Thin-film contact systems for thermocouples operating in a wide temperature range

• Published in: Journal of alloys and compounds 2021-01, Vol.852, p.156889, Article 156889
• Main Authors: Shtern, Maxim, Rogachev, Maxim, Shtern, Yury, Gromov, Dmitry, Kozlov, Alexander, Karavaev, Ivan
• Format: Article
• Language: English
• Subjects: Adhesion; Adhesive strength; Auger electron spectroscopy; Barrier layers; Bismuth tellurides; Contact resistance; Degradation; Diffusion barriers; Diffusion layers; Figure of merit; Materials selection; Molybdenum; Multi-section thermoelement; Multilayers; Nickel; Seebeck effect; Stability analysis; System effectiveness; Thermal resistance; Thermal stability; Thermocouples; Thermoelectric materials; Thin films; Thin-film contact systems
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.156889

For thermoelements operating on the Peltier and Seebeck effects, including multisection ones used at temperatures up to 900 K, the physicochemical principles of creating effective thin-film multilayer contact systems obtained by magnetron ion-plasma sputtering have been developed. The formation of contact systems was carried out on thermoelectric materials based on: Bi2Te3; Sb2Te3; PbTe; GeTe with the increased thermoelectric figure of merit. A structure of contact systems consisting of contact layers providing ohmic contact, adhesion, barrier and interconnection properties of contact systems is proposed and justified. The selection criteria for materials of contact layers are substantiated. For multisection thermoelements operating on the Seebeck effect at temperatures above 500 K, the necessity of introducing diffusion-barrier layers into the structure of contact systems providing reliability and invariability of the properties of contact systems is substantiated. Based on the physicochemical analysis, the thermodynamic and kinetic factors of the stability and degradation of diffusion-barrier layers are determined. The influence of methods for preparing the surface of thermoelectric materials on the adhesion, contact resistance, and thermal stability of contact systems is established. Using Auger electron spectroscopy, the analysis of the causes of thermal stability and degradation of contact systems was carried out. The deposition modes were determined. The effective contact systems were obtained and investigated. The respective systems are based on: Ni; Mo/Ni and Ni/(Ta–W–N)/Ni having the adhesive strength of more than 12 MPa; the contact resistance not exceeding 10−9 Ω m2 and thermal stability at temperatures up to 900 K. •Efficiency of thermoelements is determined by quality of contacts.•Contacts should have low resistance, high adhesion strength and barrier properties.•The surface state of the thermoelectric materials affects the quality of contacts.•Diffusion processes at elevated temperatures lead to degradation of thermoelements.•Thin-film contacts provide a reliable operation of multisectional thermoelements.