JAPAN NANONET BULLETIN - 6th Issue - November 27, 2003

NANONET INTERVIEW

Naoki YOKOYAMA General Manager, Nanotechnology Research Center, Fujitsu Laboratories, Ltd. 1973 Master’s degree in physics, Division of Materials Physics, Graduate School of Engineering Science, Osaka University. Researcher, Fujitsu Laboratories, Ltd. Engaged in the development of self-aligned refractory-gate gallium arsenide MESFET integrated circuits, HBT, quantum-effect devices, and compound semiconductor devices. 1984 Doctoral degree in engineering at Osaka University 2000   June Served as a fellow of Fujitsu Laboratories, Ltd. December General Manager, NanoElectronics Research Center, Fujitsu Laboratories, Ltd.   1987 Young Scientist Award at the GaAs International Symposium. 1988 IEEE Morris N. Liebmann Memorial Award 2000 Elected to IEEE Fellow.   Chairman of IEEE EDS Japan Chapter, Board member of the Japan Society of Applied Physics, the Nanotechnology Special Committee of Federation of Economic Organizations, and other academic societies and nanotech-related societies

Fig. 1 Large Image Characteristics of Carbon Nanotube The carbon nanotube can be roughly classified into multi-walled nanotubes and single-walled nanotubes. The multi-walled nanotube with metallic properties has higher thermal and electric conductivities than copper. Therefore, it is expected that the multi-walled nanotube will be profitable alternative to wiring material of LSI. On the other hand, the single-walled nanotube could be used as a semiconductor, if we could control chirality (the way a graphene sheet is rolled up) at will, and then it would be applied to transistors. For these applications, however, carbon nanotubes should be adequately controlled to the size up to 2 nm in diameter during synthesis.

Fig. 2 Large Image Selective Growth of Carbon Nanotube Considering that carbon nanotubes are used as vertical interconnection between layers of multi-layered LSI and applied to transistors, it is necessary to develop a technique for position-selective growth of carbon nanotube in the process of LSI production. They have succeeded in growing carbon nanotubes vertically embedded in holes (called vias) of the SiN dielectric using a gas mixture comprising hydrogen and methane with CVD (chemical vapor deposition).

Fig. 3 Large Image Futuristic Health Care Network Society In the futuristic health care network society where personal medical information such as medical history and genetic data is electronically available through network to an individual, the individual’s physicians, pharmacists, and health care advisors with the strictly protected privacy. Through the system, appropriate health care management and medical care will be available. The system will be essential to the aging society with fewer children and lead to the growth in healthy elderly people, medical advance, and medical cost reduction. Moreover, the system will bring a new health care industry.

Fig. 4 Large Image Aim of Nanobiology Research The sequencing and interpretation of the human genome have been virtually elucidated. In the future, the function and behavior of proteins, which are directly involved in biological phenomena, will become increasingly important. To identify behaviors of specific proteins and clarify them, it is necessary to develop a protein chip that can detect quickly and respond sensitively to specific proteins. Developing such a protein chip requires the fusion of biology and nanotechnology, or nanobiotechnology. Currently, we are engaged in the development of a protein chip with artificial antibodies attached to a nanostructure consisting of CNT or nucleotide.

Naoki YOKOYAMA,
General Manager, Nanotechnology Research Center,
Fujitsu Laboratories, Ltd.

“Fusion” Will Give Birth to a New Industry
— Focusing on the Three Fields of Nanotechnology —

Dr. Yokoyama is a pioneer toward practical use of the compound semiconductor ICs. In 1998, he received the IEEE (Institute of Electrical and Electronics Engineering) Morris N. Liebmann Memorial Award for his contribution to the technology for gallium arsenide (GaAs) integrated circuits. He is the eighth winner among the Japanese Liebmann Award winners, including Dr. Leo Esaki. As a researcher of a private company, he is the second winner following Dr. Takashi Mimura (awarded for the development of high electron-mobility transistors or HEMT) who has also been in the development of compound semiconductor devices at the same company with Dr. Yokoyama. The technology developed by Dr. Yokoyama made a breakthrough in integrating compound semiconductor devices at large scale, the possibility of which people reacted skeptically at first. Compound semiconductor ICs produced by Dr. Yokoyama’s technique were firstly installed in the heart of the supercomputer with the highest performance in the world. Currently, these are widely used in many common devices such as satellite broadcasting receivers and cellular phones.

After that, Dr. Yokoyama started research on nanotechnology in as early as the mid-1980s being confident about the importance of utilizing quantum effects in the future semiconductor devices. He developed a new transistor with utilizing the resonant tunneling effect in the quantum structure built up by atomic layers. He has been an international leader in this field for developing the new technology for the fabrication of quantum dots and the device application of quantum dot. Serving as a fellow of the company in June 2000, with the concept, “widen the research front”, he launched a plan to establish the Nanotechnology Research Center where researchers could pursue their own research objectives cross-sectionally within Fujitsu groups so that they could be integrated under the concept of nanotechnology. In December of the same year, the Nanotechnology Research Center was established and he was appointed general manager of the center.

