Understanding Pixel Defects; How Pixel Defects Occur - HP 455031-L22 - Intel Quad-Core Xeon 2.13 GHz Processor Upgrade Introduction Manual

The advent of thin-film transistor (TFT) technology allowed transistors to be placed at
each picture element or sub-pixel. These can switch very quickly, and then hold the
state of the sub-pixel while the panel drivers take care of the other rows and
columns of the display. This results in a great improvement in the contrast and
response time possible with LCD technology, and permits the manufacture of large-
size, high-resolution displays which rival any other display technology in
performance.
Figure 1. How thin-film transistors are placed in the LCD array.

Understanding pixel defects

Active-matrix TFT-LCDs require at least one transistor to be created at each subpixel
on the panel. This makes the average AMLCD an enormously complex device. For
example, producing one of today's high-resolution WUXGA displays. with a 1920
x 1200 pixel native format requires embedding nearly seven million transistors in
the screen (1920 x 1200 x 3 = 6.91 million). This is more than double the number
of transistors found in the original Intel® Pentium® processor.

How pixel defects occur

Damage to any one of the millions of transistors within the LCD panel may leave a
sub-pixel permanently on or off, creating a tiny dark spot or bright spot on the
display. This is fairly common, even for small TFT displays on handheld computers.
Minute specks of dust on the panel, slight errors in the panel processing, and other
problems encountered during manufacturing of the TFT array on the glass substrate
cause these defects. When we look at the total number of pixels and subpixels on a
1920 x 1200 display, we see that the failure of one sub-pixel out of the 6.91
million is a very low failure rate indeed—only about 14 millionths of one percent
(0.000014%). For lower-resolution SXGA displays, a single sub-pixel defect still
represents a failure rate of only 25 millionths of one percent.
To look at it another way, having 10 sub-pixel defects on a 1280 x 1024 color
panel means that the panel is still 99.9999% defect free!
Electrodes across
LC material
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