Oxide Semiconductor Transistor Composition for Mobility and Reliability
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Solution Overview
Problem
Transistors using oxide semiconductor films face challenges with high field-effect mobility leading to normally-on characteristics and adverse effects from oxygen vacancies, which affect electrical characteristics and reliability, and the formation of spinel crystal structures can further degrade performance.
Innovation Solution
A semiconductor device with a transistor structure that includes an oxide semiconductor film, where the oxide semiconductor film is composed of a composite with regions having different atomic ratios of indium, zinc, and other elements, such as aluminum, gallium, or tin, to achieve improved field-effect mobility, reduced oxygen vacancies, and stable electrical characteristics, with specific atomic ratios and cluster formations that enhance carrier mobility and switching performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the field-effect mobility of the transistor is increased to improve performance, then the transistor tends to become normally on, which degrades reliability
Solution Approach 1:
The oxide semiconductor film is divided into multiple layers with different compositions and properties. The first oxide semiconductor layer has higher field-effect mobility for fast switching, while the second oxide semiconductor layer has lower field-effect mobility to prevent normally-on characteristics. This local differentiation allows each layer to fulfill its specific function while the composite structure achieves both high performance and reliability.
2Reliability
If oxygen vacancies are present in the oxide semiconductor film, then carrier concentration increases improving conductivity, but electrical characteristics change and reliability deteriorates
Solution Approach 1:
Instead of completely eliminating oxygen vacancies which are inherent in oxide semiconductors, the invention utilizes them beneficially in the first oxide semiconductor layer to achieve high field-effect mobility and good electrical characteristics. The second oxide semiconductor layer is designed with fewer oxygen vacancies to provide stability. This approach converts the potentially harmful oxygen vacancies into a useful feature for optimizing transistor performance while maintaining reliability through the composite structure.
3Reliability
If spinel crystal structures form in the oxide semiconductor, then certain electrical properties improve, but overall device performance degrades
Solution Approach 1:
The invention carefully controls the composition parameters of the oxide semiconductor layers to prevent spinel crystal structure formation. By adjusting the atomic ratios of metal elements and oxygen content within specific ranges, the film maintains a desirable amorphous or non-spinel crystalline structure. This parameter optimization ensures good electrical characteristics and reliable transistor operation while avoiding the harmful effects of spinel phase formation.
Data Source
AI summary
To improve field-effect mobility and reliability in a transistor including an oxide semiconductor film. A semiconductor device includes a transistor including an oxide semiconductor film. The transistor includes a region where the maximum value of field-effect mobility of the transistor at a gate voltage of higher than 0 V and lower than or equal to 10 V is larger than or equal to 40 and smaller than 150; a region where the threshold voltage is higher than or equal to minus 1 V and lower than or equal to 1 V; and a region where the S value is smaller than 0.3 V/decade.