Every university student becomes familiar with the concept of thermal conductivity, a fundamental physical property of materials, 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. Theoretical support for this discovery was established by Debye in 1914.

One of the fundamental physical properties of a material is its ability to conduct heat. Understanding and controlling the thermal conductivity of nonmetallic materials has been of much interest, mainly because this transport parameter is an important factor in determining the performance and reliability of various device applications.

Since the confirmation that nonmetallic single crystals with a diamond-like structure, such as SiC, BP, and AlN, have high intrinsic thermal conductivities of over 300 W m−1 K−1,1,2 a great deal of effort has been focused on the development of nonoxide polycrystalline ceramics with high thermal conductivity.

Chemical vapor deposition (CVD) is an attractive method for producing bulk and thin-film materials for a variety of applications. In this method, gaseous reagents condense onto a substrate and then react to produce solid materials. The materials produced by CVD are theoretically dense, highly pure, and have other superior properties.

In recent years, high thermal conductivity has been found in materials with heterogeneous microstructures, that is, ceramics and films with granular microstructures having different phases. Understanding the thermal conductivities and microstructures of these materials is more difficult, however, than in the case of single-crystal materials because they consist of grains and grain boundaries.

Great progress in LSI (large-scale integration) has been made over the past 10 years, and more rapid progress is expected in the future. In recent years, the increased circuit density in LSI devices has led to remarkable heat generation, thereby creating thermalmanagement issues for microelectronics packaging. In order to develop highperformance LSI effectively, packaging and system-level configuration of the computer must be modified to handle the heat.

Sustainability is supposed to be the watchword of the coming century. Kenneth Boulding characterized the economic system of the 19th century as a “cowboy economy,” meaning that resources were essentially not a limiting factor. In contrast, he noted that in the future we must prepare to live in a “spaceship economy,” adopting Barbara Ward's famous metaphor of “Spaceship Earth.” In a spaceship, all materials must be recycled (or discarded into space).