Polysilicon TFT Luminance Uniformity Compensation
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Solution Overview
Problem
Organic light emitting devices face issues with non-uniform luminance due to variations in threshold voltages and electric field effect mobility of driving transistors, leading to degraded performance and short device lifetime.
Innovation Solution
A display device and driving method that includes a light-emitting element, capacitors, and transistors, where the transistors are connected and controlled by specific scanning signals to maintain uniform luminance, regardless of threshold voltage and mobility variations, using a combination of p-channel and n-channel electric field effect transistors and capacitors to stabilize current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If amorphous silicon TFT is used for the switching element, then the device can be manufactured at low temperature on glass substrate, but the electron mobility is low and threshold voltage varies continuously due to DC voltage application
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to polysilicon, which fundamentally alters the electrical characteristics including electron mobility and threshold voltage stability. Polysilicon provides discrete threshold voltage levels and higher electron mobility while maintaining compatibility with low-temperature processing techniques.
2Reliability
If polysilicon TFT is used to improve electron mobility and reduce leakage current, then high-frequency operation characteristics are improved, but uniform formation of polysilicon TFT across the display device is difficult
Solution Approach 1:
The patent introduces a feedback mechanism through the capacitor connected to the control terminal of the driving transistor. This capacitor stores charge and provides feedback to compensate for threshold voltage variations, ensuring uniform luminance across pixels even when polysilicon TFT characteristics vary due to manufacturing tolerances.
3Duration of action of stationary object
If polysilicon TFT is used to reduce leakage current, then device lifetime is extended, but sequential degradation still occurs causing luminance deviation between pixels
Solution Approach 1:
The patent implements beforehand cushioning by pre-charging the capacitor connected to the control terminal before the pixel operates. This pre-charged capacitor compensates for upcoming threshold voltage shifts and degradation effects, maintaining uniform luminance across all pixels throughout the device lifetime even as individual transistor characteristics drift.
Data Source
AI summary
A display device and a method of driving the same, in which the display device includes: a light-emitting element; a first capacitor connected between first and second contact points; a driving transistor that has a control terminal connected to the second contact point, an input terminal connected to a driving voltage, and an output terminal connected to the light-emitting element; a first switching transistor connected between a data voltage or a sustain voltage and the first contact point; a second switching transistor connected between the second contact point and the output terminal of the driving transistor; and a third switching transistor connected between a reference current source and the output terminal of the driving transistor.