SID 2010 Report: New technologies dispel the dark clouds on the road of FPD development

The world's largest international display exhibition was held from May 23 to 28, 2010. The number of attendees increased by 25% compared to the previous exhibition, which can be said to have regained vitality. At present, the overall atmosphere of the FPD industry is rather dull. The "king" of today's displays, liquid crystal panels, are widely equipped in various devices, and FPD has entered a mature stage and lost its direction. At this SID, new generation technologies, led by flexible displays, appeared one after another. These technologies that may break the dull situation of the FPD industry have attracted the attention of many technicians.

What technology will lead the development of the mature FPD industry?

The 48th SID International Symposium and Exhibition (SID 2010), the world's largest display conference, held in Seattle, the United States from May 23 to 28, 2010, was packed with engineers with eager expectations, all of whom hoped to see new technologies that would drive the future development of the industry.

Now, one of the technologies that is expected to lead the development of the display industry is three-dimensional (3D) imaging. In 2010, major TV manufacturers have launched 3D TVs, and the competition is rapidly heating up. At the SID 2010 exhibition, major panel manufacturers including Samsung Electronics (Samsung) and South Korea's LG Display displayed a variety of 3D-enabled displays at their booths.

Eager attention to key technologies in the next few years

In contrast to the enthusiastic atmosphere in the market, at SID It was not 3D technology that received much attention at SID 2010. Engineers looked beyond 3D and turned to three technologies that are expected to be put into practical use in a few years: organic TFT, oxide semiconductor TFT and electronic paper.

Organic thin film TFT is formed on a resin substrate by printing technology, and one of its characteristics is that it can be used as a flexible driving element. In addition, it is possible to manufacture lighter, thinner and more durable displays at low cost. At SID 2010, great technological progress was seen, including the development of products that can roll up the entire display.

Oxide semiconductor TFT has achieved a carrier mobility that is 5 to 20 times higher than that of existing amorphous silicon TFT. Large organic EL panels with high resolution of 4K×2K (4000×2000 pixels) and high-speed driving of more than 240Hz, which are difficult to achieve with amorphous silicon, are about to be mass-produced. These basic performance improvements will also improve the display performance of 3D images. Major manufacturers will present their products at SID Among the technologies released in 2010, this large panel with a size of over 30 inches was unveiled. It can be said that it is clear that it will be developed as a driving element for the next generation of large displays.

The electronic paper market has been almost completely dominated by the electrophoretic type of E Ink Company in the United States. The trend at SID 2010 shows that not only are panel manufacturers accelerating their support for color display of electronic paper, but also that they have the technical strength to compete with E Ink.

The following is a detailed introduction to the SID These three technologies were announced at SID 2010.

Organic EL panel that can be rolled up, gate drive formed by organic TFT

As the name suggests, one of the characteristics of flexible displays is that they can be bent. However, the products developed so far are almost all partially bendable.

The 4.1-inch organic EL panel developed by Sony (Paper 47.3) solves this problem. The panel is only 80μm thick and can be rolled into a cylindrical shape with a radius of less than 4mm (Figure 1). The public demonstration after the release attracted many engineers to watch. Sony proudly said: "The prototype we released at the last SID was "bendable", and this time it is "rollable"."

The biggest feature of its technology is that in addition to forming the pixel circuit on the resin substrate, the gate drive circuit is also made of organic TFT. Therefore, the external gate drive IC is omitted, allowing the entire display to be rolled up.

Figure 1 Sony has developed a rollable organic EL panel Sony has developed an organic EL panel that is only 80μm thick and can be rolled into a cylindrical shape with a radius of 4mm. This is achieved by using an independently developed organic semiconductor (PXX derivative) to form a gate drive circuit on a resin substrate.

What makes all this possible is Sony's independently developed peri-Xanthen-oxanthene (PXX) channel material. The organic TFTs produced using a derivative of PXX have a carrier mobility of 0.4 cm2 ^/ Vs, four times higher than when using pentacene channel materials. This ensures the carrier mobility required for organic EL gate drive circuits.

