Monthly Newsletter -- July 2007

CLEANROOM NEWS

Process 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.

The 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 efficiency.

Both 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).

Solvent-assisted 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 guns.

It 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 system.

At 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.

Microscopes 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).

Please 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.

A few useful spacer applicator links:
http://www.lc-tecaut.com/Dry_Spacer_Module.asp
http://danaenterprises.com/index_sekisui.htm
http://www.sunrisemedical.com/products/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524441792243

Equipment Update
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.

Cleanroom Summer Schedule
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 actual shutdown.

NEWS
KSU 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.

Prof. 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.

CPIP 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 Liquid Crystals”
• July 12 – Matt Zhang, “Stressed Liquid Crystals: Properties and Applications”
• July 13 – Yong-Kyu Jang, “Optical properties of compensated liquid crystal displays”

New employees
• Young Cheol Yang, Postdoc working for Deng-ke Yang
• Fangfu Ye, Postdoc working for Jonathan Selinger

Visitors to LCI
• 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 11, 2007.
• Dr. Yashodhan Hatwalne will be visiting Prof. Jonathan Selinger from July 6- August 30.

Summer REU students
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, (Wei)
• Rabindra Bajracharya, Tribhuvan University-Catmandu, Nepal, India, (Jakli)
• Josh Houpt, Edinboro University of PA, (Lavrentovich)

Be sure to let us know if you would like more detailed information about any activities at the LCI.
Phil Bos
pbos@lci.kent.edu
330-672-2511