Liquid Crystal Displays: Addressing Schemes and Electro-Optical Effects

2nd edition
by Ernst Lueder
© 2010, John Wiley & Sons, Ltd.
Reviewed by Ian Underwood

The SID-Wiley Display Technology series continues to evolve. I have grown accustomed to having a subset of these works on my office bookshelf for those rather frequent occasions when they are helpful. These books have become a comfortable part of my professional world, just like my calculator and my multi-tool. And that, I think, is the point. To quote series editor Tony Lowe: "The SID-Wiley Series is intended to explain the latest developments in information-display technology at a professional level." I might also append "… for practicing engineers, display developers, display users, and newcomers to the field." I have also found the books to be useful in teaching display technology to undergraduate and postgraduate students, as they elucidate physical principles, explain many engineering subtleties, and, in so far as is possible in a book, describe recent advances in the topic.



The first edition of Liquid Crystal Displays: Addressing Schemes and Electro-optical Effects by Ernst Lueder, published in 2001, was an excellent book. In terms of breadth it covered both electronic addressing schemes and electro-optical effects in a detailed and balanced manner. For good measure, it added chapters on assembly, projection, plastic substrates, and layer printing. In terms of depth, it spanned from principles to current practice, covering both at an appropriate and comfortable level. Finally, it entered a space that was ripe for this style of coverage and filled a prevailing gap quite neatly.

In the intervening nine years, two relevant things have happened – the field has advanced and the competition, i.e., the number of books covering overlapping and related fields, has increased. So, what does the new edition offer?

The author's approach has been to insert whole sections of new material to cover significant advances. New topics covered in impressive detail include MVA (multi-domain vertically aligned) cells, electronic addressing of VA-LCDs, and light-emitting-diode (LED) backlights. These advances contribute to improved display performance in key areas such as color, contrast, viewing angle, power consumption, and switching time, which are important for modern, high-performance LCDs. The transfer of fabricated AMLCDs to a flexible substrate is also described, and the treatment of ink-jet printing and its application in LCD manufacture has been greatly expanded. The recent emergence of practical blue-phase LCs is introduced briefly.

The remainder of the original text and diagrams has been almost completely unchanged. While this is perfectly acceptable for topics such as "Descriptions of Polarization" and "Propagation of Light," I am disappointed that almost 10 years of technological advances in topics such as IPS (in-plane-switching), amorphous and polysilicon technology and addressing, LCOS (liquid crystal on silicon), LC-based projectors, and flexible substrates have been neglected. Other books in the series will presumably supply much of the missing information.

In summary, the second edition of Liquid Crystal Displays is a very useful book and a recommended purchase. It is almost up there with the first edition, but not quite because the update is not sufficiently thorough. The new sections are appropriate, worthwhile, and timely, but they make some of the remaining material look, by contrast, in need of a refresh.

Ian Underwood helped establish MicroPix Technologies (now Forth Dimension Displays) and co-founded MicroEmissive Displays. He is currently Professor of Electronic Displays at the University of Edinburgh and is an Associate Editor of the Journal of the SID.


Transflective Liquid Crystal Displays

by Zhibing Ge and Shin-Tson Wu
© 2010, John Wiley & Sons, Ltd.
Reviewed by Terry Scheffer

Coming from backgrounds rich in both science and engineering, Zhibing Ge and Shin-Tson Wu have written a thought-provoking book that will appeal to display researchers and engineers alike. The work is geared toward transflective displays used in mobile devices, but covers much more than the title suggests, including fundamental continuum and optical equations that are used in simulation programs, as well as practical descriptions of state-of-the art transmissive LCDs. It also provides numerous examples for transflective modes, and explains the challenge of configuring the transmissive and reflective sections to produce similar gamma curves and wide viewing angles, while still being simple enough to be manufacturable.




Today, most transflective mobile LCDs either use the (TN) twisted-nematic mode with a transflective sheet laminated on the rear polarizer or the dual-gap ECB (electrically controlled birefringence) mode. Despite their popularity, there are shortcomings to these designs, which the authors examine throughout the book.

