Double Gate TFT Threshold Voltage Compensation
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Solution Overview
Problem
The degradation of driving thin film transistors (TFTs) in organic light emitting displays leads to non-uniform luminance and reduced lifespan due to threshold voltage shifts, which existing compensation methods fail to adequately address, particularly due to limited compensation voltage ranges and accelerated degradation during compensation processes.
Innovation Solution
The implementation of a double gate structure for driving TFTs, including a main gate electrode and a sub-gate electrode, where a compensation voltage is applied to the sub-gate electrode to recover threshold voltage shifts, allowing for bidirectional control and efficient compensation of threshold voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a data voltage is applied to the gate electrode of the driving TFT to compensate for threshold voltage degradation, then the luminance uniformity is improved, but the degradation of the driving TFT is accelerated
Solution Approach 1:
The gate electrode is divided into two separate electrodes: a main gate electrode and a sub-gate electrode. The main gate electrode receives the data voltage for normal display operation, while the sub-gate electrode receives a compensation voltage specifically for correcting threshold voltage degradation. This segmentation allows independent control of display function and compensation function, preventing accelerated degradation while maintaining luminance uniformity.
2Illumination intensity
If the threshold voltage of the driving TFT is compensated by increasing the data voltage, then the luminance is improved, but the compensation voltage range is exceeded
Solution Approach 1:
The compensation mechanism transitions from a one-dimensional approach (adjusting data voltage magnitude) to a two-dimensional approach by introducing a separate sub-gate electrode. This allows compensation voltage to be applied in a different dimensional space (sub-gate voltage dimension) independent of the main data voltage, enabling broader compensation range without exceeding driver IC limitations.
3Reliability
If the threshold voltage shift is compensated by modulating the data voltage, then the current characteristic is improved, but the degradation acceleration occurs due to increased gate-bias stress
Solution Approach 1:
The sub-gate electrode acts as an intermediary element that handles the compensation function separately from the main gate electrode. By introducing this intermediary component, the compensation voltage can be applied without increasing the gate-bias stress on the main driving TFT, thus improving current characteristic while extending device lifespan.
Data Source
AI summary
An organic light emitting display includes a display panel, which includes a plurality of pixels and displays an image, and a data driving circuit differently outputting a compensation voltage depending on a sensing value based on a driving current. Each of the plurality of pixels includes an organic light emitting diode, a driving thin film transistor (TFT) having a double gate structure including a main gate electrode and a sub-gate electrode, a switching TFT applying a data voltage determining the driving current to the main gate electrode of the driving TFT, and a compensation TFT applying the compensation voltage for compensating for a shift amount of a threshold voltage of the driving TFT to the sub-gate electrode of the driving TFT.