Site: Tohoku University
Semiconductor Research Institute
Dept. of Mechatronics and Precision Engineering
Laboratory for Microelectronics (Super
Clean Room), Research Institute of Electrical
Aza Aoba, Aramaki, Aoba-ku
Sendai 980, Japan
Date Visited: October 1, 1993
Report Authors: K. Wise and H. Guckel
Masayoshi Esashi Professor, Department of Mechatronics and
Dr. Seung-Ki Lee JSPS Visiting Fellow, Department of Mechatronics
and Precision Engineering
Mrs. Cleopatra Cabuz Assistant Professor, on leave from the Faculty of
Electronics and Telecommunications,
Polytechnical Institute of Bucharest, Romania
The JTEC team's first visit was to the Semiconductor Research Institute, where there is extensive research underway in high-speed compound semiconductor devices and advanced semiconductor process technology. Much of the work was centered around the static induction transistor (SIT) structure pioneered by Nishizawa (1986) and is aimed at the delay range from 100 fS to 1 pS (see also Yusa et al. 1992). The institute's laboratory included at least ten molecular-layer epitaxy growth systems and numerous surface analysis tools, including QMS, RHEED, AES, and XPS. The laboratory was clean, well organized, and very well equipped. It was probably the equal of any in the United States, and was impressive both for its facilities and for many of its research results.
The team next traveled to the micromachine laboratory of Professor Masayoshi Esashi. This laboratory consists of forty-three people. In addition to Dr. Esashi, there are Associate Professor Shuichi Shoji, three assistant professors, one postdoctoral researcher, fourteen researchers on leave from various companies, twenty-one students (four in the doctoral program, eight in the master's program, and nine undergraduates), one technician, and one secretary.
Efforts are focused in five areas:
In all, a total of forty projects are represented by these efforts. This is a very impressive number to be directed by a single faculty member. It was also interesting that in Japan the faculty members each independently have their own laboratories (which is similar to arrangements in Europe) and do not share combined facilities, as is usually done in the United States. A comparable laboratory in the United States would also have more permanent technical staff and perhaps more doctoral students but would sadly have many fewer industrial residents, making technology transfer much more of a problem. The industrial residents here represented individuals primarily from non-semiconductor companies who would be producers of microsystems for automotive, medical, and other applications. Funding for most of this work comes from the Ministry of Education.
Professor Esashi described some of the different research projects currently underway. Many devices from this laboratory have been successfully commercialized in the past, including two ion-sensitive field-effect transistors for measuring pH and pCO(¯2), and a capacitive pressure sensor (Matsumoto, Shoji, and Esashi 1990). There has been considerable work on vacuum-based packaging of sensors, including pressure devices (Henmi et al. 1993) and accelerometers (Esashi 1994; Matsumoto and Esashi 1992; Matsumoto and Esashi 1993). Research projects are also addressing a broad array of other topics, including resonant devices (Yoshimi et al. 1992; Cabuz et al. 1993), microactuators (Minami, Kawamura, and Esashi 1993), dry micromachining using RIE at low-temperatures (Takinami 1992), bonding (Esashi, Ura, and Matsumoto 1992), feedthroughs, and sensor-circuit integration (Nagata et al. 1992). These projects were all very well done and the work is world class. For example, work is underway on an active catheter equipped with multiple sensors and with distributed actuators along its length to allow the catheter to be mechanically bent as required for insertion in the cardiovascular system. The target size for this catheter is 1 mm OD. The integration of circuitry with sensors is viewed as a dominant trend, even though most existing sensors still operate using hybrid interface electronics. A new thrust area in this laboratory is work on nanofabrication, using techniques such as epitaxy and scanning tunneling microscopy to create new structures as well as efforts on microassembly tools for devices such as the active catheter.
The JTEC team toured Dr. Esashi's laboratory facilities, which are distributed in several nearby buildings. These were extensive and very impressive, covering a very broad range of capability. The wafer size in this facility is 20 mm, allowing the use of small process chambers in many cases. There were dedicated facilities for laser-assisted etching, in-process monitoring of anisotropic silicon etching, vacuum-sealing of devices, long-term testing of resonant structures, deflection measurements to 1 Å, cryogenic RIE-based micromachining, CVD of several materials, and circuit fabrication. The facilities were well organized and represented an impressive investment of time equal to any in the United States.
