Light-Emitting Device Pixel Circuit with Capacitor Voltage Compensation
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Solution Overview
Problem
In light-emitting devices, variations in threshold voltage among driving transistors cause uneven luminance across pixels, and deterioration of the electroluminescent layer leads to decreased luminance, as the voltage between the anode and cathode increases, affecting the gate voltage of the driving transistor.
Innovation Solution
Incorporating a first capacitor to hold the gate-source voltage of the driving transistor and a second capacitor connected in series with the light-emitting element, allowing for the application of a voltage higher than the threshold voltage and maintaining the threshold voltage in the capacitor, ensuring consistent gate voltage regardless of electroluminescent material deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an n-channel driving transistor is used with a light-emitting element having an anode connected to the source, then the device structure is simplified and manufacturing is easier, but when the voltage between anode and cathode increases due to electroluminescent material deterioration, the source potential increases, causing gate voltage to decrease and drain current to reduce, resulting in luminance decrease
Solution Approach 1:
The patent applies preliminary action by pre-charging a capacitor with a voltage higher than the threshold voltage before the electroluminescent layer deteriorates. This stored voltage compensates for future potential increases, ensuring that even when the anode-cathode voltage increases due to material deterioration, the gate-source voltage remains sufficient to maintain proper transistor operation and stable luminance output.
2Ease of manufacture
If all transistors in pixels have the same polarity to omit manufacturing steps, then manufacturing complexity is reduced, but threshold voltage variations among driving transistors cause luminance variations across pixels
Solution Approach 1:
The patent applies parameter changes by introducing a capacitor with a specific voltage parameter (higher than threshold voltage) to compensate for threshold voltage variations among transistors. This voltage parameter adjustment ensures that despite manufacturing variations causing different threshold voltages, the actual gate-source voltage experienced by each transistor is standardized, resulting in uniform luminance across all pixels while maintaining the simplicity of using transistors with the same polarity.
3Manufacturing precision
If a capacitor is added to hold gate-source voltage and compensate for threshold voltage variations, then luminance uniformity and stability are improved, but device complexity and number of components increase
Solution Approach 1:
The patent applies universality by designing the capacitor to serve multiple functions: it stores voltage to compensate for threshold voltage variations among transistors, maintains stable gate-source voltage during operation, and ensures consistent luminance output across all pixels. This multi-functionality justifies the addition of the capacitor by having it address multiple issues simultaneously rather than requiring separate solutions for each problem.
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
This configuration stabilizes the luminance across pixels by maintaining the gate voltage of the driving transistor, independent of threshold voltage variations and electroluminescent layer deterioration, thereby enhancing image quality and reducing luminance fluctuations.
Implementation Method 1
a first capacitor which holds a voltage higher than a threshold voltage
Implementation Method 2
a second capacitor which is connected in series with the first capacitor and connected in series with a light-emitting element
Data Source
AI summary
A light-emitting device according to one embodiment of the present invention includes a light-emitting element, a first transistor whose source is electrically connected to an anode of the light-emitting element, a second transistor which controls whether an image signal is input to a gate of the first transistor, a third transistor which controls electrical connection and disconnection between the gate and a drain of the first transistor, a fourth transistor which controls whether a first power supply potential is supplied to the drain of the first transistor, a fifth transistor which controls whether a second power supply potential is supplied to the anode of the light-emitting element, a first capacitor which holds a voltage between the gate and the source of the first transistor, and a second capacitor electrically connected in series with the first capacitor and electrically connected in series with the light-emitting element.