Dependence of the lateral ion transport on the driving frequency in nematic liquid crystal displays

Abstract

The presence of ions in a liquid crystal (LC) influences the transmission characteristics of LC displays. These ions follow the electric field perpendicular to the electrodes and move back and forth under the influence of the ac field. Because of their charge, they can distort the electric field, which leads to transmission changes. Recently it was discovered that due to the LC anisotropy, ion motion parallel with the plane of the electrodes (perpendicular to the electric field) is also possible, even without lateral fields. After driving a pixel for a long time, the ions will accumulate at one pixel edge, which leads to unwanted image artifacts. In this paper, we investigate the frequency dependence of the lateral ion transport in twisted nematic liquid crystal displays at high and low ion concentrations, different ion mobilities, and LC rotational viscosities, for a fixed voltage just above the LC threshold.

The Influence of the Driving Voltage and Ion Concentration on the Lateral Ion Transport in Nematic Liquid Crystal Displays

“…7) Then we explained the mechanism behind it, 8) and finally performed simulations and further measurements to explain the frequency dependence of the lateral ion transport. 9) This paper concludes our research by investigating the other important parameters: the amplitude and dc component of the driving waveform, and the ion concentration in the display.…”

“…There are a variety of effects in LCDs due to the presence of ions: vertical interpixel crosstalk, 2) flicker at low frequencies, 3) long-term image retention, 4) ion generation, 5) and leakage currents. 6) Recently, we have discovered the lateral ion transport in STN displays in the absence of lateral electric fields.…”

Ion Transport and Switching Currents in Smectic Liquid Crystal Devices

“…In some cases this anisotropy may lead to lateral transport of ions over a distance of mm [14][15][16]. The ion flux in the alignment layer is usually set to zero.…”

Dynamic charge separation in a liquid crystalline meniscus

“…by a high intensity laser field, chemical doping, 1 applying a high electric field, 2 or acquired from the surrounding atmosphere. Ionic impurities are unwanted in LC displays 3 because the presence of charged impurities may lead to (i) screening of the electrodes, 4 (ii) decrease of the quality of images via long-term image retention, 5 (iii) flickering at low frequency due to the local change of the electric field by moving ions, 6 or (iv) retention of the boundary of the image due to the distortion of transmission at the edges of the pixels. 7 A long-term constant electric field applied to LC cells leads to the phenomenon of 'image sticking', caused by the leakage of current, 8 which is also attributed to the presence of small concentrations of ionic impurities.…”