Oxide Semiconductor LCD Pixel Transistors With Ultra-Low Off-Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing liquid crystal display devices using oxide semiconductors face challenges in achieving low power consumption and high image quality due to high off-current in transistors, leading to display deterioration and variability in outdoor environments.
Innovation Solution
The use of an oxide semiconductor with a wider band gap than silicon, combined with a reduced impurity concentration and metal nitride source and drain electrodes, results in a transistor with extremely low off-current, enhancing field-effect mobility and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a thin film transistor using amorphous silicon is used, then the manufacturing process is established and panel production is feasible, but the operation speed is slow and high performance cannot be achieved
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical characteristics to achieve both high speed and low off-current. This material substitution enables field-effect mobility exceeding 10 cm²/Vs while maintaining manufacturing feasibility through established sputtering techniques
Solution Approach 2:
The patent employs a composite structure combining oxide semiconductor layer with metal nitride electrodes (TiN, TaN, WN). This composite approach leverages the high mobility of oxide semiconductor and the excellent conductivity of metal nitrides to achieve superior transistor performance with low off-current characteristics
2Speed
If a thin film transistor using polysilicon is used to improve operation speed, then speed performance increases, but a crystallization step is required causing variation in transistor characteristics and inhibiting panel area enlargement
Solution Approach 1:
The patent changes the material state from crystalline polysilicon to amorphous oxide semiconductor, eliminating the need for crystallization steps. This maintains high speed performance through intrinsic material properties while simplifying the manufacturing process to avoid variation and scaling limitations
Solution Approach 2:
The patent replaces the thermal crystallization process with a sputtering deposition process. This substitution eliminates the high-temperature crystallization step that causes variation and limits panel size, while achieving comparable or superior electrical performance through oxide semiconductor's inherent high mobility
3Reliability
If an oxide semiconductor with electron carrier concentration lower than 10¹⁸/cm³ is used, then the material shows n-type characteristics, but the off-current is high resulting in low on-off ratio of only 10³
Solution Approach 1:
The patent optimizes the oxide semiconductor parameters by controlling oxygen partial pressure during sputtering to achieve specific oxygen deficiency levels. This creates a band structure with high mobility carriers while maintaining low off-current through appropriate Fermi level positioning, achieving on-off ratios exceeding 10⁸
Solution Approach 2:
The patent combines oxide semiconductor with metal nitride electrodes (TiN, TaN, WN) to create a composite transistor structure. The metal nitride layer provides excellent conductivity and forms appropriate interfaces that reduce off-current, while the oxide semiconductor provides high mobility channels, achieving superior on-off characteristics
4Loss of energy
If the transistor off-current is high, then power consumption increases and display deterioration occurs, but reducing off-current requires material and structure optimization
Solution Approach 1:
The patent changes the oxide semiconductor deposition parameters (oxygen partial pressure, power density, temperature) to optimize the material properties. This achieves low off-current through controlled oxygen deficiency that creates favorable band alignment, reducing power consumption while maintaining simple manufacturing processes
Solution Approach 2:
The patent uses metal nitride (TiN, TaN, WN) combined with oxide semiconductor to create a composite structure that reduces off-current. The metal nitride provides excellent conductivity and interface quality, achieving low power consumption through reduced leakage without significantly increasing device complexity
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 significantly reduces power consumption and maintains high image quality by minimizing off-current, ensuring stable signal voltage and reducing display deterioration, even in varying environmental conditions.
Implementation Method 1
The use of an oxide semiconductor with a wider band gap than silicon, combined with a reduced impurity concentration and metal nitride source and drain electrodes, results in a transistor with extremely low off-current
Data Source
AI summary
A display panel for displaying an image is provided with a plurality of pixels arranged in a matrix. Each pixel includes one or more units each including a plurality of subunits. Each subunit includes a transistor in which an oxide semiconductor layer which is provided so as to overlap a gate electrode with a gate insulating layer interposed therebetween, a pixel electrode which drives liquid crystal connected to a source or a drain of the transistor, a counter electrode which is provided so as to face the pixel electrode, and a liquid crystal layer provided between the pixel electrode and the counter electrode. In the display panel, a transistor whose off current is lower than 10 zA/μm at room temperature per micrometer of the channel width and off current of the transistor at 85° C. can be lower than 100 zA/μm per micrometer in the channel width.