Abstract
A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices are aluminum and copper, with thermal conductivities of about 250 W/(m·K) and 400 W/(m·K), respectively. Significantly, the thermal expansion coefficient of metals differs markedly from those of the materials employed in semiconductor electronics (mostly silicon); one should add here the low electrical resistivity metals possess. By contrast, natural single-crystal diamond is known to feature the highest thermal conductivity of all the bulk materials studied thus far, as high as 2,200 W/(m·K). Needless to say, it cannot be applied in heat removal technology because of high cost. Recently, SiC- and AlN-based ceramics have started enjoying wide use as heat sink materials; the thermal conductivity of such composites, however, is inferior to that of metals by nearly a factor two. This prompts a challenging scientific problem to develop diamond-based composites with thermal characteristics superior to those of aluminum and copper, adjustable thermal expansion coefficient, low electrical conductivity and a moderate cost, below that of the natural single-crystal diamond. The present review addresses this problem and appraises the results reached by now in studying the possibility of developing composites in diamond-containing systems with a view of obtaining materials with a high thermal conductivity.
Highlights
The main requirements placed by electronics engineers on heat sinks, formulated possibly not in the order of descending significance, are: high thermal conductivity low cost low electrical conductivity thermal expansion coefficient of the heat sink should be equal to that of the material to be cooled low loss tangent small weightMost materials displaying high thermal conductivity, above 100 W/(m⋅K), at room temperature have diamond-like lattices; among them are diamond, cubic boron nitride and others, in particular, Silicon Carbide (SiC), BeO, BP, Aluminum Nitride (AlN), BeS, GaN, Si, AlP, and GaP [1].In applications where fairly high thermal conductivities combined with low electrical conductivities are of prime importance, SiC- and AlN-based ceramics are presently enjoying wide use
Composites produced from microcrystalline diamond with silicon binding can find application as materials for heat sinks
The papers surveyed in the present review could hardly have been expected to cover all the aspects of the problem of fabrication of diamond-based composites; neither have we succeeded in discussing the achievements of all the research groups working in this area
Summary
The main requirements placed by electronics engineers on heat sinks, formulated possibly not in the order of descending significance, are:. The interest in composites fabricated by high-pressure diamond sintering stems primarily from the fact that they exhibit good strength and high abrasive properties and find wide application in industry. We have offered such a detailed description of the sintering parameters of microcrystalline particulate diamond in this review only to provide an adequate insight into the actual conditions and mechanisms operating in the sintering process, as well as to review the parameters of the present-day composites. A particular place should have been devoted in the review to analyzing the possibility of chemical modification of DND surface, because the latter can affect noticeably the properties of the samples obtained and their thermal conductivity; regrettably, this problem is beyond the scope of the present report and, will not be dealt with here
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