Samsung Galaxy S and AMOLED

AMOLED touch screens are the latest innovation in smart phone technology and the four inch screen on the Samsung Galaxy S is one of the best examples of what can be achieved with this technology. Here we will take a look at how AMOLED screens work and see why they are so impressive when compared to alternative display technologies.

AMOLED stands for ‘Active Matrix Organic Light Emitting Diode’. The AM is the manner in which the pixels are controlled and the OLED describes the pixel technology. LEDs are very different from LCDs (Liquid Crystal Displays) in that LCDs act as filters that require an external light source, whilst LEDs generate their own light when they are stimulated by an electric current. For many years it had been possible to only fabricate LEDs from inorganic semiconductors such as silicon and gallium nitride, but although it was known that many organic materials and organometallic molecules could produce light when electrically stimulated, producing an efficient system was not possible until recent years.

Each pixel is controlled by two thin film transistors (TFTs) which inject a current to switch it on and off and these are made by depositing polycrystalline semiconductors onto the flexible substrate that also supports the OLED. This is a high efficiency system that uses relatively low currents making it suitable for use in mobile devices. Switching speeds are also very rapid meaning that the display can be quickly refreshed.

A significant advantage of AMOLED compared to other display technologies is that the colours are very bright, the contrast is high and blacks are genuinely black (no light is emitted) rather than just dark grey as in LCDs which are always semi-transparent.

One of the early disadvantages with AMOLED displays was that they could be quite difficult to see in bright sunlight due to their reflectivity. The AMOLED screen used by Samsung in the Galaxy S is a Super AMOLED. This uses thinner layers than conventional AMOLED displays and is far more efficient. The display is brighter, the power consumption lower and the reflectivity of bright sunlight is significantly lower.

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