OLED Pixel Circuit Using LTPS and Oxide TFTs for Low Leakage
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Solution Overview
Problem
Organic light emitting displays face issues with current leakage from the gate electrode of driving transistors, leading to unstable data signal voltage during frame periods, which affects image brightness and power consumption.
Innovation Solution
The use of a pixel circuit with specific transistor configurations, including p-type Low Temperature Poly-Silicon (LTPS) and n-type oxide semiconductor thin film transistors, to control current flow and maintain voltage stability, along with additional transistors for initialization and light emission control, reduces leakage current and ensures desired brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the second driving power supply is set to low voltage to improve brightness, then brightness is improved, but current leakage occurs from the gate electrode of the driving transistor
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks with distinct transistor types: the driving transistor (first transistor) uses p-type LTPS for high-speed current control, while the switch transistor (second transistor) and storage capacitor control transistors (third and fourth transistors) use n-type oxide semiconductor for low leakage. This segmentation allows each transistor to be optimized for its specific function, resolving the contradiction between brightness improvement and current leakage prevention.
2Use of energy by moving object
If the display is driven at low frequency to reduce power consumption, then power consumption is reduced, but current leakage occurs from the gate electrode of the driving transistor
Solution Approach 1:
Different regions of the pixel circuit are assigned different transistor types with optimized properties: p-type LTPS transistors provide high electron mobility for fast switching and current control, while n-type oxide semiconductor transistors provide extremely low off-state current for maintaining voltage stability during low-frequency operation. This local quality differentiation allows the circuit to maintain performance at low driving frequencies without suffering from excessive current leakage.
3Stability of the object's composition
If additional transistors are added to control current flow and maintain voltage stability, then voltage stability is improved, but device complexity increases
Solution Approach 1:
The n-type oxide semiconductor transistors (second, third, and fourth transistors) serve multiple functions: the second transistor acts as a switch for data signal input, the third transistor controls the storage capacitor, and the fourth transistor provides initialization. These multi-functional elements reduce the need for separate dedicated components, achieving voltage stability while limiting the increase in device complexity.
Data Source
AI summary
A pixel includes a pixel circuit and an organic light emitting diode. The pixel circuit has first, second, third, and fourth transistors. The first transistor controls an amount of current flowing from a first driving power supply coupled to a first node to a second driving power supply through the organic light emitting diode. The turns on when a scan signal is supplied to a first scan line. The third transistor turns on when a scan signal is supplied to a second scan line. The fourth transistor turns on when a scan signal is supplied to a third scan line. The first transistor is a p-type Low Temperature Poly-Silicon thin film transistor and the third transistor and the fourth transistor are n-type oxide semiconductor thin film transistors.