Qualcomm Mirasol – A Revolution in Display Technology?

. Tuesday, May 27, 2008

Is it a miracle of technology or a marketing trick – Time will show but, darn the specs sound so good:
The basic promise is:

  • Near zero power consumption, in line with E-Paper
  • Much Faster response time than LCD (slower than OLED thou)
  • Doesn’t need backlight in most conditions
  • Doesn’t suffer from poor viewability in direct sunlight
  • Unlike E-Paper, Mirasol Displays have full color natively, without use of multilayered filters
  • Doesn’t suffer from short life span and low manufacturing yields (vs OLED)
  • Resolution is on par with LCD and Oled
  • Thickness is on par with thinnest screens.

So, How it Works?

Without going into too much detail, the idea is very similar to DLP, based on MEMS technology, but instead of tiny moving mirrors reflecting strong light from projection Bulb,
Mirasol (or as Qualcomm (QCOM) calls it IMOD - Interferometric MODulator) reflect ambient light thru micro sized thin-film both off the top of the thin-film stack and off the reflective membrane.

“Depending on the height of the optical cavity, light of certain wavelengths reflecting off the membrane will be slightly out of phase with the light reflecting off the thin-film structure.
Based on the phase difference, some wavelengths will constructively interfere, while others will destructively interfere as shown in Figure 1.

As illustrated, the red wavelengths have a phase difference which leads to constructive interference, while the green and blue wavelengths have a phase difference which leads to destructive interference.
As a result, the human eye will perceive a red color, as certain wavelengths will be amplified with respect to others.
Color generation via interference is much more efficient in its use of light compared to traditional color filters and polarizers, which work on the principle of absorption and waste much of the light entering the display.”

Figure 1. IMOD Structure Showing Light Reflecting off the Thin-film Stack and Mirror Interfering to Produce Color.

The image on a mirasol display can switch between color and black by changing the membrane state.
This is accomplished by applying a voltage to the thin-film stack, which is electrically conducting and is protected by an insulating layer.
When a voltage is applied, electrostatic forces cause the membrane to collapse.
The change in the optical cavity now results in constructive interference at ultraviolet wavelengths, which are not visible to the human eye. Hence, the image on the screen appears black.
A full-color display is assembled by spatially ordering IMOD elements reflecting in the red, green and blue wavelengths as shown in Figure 1.

The Core of a mirasol Display by Qualcomm

Figure 2. Basic Structure of an IMOD Pixel

Figure 2 illustrates the basic structure of an IMOD pixel. The pixel consists of a glass substrate which is coated with thin films.
Beneath the glass is a reflective conductive membrane which is separated from the glass by a thin air gap.
When a voltage is applied to the membrane and the thin films on the glass, the membrane experiences electrostatic attraction and is drawn towards the glass.
This state is called the collapsed state and the pixel appears black as the light entering is shifted to the UV spectrum.
The application of a lower voltage level returns the membrane to the original position, called the open state. In this state the pixel appears bright and colored.
This color is generated by interference of light, a process which is much more efficient than using color filters.

Qualcomm mentions the screens are ready for production in existing Flat Panel Makers fab, but always limits possible applications to mobile devices and in whole sub 10” displays market.
Why?? It’s so great why not use in laptops or even big screen TVs?? My guess it’s ever too expensive to size scale it or technologically not yet doable.
And second Question – How about view angles – I didn’t noticed any solid numbers in marketing materials which leads to believe it’s a possible issue.
Like I said time will show it’ll shine or be quickly forgotten, but darn it looks so promising!

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