Metal Oxide Thin-Film Transistors as a Key Enabler for AMOLED (Active Matrix OLEDs) Displays

By AZoM

Table of Contents

Introduction

Market analysis has shown a gradual slow-down of the flat-panel display industry after years of rapid growth. This is partly because of sluggish economies globally. Market saturation is also at work. When LCDs initially reached the market there were CRT monitors and televisions. Now those have become almost extinct.

The display industry is now seeking to bring to the market new display technologies that will offer something which LCDs cannot. It is anticipated that once the new technology hits the market, consumers will be ready to wap their LCD's for the novel future technology. The new display technology will have to be attractive enough both in terms of performance as well as price.

The Problem with AMOLEDs

AMOLEDs is active matrix OLEDs (AMOLEDs). Since these promise more vibrant color than LCD, as well as flexibility and dramatic thinness, they have long been predicted as a successor to LCD. However AMOLED displays have not yet come to fruition commercially. Especially for large area displays, there have been production issues impacting the technology. Furthermore, AMOLED displays require high mobility backplanes due to the high current levels required to drive light emission from the diodes LCD displays commonly use amorphous silicon backplanes (a-si) that have not suited the AMOLED market, but low temperature poly-silicon is better suited.

LTPS is presently used in the smartphone market. It is highly expensive to manufacture for large area screens.

Introduction of Metal Oxides

According to Nanomarkets, the technology that will cut through this Gordian knot are backplanes that are based on metal oxide thin-film transistors (TFTs). Such TFTs will also be sold into the traditional LCD sector and will generate more revenues from LCD applications than for AMOLED applications. However in the AMOLED sector, they will be more essential and will prove a key enabling technology for AMOLEDs. The metal oxide TFTs can offer the following:

• A high mobility, with considerable currents to drive AMOLED displays and respond to the higher refresh rates of next generation displays;
• Relatively economical large-scale production, that is easily scalable to large substrates;
• Small pixel sizes and hence, high-resolution displays; and
• Larger aperture ratios compared to a-Si, enabling higher transmission through the backplane which can increase the brightness of the display without an increase in power requirements.

Growing Industry Interest in Oxide Backplanes for AMOLED TVs

NanoMarkets’ believes that oxide TFT-based backplanes may well be the technology that propels AMOLED displays into the display mainstream. Oxide TFTs are attracting considerable attention from big name firms such as Sharp and Samsung, the latter being especially important because it dominates OLED display manufacturing.

The major focus is television sets. While all the focus on AMOLED TVs in the large OLED display space at the present time, can OLED computer displays be far behind?

However, NanoMarkets is not suggesting that the change will come easily in either the computer sector or in the TV sector. Both computer displays and TVs are products with relatively long lifetimes and, in any case, there are other problems with large OLED displays that need to be overcome.

The advantages of oxide backplanes are:

• From the capital expenditure point of view, the dollar requirement for refitting a production line for large area LTPS production can run into the low billions of dollars. However, oxide TFTs plants are about a sixth to eighth of that capital expenditure.
• While AMOLED prototypes were demonstrated early in 2012 with both LTPS and oxide TFTs, it is the opinion of NanoMarkets that in going forward, AMOLED TVs will favor oxide TFTs, as their low cost and production scalability are enabling factors in the AMOLED TV reaching a reasonable level of penetration.

Role of Oxide Backplanes in Smartphones

The role of oxide TFT backplanes in the smart phone sector is slightly different than in the TV sector. Millions of smartphones using AMOLEDs are now shipped every year and they seem to be doing quite well in the marketplace.

Furthermore, metal oxides backplanes are ideal for satisfying important requirements of smartphone (and tablet) displays including the following:

• Low power consumption, which is essential in a handheld device with limited battery life and where the display is a major contributor to the drain on the battery.
• Screen resolution has been of growing importance as consumers expect better image, photo and video quality out of their handheld devices. This, in turn, has been due to the evolution of handheld devices into entertainment products, with cameras, games and applications becoming strong selling points
• Sunlight readability, unlike in indoor large area screens, is an important consideration for handheld displays and implies a requirement for a high degree of brightness.

NanoMarkets believes that Oxide TFT backplanes can help in all these at least to some extent. This because of the inherent high mobility of the material, combined with the small pixel sizes that it can be used to create.

The use of oxide backplanes for smartphones may be deterred due to the following:

• LTPS is already common in AMOLED displays for smartphones and displays makers in this sector may be quite reluctant to shift to oxides as many of them have only recently established LTPS facilities
• While making such a switch in the long run may be cost advantageous, equipment will have to be amortized first.
• In addition, while oxide TFTs are superior to a-Si TFTs along a number of dimensions, they are superior to LTPS TFTs only on cost. Metal oxide backplanes cannot match LTPS on mobility and driving currents.

NanoMarkets believes that high mobility backplanes have a very significant role to play in the AMOLED display industry over the course of this forecast period and beyond. As should be clear from the analysis above metal oxide TFTs represent a technology that offers value propositions for the AMOLED sector that are hard to match with any other available technology.

About Nanomarkets

NanoMarkets is a leading provider of market research and industry analysis of opportunities within advanced materials and emerging energy and electronics markets. Since the firm’s founding, NanoMarkets has published over one hundred comprehensive research reports on emerging technology markets. Topics covered have included OLED displays, lighting and materials, thin-film electronics, conductive inks, transparent conductors, renewable energy, printed electronics and other promising technologies. Our client roster is a who’s who of companies in specialty chemicals, materials, electronics applications and manufacturing.

This information has been sourced, reviewed and adapted from materials provided by NanoMarkets.

For more information on this source, please visit NanoMarkets.