OLED Pixel Circuit Reverse Current Hole Removal
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Solution Overview
Problem
Organic light emitting display devices face issues with residual images and flicker due to holes accumulated on the gate insulating layer, which affect current flow and integration density, requiring a method to efficiently remove these holes without causing screen defects like flicker.
Innovation Solution
A pixel circuit design that applies a reverse current to the driving transistor to improve current passage efficiency by removing trapped holes, enhancing the design freedom of the pixel circuit and minimizing residual image and flicker issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a black image period is extended to remove accumulated holes from the gate insulating layer, then residual image defects are reduced, but screen flicker defects occur
Solution Approach 1:
The patent applies a reverse current (negative voltage) to the gate electrode during a reset period to actively remove accumulated holes from the gate insulating layer, instead of relying on natural hole migration during extended black image periods. This inverted approach actively pushes holes back to their original locations rather than waiting for passive diffusion, thereby removing residual image defects without causing screen flicker.
2Reliability
If three or more transistors are used in each pixel for internal compensation, then transistor characteristic deviation is compensated, but pixel circuit design freedom is significantly lowered
Solution Approach 1:
The patent extracts the compensation function from the pixel-level circuit design and implements it through a gate-level technique using a reset transistor and reverse current application. Instead of requiring multiple transistors within each pixel for compensation, the invention uses a simple reset transistor that applies reverse current to the gate electrode, thereby achieving transistor characteristic compensation while maintaining pixel circuit simplicity and design freedom.
3Illumination intensity
If holes are allowed to accumulate on the gate insulating layer to drive the organic light emitting diode, then light emission is achieved, but current flow is interrupted causing screen defects
Solution Approach 1:
The patent implements periodic reverse current application to the gate electrode during reset periods between light emission cycles. This periodic action temporarily removes accumulated holes from the gate insulating layer to restore current flow continuity, while allowing hole accumulation during active emission periods to maintain light output. The cyclic alternation between emission and reset phases resolves the contradiction between light emission and current flow continuity.
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 reverse current effectively removes holes from the gate insulating layer, improving current flow efficiency and reducing residual images and flicker, thereby enhancing the display's image quality and integration density.
Implementation Method 1
When a driving transistor which drives the organic light emitting diode is a P-type semiconductor, if the driving transistor is turned on, a plurality of holes passes through the active layer. In this case, some of the holes are attracted to a potential of a gate electrode to be accumulated on the gate insulating layer.
Data Source
AI summary
The present disclosure relates to an organic light emitting display device which is implemented to reduce or suppress the residual image and the flicker. According to an embodiment, a circuit includes an organic light emitting diode disposed between a first node and a first power source, a driving transistor disposed between the first node and a second power source and driving the organic light emitting device, a first transistor transmitting a data signal to the driving transistor, and a first control transistor disposed between the first node and a second node. The first control transistor applies a reverse current to the driving transistor during a first period and holes accumulated on the active layer of the driving transistor are removed during the first period, whereby a current path efficiency is improved.