OLED Cathode Layer for In-Cell Touch Sensing
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Solution Overview
Problem
Conventional self-capacitance touch display panels face challenges with complex fabrication processes, unstable electric current due to touch interactions, and slow response times, primarily due to the use of indium-tin oxide electrodes.
Innovation Solution
An OLED array substrate with a cathode layer designed for self-capacitance in-cell touch functions, incorporating a voltage-compensating circuit and cathode compensating electrodes, allowing for simultaneous image display and touch sensing with improved sensitivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ITO electrodes are used for cathode in self-capacitance touch display panels, then the fabrication process is simplified, but the response time becomes slow and resistivity is high
Solution Approach 1:
The patent changes the material parameter of the cathode from ITO (indium tin oxide) to low-resistivity metal materials such as aluminum, silver, or their alloys. This material substitution fundamentally alters the electrical conductivity parameter, reducing resistivity from typical ITO values (10^-3 to 10^-4 ohm·cm) to metal-level conductivity (10^-6 ohm·cm or lower), thereby achieving faster touch response times while maintaining ease of fabrication through conventional metal deposition processes.
2Adaptability or versatility
If a touch sensing pattern is formed in the patterning process, then touch sensing capability is achieved, but the fabrication complexity and cost increase
Solution Approach 1:
The patent makes the cathode layer serve dual functions: as the common electrode for OLED operation and as the touch sensing electrode for self-capacitance touch detection. By applying different voltages to the cathode at different time periods (display voltage during display phase, sensing voltage during touch detection phase), the same structural layer performs both display and touch functions, eliminating the need for separate touch electrode patterns and reducing fabrication complexity.
Solution Approach 2:
The patent employs time-division multiplexing where the cathode voltage is periodically switched between display mode and touch sensing mode. During the display period, the cathode operates as a common electrode with display voltage; during the touch detection period, it switches to sensing voltage for capacitance measurement. This periodic voltage switching enables one structure to perform multiple functions without additional fabrication steps.
3Adaptability or versatility
If touch motion changes the voltage applied on OLEDs, then touch sensing is enabled, but the electric current stability through OLEDs deteriorates
Solution Approach 1:
The patent incorporates voltage compensation mechanisms that detect changes in OLED voltage caused by touch events and apply corrective compensation voltages. When a touch event alters the voltage applied to OLEDs, the compensation circuitry measures this deviation and adjusts the driving voltage to maintain stable current flow through the OLEDs, preventing display artifacts while preserving touch sensing capability.
Solution Approach 2:
The patent applies preliminary voltage compensation to counteract the expected voltage changes caused by touch motions. By anticipating the voltage disturbance that will occur during touch detection and pre-applying compensating voltages, the system prevents current fluctuations before they affect OLED performance, ensuring display stability during touch sensing operations.
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
The solution enables thinner, lighter, and more cost-effective display panels with improved touch sensitivity and faster response times, maintaining unimpaired brightness during touch interactions.
Implementation Method 1
Holes are injected into the organic layer from the anode and electrons are injected into the organic layer from the cathode. Holes move toward electrons and combine with electrons in the organic layer to form excitons, i.e., a bound state of electron and hole. The decay of the excitons results in relaxation of energy, accompanied by emission of radiation, e.g., visible light.
Implementation Method 2
When a human finger or a conductive stylus is near the electrodes, the human-body capacitance changes the self-capacitance of the electrode, and the changed capacitance can be sensed by an integrated circuit (IC) connected to the electrode.
Data Source
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AI summary
An array substrate for an organic light emitting diode (OLED) display panel (401). The array substrate includes a substrate; a thin film transistor layer comprising a plurality of thin film transistors, each including a source and a drain; and an anode layer (2015) comprising a plurality of anode electrodes for applying an anode voltage, and each connected to one of the source and the drain of a corresponding transistor. The array substrate also includes a cathode layer (101, 1018, 2018, 401) comprising a plurality of touch electrodes insulated from one another for a time-sharing operation, wherein a cathode voltage and a touch-sensing voltage are applied on the plurality of touch electrodes.