Site: NTT Interdisciplinary Research Laboratories
Nippon Telephone and Telegraph Corporation
3-9-11, Midori-Cho, Musashino-Shi
Tokyo 180, Japan
Date Visited: September 30, 1993
Report Author: L. Salmon
Dr. Hiroki Kuwano Senior Research Engineer, Supervisor
Sensing Systems Research Group,
Dr. Reizo Kaneko Associate Vice President, NTT
Director, Kaneko Research Laboratory
Renshi Sawada Senior Research Engineer, Supervisor
Dr. Hiroshi Hosaka Senior Research Engineer, Sensing Systems
Research Group, Optomechatronics Laboratory
Dr. Kuwano began by providing an overview of NTT and the Interdisciplinary Research Laboratories. He indicated that the downturn in the economy and NTT's current financial difficulties will not cause reduced research efforts at his laboratory because NTT views research as the mechanism to develop future opportunities for growth.
The Interdisciplinary Research Laboratories employs approximately 300 researchers and consists of three major laboratories: Mechaphotonics, Energy Electronics, and New Materials and Properties. The Energy Electronics Laboratory concentrates on development of new energy systems, and the New Materials and Properties Laboratory concentrates on the characterization and development of new materials. Dr. Kuwano is Manager of the Sensing Systems Research Group in the Mechaphotonics Laboratory. The mission of the Mechaphotonics Laboratory is to use micromechanical technology to improve the density and performance of optical storage media, and to improve the assembly and alignment of optical fiber systems. There are approximately thirty researchers at NTT working on MEMS technology. NTT is not a participant in the MITI/AIST micromachine effort.
The NTT researchers indicated that they believe that planar lithographic-based fabrication is most appropriate for MEMS because of its potential for manufacturability. They also indicated that the NTT group is rare in Japan because it combines the talents of individuals with skills in the areas of microfabrication and mechanical engineering. They spend much of their efforts testing MEMS structures and measuring their properties.
During a discussion of the commercial applications of MEMS, the NTT researchers indicated that the major driver for MEMS technology is reduction in cost of completed systems. Another strength of MEMS that they plan to exploit is the possibility of integrating electronics with the mechanical system. Renshi Sawada estimated that it would take approximately five years to commercialize a product such as the optical encoder he is working on.
After the overview discussion, the JTEC panel toured the Kaneko Research Laboratory. Dr. Reizo Kaneko is the director of the laboratory and has a position analogous to that of an IBM Fellow. His laboratory concentrates on microtribology and micromotion in biology. Researchers in the laboratory are using STMs to study wear on surfaces by measuring the damage caused by motion on clean surfaces and on surfaces that have foreign species adsorbed on them. STM micrographs show the effect of wear at the atomic level, and indicate the sources of friction on an atomic scale. The laboratory is also studying method of locomotion in bacteria. Researchers are using STM micrographs of the physical structures responsible for bacteria locomotion in order to better understand the mechanics of that motion. The physical structures in bacteria are complicated, and it is difficult to determine the mechanics of their locomotion.
After the tour of the Kaneko Laboratory, the JTEC panel toured the Mechaphotonics Laboratory facilities. Mr. Sawada described a microoptical encoding head that was reported at the MEMS '91 meeting. The encoder is a monolithic integration of a multiple quantum well laser source, a split beam interferometer, a photodiode, and the lenses needed to focus the lasers on the surface of the optical media. Mr. Sawada indicated that the encoder can improve resolution to better than 10 nm. A schematic of the encoder is shown in Figure NTT.1. The laser used internal reflection at the edges of the laser to provide the two split laser beams. The laser light is then focused through two lenses made of graded SiON. The light is focused in three dimensions. It is focused in the plane of the wafer surface by the physical curvature of the lens, and in the direction perpendicular to the surface by the grading of the nitrogen concentration of the sputter-deposited SiON film. The encoder head structure can accurately measure the distance to the optical media because the optical media forms one side of the laser cavity. If the encoder to disc distance is not correct, laser output will be sharply reduced.
Figure NTT.1. Schematic of the monolithic optical encoder.
The JTEC panel also saw a project that uses micromechanical structures to align optical fibers during assembly. Figure NTT.2 illustrates the basic concept used. Metal is deposited on the side walls of a "V" groove etched in a substrate; the end of the optical fiber is also metalized. When a bias is applied between the metalized fiber and the electrodes on the groove, the end of the fiber can be moved to the left or the right. Optical power output can be utilized as a feedback source to the electrode bias in order to optimize optical coupling between the fiber and the next optical channel. The structure is sufficiently robust to withstand shorting of the fiber to the electrode. Unfortunately, this method cannot be used to keep the fiber fixed during cure of the epoxy used to cement the fiber in place, but optical losses caused by movement during the cure are relatively small. The NTT researchers also described use of a flat spring structure as a relay and as a microvalve actuator. A schematic of the flat spring, which is made from permalloy on silicon, is shown in Figure NTT.3. Actuation is currently made through application of an external magnetic field produced by coil. Future work will attempt to fabricate integrated electromagnets for actuation. The spring is made of 2 micron thick permalloy (Ni 80%/Fe 20%) and is deposited using sputtering.
Figure NTT.2. Schematic of the fiber alignment approach.
Figure NTT.3. Schematic of the flat spring actuator.
For use as a relay, movement of the flat spring closes or opens a relay contact. The relay can withstand up to 400 V, has a contact force of approximately 10 mg, and has a response time of less than 1 ms. The staff at the Interdisciplinary Research Laboratories see this relay fulfilling an important function as a relay for the high voltage signals in telephone terminal switches.
The flat spring can also be used as an actuator for a microvalve as shown in Figure 6.16. The throat of the valve is 30 microns in diameter, and the valve has a leak rate of 1.5 x 10(¯-5) Torr liters/second, and a standing pressure of greater than one atmosphere.