Emerging blue-phase LCDs

Abstract

Following more than four decades of active research, device development, and massive investment in manufacturing technology, thin-film-transistor LCDs (TFT-LCDs) have finally taken off, to the point where they dominate the flat-panel display market. LCDs have become indispensable to everyday life. They are used in a range of applications that includes cell phones, computers, TVs, and data projectors. LCD technology can thus be said to be relatively mature. A problem with the viewing angle has been solved using multidomain structures and optical-film compensation. Response time has been improved to 2–5ms by employing low-viscosity liquid-crystal (LC) material, a special voltage waveform, and a thinner LC layer. Color shifting at oblique-angle viewing has been significantly reduced, as has motion image blur. The contrast ratio currently exceeds 1,000,000:1 through local dimming of the LED backlight. The color gamutwould exceed 100%NTSC (National Television Systems Committee standards) if RGB (red, green, blue) LEDs were used, although white currently predominates because of its lower cost. The question is, what is next? Blue-phase LC (BPLC) exists in a very narrow temperature range ( 1–2C). Its molecular structure consists of doubletwisted cylinders arranged in a cubic lattice with periods of 100nm.1, 2 BPLCs have been studied for several decades, but up to now, their mesogenic (LC) temperature range has been too narrow for practical applications. However, when a small amount of polymer is embedded to form an LC composite, the polymer-stabilized BPLC shows a reasonably wide mesogenic temperature range that includes room temperature.3 Consequently, enthusiasm for developing new BP-LCDs has been revived. We previously showed that, in comparison to conventional, nematic LCDs, polymer-stabilized BP-LCDs exhibit four transformative features.4 First, response time is in the submillisecond range, which helps to minimize motion image blur and, more Figure 1. Blue-phase liquid crystals (BPLCs) in an in-plane-switching electrode cell. (left) Voltage-off state. (right) Voltage-on state. w: Electrode width. l : Electrode spacing. A: Analyzer. E: Electric field. P: Polarizer.