macrabbit

Intro

(July 2008) Just a few weeks ago, I heard for the first time the word "Zero-power LCD". As - in general - power consumption gets more and more an issue, I was interested to learn what it is all about. So, I started to dive into the bits and bytes of display technology. Let's start with the basics first: there are basically three different types of display technologies today.

  • transmissive
  • You have some kind of static backlight and each pixel can be turned on or off to let the light shine through or not. Example: TFT LCD, DLP (Beamer)
  • emissive
  • Each pixel can be seen as a very small light bulb that can be turned on or off. The pixel itself emits light. Example: OLED, CRT
  • reflective
  • There is no active light source involved as in the previous two. Instead the pixels are turned on or off and the ambient light is reflected accordingly. Example: see below

As normal paper is a reflective media too, the reflective display technology is called "electronic paper" or "ePaper". As ePaper only depends on ambient light and has no own light source, it obvioulsy needs less power than the transmissive or emissive technologies. On the other hand, if it's dark, you can't read ePaper... Today, four different kind of ePaper exist: EPD, ChLCD, IMOD and Electro wetting.

EPD

Electrophoretic Display, sometimes wrongly called "ePaper Display". Put white particles (e.g titanium dioxide, 1 micrometer) in a black dyed oil. Place this mixture between two parallel plates of glass. If you apply an electric field across the plates, the white particles move due to the effect of electrophoresis. By reversing the sign of the electric field you can move the white particles up and down.

The two companies "E Ink Corporation" and "SiPix" invented modifications to this basic principle to be able to offer flexible, rollable ePaper. E Ink put the mixture (dyed oil with white particles) in microcapsules (40 micrometer) and put those capsules between two layers of plastic film. SiPix emboss small microcups (100 micrometer) on a plastic surface, fills those cups with the mixture and seals it with a second plastic layer.

E Ink produces at PVI, SiPix produces at CMO. All commercial eReaders today use EPDs.

ChLCD

Bi-stable cholesteric nematic LCD, sometimes also called "BCD". The main promoters are ZBD and Nemoptics (BiNem). Mainly used for electronic shelf labels (ESL) in retail stores. Varitronix produces them.

IMOD

Interferometic modulation. Qualcomm's "mirasol" is based on this technology.

Electro wetting

Electro wetting is the latest approach in ePaper. Originally invented by Philips, it's now promoted by Liquavista (a Philips spin-off). First commercial display to be expected in 2008. Color displays in 2009.