The heat-spreader assembly is a major bottleneck for management of junction temperature. Therefore, successful device manufacturers must pay special attention to materials choice and heat-spreader assembly design.
When compared to conventional materials, chemical-vapor-deposition (CVD) diamond is emerging as an effective heat spreader by a large margin. Diamond has a much greater thermal conductivity than other material choices-three times greater than copper, five times greater than AlN or BeO, and five times greater than refractory metals such as copper tungsten or molybdenum copper (see Table 1). Diamond-metal composites made from diamond particles sintered in various metal choices can provide tailoring of heat-spreader coefficient of thermal expansion (CTE) with thermal conductivities better than copper but half that of CVD diamond.
Depending on attachment choices, use of diamond for thermal management in laser devices can improve the cooling capability of the chip in assembled devices from 30% to 100%.
The Kinik Company of Taiwan demonstrated the superior cooling capability of diamond heat spreaders relative to conventional ceramic heat spreaders in 2003. Computer chips were mounted on heat spreaders and operated at power levels that produced a constant 110°C chip junction temperature (see Table 2). Diamond heat spreaders of the same thickness were able to remove 7.6 times more heat than alumina heat spreaders and 4.1 times more heat than BeO heat spreaders.
In another example of improved optoelectronic device power enabled by using diamond, the thermal resistivity (Rth) of multiple-emitter vertical-cavity surface-emitting arrays was measured on copper and diamond substrates and the Rth with the diamond substrate was 34.5% less than with the copper (see Fig. 2).
The diamond prepared by CSMH has ultra-high thermal conductivity, up to 2200W/(m.K). For laser applications, it provides high-quality diamond heat sinks, diamond wafers, diamond windows, diamond heterogeneous integrated composite substrates and other products.
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