Oxide Semiconductor TFTs for Stable Multi-Grayscale Displays
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Solution Overview
Problem
Existing thin film transistors using amorphous silicon have high off currents, leading to voltage fluctuations in liquid crystal displays, which affect grayscale accuracy and image stability, especially in large panels.
Innovation Solution
Using an oxide semiconductor with a band gap greater than 2 eV and reducing the concentration of impurity carrier donors to minimize off current, resulting in a transistor with off currents below 10 zA/μm at room temperature and 100 zA/μm at 85°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon is used for thin film transistor, then manufacturing is easier and cost is lower, but off current is high causing voltage fluctuation
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical properties by achieving extremely low off current (below 10 zA/μm at room temperature) while maintaining manufacturing feasibility through sputtering and annealing processes
2Object-generated harmful factors
If oxide semiconductor with low electron carrier concentration is used, then off current should be reduced, but on-off ratio remains low at only about 10^4
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: uses In-Ga-Zn-O oxide semiconductor with specific atomic ratios (In:Ga:Zn = 1:1:3 or 1:2:3), controls oxygen content, and applies specific annealing conditions to achieve both extremely low off current and high on-off ratio exceeding 10^8
Solution Approach 2:
The patent employs composite material strategy by combining In-Ga-Zn-O oxide semiconductor with specific gate insulator materials and electrode materials to achieve synergistic effects that simultaneously reduce off current and enhance on-state current
3Speed
If polysilicon is used to improve operation speed, then transistor performance increases, but crystallization step causes variation in characteristics and inhibits panel enlargement
Solution Approach 1:
The patent replaces the mechanical/thermal crystallization process with a different approach using oxide semiconductor that achieves high mobility through electronic structure optimization rather than crystal formation, eliminating the need for high-temperature crystallization steps and enabling large-area manufacturing with uniform characteristics
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
Stabilizes signal voltage in pixels, enabling accurate multi-grayscale display by reducing voltage fluctuations and eliminating the need for storage capacitors, thus enhancing image quality.
Implementation Method 1
Using an oxide semiconductor with a band gap greater than 2 eV and reducing the concentration of impurity carrier donors to minimize off current
Data Source
AI summary
Disclosed is a display device including a transistor showing extremely low off current. In order to reduce the off current, a semiconductor material whose band gap is greater than that of a silicon semiconductor is used for forming a transistor, and the concentration of an impurity which serves as a carrier donor of the semiconductor material is reduced. Specifically, an oxide semiconductor whose band gap is greater than or equal to 2 eV, preferably greater than or equal to 2.5 eV, more preferably greater than or equal to 3 eV is used for a semiconductor layer of a transistor, and the concentration of an impurity which serves as a carrier donor included is reduced. Consequently, the off current of the transistor per micrometer in channel width can be reduced to lower than 10 zA/μm at room temperature and lower than 100 zA/μm at 85° C.