The major application of MEMS technology to date is in sensors. These include sensors for medical (blood pressure), automotive (pressure, accelerometer), and industrial (pressure, mass air flow) applications. Commercial sensor applications in Japan are in the same areas that both Europe and North America are concentrating on. In most cases the markets for these products are international.
There are extensive efforts in Japan to apply MEMS to actuators. Dr. Higuchi and his associates at Kanagawa Academy of Science and Technology (KAST) have developed an instrument that is in commercial use to fertilize eggs (1990). The instrument uses a piezoelectric vibrating element to avoid the problem of egg deformation that occurs with conventional methods.
While the commercial applications of actuators have been limited, there is a vast array of actuator needs that MEMS researchers are addressing. These include muscle-like electrostatic actuators, microrobots, noncontacting wafer transport systems, and ultraprecise positioning.
Most researchers estimate that it takes approximately five years to commercialize a product based on a new technology. There are some estimates that it takes two years to do the research prototype, four years to do the engineering prototype, and four years to get the final design to market. There is a large variation in time requirements based on how much process development and trial-and-error development is required, as well as the complexity of the device and how much invention is required.
Many Japanese researchers look on high-aspect-ratio technology (LIGA, polyimide ultraviolet) as new technology for MEMS applications. A substantial number of those visited by JTEC look on the refinement of conventional machining as a new technology for MEMS. This includes conventional milling and EDM. Some researchers consider nanotechnology as a technology potentially competitive with MEMS.
Most Japanese researchers agree that the driving forces for MEMS are size, cost, and intelligence of the sensor. One of the challenges of dealing with MEMS is learning how to effectively package devices that require more than an electrical contact to the outside. Pressure sensors are the most commercially successful MEMS-type sensors to use nonintegrated circuit-type packaging. Hall sensors, magnetoresistive sensors, and silicon accelerometers have used IC-based packaging. The IC packaging is viable since the measurand can be introduced without violating package integrity. Some optical systems use IC-type packages with windows. MEMS will require the development of an extensive capability in packaging to allow the interfacing of sensors to the environment. The very advantage of small size becomes a liability when a device is open to the environment. At the time of the JTEC visits, most Japanese predicted that MEMS sensors would be on the market in three to five years, and that micromedical sensors would probably be the most likely application. Some researchers were predicting that these micromedical sensors would be chemical sensors.
U.S. researchers forecast that in the near future (ten years), MEMS systems will have applications in a variety of areas, including:
The Japanese forecast for MEMS actuators was not at all clear at the time of the JTEC visit. There was much interest expressed in exploring arrays of actuators as a method of obtaining useful work. Some researchers expressed interest in pursuing low mass applications such as directing light beams, based on the success of the Texas Instruments optical array (Sampsell 1993).
One of the major concerns with some true MEMS systems (those on the micron level) is that they must at some point be coupled to a macroworld. Some researchers see an application for a "milli" system, where the problems of coupling to the macroworld are made easier. If one can have a useful product that is all on the microlevel with only an electrical output, then the concern is eliminated.
A broad overview of the potential applications of MEMS is seen in MITI'S "Techno-Tree of Micromachine" (Figure 7.1.
In its Micromachine Technology Project, MITI has targeted two major application areas for MEMS -- maintenance of power plants and medical applications. The advance maintenance system for power plants (see Figure 6.5) consists of:
Figure 7.1. MITI "Techno-Tree of Micromachine."
Figure 7.2. Mother ship.
Figure 7.3. Microcapsule.
Figure 7.4. Inspection module.
Figure 7.5. Work module.
The purpose of this elaborate system is to do repairs in heat exchanger tubes with no or minimum down time. It should be noted that even if only a portion of this task is completed, a large number of the resulting MEMS components could be utilized in other industrial applications.
Another MITI-targeted area is medical use of a microcatheter for cerebral blood vessel procedures. The inner and outer duct of the potential microcatheter are shown in Figure 7.6 and Figure 7.7.
A potential third application under investigation by MITI is targeted at energy savings in manufacturing. The development of microrobots could aid in the manufacturing and assembly of semiconductor devices in clean rooms much smaller than those now in use.
It is obvious that the MITI-proposed applications are both broad in scope of application and in their social impact.
Other Japanese researchers also are investigating making small factories to build small MEMS machines.