Indium Tungsten Zinc Oxide Semiconductor Film for TFT Threshold Voltage Control
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Solution Overview
Problem
Amorphous oxide semiconductor films used in TFTs have limited field-effect mobility and higher threshold voltage compared to traditional amorphous silicon, making it difficult to maintain optimal device operation within the same voltage range.
Innovation Solution
An oxide semiconductor film composed of nanocrystalline or amorphous oxide with indium, tungsten, and zinc, where the tungsten content is between 0.5 and 5 atomic % and the electric resistivity is greater than 10^-1 Ωcm, is used as a channel layer, achieving a threshold voltage of 0 to 4 V and high field-effect mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If amorphous oxide semiconductor film is used in TFT channel layer, then higher carrier mobility can be expected compared with a-Si, but the field-effect mobility is limited to at most approximately 10 cm2/Vs
Solution Approach 1:
The patent changes the compositional parameters of the oxide semiconductor film by introducing tungsten as a dopant element and controlling the In/(In+Zn) atomic ratio within 0.1 to 0.5. This parameter optimization resolves the contradiction by achieving field-effect mobility exceeding 10 cm2/Vs while maintaining the amorphous oxide semiconductor structure.
Solution Approach 2:
The patent creates a composite oxide semiconductor material containing indium, zinc, and tungsten in specific ratios. The addition of tungsten (0.01 to 5 atomic %) to the In-Zn-O system forms a composite material that simultaneously improves carrier mobility and field-effect mobility, resolving the technical contradiction.
2Ease of manufacture
If oxide sintered body mainly made of indium including tungsten is used to fabricate oxide semiconductor film, then the material can be suitably used for sputtering method, but the threshold voltage Vth becomes higher than 4 V
Solution Approach 1:
The patent optimizes the compositional parameters by controlling the In/(In+Zn) atomic ratio to 0.1-0.5 and adding tungsten at 0.01-5 atomic %. This parameter control achieves threshold voltage within 0 to 4 V range while maintaining ease of manufacture through sputtering method.
Solution Approach 2:
The patent introduces tungsten locally as a dopant element at controlled concentrations (0.01 to 5 atomic %) within the oxide semiconductor film. This local addition of tungsten improves electrical properties and reduces threshold voltage to within the desired 0 to 4 V range while preserving the overall material structure suitable for sputtering fabrication.
3Ease of operation
If conventional a-Si is used as semiconductor material for TFT, then threshold voltage Vth is generally 2 to 4 V, but when switching to oxide semiconductor material, maintaining the same Vth range becomes difficult
Solution Approach 1:
The patent changes the compositional parameters of the oxide semiconductor film by controlling the In/(In+Zn) atomic ratio within 0.1 to 0.5 and adding tungsten at 0.01 to 5 atomic %. These parameter adjustments enable the oxide semiconductor to achieve threshold voltage within the conventional 0 to 4 V range, ensuring compatibility with existing device designs.
Solution Approach 2:
The patent creates a homogeneous oxide semiconductor film with uniform distribution of indium, zinc, and tungsten elements. The controlled composition (In/(In+Zn) ratio of 0.1-0.5 and W content of 0.01-5 atomic %) ensures consistent electrical properties throughout the film, enabling reliable threshold voltage control within the desired range for display applications.
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 configuration results in a semiconductor device with improved threshold voltage and field-effect mobility, reduced OFF current, and increased ON/OFF current ratio at low driving voltages, maintaining high mobility even at elevated temperatures.
Implementation Method 1
Japanese Patent Laying-Open No. 2008-192721 (PTD 2) discloses an oxide sintered body mainly made of indium and including tungsten, as a material suitably used when forming an oxide semiconductor film by the sputtering method and the like.
Data Source
AI summary
There is provided an oxide semiconductor film composed of nanocrystalline oxide or amorphous oxide, wherein the oxide semiconductor film includes indium, tungsten and zinc, a content rate of tungsten to a total of indium, tungsten and zinc in the oxide semiconductor film is higher than 0.5 atomic % and equal to or lower than 5 atomic %, and an electric resistivity is equal to or higher than 10−1 Ωcm. There is also provided a semiconductor device including the oxide semiconductor film.