Oxide Semiconductor Pixel Transistors for Low-Leakage LCDs
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Solution Overview
Problem
Liquid crystal display devices face challenges in reducing power consumption and maintaining display quality due to signal leakage through transistors, especially at varying temperatures, leading to display degradation.
Innovation Solution
The use of a transistor with a channel formation region formed using a highly purified oxide semiconductor layer, which has a band gap of 2.0 eV or more, significantly reduces off-state current and signal leakage, thereby minimizing power consumption and display degradation across different temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional transistor is used in the pixel to control image signal input, then power consumption can be reduced by keeping the transistor off during inactive periods, but image signal leakage through the transistor causes display degradation
Solution Approach 1:
The patent changes the material parameter of the transistor channel from conventional semiconductor to oxide semiconductor, which has fundamentally different electrical characteristics. The oxide semiconductor channel exhibits ultra-low off-state current due to its wide bandgap (3.0 eV or more), enabling the transistor to maintain excellent blocking performance during inactive periods while preventing image signal leakage that would otherwise cause display degradation.
2Use of energy by moving object
If the transistor is kept off for long periods to save power, then energy consumption decreases, but the leakage current through the transistor increases with temperature causing non-uniform display quality
Solution Approach 1:
The patent utilizes the temperature-stable electrical characteristics of oxide semiconductor transistors. The ultra-wide bandgap (3.0 eV or more) of the oxide semiconductor channel suppresses thermal generation of carriers, making the off-state current virtually independent of temperature variations. This ensures uniform display quality across different operating temperatures while maintaining low power consumption during inactive periods.
3Ease of manufacture
If a transistor with higher off-state current is used, then easier manufacturing is achieved, but image signal leakage increases leading to display degradation
Solution Approach 1:
The patent employs oxide semiconductor materials that can be processed at relatively low temperatures compared to conventional semiconductors, maintaining ease of manufacturing. The key parameter change is the material composition - using In-Ga-Zn-O-based oxide semiconductor with specific atomic ratios (In:Ga:Zn = 1:1:1 to 1:3:6) that provides both manufacturability and ultra-low off-state current characteristics, thereby preventing image signal leakage without compromising fabrication feasibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces power consumption and suppresses display degradation, ensuring consistent display quality even in varying environments, such as outdoors, by minimizing signal leakage through the transistor.
Implementation Method 1
the oxide semiconductor layer has a band gap of 2.0 eV or more, preferably 2.5 eV or more, still preferably 3.0 eV or more
Data Source
AI summary
To reduce power consumption and suppress display degradation of a liquid crystal display device. To suppress display degradation due to an external factor such as temperature. A transistor whose channel formation region is formed using an oxide semiconductor layer is used for a transistor provided in each pixel. Note that with the use of a high-purity oxide semiconductor layer, off-state current of the transistor at a room temperature can be 10 aA/μm or less and off-state current at 85° C. can be 100 aA/μm or less. Consequently, power consumption of a liquid crystal display device can be reduced and display degradation can be suppressed. Further, as described above, off-state current of the transistor at a temperature as high as 85° C. can be 100 aA/μm or less. Thus, display degradation of a liquid crystal display device due to an external factor such as temperature can be suppressed.