Liquid Crystal Displays

Addressing Schemes and Electro-Optical Effects

Ernst Lueder, Peter Knoll, Seung Hee Lee

• Publisher: Wiley
• Year: 2022
• Print ISBN:
  9781119667919
• Edition: 3
• eBook ISBN:
  9781119668008
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

LIQUID CRYSTAL DISPLAYS

THE NEW EDITION OF THE GOLD-STANDARD IN TEACHING AND REFERENCING THE FUNDAMENTALS OF LCD TECHNOLOGIES

This book presents an up-to-date view of modern LCD technology. Offering balanced coverage of all major aspects of the field, this comprehensive volume provides the theoretical and practical information required for the development and manufacture of high-performance, energy-efficient LCDs.

The third edition incorporates new technologies and applications throughout. Several brand-new chapters discuss topics such as the application of Oxide TFTs and high mobility circuits, high-mobility TFT-semiconductors in LCD addressing, liquid crystal displays in automotive instrument clusters and touch-screen systems, and the use of ultra-high-resolution LCD panels in augmented reality (AR) and virtual reality (VR) displays. This practical reference and guide:

• Provides a complete account of commercially relevant LCD technologies, including their physics, mathematical descriptions, and electronic addressing
• Features extensively revised and expanded information, including more than 150 pages of new material
• Includes the addition of Oxide Transistors and their increased mobilities, the advances of fringe field switching and an overview of automotive displays
• Presents quantitative results with full equation sets, their derivation, and tabular summaries of related information sets

1
Introduction

Liquid Crystal Displays (LCDs) have established a firm foothold on the market as flat panel displays for computers, transportation, communication (especially in its mobile version), instrumentation and, in the future, with increasing importance for television. The understanding of LCDs requires knowledge about the various electro-optical effects of liquid crystal cells, and about the control of the grey shades and colours in the picture elements (pixels, or pels) by addressing circuits.

The electro-optical effects are based either on the propagation of polarized light through anisotropic liquid crystal cells, or on the propagation of unpolarized light through scattering cells. The grey shade controlling voltage across each pixel is provided mainly by either passive matrix or active matrix addressing. In passive matrix addressing, the voltage in each pixel is generated by voltages at the end of the rows (or lines) and the columns of the display, whereas active matrix addressing uses Thin Film Transistors (TFTs) or Metal Insulator Metal (MIMs) devices as switches in each pixel.

Further topics are the fabrication of conductors, transparent electrodes, TFTs and MIMs with thin film technology, the generation of colour filters, and the assembly and bonding of liquid crystal cells.

It is not only manufacturers of LCDs but also the vast community of users which need to grasp the essence of the physics and engineering of LCDs. The understanding of these topics enables users to select the appropriate LCD for their application, to tailor the optic performance to their needs (e.g. by optimizing the waveform at the addressing circuit by the addition of performance- enhancing sheets, or by selecting the appropriate location of the external ICs for signal processing), as well as for storing and feeding in of the picture information.

Further, manufacturers and users should be enabled to judge the suitability of future developments and trends for their purposes.

The first section of this book presents an overview of the properties of liquid crystal materials and a phenomenological description of the most frequently used type of LCDs, the TFT- addressed twisted nematic (TN) LCD. The aim is to familiarize readers with the main aspects of LCDs, to introduce most of the terminology, to establish an understanding without doing calculations, and to alleviate the subsequent more detailed discussion without losing the overall picture in which the details are embedded.

The remaining portions of the book are devoted to an analytical investigation of the electro-optic effects, and to an elaboration of the addressing schemes complemented by the manufacture of the thin film components.

Applications are centred around transmissive and reflective displays and light valves for projectors. Plastic substrates and printing of layers replacing vacuum processes are examples of an emerging new display technology.

2
Liquid Crystal Materials and Liquid Crystal Cells

2.1 Properties of Liquid Crystals

2.1.1 Shape and phases of liquid crystals

Most liquid crystals consist of molecules shaped like the rod in Figure 2.1(a). The direction of the long axis is called the director, given by the vector n, which is an apolar vector as

and

are equivalent. Rod-shaped molecules are also termed calamitic. Other shapes of molecules are disc-like or discotic, as in Figure 2.1(b), and lath-like.

We focus on calamitic (Bahadur, 1990; Demus et al., 1998a,b) liquid crystals as they are the most important for applications. Below the melting point T_m they are solid, crystalline and anisotropic, whereas above the clearing point with temperature T_c > T_m they are a clear isotropic liquid. In the mesophase in Figure 2.2 in between T_m and T_c, the material has the appearance of a milky liquid, but still exhibits the ordered phases shown in Figure 2.2. These phases are now described in the sequence given by increasing temperature. The first phase above T_m is the smectic C phase (smectic is derived from the Greek word for soap). As all smectic phases, it is ordered in two dimensions. The molecules are arranged with random deviations tilted to the plane of the layer. In the smectic A phase the directors of the molecules are again with random deviations perpendicular to the plane of the layer. Next to the clearing point, the nematic phase appears with only a one-dimensional order (nematic in Greek means a thread, indicating the thread-like defects in the material). All members of the mesophase are anisotropic, as is the solid phase.

Some other phases of minor importance for display applications are below the smectic C phase, the smectic B_hex phase (hexatic B phase), with the same layers as smectic C but a short-range close-packed hexagonal structure, in Figure 2.3(a) seen against the director

; in this direction, the sm...

Table of contents

• Cover
• Table of Contents
• Series Page
• Title Page
• Copyright Page
• Dedication Page
• Foreword
• Preface to the Third Edition
• Preface to the Second Edition
• Preface to the First Edition
• About the Authors
• 1 Introduction
• 2 Liquid Crystal Materials and Liquid Crystal Cells
• 3 Electro-optic Effects in Untwisted Nematic Liquid Crystals
• 4 Electro-optic Effects in Twisted Nematic Liquid Crystals
• 5 Descriptions of Polarization
• 6 Propagation of Light with an Arbitrary Incident Angle through Anisotropic Media
• 7 Modified Nematic Liquid Crystal Displays
• 8 Bistable Liquid Crystal Displays
• 9 Continuously Light Modulating Ferroelectric Displays
• 10 Addressing Schemes for Liquid Crystal Displays
• 11 Direct Addressing
• 12 Passive Matrix Addressing of TN Displays
• 13 Passive Matrix Addressing of Bistable Displays
• 14 Addressing of Liquid Crystal Displays with a-Si Thin Film Transistors (a-Si-TFTs)
• 15 Addressing of LCDs with Poly-Si TFTs
• 16 Liquid Crystal on Silicon Displays
• 17 Addressing of Liquid Crystal Displays with Metal-Insulator-Metal Pixel Switches
• 18 Addressing of LCDs with Two-Terminal Devices and Optical, Plasma, Laser and e-beam Techniques
• 19 Components of LCD Cells
• 20 Projectors with Liquid Crystal Light Valves
• 21 Liquid Crystal Displays with Plastic Substrates
• 22 Printing of Layers for LC Cells
• 23 Advances of TFTs and Structures for Enhancing Mobility
• 24 Fringe-Field Switching (FFS) Technologies
• 25 Automotive Applications of Liquid Crystal Displays
• Appendix 1: Formats of Flat Panel Displays
• Appendix 2: Optical Units of Displays
• Appendix 3: Properties of Polarized Light
• Index