E-ink and the IoT

E-ink has the potential for delivering wireless color screens on IoT devices that consume little power.

Despite being conceived in the 1970s, e-ink only received wide recognition after the introduction of the Amazon Kindle in 2007. Other manufacturers had used the technology, but none had the practical elegance and reach of Amazon. Though e-ink’s use in the Kindle was revolutionary, Amazon’s flagship e-reader was just the beginning for e-paper. The technology remains mostly confined to simple devices, but it’s about to have a breakout moment.

E Ink is made into a film and then integrated into electronic displays. It provides a display with images so tactile they are synonymous with paper and power consumption levels low enough to allow devices to run for days.

Consumer-oriented screens and displays still demands ever-more full-color, hi-rez pixels, but uses for e-ink are often quite different. While e-ink might not provide the same experience as the latest smartphone or laptop, its technology is progressing quickly. The potential applications for e-ink are seemingly limitless.

E-paper – A brief history

Electrophoretic, or e, ink makes use of reflected light to show images in a way analogous to LCD technology. E ink employs tiny capsules called microcapsules each about the diameter of a human hair. The simplest microcapsules contain black and white particles

In a simple electrophoretic display, 1-µm-diameter titanium dioxide particles are dispersed in a hydrocarbon oil along with a dark-colored dye and charging agents that cause the particles to take on an electric charge. This mixture resides between two parallel, conductive plates separated by a gap of 10 to 100 µm. A voltage applied across the two plates forces the particles migrate electrophoretically to the plate that bears the opposite charge from that on the particles. The rear electrode is divided into a number of small picture elements (pixels) to create a pattern of reflecting and absorbing regions.

in a clear fluid. The microcapsules are sandwiched between two sets of electrodes with the electrodes on top being transparent. When a positive or negative electric field is applied, corresponding particles move to the top of the microcapsules where they become visible to the viewer. This makes the surface appear white or black at that spot. The particles stay in their place when the electric field is removed. Reversing the electric field forces the particles to exchange places. Consequently, the display uses almost no energy while the particles are suspended. Energy use is minimal until the user moves to a new page.

Initially, E Ink technology could only show images and text in grayscale. Today, E Ink is able to produce color images via various means. For example, a technology called E Ink Spectra uses standard black and white particles along with particles of one other color residing in what’s called a microcup. Applying a positive, negative, or half-charge brings the black, white, or colored particles to the surface. Spectra is engineered specifically for Electronic Shelf Labels (ESL). Another technology called Advanced Color ePaper (E Ink ACeP) uses four colored particles (often magenta, cyan, yellow, and white) and manipulates charge profiles in ways that bring one of them to the top to create visible color.

E-Ink’s designs have been deployed in displays in some of the world’s most widely used mobile devices. Manufacturers such as Sony, Motorola, and Amazon all use the fundamental technology. However, a point to note is that E Ink displays will likely never respond as quickly as other display technologies such as those based on LEDs. The reason is E Ink employs particles that must physically move around in a microcapsule or microcup. It takes on the order of hundreds of milliseconds for the particles to move into position. So prime candidate applications for E Ink are those where update rates of several hundreds of milliseconds are acceptable.

The E-Ink pixel electrodes are driven with typical driving waveforms containing four stages: erasing the original image, resetting to the black state, clearing to the white state, and writing the new image. The voltages involved in driving E-ink display electrodes are compatible with commercial TFT backplanes, typically in the 15 to 20-V range. However, it’s generally unnecessary to provide a 15-V supply for the display because E-Ink controller ICs contain dc-dc converters that produce these levels from the 1.5 to 3 V supplying the controller chip.

EPD controllers can take the form of either special ICs or SoCs (System on Chips). But the processor sending data to the controller IC is ordinary; some development boards use simple Arduino processors to generate display data.

E-Ink origins

The concept of electronic paper can be traced back to companies such as Xerox in the 1970s. However, it was the E Ink Holdings Inc., an MIT spin-out, that released the world’s first commercial e-paper technology in 1997 and which still develops and manufactures most e-paper screens today.

The first iteration of E Ink’s tech was the Vizplex system debuting in May 2007. Since that time the company has continued to develop its e-paper products. These now include nascent technologies yet to see wide use such as the four-pigment ACeP displays.

Each of these innovations share a few common benefits, making them preferable to LCD or OLED and other technologies in certain applications. These benefits include unparalleled paper-like contrast with a wide viewing angle that’s readable in sunlight, low power consumption with an “always on” operating mode, and durability. Interestingly, these same qualities are behind many innovative IoT devices.

E-Ink and the IoT

Today, you’ll find e-ink displays in devices ranging from e-readers through smartwatches and smartphones. However, both color displays and touch-screens are at the bleeding edge of the e-ink industry. Both technologies are only beginning to provide the types of user experiences and interfaces that LCD, LED, and OLED displays now deliver. But e-paper really shines in IoT devices that don’t necessarily require high-performance multimedia.

display assemblies — The cross section of a typical LCD (from Orient Display) compared to that of Kaleido e-paper technology from E-Ink Holdings illustrates some of the differences in the two display technologies. E Ink Kaleido is comprised of a TFT backplane, ink layer, color filter layer and a protective sheet. The printing process alleviates the need for a glass-based color filter array. Putting the color filter array on plastic has made it possible to develop writing tablets with color highlighters, pens and markers.

For example, you’ll find e-ink in retail signage and public transport information displays. You may see it in healthcare facilities in hospital equipment. You might also find it in smart meters or employee badges. At the moment, these devices simply do not require the same sophisticated screens as smartphones and laptops.

In 2019, wireless power company Ossia Inc., Belgium energy harvesting provider e-peas, and E-Ink collaborated on a battery-free wirelessly charged e-paper display. The device is still in the prototype stage, but applications envisioned for it include electronic shelf labels for retailers, digital signage, logistics tags and distributed sensor networks.

Another point to note about e-ink displays is that they don’t bombard their viewers with blue light. Other advantages of battery-free e-paper displays are obvious. For example, retailers can eliminate the cabling to multimedia signage that provides touch-screen feedback to customers. E-ink public transport signs can be internet-connected to e-paper-enabled vehicles through GPS for real-time travel information. Machine or equipment operators will have instant access to detailed, full-color-multimedia 3D schematics or tutorial videos.

Somewhat surprisingly, even a few smartphones use e-ink displays. TV maker Hisense in China released the world’s first color e-ink display smartphones called the A5C, A5 Pro, A5 Pro CC, and the 5G-enabled A7 5G. The latest model comes with a 6.7-in standard black and white e-ink display with 300 ppi. The e-ink displays provide an experience different from that of a conventional smartphone, and the technology still has some way to go. (The 5G handset is available only in China. All the other Hisense phones are available in the U.S. for around $300.)

In January, E Ink and BLE chip supplier Atmosic Technologies announced a first-of-its-kind smartbadge reference design. The design features one of E Ink’s 2.9 or 3.7-in. black and white displays, or 4.1-in. Gallery Palette color displays. The kit utilizes Atmosic’s M series extreme low-power Bluetooth LE platform to make possible a multiyear battery life which can be extended via optional on-chip energy harvesting. The kit can be used in landscape or portrait mode, and under a typical eBadge use case of three image changes daily, a small CR2032 coin cell battery will last over three years. The low-power eBadge can also provide visual updates including a photo, location information, alert messages, and text messages.