Thermally induced light leakage in in-plane-switching liquid crystal displays

Abstract

In this paper, we report the thermally induced light leakage in in-plane-switching liquid crystal displays (IPS LCDs) that have a built-in small-angle deviation (<4 deg) between the polarization axis of a polarizer and the rubbing directions for liquid crystal (LC) alignment. We have found that the thermally induced light leakage depends strongly on the phase retardation which is a function of cell gap, wavelength, and birefringence of LCs used in the IPS LC cells. In addition, we have measured the light leakage of vertically aligned LC cells, which is independent of temperature and the deviation angle. A temperature-scanning method is proposed to reduce the light leakage of the IPS LCDs.

P‐153: High Contrast Ratio LCD with an In‐cell Polarizer

“…The origins of depolarization are rather complicated; they may come from the diffraction effect of patterned thin-film transistors (TFTs) and electrode, light scattering from LC layer and color filter (CF) array, misalignment of crossed polarizers, and rubbing scratches, etc. [4][5][6][7][8] Fig. 2 schematically depicts some of these factors.…”

“…In fact, it is fairly easy to get CR > 100,000:1 with two high-quality crossed polarizers, but the final CR of an LCD is still limited to 5,000:1, which is mainly governed by the depolarization effect inside the LCD panel. However, the origins for this depolarization are so complicated [7,8], for a long time, how to simulate this effect remains to be a big challenge [9]. In fact, for the commercial software DIMOS or TechWiz, this depolarization effect is completely neglected, and the calculated CR is solely determined by the polarizers without considering the depolarization or scattering effect.…”

Depolarization effect in liquid crystal displays

“…In fact, it is fairly easy to get CR>100,000:1 with two high-quality crossed polarizers, but the final CR of an LCD is still limited to 5,000:1, which is mainly governed by the depolarization effect inside the LCD panel. The origins for this depolarization are rather complicated, including diffraction effect, scattering effect, misalignment effect, etc [13][14][15][16][17][18]. After extensive studies, the underlying physical mechanisms have been gradually understood, and their contributions to the total depolarization can be evaluated quantitatively [19,20], as will be discussed later.…”

Effects of thermomechanical properties of polarizer components on light leakage in thin-film transistor liquid-crystal displays

“…Typically, TFT-LCDs are aged at a standard high temperature (60°C) for durability evaluation. 4,5) Depending on the Young's modulus of pressure-sensitive adhesives (PSA) layer, two light leakage phenomena are observed in twisted nematic (TN) mode displays after durability test: (1) light leakage that is concentrated on the edges of LCD panel having hard PSA (PSA-h) and (2) funnel-shaped light leakage in LCD with soft PSA (PSA-s), as shown in Fig. 1.…”

“…6) Product reliability concerns have stimulated significant interest in stress characteristics and their impact on durability and reliability of LCDs. The effect of stress on light leakage phenomenon has been explained with numerous mechanisms including thermally induced light leakage due to phase retardation of liquid crystal (LC), 1) polarizer shrinkage induced bending of poly(vinyl alcohol) (PVA) absorption axis, 7) warpage of LCD panel, 8,9) disturbed orientation of LC due to stress, 10) and thermal stress on glass due to nonuniform temperature distribution. 11,12) Recently, three-dimensional (3D) finite element analysis (FEA) has been employed to analyze the probable causes for light leakage.…”