Reduced Off-Current Switching Transistor for OLED Flicker Suppression
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Solution Overview
Problem
Conventional OLED devices lack a functional structure to meet various requirements across different application fields, particularly in terms of power consumption and reliability, especially when operating at low-frequency driving frequencies, which can result in flicker phenomena and inefficient luminance control.
Innovation Solution
An active matrix OLED display device is designed with pixels comprising an OLED, a driving transistor, a switching transistor, a storage capacitor, and a timing controller that updates charge on the storage capacitor at frame rates between 1-10 Hz, utilizing low-temperature polysilicon and oxide semiconductor transistors to minimize off-current and prevent flicker, while allowing for flexible frame rate operation from 1-10 Hz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If conventional OLED devices operate at low-frequency driving rates, then power consumption is reduced, but flicker phenomena occur and luminance control becomes inefficient
Solution Approach 1:
The storage capacitor is pre-charged to a specific voltage level before the low-frequency driving cycle begins. This preliminary charging action ensures that sufficient charge is stored to maintain stable luminance throughout the extended frame period, preventing flicker while enabling ultra-low power consumption operation at 1Hz or lower refresh rates
Solution Approach 2:
The patent optimizes the storage capacitor's capacitance value and the switching transistor's off-current characteristics by changing material parameters and device dimensions. These parameter adjustments ensure that the capacitor can hold charge sufficiently long at ultra-low refresh rates while the transistor maintains minimal leakage, enabling stable luminance control at extremely low power consumption levels
2Reliability
If the switching transistor's off-current is reduced, then flicker is suppressed and luminance stability improves, but device complexity increases
Solution Approach 1:
The patent applies different material qualities to different regions of the switching transistor. The channel region uses oxide semiconductor material with inherently low off-current characteristics, while other regions use conventional materials. This localized quality differentiation achieves superior luminance stability without requiring complete redesign of the entire transistor structure
Solution Approach 2:
The switching transistor employs a composite structure combining oxide semiconductor material in the channel region with conventional semiconductor materials in other regions. This composite approach leverages the low off-current property of oxide semiconductors to suppress flicker and maintain luminance stability while avoiding the complexity of entirely new transistor architectures
3Reliability
If the storage capacitor's capacitance is increased, then charge holding ability improves and flicker is reduced, but pixel area increases
Solution Approach 1:
The patent optimizes the storage capacitor's capacitance value by changing the dielectric material properties and layer thickness parameters. By selecting materials with higher dielectric constants and optimizing layer dimensions, the capacitor achieves enhanced charge holding ability with a compact structure that fits within the pixel area without causing flicker
Data Source
AI summary
An active matrix organic light emitting diode (OLED) display device includes an array of pixels, each pixel including an OLED, a driving transistor (DT) coupled to drive current through the OLED, a storage capacitor, and a scanning transistor (ST) coupled to control charge on the storage capacitor corresponding to a data voltage for said pixel. The display device also includes a timing controller configured to control the ST of each pixel to update the charge stored on the storage capacitor of each pixel at a frame rate including at least one frequency within a range of 1-10 Hertz (Hz).