Advances in Materials for Display Applications
by Ion Bita
As we find ourselves at the turn of the year, let me first wish all of you avery Happy New Year and welcome you back to a new year of Information Display magazine. We start 2013 with a look at the topic of advances in materials for displays.
Reflecting back on 2012, what comes to mind is the celebration of the 50th anniversary of the Society for Information Display. This stands out not only because of the amazing evolution of displays during this time, but also, relevant to the context of this issue because we can find in this history a reflection of the very impact of advances in display materials coupled with cycles of device innovations. (For a description of the celebration, see this issue’s SID News by Larry Weber.)
While CRTs dominated the commercial landscape for many decades, for about the last 10 years we have seen an unprecedented pace for the development and commercial introduction of new display technologies. In this timeframe, AMLCDs have pretty much become the de facto display standard, accounting for over 85% of total display sales. They span virtually the entire range of diagonal sizes and applications.
In parallel, just in the past 5 years, AMOLED displays have secured a firm place in the premium mobile-display market, and in 2012 came very close to reaching critical mass in terms of widescale production of high-performance TV sets.
Without trying to be exhaustive, I would also highlight the younger display technologies based on electrophoretic, electrowetting, and MEMS pixel devices, which further fuel the display-industry roadmaps. The rapid progression of these commercial milestones would not be possible without an underlying wealth of technology initiatives, many of which incubated in academic and industrial labs for much longer times than these “overnight” commercial transformations may suggest.
In this issue, we highlight a few such notable technologies that showcase particularly well the importance of applied materials research in enabling significant display-industry advances: amorphous oxide semiconductors, semiconducting quantum dots, and color-filter materials.
Professor Arokia Nathan from the University of Cambridge, UK, and co-authors Sungsik Lee, Sanghun Jeon, Ihun Song, and U-In Chung from the London Center for Nanotechnology, University College, London, UK, prepared this issue’s opening article, which presents an overview of the development and use of transparent oxide semiconductors for advanced display applications. With the initial basic research on TFT devices employing these semiconductors dating back to 2003–2004, the ongoing introduction of these materials in production lines across Japan, Korea, Taiwan, and China is evidence of the impact of research synergies with powerful trends in the display industry. Transparent oxide semiconductors derive combined benefits from a large field-effect mobility (~50× larger than a-Si and about half that of LTPS) in amorphous films such as indium-gallium-zinc oxide (IGZO) and a relatively low processing cost.
Furthermore, because these materials and their TFT implementations are very compatible with existing a-Si TFT production lines, they became subject to an irresistible commercialization pull fueled by the need for differentiation in the display market. For example, as HD-resolution LCD panels have became widely available, flat-panel-TV trends indicate that higher-resolution 3-D LCDs (such as quadHD, 4K × 2K, or 8K × 4K looking further out) and 3-D OLEDs are likely candidates for the next generation of TVs – both of which greatly benefit from transparent oxide semiconductor TFTs. While not without challenges, as reviewed in the article by Professor Nathan, transparent oxide semiconductor materials such as IGZO have already been selected to enable production of next-generation displays such as LG Display’s 55-in. 3-D OLED TV (recipient of a SID 2012 Best-in-Show award). Other examples demonstrated at SID 2012 include Sharp’s 500-ppi-resolution mobile LCD panel and 31.5-in. UHD LCD panel, each of which use IGZO TFT backplanes.
The next article, by Dr. Jian Chen, Veeral Hardev, and Jeff Yurek from Nanosys, describes the use of semiconductor quantum dots to both enhance the color performance of LCD panels and to enable their image quality to compete with OLEDs. While the basic size-dependent photoluminescence property of this class of nanomaterials has been known since the early 1990s, when the synthesis and study of these materials exploded, it took the confluence of a few factors to identify breakthrough opportunities in display applications. The Nanosys team describes the development of a quantum-dot enhanced film (QDEF) to be used as a drop-in solution in minimally modified LCD backlights for improving the spectrum emitted by LCDs. The minimal modification consists of employing blue LEDs instead of the regular white LEDs, with the QDEF acting as a downstream color-conversion layer that produces red and green colors from a portion of the blue light emitted from the edgelit lightguide. The LCD color improvement is so noticeable, with a measured gamut in excess of 100% NTSC, that it garnered this technology the SID 2012 Display Component of the Year Gold Award.
Next, in our Display Marketplace article, Paul Semenza from NPD DisplaySearch gives an overview of LCD color-filter materials, architectures, and manufacturing topics. The key role played by these materials in LCD image quality and power consumption is described, as well as current manufacturing trends across various panel makers.
We would like to thank all the authors for sharing with us their expert opinions on these important developments in display materials and applications. The undersigned never ceases to be fascinated by the contributions of materials science and engineering that enable the visually rewarding experience working with displays and hopes that you will also enjoy reading the articles in this issue. •