Oxide Semiconductor Pixel Transistors for Temperature-Stable LCDs
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Solution Overview
Problem
Existing liquid crystal display devices face challenges in reducing power consumption and maintaining uniform display quality, especially under varying outdoor environments, due to signal leakage through transistors which degrades display quality.
Innovation Solution
The use of a transistor with a channel formation region formed using a high-purity oxide semiconductor layer, which has a band gap of 2.0 eV or more, significantly reduces off-state current, minimizing signal leakage and enhancing display stability across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional transistor is used in the pixel, then the device can operate normally, but the transistor causes signal leakage in off-state which degrades display quality over time
Solution Approach 1:
The patent changes the material parameter of the transistor channel formation region from conventional semiconductor materials to oxide semiconductor material. This material substitution fundamentally alters the electrical characteristics, achieving ultra-low off-state current (10 aA/μm or less at room temperature) while maintaining on-state functionality, thereby eliminating signal leakage without affecting normal operation.
Solution Approach 2:
The patent employs oxide semiconductor material which can be processed using low-temperature fabrication techniques. This approach allows for the creation of transistors with exceptional off-state characteristics without requiring complex high-temperature processing, effectively providing a practical solution that can be manufactured cost-effectively.
2Adaptability or versatility
If the transistor operates at higher temperatures, then the device can function in outdoor environments, but the off-state current increases causing display degradation
Solution Approach 1:
The patent utilizes the inherent material properties of oxide semiconductors, specifically their wide band gap (2.0 eV or more), which fundamentally changes the temperature dependence of off-state current. Unlike conventional semiconductors where off-state current increases exponentially with temperature, the oxide semiconductor maintains ultra-low off-state current (100 aA/μm or less at 85°C) across a wide temperature range, enabling outdoor use without display degradation.
Solution Approach 2:
The patent employs oxide semiconductor material with specific compositional characteristics (high purity, thoroughly removed impurities) to achieve the desired temperature stability. The material's composite structure and purification process create a channel formation region that resists thermal excitation of carriers, maintaining stable electrical characteristics in varying outdoor temperatures.
3Use of energy by moving object
If the transistor is kept turned off during inactive period to reduce power consumption, then power consumption decreases, but signal leakage through the transistor becomes apparent causing display degradation
Solution Approach 1:
The patent changes the fundamental electrical parameter of the transistor's off-state current through material substitution. The oxide semiconductor transistor achieves off-state current levels (10 aA/μm or less) that are several orders of magnitude lower than conventional transistors. This parameter change enables the transistor to remain truly non-conductive during inactive periods, allowing extended image holding without refresh while preventing signal leakage-induced display degradation.
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 approach reduces power consumption and suppresses display degradation, ensuring consistent display quality even in outdoor conditions where temperature fluctuations are significant.
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.