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公益財団法人永守財団から、ラボ教員が第４回永守賞をいただきました。受賞題目は、「ＭＥＭＳアクチュエータの基礎と産業応用に関する先駆的研究」です。２０１８年９月２日に京都ホテルオークラで開催された授賞式に参加しました。
The 2018 Nagamori Award is presented to the lab faculty for "Leading study on the fundamentals and industrial applications of MEMS actuators." Presentation ceremony took place at the Hotel Okura Kyoto on 2 Sept. 2018.
右から推薦者の藤田博之先生、受賞者の年吉、当日アシスタントの佐野智華子、撮影：堀先生 (from right to left, Prof. Hiroyuki Fujita the recommender, H. Toshiyoshi the recipient, and Chikako Sano the presentation assistant. Photo by Prof. Yoichi Hori.)
Professor R. P. Feynman is said to be the father of MEMS due to his lecture note on nanotechnology in 1959, “Plenty of Room at the Bottom,” in which he called for an idea of micro motor (1/64 inch) for a $1,000 award. A year later, a Caltec researcher won the prize by developing a miniature version of electromagnetic motor.
It took almost 30 years to produce a motor of a true micro dimension. Meanwhile, the semiconductor microfabrication technologies have become matured to let the people use it to produce “micro machines” on the surface of a silicon wafer. The micro motors on the right are less than 100 µm in diameter, far smaller than the Feynman's condition.
Given the device footprint, the electrostatic force is written in proportional to the edge length / gap of the electrodes, implying that the force becomes large when a gap is made to be small due to the enhancement of electrical fields. On the other hand, the electromagnetic force is simply proportional to the wire length only, because the magnetic field is independent of the gap between the magnets. As a result, the electrostatic force becomes more significant in a small scale.
Motors in a macroscopic scale are made of coils and magnet, because such combinations give more torque. In a microscopic scale, on the other hands, motors are based on the electrostatic actuation. Besides, electrostatic mechanisms are handy in the small scale because of
Nonetheless, electrostatic field and magnetic field are from the same origin, from the theory of relativity point of view.
Here we show examples of MEMS actuators developed in the lab. Some of them are already commercialized.
Electrostatically tunable tilt mirrors are used everywhere in the WDM (wavelength division multiplex) system to control the intensity of light traveling in the fibers.
Electrostatic fast scanner is used in the wavelength tunable laser for the OCT (optical coherence tomography) system. Thin tissues such as retina can be visualized in cross-section.
Electrostatically addressable micro shutter array is under development to automate the deep-space galaxy mapping task of the TAO (U-Tokyo Atacama Observatory) in Chile.
Fast MEMS scanner is utilized in the pico-projector for image display. It is also used in the pier-to-pier free-space optical communication of high security.
Capacitance is tuned by the electrostatic force to compose a VCO (voltage controlled oscillator) circuit that is used in a cognitive wireless communication systems.
Just like an electromagnetic motor can generate power when forced to turn, the electrostatic mechanism can also generate power when the electrodes are finished with permanent electrical charge so called “electrets.” Such an electrostatic induction current is thought to be a powerful version of electrostatic sensors.
We are currently developing an electrostatic power generator or so-called energy harvester that can retrieve electrical power of 100 µW to 1 mW from the environmental vibrations. We have experimentally confirmed operation of wireless sensor node such as ZigBee driven by the MEMS energy harvesters.
In conclusion, MEMS actuator was a last missing piece but finally found by the recent R&D of MEMS (including ours!) to provide microelectronics with significant added value through the physical interface to the real world. Furthermore, the mechanism can also be used as an electrical power source when inversely used. It will be in no time before we see a tiny electronics chip that feels, thinks, and talks for itself, made possible by the advanced MEMS technology.