The organic TFT driving element of the developed product uses vapor deposition technology to form PXX derivatives and electrodes, while other insulating films are trial-produced using solution materials in a coating process below 180°C. Sony said, "Equivalent performance can be achieved when all TFTs are made using a coating process." It is also considering the goal of trial-producing organic TFTs using only a coating process in the future.

[page]

Plastic Logic's technology

Organic EL panels that use organic TFTs as drive devices still have problems to be solved in terms of display performance and reliability. In fact, Sony has not disclosed the mass production schedule. It is generally believed that electronic paper (e-paper) will take the lead in the practical application of organic TFTs. This is because, compared with liquid crystal panels and organic EL, e-paper has lower requirements for driving TFTs such as carrier mobility and threshold voltage.

Plastic Logic announced a 10.7-inch e-paper driven by organic TFTs at SID2010 (Paper 33.1) (Figure 2) that will be mass-produced. The company plans to launch the QUE e-book terminal equipped with this e-paper in June 2010. The display of this terminal cannot be bent, but it is very thin and very light.

Figure 2: Organic TFT technology to be mass-produced soon Plastic Logic has released its organic TFT-driven e-paper technology (a) that will be used in the e-book terminal QUE. It uses a top-gate TFT structure and is formed by printing technology at room temperature (b). Figure (b) is based on data provided by Plastic Logic.

The technology announced by Plastic Logic is limited. Its organic TFT is formed on a PET substrate using inkjet technology at room temperature. The channel material is manufactured by Merck KGaA of Germany, but details such as the carrier mobility of the trial-produced organic TFT have not been announced. Samsung Electronics, the largest LCD panel manufacturer of

Samsung's organic TFT,

is also developing electronic paper driven by organic TFT (Paper 40.3, Figure 3). It has developed a liquid crystal panel using polymer dispersed liquid crystal (PDLC).

Figure 3 Samsung releases e-paper driven by organic TFT Samsung Electronics has developed e-paper that uses organic TFT as the driving element and supports color display (a). It is 4.8 inches with a resolution of 320×240 pixels (QVGA). It uses materials developed independently by Samsung and uses printing technology to form the channel layer. The display uses PDLC (b). The figure is drawn based on data provided by Samsung Electronics.

The product it has developed is a reflective liquid crystal panel that does not use a backlight. Since it is a trial product using a glass substrate, the panel cannot be bent. However, it is planned to use a resin substrate in the future to achieve flexibility. Its organic TFT uses a self-developed channel material, but the molecular structure is not disclosed. It is formed using inkjet technology, and the carrier mobility of the TFT is said to be 0.15cm2 ^/ Vs. The PDLC used for display is made by dispersing liquid crystal in a polymer. When no voltage is applied, the liquid crystal molecules are in a scattered state (white), and when voltage is applied, the panel becomes transparent. Samsung Electronics has colored the PDLC black, so the display panel is black when no voltage is applied. When voltage is applied, color filters of RGB colors are used to achieve color display.

Major manufacturers released IGZO TFTs

, along with organic TFTs, which attracted engineers' attention at SID 2010. Taiwan's AU Optronics (AUO) and LG Display exhibited LCD panels, while Sony, Samsung Mobile Display (SMD) and AUO exhibited organic EL panels (Table 1).

[page]

