Diamond for Electronics: Future Prospects of Diamond SAW Devices
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Diamond for Electronics: Future Prospects of Diamond SAW Devices J.T. Glass, B.A. Fox, D.L. Dreifus, and B.R. Stoner Electronic-Applications Overview From a commercialization standpoint, electronic applications have been particularly elusive for diamond. Market estimates of $560 million per year by the year 2000 indicate the original enthusiasm in this area.1 Now such projections seem unreasonably optimistic, and even a niche commercial application in the area of electronics would be considered a success. However when taken in a broader context, this extended time frame for commercialization is not at all unusual for new technologies,2 and many new advances have continued to bolster the enthusiasm of diamond electronics research groups. Diamond has such an extensive list of exceptional properties that it continues to be a candidate for numerous electronic applications from heat spreaders to detectors to microvacuum tubes. A variety of theoretical calculations established diamond's potential in the early years of CVD-diamond research. As shown in Table I, figures of merit indicated that diamond's potential far exceeded the potential of more common semiconductors such as silicon and gallium arsenide for certain applications.3 Typically these applications revolved around high power or high temperature. , However more accurate assessments of diamond's capability after further development uncovered several issues with many electronic applications of interest: (1) n-Type doping: Although scattered
MRS BULLETIN/SEPTEMBER 1998
reports of n-type doping have been made, 4 ' 6 a high-quality, low-resistance n-type material is not available, limiting the potential applications for diamond. (2) Deep activation of p-type carriers: At reasonable dopant levels, the activation energy for p-type carriers is approximately 0.3 eV, causing diamond to be highly resistive and sensitive to temperature variations at normal operating temperatures. (3) Viable substrates for single-crystal growth: Although some exciting developments in the area of heteroepitaxy have been reported,7'8 the small area and defec-
tive material have significantly limited the electronic quality of the substrates. Equally as important as the technical issues are the costs of diamond deposition and polishing. Many applications that would drive the high-volume markets for diamond are very cost-sensitive and simply cannot tolerate the current expenses of deposition and polishing, which usually exceed several hundred dollars per wafer. At present the most promising electronic applications are the following: (1) electron-beam devices, 9 (2) electrodes,10 (3) sensors such as ultraviolet detectors,11 (4) surface-acoustic-wave (SAW) devices,12 and (5) heat spreaders.13 These applications are listed in order of electronic activity from the most active to the most passive applications. One can imagine that the most passive devices are likely to be commercialized more quickly than the most active because of the reduced complexity. Each of these applications requires diamond'
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