Two of the main bottlenecks of these OLED based display are the resolution, and the
second bottleneck is degradation of this display,
or this brightness of the display with time.
So the resolution of these OLED based displays are limited because we
use this process of fine metal mask which is a fancy name for.
Using shadow
mask to deposit these RGB layers in since
these are deposited using RGB mask,
or they are and also they are you know, in a semi solid phase, you.
Can't really place these RGB pixel very close to each other.
And typically they are separated by, you know, a distance of 15 micron or so.
And that limits your resolution of these OLED
based displays to less than 300 pixel per inch.
And more typically, what you get is around 200 to 250 pixel per inch.
And that's, you know, inferior to what you get in a LCD based display.
Another you know, bottleneck of these display is
that the quality of the display, or the brightness
of the display degrades over time. So the
luminescence it falls like this for a green
pixel. And it degrades even more for a red pixel.
So the red pixel degrades more than a green pixel.
A blue pixel is even worse, it's the worst.
So the blue pixel, you know, the luminescence will degrade even
faster if you, sorry, it will degrade
even even faster if you pass a lot of current through it.
So to improve both of these bottlenecks, a lot of
ideas which are being worked on in the labs to improve the
resolution, people are looking at you know non shadow mask based techniques.
Such as laser induced thermal transfer. ink jet printing and what not.
at the same time, to you know, to improve the degradation
or, you know, to reduce this degradation, people are looking at newer kind of
organic molecules. Which overcome this degradation bottleneck
But these are thing, which are you know, currently in the research stage.
So, what I want to emphasize in this video is
that how people have been able to get around these bottlenecks.
So as you can, you already know these displays are currently shipping.
And they won't be shipping if the, luminance degrades, very rapidly.
At the same
time, they won't be shipping unless you
achieve this, 300, pixel per inch resolution.
So.
How do people have been able to get around some of these bottlenecks?
And there has been very clever engineering & very clever
techniques that people have applied to overcome these bottlenecks, and you
can witness these techniques in action.
If you take a closer look at any of these displays.
So what I highly recommend you to do is take your smartphone, so if you have
an iPhone, and you take it and you know, take it under
a microscope and just look at the pixel So you'll see that if it's a LCD-based
display that is used in your iPhone, you'll see these regular matrix
of these RGB pixel very much like that
you know, what you expect that you have each of these RGB pixel
equal in size and they make one of these individual pixel.
If you open up if you take a closer look at a
Samsung phone, it, there's a large probability that it would look something
like this. So a Samsung phone, a Galaxy
S3, it it uses OLED based display and there's a
large probability that if you take a look at it, it would look something like this.
So you'll see that you have first of all, smaller green
pixels, then you see that you have much larger density of green pixels.
If you take a look over here You will see that you have these,
alternate, columns. And, you have twice the number of,
green pixel as compared to what you have, for your red and your, blue pixels .
And this is a very, clever design. And there's a name for it.
It's, called a PenTile, design. Or a PenTile, technology.
It's operated by this, company, nouvoyance which
is now owned by Samsung, located in the Bay Area.
So in a traditional RGB display you
essentially have these RGB pixels and.
For, to make a pair of these RGB columns, you require six of these individual
columns, one for each R, G and B. So, what this
pen tile based technology does is that, instead of having
these RGB layers alternate, you have these green columns which alternate.
And then in between you have these blue and
red pixels, so you have these red and blue pixels.
And now they have
now, to get two of these rows of pixels, you now only need four of these columns.
So now you need four of these columns
instead of having six of thse columns over here.
So, now you can place these columns more closer each other.
So and, still have a higher density of these columns.
And each of thse RGB these, these four things
over here, they make a one pixel. And you can see here, I have
twice the number of green pixel as compared to what you have for your red
and you blue. And this leverages
on the fact that our, this PenTile based technology,
it It leverages on the fact that our eye,
our human eye has a much higher responsivity to a green signal.
So they make more number of green pixels, which
you can turn on and off individually, so It
meets the sensitivity
requirement of our eye, which is more responsive for green.
Your blue and your red pixels, our eye
has you know, less response, is less responsive to
these blue and red colors.
So you have less of those pixels, and at the same time, you know,
you have higher density of green pixels, so when you report the numbers for
these resolution, you can report that you have more than 300 pixel per
inch, but that would really be counting the number of, green pixels that you have.
Many time people insert this white pixel also so you have this red green blue.
But you insert this white pixel also and that helps in, improving the over all.
overall brightness of this display.
in either case the point I want to emphasize is that instead
of having these three columns for these of for each of these
three lines for each of these columns, you now have these two lines, so
you get higher density of these lines in a given area
and that helps in increasing your resolution and you're leveraging
this fact that your eye is more responsive to
green. So that's that's currently used
as you know, as a get
around for this resolution problem of your OLED display.
Another way cool technique which is used to design this pixel,
is that we, your blue color, your blue OLED, or your
blue organic layer degrades the most, also it degrades very fast
if you expose it to even a little amount of water.
So, why do, in, instead of having a traditional design where you have equal
size of your R and your G and your Blue pixel?
there's this company called Ignis, a Canadian company.
What they have come up with is a new cell design where you have your green
green degrades less, that is your smallest pixel,
your red which degrades more is, you know, a slightly bigger pixel.
And then your blue which degrades the most is your biggest pixel.
So what you do is you reduce the current density through
your red and blue pixel if you use a design like this.
So even though you pass the same amount of current,
since your blue is now you know, three times bigger
than your green or your red is twice
bigger as compared to your green, you reduce
the amount, of, current density and that, helps
then reducing the degradation of these individual cells.
So there is also technology that is being, that is
being adopted by some of the OLED manufactures and these are.
These are a workaround 'til you actually figure
out some more concrete solutions to these
problems or these bottlenecks with OLED displays.