LCD Pixel Transistors Using Oxide Semiconductors to Cut Leakage
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Solution Overview
Problem
Existing liquid crystal display devices face issues with high power consumption and display degradation due to leakage of image signals through transistors, especially under varying environmental conditions, which are exacerbated by increased operation temperatures.
Innovation Solution
Utilizing a transistor with a channel formation region formed using a highly purified oxide semiconductor layer to reduce off-state current, minimizing signal leakage and maintaining display quality even under temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional transistor is used in the pixel to control image signal input, then the liquid crystal display device can operate with standard power consumption levels, but the transistor exhibits significant off-state current leakage that increases with temperature, causing display degradation and inconsistent image quality under varying environmental conditions
Solution Approach 1:
The patent changes the material parameter of the transistor channel from conventional semiconductor materials to oxide semiconductor material, which fundamentally alters the electrical characteristics to achieve ultra-low off-state current and temperature insensitivity
Solution Approach 2:
The patent employs oxide semiconductor material with specific compositional characteristics (high purity, controlled stoichiometry) to create a transistor channel that combines low conductivity in off-state with thermal stability, resolving the contradiction between reliability and temperature sensitivity
2Use of energy by moving object
If the transistor is kept turned off during the inactive period to reduce power consumption, then power consumption is reduced, but the leakage of image signal through the transistor becomes apparent causing voltage reduction and display degradation
Solution Approach 1:
The patent changes the off-state current parameter of the transistor to ultra-low levels through oxide semiconductor material, enabling the transistor to maintain negligible leakage even when turned off for extended periods, thus allowing long inactive periods without display degradation
Solution Approach 2:
The patent enables extended periodic inactive periods where the transistor remains turned off without causing display degradation, allowing the liquid crystal display device to enter low-power states for longer durations while maintaining image quality upon reactivation
3Use of energy by stationary object
If the inactive period is extended to reduce power consumption further, then power consumption is reduced, but the amount of leakage through the transistor increases with temperature, making it difficult to maintain uniform display quality
Solution Approach 1:
The patent changes the thermal characteristics parameter of the transistor by using oxide semiconductor material, which exhibits minimal variation in off-state current across a wide temperature range, enabling the device to adapt to varying environmental conditions while maintaining display quality
Solution Approach 2:
The patent employs oxide semiconductor material that can be processed using low-cost fabrication techniques, making the temperature-stable transistor economically viable for mass production in various electronic devices
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
The use of high-purity oxide semiconductor transistors significantly reduces power consumption and suppresses display degradation, ensuring consistent image quality across varying temperatures and environments.
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
Implementation Method 2
The liquid crystal element includes a liquid crystal material which changes its alignment in accordance with voltage applied
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.