Oxide Semiconductor Transistor Channel Length Optimization
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Solution Overview
Problem
Transistors with oxide semiconductors in display devices face degradation due to uneven oxidation levels in the channel forming regions, leading to negative threshold shifts and hump characteristics in voltage-current curves, which affect overall performance.
Innovation Solution
The transistor design includes a gate electrode with varying lengths overlapping different oxidation regions of the oxide semiconductor layer, where the channel length in the under-oxidized region is made greater than in the oxidized region to prevent negative threshold shifts and hump characteristics, using a configuration with both top and bottom gates and specific electrode shapes to optimize channel lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the channel length is made longer in the under-oxidized region to suppress negative threshold shifts, then transistor reliability improves, but the device complexity increases due to varying channel lengths in different regions
Solution Approach 1:
The patent applies local quality by creating different channel lengths in different regions of the oxide semiconductor layer. Specifically, the channel length in the under-oxidized region is made longer than in the oxidized region, allowing each region to be optimized for its specific oxidation state. This local differentiation suppresses negative threshold shifts in the under-oxidized region while maintaining good electrical characteristics in the oxidized region, thereby improving overall transistor reliability without requiring a complete redesign of the entire channel structure.
2Reliability
If the gate electrode length is increased to cover the entire oxide semiconductor layer, then control over the channel improves, but the manufacturing precision requirements increase due to alignment constraints
Solution Approach 1:
The gate electrode is designed with local quality variations, having different lengths in different regions. The gate electrode extends over the oxidized region with a first length and over the under-oxidized region with a second length that is longer than the first length. This localized approach allows effective channel control in each region according to its oxidation state, while reducing the overall alignment precision requirements compared to a single long gate covering the entire oxide semiconductor layer.
Data Source
AI summary
According to one embodiment, a transistor includes a gate electrode, an oxide semiconductor layer which overlaps the gate electrode and including a central portion and an end portion, and a source electrode and a drain electrode each connected to the oxide semiconductor layer, wherein an oxidation degree of the end portion is lower than an oxidation degree of the central portion, and a length of the gate electrode overlapping the central portion is greater than a length of the gate electrode overlapping the end portion.