Newsletter -- July 2007
Spotlight: Spacer Application
Last month’s newsletter included a discussion of spacer technologies
for liquid crystal device fabrication. This month’s topic is various
methods of application of spacer particles.
two main issues that cause problems with spacer application
are moisture and static charge. Most spacer particles
(both silica and polymer) are supplied as a dry powder,
which is very susceptible to moisture. Moisture can
cause clumping of the particles, which can cause non-uniform
cell gap, as well as (possibly) visible light scattering
sites in the display. Spacer bottles are kept tightly
sealed, and stored in desiccator cabinets. Static charge
is more challenging during application, causing particles
to clump or to coat surfaces irregularly, or with low
silica and polymer spacers may be applied with similar
processes. All techniques require three different steps:
1) air or solvent carrier; 2) a dispersing device,
to atomize or create a cloud of particles; and 3) an
enclosure to protect the operator from excessive contact
with spacer material, and to provide an environment
for reproducible application (no air turbulence).
application is very straightforward and easy to implement.
Spacer materials can be mixed with a carrier solvent
and sprayed onto substrates using techniques similar
to paint spraying. A few weight percent of spacers
(lower is better to prevent clumping) is added to an
alcohol mixture (isopropanol, methanol, with some water),
agitated thoroughly, and sprayed on using a spray tool.
At the lowest level, this can be an aerosol type paint
sprayer from the hardware store, but an airbrush is
better at generating small droplets. Various atomizing
nozzles can be chosen for manufacturing application.
The goal is to have the carrier solvent evaporate before
the spacer particles reach the substrate. Freon provides
an ideal solvent, but is no longer a real option. Alcohol
mixtures work fairly well, but usually result in some
solvent reaching the surface of the substrate. This
can potentially cause changes in the behavior of the
alignment layer (destroy alignment, subtle pretilt
effects, etc.), and can cause clumping of spacers if
the evaporating solvent pulls the spacer particles
into droplets. Additionally, spacers applied in this
way are difficult to rework or remove with blowoff
is much more desirable to eliminate solvents in the
process altogether. Dry methods are more sensitive
to room conditions (mostly humidity), but are easy
to rework if necessary. Most commercial spacer applicators
blow measured quantities of particles through electrostatic
guns (to minimize clumping), and place the substrate
on or above a grounded plate. Some use high voltage
wires around the flight path of the particles, and
allow voltages to be tuned to optimize coating uniformity.
Commercial applicators generally quote +/- 10-20% uniformity
for spacer densities, with little or no clumping. The
disadvantage of these tools is flexibility—changing
of spacer sizes requires an extensive cleaning of the
the LCDRF, we have used a very low cost approach to
give results similar (though not as reproducible) to
commercial sprayers. A controller unit for a handheld
adhesive dispenser can be used to supply a timed pulse
of air to a pocket nebulizer containing dry spacers.
Nebulizers are available through pharmacies for patients
suffering from asthma or allergies who need to inhale
medications. As such, they are well suited to generating
a fine cloud of particles. There is no charging involved,
so care must be taken with spacer materials to avoid
moisture (though room humidities that are too low can
lead to static problems). Antistatic nitrogen guns
are extremely useful to prevent surface charges on
the substrate from affecting particle distribution.
with a calibrated field of view can be used to count
spacer densities, to ensure accurate cell gap control.
Inspection lamps (bright light / dark background) can
be used to compare large scale uniformity, or clumping
problems. In an R&D setting, it is often possible
to remove a few larger clumps of spacers with a needle
tip (often the charge will cause the clump to “jump” off
the substrate with no physical contact).
feel free to forward any suggestions for future “Process
Notes” topics. If you are interested in learning
more about our capabilities, or reserving time in the
facility, please contact Doug Bryant.
few useful spacer applicator links:
The Oxford Systems reactive ion etcher is not yet installed. Contractors should
complete facilitization of the unit in mid-July, with manufacturer installation
and training expected late in the month. Any IPP members interested in taking
part in this training should contact Doug Bryant.
The cleanroom will be available throughout the summer months for IPP usage.
During July and August, staff members will be taking some vacation time, so
please contact us if your project has any timeline constraints during the summer
months. In late August, we have tentatively scheduled a routine shutdown to
move equipment and reorganize. A notice will be sent well in advance of the
LCI hosted a two week conference on the topic of
Ferroelectric Phenomena in Liquid Crystals, led by
Dr. Tony Jakli. Many good oral presentations and
lectures were given over the two week period. Industrial
Partner Program staff videotaped most of the main
presentations and are getting permission from the
presenters to place streaming videos of the talks
on the IPP website. The first of these videos will
appear on the IPP web site within the next week or
so, and more will be added each week.
Deng-Ke Yang has secured a three-year grant from the
Ohio Department of Development's Third Frontier program.
The grant is a subcontract to the University of Akron's
project entitled, "Commercialization of functional
polyimide films and nanocomposites." Prof. Yang's
group will characterize optical properties of thin
polymer films in collaboration with Prof. Jack Kelly's
group and Prof. Oleg D. Lavrentovich's group.
Ph.D. Defenses in July 2007
• July 3 - Hailing Zhang, “Wavelength Tunable Devices Based on Holographic
Polymer Dispersed Liquid Crystals”
• July 9 - Shouping Tang, “Multidimensional Optics and Dynamics of
• July 12 – Matt Zhang, “Stressed Liquid Crystals: Properties
• July 13 – Yong-Kyu Jang, “Optical properties of compensated
liquid crystal displays”
• Young Cheol Yang, Postdoc working for Deng-ke Yang
• Fangfu Ye, Postdoc working for Jonathan Selinger
• Sergio Diez for one year with Daniele Finotello and Prof. Lavrentovich
• Dr. Myong Hoon Lee will be visiting Prof. L.-C. Chien from July 12 – August
• Dr. Yashodhan Hatwalne will be visiting Prof. Jonathan Selinger from
July 6- August 30.
The following undergraduate students are participating in a summer research
experience at the LCI:
• Matthew G. Myers (Matt), Ohio Northern University, (Palffy-Muhoray)
• Richelle Teeling, Kent State University, (Jakli)
• Kim Worst, Westminster, New Wilmington, PA, (Wei)
• Jia Ning Chen, Kent State University, (Chien)
• Anna Bice-Baum, University of South Alabama, (Jakli)
• Bhuwan Prasad Joshi, Tribhuvan University-Catmandu, Nepal, India, (Wei)
• William Edward Ryan (Bill), Shippensburg University, Shippensburg, PA,
• Rabindra Bajracharya, Tribhuvan University-Catmandu, Nepal, India, (Jakli)
• Josh Houpt, Edinboro University of PA, (Lavrentovich)
sure to let us know if you would like more detailed
information about any activities at the LCI.