Pixel Circuit Initialization Transistor Merging for OLED Yield
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Solution Overview
Problem
In internal compensation type pixel circuits, the high number of elements and high layout density make it difficult to achieve high-resolution display images, and the yield of manufacturing is likely to be lowered.
Innovation Solution
A display device with a pixel circuit configuration that includes a drive transistor, a holding capacitor, and switching elements for threshold compensation and light emission control, where the control terminal of the drive transistor is connected to a fixed voltage line via the holding capacitor and the threshold compensation switching element, and the initialization voltage is supplied to the holding capacitor during an initialization period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an anode voltage initialization transistor is provided in addition to a gate voltage initialization transistor in internal compensation type pixel circuits, then display quality deterioration is suppressed, but the number of elements increases and layout density becomes high
Solution Approach 1:
The patent combines the initialization function for both the gate voltage and anode voltage into a single initialization transistor. This transistor is configured to initialize both the holding capacitor (gate voltage) and the display element (anode voltage) simultaneously, thereby reducing the total number of elements while maintaining the necessary initialization functions for display quality
Solution Approach 2:
The initialization transistor is designed with multi-functionality to serve dual purposes: initializing the gate voltage of the drive transistor and initializing the anode voltage of the display element. This universal approach eliminates the need for separate initialization transistors, reducing device complexity while preserving display quality
2Productivity
If the number of elements in pixel circuits is reduced, then manufacturing yield is improved, but the ability to suppress display quality deterioration may be compromised
Solution Approach 1:
By merging the initialization functions into a single transistor, the patent reduces the number of elements in the pixel circuit, which directly improves manufacturing yield by reducing the number of components that could potentially fail during manufacturing
Solution Approach 2:
The multi-functional initialization transistor ensures that both gate voltage and anode voltage are properly initialized, maintaining display quality while reducing element count for improved manufacturing yield
3Manufacturing precision
If high-resolution display images are achieved, then layout density must be high, but this increases the difficulty of manufacturing and reduces yield
Solution Approach 1:
The patent merges multiple initialization functions into a single transistor, which reduces the minimum layout area required for each pixel circuit. This enables higher display resolution by allowing tighter pixel spacing while maintaining manufacturability
Solution Approach 2:
The universal initialization transistor reduces the number of components per pixel, simplifying the layout and making high-resolution displays more manufacturable by reducing the complexity associated with high layout density
Data Source
AI summary
The present application discloses a current-driven display device employing an internal compensation method capable of achieving high-resolution of the display image while suppressing a reduction in the yield of manufacturing, the deterioration in display quality, an increase in the circuit amount. In a pixel circuit of an organic EL display device, a voltage of the gate terminal of a drive transistor is initialized before the voltage of a data signal line is written into a holding capacitor via the drive transistor in a diode-connected state. At this time, a current flows from the holding capacitor connected to the gate terminal of the drive transistor to an initialization voltage line via a threshold compensation transistor, a second light emission control transistor, and a display element initialization transistor, and the voltage of the gate terminal is initialized. Thus, an initialization transistor provided between the gate terminal and the initialization voltage line in the related art comes to be unnecessary.