Site: Yokogawa Electric Corporation
Headquarters, 2-9-32 Nakamachi, Musashino-shi
Tokyo 180, Japan
Date Visited: September 30, 1993
Report Author: K.D. Wise
Dr. Hiro Yamasaki Senior Vice President, Corporate Technology
Kinji Harada Center General Manager, Sensors Engineering
Center, Industrial Measurement Business Div.
Dr. Hideto Iwaoka General Manager, R&D Dept. 1, TERATEC Corp.
Hideaki Yamagishi Mgr., Devices Laboratory, Corporate R&D Div.
Gen Matsuno Sr. Researcher, Electronics Laboratory,
Corporate R&D Division
Takashi Yoshida Devices Laboratory, Corporate R&D Division
Dr. Hiro Yamasaki gave an overview of Yokogawa Electric Corporation, which is the largest manufacturer of measuring instruments in Japan and the Japanese equivalent of Hewlett Packard in the United States. Principal areas addressed by Yokogawa include measurement, control, and information, with annual sales of about $1.5 billion. Industrial automation systems (controls) make up about 85 percent of these sales, followed by test and measurement instruments, which comprise about 11 percent of sales, with 4 percent devoted to aerospace products. The annual expenditures on research are about 9 percent of sales. The company is about 10.6 percent foreign owned; in 1992 it employed about 6,880 people worldwide and had joint ventures with Hewlett Packard (in test/measurement), Johnson Controls (in industrial controls), and other U.S. companies. Work on MEMS is conducted under the industrial controls sector, which is very diversified. The largest application of Yokogawa sensors was seen in the oil and petrochemical production area, although there was obvious interest in a wide range of other industrial control applications and in medical products. R&D activities address four principal areas: machines and electronics, electronics and optical measurements, information processing, and sensors and solid-state device technologies. A 400 M sample/s analog-to-digital converter, high-speed photodetectors, and a silicon resonant sensor were mentioned as examples of recent state-of-the-art products.
From the standpoint of application areas, Yokogawa is very well positioned to address the sensor area, and the corporation is very active in the area of programmable controllers for use in factory automation. This includes work on flat panel displays. Among the recent sensing instruments addressed are those for pH measurement, gas chromatography systems, a magnetic flowmeter, a pressure transmitter (smart pressure sensing module), a vortex flowmeter, and an instrument for measuring paper thickness/moisture in paper production.
Work on the photo-induced anodization of silicon for use in micromachining was next presented by Takashi Yoshida (1993). Conventional anodization of silicon is done under applied electrical bias in an appropriate solution containing hydrofluoric acid (HF). This requires contacts to all of the p-type regions on the chip that are to be anodized, which is often difficult or inconvenient to supply in a production situation. In this work, light is used instead, generating electron-hole pairs in the depletion regions surrounding the p-n junctions. The electrical contacts are thus eliminated. The anodized areas of porous silicon can be oxidized and then removed as desired with preferential etching. This has been used, for example, to form an n-type beam (microbridge) in a silicon substrate. The creation of the oxidized porous silicon areas, however, does create some stress problems due to material expansion, and these problems have prevented the use of this technique in devices such as the Yokogawa resonant pressure sensor. It does add another processing technique to the arsenal of available structures that can be created using micromachining, however, and may be useful in other areas.
Hideaki Yamagishi next presented a short description of the Yokogawa project under the MITI micromachine effort, which involves the use of focused ion beam (FIB) technology to realize an optical microspectrometer. The device is intended for an inspection module aimed at examining small, 1 centimeter in diameter cooling pipes in power-generation stations for buildup on the pipe walls. The device seeks to realize an optical sensor with a wide spectral range based on a tunneling device, a microantenna, and a variable optical filter with a very short optical path. The entire module is only 2.5 mm in diameter (Micromachine Center Staff 1992). A spiral antenna is photoengraved on a monolithic substrate. Radiation is launched from an optical source and bounced off of the inner surface of the pipe to be incident on the sensor. The voltage induced is used to induce tunneling across a very narrow gap of less than 10 nm. The use of FIB is essential in generating the small gaps. The ability to realize structures less than 50 nm in size has been demonstrated using point ion surfaces. The project appeared very innovative. The possibility of using X-ray lithography as an alternative to FIB was discussed; the high expense associated with the former was cited, along with the convenience and availability of FIB. The FIB may also be used in other related applications.
