OLED Pixel Circuit Combining LTPS and Oxide TFTs for Stable Brightness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing organic light emitting displays face issues with current leakage from the gate electrode of driving transistors, leading to inconsistent data signal voltages and inadequate brightness during one frame period.
Innovation Solution
Incorporation of p-type Low Temperature Poly-Silicon (LTPS) thin film transistors and n-type oxide semiconductor thin film transistors in the pixel circuit to control current flow, along with specific transistor configurations and a storage capacitor to maintain stable voltage levels, reducing leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the second driving power supply is set to a 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 specialized transistors: the first transistor (LTPS) handles main current control for brightness, while the second transistor (oxide semiconductor) specifically manages gate electrode leakage current. This segmentation allows independent optimization of brightness and leakage control functions.
Solution Approach 2:
Different transistor types are assigned to different locations within the pixel circuit based on their specific characteristics. The LTPS transistor is used where high current control capability is needed (main driving function), while the oxide semiconductor transistor is placed where low leakage is critical (gate electrode protection). This local optimization matches material properties to functional requirements.
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 from the gate electrode causes data signal voltage to not be maintained
Solution Approach 1:
The transistor functions are segmented such that the oxide semiconductor transistor specifically addresses gate electrode leakage protection, allowing the display to operate at lower frequencies with maintained signal integrity. The dedicated leakage control path enables relaxed timing requirements.
Solution Approach 2:
The oxide semiconductor transistor acts as a sacrificial or auxiliary component that compensates for leakage effects, allowing the main LTPS transistor to operate with simpler control logic. This auxiliary component handles the reliability burden that would otherwise require complex voltage maintenance circuits.
3Device complexity
If conventional transistors are used in the pixel circuit, then device complexity is low, but data signal voltage cannot be maintained during one frame period
Solution Approach 1:
The pixel circuit uses two different transistor types (LTPS and oxide semiconductor) with distinct functions: one for current control and one for leakage protection. This segmentation of functions within a moderate complexity architecture achieves reliable voltage maintenance without requiring overly complex circuit designs.
Solution Approach 2:
The pixel circuit employs a composite transistor architecture combining LTPS and oxide semiconductor materials. Each material's unique electrical characteristics are leveraged: LTPS for high current drive capability and oxide semiconductor for low leakage properties, creating a synergistic effect that improves voltage stability.
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.