The first chapter, "Device Concept of Transflective Liquid Crystal Displays," introduces the concepts with a detailed description of thin-film-transistor (TFT) LCDs using TN, ECB, IPS (in-plane switching), FFS (fringe-field switching), VAN (vertically aligned nematic), HAN (hybrid aligned nematic), and OCB (optically compensated bend) modes. These modes are returned to in later chapters, with discussions of their adaption to transflective displays. With similar energy, the authors provide detailed descriptions of compensation films, reflectors, polarizers, and backlights.

The authors then discuss the basics of the continuum equations and Maxwell's equations that are needed to compute an LCD's director field, optical properties, and response times. There is a lot here to interest those who are curious about the methods used in their commercial LCD simulation software packages. And all of it will be of intense interest to those contemplating writing their own simulation programs, perhaps using commercial software such as MATLAB. The authors also explain the basics of transflective LCDs for mobile applications, breaking them down into four main categories: (1) dual-cell-gap method, (2) dual-gamma-curve method, (3) dual-field method, and (4) dual-alignment method. Detailed examples with simulated and measured results are provided for each category, along with their merits and demerits, and always with an eye on cost and manufacturability.

A detailed tutorial on the Poincaré sphere is included. As the authors point out, the Poincaré sphere is a natural way to visualize the evolution of the state of polarization as light passes through the liquid-crystal layer and compensation films. Here, the authors take special pains to show how the Poincaré-sphere approach can be applied to obliquely incident light to help researchers intuitively understand ways to widen the viewing angle. The remainder of this section offers examples of using this method to minimize light leakage at oblique viewing angles in transmission and reflection.

The chapter on "Wide View Transflective LCDs" is perhaps the most interesting in the book because it gathers the information presented in the earlier chapters to design transflective displays based on MVA (multidomain vertical alignment), IPS, FFS, and ECB, as well as hybrids of these that can fall into any one of the four basic transflective categories listed above. The reader is advised to proceed slowly here, as there is much to consider as each new design is revealed. The authors compare the performances of the diverse designs in terms of gamma response in the T and R sections at both a normal incidence and at oblique viewing, response times, and color shifts. They point out how small modifications can result in major improvements. The authors also present designs that might be considered exotic today, such as the incorporation of an internal wire-grid polarizer or an in-cell retarder. These materials, however, could very well become mainstream as these technologies mature.

A section on "Color Sequential Mobile LCDs" briefly explores the exciting possibilities of field-sequential color, with its promise of higher efficiency, higher resolution, and wider color gamut than RGB color-filter displays. However, to do this the LC must be able to switch much faster than in a conventional LCD. This is because the time needed for scanning data into the display, the LC response time, and backlight flashing time must all fit within the color subframe time of 5.56 msec for a 60-Hz frame refresh rate or even faster to minimize color break up. The LC response time needs to be less than ~2 msec; the authors consider the TN mode with a cell cap of 1.6 μm and LC with Δn ~ 0.30 as well as a 4.2-μm pi-cell, which both satisfy this speed requirement. As one can imagine, because ambient light is generally continuous and unsynchronized to the display, the reflective portion of a color-sequential transflective LCD must necessarily show monochrome and not color. In the final example of this chapter, the authors disclose a clever hybrid scheme to achieve color where color filters are used only on the reflective portion.

The final chapter, "Technological Perspective" offers a realistic account of the outdoor readability of transflective displays and the contrast ratios that can be expected due to the effect of surface reflections coming both from a direct light source, such as the sun, and from diffuse ambient sources. Anti-reflective and anti-glare coatings are essential here. The authors also cover touch-screen applications, which have special requirements for transflective displays.

Because of the rapid technological progress that will undoubtedly be made in this field, this book belongs on every LCD researcher's and engineer's bookshelf to be referred to again and again. References to published works are also plentiful. •

Terry Scheffer is an LCD technical consultant living in Hilo, Hawaii.