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Frontiers of Future MEMS Devices: Process Integration
Nobuyuki Moronuki, Professor, Faculty of System Design, Tokyo Metropolitan University
Previous columns have introduced green, white,and blue devices as applications of MEMS devices we
could have twenty years from now. The processing
technologies needed to support these applications will
require severe specifications, such as themanufacturing of microstructures in units ofnanometers over a range on the order of meters. Thismay be difficult to achieve through a simple top-down
approach based on the “copying principle” applied tocuthing, for example. While it may be possible tomanufacture nanometer-order structures according toprocesses applying the principle of self-assembly andthe like, developing such structures directly intometer-order structures will not likely be easy.
Therefore, our workgroup has been studying thedevelopment of technologies fusing manufacturing andassembly that can be applied seamlessly across both ofthese orders by merging a top-down process with abottom-up process, as shown in Fig. 1 (members of
the workgroup are listed in Table 1). Whileconventional machining and energy beam machining
can conceivably be combined for larger structures, itwould be necessary to control the temperature andother aspects of the environment to ensure precise
positioning, for example.
In addition, imprinting or other transfer techniques
would be essential to attain high-throughput, low-cost
manufacturing. Device designs themselves may also beaffected when one considers the possibility of further
developing the framework of simple shape transfers to
the transfer and assembly (integration) of specificfunctional materials and molecules, as well as
biotechnological devices.
A self-assembly process, i.e., a bottom-up approach,will likely be required for dimensional scales on theorder of nanometers or less. Moreover, rather than
producing uniform monolayers, we can imagine
techniques for fixing and orienting molecules based on
their location. The following are three features of thisprocess.

hand, the printing technology most suited to smoll lot
production is inkjet technology. While throughput islower, this technology is promising for processes
supporting individual, customized product designs.
There remains much room for research on materials
used with this technology. It is conceivable that future
processes may be able to deposit actual MEMS devices
containing biomaterials.
Scale extension is another important issue.

(1) Technology for manufacturing threedimensional nanostructures
The so-called 2.5-dimensional structures (columns,etc.) are produced through a combination oflithography and etching. Of course, higher resolutions
will be in demand. However, existing technologies are
not likely sufficient to support demands for threedimensional processing, such as the formation oftapers and free-form surfaces. It will also be necessary
to develop techniques for machining periodic threedimensional microstructures on nanometer scale.

Table 1 Members of the process integration workgroup(3) Interface control
Self-assembly can be performed locationselectively by modifying the wettability at specificlocations on a solid surface. For example, we expect tobe able to fix functional devices to only hydrophilic
portions of a substrate simply by drawing thesubstrate up from water in which the functional
devices are dispersed. It will be necessary to develop
many techniques including surface modification inorder to control the assembly of a variety of functional
devices. To achieve this in resolutions at the molecularlevel, extremely preoke interface control will berequired.
As can be seen from the above issues, it will not beeasy to implement comprehensive process integration.
However, we believe these technologies are critical for
implementing various applications and will produce agreat ripple effect.
Represented dimensionsmm

Top-down approach(Copying principle (transfer))
Ambient
Imprinting:controlCutting, grinding,transferring shapes andenergy beam machining
materials
Functional material
3D structures/
Scanning
devicesNanostructure-type

SubstrateScanning(improved precision)

Sub-nm
Bottom-up approach
Self-assembly
functional membrane/
deviceControlling assembly andorientation of functional
molecules

Process material

Fig. 1 Next-generation processing

Nobuyuki Moronuki
Kiwamu Ashida
Gen Hashiguchi
Seiji Samukawa
Harutaka Mekaru
Ko Fuwa
Yasuhiro Igarashi
Chieki Mizuta
Koichi Tanaka
Nobuaki Kawahara
Takayuki Masunaga
Hirokazu Hashimoto
Masatsugu Tomotaka
Masao Kubo
Kazuo Asaumi(2) Large surface areas
Printing technologies must be applied to large
surface area applications of a poster size scale,enabling high-speed mass-production. On the other6

Tokyo Metropolitan University
National Institute of Advanced Industrial Science andTechnology (AIST)

Shizuoka University
Tohoku University
National Institute of Advanced Industrial Science andTechnology (AIST)ULVAC, Inc.
Oki Electric Industry Co., Ltd.
Mathematical Systems Inc.
Sony Corporation
DENSO Corporation
Toshiba Corporation
Fujikura Ltd.
Fuji Electric Systems Co., Ltd.
Matsushita Electric Works, Ltd.
Mizuho Information & Research Institute, Inc.