Multilayer Oxide Semiconductor Transistor for Oxygen Vacancy Stability
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Solution Overview
Problem
Transistors using oxide semiconductor films face issues with high field-effect mobility leading to normally-on characteristics and electrical characteristic changes due to oxygen vacancies, which affect reliability and power consumption.
Innovation Solution
A semiconductor device structure with multiple oxide semiconductor films, including a region with lower crystallinity acting as a diffusion path for excess oxygen, and higher crystallinity films to inhibit impurity entry and improve reliability, along with a specific atomic ratio of In, M, and Zn, and a composite oxide semiconductor film with regions of varying oxygen content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the field-effect mobility is increased to improve transistor performance, then the mobility is improved, but the transistor tends to be normally on which deteriorates reliability
Solution Approach 1:
The patent applies local quality by creating a multi-layer oxide semiconductor structure where different layers have different oxygen vacancy concentrations. The first and third oxide semiconductor layers have lower oxygen vacancy concentrations to prevent normally-on characteristics, while the second layer has higher oxygen vacancy concentration to provide carrier supply. This spatial differentiation of material properties allows simultaneous achievement of high mobility and reliability.
Solution Approach 2:
The patent uses composite materials by stacking multiple oxide semiconductor layers with different compositions and crystallinities. The composite structure includes crystalline regions (for high mobility) and amorphous regions (for oxygen supply and stability), creating a material system that combines the advantages of both ordered and disordered structures to achieve high performance and reliability.
2Speed
If oxygen vacancies are increased to improve field-effect mobility, then the mobility is improved, but electrical characteristics change which deteriorates reliability
Solution Approach 1:
The patent segments the oxide semiconductor film into multiple distinct layers, each with controlled oxygen vacancy concentrations. The first oxide semiconductor layer has low oxygen vacancies for stability, the second layer has high oxygen vacancies for carrier supply and high mobility, and the third layer has low oxygen vacancies for stability. This segmentation allows independent optimization of each layer's oxygen vacancy content to simultaneously achieve high mobility and electrical characteristic stability.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the oxygen vacancy concentration as a key parameter in each oxide semiconductor layer. By varying this parameter across different layers (low in first and third layers, high in second layer) and controlling crystallinity parameters, the patent achieves optimal balance between mobility enhancement and electrical characteristic stability.
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
Enhances field-effect mobility, reduces oxygen vacancies, and improves reliability by minimizing changes in electrical characteristics and power consumption, resulting in a highly reliable and low-power semiconductor device.
Implementation Method 1
the amorphous oxide semiconductor film includes a region serving as a diffusion path of excess oxygen
Implementation Method 2
both the first oxide semiconductor film and the third oxide semiconductor film include a crystal part
Data Source
AI summary
The field-effect mobility and reliability of a transistor including an oxide semiconductor film are improved. One embodiment of the present invention is a semiconductor device which includes a gate electrode, an insulating film over the gate electrode, an oxide semiconductor film over the insulating film, and a pair of electrodes over the oxide semiconductor film. The oxide semiconductor film includes a first oxide semiconductor film, a second oxide semiconductor film over the first oxide semiconductor film, and a third oxide semiconductor film over the second oxide semiconductor film. The first oxide semiconductor film, the second oxide semiconductor film, and the third oxide semiconductor film include the same element. The second oxide semiconductor film includes a region having lower crystallinity than one or both of the first oxide semiconductor film and the third oxide semiconductor film.