KOSEN 한인과학기술자네트워크

Terahertz circuits: The terahertz band is roughly defined as the frequency range of 0.1 - 10 THz and falls on roughly between the microwave and optical bands. Hence, it generally indicates the band with even higher frequencies than the millimeter-wave band, although there is an overlap. Compared to the neighboring microwave and optical bands, which have been extensively exploited for a myriad of applications, the terahertz band has long remained as a territory only scarcely explored. For this reason, the spectrum has popularly been called the terahertz gap. There have been two approaches for the terahertz band development: downward approach from the optics and upward approach from the electronics. Although the downward approach has been more widely used, there are recent efforts for the upward approach based on the electronics owing to the progress in the high speed semiconductor technologies. The systems based on this electronics-based approach is expected to more compact and compatible with existing electronic systems, making it more attractive for practical and commercial applications. Our lab has taken this upward approach to the terahertz applications and is working on implementation of basic circuit blocks such as LNAs, VCOs, mixers, switches, detectors, and integrated transceivers and imagers operating beyond 100 GHz all based on Si-based technologies, mainly focusing on the applications of high-speed communication systems and high-resolution imagers. Millimeter-wave circuits. Until recently, the application of the millimeter-wave spectrum (f > 30 GHz) has been limited to special-purpose applications. However, with the recent rapid progress in the development of low cost Si-based technologies, the performance of Si RFCMOS and SiGe technologies became comparable to those of III-V technologies and now their device speed has reached a few hundreds of GHz. Such technological advances, combined with the ever increasing demand for raised system operation speed and wider bandwidth, have enabled the various commercial applications of millimeter-wave spectrum. There are rapidly growing applications on WPAN (Wireless Personal Area Network) systems at 60 GHz, automotive radar systems at 77 GHz, image sensing systems at 94 GHz, etc. In HSISL, various research activities are going on related to the key millimeter-wave circuits such as low noise amplifiers (LNAs), voltage-controlled oscillators (VCOs), mixers, etc, all based on Si-based technologies. Device innovations for mm-wave and THz circuits. For the improved performance of millimeter-wave and THz circuits, innovative approaches are desired for not only the circuit design techniques, but also for the device structures. It is true that, to some degree, the device performance is determined for a given semiconductor technology provide by foundries. However, there are rooms for further improvement of device performance by optimization of device layout and/or novel lateral structure design. In HSISL, exciting researches are going on to improve the device performance of transistors such as RFCMOS and SiGe HBTs as well as that of varactors.