Amorphous Silicon TFT OLED Luminance Stability
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Solution Overview
Problem
Conventional OLEDs using amorphous silicon TFTs face issues with bias stress stability, leading to reduced output current and inefficient use of data voltages due to varying node voltages, which affects luminance consistency.
Innovation Solution
A display device incorporating a light emitting element, a storage capacitor, and a driving transistor, along with a light sensor and signal controller that adjusts data voltages based on sensed luminance to maintain target luminance, using amorphous silicon nMOS thin film transistors, and applying reverse bias voltage and inversion signals to improve stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon TFTs are used in OLEDs, then manufacturing complexity is reduced and large-size OLEDs can be made, but bias stress stability deteriorates causing output current reduction and luminance variation
Solution Approach 1:
The patent applies preliminary action by performing a reverse bias stress treatment on the amorphous silicon TFT before normal operation. This pre-treatment stabilizes the transistor characteristics by reducing bias stress effects in advance, ensuring stable output current and luminance during subsequent display operation without requiring complex manufacturing processes
Solution Approach 2:
The patent changes the electrical parameters of the amorphous silicon TFT by applying reverse bias voltages during specific time periods. This parameter change stabilizes the threshold voltage and reduces bias stress accumulation, maintaining reliable performance while using simple amorphous silicon manufacturing processes
2Power
If high DC control voltages are applied to amorphous silicon TFTs, then driving capability is improved, but bias stress stability deteriorates causing output current reduction over time
Solution Approach 1:
The patent implements periodic action by alternately applying reverse bias voltages and normal driving voltages to the amorphous silicon TFT. During non-display periods, reverse bias is applied to reduce bias stress; during display periods, normal driving voltages are applied for image output. This periodic switching maintains driving capability while preventing bias stress accumulation
Solution Approach 2:
The patent applies reverse bias stress treatment in advance during non-display periods to prepare the amorphous silicon TFT for stable operation. This preliminary stabilization ensures that when high DC control voltages are applied for image display, the transistor maintains stable output current characteristics
3Adaptability or versatility
If node voltage varies with data voltage, then data transmission flexibility is improved, but control voltage range is reduced leading to inefficient data voltage utilization
Solution Approach 1:
The patent implements feedback by using a light sensor to detect the luminance output of the OLED and comparing it with target luminance values. The signal controller uses this feedback information to determine appropriate control voltages for the amorphous silicon TFT, ensuring efficient utilization of data voltage range while maintaining stable node voltage for reliable control
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 enhances the stability and efficiency of OLEDs by maintaining uniform luminance and effectively using data voltages, addressing the limitations of amorphous silicon TFTs in conventional OLEDs.
Implementation Method 1
a light sensor sensing amount of light according to the light emission of the light emitting element and generates a sensing signal depending on the sensed light amount
Data Source
AI summary
A display device is provided, which includes: a light emitting element; a storage capacitor; a driving transistor supplying driving current to the light emitting element to emit light; a first switching transistor applying a data voltage to the driving transistor and the storage capacitor in response to a first scanning signal, a light sensor sensing amount of light according to the light emission of the light emitting element and generates a sensing signal depending on the sensed light amount; and a signal controller determining luminance corresponding to the sensing signal, comparing the determined luminance and a target luminance corresponding to the data voltage, and modifies an image signal.