i.The luminous Principle
OLED emitting principle is: the glass is sandwiched between two cathodes, the anode electrode and the electron-transporting layer, a hole transport layer and the luminescent layer, in case there is a bias, electrons injected from the cathode, holes injected from the anode, is injected electron and hole transport in the organic layer. The injected electron and hole transport in the organic layer (wave form transmission to the collision), and in the composite light-emitting layer, thereby emitting layer molecules excited singlet excitons, the singlet exciton radiative decay to emit light.
ii.The driving Mode
OLED driver as well as two divided into passive (PMOLED) active (AMOLED), which PMOLED simple structure, each pixel is represented by a separate cathode and anode control, no additional driver circuit, but too much control lines restrict its application of high-resolution large screen; AMOLED entire cathode surface electrode via a drive circuit driving the light emitting anode, significantly reducing the number of control lines, it has a low-power, high-resolution, fast response and other characteristics, AMOLED therefore gradually become the mainstream OLED display.
For high-resolution AMOLED, the size of the driving circuit smaller and smaller, but the electrical performance requirements have become more sophisticated, conventional Si (Amorphous Silicon, A-Si) technology has been difficult to meet the requirements, and low-temperature polysilicon (low Temperature Poly Silicon, LTPS) a technical solution to this problem, the core is by an excimer laser annealing the amorphous silicon into polysilicon, has higher carrier mobility, lower defect density, the device in a small size can still have better electrical properties.
The structure of the LTPS-AMOLED and the LCD is basically the same in the structure of the driving circuit, but since the AMOLED is a self-luminous structure and does not require a backlight, it is thinner and lighter. At the same time, due to the self-illuminating characteristics, the power consumption under the dark picture is much lower than the constant power consumption of the LCD backlight, so that the AMOLED display panel has energy-saving characteristics.
AMOLED also has two structures, bottom-emission structure and top-emission structure. In the top-emission structure, the light is not blocked by the driving circuit, and has a higher aperture ratio than the bottom-emitting structure, thereby having a greater advantage in high-resolution applications, and thus has gradually become the mainstream of AMOLED.
LTPS-TFT technique is to turn Amorphous-Silicon into Poly-Silicon through ELA method.Compared to the a-Si, Poly-Si’s inner structure is arranged in better order, embracing higher mobility and stability. As a result, it becomes the best choice of driving AMOLED currently.
The Backplane driving Process is similar to the semiconductor Process, whose main purpose is to do LTPS-TFT on the glass . The entire process includes deposition, photo and etching:
•The deposition process is to use deposition equipment to deposit materials on the glass substrate through physical or chemical methods. (2)
•Photo process is to define the photo mask pattern on the glass through the exposure equipment.(3, 4, 5)
•Etching Process is to etch the film, which is not covered by the Photo Resist through physical or chemical methods. Finally, wash the Photo Resist on the covered film, remaining the wanted pattern. (6, 7)
Use multiple organic materials to evaporate on the limited area of backplane and combine with driving circuit to form the emission device. The evaporation line is around 100 meters. Then the encapsulation of backplane and frontplane will be located in the specfic environment that oxygen concentration under 5%. The alignment accuracy of evaporation and humidity free of encapsulation are the challenges.
After encapsulation, panel will through cutting, polarizer attachment and driver IC/FPC bonding process. Then put into aging test and judgment. The passed panel will be packaged to the product for costomer finally.