Overview of Device Physics Research

Toshio Ogino
Device Physics Laboratory

@In the Device Physics Laboratory, we are studying silicon (Si) nanotechnology as a means of creating the ultimate Si integrated devices to further the evolution of information technology. In terms of device functions, single electron switching is the ultimate technology. In signal transmission, the ultimate goal is single electron transfer to the nearest neighbor site or long-distant sites. In fabrication technology, the final goal is the wafer-scale fabrication of atomically controlled device structures. There are two approaches available to achieving the latter: one is to refine lithographic techniques to achieve higher resolution and finer patterns (top-down approach), and the other is self-assembly based on the atomic structures of the Si substrate (bottom-up approach). Our aim is to create new concepts towards the ultimate Si integrated systems.
@The Si Nanodevice Research Group is investigating the operation mechanism of Si single electron transistors (SETs) and their application to logic circuits, and performing fabrication process simulations. We have already demonstrated inverters and adders using SETs. We recently fabricated multi-valued logic circuits and a multi-bit adder as demonstrations of the wide range of functionality in SETs. Negative differential conductance in SETs has also been analyzed and applied to a new functional circuit. In single electron transfer devices (charge-coupled devices), we have succeeded to detect single-electron and single-hole transfer at room temperature. Operation mechanisms of SETs are being analyzed based on a structural model developed by the Nanostructure Technology Research Group. Si oxidation is the most important process in Si technology. We have shown that oxidation characteristics under various conditions can be explained using a universal model based on an atomic-level theory proposed by us.
@The Nanostructure Technology Research Group is investigating nanofabrication techniques based on the top-down approach. We have established an ultrafine resist pattern formation process through improvement of electron beam lithography and optimization of resist materials and processes. We have proposed an original ultrafine patterning technique that uses supercritical fluid. Its outstanding performance was demonstrated in resist patterns with a high aspect ratio and ultrahigh density. A structural model of SETs fabricated in the Nanodevice Research Group has been established.
@The Surface Science Research Group is investigating a bottom-up approach, aiming for Si nanointegration through surface structure control, nanostructure self-assembly, and carbon nanotube interconnection. For surface structure control, we are investigating atomic structures on step-controlled Si surfaces to control all atom positions on the surface. In nanostructure self-assembly, we have established strain engineering for control of the shape, distribution, and spacing of self-assembling Ge quantum nanostructures on Si surfaces. A new technique for functionalization of Si surfaces based on the incorporation of chemically synthesized nano-particles has been developed. In applications of synchrotron radiation, we have developed a technique for in-situ observation of growing surfaces and photoelectron microscopy for nanostructure characterization. During the past year, we put emphasis on our carbon nanotube project and started NEDO International Joint Research Grant Program. We have succeeded in bridging Si pillars by carbon nanotubes. Characterization of the electronic and atomic structures of the carbon nanotubes has also proceeded.