Layered Oxide Semiconductor Transistor for Light-Stable Mobility
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Solution Overview
Problem
Oxide semiconductor films with smaller energy band gaps are prone to reliability issues due to light irradiation, as evidenced by significant shifts in threshold voltage during negative bias-temperature stress tests, affecting the stability of transistors.
Innovation Solution
A semiconductor device structure incorporating a layered oxide semiconductor film with varying In and M (Al, Ga, Y, or Sn) compositions, where the second oxide semiconductor film has a lower In content and includes a metal element, and is formed using a sputtering method with controlled oxygen gas flow, reducing oxygen vacancies and hydrogen impurities to enhance stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an oxide semiconductor film containing much In is used, then field-effect mobility is improved, but reliability deteriorates due to smaller energy band gap and light irradiation sensitivity
Solution Approach 1:
The oxide semiconductor film is divided into multiple layers with different In content. The first oxide semiconductor film contains much In for high field-effect mobility, while the second oxide semiconductor film contains less In for larger energy band gap and light resistance. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the oxide semiconductor film have different compositions tailored to local requirements. The channel region uses high-In content for mobility, while the region exposed to light uses low-In content for stability. This local quality differentiation resolves the contradiction between mobility and light resistance.
2Reliability
If the energy band gap is reduced to improve conductivity, then field-effect mobility increases, but sensitivity to light irradiation increases causing threshold voltage shift
Solution Approach 1:
The film is segmented into regions with different band gaps. The high-conductivity region has smaller band gap for mobility, while the light-exposed region has larger band gap for light resistance. This resolves the contradiction between conductivity and light sensitivity.
Solution Approach 2:
The oxide semiconductor film is constructed as a composite material with varying In content to create regions with different band gap characteristics. This composite structure allows simultaneous achievement of high conductivity and light resistance in different parts of the film.
3Device complexity
If a single-layer oxide semiconductor film is used, then device complexity is reduced, but reliability under bias stress with light irradiation deteriorates
Solution Approach 1:
The oxide semiconductor film is segmented into multiple layers, each with specific composition optimized for different functions. This segmentation improves reliability under bias stress with light irradiation while maintaining manageable device complexity through systematic layer design.
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
The solution effectively suppresses changes in electrical characteristics and improves reliability by reducing oxygen vacancies and hydrogen impurities, leading to higher field-effect mobility and resistance to negative bias stress tests with light irradiation.
Implementation Method 1
a second oxide semiconductor film over the first oxide semiconductor film
Data Source
AI summary
To suppress a change in electrical characteristics in a transistor including an oxide semiconductor film. The transistor includes a first gate electrode, a first insulating film, an oxide semiconductor film, a source electrode, a drain electrode, a second insulating film, a second gate electrode, and a third insulating film. The oxide semiconductor film includes a first oxide semiconductor film on the first gate electrode side, and a second oxide semiconductor film over the first oxide semiconductor film. The first oxide semiconductor film and the second oxide semiconductor film include In, M, and Zn (M is Al, Ga, Y, or Sn). In a region of the second oxide semiconductor film, the number of atoms of In is smaller than that in the first oxide semiconductor film. The second gate electrode includes at least one metal element included in the oxide semiconductor film.