Schematic of an active matrix OLED display
Active-matrix OLED (Active-matrix organic light-emitting diode or AMOLED) is a display technology for use in mobile devices and televisions. OLED describes a specific type of thin film display technology in which organic compounds form the electroluminescent material, and active matrix refers to the technology behind the addressing of pixels. AMOLED technology is currently used in mobile phone and media players and continues to make progress towards low power, low cost and large size (for example 40 inch) for applications such as televisions.
The organic materials used in AMOLED displays are prone to degradation over a period of time. However, technology has been developed to compensate for material degradation.
An active matrix OLED display consists of a matrix of OLED pixels that generate light upon electrical activation that have been deposited or integrated onto a thin film transistor (TFT) array, which functions as a series of switches to control the current flowing to each individual pixel.
Typically, this continuous current flow is controlled by at least two TFTs at each pixel, one to start and stop the charging of a storage capacitor and the second to provide a voltage source at the level needed to create a constant current to the pixel and eliminating need for the very high currents required for passive matrix OLED operation.
TFT backplane technology is crucial in the fabrication of AMOLED displays. Two primary TFT backplane technologies, namely polycrystalline silicon (poly-Si) and amorphous silicon (a-Si), are used today in AMOLEDs. These technologies offer the potential for fabricating the active matrix backplanes at low temperatures (below 150°C) directly onto flexible plastic substrates for producing flexible AMOLED displays.
Manufacturers have developed in-cell touch panels, integrating the production of capacitive sensor arrays in the AMOLED module fabrication process. In-cell sensor AMOLED fabricators include AU Optronics and Samsung. Samsung has marketed their version of this technology as Super AMOLED.
Advantages
Active-matrix OLED displays provide higher refresh rates than their passive-matrix OLED counterparts, and they consume significantly less power. This advantage makes active-matrix OLEDs well suited for portable electronics, where power consumption is critical to battery life.
The amount of power the display consumes varies significantly depending on the color and brightness shown. As an example, one commercial QVGA OLED display consumes 3 watts while showing black text on a white background, but only 0.7 watts showing white text on a black background.
AMOLED displays may be difficult to view in direct sunlight compared to LCD displays. Samsung's Super AMOLED technology addresses this issue by reducing the size of gaps between layers of the screen.
The organic materials used in AMOLED displays are prone to degradation over a period of time. However, technology has been developed to compensate for material degradation.
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