Oxide Drive Transistors for OLED In-Pixel Compensation
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Solution Overview
Problem
Organic light-emitting diode (OLED) display pixels face variations in transistor threshold voltages due to process, voltage, and temperature (PVT) variations, leading to inconsistent light production and issues like luminance jumps and image sticking.
Innovation Solution
Implementing semiconducting-oxide transistors for the drive, gate voltage setting, and initialization transistors, along with p-type silicon transistors for emission and data loading transistors, reduces threshold voltage hysteresis, leakage, and manufacturing costs, and enables in-pixel threshold voltage cancellation for consistent light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If semiconducting-oxide transistors are used for drive, gate voltage setting, and initialization transistors, then threshold voltage hysteresis is reduced and first frame response is improved, but device complexity increases due to multiple transistor types
Solution Approach 1:
The patent applies different transistor types (semiconducting-oxide vs. p-type silicon) to different functional locations within the display pixel circuit. Specifically, semiconducting-oxide transistors are used for the drive transistor, gate voltage setting transistor, and initialization transistor where low hysteresis is critical, while p-type silicon transistors are used for emission and data loading transistors. This localized differentiation resolves the contradiction by optimizing performance at critical points without unnecessarily complicating the entire circuit.
2Reliability
If multiple types of thin-film transistors are used, then performance is improved through reduced hysteresis and leakage, but manufacturing cost increases due to additional lithographic masks
Solution Approach 1:
The patent achieves multi-functionality by using semiconducting-oxide transistors for multiple critical functions (drive, gate voltage setting, and initialization) within the same pixel circuit. This approach reduces the need for additional specialized transistor types while still achieving low leakage and low hysteresis performance, thereby simplifying the manufacturing process and reducing lithographic mask requirements.
3Manufacturing precision
If in-pixel threshold voltage cancellation is implemented, then consistent light production is achieved despite PVT variations, but device complexity increases due to additional circuit components
Solution Approach 1:
The display pixel circuit performs self-compensation for threshold voltage variations through the gate voltage setting transistor, which automatically adjusts the gate voltage to cancel out PVT-induced threshold voltage shifts. This self-service mechanism achieves consistent light production without requiring external calibration or additional complex control circuits, thereby resolving the contradiction between precision and complexity.
Data Source
AI summary
A display pixel may include an organic light-emitting diode, one or more emission transistors, a drive transistor, a gate setting transistor, a data loading transistor, and an initialization transistor. The drive transistor may be implemented as a semiconducting-oxide transistor to mitigate threshold voltage hysteresis to improve first frame response at high refresh rates, to reduce undesired luminance jumps at low refresh rates, and to reduce image sticking. The gate setting transistor may also be implemented as a semiconducting-oxide transistor to reduce leakage at the gate terminal of the drive transistor. The initialization transistor may also be implemented as a semiconducting-oxide transistor so that it can be controlled using a shared emission signal to reduce routing complexity. The remaining transistors in the pixel may be implemented as p-type silicon transistors. Display pixels configured in this way can support in-pixel threshold voltage compensation and on-bias stress phase to further mitigate the hysteresis.