Organic EL Display Device Gate-Cathode Short Prevention
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Solution Overview
Problem
In organic electroluminescent (EL) display devices, electrical shorts between the gate and cathode of a driving transistor can cause non-light emitting pixels, leading to perceived linear defects in luminance, which are not permitted in standard visibility criteria, and there is a risk of wiring shorts between storage and auxiliary capacitors during fabrication, resulting in defective pixels and luminance changes.
Innovation Solution
The solution involves setting the video signal reference potential equal to the cathode potential of the organic electroluminescent element and arranging storage and auxiliary capacitor wirings in different layers to prevent electrical shorts and ensure uniform luminance, even if a short occurs between the gate and cathode of a driving transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate and cathode of a driving transistor are electrically shorted, then the pixel cannot emit light, but this creates a perceived linear defect in luminance that is not permitted by visibility standards
Solution Approach 1:
The patent converts the harmful effect of gate-cathode shorts into a beneficial outcome by setting the video signal reference potential equal to the cathode potential. This potential equalization ensures that even when shorts occur, no current flows through the organic EL element, preventing luminance changes that would be perceived as linear defects, thereby transforming a reliability issue into a quality assurance solution
Solution Approach 2:
The patent applies equipotentiality by setting the video signal reference potential equal to the cathode potential of the organic EL element. This creates an equipotential condition between these two points, ensuring that electrical shorts between them do not create voltage differences that would drive current through the pixel, thus preventing visible defects while maintaining uniform luminance across the display
2Ease of manufacture
If storage and auxiliary capacitor wirings are arranged in the same layer, then fabrication is simpler, but there is a risk of electrical shorts during the manufacturing process
Solution Approach 1:
The patent resolves the contradiction by transitioning from a two-dimensional planar arrangement to a three-dimensional layered structure. Storage capacitor wirings and auxiliary capacitor wirings are placed in different layers, separated by an insulating film, which eliminates the risk of electrical shorts during fabrication while maintaining manufacturing feasibility through standard multi-layer PCB or thin-film transistor fabrication processes
3Stability of the object's composition
If the video signal reference potential is set equal to the cathode potential, then luminance uniformity is maintained even with gate-cathode shorts, but this requires precise potential control during operation
Solution Approach 1:
The patent simplifies potential control by establishing an equipotential relationship between the video signal reference potential and the cathode potential. This design choice eliminates the need for complex active control mechanisms, as the potential equality is structurally embedded in the circuit design, making the system easier to operate while maintaining stable luminance uniformity across all pixels including those with gate-cathode shorts
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 approach prevents luminance changes from being perceived as linear defects and avoids electrical shorts between the gate electrode of a drive transistor and the cathode electrode, maintaining uniformity in pixel illumination and preventing defective pixels from affecting adjacent pixels.
Implementation Method 1
organic EL elements that utilize a phenomenon in which the application of an electric field to an organic thin film induces light emission
Data Source
AI summary
A display device including a pixel array unit having a matrix of pixels each configured such that an anode electrode of an organic electroluminescent element is connected to a source electrode of a drive transistor, a gate electrode of the drive transistor is connected to a source or drain electrode of a writing transistor, and a storage capacitor is connected between the gate and source electrodes of the drive transistor, scanning lines and power supply lines for individual pixel rows, and signal lines for individual pixel columns. A video signal reference potential is supplied to the signal lines for a period during which a scanning signal is supplied to the scanning lines during driving of pixels in a preceding row. During threshold correction for the drive transistor in a current pixel, the video signal reference potential and a potential of the cathode electrode of the organic electroluminescent element are equal.