Gen Matsuno next described an odor sensor aimed at environmental monitoring. The device corresponds very closely to human odor sensitivity, and consists of a resonator coated with a membrane selective to specific molecular absorption. The stability and reproducibility of the device are still being studied. There was discussion of the possibility of realizing a microgas chromatograph at this point. Such a structure had clearly been carefully considered; however, Yokogawa felt that such a device would need a leak-free microvalve, and that the microvalve and the column were the key issues.
Dr. Hideto Iwaoka next described work on advances in compound semiconductor lasers and optical waveguides under way at the Optical Measurement Technology Development Company, a joint effort with the Japan Key Technology Center. Significant advances have been made with distributed feedback semiconductor laser structures (Hirata et al. 1990) and monolithically integrated waveguides by compositional disordering (IWD) lasers (Hirata et al. 1991). This appeared to be very good work, but did not appear to be closely related to MEMS.
Yokogawa produces two pressure sensors: an older piezoresistive pressure sensor and a more recent resonant device aimed at high-performance applications and DPharp. The latter device was described at the 1988 Japanese Sensor Symposium (Ikeda et al. 1988) and at the 1989 International Conference on Solid-State Sensors and Actuators (Ikeda et al. 1989), where it received considerable attention. It is a high-performance device produced by a very challenging process involving the use of four sequential selective-epitaxial growth steps to produce an electromagnetically-driven resonant beam in a batch vacuum-sealed (<1Pa) cavity. The beam is formed in a diaphragm and is subjected to stress as the diaphragm flexes in response to differential pressure (DP), causing the beam to alter its natural frequency. Two beams are actually used differentially so that the actual output is the difference in two frequencies. The present DPharp does not have on-chip circuitry and is produced in the facility at Yokogawa headquarters. It is an excellent device for high-precision measurement applications, but due to the associated process complexity was not viewed as likely to replace conventional diaphragm devices at the lower end of the performance scale. The DPharp can be realized to cover differential pressure ranges from 1 kPa to 14 MPa (full scale) by varying the diaphragm thickness. Accuracy is achievable to ±0.1 percent over a span of about 40:1 (Ikeda 1992). Typically it is closer to ±0.01 percent according to data in Saigusa et al. (1992).
There has been considerable work at Yokogawa on smart sensing modules (pressure transmitters) based on this transducer (Ikeda 1992; Saigusa et al. 1992). These transmitters consist of a differential pressure sensor capsule that couples to the sensor chip and its associated drive/detection circuitry. This assembly drives a microprocessor, which carries out linearization, temperature compensation, self-diagnostics, and communication with the outside world. EPROMs store sensor parameters to enable compensation. Output format is currently a 4-20 mA current loop. The overall assembly is complex, especially from the standpoint of its mechanical/packaging aspects. This general approach to the realization of a smart sensing node is very much in line with approaches currently being developed in the United States, however. The drive/readout electronics for the sensor is implemented in a multichip hybrid configuration and has not been merged monolithically with the transducer at this point.
Hirata, T., M. Maeda, M. Suehiro, and H. Hosomatsu. 1990. "GaAs/AlGaAs BRIN-SCH-SQW DBR Laser Diodes with Passive Waveguides Integrated by Compositional Disordering of the Quantum Well Using Ion Implantation." Japan Journal of Appl. Phys. 29, June: L961-L963.
Hirata, T., M. Maeda, M. Suehiro, and H. Hosomatsu. 1991. "Fabrication and Characteristics of GaAs-AlGaAs Tunable Laser Diodes with DBR and Phase-Control Sections Integrated by Compositional Disordering of a Quantum Well." IEEE J. Quantum Electron. 27, June: 1609-1615.
Ikeda, K., et al. 1988. "Silicon Pressure Sensor with Resonant Strain Gauge Built into Diaphragm." Technical Digest of the 7th Sensor Symposium. Pp. 55-58.
Ikeda, K., et al. 1989. "Silicon Pressure Sensor Integrates Resonant Strain Gauge on Diaphragm." Digest 5th Int. Conf. on Solid-State Sensors and Actuators. June: 146-150.
Ikeda, K. 1992. "Applications of Micromachining for Resonant Pressure Sensors." (Obtained at Yokogawa). Micromachine Center Staff. 1992. Micromachine: Introduction to the Micromachine Center. (Booklet).
Saigusa, T., H. Kuwayama, S. Gotoh, and M. Yamagata. 1992. "DPharp Series Electronic Differential Pressure Transmitters." Tokogawa Technical Report (English Edition). No. 15. Pp. 30-37.
Yoshida, T., T. Kudo, and K. Ikeda. 1993. "Photo-Induced Preferential Anodization for Micromachining." Sensors and Materials. 4: 229-238.