Materials and Manufacturing Panel

August 6, 2013, Emerging Display Technologies Conference, San Jose, CA-Charles Annis from NPD DisplaySearch moderated a panel on materials and manufacturing. Panelists were Jeff Yurek from Nanosys, Margaret Hines from Nanoco Technologies, and Conor Madigan from Kateeva.

Yurek noted that the NTSC broadcast color gamut is only 35 percent of possible colors in the human visible range. In fact, the natural range of colors is larger than the broadcast standard as noted by Pointer. Even some standard colors are outside the broadcast standard, and the broadcast colors are unable to equal the cinematic range.

One way to improve the color balance is to use white LEDs and color filters to add more color in areas where the LED is weak. Problems include color overlap, intensity peaks, and mismatched intensities. Quantum dots absorb short wavelength light and emit longer wavelengths. Emission wavelength is determined by the size of the dot, with larger dots giving longer wavelengths.

Because the dots are narrow band, the color distribution is much better than that possible with color filters. The mixtures of dot sizes can balance the intensities of the various colors with good color separation. The colors can be tuned with different sized dots allowing for a range of color temperatures and color distributions.

These quantum dots are integrated into a film, distributed by 3M, that has high efficiency, allowing for reduced LED counts, lower costs, and simpler assemblies compared to white LEDs and color filters. The film is 20 percent more efficient than transmissive filters in the sRGB, and 50 percent more efficient at Adobe 1998. in a demonstration in a Sony 4k TV, film was brighter and had a wider viewing angle than edge optics. The integrated film reduced the light stack and improved uniformity. The Nanosys Quantum Dot technology is the only current quantum dot nanotechnology that is manufacturing at the level of kTons per year vs grams/kgrams per year.

Hines commented that their basic technology is also quantum dot, but they do not use any Cd in the dots. The dots can be tuned and emit lower wavelengths as a function of size. The materials are organic and can be formulated as a resin. These resins are integrated into other forms for applications into final display products.

One use model is to provide red, green, and blue light for TV backlights. In comparison to white CCFL, the dots are significantly more efficient, since over 90 percent of the white light is wasted. Blue LEDs with YAG phosphors don’t have enough red and green intensity, and increasing the LED output increases waste and accelerates burn-out.

The outputs can achieve up to 92 percent of the NTSC color triangle, better than the other direct light alternatives. The dots are integrated into films for TV backlights, and the color emissions can be altered in manufacturing by changing the quality of dots for particular colors.

The materials use molecular cluster compounds to nucleate nano-particle growth. Although they don’t have Cd in their dots, they use Zn, In, and P in some of their dots. The process is a low-temperature process that uses readily-available precursors. Size control for absorption and emission allows for narrow distributions of the dots in manufacturing. The manufacturing facilities currently produce about 25 kG a year, and high volume production of 4,000 kG per year are scheduled for next year.

Other applications include production-level, color-tuned lighting, signage, and electroluminescent displays.

Madigan offered an alternative to LCD improvements, OLED. Although there are many issues to be resolved, OLED benefits from a simpler structure and processing. The issues of carrier mobility in amorphous silicon or low-temperature poly-silicon are overcome with oxide transistors.

The technology is ready to scale up to the gen-8 level at LG, which uses white OLEDs and color filters to get color spectrum. The front-plane color pattern layer deposition still needs development work to scale and improve yields. Once the yields reach volume levels, the costs will drop to be competitive with LCD.

The manufacturing process uses inkjet printing to achieve mura-free displays, and emitter lifetimes are approaching those of thermal evaporation. This foundational technology is moving into production with a very small nitrogen enclosure for low particle contamination and fast cycling. The application process has a wide production processing window, for a robust manufacturing flow.

Diffuser film versus collimated light?
Yurek answered that the dots use isotropic emission, so the film can recycle any light.
Hines agreed, but the changes in the film would require more development.

Film or inkjet?
Yurek noted that the process is not inkjet compatible, but can be used in a roll-to-roll process.
Hines commented that film is not as high resolution as inkjet.

Gen-8 purpose?
Madigan commented that the equipment can be scaled up to work in a gen-8 production line if the technology changes are successful.

NTSC gamut changes to get to consumer?
Yurek postulated that the changes to gamut will happen in the UHD 4k displays. These displays will be the drivers for new standards for wider gamut. Sony is already shipping wide gamut displays in their 4k models.
Hines was intrigued that Sony is using quantum dots, because this technology requires a high-level setup at the customer site.

Productivity versus vacuum evaporation, pixel edge definition?
Madigan claimed that their equipment runs with a 90 second path time compared with 3-4 minutes in a gen-5 fab. The resolution in 4k TV above 31 inches is about 120 PPI. Moving to the UHD format with a change in pixel design could resulting a 400 PPI display over time.

Market size in 3 years?
Yurek considered that quantum dots are a part of the larger LCD market. Other applications like general lighting are not seeing any activity at the production levels at this time.