E-paper displays explained
We so often eulogise about the limitless possibilities e-paper displays enable and the exciting opportunities the technology creates for market growth, differentiation and competitive advantage — but for the uninitiated reader, we thought it might be helpful in this blog to take a step back and look at how e-paper works.
E-paper goes by many names and spellings — electronic paper, ePaper, electronic ink, e ink, electrophoretic displays, EPD — but all these terms effectively describe the same thing: an electrically-charged surface that replicates the look and experience of ink on paper.
Instead of a traditional display that uses backlighting to illuminate pixels, e-paper is based on the science of “electrophoresis” — i.e. the movement of electrically charged molecules in an electric field.
In every e-paper display there are millions of tiny microcapsules containing (negatively charged) black and (positively charged) white pigments suspended in a clear fluid. This encapsulated ‘ink’ is then printed onto a plastic film and laminated on to a layer of circuitry, or — to be even more specific — a transistor matrix layer. The circuitry forms a pattern of pixels that is then controlled by a display driver (EPD controller).
When a negative electric field is applied to the ‘ink’, the white particles move to the top of the capsule making the surface appear white at that specific spot. Reverse this process and the black particles appear at the top making the surface of the capsule appear dark. The technology can also work in colour in just the same way but using a combination of different colour pigments and electric charges, or just by adding a colour filter on top of the display.
The way e-paper works differs from traditional displays in two key ways:
- E-paper screens are reflective — light from the environment is reflected from the surface of the e-paper display towards the user’s eyes, just like with traditional paper. This gives e-paper a wide viewing angle that is readable in direct sunlight.
- E-paper screens are bi-stable — unlike conventional backlit flat panel LCD displays, which refresh about 30 times per second and require a constant power supply to maintain content, e-paper displays will hold a static image ‘forever’, even without electricity. E-paper only consumes power when the content on it changes – for example if an e-paper shelf label in a supermarket is updated with a new price. The rest of the time the display will simply show the content you want it to, where it doesn’t draw any power until the next update.
Making e-paper flexible
Here at Plastic Logic Germany, we took e-paper one stage further and successfully industrialised a process to create glass-free backplanes, which represents the transistor matrix layer mentioned above. We are the first company worldwide able to manufacture transistor arrays on plastic. Instead of using traditional silicon transistors, our active-matrix backplane consists of organic thin film transistors (OTFTs) made from the same plastic used to for cola bottles (PET). This means we can couple a flexible backplane with a flexible display medium, such as flexible OLED or flexible electrophoretic layer, to create a fully flexible display with limitless possibilities. In addition to the flexibility, our glass-free electrophoretic displays also more robust, shatterproof and lightweight compared to glass-based displays.
If you want to know more about flexible plastic e-paper display technology’s suitability for a given use case and to get some inspiration via the applications which are already successfully showcasing the opportunities and rewards achievable through flexible e-paper innovation check out our latest flexible e-paper whitepaper.