18-19 N/mm 2 . It was found that high adhesion is caused by the existence of transition layer in the metal-thermoelectric material contact range, formed due to the interaction of metal with the components of thermoelectric material. Proposed technology allows obtaining ohmic contacts with the resistance of the unit area not exceeding 10 −10 Ohm m 2 .

Thermoelectric Modules: Key Issues in Architectural Design and Contact Optimization

“…However, metallization using barrier layers at both the ends of the thermoelectric legs can enrich the wettability of the solder and can restrict the diffusion of the solder into the thermoelectric material. An ohmic contact is essential to minimize the parasitic losses evolving due to the additional thermal and electrical resistance at the boundary [70–71] . If $${{R}_{c}}$$ is the electrical contact resistances at the interface of the contact and thermoelectric material, then it can be obtained by subtracting the resistance of the material and the resistances due to wiring from the total resistance of the module.…”

“…An ohmic contact is essential to minimize the parasitic losses evolving due to the additional thermal and electrical resistance at the boundary. [70][71] If R c is the electrical contact resistances at the interface of the contact and thermoelectric material, then it can be obtained by subtracting the resistance of the material and the resistances due to wiring from the total resistance of the module. R c also considers the effect of the area in contact.…”

Metallization of ZnSb and contact resistance

“…Different metallization techniques have been investigated for other thermoelectric materials. For instance, electroplating followed by thermo-compression bonding has been reported for indium contacts with nickel diffusion barriers on Bi 2 Te 3 , 10 while Shtern et al 11 reported on the optimization of evaporated Ni films for contacts to Bi 0.5 Sb 1.5 Te 3 and Bi 2 Te 2.8 Se 0.2 , and Jung et al 12 presented a review on the lead free transient liquid phase soldering addressing thermoelectrics. Yet, there are only a few reports on the metallization of ZnSb.…”