Jpn. J. Appl. Phys. Vol. 39 (2000) pp. 3835–3849 Part 1, No. 7A, July 2000 c 2000 The Japan Society of Applied Physics Invited Review Paper Prospects and Problems of Single Molecule Information Devices Yasuo WADA 1,2 , Masaru TSUKADA 3 , Masamichi FUJIHIRA 4 , Kazumi MATSUSHIGE 5 , Takuji OGAWA 6,7 , Masaaki HAGA 8 and Shoji TANAKA 9 1 Advanced Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-0395, Japan 2 CREST, Japan Science and Technology Corporation (JST) 3 Faculty of Science, University of Tokyo, Tokyo 113-8654, Japan 4 Faculty of Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan 5 Faculty of Engineering, Kyoto University, Kyoto 606-8501, Japan 6 Faculty of Science, Ehime University, Matsuyama, Ehime 790-8577, Japan 7 PRESTO, Japan Science and Technology Corporation (JST) 8 Faculty of Science, Chuo University, Tokyo 112-8551, Japan 9 Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan (Received February 28, 2000; accepted for publication April 18, 2000) Current information technologies use semiconductor devices and magnetic/optical discs, however, it is foreseen that they will all face fundamental limitations within a decade. This paper reviews the prospects and problems of single molecule devices, including switching devices, wires, nanotubes, optical devices, storage devices and sensing devices for future informa- tion technologies and other advanced applications in the next paradigm. The operation principles of these devices are based on the phenomena occurring within a single molecule, such as single electron transfer, direct electron-hole recombination, mag- netic/charge storage and regand-receptor reaction. Four possible milestones for realizing the Peta (10 15 )-floating operations per second (P-FLOPS) personal molecular supercomputer are described, and the necessary technologies are listed. These include, (1) two terminal conductance measurement on single molecule, (2) demonstration of two terminal molecular device character- istics, (3) verification of three terminal molecular device characteristics and (4) integration of the functions of “molecular super chip”. Thus, 1000 times higher performance information technologies would be realized with molecular devices. KEYWORDS: molecule, single molecule device, molecular electronics, information technology, information processing, informa- tion storage, information transmission, single molecule information processing devices 3835 1. Introduction: Historical Aspects of Single Molecule Devices Tremendous progress has been made in information tech- nologies since the dawn of civilization several thousand years ago. However, information processing, transmission and stor- age were performed almost exclusively on paper, since its in- vention about 2000 years ago until about 50 years ago, except wireless communication using noroshi or smoke, and calcu- lation using soroban or abacus, as indicated in Table I. In the latter half of the 20th century, electronic information tech- nologies started to emerge, and transistor based information processing, semiconductor laser based information transmis- sion and magnetism based information storage are predomi- nant and have completely changed human life into an “infor- mation society”. Optical storage systems and sensors have also contributed to progress in the knowledge and welfare of humanity. However, these devices are facing very fundamen- tal physical, chemical and materials limitations in terms of operation speed, density and sensitivity. Take the example of information processing switching de- vices, such as metal-oxide-semiconductor field effect tran- sistors (MOSFETs). Switching devices used in information processing systems have to fulfill five fundamental require- ments, (1) input/output (I/O) signal balance, (2) I/O isolation, (3) fast switching speed, (4) dense integration and (5) fabri- cability. 1) Among dozens of semiconductor devices that have been proposed, 2) only MOSFETs survived the harsh compe- tition, with the rare exception of bipolar transistors. The rea- son behind this is that MOSFETs meet the above five fun- damental requirements of information processing devices al- most perfectly in a very balanced manner. Furthermore, their performance can be improved by simply reducing their di- mensions, according to the “scaling principle”. 3) Dozens of “new concept semiconductor devices” have been proposed as candidates to replace MOSFETs, however, their overall per- formances are not necessarily superior to those of MOSFETs. Therefore, MOSFETs are expected to continue evolving un- til they reach their limitations of around 100 nm, which will probably be within ten years from now, 4, 5) as shown in Fig. 1. In order to enable further progress in information technolo- gies, several information processing device ideas were pro- posed, including quantum devices, 6) single electron devices 7) and single molecule devices. Figure 2 shows the switching speed and integration density relationship of historical infor- mation processing devices, which clearly indicates that or- ders of magnitude improvement is essential to bring about a paradigm shift. 1) The figure implies that the information pro- cessing devices under the next paradigm will have switching speeds of more than 1Tera (T: 10 12 ) Hz and will integrate Table I. The historical aspects of information processing devices: before the 19th century, information processing, transmission and storage were made almost on papers. In the 20th century, electronics devices emerged, however, in the 21st century, molecules will dominate the information pro- cessing technologies.