OLED Array Substrate Capacitor Stacking for Stable Pixel Current
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Solution Overview
Problem
OLED displays face challenges in maintaining consistent driving current to control illumination due to variations in voltage, which affects brightness and efficiency.
Innovation Solution
The array substrate incorporates a stacked structure of capacitor electrodes with specific transistor configurations and capacitors to stabilize the driving current, including a 9T2C pixel driving circuit with capacitors and transistors to maintain consistent voltage levels for stable light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional voltage control method is used in OLED display, then the control is simple, but the driving current varies causing brightness inconsistency
Solution Approach 1:
The patent changes the control parameter from voltage to current by introducing a current mirror circuit. The driving transistor T3 operates in saturation mode with its gate connected to node N1, and the current mirror (T5-T6 and T7-T8) converts the voltage at node N1 into a stable driving current that is insensitive to voltage fluctuations, thereby achieving consistent brightness
Solution Approach 2:
The patent implements feedback through the capacitor C1 connected to node N1, which stores the voltage representing the threshold voltage compensation information. The bootstrap transistor T4 and capacitor C2 provide additional feedback to maintain the gate voltage of T3, ensuring that the driving current remains stable despite variations in OLED device characteristics or voltage supply
2Reliability
If voltage is kept constant to control brightness, then the control is stable, but the driving current varies due to voltage fluctuations
Solution Approach 1:
The patent changes the control parameter from voltage to current by introducing a current mirror circuit. The driving transistor T3 operates in saturation mode with its gate connected to node N1, and the current mirror (T5-T6 and T7-T8) converts the voltage at node N1 into a stable driving current that is insensitive to voltage fluctuations, thereby achieving consistent brightness
Solution Approach 2:
The patent applies preliminary anti-action by pre-compensating for threshold voltage variations through the compensation transistor T2 and capacitor C1 before the driving transistor operates. The bootstrap circuit (T4 and C2) also pre-establishes the correct gate voltage for T3, preventing the harmful effects of voltage fluctuations before they can affect the driving current
3Reliability
If more capacitors and transistors are added to stabilize driving current, then the current stability improves, but the pixel area increases
Solution Approach 1:
The patent utilizes vertical stacking in the cross-sectional structure, with multiple layers of transistors and capacitors arranged in different vertical levels. This three-dimensional arrangement allows the pixel driving circuit to achieve stable current control while minimizing the horizontal footprint, effectively reducing the pixel area occupied by the circuit components
Data Source
AI summary
An array substrate includes a plurality of pixel driving circuits. A respective pixel driving circuit includes a driving transistor, a data write transistor, a first capacitor including a first capacitor electrode and a second capacitor electrode, and a second capacitor including a third capacitor electrode and a fourth capacitor electrode. The second capacitor electrode and the third capacitor electrode are coupled to a second electrode of the data write transistor. The array substrate includes a stacked structure of capacitor electrodes. The stacked structure includes the first capacitor electrode; an insulating layer on the first capacitor electrode; an electrode block including the second capacitor electrode and the third capacitor electrode on a side of the insulating layer away from the first capacitor electrode; an inter-layer dielectric layer on a side of the electrode block away from the insulating layer; and the fourth capacitor electrode on the inter-layer dielectric layer.