Chasing After Quantum Dots

In the 1980s, researchers stumbled upon a tiny particle or nanocrystal with unique electrical properties. These mysterious nanocrystals, which are based on semiconductor materials, were later named quantum dots.

Quantum dots were curiosity items until 2013, when Sony launched the world’s first LCD TV using these inorganic semiconductor nanocrystals. Basically, when inserted into an LCD TV, quantum dots can boost the color gamut in the display, enabling vivid picture quality with relatively little capital.

Based on 10nm to 2nm feature sizes, quantum dots are produced using a chemical process. The dots are bundled and sold in the form of glass tubes or films. They are tunable and can convert short-wavelength light into colors spanning the visible spectrum.

Quantum dots have created a buzz and prompted other LCD TV makers to jump on the bandwagon. And today, LG, Samsung and other OEMs are shipping a new wave of quantum dot TVs. In addition, quantum dots are also moving into other markets, such solid-state lighting and solar.

All told, quantum dots are fast becoming what could be the next Wild West in the electronics materials business. At last count, some 60 entities, including companies, R&D organizations and universities, are working on quantum dots, according to Touch Display Research.

In total, the quantum dot component market was a $75 million business in 2013, according to Touch Display Research. The firm forecasts that the quantum dot display and lighting component market will surpass $2 billion by 2016 and reach $10.6 billion by 2025.

“We are in the beginning of what we believe is a major industry for a new set of materials,” said Michael Edelman, chief executive of Nanoco, one of the larger players in the emerging quantum dot business.

“As quantum dot volumes and the capacities come on stream, you will see the technology work its way through the LCD industry in all sizes of screens, from 110 inches to your cell phones,” Edelman said. “In addition, we’ve already started sales in the lighting industry using quantum dots to enhance LED lightening. This is initially for niche applications, but eventually that could be rolled out across a lot of areas.”

Still, the technology faces some challenges to move beyond its current market, which is high-end LCD TVs. Most are shipping quantum dots based on cadmium, which is a II-VI material. There are environmental issues with cadmium, prompting the push for cadmium-free dots. Cadmium-free dots are less efficient, though.

And there are some cost and manufacturing challenges associated with quantum dots in general. “The cost is still too high,” said Max McDaniel, director and chief marketing officer for the Display Business Group at Applied Materials. “Quantum dots are also sensitive materials. The surface area to volume is high. They are easily oxidized. The smallest amount of ambient air or moisture can render them useless.”

The quantum landscape
By all accounts, the fledgling quantum dot industry is a dynamic field. It takes a scorecard to keep track of the vendors, business alliances and the technology.

Today there are three main merchant players in the quantum dot field—Nanoco, Nanosys and QD Vision. Other vendors include NanoPhotonica, Merck KGaA and Quantum Materials.

TV makers from China have been the early adopters for quantum dots. But the industry received a huge boost earlier this year when TV market leader Samsung endorsed the technology and rolled out its SUHD line of high-end LCD TVs.

To boost the picture quality, Samsung’s SUHD LCD TVs incorporate two separate technologies—4K and quantum dots. 4K, or ultra-high definition (UHD), has four times the resolution of today’s high-definition LCD TVs. In addition, the SUHD line also includes cadmium-free quantum dots, based on the technology licensed from Nanosys. “(The SUHD TVs) set a new industry standard for the best picture quality available today,” said Dave Das, senior vice president of Samsung Electronics America.

Samsung’s SUHD LCD TVs are significant for other reasons. Over the years, Samsung and others have invested millions of dollars to develop TVs based on a rival high-end technology called OLED. To date, OLED is used for small-screen displays, but the technology has barely made a dent in the large-screen TV market. OLED TVs are difficult to make and require complex processes in a fab. In contrast, OEMs can use their existing LCD fabs and equipment to produce quantum dot TVs.

As a result, some OEMs are moving away from OLED TVs and backing quantum dots. So in effect, quantum dots extend and breathe new life into the LCD TV market. “Quantum dots allow OEMs to produce high-end, 4K color-enhanced TVs,” Nanoco’s Edelman said. “They go head-to-head with OLED TVs in terms of color performance, but are only a fraction of the cost.”

On the technology front, meanwhile, OEMs face some tough choices. Each quantum dot vendor offers a different technology with some complex, if not confusing, trade-offs.

