Nippon Telegraph and Telephone Corp. (NTT) has developed a diamond semiconductor that operates at an 81GHz frequency, more than twice the speed of preceding chips and enabling for the first time amplification in a millimeter wave band of 30 to 300GHz, according to the company.
With operating frequencies and power requirements rising in a variety of communication electronics applications, diamond is expected to be used as a next-generation semiconductor material because of its high thermal conductivity, breakdown voltage, and carrier mobility.
However, diamond semiconductors also suffer from defects and impurities that have prevented prototype devices from achieving the performance level designers say is possible.
NTT's Basic Research Laboratory (BRL) said it resolved these problems with the development last year of a diamond semiconductor thin-film layer.
Lab researchers found that crystal defects, carbon graphite, and other impurities were the cause of unsatisfactory performance. NTT said that it has since eliminated the crystal defects and graphite, and reduced overall impurities to 1/20th that of previous levels by using a high-purity gas to grow the diamond layer at temperatures of 650°C to 750°C, compared with conventionally used temperatures of 850°C to 900°C.
Recently, NTT BRL has been collaborating with the University of Ulm, Germany, which had already successfully fabricated diamond-based FET devices, to develop semiconductor products using NTT's diamond thin-film layer.
The joint team developed a device capable of continuous operation at 81GHz. Once the peripherals technology is established, NTT BRL researchers said they expect to make the output power of the device as high as 30W/mm, which the lab said is the level required for practical use.
NTT BRL is now working to decrease impurities further to improve the quality of the diamond crystal, hoping to develop a device with an operating frequency of 200GHz and output power of 30W/mm.
Such diamond chips are expected to come into demand as replacements for vacuum tubes that are used in high-frequency, high-power applications such as receivers and transmitters at digital TV broadcasting stations.