This article is part of the TechXchange: Advanced Display Technology.
What you’ll learn:
- Popular applications for ePaper technology.
- How bistable properties make it ultra-low power.
- The difference between reflective ePaper and bright emissive displays.
ePaper is a display technology that’s designed to replicate the appearance of traditional printed paper. It employs reflective technology rather than emitting light like that of LED and OLED displays.
The basic construct of ePaper is that it uses countless tiny microcapsules packed with positively charged white particles and negatively charged black particles suspended in fluid, which act like pixels. When an electric field is applied to the microcapsules, the charged particles move to the top or bottom of the capsules, creating different shades of gray. That movement creates visible text or images on the display.
Like any technology, ePaper has its own share of myths. Timothy O’Malley from E Ink helps quell some of the more popular ones surrounding the technology.
1. ePaper is a recent innovation.
The idea for a low-power, reflective display has been around since the 1970s, but ePaper was brought to life in 1997 at the MIT Media Lab. The technology sprang into the global spotlight through the launch of the Amazon Kindle in 2007. There are currently more than 6,000 patents worldwide on the technology.
2. ePaper is mainly used in eReaders.
Most people immediately think of eReaders when they think of ePaper, and for a good reason. For over a decade, eReaders have been a popular consumer product, reaching over 100M people. This popularity stems from the natural paper-like experience. Also, reading on a paper-like display is up to 3X healthier than reading on an LCD-based device.
However, eReaders aren’t the most common use of ePaper displays, and odds are that you’ve been around many more of them than eReaders. The majority of ePaper displays are found in retail: electronic shelf labels (ESLs). Stores use ESLs as a sustainable, smart alternative to paper price tags. They automate pricing updates and can display discounts in real-time as the market demands.
Moreover, ePaper's compatibility with solar power systems and its low power consumption makes it an environmentally friendly display option compared to LCD screens and even paper. By using ePaper signage instead of traditional printed paper signs that are discarded after use, the reduction of CO2 emissions can amount to millions of tons.
Other popular uses for ePaper include eNote writing tablets, secondary monitors, and mobile phones. It goes beyond consumer devices, too. Tens of thousands of large-scale signs, including those used for wayfinding and bus and train arrivals in cities, as well as in professional environments like hospitals and offices, commonly use ePaper.
3. Are all reflective displays E Ink?
This is where things get sticky. E Ink is the trademarked name of the E Ink Corporation, the proprietor of ePaper technology and the company that spun out of the MIT Media Lab in 1997. So “E Ink,” “electronic ink,” and “ePaper” are all reflective displays.
4. A power source is always required.
Yes and no. Yes, a power source is needed for display updates. Also, no, as an ePaper display is bistable and will hold its image with no power attached. This property of bistability highlights one of the key differences between ePaper and LCD.
Because bistability means that ePaper only draws power during updates, long-lasting ePaper displays can frequently be found running on battery power or solar power in outdoor situations.
5. ePaper is slow and low-res.
The earliest iterations of ePaper illustrated the physics behind the technology: When an electric field is applied, the particles rearrange to form a new image. You can practically see the ink particles move.
Since then, the ink has become exponentially faster. Devices like the reMarkable, Kobo Elipsa, and the Amazon Kindle Scribe are on the cutting edge of ePaper. They’re high-res, high-def, and have faster refresh rates of up to 350 ms. These eNote applications also showcase the low-latency with fast-response writing that feels as natural as pen-on-paper.
6. Driving an ePaper display is difficult.
Driving an ePaper display is no more difficult than an LCD—it’s just a different driving scheme. There are dedicated drivers for ePaper, with waveforms specific to the material. Waveforms and driving instructions are provided with the module.
In comparison to driving an LCD, ePaper is more customizable based on the variable attributes that need to be emphasized in a particular application. For example, the developer of an eNote likely wants to prioritize speed for low-latency writing. An eReader also prioritizes speed for quick page turns. In contrast, the developer of a retail shelf tag likely trades speed for increased color saturation since prices only need to be updated a few times a day.
7. ePaper is only in black and white.
While the original ePaper was designed in black and white, the technology has evolved. There are now a variety of ways to get ePaper in color, including using a color filter or with a multi-particle system.
Multi-particle systems work similarly to the two-particle black and white system—they add a third (and sometimes fourth) pigment to increase color options. In a color-filter display, a printed color-filter array (CFA) is layered over black-and-white ePaper.
8. ePaper is fragile.
Though a technology built on individual liquid-filled microcapsules sounds like it would be fragile, its structure makes it incredibly rugged. Built on a flexible film, it lasts a long time. There are ePaper displays in products that have operated for more than 15 years and hundreds of thousands of display switches.
E Ink’s displays have comparable usage and storage specs than other display products. In some cases, it’s better. Leading destruction influencer JerryRigEverything even tried lighting an E Ink display on fire, and it still worked.
9. ePaper displays are made with glass.
ePaper is completely non-glass. As a flexible material, this is a critical attribute for developers integrating the display into a final product or laminating the film directly to a surface.
For example, segmented ePaper displays are 100% non-glass. Additional materials can enhance ePaper applications, like non-segmented displays. Also referenced as matrix displays, often found in eReaders and eNotes, they largely use thin-film transistors (or TFTs) that are on glass. However, plastic substrates for TFTs are available and integrated into products by partners like Sony and reMarkable.
10. ePaper displays take up a lot of space.
Most ePaper displays are less than 2 mm thick, and segmented ePaper displays are closer to 0.5 mm. Because of the lamination process, ePaper takes up much less space compared to LCD displays.
11. ePaper displays come in defined shapes and sizes.
ePaper technology is extremely customizable. The BMW i Vision Dee wrapped in E Ink is a great example. The “wrap” is actually hundreds of individual E Ink panels with custom laser cuts to align with the curves of the car.
The standard rectangle sizes that define ePaper displays are a result of efficiency. Take, for instance, the idea of a circular tablet. ePaper film shaped like a circle needs a custom circular TFT. And cutting a circle of glass means lots of wasted glass in the process, which leads to an increase in cost. With the possibilities of endless ePaper applications, standard sizes are a priority for optimizing material utilization.
Conclusion
ePaper has evolved and diversified over the years, dispelling many of the myths and limitations associated with the display technology. It provides unique advantages in terms of readability, power efficiency, and outdoor visibility, making it versatile display option for various applications.
Read more articles in the TechXchange: Advanced Display Technology.