Fabrication of Π-structured Bi-Te thermoelectric micro-device by electrodeposition

Comprehensive Review on Thermoelectric Electrodeposits: Enhancing Thermoelectric Performance Through Nanoengineering

Thermoelectric devices based power generation and cooling systemsystem have lot of advantages over conventional refrigerator and power generators, becausebecause of solid-state devicesdevices, compact size, good scalability, nono-emissions and low maintenance requirement with long operating lifetime. However, the applications of thermoelectric devices have been limited owingowing to their low energy conversion efficiency. It has drawn tremendous attention in the field of thermoelectric materials and devices in the 21st century because of the need of sustainable energy harvesting technology and the ability to develop higher performance thermoelectric materials through nanoscale science and defect engineering. Among various fabrication methods, electrodeposition is one of the most promising synthesis methods to fabricate devices because of its ability to control morphology, composition, crystallinity, and crystal structure of materials through controlling electrodeposition parameters. Additionally, it is an additive manufacturing technique with minimum waste materials that operates at near room temperature. Furthermore, its growth rate is significantly higher (i.e., a few hundred microns per hour) than the vacuum processes, which allows device fabrication in cost effective matter. In this paper, the latest development of various electrodeposited thermoelectric materials (i.e., Te, PbTe, Bi₂Te₃ and their derivatives, BiSe, BiS, Sb₂Te₃) in different forms including thin films, nanowires, and nanocomposites were comprehensively reviewed. Additionally, their thermoelectric properties are correlated to the composition, morphology, and crystal structure.

Electrodeposited Thin-Film Micro-Thermoelectric Coolers with Extreme Heat Flux Handling and Microsecond Time Response

Thin-film thermoelectric coolers are emerging as a viable option for the on-chip temperature management of electronic and photonic integrated circuits. In this work, we demonstrate the record heat flux handling capability of electrodeposited Bi₂Te₃ films of 720(±60) W cm^-2 at room temperature, achieved by careful control of the contact interfaces to reduce contact resistance. The characteristic parameters of a single leg thin-film devices were measured in situ, giving a Seebeck coefficient of S = -121(±6) μV K^-1, thermal conductivity of κ = 0.85(±0.08) W m^-1 K^-1, electrical conductivity of σ = 5.2(±0.32) × 10⁴ S m^-1, and electrical contact resistivity of ∼10^-11 Ω m². These thermoelectric parameters lead to a material ZT = 0.26(±0.04), which, for our device structure, allowed a net cooling of ΔT_max = 4.4(±0.12) K. A response time of τ = 20 μs was measured experimentally. This work shows that with the correct treatment of contact interfaces, electrodeposited thin-film thermoelectrics can compete with more complicated and expensive technologies such as metal organic chemical vapor deposition (MOCVD) multilayers.

Electrodeposition of Bi-Te Thin Films on Silicon Wafer and Micro-Column Arrays on Microporous Glass Template

Electrodeposition is an important method for preparing bismuth telluride (Bi₂Te₃)-based thermoelectric (TE) thin films and micro-column arrays. When the concentrations of Bi:Te in electrolytes were 3 mM:4 mM, the TE films satisfied the Bi₂Te₃ stoichiometry and had no dependence on deposition potential. With increasing over-potential, crystal grains changed from lamellar structures with uniform growth directions to large clusters with staggered dendrites, causing a decrease in the deposition density. Meanwhile, the preferred (110) orientation was diminished. The TE film deposited at −35 mV had an optimum conductivity of 2003.6 S/cm and a power factor of 2015.64 μW/mK² at room temperature due to the (110)-preferred orientation. The electrodeposition of TE micro-columns in the template was recently used to fabricate high-power micro-thermoelectric generators (micro-TEG). Here, microporous glass templates were excellent templates for micro-TEG fabrication because of their low thermal conductivity, high insulation, and easy processing. A three-step pulsed-voltage deposition method was used for the fabrication of micro-columns with large aspect ratios, high filling rates, and high density. The resistance of a single TE micro-column with a 60 μm diameter and a 200 μm height was 6.22 Ω. This work laid the foundation for micro-TEG fabrication and improved performance.

Towards a 3D GeSbTe phase change memory with integrated selector by non-aqueous electrodeposition

We have recently reported a new method for the electrodeposition of thin film and nanostructured phase change memory (PCM) devices from a single, highly tuneable, non-aqueous electrolyte. The quality of the material was confirmed by phase cycling via electrical pulsed switching of both 100 nm nano-cells and thin film devices. This method potentially allows deposition into extremely small confined cells down to less than 5 nm, 3D lay-outs that require non-line-of-sight techniques, and seamless integration of selector devices. As electrodeposition requires a conducting substrate, the key condition for electronic applications based on this method is the use of patterned metal lines as the working electrode during the electrodeposition process. In this paper, we show the design and fabrication of a 2D passive memory matrix in which the word lines act as the working electrode and nucleation site for the growth of confined cells of Ge-Sb-Te. We will discuss the precursor requirement for deposition from non-aqueous, weakly coordinating solvents, show the transmission electron microscopy analysis of the electrodeposition growth process and elemental distribution in the deposits, and show the fabrication and characterisation of the Ge-Sb-Te memory matrix.