March 2, 2011 — A solid composite heat-conducting material created by Georgia Tech Research Institute (GTRI) scientists has a thermal conductivity that is higher than any metal and takes advantage of the properties of diamond, which is the most thermally conductive material at 2000W m^-1 K^-1.

Single-crystal diamonds are sometimes used as heat spreaders for semiconductor lasers. The silver-diamond composite is being aimed at cooling wide-bandgap semiconductors planned for next-generation phased-array radars.

The material is made of very small particles of diamond in a matrix of silver. Unlike single-crystal diamond, the small particles are relatively inexpensive. The silver, which is conductive at 400W m^-1 K^-1, bonds the loose diamond particles into a stable matrix, allows precise cutting of the material to form components of exact sizes, and creates a thermally effective interface between the diamonds.

One of the most important qualities of the silver-diamond composite is that its coefficient of thermal expansion (CTE) can be tailored to match the semiconductor that is being cooled. Otherwise, the heat-conducting layer would delaminate from the semiconductor as temperature changes.

The researchers want to use the composite as a thermal shim with 250µm or thinner thicknesses. Some versions of the composite are up to 85% diamond. The thermal shims made so far are very small, making in-depth testing (which would help to explain the material’s performance in terms of materials science rather than just in terms of performance results) difficult; the GTRI group is evaluating several testbed technologies that hold promise for detailed thermal-conductivity analysis.