N-Channel Transistor Pixel Circuit for OLED Short-Circuit Insulation
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Solution Overview
Problem
The short life of organic light-emitting diode (OLED) displays due to deterioration of the EL layer, caused by factors such as electrode short-circuiting and non-uniform electroluminescent layer formation, leading to initial and progressive failures that affect the display's ability to emit light consistently.
Innovation Solution
A display device structure incorporating N-channel transistors that control both forward and reverse currents to the light-emitting element, with a specific wiring configuration that includes a switching transistor, a driving transistor, and an AC transistor to manage video signals and apply reverse bias currents, thereby extending the life of the light-emitting element and preventing failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If direct-current electricity is supplied to the anode and cathode sandwiching the EL layer, then the EL layer emits light, but the life of the light emitting element deteriorates due to electrode short-circuiting and non-uniform electroluminescent layer formation
Solution Approach 1:
The patent applies alternating current (AC) instead of direct current (DC) to drive the EL display. By periodically reversing the current direction, the patent prevents electrode short-circuiting and extends the life of the light emitting element while maintaining light emission capability. The AC driving method alternates between forward bias (for light emission) and reverse bias (for preventing degradation).
2Reliability
If a reverse driver voltage is applied to the light emitting element, then a current sufficient to insulate a short-circuited point can be supplied, but the device complexity increases due to additional transistors and wiring configuration
Solution Approach 1:
The patent combines multiple functions into a single AC transistor that controls both the reverse bias current application and the insulation of short-circuited points. The AC transistor is integrated into the existing pixel circuit architecture, sharing wiring and control signals with other transistors, thereby reducing overall device complexity while achieving the reliability benefit.
3Ease of manufacture
If N-channel transistors are used to control forward and reverse currents, then the manufacturing process is simplified by eliminating crystallization, but the precision of current control may be affected
Solution Approach 1:
The patent employs N-channel transistors made from amorphous silicon instead of requiring crystalline silicon, eliminating the complex crystallization process. The patent compensates for any potential reduction in current control precision by optimizing transistor dimensions, doping concentrations, and circuit design parameters to achieve the desired performance with the simplified manufacturing process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of N-channel transistors in the display device structure allows for the application of sufficient reverse bias currents to insulate short-circuited points, preventing failure and maintaining luminance, while also simplifying the manufacturing process and reducing costs by eliminating the need for crystallization of semiconductor films.
Implementation Method 1
In order to make an EL layer emit light, a method in which direct-current electricity is supplied to an anode and a cathode sandwiching an EL layer has been conventionally used
Implementation Method 2
a current sufficient enough to insulate a short-circuited point can be supplied to the short-circuited point when a reverse driver voltage is applied to the light emitting element
Data Source
AI summary
It is an object of the present invention to provide a display device in which a reverse current sufficient enough to insulate a short-circuited point flows and a transistor using amorphous silicon is used is applied. The display device includes a switching transistor that controls an input of a video signal, a driving transistor that controls a current flowing in a forward direction to a light emitting element, and an AC transistor that controls a current flowing in a reverse direction to the light emitting element; and a reverse bias current can be applied to the light emitting element. Furthermore, the above-described transistors are N-channel transistors.