Layered Oxide Semiconductor Transistor for Light-Induced Stability
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Solution Overview
Problem
Oxide semiconductor transistors with small energy band gaps are prone to reduced reliability due to light irradiation, as evidenced by significant shifts in threshold voltage during negative bias-temperature stress tests, which affects their electrical characteristics and long-term performance.
Innovation Solution
A semiconductor device structure incorporating a layered oxide semiconductor film with a first region having a higher indium atomic proportion and a second region with a lower indium atomic proportion, where the second region is thinner, and includes a crystal part with the c-axis parallel to the surface, and excess oxygen is introduced to reduce oxygen vacancies, enhancing the device's resistance to light-induced changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an oxide semiconductor film with small energy band gap is used, then electrical conductivity is improved, but reliability under light irradiation deteriorates
Solution Approach 1:
The oxide semiconductor film is divided into multiple layers with different compositions and thicknesses. The first layer contains In at 30-70 atomic % for high conductivity, while the second layer contains In at 10-40 atomic % for light resistance, creating a segmented structure that resolves the contradiction between conductivity and reliability
Solution Approach 2:
Different regions of the oxide semiconductor film are given different local compositions tailored to specific functions. The region closer to the gate electrode has higher In content for conductivity, while regions exposed to light have lower In content and higher light-resistant elements, achieving local optimization of both conductivity and light resistance
2Speed
If indium atomic proportion is increased, then field-effect mobility is improved, but threshold voltage shift under stress increases
Solution Approach 1:
The oxide semiconductor film is segmented into layers with different In concentrations. The first layer has In at 30-70 atomic % for high mobility, while the second layer has In at 10-40 atomic % for stability, allowing both high mobility and threshold voltage stability to coexist
Solution Approach 2:
The oxide semiconductor film is formed as a composite structure combining materials with different In content. This composite approach allows the system to achieve both high field-effect mobility from the In-rich layer and threshold voltage stability from the In-poor layer
Data Source
AI summary
The transistor includes a gate electrode, a gate insulating film over the gate electrode, an oxide semiconductor film over the gate insulating film, a source electrode and a drain electrode electrically connected to the oxide semiconductor film. The oxide semiconductor film includes a first oxide semiconductor film on the gate electrode side and a second oxide semiconductor film over the first oxide semiconductor film. The first oxide semiconductor film includes a first region in which an atomic proportion of In is larger than that of M (M is Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf). The second oxide semiconductor film includes a second region in which an atomic proportion of In is smaller than that of the first oxide semiconductor film. The second region includes a portion thinner than the first region.