Nanosys Sheds Light On Next-Gen Quantum Dot Displays
Jason Hartlove, Nanosys CEO
Samsung in association with partner Nanosys from Milpitas, Calif. is looking to reshape our image of television using nano-scale particles, called quantum dots, to produce new ranges of color and brightness.
Recently, Samsung revealed it has been working in association with Nanosys to develop what it expects to be the new future of television display technologies called QLED. This technology is essentially a hybrid between Samsung’s SUHD Quantum Dot 4K Ultra HD HDR LED LCD TVs and OLED technology, now marketed by LG Electronics and others.
With the new approach, pioneered by Samsung and Nanosys, quantum dots will be applied to a self-emissive inorganic LED light source to produce QLED displays that are brighter, more efficient and more color accurate than LED and OLED TVs. In addition, Samsung is working on technologies for ink-jet like printing of these quantum dot substances to help reduce production costs.
Nanosys is also working on a new quantum dot film technology due next year called Hyperion, which will enable LED TVs to reach 90 percent of the very wide color gamut Rec. 2020 standard.
Samsung recently brought HD Guru and a group of technology reviewers out to the Nanosys manufacturing operations in Milpitas to meet Jason Hartlove, Nanosys president and CEO, to find out more about what’s going on with his company’s approach to quantum dots and the Samsung/Nanosys plans for new technologies like QLED just ahead of us.
Read our Q&A report with Hartlove after the jump:
What is Nanosys’ mission?
Hartlove: We make the quantum dots here at our facility in Milpitas, CA, and we polymerize them into what we call a quantum dot ink. That ink is then used to make a component, in this case an optical film. Those optical films are then integrated into video displays.
We were founded out of the leading research institutes doing work into quantum dots back in the eighties and early nineties. Those include MIT, U.C. Berkeley, Harvard and others. We exclusively end licensed their technology to our company in 1999. On the basis of that, and after hiring some of their students, we began our program in quantum dots. In 2008 and 2009, we were at a point where we understood the technology well enough that we could begin a commercialization effort.
I came on board and we began to look at areas where these technologies could be well deployed. They are characteristic of very narrow band emitters with very tuneable condition spectra with very high efficiency that made them an ideal light source for RGB displays. These need to be very pure red, green and blue colors in order to have both high efficiency and high color gamut.
We started to target that area and we were very fortunate to become very close with Samsung. I was very fortunate to have been able to do a lot of business with Samsung earlier in my career, and they saw a lot of promise in the technology. In the 2009-2010 time frame Samsung became a key collaborator with us for the development and commercialization of the technology, and they also became our largest strategic investor. The first commercial product we came out with was a tablet in 2013. Samsung introduced the technology officially this year under the name Quantum Dots, although it was first introduced in its SUHD TV products under the nomenclature of “nano crystals,” in 2015.
What are quantum dots?
Hartlove: Quantum Dots are perfectly tiny nano crystals formed from semiconductor materials. We looked at a periodic table and found indium phosphide to be one material set that has a photo electric property. This makes it ideal for forming photo-electric devices, like solar cells or LEDs. Bulk indium phosphide has a certain photo-electric characteristic to make an indium phosphide LED actually emit Red and just Red at somewhere around 620 nanometers. To generate the other colors Green and Blue, is where quantum confinement comes in. That’s what these devices are. They are very small quantum physics devices that actually confine the electron whole pair below normal emission. We are talking about particles that are 60 million times smaller than a tennis ball and just 2 to 10 nanometers in diameter. There are billions of billions of these things that go into a quantum dot television. The number of semiconductor emitting particles in a television is something like 10 to the 22nd power. At that size of matter different things start to happen and happen at the larger scale of matter and that is what the phenomenon of quantum technology is all about.
If you take the exact same thing and keep pushing it down smaller and smaller and smaller what happens to it? In this particular case you get quantum confinement. But other interesting things happen at nano scale as well. We can make use of this by selectively making the dots in our manufacturing process at the sizes that are relevant to what we want to do with the emission barriers. By making the quantum dots made out of indium phosphide material smaller than the bulk characteristic – where the bulk characteristic starts to change – we can actually begin to get an excitation event.
When a blue photon (from an LED) strikes one of these particles, the total distance of the effective Bohr rating that the electron can travel is actually physically confined. It can’t go farther than the size of the crystal. Then it starts to bleed off that excess energy and it does it in a very rapid period of time. You get recombination but now it is recombining at a lower level of energy. The tighter we confine it, the more energy burns off. So by making very tiny crystals out of the same bulk material we can vary the emission characteristic continuously through the spectrum: blue, light blue, turquoise all the way up to the red. The other thing is that we can make these crystals to be a very reproducible process, whereby they are all almost virtually perfect, which means the efficiency of that conversion is also extraordinarily high.
