G. Mozolevskis, A. Ozols, E. Nitiss, E. Linina, A. Tokmakov and M. Rutkis
Liquid crystal display (LCD) industry is among the most rapidly growing and innovating industries in the world. Here continuously much effort is devoted towards developing and implementing new types of LCDs for various applications. Some types of LCDs require relatively high voltages for their operation. For example, bistable displays, in which an altering field at different frequencies is used for switching from clear to scattering states and vice versa, require electric fields at around 10 V/μm for operation. When operated at such high voltages an electrical breakdown is very likely to occur in the liquid crystal (LC) cell. This has been one of the limiting factors for such displays to reach market.
In the present paper, we will report on the results of electrical breakdown investigations in high-voltage LC cells. An electrical breakdown in the cell is observed when current in the liquid crystal layer is above a specific threshold value. The threshold current is determined by conductivity of the liquid crystal as well as point defects, such as dust particles in LC layer, pinholes in coatings and electrode hillocks. In order to reduce the currents flowing through the liquid crystal layer several approaches, such as electrode patterning and adding of various buffer layers in the series with LC layer, have been tested. We demonstrate that the breakdown voltages can be significantly improved by means of adding insulating thin films.
J. Klavins, G. Mozolevskis, A. Ozols A., E. Nitiss and M. Rutkis
We report on a screen printing fabrication process for large-area SU-8 layers utilised for the preparation of microstructures in display devices such as microelectronic, electrowetting or bistable devices. The screen printing method has been selected for its effectiveness and simplicity over traditionally used spin-coating ones. Layers and microstructures produced thereof have shown proper homogeneity. Relationships between screen parameters to coating thickness have been established. Coating on an ITO (indium tin oxide) hydrophobic surface is possible when surface has been treated by UV/Ozone to increase its aqueous ability. To this end, the hydrophilic microstructure grids have been successfully built on a hydrophobic layer by screen printing and traditional lithography processes. Compared to conventional spin-coating methods, the screen printing method offers the advantages of simple, cheap and fast fabrication, and is especially suitable for large-area display fabrication
M. Maltisovs, K. Krumins, A. Ozols and D. Pikulins
Nowadays liquid crystal display (LCD) is an integral part of humans’ everyday life. High demand for new and innovative LCD products force LCD industry to develop and implement new types of LCDs. Bistable smectic-A (SmA) LCD is one of the most promising devices for smart glass applications due to long-term bistability, low haze at clear state, low transmittance at scatter state and low power consumption.
The study describes the most relevant conclusions obtained from frequency response testing and electric current measurements of bistable SmA LCD samples. Bistable LCDs have two states: opaque (light scattering state) and focal conic (transparent state). Switching between clear and scatter states and vice versa is a frequency dependant process. The conducted research on bistable SmA LC frequency response provides important knowledge about operation principles of the smart glass devices.