The team's last stop was at the Laboratory for Microelectronics (Super Clean Room), Research Institute of Electrical Communication, directed by Professor Yasuji Sawada. Aimed at exploring semiconductor manufacturing techniques and device structures for the next century, this facility is a major resource probably larger and better equipped than any university facility in the United States. Built at an estimated cost of ¥1 billion (building only), and with an annual budget for utilities and materials/supplies of about ¥200 million, this clean room is particularly remarkable in that it runs with only two staff members and one technician. There are a total of 232 users of the clean room, which offers a broad array of fabrication equipment in an environment estimated at Class 1. Most of the students here are at the B.S. and M.S. degree levels. The facility is in part maintained by these students and in part by industrial visitors. In this facility, 33 mm wafers are processed. The laboratory has a full range of process equipment, including facilities for mask making, ion implantation (200 keV), extensive surface analysis (XPS, RHEED, SIMS, and STM), and specialized processes such as CVD aluminum. The facility is entirely built with a perforated floor and is composed of three levels.
Overall, the projects and facilities at Tohoku University were outstanding and state of the art. The university is clearly having important impacts and is exerting leadership in the fields of semiconductor electronics and MEMS on a worldwide basis.
Cabuz, C., S. Shoji, E. Cabuz, K. Minami, and M. Esashi. 1993. "Highly Sensitive Resonant Infrared Sensor." Digest Int. Conf. on Solid-State Sensors and Actuators. C6-5.
Esashi, M. 1994. "Sensor for Measuring Acceleration." In Mechanical Sensors, ed.N.F. de Rooij, VCH Pub.
Esashi, M., N. Ura, and Y. Matsumoto. 1992. "Anodic Bonding for Integrated Capacitive Sensors." Proc. IEEE MEMS Workshop. Pp. 43-48.
Henmi, H., K. Yoshimi, S. Shoji, and M. Esashi. 1993. "Vacuum Packaging for MicroSensors by Glass-Silicon Anodic Bonding." Digest Int. Conf. on Solid-State Sensors and Actuators. C1-2.
Matsumoto, Y., and M. Esashi. 1992. "Integrated Capacitive Accelerometer with Novel Electrostatic Force Balancing." Digest of the 11th Sensor Symposium. Pp. 47-50.
Matsumoto, Y., and M. Esashi. 1993. "Low-Drift Integrated Capacitive Accelerometer with PLL Servo Technique." Digest Int. Conf. on Solid-State Sensors and Actuators. C13-5.
Matsumoto, Y., S. Shoji, and M. Esashi. 1990. "A Miniature Integrated Capacitive Pressure Sensor." Abstracts of the 22nd Conf. on Solid-State Devices and Materials. Pp. 701-704.
Minami, K., S. Kawamura, and M. Esashi. 1993. "Distributed Electrostatic MicroActuator." Digest Int. Conf. on Solid-State Sensors and Actuators. Mizoguchi, T., Y. Ohta, and M. Takayama. 1986. "SIT Image Sensor: Design Considerations and Characteristics." IEEE Trans. Electron Devices. 33, June: 735-742. Also, many other publications based on SIT structures.
Nagata, T., H. Terabe, S. Kuwahara, S. Sakurai, O. Tabata, S. Sugiyama, and M. Esashi. 1992. "Digital Compensated Capacitive Pressure Sensor using CMOS Technology for Low-Pressure Measurements." Sensors and Actuators. A34:173-177.
Nishizawa, J., T. Terasaki, and J. Shibata. 1986. "Field-effect Transistor versus Analog Transistor (Static Induction Transistor)." IEEE Trans. Electron Devices 22, April: 185-197.
Yoshimi, K., K. Minami, Y. Wakabayashi, and M. Esashi. 1992. "Packaging of Resonant Sensors." Digest of the 11th Sensor Symposium. Pp. 35-38.
Yusa, A., J. Nishizawa, M. Imai, H. Yamada, J. Nakamura, M. Takinami, K. Minami, and M. Esashi. 1992. "High-Speed Directional Low-Temperature Dry Etching for Bulk Silicon Micromachining." Digest of the 11th Sensor Symposium. Pp. 15-18.