No.24(AUGUST 2005)

Holey fiber with extremely low transmission loss of 0.205 dB/km at a wavelength of 1.55 µm (the same as that of conventional SM fibers) has been devel- oped. This fiber also has a low bending loss of 0.05 dB/turn with a bending diameter of 10mm, which is less than 1/500 of that of conventional SM fibers. Since this holey fiber has a very low bending loss, it is applicable to optical indoor cords. Its fiber-joint characteristics and reliability also make it suitable for such application.

Ultra Wide Band (UWB) communication (now being standardized by IEEE802.15 TG3a) is expected to be widely adopted for high-speed communication systems by 2006. A transfer rate as high as 1 Gbps will be realized in the future, thus enabling the speedy transmission of such high-density files as high definition TV images. We designed and developed a film type of UWB antenna that is small and thin, and able to oscillate in a wide-band frequency range of 2.3 to 6 GHz, including the wireless LAN (Local Area Network) region. This includes the frequency ranges of 2.4 to 2.5 GHz (IEEE 802.11b/g), 5 to 6 GHz (IEEE 802.11a), and WiMAX (2.3, 2.5, 3.5, and 5.8 GHz being standardized by IEEE802.16). The antenna achieved the omnidirectional radiation pattern and high average gain. The group delay fluctuations of this antenna was less than 1.2 nanoseconds in the field of 2 to 6 GHz.

GaN HEMT (Gallium Nitride High Electron Mobility Transistor) devices exhibit excellent power-handling capability in the RF (Radio Frequency) region and are considered the next-generation transistors in future mobile communication systems. In order to facilitate heat radiation from these devices, GaN HEMTs should be formed on SiC (Silicon Carbide) substrates, whose thermal conductivity is higher than that of any other conventional semiconductor materials. We developed an epitaxial (thin film mono crystalline) growth technique and optimized MOVPE (Metal Organic Vapor Phase Epitaxy) process conditions to achieve an atomically flat-surface morphology of nitrides on the SiC substrate. Thus, a HEMT epitaxial wafer with high electron mobility of 1,730cm² /Vs and adequate sheet resistance of 360/sq. could be realized by applying our modified process technology. Moreover, since the residual background carrier in the non-doped GaN layer was also confirmed to be less than 1×10¹⁴cm^-3, sufficient breakdown voltage for device isolation can be expected.

It is now required that cables in clean room used with semiconductor and liquid crystal devices do not emit airborne molecular contaminants (outgas). To meet this demand, high-precision outgas analysis and low outgassing insulations applied low volatile ingredients with high molecular weight and purity were developed. Furthermore, contamination during production, packing and delivery processes can now be controlled. We have succeeded in developing low outgassing cables using polyvinyl chloride, eco-material and fluoride resin insulations. The developed cables are expected to be applied in the bio technology, medical, pharmaceutical, and construction fields, as well as semiconductor and liquid crystal fields, in the future.

RoHS(Restriction of the use of certain hazardous substances in electrical and electronic equipment) directive will be enforced in Europe starting from July, 2006, and the requirements for reducing heavy metals (cadmium, lead, chromium(VI), mercury) and specific brominated flame-retardants (PBB, PBDE) will become even stricter. The authors have developed and comercialized various electric wires for eco-friendly equipment.1) Moreover, the analysis method of those hazardous substances has been developed, and the system for controlling the substances level has been established.

In recent years, increases in the performance and density of electronic equipment have been matched by increased amounts of heat generated; hence the intensifying problem of how to cool such equipment efficiently during the development stage. On the other hand, ensuring the equipment is sufficiently cooled often involves disadvantages such as bulky or noisy coolers due to complicated and lengthy cooling parts such as fins, high fan rotation speeds and so on.
Once our company had obtained a technical license for a notebook PC liquid cooling module, Hitachi, Ltd was the first to announce this news globally in 2002 and the item in question has since been produced.
We have now developed a revised liquid cooling module featuring high reliability and cooling performance. Noise levels have been successfully reduced while still retaining the same or improved cooling performance compared to conventional air cooling methods.