OLED Technologies
OLED ― Organic Light Emitting Diode
OLED panels are made from organic materials that emit light when electricity is applied through them. Since OLEDs do not require a backlight and filters (like LCD displays do), they are thin and efficient, they can provide the best image quality ever and they can also be made transparent, flexible and foldable.
The basic OLED cell structure consists of a stack of thin organic layers sandwiched between a conducting anode and a conducting cathode. Breakdown of an OLED structure:
· Cathode (may or may not be transparent depending on the type of OLED) – Negatively charged to inject electrons into the organic layers that make up the OLED device.
· Electron Transport Layer (ETL) – Supports the transport of electrons across it so they can reach the emissive layer.
· Blocking layer (BL) – Commonly used to improve OLED technology by confining electrons (charge carriers) to the emissive layer.
· Emissive Layer – The heart of the device and where light is made, the emissive layer consists of a color defining emitter doped into a host. This is the layer where the electrical energy is directly converted into light.
· Hole Transport Layer (HTL) – This layer supports the transport of holes across it so they can reach the emissive layer.
· Hole Injection Layer (HIL) – Deposited on top of the anode this layer receives holes from the anode and injects them deeper into the device.
· Anode (may or may not be transparent depending on the type of OLED) – Positively charged to injects holes (absence of electrons) into the organic layers that make up the OLED device.
· Substrate (can be plastic, glass, or metal foil) – Foundation of the OLED.
An OLED display have the following advantages over an LCD display:
1.Improved image quality - better contrast, higher brightness, fuller viewing angle, a wider color range and much faster refresh rates.
2.Lower power consumption.
3.Simpler design that enables ultra-thin, flexible, foldable and transparent displays
4.Better durability - OLEDs are very durable and can operate in a broader temperature range
PMOLED ― Passive Matrix OLED
A PMOLED display uses a simple control scheme in which you control each row (or line) in the display sequentially (one at a time). PMOLED display do not contain a storage capacitor and so the pixels in each line are actually off most of the time. To compensate for this you need to use more voltage to make them brighter. If you have 10 lines, for example, you have to make the one line that is on 10 times as bright (the real number is less then 10, but that's the general idea).
So while PMOLEDs are easy (and cheap) to fabricate, they are not efficient and the OLED materials suffer from lower lifetime (due to the high voltage needed). PMOLED displays are usually small and are used to display character data or small icons: they are being used in wearable devices, small gadgets and sub displays.
Features:
1.Simple structure and low cost
2.Time-resolved dynamic drive (line sequential drive) requires higher voltage than AMOLED
3.The larger the screen, the shorter the duty ratio (time to apply voltage to each single pixel), and the lower the brightness.
AMOLED ― Active Matrix OLED
An AMOLED display is an OLED display that is driven by an active matrix backplane, it is a type of OLED display that can achieve high performance.
AMOLED also light up pixels that are energized in both axes. Each pixel has switches made of transistors and capacitors connected to it to store power, and the voltage on the X axis controls the switching on and off.
Features:
1.The formation of semiconductor elements in each pixel complicates circuits and manufacturing processes, and increases costs.
2.Switches can prevent current leakage (crosstalk)
3.Since the voltage does not drop immediately due to capacitor storage, brightness can be maintained even when the duty ratio is shortened.
Micro-OLED
Micro-OLED, also known as OLEDoS and OLED microdisplays, is one of the rare cases where the tech is exactly as it sounds: tiny OLED "micro" displays. Micro OLED displays are silicon-based OLED display that use a monocrystalline silicon wafer as the actively driven backplane, so it is easier to achieve high PPI (pixel density), a high degree of integration, and small size. This ensures they are easy to carry, have good anti-seismic performance, and have ultra-low power consumption.
On the backside of Micro OLED, it has an integrated CMOS driver circuit on the semiconductor, so it won't need an extra driver IC like LCD or OLED. Then it`s pixel pattern conducting layer above the CMOS circuit.
The other layers are just like OLED, from bottom to top, there are a lower electrode, an isolation layer, an organic light-emitting layer, and an upper electrode (for connecting cathodes of all pixels).
In a word, the white light and color filter layer is to generate FULL-COLOR images. The color filter layer is comprised of an RGB color filter and a black material matrix isolation strip.
The last step is to use a closed glass cover for encapsulation, a complete silicon-based OLED display comes out.
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