For example, the quantum dots are generally spherical, but they also come in rod-like shapes as well as tetrapod configurations with short and long arms. “The shape difference gives rise to slightly different optical and electronic properties that makes each of them useful in certain applications,” said Jesse Manders, director of materials development at NanoPhotonica.

But making quantum dots is difficult. Producing them in high volumes without variability is one issue. “Tailoring the quantum dot ink formulation to meet the requirements of the manufacturing equipment without losing the high efficiency or color purity (is another challenge),” Manders said.

Meanwhile, there are two types of quantum dot technologies—photoluminescent (PL) and electroluminescent (EL). Today, the industry is shipping PL-based quantum dots for LCD TVs and other applications. EL-based quantum dots are still in R&D.

“In PL mode, you are using light to excite the quantum dot, which then absorbs that light and re-emits it at a different color. This process is called down conversion,” said John Ho, product marketing manager for QD Vision. “EL mode is where you are introducing electrical current into the quantum dots to excite them.”

From there, PL-based quantum dots are bundled and sold in two forms—glass tubes or films. QD Vision sells quantum dots in a glass tube. Most vendors sell them in the form of a sheet or film.

“We don’t sell our quantum dots in its raw form. We realized early on that customers don’t really know what to do with it because it’s a new type of material,” Ho said. “We are making a glass tube. The glass tube is hermetically sealed with quantum dots.”

Using either tubes or films, quantum dots solve a problem with today’s LCD TVs. In an LCD TV, an LED backlight projects light through the display layers. These layers include the glass, polarizers, thin-film transistors, liquid crystals and color filters.

The big problem is the LED backlight. “Traditionally, people use white LEDs, which are actually blue LEDs with gallium nitride and a yellow phosphor or a YAG phosphor. The problem with that is the phosphor is spectrally broad,” Ho said. “What you get coming out of the backlight is white light that’s going through the glass panel. But the white light isn’t very pure. The filter, which consists of a red, green and blue dye, is supposed to cut out sections of the spectrum to make a blue, green and red channel. But in fact, most color filters don’t do a great job. There’s a lot of leakage between the blue, green and red channels.”

To solve the problem, quantum dots in one form or another are inserted into the LCD TV. “What we do is take the GaN LEDs. Instead of putting the yellow phosphor on top, we remove that phosphor and put a tube in front of those LEDs on the edge. We fill that tube with a combination of red and green quantum dots,” Ho said. “What happens is the blue light will get emitted from the LEDs. Before it goes into that guide-light plate, it will hit this tube. The red and green quantum dots in that tube will absorb that high energy blue light and it will re-emit it with nearly 100% efficiency.”

While QD Vision’s tube technology is making inroads, the film-based approach is also gaining steam. In the film approach, quantum dots are dispersed on a sheet. The sheet fits within the display layers of the LCD TV. “It’s a drop-in solution for manufacturers,” said Steve Reinhard, vice president of business development for Nanoco.

Nanoco itself is taking the film-based approach. To lower the cost and bring the technology into the mainstream, Nanoco last year signed a manufacturing deal with Dow Chemical. Today, Dow Chemical is ramping up the world’s largest quantum dot manufacturing plant, which is based in Korea.

In addition, Nanoco, LG, Samsung and others are also making a concerted effort to push cadmium-free dots, and for good reason. The European Union has a directive that limits the amount of cadmium in electronic equipment.

The problem? “Cadmium-free dots are not as efficient as a cadmium-type quantum dot,” said Jennifer Colegrove, chief executive of Touch Display Research.

To solve the problem, Nanoco has developed a proprietary molecular seeding technology. With the process, Nanoco has narrowed the performance gap between cadmium and cadmium-free dots.

Other approaches
Even so, there are still some issues with quantum dots. “Besides cost, they can’t handle the heat,” said Art Lamstein, director of marketing at Quantum Materials, a supplier of tetrapod quantum dots.

Heat and moisture tend to degrade the performance of quantum dots. Hoping to solve the heat issues, Quantum Materials recently introduced cadmium-free quantum dots with heat resistances up to 260 degrees Celsius.

To reduce the costs, Quantum Materials has developed an automated process using micro-reactors. In contrast, some vendors use a manual batch process, which produces a small amount of quantum dots per cycle. “Most of the industry does not have the ability to form full-shape quantum dots. The reason is that they use a batch process,” Lamstein said. “Our process delivers over 95% full-shape quantum dots, especially full-shape tetrapod quantum dots, which are four-armed quantum dots.”