Quantum dots are semiconductor materials. When designed for displays, they accept blue LED light and re-emit in the green or red range. The size of the quantum dot determines the peak wavelengths and the distribution of sizes determines the Full Width Half Maximum (FWHM or the ‘peakiness’ of the output).quantum dots by wavelength 2

To learn more, we had a conversation with new CEO Mustafa Ozgen. He recently joined after working with Sigma Designs where he was quite active in the development of the new Vizio 65” reference TV which offers Dolby Vision HDR and a quantum dot solution from competitor 3M.

The Vizio set features a direct-lit backlight, which many prefer for the best HDR solution because of the 2D dimming capabilities. Ozgen acknowledged this but noted that edge-lit TVs can offer HDR as well. In fact, that is one of the messages they are communicating to their TV customers – you don’t have to change your tooling to make your current WCG edge-lit TV HDR capable. Yes, it requires an upgrade to the main board and HDMI connectivity to decode and process the HDR signals, but quantum dots already offer the wide color gamut for the HDR content.

QD Vision offers an optic that contains their red and green quantum dots. This is placed between the bank of blue LEDs and the lightguide for edge-lit displays. If the TV maker’s electronics will support it, they can also create 8-16 1D zones to improve contrast and color volume.

Ozgen sees TV makers moving to a differentiated strategy when it comes to the choice of QD implementation. For the top of the line, direct-lit film-based quantum dots will be used, especially for HDR-capable sets. But the film-based solution is expensive and he is not sure it can migrate down the TV line. That’s where the QD optic solution comes in. It allows wide color gamut and HDR in edge-lit TVs that are more mainstream and affordable.

“Many TV makers, especially in China, have spent years making their TVs slimmer while reducing the bezel. They recognize that direct-lit has its place, but they – and many consumers – like the thin styling, which is why the QD optic solution will be popular,” said Ozgen.

QDVisionTubesQDVision uses tubes alongside an edge-lit LCD.Announced QD Vision customers include HiSense, TCL, TPV/Philips and TPV/AOC. He expects additional customer announcements after the Chinese New Year when the sets go into mass production. “We already see this differentiated strategy in play at Hisense and we expect TCL, Sharp and others to follow suite”

We also asked about the Cadmium-based vs. Cadmium-free debate roiling the industry. “Cadmium-free quantum dots will be needed in the US, Europe and Japan because of regulations and environmental sensitivity, but we not seeing the same level of concern in the domestic China market,” noted Ozgen. “But these makers are concerned about the European market. Currently the Cd-based quantum dots are exempt but that policy will be reviewed. We and 3M/Nanosys have prepared some documentation to support this review which looks at the spectrum and efficiency of Cd-free vs. Cd-based QD solutions. We can’t release this data yet, but it supports the claim that InP (Cd-free) does not have as large a color gamut as CdSe and it is less efficient. This is important when considering how display makers will get to a full 2020 color gamut.”

Ozgen noted that QD Vision has worked on InP QDs as well, but slowed developments down to focus on commercializing CdSe QDs first. He also told us that Samsung’s Nanocrystal QD technology is based on InP. But he then surprised us by saying that not all of the Nanocrystal-branded SUDTVs actually use the QD technology. “Our understanding is that only 20-30% use QDs and the rest offer a narrow color filter solution,” claimed Ozgen. Samsung does not publish any data on the color volume of its SUHD TVs.

Ozgen realizes that they will need a direct-lit solution and they are working on approaches. One is a film-based solution they hope to bring to market in Q2’16, but they need to solve the same pricing issues that 3M is facing first. The technology was demonstrated at SID behind closed doors.

One might also imagine a hybrid solution that places a QD film over a blue LED. That would be more cost effective as you don’t need as much film material, but there are packaging concerns as the LED would need to be thicker to add some separation between the LED and QD film (to manage thermal loading).

The long term play is on-chip quantum dots that are part of the LED solution the way phosphors are packaged today. That requires stability in a high flux environment – something no one has solved yet – to offer a commercial product. “Part of the new funding will go in this direction,” said Ozgen. “We think commercial displays using such an approach are about 3 years away.”

We also asked what he thought about the competitive LED-phosphor solution for wide color gamut. “The phosphor-based solutions can’t achieve as wide a color volume as QDs and they have a long decay time. Any displays that have 120 or higher refresh rates will experience some image sticking issues and smaller color volumes, so phosphors may not be best for premium products,” commented Ozgen.

However, the phosphor approach got a big boost last May with the announcement by GE Global Research that it had developed a new red phosphor solution called potassium fluorosilicate doped with manganese (PFS or KFS). It has a very narrow 10nm FWHM and GE says they have licensed the technology to Sharp and Nichia for commercialization.

Ozgen says he is not sure if LEDs using PSF have reached mass production, but one commentator on the AVS Forum web site claims to have measured the spectrum on the Sony Triluminous X850B WCG display and it looks like it includes the PSF red boost.

While quantum dots seem to be the best choice today for a wide color gamut display, other options continue to emerge including hybrid solutions that mix QD, phosphors, LEDs and maybe even lasers to create unique illumination architectures. This field should only get more interesting going forward.