Chances are you’re familiar with HDTV. Most of us have one of these in our living rooms. In fact, according to a recent study, more than 80% of US residents probably have at least one HDTV in their homes. And there’s a good possibility these sets are LCDs. They may be a few years old but they’re thin, look great hanging on the wall and basically do their job well. Some of these HDTVs also have 3D capabilities but the required glasses have long been lost to the couch cushions or the dog ate them or they just never made it out of the packaging due to lack of content support by broadcasters.

Quantum-dot enhancement film (QDEF) is designed to replace the diffuser in an LCD backlight unit (BLU) and is placed between the BLU and the LCM. The QDEF contains red- and greenemitting quantum dots that are tuned to each display system and is illuminated by blue LEDs in the BLU. In the above image, a sheet of QDEF (right) can be seen converting some of the blue light emitted by a blue BLU (left) into white.
If you’ve heard of Ultra HD TV (or UHD) at all, you probably know that UHD means a big increase in resolution. Just like the jump to HDTV, UHD promises to show us a lot more pixels — four times more pixels in fact. What you may not know is that UHD brings with it a number of other improvements in image quality that may get consumers excited about TV again.

Technology has changed tremendously since we first started broadcasting HD in the late 90’s. It’s now possible for content creators to capture not just higher resolution but more colorful, dynamic and lifelike images than ever before with powerful production tools. At the same time, new display technologies like quantum dots make it possible to actually see everything that these cameras can capture.

This sounds great, you’re probably thinking, but how does the UHD experience really compare to the HD set in my living room today? Will I be able to see the difference or is this just the next 3D?

UHD Experience

Let’s take a look at UHD’s top three image quality features — resolution, color and dynamic range — to get a sense of how they compare to HD.

Resolution is probably the most talked about new UHD feature and just about all UHD sets will ship with a super-sharp resolution of 3840 by 2160 pixels. That’s four times the resolution of today’s 1920 by 1080 HDTVs. It’s a big improvement, but it’s actually not the most noticeable feature of UHD. This is because HDTV was already close to the limit of what the average human eye can resolve from a distance of nine feet away (the distance most of us sit from our TVs).

Color is a different story. The standard for today’s HDTV color broadcast was set in the early 90’s, around the time that cellphones were brick-sized, and it was designed to work within the limited capabilities of the CRT computer monitors of the day. As a result, HDTVs can only display about one third of the range of colors our eye can detect. So there’s a lot of room for improvement in color. UHD sets with wide color gamut will deliver about 5,000 times more color information to consumers in terms of both a wider range of colors and more accuracy. The difference is striking.

The size of a quantum dot determines its wavelength and therefore its color output. Dots of different sizes are seen here emitting light from cyan (500nm) to deep red (640nm).
Finally there’s High Dynamic Range (or HDR). You’ve probably heard that a good “black level,” a measure of just how inky-black a TV can make a black pixel, is important to look for when choosing a new TV. This is because black level translates directly to contrast ratio — the deeper the black, the better the contrast, the richer and more lifelike the image, especially in darker scenes.

You can think of HDR like contrast ratio on steroids. HDR TVs push the dynamic range in both directions with deeper blacks and brighter whites. Most HDR UHD sets will deliver about 1,000 nits of brightness, which is roughly two and a half times brighter than the average HDTV. Sounds almost painfully bright but the idea here isn’t to blast users into snow blindness with full white screens at full brightness. Having extra brightness headroom available can add tremendous depth and realism to the kinds of tough-to-capture scenes that used to make cinematographers lose sleep. Think super bright stars popping out against a black sky or a bright candle in a dimly lit room or sunlight glinting off of a suit of armor.

Display Technology

The UHD experience sounds awesome but how will we deliver it to consumers in a cost effective way? Can the venerable LCD technology platform that worked so well for HD step up and deliver UHD or do we need to look to totally new approaches like OLED?

LCDs have faced a practical limit in terms of color performance, at best reaching about 50% of the UHD color standard, because of the white LED light source used in most LCD backlights. While LCD makers have experimented with other wide gamut backlight technologies, such as discrete RGB LED and cold cathode fluorescent (CCFL), all have proven too costly, too power hungry, or too bulky to be viable. It has seemed that high brightness, portability and wide gamut color performance simply could not be had in the same LCD package at the same time.

Although emerging technologies, like OLED, continue to promise great things for the future, the technology has yet to capture a large share of the overall display market. LCD remains the standard in nearly all display product categories and with good reason. With over a decade of explosive growth in manufacturing capacity by LCD makers, and over $180 billion in capex in the ground, the cost of LCDs of all sizes is tough to beat for upstart technologies like OLED.

