NTT develops 81 GHz diamond device
NTT believes that diamond devices will one day replace the vacuum tubes now used in very high frequency and very high power applications, leading to increased output power in communication satellites, television broadcasting stations, and radar.
Theoretical predictions, however, have shown that ideal diamond semiconductor devices would operate at five times the temperature, 30 times the voltage, and 3 times the frequency of silicon devices. This is because diamond has very high thermal conductivity, high breakdown voltage, and high maximum carrier velocity, which respectively result in rapid heat dissipation, long lifetime, and high-frequency operation. Therefore, diamond has been touted as the ultimate semiconductor; the one most suitable for high-frequency high-power electronic devices.
The major problem in fabricating devices from diamond semiconductor had been that the diamond films contained many more defects and impurities than silicon and other semiconductors.
In April 2002, NTT unveiled technology for fabricating high-quality diamond, which eliminated graphite contaminants and crystalline defects from the material and reduced impurities by a factor of 20 (see Fabrication technology for high-quality diamond). This technology opened the way to diamond semiconductor devices having the superior properties of ideal diamond.
In collaboration of the University of Ulm, NTT fabricated diamond semiconductor devices using its high-quality diamond material (see Fabrication technology of diamond semiconductor devices). The process technology included the fabrication of a 0.2-micron T-gate.
With these technologies, NTT obtained the maximum operation frequency of 81 GHz, the highest among diamond devices and about two times higher than the previous record for diamond. The group says that once it establishes device peripheral technologies, it will reach a power of 30 W/mm, the level needed for practical use.
NTT says that it is now working to further improve the quality of diamond crystal by decreasing the impurities. The target is a frequency of 200 GHz with an output power of 30 W/mm.