So for every one blue photon that comes in with relatively high energy we’ll get a lower energy photon coming out depending on the size. So that’s what we call the quantum yield of these particles. If we get one blue photon in and one red photon out it’s 100 percent quantum yield. In our particular case our quantum yield is typically between 90 and 100 percent. That means the conversion efficiency is very, very high. So we have blue light coming from a source, it is converted with very high efficiency into the color that we care about, with the specific wavelength that we care about, and we are basically making the perfect white light source—that RGB source—by combining these particles together.
In display technology almost everything is red, green and blue. There are different color standards, Adobe RGB of course is one that is used principally for reproduction purposes for things like magazines in print. sRGB, or REC. 709, is the HD broadcast standard. REC. 2020 is a new and emerging standard, and DCI P3, which is out today and is used for the content which Hollywood is making. Hollywood sends their content to digital theaters for playback on projectors calibrated for DCI P3.
If something in the value chain is stretching that or making it somehow different, the content is not going to have the original artistic intent. It is going to look different, and of course people pay millions of dollars to make the content what it is, so, we want to try as faithfully as possible to reproduce that.
So what does that ideal primary system look like? Well, it doesn’t look anything like the primary system that you find with the white OLED system. White OLED is an interesting technology with two energy points, one in the blue and one in the yellow. When you go to make a red pixel, what you have to do is apply color filters to the red to try to filter out all of this other information. Where you really want the energy to be is in the green and red, where the primaries are for the DCI P3 color gamut, and that’s not where they are for white OLED. What you end up with is a very compromised appearance in those red and green colors.
They overcome this by including a white sub pixel to the red, green and blue elements. They turn that on to increase the overall brightness. But it does two things: it compromises the resolution because we no longer have as many red, green and blue sub pixels, and it also gives you a kind of weird looking light instead of the exact true light that you may want. So it adds brightness but it also corrupts the image. On the other hand, if we were to design the perfect spectra for matching what content needs, you would have blue primaries centered up around 455, 460 nanometers; we have a green primary centered around 430 nanometers and we have a red primary centered around 625 or 630 nanometers.
Now my color filter comes along and cuts off the green and the blue. By making component red and green from quantum dots they are specifically designed to emit this kind of a characteristic. And by illuminating using a blue LED light source we allow some of that light to come and get a perfect green and a perfect red.
How close are you to having Rec.2020 nano particles?
Hartlove: We have had a difficult time making a fully cadmium-free system, which meets the Rec. 2020 color gamut requirements. That’s because the blue and the green primaries for Rec. 2020 are very close together. So what we need to make Rec. 2020 is a much narrower green. For that nanosys has recently developed a hybrid system we call Hyperion, which is almost a cadmium-free material. Hyperion Quantum Dots mix cadmium-free red and cadmium-based green quantum dots into a single film.
Hyperion film meets the European Union’s Restriction on Hazardous Substances (RoHS) Directive without having to use an exemption, since the overall system is expected to have less than 100ppm of cadmium, which is considered to be below a toxic level. That means that a television will have less than a microgram of cadmium. Mass production is expected in early 2017 and it is able to meet Rec.2020 requirements. There are cadmium-based systems on the market today that use our quantum dots to achieve a color space that exceeds 90 percent of the Rec. 2020 color space. We offer whatever our customers want. We aim to be the very best quantum dot material company in the entire world.
What makes the Nanosys technology superior to other quantum dot television solutions in the market today?
Hartlove: Many of the competing quantum dot televisions today have very high concentrations of cadmium. There is no cadmium-free product or Hyperion-type product that they offer. From an environmental perspective and from a regulatory perspective, products containing higher than 100ppm of cadmium are allowed under (European) RoHS regulations under something called Exemption 39, which basically says that at the time that the RoHS rules were written there was not a suitable alternative to the cadmium technology. That exemption is due to expire in the spring of 2017. So, if that exemption is no longer permitted everyone will be required to have a solution that is cadmium free. Cadmium-based televisions are still legal for sale in the United States. The RoHS regulations are for Europe, but generally speaking the United States and even China do follow them within a few years’ time. From a manufacturers’ perspective, people don’t usually like to have specialized products for different markets. They like to be able to make the same product for all regions, at least on the panel level and then do whatever localization needs to be done to the power supply and things like that.
How is the development of QLED technology progressing?
Hartlove: We can basically charge a quantum dot by hitting it with a blue photon that absorbs that photonic energy because it has that peak effect for creating an emission. To explain the background, quantum dots have been used in research to make, for example, photo voltaic solar cells, so you can have a photon come in, excite the particle and instead of having it re-emit another particle in a different wavelength, you steal the charge coming off the quantum dot. And by doing that you basically create a photo voltaic.
QLED uses a similar process. It is essentially a different way of using the quantum dots, basically the same concept as PV, but in this case we inject the electron whole-pair heat into the quantum dot and then heat emits light.
This is a thin-film device. It’s basically all-solution printed. This is something which QLEDs offer out the door, which OLEDs have struggled to get to for a long, long time. The display is emissive in basically the same way as an OLED device.