He selected professionals from various fields, organized new research groups independent of established organizations, and then started a new project. The project themes include the development of post-copper and post-silicon materials; fusion of nanotechnology and biotechnology; and quantum information technology. The approaches towards those themes are based on the following three essentials, that is, the researches on (1) “nanomaterials” (nanostructures such as carbon nanotubes); (2) “nano-biotechnology” (protein chips representing the fusion of semiconductor nanotechnology and biotechnology); and (3) “nanodevices/ nanosystems” (quantum bit devices for achieving quantum communication and producing quantum computers). Since then, the project groups have been vigorously advancing their researches with their background in electronics technology.

One of the most promising nanomaterials is carbon nanotubes discovered in Japan. Dr. Yokoyama says, “We are pouring the greatest efforts into developing the application of carbon nanotubes to LSI.” The wiring material of the most-advanced LSI is copper. However, extremely thin copper wires may cause troubles such as wire breakage due to the intensive electric current passing through the wires. Therefore, Dr. Yokoyama and his research group have been trying to grow carbon nanotubes with using CVD (chemical vapor deposition) to replace copper wires. What they aim at using carbon nanotubes is to use them as vertical interconnection between layers of multi-layered LSI.

Last year, news reporting that IBM succeeded in the development of carbon nanotube transistors rapidly spread over the world. This news made us expect that the carbon nanotube would be one of the post-silicon materials. However, things did not go as expected. Carbon nanotube has the structure obtained by rolling up a graphite sheet. Depending on how it is rolled up, the electric property of carbon nanotube can be a metallic or semiconductive. He believes that catalyst is the key to obtaining a desired electric property for carbon nanotube. He pointed out, “We need to develop ways of controlling catalyst configuration to control the structure of carbon nanotubes at will.” Thus, for putting the carbon nanotube to practical use, they have focused on what catalysts to use and how to utilize them in the production processes of carbon nanotubes.

In nanobiotechnology, what they aim at is to develop protein chips. If a malignant cancer develops in a human body, the cancer cells produce certain types of proteins. Identifying such proteins enables early detection of cancer. By developing a protein chip with artificial antibodies that is sensitively responsive to a very tiny amount of specific proteins, the diagnosis of diseases and general health checkups would be possible as well.

Dr. Yokoyama remarks, “What seems difficult to do for those in biology, it may be nothing to those in the semiconductor field. On the other hand, synthesizing DNA or the technique which those in the semiconductor field may think difficult to do, it may be nothing to those in biology.” Fusing the two different fields with “nanotechnology” will promote the field of nano-biotechnology. That is his scenario. If the quantum information technology were successfully developed, it would bring about a revolutionary change in information technology. The key technique of this theme is how to produce quantum bits as fundamental units of quantum computers. They have proposed a method using nanotechnology to utilize the electron spins in quantum dots to produce quantum bits. They have succeeded in arranging quantum dots with the desired size and at the desired location on a substrate.

Dr. Yokoyama explains, “Unlike classical computers, in quantum computer, the bit called as quantum bit or qubit can exist in coherent superposition of 0 and 1 states. A successful development of quantum dot fabrication technique will lead to development of a quantum computer.” A quantum computer can do the same calculations in a few days that a classical computer would take hundreds of millions of years to complete. Developing fully operated quantum computer may take twenty years or longer. However, it is expected that quantum encryption secured communication that makes the Internet secure and high speed will be introduced around 2007 for the special use such as banking security. Quantum information technology will eventually find a way to practical use in quantum encryption secured communication.

Dr. Yokoyama notes, “We have to overcome barriers in developing carbon nanotubes, protein chips, and quantum information technology. There are many approaches to be considered for the successful developments in each field mentioned above. Since we are not sure which one is right yet, we have been trying possible approaches.” In such challenging and pioneering research, “a good idea often comes from a genius.” Thus, he is paying attention to the worldwide new developments and scientific trend, and exchanging information with other researchers. He also stresses the importance of financial support, saying, “More government funds should be invested in the advancement of pioneering researches promoted in the industrial world.” He also directs his attention to young researchers by saying; “The bottom-up nanotechnology requires novel ideas that lead to discovery and application of new materials. The ideas may develop directly into business. This bottom-up nanotechnology may attract young researchers.”

Fig. 5 Large Image Aim of Quantum Information Technology Research The performance (high speed and high density integration) of semiconductors has improved over the past half century mainly as the achievement of miniaturizing transistors. However, the present technology of miniaturizing transistor is reaching its limit. In the information society, security is the highest primary issue. Encrypted communication, which maintains the security of communication, is not as perfect as the principle says. To give fundamental solutions to these problems, it is necessary to develop new concepts of semiconductor devices and communication technology. The solutions are quantum computers and quantum encryption. These are quite new technologies utilizing quantum superpositions and quantum entanglements, and extensive research is required in the fields. We are currently engaged in the research on fabricating quantum bits used as fundamental units of quantum computers and utilized in quantum encryption secured communication.

Fig. 6 Large Image Fabrication of Quantum Dots Using AFM Many methods have been proposed for producing quantum bits. We are currently engaged in the research on producing quantum bits, which will be used in the operation of both quantum computers and quantum communication. The technology that the electron spins in quantum dots are operated as quantum bits is necessary for the research. We have succeeded in developing the technology, which arrange quantum dots with the desired size and at the desired location on a substrate by combining technologies of local oxidation using AFM with technique of selective growth by MBE.