A New Material Moves Heat Almost Three Times Better Than Copper

A UCLA-led team has measured a metallic compound that carries heat nearly three times better than copper, the highest thermal conductivity ever recorded in a metal. The result, published in Science, points to a different ceiling for how well metals can move heat and to a new tool for cooling the densest electronics.

The compound is theta-phase tantalum nitride, written θ-TaN, a ceramic nitride that behaves more like a metal than a ceramic for heat. In conventional metals, free electrons do almost all of the heat-carrying work, while atomic vibrations, called phonons, play a small role. In θ-TaN, both carry heat, and unusually strong coupling between them pushes the total to about 1,100 W/m·K, the standard unit for how efficiently a material moves heat. Copper, the workhorse of today's heat sinks, sits near 400 W/m·K. Aluminum runs 167 to 237 W/m·K depending on alloy.

The team, led by Yongjie Hu, a professor of mechanical and aerospace engineering at the UCLA Samueli School of Engineering, used measurements at Argonne National Laboratory and a multi-institution collaborator network to pin down the number (UCLA Samueli; UCLA Newsroom).

The mechanism is the part that breaks a long-standing assumption. Textbook metal heat transport treats the electron flow and the lattice vibrations as mostly separate channels, each with its own ceiling. The θ-TaN data, and the team's analysis, argue that the two channels can be made to cooperate so strongly that the combined conductivity far exceeds what either would carry alone. That reframes the limit on metal heat transport as a materials-design problem rather than a fixed physics line.

For chip designers, the practical lever sits in thin heat-spreading layers rather than bulk heat sinks. As AI accelerators and 3D-stacked packages concentrate more power into smaller footprints, the bottleneck is no longer the bulk heat sink on top of the chip. It is the millimeter-scale layer that pulls heat from a hot spot and feeds it to whatever sink sits above. Diamond, at roughly 1,500 to 2,200 W/m·K for high-purity synthetic, is already used as an ultra-thin interposer in some advanced IC packages for that reason (EE Times). θ-TaN, if it can be deposited as a thin film, would give designers another option in the same regime, with manufacturing processes closer to existing metallization than to diamond growth.

That is also the limit on what θ-TaN can replace. Copper today makes up roughly 30% of commercial thermal-management materials, a market-share figure that UCLA cites as context for the result. θ-TaN is not a candidate to displace copper at the bulk heat-sink level, where the incumbent's cost, manufacturability, and mature supply chain still rule. Its near-term use, if any, is in the package itself, where copper's thermal ceiling is the actual constraint.

Two limits frame the result. The figure is a single-team measurement, not an industry-validated benchmark, and independent replication of the ~1,100 W/m·K number on production-grade samples is the obvious next step. The work is at the materials stage rather than the packaged-device stage. The path from a record-measured thin film to a shipping AI accelerator is years, and runs through deposition, adhesion, cost, and yield.

The next milestone worth watching is whether other groups reproduce the ~1,100 W/m·K figure on independently grown θ-TaN samples, and whether the same electron-phonon trick can be engineered into more familiar metal nitrides that the chip industry already knows how to deposit.