Oxide TFT - Page 15

Sharp announced that it will start making IGZO (InGaZnO) based LCD panels for mobile phones and tablets towards the end of 2011. Sharp says that the new displays will be brighter, clearer, thinner and more efficient than existing LCDs. Sharp will make these new displays in their 8-Gen plant using the company's UV²A ultra-violet alignment technology.

IGZO can also be used to for OLED backplanes. Chimei Innolux, for example, announced plans to built a 5.5-Gen OLED plant an IGZO TFT.

We're still not sure whether Chimei Innolux (CMI) is producing AMOLED panels or not - but according to Digitimes the company is showing AMOLED panels at FPD China 2011. This seems to be a good sign.

According to their financial presentation, CMI has two OLED plants planned (A Gen-3.5 LTPS in Jhunan and a Gen-5.5 IGZO-TFT fab in Tainan).

Back in December 2009, Chimei bought both TPO and CMO (and its CMEL OLED subsidiary). It wasn't clear what will happen to TPO and CMEL's OLED programs. CMEL had an active AMOLED program and even offered 7.6" panels, but production halted after the merger. TPO was said to develop small (3" and 4") AMOLEDs but had technical difficulties. Now we found out that Chimei Innolux is back into AMOLED production. In their 3Q 2010 financial results presentation they list their Fab status:

There are two OLED plants. The first is a Gen-3.5 (620x750mm) LTPS/OLED Plant in Jhunan, Taiwan targeting small/medium displays. There's also a Gen-5.5 (1,300x1,500) plant in Tainan (also in Taiwan). The Gen-5.5 line will produce OLEDs for monitors or TVs. The new OLEDs in the Gen-5.5 line will use an IGZO (InGaZnOx) TFT - a transparent amorphous oxide semiconductor.

The Flexible Display Center (FDC) at Arizona State University and AU-Optronics will co-develop mixed oxide thin film transistors (TFTs) for flexible AMOLED displays. AUO and the FDC will work in active partnership with dedicated engineering teams to advance mixed oxide transistor technology and the handling capabilities of conventional flat panel display (FPD) manufacturing processes to accommodate the thin, plastic substrates used for AMOLED flexible displays. Mixed oxide TFTs offer a better ability to drive currents and improve the lifetime and stability of transistors used for OLED displays.

Flexible AMOLED by ITRI

AUO is also working towards flexible displays together with Taiwan's ITRI. AUO plans to start mass producing AMOLED displays in Q2 2011 (but these will not be flexible...).

Andrew Rinzler, professor of physics at the University of Florida has developed a new driving method for large OLED panels which basically brings the source and drain electrodes of a transistor closer together by stacking components on top of one another instead of side by side. The transistors are made from thin aluminum oxide film on a glass subtrate (as the drain electrode) and a layer of organic molecules as a channel. This enables good performance without the need for high-resolution lithography techniques. The new device also uses a tenth of the voltage of current OLEDs - which saves power.

Transistors on glass

They haven't yet made a large-sized panel, but it should be possible with the new design. It can also be used to make flexible OLEDs. They are currently working to simplify the architecture in hope to bring down the cost and complexity even further.

Samsung are still keen on OLED TVs, which will be the "dominant technology in next-generation TVs by 2015". They will be the ultimate active-shutter 3D TVs. Samsung has plans to use an Gen 8 (2200mm x 2500mm sheet size) production line for the OLED TVs. There's no date or real commitment yet, but this will hopefully happen within the next few years.

Samsung 14-inch 3D OLED prototype

There are still some technical issues to overcome. For their upcoming 5.5-Gen plant, SMD plans to introduce LTPS TFTs using conventional excimer laser annealing (ELA). TFTs formed with this technology often exhibit variation in characteristics, and this method might prove difficult in larger line. SMD is also working on other technologies: improved ELA technology, sequential lateral solidification (SLS) and super grain silicon (SGS). The company is also developing oxide semiconductor TFTs.

Samsung is aiming to improve their AMOLEDs in the near future. They claim they will double the efficiency (from 20cd/A to 40cd/A), the lifetime (from 50,000 to 100,000 hours) and the power consumption (from 62W to less than 30W). Samsung will use advanced color pattern methods to overcome the current FMM method large-size limitation. They will also move from glass encapsulation to thin-film, and apply Oxide substrate. They will also use only triplet OLED emitters instead of using both singlets and triplets.

Samsung has recently began to construct their new 5.5-Gen AMOLED plant, which will start production in July 2011. Samsung plans to invest $2.2 billion on that plant that will have 3 production lines (1300X1500mm). Having a larger wafer size results in better efficiencies for both small and large panels (such as 30" or 40" OLED TV panels). Samsung did not say whether the new methods will apply in the new plant only, or also in the current one.

Sony has developed a Top-Emission 11.7-inch 960 x 540 OLED panel using oxide semiconductor TFTs as its driver elements. Sony says that the new panel has a lifetime of over 10 years and better colors than the XEL-1. The OLED panel features a peak brightness of 600cd/m² or more, a contrast ratio of 1,000,000: 1 or more, and 100% or higher color gamut vs NTSC.

The panel improvements were achieved by reducing the property degradation of the oxide semiconductor TFT. Sony made the following three improvements. First, the company prevents the oxidation of the electrode by changing the structure of the source/drain electrode from the commonly-used Ti/Al/Ti three-layer structure to Ti/Al/Mo structure (Mo is in contact with the amorphous IGZO).

LG Display has revealed their OLED TV roadmap: 15" displays in 2009, 20" in 2010, 30" in 2011 and 40" or larger panels in 2012. The 40" panels in 2012 will be "fairly expensive", but they will be available in the market. These details were given by Won Kim, LG Display's OLED sales and marketing VP.

Kim says that the technical challenges for large-size OLED panels are:

• driver elements (Kim says that LG Display will probably use a TFT based on low-temperature polycrystal silicon, or an oxide-semiconductor such as IGZO).
• Organic materials and film forming process (LG will use fluorescent materials until 2011 and phosphorescent materials afterwards. LG are considering using printing technologies).
• Sealing process  (LG believes that solid sealing is desirable for TV panels).

Korea's state-run ETRI (Electronics and Telecommunications Research Institute) says they developed a transparent, oxide transistor and using this, a very stable light modulator that enhanced the aperture ratio of a AMOLEDs.

Samsung Transparent AMOLED

ETRI said it developed the new oxide transistor by using atomic layer deposition process that greatly enhances operational stability and showed excellent electronic and optical qualities. This will mean faster production of such displays.