30-nano class Gallium Arsenide (GaAs) nano-transistor: comparative advantages in its performance
Easy manufacturing process: less than half the cost of commercialization

It is possible to receive and enjoy various multimedia contents such as music, movies, and other data, at speeds of several tens of Mbps using high-speed internet widely available in households. Studies on the improvement of communication speeds have been continuously conducted over the recent years.

Professor Yoon-Ha Jeong and research team have successfully succeeded in developing 35-nano GaAs nano-transistors (metamorphic HEMT) that are more than 10 times faster than existing transistors. It will be now possible to develop the world’s fastest 30-nano GaAs transistors and is expected to lead to the development of next generation ultra high-speed semiconductor elements.

The transistor developed by the research team is a type of ultra-high frequency nano-electronic element becomes a core element in such ultra high-speed communication system. Because the various composites-based elements including HEMTs (High Electron Mobility Transistors) can be operated in an ultra-high frequency band differed from the silicon-based element that can be operated within a frequency band of several GHz, it is considered as important factor in the development of ultra high-speed wire and wireless communication system in an ultra-high frequency band. Studies on the HEMT have been conducted all over the world, as part of the endeavor to develop ultra-high frequency nano-electronic elements.

mHEMT adequate to the production of ultra-high frequency nano-electronic elements

HEMT is an electronic element that is produced by a heterojunction method based on characteristics of 2DEG (two-dimensional electron gas) which makes possible ultra high-speed operation using fast movements in electrons. Presently, InP (Indium Phosphide)-based HEMT represents the highest performance. However, it is difficult to use InP boards with a large area due to difficulties in handling (easy breakable), even though the InP-based HEMT shows very high performance. In addition, it represents a low rate in price versus performance due to its high prices. The mHEMT (metamorphic HEMT) solves these disadvantages.

Technical difficulties in the production of ultrahigh frequency nano-electronic elements

It is possible to obtain faster operation speeds by reducing the length of its gate based on the characteristics of such elements. Thus, the production of microscopic gates plays an important role in improving the ultra-high frequency nanoelectronic elements. The gate used in the HEMT is called a “T-gate” because of its similar shape to the letter T. The T-gate has been widely used because it is able to reduce the gate resistance and minimize the gate length at the same time. The T-gate is easily fallen due to the weight of its head section during the production of elements while the gate length is reduced to increase operation speed. Therefore, it represents difficulties in overcoming of technical limitations in production of nano-class electronic elements.

The scales of such a gate reported has been usually approached to the circuit production technology with a level of 100-nano class represented by MIT, including the 50-nano class gate technology published by the Nano Research Center at the University of Glasgow, Scotland. In addition, the 25-nano class gate production technology represented by the Fujitsu Research Center, Japan, using oxides (SiO2) was reported
as a gate support as the case stands.

Increasing the element performance and re-productivity with a zigzag T-gate

The research team solved the problem in the production of microscopic T-gates by creating a new zigzag T-gate method. It is possible to support the heavy head section of a T-gate while the gate length is maintained if the leg of a T-gate is fabricated as a zigzag shape. It is the same idea as the fact that a sheet of folded paper with a zigzag shaped edge shows more easy standing on a floor than a sheet of thin and sharp edged paper.
The new technology using a zigzag T-gate method increases the performance and re-productivity of elements and that is highly evaluated as a new technology that achieves the stable gate forming technology without oxides, which have been used as a gate support.

The recently developed 35-nano mHEMT has a zigzag shaped T-gate structure which represents more than 520 GHz of the maximum oscillation frequency (fmax) determining the operation speed of the ultra-high frequency of nano-electronic elements. This speed is similar to that of InP-based transistors and is the fastest among GaAs-based nano-electronic elements. In addition, it represents a balance due to its excellent current gain cutoff frequency and maximum oscillation frequency, and shows a 520 GHz of maximum oscillation frequency through improving the maximum oscillation frequency of the conventional mHEMT more than 120 GHz. This will improve the operation speed more than 10 times faster than the existing silicon elements.
Furthermore, it makes possible to perform mass production due to less than half the cost of conventional products and easy production process. These factors will boost the development of next generation ultra high-speed semiconductor elements.

Professor Y. S. Park of Rensselaer Polytechnic Institute (RPI), one of the world’s experts in this field, commented that the nano-electronic element developed by Professor Jeong will play an epochal role in the development of ultra-high frequency elements and circuits.

The basic technology developed by the team was published in IEEE Electron Device Letters in its August 2007 issue and have domestic and international patents pending.

Professor Yoon-Ha Jeong
Department of Electronic and Electrical Engineering
Director, National Center for Nanomaterials Technology
Tel: +82-54-279-2220/0201
Fax: +82-54-279-5109/0210
Email: yhjeong@postech.ac.kr