About AMOLED for young and old

Everything you need to know about AMOLED.

First of all, what does this adjective known to us all cover? Its exact meaning is Active Matrix Organic Light Emmiting Diode, i.e. Active Matrix Organic Light Emitting Diode. Active Matrix refers to the operation and arrangement of pixels, and OLED refers to a very thin electrical display panel that, due to its design, does not require special backlighting, making it more energy efficient than its traditional design counterparts. Let’s go around this OLED thing a bit first!

Two types are known, the so-called. “Tiny molecule” and polymer OLED, the former having a longer lifespan, the latter being cheaper and more common. The OLED itself is basically nothing more than an LED, i.e. a light emitting diode. Based on its size, it can be between 100 and 500 nanometers, roughly 200 times smaller than the thickness of a human hair. Its working principle is to conduct current through two (sometimes three) thin film layers of organic - mostly carbon-based - semiconductors enclosed between a transparent anode and a cathode surface before it begins to illuminate. One of the two layers is the light emitting layer and the other facilitates the passage of electrons towards the anode. The third possible layer is also an electron transport film that facilitates the entry of electrons from the cathode.

Interestingly, in connection with the layers, it can be mentioned that a carbon-based semiconductor can be practically any material from sugar to wood to most plastics.

So the whole OLED misery is imagined as a creamy cake. The already mentioned light-emitting film layers form the “cream” in the middle of the “cookie” and on top of this is the metal or transparent plastic layer acting as a cathode (depending on the OLED display), from where the electrons start their journey. Under the "cream" is the transparent (mostly glass, plastic) anode, where the path of the electrons ends, and below it is the also transparent base layer, on which the whole "baking" is placed. This is therefore the OLED diode, the color of the light emitted by which depends on the type of polymer used. A pixel consists of three of these to display the three base colors (red-green-blue, RGB).
How does this become an active matrix display? Our pixels are organized into rows and columns to give the display, i.e. the matrix. Each pixel consists of OLED diodes, and each diode has its own transistor for switching on and off, so they can be controlled directly (actively), unlike traditional passive) displays.

The combined thickness of the AMOLED layers is considered minimal, the thinnest prototype is 50 microns thick, but a transparent and even soon to be rolled up version is commercially available.

The turn-on and turn-on response times for each pixel (pixel) are approximately three times as fast as the playback speed of a traditional movie, making these displays ideal for use in multimedia devices. It is worth noting here that due to the structure of the technology, each pixel appears black when switched off, i.e. the display of white text on a black background e.g. a QVGA display consumes 0,7 watts of power and 3 watts of black text on a white background.

The brightness of AMOLED displays is one and a half times that of traditional LCD displays, their contrast ratio is incomparably higher, they do not show color distortion, so at the same viewing angle, the displayed image can be read better.

In addition to the many advantages, the disadvantages can be attributed to the fact that organic materials lose their properties beyond a certain operating time (although this has largely been eliminated) and that readability deteriorates typically with an external light source (outdoors, in the sun) as OLED pixels are relatively they emit little light, averaging 200 nits, but the external light falling on them is strongly reflected back.

One of the pioneers of the technology is Samsung, which recently announced Super AMOLED displays. In practice, this means that instead of the previous solution (display + touchpad separately), the touch-sensitive layer is integrated into the display.

The thickness of this layer is only 0,001 mm and, as it is transparent, it does not degrade the image quality of the display, but it is much more sensitive to touch than its traditional counterparts and has a longer lifespan.