IMOD technology

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Overview of Portable Display Technologies
Ink and paper are arguably the de facto standard for information display. Developed over 5,000
years ago, today’s inks and dyes provide lifelike color imagery. Display technologies, on the
other hand, are relatively new. The CRT was developed less than 100 years ago and the
increasingly popular flat-panel display less than 40 years ago. For roughly a decade now,
engineers have been working to create a display technology capable of providing a paper-like
reading experience, not only with regards to superior viewability, but also with respect to cost,
power and ease of manufacture. Display technologies such as backlit LCDs, reflective LCDs,
electroluminescent (EL) displays, organic light-emitting diodes (OLED) and electrophoretic
displays (EPD) were all steps in this direction. mirasol displays, based on industry-proven
MEMS technology, promise to take the quest for paper-like displays to a new level.


Emissive/Transmissive Displays
Displays are classified as one of three types: emissive/transmissive, reflective or transflective.
A transmissive LCD consists of two transmissive substrates between which the liquid-crystal
material resides. By placing a backlight underneath one of the substrates and by applying a
voltage to the liquid-crystal material the light reaching the observer can be modulated so as to
make the display pixel appear bright or dark. A display can also directly emit light, as in the
case of an OLED display, whose active display material emits light. In the case of an LCD, a
constant source of power is required to both modulate the liquid-crystal material and to power
the backlight. An LCD requires constant refreshing—at least sixty times per second—in order
to prevent the liquid-crystal material from transitioning to a different modulation state, resulting
in image degradation or flicker. Such is also the case with OLED and EPD—constant power
must be provided to the light-emitting materials in order to prevent screen flicker.

Reflective Displays (Continuous refresh type)
In a reflective display, one of the substrates found in a transmissive display is replaced with a
reflective substrate. Reflective displays usually employ liquid-crystal material on top of the
reflective substrate so as to modulate the ambient light reflecting off the reflective substrate.
Since there is no backlight in reflective displays, they consume substantially less power than
emissive displays. However, since the material providing modulation is liquid-crystal, the
majority of these types of displays must constantly be refreshed or the displayed image will be
lost. So far, most portable devices employing reflective displays are the continuous refresh
type.