These companies are developing oxide semiconductor TFTs based on amorphous In-Ga-Zn-O (IGZO). The carrier mobility of the IGZO TFTs released is as high as 5cm2 ^/ Vs to 20cm2 ^/ Vs. On the other hand, many people point out that the TFT characteristics are degraded and there are differences in the manufacturing process. When AUO first demonstrated a 32-inch LCD using IGZO TFT to drive the liquid crystal panel, it not only improved the carrier mobility, but also reduced the number of steps in the TFT manufacturing process. Because of its cost, it needs to compete with the amorphous silicon TFT production process used in the current large-size liquid crystal panels. This time, the technology released by AUO and LG Display takes into account both the improvement of IGZO TFT characteristics and the simplification of the process. For example, AUO used its own sixth-generation (1500mm×1850mm) liquid crystal panel production line to develop a 32-inch IGZO TFT liquid crystal panel (Paper 76.3). The TFT adopts a coplanar structure in which the channel is formed after the source/drain electrodes. The manufacture of this TFT requires six layers of masks, which is only 1-2 layers more than the conventional amorphous silicon TFT. In addition, in order to minimize the characteristic differences generated during the manufacturing process, after the TFT array is formed, it is subjected to a heat treatment of 250°C for 1 hour. The additional manufacturing process is kept to a minimum. The company also successfully trial-produced a 37-inch product using the same production line, but it was not exhibited this time. LG Display has developed a 2.8-inch LCD panel using IGZO TFT driver elements (Paper 76.2). Its TFT adopts an improved version of the inverse staggered type commonly used in large-size LCD panels, with a structure that protects the IGZO layer with the source/drain. Specifically, the source/drain uses molybdenum/titanium (Mo/Ti) electrodes, and the lower titanium electrode in contact with the IGZO layer completely covers the IGZO layer. The titanium electrode is used as a protective layer when the upper molybdenum electrode is etched, thereby reducing the degradation of the IGZO layer caused by the etching solution. The titanium electrode remaining in the upper part of the channel is oxidized to TiOx medium by oxidizing plasma treatment. Sony disclosed that the degradation of IGZO TFT characteristics has a greater impact on organic EL panels than on liquid crystal panels. At SID 2010, the organic ELIGZO TFTs released by various companies all adopted a more complex structure than the aforementioned ones used for liquid crystal driving. For example, Sony's TFT has an etch-stop layer on the channel surface (Paper 69.2). Sony has made the following three improvements to control the degradation of IGZO TFTs: First, the source/drain electrode structure was changed from the general titanium/aluminum/titanium (Ti/Al/Ti) three-layer structure to the lower point in contact with the amorphous IGZO to molybdenum titanium/aluminum/molybdenum (Ti/Al/Ti/Mo). This can control the oxidation of the electrode. Second, the surface protection film is not ordinary silicon nitride (SiNx) or silicon oxide (SiOx), but aluminum oxide (Al2O3) with high protection performance, and is formed by sputtering with cheap direct current (DC). Third, the IGZO layer is completely sealed with an etch-stop layer, source/drain electrodes and surface protection film. This ensures that the service life of organic EL TVs can reach more than ten years. The 19-inch display developed by South Korea's SMD uses an etch stop layer for TFTs, just like Sony, to suppress the degradation of characteristics that may be caused by the etching process of the source/drain electrodes (Paper 69.3). Its IGZO TFT manufacturing uses a seven-layer mask. AUO's 2.4-inch organic EL panel uses the same planar structure as the company's 32-inch LCD panel (Paper 11.2). However, it also adds a silicon oxide (SiOx) etch stop layer on the top of the channel to reduce the degradation of the characteristics of the IGZO TFT. Color electronic paper is becoming more mature. At SID 2010, the attention to electronic paper was also very high, and various panel manufacturers exhibited electronic paper that supports color display. The largest electronic paper manufacturer, E Ink, exhibited color electronic paper with a contrast ratio of 20:1; while Japan's Bridgestone exhibited color electronic paper made with "electronic powder". In addition, LG Display and Samsung Electronics also exhibited development products that support E Ink's electrophoretic liquid technology. The most notable of these are Qualcomm MEMS Technologies (QMT) of the United States and Liquavista BV of the Netherlands, which intend to compete with E Ink, which has dominated the e-paper market so far. QMT exhibited a mirasol display using its own technology. This display uses micro-resonators (IMODs) using MEMS technology as pixels. IMODs can increase the intensity of specific wavelengths in reflected light and can be used to express gradations. The screen size is 5.7 inches and mass production is planned for the second half of 2010. QMT has exhibited its development products at "CES 2010" and "MWC 2010", but this is the first time it has been released at a display-related exhibition. "As an e-paper that supports color display, it is very complete" (a Japanese display engineer) praised it. Liquavista unveiled a 6.2-inch e-paper using electrowetting technology for the first time, and its driving element uses amorphous silicon TFTs. This e-paper is a reflective display that uses a black oil film and RGB color filters to achieve color display. The company plans to start mass production in 2011. The company explained the panel manufacturing technology as "having many similarities with existing LCD panel production lines, so it can be manufactured using the 10th generation (2880mm×3100mm) panel production line."