As a direct relative of diamonds, diamond—with its properties as a form of elemental carbon—possesses remarkable capabilities, including the highest known thermal conductivity, stiffness, and hardness, as well as high optical transmission over a broad wavelength range, a low coefficient of thermal expansion, and low density. These properties make diamond an ideal material for thermal management applications capable of significantly reducing thermal resistance.
To synthesize diamond for thermal management applications, the first step is to select the most appropriate deposition technique. Microwave-assisted CVD allows for better control of grain size and grain boundaries, thereby producing high-quality, highly reproducible polycrystalline diamond that meets the thermal conductivity levels required for specific applications. Currently, CVD diamond has been commercialized, with thermal conductivity grades ranging from 1000 to 2000 W/m·K available. CVD diamond also exhibits fully isotropic properties, enhancing heat diffusion in all directions. Figure 1 shows a comparison of thermal conductivity between CVD diamond and other traditional heat dissipation materials.
Thanks to recent technological advancements, CVD diamond has achieved mass production, and its cost has rapidly decreased. The mass production cost of unmetallized CVD diamond heat sinks is $1 per mm³, with pricing primarily dependent on the thermal conductivity grade. For common thicknesses between 0.25 and 0.40 mm and applications where the lateral dimensions match the wafer size, RF device diamond heat sinks typically measure less than 5 mm³. Consequently, system costs can be significantly reduced with only a few dollars in incremental cost at the chip level. For example, enabling a system to operate at higher temperatures can lower both the initial cost of the cooling subsystem and subsequent operating costs. With appropriate chip bonding methods, diamond heat sinks provide a reliable thermal management solution for semiconductor packaging.
