Pixel Circuit Bottom Gate Threshold Shifting
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Solution Overview
Problem
Existing organic light emitting display devices face issues with instantaneous afterimages and reliability due to increased leakage current in driving transistors, which is not effectively addressed by existing technologies that require additional voltage sources.
Innovation Solution
A pixel circuit design that includes a driving transistor with a first bottom gate electrode and a switching transistor with a second bottom gate electrode, both receiving a first voltage to shift the threshold voltage without the need for an additional voltage source, thereby reducing leakage current and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bottom gate electrode is added to apply back-biasing voltage to shift threshold voltage, then leakage current is reduced, but an additional voltage source is required which increases non-display area
Solution Approach 1:
The patent merges the back-biasing voltage source with the existing power supply voltage (ELVDD) by electrically connecting the bottom gate electrode to the power supply line. This eliminates the need for a separate voltage source while maintaining the threshold voltage shifting effect, thereby reducing non-display area while improving reliability
Solution Approach 2:
The power supply voltage ELVDD serves dual functions: it provides the operating voltage for the pixel circuit and simultaneously provides the back-biasing voltage to the bottom gate electrode. This multi-functionality eliminates the need for additional voltage sources and reduces the non-display area
2Object-affected harmful factors
If back-biasing voltage is applied to shift threshold voltage, then instantaneous afterimage is improved, but voltage level may be too low to ensure sufficient reliability improvement
Solution Approach 1:
The patent changes the voltage level parameter by connecting the bottom gate to the power supply voltage ELVDD, which provides a sufficiently high voltage level to effectively shift the threshold voltage. This ensures both instantaneous afterimage reduction and reliable display device operation
3Ease of operation
If switching transistor on/off characteristic deteriorates, then data voltage transfer is affected, but device complexity increases with additional components
Solution Approach 1:
The patent combines the bottom gate electrode integration into the existing switching transistor structure without adding separate control circuits or components. This maintains ease of operation while avoiding increased device complexity
Data Source
AI summary
Provided are a pixel circuit and a display device having the pixel circuit. The pixel circuit includes an organic light emitting diode, a switching transistor, a storage capacitor, and a driving transistor. The switching transistor is turned off when a scan signal has a first voltage and turned on when the scan signal has a second voltage. The storage capacitor stores a data voltage when the switching transistor is turned on in response to the scan signal. The driving transistor is electrically connected with the organic light emitting diode between a high power supply voltage and a low power supply voltage to provide a driving current to the organic light emitting diode, and includes a first bottom gate electrode that is provided with the first voltage. The driving current corresponds to the data voltage stored in the storage capacitor.