As microelectronics continue to shrink and pack more power into each square millimeter, managing heat has become one of the defining engineering challenges of the decade. The hotspots in modern CPUs, 5G RF amplifiers, and laser diodes can exceed 40 W cm⁻² , enough to degrade performance, shorten lifetimes, and ultimately limit what the hardware can do.
The standard solution is the thermoelectric cooler (TEC): a solid-state device that pumps heat away from a hot spot when an electric current is passed through it. But the best-performing TECs rely on bismuth telluride (Bi₂Te₃), and tellurium is one of the rarest elements in the Earth’s crust , less abundant than platinum, with global production measured in hundreds of tonnes per year.
Now, a team of researchers from Beijing Normal University, Songshan Lake Materials Laboratory, and Wuhan Textile University has developed a promising alternative: Mg-based micro thermoelectric coolers (μ-TECs) that minimize tellurium use and can be fabricated with industry-compatible processes.
The fabrication challenge
Magnesium-based thermoelectrics have long been attractive because magnesium is abundant, non-toxic, and the compounds n-type Mg₃(Bi,Sb)₂ and p-type MgAgSb have good thermoelectric performance. But there has been a fundamental manufacturing problem: Mg compounds are highly sensitive to moisture and oxygen. Standard fabrication routes that involve water or high-temperature sintering cause the material to degrade, volatilize, or drift in composition.
The team solved this with a low-temperature, water-free fabrication route using magnetron sputtering as a cold bonding technique. Rather than sintering thermoelectric legs at high temperatures (400–600 °C, as is typical for Bi₂Te₃), they deposited the Mg-based materials directly onto substrates via sputtering in a controlled environment, avoiding water exposure and keeping processing temperatures low enough to preserve the materials’ thermoelectric properties.
This choice is not incidental: p-type MgAgSb undergoes a phase transition at approximately 573 K (300 °C) to a structure with severely degraded thermoelectric performance. Keeping the entire process below this threshold means the material’s properties are not compromised during manufacturing.
The performance numbers
The resulting μ-TEC, measuring just 2.95 × 4.35 × 1.4 mm³ with 12 thermocouple pairs, achieved the following verified metrics:
- Power density: 4.34 W cm⁻² , sufficient for many hotspot cooling applications
- Packing density: 93.5 pairs cm⁻² , enabling the device to fit in tight spaces
- Leg size: approximately 3% of the volume of previously reported Mg-based thermoelectric devices, a dramatic miniaturization
The magnetron sputtering approach proved capable of creating thermoelectric legs far smaller than any previously demonstrated Mg-based device, closing the miniaturization gap with established Bi₂Te₃ technology.
The tellurium problem
Tellurium’s extreme scarcity , 0.001 parts per billion in the Earth’s crust , is not just a cost issue; it is a scalability constraint. A widespread deployment of thermoelectric cooling in consumer electronics, data centers, or electric vehicles would require tellurium at volumes the current supply chain cannot support. Bismuth and silver (still present in the Mg-based compounds) are also non-trivial in cost, but both are orders of magnitude more abundant than tellurium.
The Mg-based approach does not eliminate scarce elements entirely , it still uses bismuth in the n-type leg and silver in the p-type leg , but it eliminates tellurium, which is by far the most critical bottleneck.
Caveats
The Nature Communications paper describes an unedited early-access manuscript, meaning final copy-editing has not yet been applied. Some details , including the exact comparison benchmark for the “3% of prior size” claim , are not specified in the abstract.
Additionally, while 4.34 W cm⁻² is competitive for many applications, state-of-the-art Bi₂Te₃ thick-film μ-TECs have demonstrated up to 56.5 W cm⁻². The Mg devices are not yet at the top end of Bi₂Te₃ performance, though they offer sustainability advantages that Bi₂Te₃ cannot match.
The operational stability of Mg-based thermoelectrics in humid environments , a known weakness of the material class , also remains to be demonstrated over long device lifetimes.
What’s next
The device was demonstrated at the laboratory scale with 12 thermocouple pairs. Scaling to higher pair counts for practical applications will require solving contacting and uniformity challenges that come with larger arrays. Magnetron sputtering, however, is a mature, high-throughput industrial process already widespread in semiconductor fabrication , so the manufacturing path is, in principle, clear.
The key question is whether continued optimization can push the power density closer to Bi₂Te₃ benchmarks while maintaining the sustainability and abundance advantages. Given the pace of development in Mg-based thermoelectrics, that question may be answered sooner rather than later.
Funding: National Key R&D Program of China (2022YFB3803902).
Source
Yang, J., Zhu, R., Li, M., Mei, Z., Chen, L., and Wu, L.-M. “A low-temperature, water-free fabrication route to Mg-based micro thermoelectric coolers for thermal management.” Nature Communications (2026). DOI: 10.1038/s41467-026-75165-8