1. Transparent electrode
Transparent electrodes are key elements in optoelectronic devices
such as touch panels, organic solar cells, organic light emitting diodes, smart
windows, and transparent heaters. They require high optical transmittance and
low sheet resistance, which are determined by the materials, fabrication
process, and pattern design used.
1-1) Metal mesh
Metal mesh is comprised of microscale patterns consisting
of metal such as gold, silver, or copper. The design of the mesh pattern, which
is expressed as the line width, pitch, and height, enables adjustments to its
performance. The metal mesh is fabricated by using UV embossing and doctor
blading process. These processes are relatively simple and do not require
high temperature, vacuum environment, and expensive facilities.
1-2) Hybrid nanocomposite
The hybrid nanocomposite combines the enhanced mechanical
compliance, electrical conductivity, and optical transparency of small CNTs (d ≈ 1.2 nm) and the enhanced electrical conductivity of relatively
bigger Ag nanowire (d ≈ 150 nm) backbone to provide
efficient multiscale electron transport path with Ag nanowire current backbone
collector and local CNT percolation network. The highly elastic hybrid
nanocomposite conductors and highly transparent flexible conductors can be
mounted on any non-planar or soft surfaces to realize human-friendly electronics
interface for future wearable electronics.
2. LIGA & UV-LIGA
LIGA is the
German acronym for X-ray lithography (X-ray LIthographie), electroplating
(Galvanoformung), and molding (Abformtechnik). Since a synchrotron radiation
source is used in the lithography, this process is generally used to fabricate
high-aspect-ratio microstructures with a thickness in the range of dozens of
micrometers to several centimeters. In addition, the structures have precise
dimensions and good surface roughness. UV-LIGA use ultra-violet light instead
of X-ray source. Photoresists like SU-8 is used for high aspect ratio of molds.
2-1) Micro nozzle array for electrospray
air purification
Electrospray technique has been widely used due to its uniform and
fine droplets generation characteristics. The electrospray also shows excellent
air purification (fine dust collection and anti bacterial function) properties
when the spray liquid is pure water. However, it is extremely difficult to
spray water electrically due to its high electrical conductivity and surface
tension. Micro nozzle array made of dielectric material is being developed to
produce large amount of water nano-droplets in a stable electrospray condition. With the help of MEMS technology, high aspect ratio of micro nozzle can be
fabricated uniformly and is expected to be applied in commercial air
purifier and humidifier.
2-2) MEMS-based Safety and Arming Device
(SAD)
The SAD (Safety and Arming Device) that ensures safe and reliable
performance of ammunition is now often miniaturized to enable artillery fuses
to be equipped with electronic devices. Although many miniature SADs have been
developed using MEMS technology, most of them have been found inappropriate for
actual munitions application due to the harsh conditions of use. Our group proposed
MEMS-based SAD. The proposed MEMS-based SADs were found to be appropriate for
artillery fuses in every specific criterion by conducting environmental tests
and actual field tests.
2-3) Microneedle
Using a deep x-ray, high-aspect-ratio (HAR) 3D microstructures can
be fabricated. The fabrication process consists of a vertical deep x-ray
exposure and a successive inclined deep x-ray exposure. The first vertical
exposure makes a triangular column array with a needle conduit through a deep
x-ray mask having a triangular and hollow circle shape pattern. The column
array is shaped into the microneedle array by the second inclined exposure
without additional mask alignment. Changing the inclined angle and the gap
between the mask and polymethylmet-acrylate (positive photoresist) substrate,
different types of microneedle arrays are fabricated. The fabricated
microneedle fulfills the structural requirements for painless drug delivery and
blood extraction including a 3D sharp tapered tip.
2-4) Superhydrophobic surfaces
Superhydrophobic materials have a water contact angle (CA) higher
than 150 °C, where water droplets roll off the surface. These surfaces have special
usages, such as anti-ice, anti-fog, and the creation of self-cleaning clothes,
and some surfaces have both superhydrophobicity and antireflective
characteristics. Mass-producible superhydrophobic surfaces with remarkably
identical appearance and efficiency are obtained through a mold fabrication and
hot embossing process.
2-6) Privacy filter film
The SU-8 100 mold for the privacy filter is fabricated by UV
lithography. After that, PDMS is poured into the SU-8 mold and later released
from the mold, transcribing the pattern. The proposed privacy filter does not
require any opaque materials and therefore provides maximum transparency,
yielding a myriad of benefits on mobile devices given their limited battery
capacity. In addition, these privacy filters with micro-cuboid arrays are
suitable for commercialization and the roll-to-roll process using thermosetting
resin.
3. Applications
3-1) Near-field thermal radiation
We developed the novel integrated MEMS-based
platform which can be employed for measuring near-field thermal radiation
between hyperbolic metamaterials (HMMs). For HMMs, Ti and MgF2 are
selected for the easiness of fabrication. It was shown that near-field thermal
radiation between HMMs of Ti/MgF2 is much larger than that
between bulk Ti. The MEMS-based micro-devices with HMM source/receiver, heater,
temperature sensors, and capacitance sensors enable us to measure radiative
heat flux together with vacuum gap width. Further, 3-axis nano-positioner can
freely change the distance between the source and the receiver. With this new
platform, the enhanced radiative heat flux between HMMs can be measured
depending on the vacuum gap width and the source temperature.
3-2) Micro pyramidal mirror for
magnetic-optical trap
The traditional
magneto-optical trap (MOT) requires six laser beams and anti-Helmholtz coils. The
pyramidal mirror was suggested to extend applications. We fabricated a pyramidal
micro-mirror using bulk etching with an integrated anti-Helmholtz coils.
3-3) Thermal Imprinting of Perovskite
Layers for Solar Cells
Photonic nanostructures are thermally imprinted in triple cation perovskites by hot embossing. The imprinted layers are observed to have
recrystallized into a significantly smoothened surface with larger crystal
grain size compared to the non-imprinted rough, polycrystalline layers. These
imprinted layers show improved performances in PL and are expected to improve
performances in lasing and solar cell applications.
3-4) Piezo-MEMS
Piezoelectricity is the charge on the surface of crystals generated by external forces applied to single crystals of
quartz and several other minerals. The charge is roughly proportional to the applied mechanical stress.
These so-called piezoelectric materials discovered in 1880-81 by Pierre Curie
and his brother Paul-Jacques. A year later, the Curie brothers discovered the
inverse effect which is that an applied voltage generates a deformation of the
crystal. This property of materials can be utilized for electric-mechanical
actuators and sensors.
