The Need for Heat Dissipation

To remove this unwanted heat (also known as thermal management), it is often necessary to use hybrid circuits and bulky heat-dissipation devices or complicated and expensive refrigeration. Metals with good thermal conductivity, such as copper or aluminum, are presently used as heat sink materials but, since being metals they also have high electrical conductivity, they require an electrical-insulation barrier. 

Heat dissipation can be effectively dealt with by using substrate materials such as aluminum nitride, beryllia and, more recently, diamond which combine electrical insulation with high thermal conductivity. The relevant properties of these three materials are shown in Table 14.1. 

Beryllia (BeO) is an excellent heat-sink material which is presently widely used but is being phased out because it presents acute safety problems.It is being replaced by aluminum nitride which extensively produced by CVD, mostly in Japan (see Ch. 10, Sec. 2).P2] 

Diamond is an electrical insulator with the highest thermal conductivity at room temperature of any material and compares favorably with beryllia and aluminum nitride. P3]-P5] jg undoubtedly the optimum heat-sink material and should allow clock speeds greater than 100 GHz compared to the current speed of less than 40 GHz. 

Heat sinks, in the form of thin slices prepared from single-crystal natural diamond, are already used commercially but are limited in size to approximately 3x3x1 mm. These single-crystal diamonds are gradually being replaced by CVD diamond, which is now available in shapes up to 15 cm in diameter. P6]-[28] gQg - gf cVD diamond may remain a 

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Philip Troyk from the Illinois Institute of Technology spoke about the issues of implantable hardware. One issue raised was that the next-generation neuroprostheses would be five to ten times denser, electrically and physically than current neuroprosthetic devices. Dr. Troyk discussed the need for heat dissipation by... 

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