Scientists and engineers have been developing the idea of using quantum dots for light sources and displays since the 1980s, but it has only been in the last few years that the adoption of this technology appears to be gathering pace.
A quantum dot, or a semiconductor nano-crystal, is a solid state semiconductor material with light emitting properties that can provide enhanced colour purity, depending on the dot’s size and its composition.
During the manufacturing process, these particles, which have a very narrow emission spectra, can have their wavelengths tuned to precise colours, by changing the size of the dots. It is possible for the particles to be manipulated to allow for the precise control of their electronic and fluorescent properties.
Conventional LCD backlights use white LEDs – in reality, blue LEDs with a yellow phosphor – the result being that the various components, the blues, greens and reds are either too strong or too weak.
While the talk around quantum dots has tended to focus on the enhanced colour performance they can provide for televisions, they have the potential to be used in a wider variety of applications; manufacturers are now talking about using quantum dots in computer monitors to deliver levels of colour saturation usually associated with organic light emitting diodes (OLEDs).
QD development
QD Vision, founded in 2004, is among a group of companies developing quantum dot technology for displays.
“Quantum dot technology is a much improved next generation alternative to LED and OLED displays,” says John Volkmann, chief marketing officer. “Since 2013, we have shipped more than 1million of our Color IQ optics and are partnering with a number of TV brands like Hisense and Philips. The Color IQ solution emits very pure, very saturated, narrow bandwidth red, green and blue light. I think we’ll start to see the technology being deployed in a wider variety of products.”
Ideally, the quantum dots should be placed directly on the LED, described as ‘on-chip’, but current materials don’t perform effectively at high temperatures, so need to be separate from the chip itself.
Two different TV set architectures exist and there are two competing quantum dot technologies.
The first of TV architecture is based on very thin TV sets which deploy LED edge lighting and it is this architecture at which QD is targeting its technology.
The other architecture is for thicker TV sets that come with direct backlighting. This architecture is, perhaps, better suited to the alternative approach that involves a film-based solution and which is being developed by companies such as Nanosys and Nanoco.
More expensive – ‘significantly more expensive’, according to Volkmann – these ‘films’ are not available, as yet, in the commercial market.
This approach, adding quantum dots as a film, involves offering a diffuser sheet loaded with quantum dots and because the sheet is part of a conventional backlight, display manufacturers do not have to change their designs.
It is, according to Nanosys – which has been working with 3M to develop the film – ‘a direct drop-in replacement’.
“Cost is the fundamental difference between these two different technologies,” suggests Volkmann. “While they are both capable of delivering improved colour performance when compared to existing LED technologies – and even when compared to emerging OLED technologies – the film based solution tends to be more expensive than edge lit solutions. That is down to the cost of the oxygen-barrier film and, as a result, not only is it a difficult technology to employ but we also think it is only suitable for high end monitors or TVs. Another problem is supply – only a handful of companies can make this type of film.”
HDR technology
Despite QD Vision’s focus on its edge-lit optic solution, the company is aware the fast moving consumer market may mean it has to shift its focus.
One driver is the rise of high dynamic range (HDR) TV technology. HDR is a photographic technique that produces brighter and more detailed images.
“The rise of HDR TV technology has been explosive,” suggests Volkmann, “and, in terms of the TV architecture, the backlit option is preferable. We may very well get into the film business if we start to see the market shifting and, over the past two years, the move to HDR has accelerated. But you have to bear in mind that it will only affect the very top end of the TV market.”
According to research from IHS/DisplaySearch, quantum dot backlight enhancement is expected to only take a limited share of the market in 2015, with only 1.3m TV sets expected to have been sold by the end of year. Sales are forecast to grow significantly though and are set to top 18.7m by 2018. Touch Display Research, meanwhile, expects quantum dot TVs to account for more than 50% of the market by 2025.
If these figures are accurate, the market could be support both competing technologies.
Dot manufacturing
The use of quantum dots to improve displays offers a simple solution but, aside from the costs associated with their use, there are issues with the manufacturing process.
Cadmium is currently the best material from which to produce them; it can be readily turned into nanoparticles which are, in turn, more easily controllable and manageable. Cadmium is, however, a heavy metal poison, making its use in consumer electronics problematic, even though the amounts needed are small.
In Europe, the element is banned under RoHS regulations and QD Vision and 3M are attempting to have the regulations amended.
Nanoco, however, uses indium, but display makers have been trying to remove indium from existing designs because the element is so rare and there are potential carcinogen issues with its use.
Dr Guillaume Chansin, a senior technology analyst with IDTechEx, said: “While this debate is much needed to fully assess the risks, there is no denying that it has also been damaging to the whole industry and the wider acceptance of the technology.”
As manufacturing methods improve, however, it may be possible to extend the range of elements that make suitable quantum dots.
Quantum dot technology is moving rapidly and while its entry into the market has been relatively slow, it is beginning to gain momentum.
As a disruptive technology, it could prove beneficial for both manufacturers and consumers.
One additional benefit could be that, as the quality of the images generated improves, the impact on content producers could also be significant. New media will need to be able to supply content that is capable of taking full advantage of the quantum dot revolution.
