Researchers at Advanced Diamond Solutions Inc. have successfully created a low-cost diamond-copper composite material called Heathru, with immediate thermal management applications for semiconductor devices with high power densities.  With thermal conductivities demonstrated over twice that of copper, the material will have dramatic impacts in the microprocessor, memory/graphics, optoelectronics, and power electronics industries, where power dissipation concerns are paramount.

Heat has become the most critical issue in computer and semiconductor design in recent years.  The semiconductor industry has consistently followed Moore’s Law, which states that the number of transistors within semiconductor chips doubles every 18 months since the beginning days of modern semiconductor manufacturing.  As the same time, the size of transistors are getting smaller, resulting in as increase in the number of transistors packed into a given area.  This, combined with the inexorable increase in the clock speed of running such devices, results in skyrocketing power densities in modern day devices such as microprocessors and other high-performance chips.  As Intel CTO Patrick Gelsinger prognosticated, the semiconductor industry is “heading for a meltdown,” with the trend of power densities of modern microprocessors literally escalating toward levels found within a nuclear reactor over the next few years. 

The main problem boils down to basic material science.  A material’s thermal conductivity is the core property that determines its ability to efficiently conduct heat away from a power source.  Most modern high-end semiconductor devices have made the move to copper as the material of choice to transfer heat away since it has one of the highest thermal conductivities any metal (silver is the only metal with a slightly higher conductivity, but is cost-prohibitive for most applications).  Unfortunately, copper has already started to become a bottleneck in removing heat from semiconductor devices.

Diamond, on the other hand, has always been considered a miracle material, being both the hardest known material as well as having the highest thermal conductivity, estimated to be around 6 times that of copper.  However, even with such superlative heat transfer characteristics, diamond has historically been limited in commercial scope because of the associated cost in producing the material.  In fact, only in specialty markets such as heat spreaders for laser diodes has diamond established itself as a viable solution.

Advanced Diamond Solutions Inc. has perfected a proprietary process for producing a high-quality diamond-copper composite material that retains a lot of the thermal properties of diamond, but at an order of magnitude cost reduction over conventional diamond manufacturing processes such as chemical vapor deposition (CVD).  By using conventional diamond synthesis technology, Advanced Diamond is able to create a low-cost sintered diamond composite, with the ability to tailor the exact diamond and filler content to dovetail with the thermal specifications of the device it is to be attached to.  In addition, Advanced Diamond can create very large geometries not physically possible with CVD, currently up to over 3 mm in thickness, 50 mm diameter wafers with 90 mm diameter wafers available in the near future. 

In addition to bulk thermal conductivity, engineers in semiconductor packaging are also extremely concerned about the thermal expansion rate of a material.  If the thermal expansion rates of a thermal transfer material is not properly matched to the device’s semiconductor substrate, micro-cracking will occur at the interface between the two materials as the device is turned on and off, resulting in reliability problems and reducing the life-time of the device.  Since copper and other metals exhibit thermal expansion rates that are an order of magnitude that of silicon and gallium arsenide, it is problematic to attach these materials to semiconductor chips.  In fact, many packaging solutions sacrifice on thermal conductivity, choosing less efficient heat conductors such as ceramics in order to address this issue.  On the other hand, since Advanced Diamond’s Heathru products are made primarily of diamond, its thermal expansion rate is very semiconductor-compatible.  In addition, Advanced Diamond can tightly control the exact thermal expansion rate of its material by varying the diamond content of the diamond through our patent-pending process, making it particularly easy to engineer a thermal solution to match a particular semiconductor device.