Site: Mitsubishi Electric Corporation
8-1-1 Tsukaguchi Honmachi
Hyogo 661, Japan
Date Visited: September 30, 1993
Report Author: J. Giachino
Dr. Hideharu Tanaka Deputy Manager, Advanced Mechanical Systems
Dr. Ken Morinushi Manager, Advanced Mechanical Systems, 5th Group Department
Minoru Kobayashi Research Manager
Takuji Oda Research Engineer, Materials Processing Engineering Department
Mitsubishi Electric Company has 102,704 employees and annual sales of $25.7 billion. There are four laboratories:
The MEMS work has approximately twenty researchers involved and is funded at the level of ¥2 to ¥3 billion per year.
Following are some of the areas that these laboratories are working in:
Materials and Electronics Devices
Industrial Electronics and Systems
The JTEC panel saw a video that included pictures of a synchrotron X-ray source and extensive automated packaging and assembly equipment.
Following are the Mitsubishi responses to a series of questions submitted before the JTEC panel's visit. Only those questions for which a response was given have been included.
A. Advanced Materials and Process Technology
1. What materials and fabrication techniques are most likely to be used in production for MEMS? Will MEMS continue to be based primarily on silicon technology?
Magnetic layers and structures is the key to MEMS. [These factors are] more important than electrostatic. Silicon is just one technology. Silicon suffers from the fact that it is basically a two-dimensional technology, and for MEMS one needs a three-dimensional technology.
2. What, in your opinion, is the most important new process or material needed for extending the capabilities of MEMS?
Three-dimensional capability and high aspect ratio. Thick film-type materials are also important, as well as the capability of measuring the internal stresses in these thicker materials. These materials need to have improved conducting, insulating, and magnetic properties.
Questions 3, 4, and 5 are all answered in one response:
3. Are there plans to use X-ray lithography for micromechanics?
4. How attractive is the LIGA process for commercial use in MEMS at the present time? How attractive do you expect it to be in five years? Ten years?
5. If you are pursuing LIGA and LIGA-like high-aspect-ratio structures, what materials are being investigated and why? To what extent do you feel that structures produced using high-aspect etching will be competitive with those formed by plating?
[Mitsubishi is] getting a synchrotron ring internally. There is one already available in the area for use. Compared to IC industry, MEMS volumes are low so that there is a need to develop low-cost equipment and low-learning costs. The [corporation is] looking for new processes for plating and fabrication.
6. What are the prospects for a low-temperature wafer-scale bonding process for MEMS? How low in temperature can we go? Do you feel metal-metal, silicon-glass, or other interfaces are most promising?
[Mitsubishi is] doing atomic bonding at room temperature. This requires very clean surfaces (sputter etch) and ultralow vacuum 10 exp-10 Torr. The [company has] done Si/Ag and Si/Si bonds with no pressure at room temperature.
7. What polymeric materials are being explored as photomasks for high-aspect-ratio structures? Is the use of conformal coating processes practical?
[The company uses] material from Hoechst in 20 to 30 micron layers per application. This requires three coats to get to 100 microns. This is not very practical. [The company is] trying to develop a new material.
8. Do you feel that nested/stacked wafer-level microstructures based on multiple bonding and/or etch-back operations will be feasible within the next five years? Are they important for MEMS?
Silicon is not [the company's] main technology for MEMS. This has been done in the semiconductor group.
9. It appears that precision injection molding could play a major role in MEMS. Would you comment on this, please.
Plastics are useful in the millimeter size. In the micron size it is difficult [since] viscosity becomes a problem for cavity injection of the polymer.
10. Are room-temperature superconductors being explored, and if so, what materials and processing techniques are being used?
[Mitsubishi has] developed a Bi/Sr/W/CuO superconductor by sputtering. [This] application is not available for discussion.
11. Do you expect major advances in micromachining in the coming decade? Will photo-assist etching or new etch-stops emerge to play a major role? What other technology additions do you consider promising?
[The company is] working on a new technology and [has] substantial funding to pursue it.
C. Microactuators and Actuation Mechanisms
1. Can designs using arrays of microactuators achieve large and useful forces? Are there other devices similar to the large optical projection displays that have been reported that can be realized using MEMS technology?
There is a need to do arrays in order to realize a useful device. [The company has] been working on sensor and actuator arrays, [and believes] that in five years a sensor array will be in a product. MEMS displays will be a product for an actuator array. Sony [already] has an actuator display.
2. Considering their importance to MEMS, in what order of importance would you place the following microactuation mechanisms: shape-memory alloys, electromagnetics, electrostatics, thermal bimorphs, piezoelectric bimorphs, piezoelectrics, electrostriction devices, and phase-change devices? How many of these do you expect will find commercial applications in high-volume products?
Electromagnetism for high power density, piezoelectric for large force, electrostatic for simplicity.
3. What are the most reasonable candidates for prime movers for microactuation?
4. To what extent can sticking problems due to surface forces be suppressed in microactuators? Will these problems seriously constrain the practical application of microactuators based on narrow gaps?
[Mitsubishi] believes that one must [achieve] a noncontacting system. [The company is] working on an air bearing.
5. What is the most promising candidate for a microrelay? Where are such devices most likely to be used?
[Mitsubishi has] no interest in a microrelay.
6. What are the main design issues in microfluidic systems? Where will such systems find their primary application?
[The] main design issues are high viscosity and friction reduction. The primary applications will be in cooling systems for VLSI.
7. What designs are most likely to be adopted for practical microvalves and micropumps? What is holding up the practical realization of these devices?
Piezoelectric valves are the most likely. For greater than 1 mm, rotary pumps will be used; for less than 1 mm, positive displacement pumps [will be used]. Friction and leakage problems are the major concerns.
F. MEMS Design Techniques, Application, and Infrastructure
1. The term "MEMS" has many meanings. Could you tell us your interpretation?
The key to be[ing] successful is to combine sensors and actuators in arrays. So "array" is probably the best definition. Machine has no meaning.
2. Is there a MEMS technology driver equivalent to the DRAM in the IC industry? If so, what is it?
Optical applications using arrays.
3. Is the integrated circuit industry the principal application driver for MEMS? If so, what are the alternative drivers during the next decade, if any?
[Mitsubishi does] not see silicon as a major driver. MEMS needs new ideas for applications.
4. In what sensor application areas do you see MEMS technology having the greatest importance? (Examples might be: automotive, medical, robotics, consumer products, etc.) What are the key advantages of MEMS technology for these applications?
Consumer products, robotics, medical, automotive.
5. Looking ahead five years, what new MEMS-based sensors and sensor applications do you anticipate?
6. In what time frame do you anticipate MEMS technology having the most impact on sensor products (for example, three years, five years, ten years, etc.).
Three to five years.
7. What is the prognosis for MEMS foundries? Are they needed? What technologies would need to be present in a MEMS foundry?
[A MEMS foundry] would not be commercially viable.
8. What is the "state of the art" in MEMS reliability? Where are the principal problems?
The major concerns [are] erosion and environmental dirt.
9. What is the "state of the art" in MEMS designability? How important are CAD tools for MEMS? Do you have an active CAD effort for MEMS in your organization?
[The company needs] to develop tools to measure material properties. [Mitsubishi does] not yet have good material property data.