By: Barry Young

Barry Young — Thu, 16 Dec 2010 22:24:38 +0000

You are to be commended for trying to deal with such a difficult subject. Most of what you write is reasonable, but I have a few comments:
1. The low temperature of LTPS does not refer to an actual temperature, it is a relative term addressing the difference between using a laser and using annealing — rapid thermal annealing (RTA), which operates at very high temperatures (>600 degrees C. LTPS operates at temperatures comparable to a-Si processing 300 to 400 degrees C. Therefore LTPS is “too hot” for use directly with flexible backplanes. Manufacturers, such as Samsung make the active matrix on glass and then use a lift-off process to take it off the glass and put it on the flexible material.
2. OLEDs have a number of benefits vs. LCDs, other than the darkest blacks; they switch ~1000 times faster; contrast ratio is not reduced when looking at the display off axis as with LCDs, yes even with IPS the contrast ratio declines as the off axis increases, they are thinner, and actually trace the gamma curve more accurately. Power consumption depends on the image and in most cases OLEDs use less power than LCDs, especially for video applications.
3. Passive matrix and active matrix designs are addressed by sub-pixel not by pixel for color displays.
4. OLEDs are challenged in bright sunlight as are LCDs. because they have a cathode layer which reflects light. The more reflective the greater the interference. When a touch capability is added external to the display, there is a gap between the display and the touch material, which causes greater reflectivity. By eliminating the external touch and integrating it into the display, there is no gap. Ambient light reflection is also reduced by minimizing the reflectivity of the cathode material and by running the display at a high brightness. These are all issues of design, not fabrication.
5. OLEDs have excellent color reproduction and the display designer can select what level they want to achieve. Most choose to use highly saturated colors greater than the NTSC standards, which the reviewers choose to assess negatively. The color saturation has nothing to do with the Pentile approach, which produces colors and lines consistent with the standards
6. Display makers have several ways to improve the viewing angles and IPS is just one method. In IPS, the liquid crystal is positioned horizontally, instead of vertically and one of the conductors is patterned on the color filter instead of the active matrix. However, IPS monitors are not 3X the price of other designs, they are competitively priced.
7. The term retina display is a marketing definition and is beginning to mean greater than 300 ppi.

Comments on: IPS vs AMOLED vs SLCD – smartphone displays explained

By: Barry Young