In concept you have an electron donor and a whole-donor layer, and you have an emitting layer of material in between. You inject a charge into the emitting layer and the emitting layer will in turn create your emitting photons. Conceptually, it is a very interesting idea. If you can solution print this you have something really compelling compared to the way we make LEDs today, which use a very expensive reactor.
We make very tiny bits of LED material that is solution printed over a very large area. But so far all of the OLED technology that’s commercially available has been unable to make use of this solution printing capability. All of QLED development that is going on is solution based. There is no evaporative process. You don’t need an LCD panel any longer. This becomes your blue back light.
This technology is three to five years out from being commercially available. The efficiencies of blue emitting material today are within striking distance of the efficiencies of blue OLED material. But the lifetime is still short relative to blue OLED material, which as you probably know, is short relative to the red and green OLED emitting material. We are working with our partners to try and further improve the lifetime on our solution-based QLED material, and then based on our progress we see this happening on a three-to-five-year time horizon.
Samsung was also quoted at the recent quantum dot conference that they see it coming to market in 2019.
What is the advantage of QLED technology?
Hartlove: The advantage of QLED is that instead of using the white OLED material, for example, we can use a blue OLED back light and then in front of that blue light we can put selectively patterned red and green quantum dots. So now we have all of the efficiency advantage and no color filter in the system. You can actually get rid of the color filter. The color filter on every sub pixel throws away two thirds of the light energy that’s coming from the back light. The filter comes off of the sub pixel level but the quantum dot technology is delivering red, green and blue light. Today’s OLED approach is very lossy. But if we can have a blue light source, pixelate it, and in front of it have either no conversion layer or red quantum dots then the whole system efficiency would increase mathematically by a factor of 2.8 over a system using color filters.
Are there any differences in conversion efficiency between the larger nano particles and the smaller ones?
Hartlove: They are all very close. The challenging aspect of making three nano crystals is that one of the material systems that has been around for quite a long time to make quantum dots is a compound semiconductor called cadmium selenide. Cadmium is a very hazardous substance, so people generally don’t like to use this material in their sets. Samsung has taken the position that they won’t use any in their sets. So we needed to work with them to develop a cadmium-free quantum dot. This is why we have moved to an indium phosphide material system. Getting those high efficiencies out of those indium phosphide materials is what we’ve spent a great deal of time on. This is the only product on the market today with this high efficiency indium phosphide material in it.
Why start with a blue back light instead of starting with a red or green light?
Hartlove: What quantum dots can do is down covert energy. So a blue photon has a very high amount of energy. A green photon has less energy than a blue photon and a red photon has less than a green photon. We can’t make energy, but UV light has a lot of energy. We do the math and calculate what the given wavelength of light is. What we see is that UV light has very, very high energy, and infrared light has relatively low energy levels. So we want to take high energy materials for high energy wavelengths of light and down covert them. You can’t take the green and up convert it. Today, the one highest efficiency materials in terms of conversion efficiency is gallium nitride, which is blue, and it is also very cheap and readily available.
On the blue LEDs, are there variations in terms of frequency of the individual LEDs or are they consistent?
The LED industry has gotten very good and the outlet efficiency is generally within a small range. So there is not what we would call any binning required any longer. Now we have a process that has been approved by the industry so there is less binning required. The eye is not uber sensitive to variations in blue wavelength. If you have a wavelength at 455 or 457 it pretty much looks the same because the eye’s spectral sensitivity is very low. On the other hand, if you have just one nanometer difference in green you see it immediately because the high spectral sensitivity to green is very high.
Is the film on which the quantum dots are placed sealed?
Hartlove: The film is not sealed. The film is a sandwich, like an Oreo sandwich. You have two layers of plastic on either side and in between you have a layer of quantum dots embedded in a polymer. There is no edge seal around this. Then there is a UV cure. That plastic is a very special plastic that we call a barrier-coated plastic. Garden variety plastic is not going to have the ability to last over the length of time of a television set. But it’s not an extraordinarily expensive material.
Because of their small size, nanocrystals can be toxic, so we made a decision early on that these materials should never be free in their nano state. So these materials are always bound into other systems such as polymers for example and other materials, so you can never actually separate these materials into their nano phase. Even in the synthetic process they are never in their nano phase. They are always in a liquid phase so they are always in some other material. This is to eliminate any concern about possible inhalation or exposure to skin, etc.
How do you apply this to zones in edge-lit LEDs versus full-array back light?
Hartlove: They are exactly the same. The film is in front of the light guide plate so diagrammatically in an edge-lit system the LEDs lie along one edge, there’s a plastic light-guide plate which has various different extraction features so that you can see the blue light coming out is relatively uniform even though it is all being emitted from the lower edge of the screen. Different extraction features are extracting the light as it comes out.
In the case of a direct back light system it is a very similar configuration except the LEDs are in an array directly behind this. What that allows is to use local dimming so they can selectively turn off LEDs in zones where there is no data content or where the brightness should be much lower in the frame. They do this on a frame by frame basis.
By Greg Tarr
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