Because the entire display stack can be screen printed on a flexible plastic substrate, the 100 to 200µm-thin displays can be produced cheaply, either on a sheet-to-sheet process for small-scale and rapid prototype manufacturing or via a roll-to-roll process for large volumes.
Unlike electrophoretic displays based on e-Ink, which are truly bistable, rdot’s displays are semi-stable, based on reversible redox reactions responsible for the colour changes of the electrochromic materials. After a while, the turn-on colour fades away until a short voltage pulse is applied to turn the segment to maximum contrast again. But since rdot are using proprietary material recipes and printing processes, the company is able to tune a display’s bi-stability period from minutes to days for custom applications.
In the process, it can make its displays faster switching (being less stable) or slower for very low update rate applications, so can it customize the display’s colours, shapes and transparency.
But lacking of true bi-stability, how can such a display compete with incumbent ePaper solutions such as those provided by E Ink? eeNews Europe candidly asked rdot’s CEO Felix Karlsson.
After all, using segmented cells, every display becomes a custom solution requiring Non-Recurring Engineering (NRE) fees, wouldn’t it be simpler to use full active matrix ePaper instead?
One competitive advantage Karlsson is keen to emphasize is lower cost. “Because we do everything in a few printing steps, the manufacturing cost is certainly lower than any E Ink solutions. They need an active matrix backplane, which we don’t, and this adds to the costs. Our solution is ITO-free, environmentally friendly and can be made with 100% organic materials” said Karlsson.
Now tackling NRE costs, the CEO noted that even with an active matrix, you still need to customize your displays. Often, the NRE costs for designing a custom solution with E Ink are way above those for customizing rdot’s segmented displays, Karlsson said referring to customers who approached rdot to find alternative solutions for their wearables and accessory designs.
On power consumption, Karlsson doesn’t want to generalize as every application has specific requirements and refresh rates that directly impact power consumption.
“We can tune the bi-stability time, so we can design a display that only requires to be refreshed every two hours, or more frequently, according to the application needs” explained the CEO. According to the company’s own calculations and comparing its solution to different display technologies, if a display requires over 6 updates per day or more, then the electrochromic display is the most energy efficient.
“We gave a few samples to global display manufacturers so they could carry out their own tests and measurements, and they reported that starting with two updates per day, our solution was more energy efficient than E Ink. That is because each E Ink switch will require up to twenty times more energy than our solution, depending on the E Ink used”, said Karlsson.
When they start to fade-out, rdot’s displays only need a very small 3V refresh pulse to remain active. According to the company’s technical documentation, a 21 (3×7) segments display (capable of displaying three digits) with a total segment area of 2.1cm2 only draws 1.26mJ of energy to switch all its elements at a 3V driving voltage. With such low power capabilities, the startup expects its displays to open up new types of applications, including for disposable medical electronics, such as smart patches. But they could also reach into other kinds of disposable/consumable products that typically have not included electronics or displays before, such as packaging and labels.
Together with research institute RISE Acreo in Norrköping Sweden, Rdot is also developing an entirely printed passive matrix version of its display, using organic transparent conductors which it hopes to have ready by the middle of 2019. As a first development step, rdot will use the matrix to drive segmented displays, to reduce the number of driving pins required at the microcontroller (which typically adds costs). Then the startup wants to address the paper-thin displays at pixel level.
It could be a few years before rdot’s displays reach the consumer market though, the company’s products are in a qualification phase, with samples being tested by various partners. Founded in 2016, the company has managed to fund itself through grants, EU programs and government support. “We’ve closed quite some good deals with joint-development partners and we’ll try to avoid having to raise capital if we don’t need to, to favour an organic growth” Karlsson said discussing the company’s finances. “We may need some capital in a year or so to scale up our company, but we want to be more established before and find our right market. The startup also wants to collaborate with other printed and flexible electronics companies to design full flexible products.
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