Display Device Blocking Leakage Current in Oxide Transistors
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Solution Overview
Problem
Organic light emitting display devices face issues with the accuracy and stability of driving transistors and switching transistors, leading to undesirable charge injection and noticeable flicker during low-speed operation due to the kick-back phenomenon in oxide transistors.
Innovation Solution
A display device configuration that includes a light-emitting element, a driving TFT, a switching circuit, and a blocking unit with a capacitor to minimize leakage current and charge injection by using n-type oxide transistors and a dual gate structure for the switching transistors, which reduces the impact of charge injection during the off-state of the switching transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oxide transistor is used as a switching transistor connected to the gate electrode of the driving transistor, then the switching transistor can be turned on and off effectively, but a kick-back phenomenon occurs that causes undesirable charge injection and temporarily increases luminance leading to noticeable flicker
Solution Approach 1:
A blocking unit comprising a capacitor is introduced as an intermediary component between the switching transistor and the gate electrode of the driving transistor. The capacitor blocks leakage current from flowing to the gate electrode during the off-state, preventing charge injection while maintaining the switching function. This mediator component resolves the contradiction by allowing the switching transistor to operate effectively without causing harmful charge injection effects.
Solution Approach 2:
The blocking unit is configured to preemptively block leakage current before it can cause charge injection into the gate electrode. By applying the inverted scan signal to the capacitor, the blocking action occurs in advance during the off-state, preventing the kick-back phenomenon from occurring in the first place, thus eliminating the harmful effect before it can manifest as luminance flicker.
2Use of energy by moving object
If the switching transistor is turned off to stop current flow, then power consumption is reduced, but leakage current still flows to the second node causing charge injection
Solution Approach 1:
The capacitor in the blocking unit serves as an intermediary that blocks leakage current during the off-state. When the switching transistor is turned off, the capacitor prevents the leakage current from reaching the gate electrode, thereby maintaining low power consumption while eliminating the harmful leakage effect through this intermediate blocking component.
3Stability of the object's composition
If a dual gate structure with n-type oxide transistors is used, then charge injection is reduced and luminance stability is improved, but device complexity increases
Solution Approach 1:
The switching circuit is segmented into multiple n-type oxide transistors with dual gate structures, where each transistor is controlled by separate scan signals. This segmentation allows independent control of different switching functions, reducing charge injection through optimized voltage application while maintaining luminance stability. The segmentation of the switching function into multiple specialized components achieves the stability improvement despite increased structural complexity.
Solution Approach 2:
The patent employs composite transistor structures combining n-type oxide semiconductor materials with specific gate configurations. This composite approach uses multiple layers and material properties to achieve reduced charge injection and improved luminance stability, where the combination of materials and structures works synergistically to overcome the limitations of single-material transistors.
Data Source
AI summary
A display device can include a light-emitting element; a driving transistor including a first electrode connected to a first node, a gate electrode connected to a second node, and a second electrode connected to a third node connected to the light-emitting element, the driving transistor being configured to apply a current the third node during a sampling operation and control a high-potential voltage applied to the first node according to a data voltage applied to the gate electrode to apply the high-potential voltage to the third node during a light-emitting operation. Also, the display device can include a switching circuit to apply a current for charging the data voltage to the second node by connecting the second node with the third node during the sampling operation; and a blocking device to block leakage current from flowing from the switching circuit to the second node when the switching circuit is off.