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

General strategy for developing thick-film micro-thermoelectric coolers from material fabrication to device integration

Micro-thermoelectric coolers are emerging as a promising solution for high-density cooling applications in confined spaces. Unlike thin-film micro-thermoelectric coolers with high cooling flux at the expense of cooling temperature difference due to very short thermoelectric legs, thick-film micro-thermoelectric coolers can achieve better comprehensive cooling performance. However, they still face significant challenges in both material preparation and device integration. Herein, we propose a design strategy which combines Bi2Te3-based thick film prepared by powder direct molding with micro-thermoelectric cooler integrated via phase-change batch transfer. Accurate thickness control and relatively high thermoelectric performance can be achieved for the thick film, and the high-density-integrated thick-film micro-thermoelectric cooler exhibits excellent performance with maximum cooling temperature difference of 40.6 K and maximum cooling flux of 56.5 W·cm-2 at room temperature. The micro-thermoelectric cooler also shows high temperature control accuracy (0.01 K) and reliability (over 30000 cooling cycles). Moreover, the device demonstrates remarkable capacity in power generation with normalized power density up to 214.0 μW · cm-2 · K-2. This study provides a general and scalable route for developing high-performance thick-film micro-thermoelectric cooler, benefiting widespread applications in thermal management of microsystems.

Optimization of Interface Materials between Bi2Te3-Based Films and Cu Electrodes Enables a High Performance Thin-Film Thermoelectric Cooler

Thermoelectric interface materials (TEiMs) are key to optimizing the electrical contact and stability of the interface between thermoelectric material and metal electrode in high-performance thin-film thermoelectric coolers (TECs). Herein, we explored TEiMs applicable to representative Bi-Te films and found that Cr and Ag are effective TEiMs for p-type Bi_0.5Sb_1.5Te₃ and n-type Bi₂Te₃, respectively. By introducing 200 nm Cr and 200 nm Ag as TEiMs for p-type Bi_0.5Sb_1.5Te₃/Cu and n-type Bi₂Te₃/Cu interfaces, Cu diffusion is suppressed, and excellent electrical contact is achieved (1.81 × 10^-12 Ω m² for p-type and 3.32 × 10^-12 Ω m² for n-type) and remains stable after heat treatment (2.37 × 10^-12 Ω m² for p-type and 1.63 × 10^-12 Ω m² for n-type). Furthermore, the cooling flux of TECs with optimized TEiMs increases from 122.74 to 296.56 W/cm², while the performance degradation caused by contact resistance decreases from 50.81 to 4.15%. In addition, our results show that diffusion occurs between not only Cu but also Ag and the thermoelectric material, as TEiMs diffuse slightly. The diffusion of Cu and Ag at the interface can optimize the electrical contact of Bi₂Te₃/Cu but strongly degrade the electrical contacts of Bi_0.5Sb_1.5Te₃/Cu. Our work provides an optimal selection of TEiMs for high-performance Bi-Te thin film coolers and provides guidance for further miniaturization of devices.

Structural Design Optimization of Micro-Thermoelectric Generator for Wearable Biomedical Devices

Wearable sensors to monitor vital health are becoming increasingly popular both in our daily lives and in medical diagnostics. The human body being a huge source of thermal energy makes it interesting to harvest this energy to power such wearables. Thermoelectric devices are capable of converting the abundantly available body heat into useful electrical energy using the Seebeck effect. However, high thermal resistance between the skin and the device leads to low-temperature gradients (2–10 K), making it difficult to generate useful power by this device. This study focuses on the design optimization of the micro-thermoelectric generator for such low-temperature applications and investigates the role of structural geometries in enhancing the overall power output. Electroplated p-type bismuth antimony telluride (BiSbTe) and n-type copper telluride (CuTe) materials’ properties are used in this study. All the simulations and design optimizations were completed following microfabrication constraints along with realistic temperature gradient scenarios. A series of structural optimizations were performed including the thermoelectric pillar geometries, interconnect contact material layers and fill factor of the overall device. The optimized structural design of the micro-thermoelectric device footprint of 4.5 × 3.5 mm2, with 240 thermoelectric leg pairs, showcased a maximum power output of 0.796 mW and 3.18 mW when subjected to the low-temperature gradient of 5 K and 10 K, respectively. These output power values have high potential to pave the way of realizing future wearable devices.