Electrophoretic display technology is one of the prime examples of electronic paper technologies applied for the development of a particular type of electronic display that mimics the appearance of ordinary ink on paper.
E Ink Corporation has popularised the application of electrophoretic display technology with the introduction of electronic ink. The company has partnered with several consumer electronics manufacturers such as Sony and Motorola to develop devices equipped with electronic ink displays.
The Motorola F3 was the first mobile phone to use electronic ink display form E Ink Corporation. Other products that featured the display technology include the e-readers such as Amazon Kindle and Kobo eReader Touch and smartwatches from Pebble Technology.
Commercial and industrial applications of electrophoretic display include electronic display for retailers, electronic signage for outdoor advertising, and other devices used in the field of medicine and engineering.
What is electrophoresis? How does electrophoretic display works?
Note that the word “electrophoretic” came from the Greek words “elektron” that pertains to charge or attractive properties and “phoresis” that means migration or movement. In a more technical definition, electrophoresis is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field.
Electrophoresis is actually a technique used in laboratories. Researchers from the fields of genetics and molecular biology use electrophoresis for DNA and RNA analysis. The technique involves separating macromolecules based on size by applying a negative charge so molecules move toward a positive charge. This same process applies in electrophoretic display technology.
For a more simplistic description, electrophoretic display works by moving negatively and positively charged pigment particles by applying a positive or negative electric field. Switching between the positive and negative electric field results in varied movement and placement of the negatively and positively charged pigment particles.
E Ink Corporation further describes their electronic ink technology as a type of display made of millions of tiny and transparent microcapsules—measuring about the diameter of a human hair. Each microcapsule represents a pixel and each contains a positively charged white pigment particle and a negatively charged black pigment particle.
Upon the application of positive or negative electric, corresponding particles move to the top of the microcapsule where they become visible to the user. This makes the surface appear white or black at that spot. Note that E Ink Corporation has also developed a three-pigment ink system to for coloured electronic ink display.
In other words, an electrophoretic display or electronic ink display forms images by rearranging charged pigment particles with an applied electric field. Despite its novelty, this display technology has several advantages and disadvantages.
Advantages of electrophoretic display and electronic ink display
1. Low power consumption: One of the advantages of electrophoretic display and electronic ink display is that it consumes less power. Note that this display technology is a bistable display. This means that the image on an electrophoretic display screen is retained even when all power sources are removed. The display is only consuming power whenever the displayed image changes.
This low power consumption makes electrophoretic display and electronic ink display makes suitable for electronic readers and for second displays in smartphones or other consumer electronic devices.
2. Reflective display: An electrophoretic display or electronic ink display is a type of a reflective display. Take note that liquid crystal display technologies such as in-plane switching or IPS technology and most twisted nematic or TN display screens are emissive display. They require a backlight or internal light source to make the displayed image brighter to the users.
There is no need for a backlight in electrophoretic display or electronic ink display. Ambient light from the environment is reflected from the surface of the display back to the eyes of the users. The more ambient the light, the brighter the display looks.
An advantage of reflective display is that they do not strain the eyes of the users compared to LCD display technologies. Another advantage is that the absence of backlighting means that the device using an electrophoretic display or electronic ink display consumes less power.
3. Same readability as print: Another advantage of electrophoretic display and electronic ink display is that the images produced are similar with printed materials such as newspapers. This is because these displays use the same pigment or ink commonly used in print media.
This print-like readability makes this display technology popular in electronic readers. Because of this print-like readability, the result is a more natural reading or viewing experience that are less straining to the eyes.
4. Same LCD monitor resolution: Current electrophoretic displays can support a pixel density of 170 pixels per inch. This is similar to most LCD monitors. However, compared to LCD, electrophoretic display and electronic paper display have better readability in direct sunlight. It also has wider viewing angles than standard LCD monitors—especially TN displays.
This display can become the future of computer display monitors nonetheless. It can also become a standard display technology for other electronic devices such as smartphones and tablet computers.
5. Thin and flexible displays: The components of electrophoretic or electronic ink display can be made thin and flexible due to advancements in the technology behind polymer transistors.
Factoring in low power consumption and print-like readability, electrophoretic display technology can be used for the development of bendable displays and other novel consumer electronic applications such as a smartphone with curved screens or a tablet computer that can be rolled or folded.
Disadvantages of electrophoretic display and electronic ink display
1. Very low refresh rate: A notable disadvantage of electrophoretic display and electronic ink display is that it has very low refresh rate when compared to LCD IPS technology and AMOLED display technology. This is also true for other electronic paper display technologies.
A low refresh rate is disadvantageous because it prevents manufacturers for using this display technology in electronic devices that have high degree of user interactivity. Note that user interactivity is high in devices such as smartphones and tablet computers.
2. Ghosting effect: Electrophoretic display and electronic ink display are prone to ghosting effect. A shadow of an image may be visible after refreshing parts of the screen. This ghosting effect is due to the low refresh rate and the fact that the display technology works by moving charged pigment particles. Some particles end up stuck in the visible surface of a microcapsule.
3. High market competition: Another disadvantage of electrophoretic display and electronic ink display is that it competes with existing display technologies that have become industry standards. Note that IPS displays and AMOLED displays have become very popular in smartphones and tablet computers, as well as in large screens such as televisions and computer monitors.
Advancements in IPS and AMOLED display technologies have addressed issues concerning power consumption or energy efficiency, display longevity, and pixel density capacity, among others.
4. Still needs backlighting: One of the advantages of reflective displays is their reliance on ambient light. This means less power consumption form backlighting. However, this advantage can also be a disadvantage for electrophoretic display and electronic ink display.
Devices that use this display technology still need some light source such as backlighting in order to be usable when in the dark. Note that some electronic readers are actually unreadable when in the dark—just like books or newspapers.