High Thermal Conductivity Materials
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High Thermal
Conductivity Materials
Koji Watari and Subhash L. Shinde, Guest Editors Every university student becomes familiar with the concept of thermal conductivity, a fundamental physical property of materials,1 through his or her textbooks. Initial work on high thermal conductivity was carried out in 1911 by Eucken, who discovered that diamond was a reasonably good conductor for heat at room temperature.2 Theoretical support for this discovery was established by Debye3 in 1914. In 1951, Berman et al. determined that the intrinsic thermal conductivity of diamond is 2000 W m1 K1 at room temperature, much higher than that of either copper (400 W m1 K1) or silver, which has the highest thermal conductivity4 of any metal at room temperature (430 W m1 K1). In nonmetallic materials, heat is carried primarily by phonons, while in metals, heat is carried primarily by electrons. Extensive investigation and characterization of high thermal conductivity solids other than metals were carried out from 1960 to 1985. A thorough thermal conductivity evaluation of synthetic single crystals, combined with theoretical calculations, revealed that most of the high thermal conductivity materials (100 W m1 K1 at room temperature) are adamantine (diamond-like) compounds, for example, diamond, BN, SiC, BeO, BP, AlN, BeS, GaN, Si, AlP, and GaP. The results are systematically summarized by Slack et al.5 It is well known that efficient heat removal is critical to the performance of many semiconductor devices; a lack of it can often lead to overall system failures. The steady increase in energy density has imposed phenomenal thermal-management requirements on material components in applications such as microelectronics, optical communications, and semiconductor processing equipment. It is therefore evident that to comply with these requirements,
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reliable components require materials with enhanced thermal conductivity properties. Figure 1 shows the trend in the combined production of three high thermal conductivity, electrically insulating materials and components—diamond, SiC, and AlN— for use in semiconductor processing equipment in Japan. The graph shows a sharp increase in recent years. Production of high thermal conductivity ceramic substrates in Japan alone achieved the equivalent of about $50 million in sales in 1998. To sustain the rapid increase in the component density of electronic circuits and devices, continued development and commercialization of high thermal conductivity materials will be needed. This issue of MRS Bulletin is timely, as it presents articles
Figure 1. The market for material components used in semiconductor processing equipment in Japan during the period 1992–2005. The components include susceptors and rings for rapid thermal processing, components for plasma-etch systems, and rf heated susceptors. Data from Japan Fine Ceramics Association reports.
concerning the science and technology of high thermal conductivity insulating materials and related fields. In the first article, Srivastava desc
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