Application of silver-doped diamond composites in the field of heat conduction
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Ultra-thin silver-doped diamond composite developed by Professor Jason Nadle of the GTRI team
High-power semiconductors typically require a thermal pad to transfer heat to a scaly, fan-shaped or tubular heat sink to dissipate heat, thereby reducing device temperature. Since semiconductors are typically assembled in very tight, confined spaces, the choice of thermally conductive gasket materials requires a high thermal conductivity while not taking up too much space.
Diamond has excellent thermal conductivity, and the incorporation of silver allows the diamond particles to be suspended in the composite, resulting in a thermal conductivity that is nearly 25% higher than copper. At present, this silver-doped diamond composite has been successfully tested in two important fields of heat conduction and thermal expansion.
According to Jason Nadler, who led the research project, the temperature of the device was reduced from 285 ° C to 181 ° C using this silver-doped diamond composite. The gasket sample contains 50% diamond and is only 250 microns in size. In addition, the scientists also tried to increase the diamond composition in the gasket sample to 85%, and still maintain a thickness below 250 microns; the results show that the thermal conductivity of the gasket with increased proportion of diamond components is greatly increased.
Nadler also added: At present, there is no material material that has thermal conductivity and thickness comparable to that of silver-doped diamond composites; its technical application prospects are very broad.
Natural heat conductor
Diamond is a natural thermal conductor material with a thermal conductivity of up to 2000 W/(m•K). Silver is one of the best metallic materials for thermal conductors with a thermal conductivity of 400 W/(m•K). Silver doping in diamonds is very important in the following four areas:
1 helps to loosen loose diamond particles on a stable substrate
2 For parts with high dimensional accuracy requirements, precision cutting is possible
3 can well match the thermal expansion of silver itself and the thermal expansion of semiconductor equipment to be cooled and cooled.
4 Create a more efficient thermal interface between diamond particles
Nadler and his team used diamond pellets for molding. But like a disc of sand-like diamond particles that do not gather well together, the staff used a silver matrix, a soft, ductile and viscous material to concentrate the diamond particles and make a stable composite.
In addition, the ductile silver matrix completely surrounds the diamond particles, which can be precisely cut for parts requiring high dimensional accuracy, such as thermal pads, so that these parts are firmly bonded to other interfaces such as semiconductors.
Adjustment of thermal expansion coefficient
Any substance that heats up will expand at its own rate, which scientists define as the coefficient of expansion, called CTE (coefficient of thermal expansion).
When the different structures of the material, such as the wide band gap semiconductor and the thermal pad, are combined, it is necessary to unify the coefficients of thermal expansion of the two materials. Otherwise, composite consolidation materials with different thermal expansion coefficients are easily separated.
Diamond has a thermal expansion coefficient of only 2 ppm/K, while materials that make wide-bandgap semiconductors such as silicon carbide and gallium nitride have a thermal expansion coefficient of 3 to 5 ppm/K.
In view of this, GTRI team workers added silver with a thermal expansion coefficient of 20 ppm/K to the diamond particles, and adjusted the thermal expansion coefficient of the composite with the thermal expansion coefficient of the wide-bandgap semiconductor material by adjusting the proportional components of diamond and silver. be consistent. By adjusting the thermal expansion coefficients of diamond and silver during heating and cooling, the researchers successfully consolidated the two materials together.
Metals conduct heat by moving electrons, while diamonds conduct heat through phonons. The incorporation of silver into the diamond particles helps the phonons move between the particles and increase the thermal conductivity.
Efficient and stable filling of diamond particles in the panel of a thermally conductive gasket is a technical challenge. At present, Nadler's team has built and developed image analysis methods and tools to analyze the structure of their experimental products to help them study the distribution of diamond particles in this composite and how silver is surrounded. Around the diamond. (Compiled from "Taking the Heat: Silver-Diamond Composite Offers Unique Capabilities for Cooling Powerful Defense Microelectronics"; Translation: Wang Xian)