It’s not all about cost though. LCD has also been able to match or surpass just about every feature advantage that new technologies have offered. Advancements like local dimming, in-plane switching and in-cell touch respectively brought great contrast, improved viewing angle and reduced thickness to LCDs. Outside of marketing hype, there has not yet been a strong enough case for the industry to move beyond LCD.

Exploded view diagram of an LCD display showing how Quantum Dot Enhancement Film can be dropped-in to replace the existing diffuser film.
A new class of phosphor material called quantum dots is changing the equation for LCD makers. First developed in the 1980’s at Bell Labs, quantum dots have the unique ability to efficiently emit light at a single spectral peak with narrow line width creating highly saturated colors. In addition, the emission wavelength can be tuned continuously based on the size of the quantum dots. This capability enables display designers to custom engineer a spectrum of light to maximize the efficiency, brightness, and color performance of their display.

Quantum Dots

Quantum dots are tiny man-made crystals. They are so small that you can’t see them with a typical microscope. In fact, they’re 10,000 times narrower than a human hair. That’s incredibly small and it’s their size that gives them the unique ability to convert light into nearly any color in the visible spectrum with very high efficiency.

Each quantum dot is actually a tiny semiconductor, which means it can convert incoming energy. The electronic characteristics of quantum dots are determined by their size and shape. This means we can control the color of light given off by a quantum dot just by changing its size. Bigger dots emit longer wavelengths like red, while smaller dots emit shorter wavelengths like green. Think of a guitar string. When a guitar string is shortened, it produces a higher pitch and when it is lengthened, it creates a lower pitch. The tune of a quantum dot — the wavelength of the light it emits — behaves in a similar way.

Quantum dots’ ability to precisely convert and tune a spectrum of light makes them ideal for LCD displays. From smartphones to tablets to TVs, we can make all the colors we see even better by remixing white light into red, green and blue components. Until now, the white light that LCDs have had to work with wasn’t very good; it contained a lot of blue and yellow but not very much red or green. This meant displays had to waste a lot of energy to make enough red and green for a bright display while also making for broad primary colors. Using the size-dependent emission prosperities of quantum dots, it is now possible to design an ideal spectrum of white light for an LCD, one that contains only the red, green and blue that the display needs to make a great image. The precise spectrum created by the dots makes colors pure. And since we’re only making the colors the display needs we can use less power. The result is a display that’s brighter, more power efficient and incredibly vibrant.

Getting QDs Into Displays

Quantum dots are an exciting technology, but that is not enough to drive adoption in the display industry. Manufacturers are not willing to risk altering processes they have invested billions in to try a new, novel technology. If quantum dots are going to have an impact in the display industry, they need to be packaged into a process-ready system that is compatible with existing, standard LCD manufacturing processes. Nanosys has done this in creating its Quantum Dot Enhancement Film (QDEF) product.

Designed to replace, although with significantly more functionality, an existing film in LCD backlights called the diffuser, QDEF combines trillions of red and green emitting quantum dots in a thin sheet that emits finely tuned white light when stimulated by blue light. Each sheet of QDEF is comprised of three layers, consisting of two plastic barrier films sandwiching a layer of quantum dots that are suspended in a polymer matrix.

The result is a simple, ready-to-use product that manufacturers can directly integrate into existing processes. By adding QDEF, they can immediately begin producing LCD panels with color and efficiency performance beyond even the best OLEDs, without making any changes to processes they have invested billions in.

Conclusion

The combination of resolution, color and dynamic range offered by the UHD experience is much more than another incremental improvement in image quality.

Quantum dots are playing a key role in enabling UHD adoption with a cost-effective, process-ready, proven and power efficient solution that can bring the full UHD experience to all of the screens in our lives, from the smallest mobile devices to the biggest TVs. As a result, UHD is already taking off, with shipments of UHD TVs growing an amazing 633% in the last year to over 12 million units.

Seeing is believing of course so I’d recommend taking a test drive at your favorite local electronics store. I think you will find that, for the first time in quite a while, the differences between the TVs consumers have in their living rooms and the new sets at their local retailer is dramatic.

This article was written by Jeff Yurek, Corporate Communications Manager, Nanosys (Milpitas, CA). For more information, contact Mr. Yurek at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit http://info.hotims.com/55595-201 .


Photonics Tech Briefs Magazine

This article first appeared in the November, 2015 issue of Photonics Tech Briefs Magazine.

Read more articles from this issue here.

Read more articles from the archives here.