Oxide Semiconductor Transistor Gate Electrode Overlap
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Solution Overview
Problem
Transistors using oxide semiconductor films exhibit unstable electric characteristics due to impurity entry or oxygen release, particularly at the end portions, leading to the formation of parasitic channels, which affect threshold voltage and current drive capability.
Innovation Solution
A semiconductor device structure where at least one of the source or drain electrodes is positioned such that it is not electrically connected to the end portion of the oxide semiconductor film, using a specific layer configuration and materials to prevent impurity entry and oxygen release, including a gate electrode layer with barrier layers and an oxide semiconductor film with aligned crystal parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the source and drain electrodes are electrically connected to the end portion of the oxide semiconductor film, then the transistor structure is simplified and easier to manufacture, but parasitic channels are formed at the end portion causing unstable electric characteristics
Solution Approach 1:
The patent extracts the harmful electrical connection between the drain electrode and the end portion of the oxide semiconductor film. By positioning the drain electrode to overlap only with the inner edge portion of the gate electrode layer (not extending to the end portion), the parasitic channel formation is eliminated while maintaining the essential transistor functionality through the controlled channel region.
Solution Approach 2:
The patent applies different spatial configurations to different regions: the source electrode is allowed to contact the end portion for easy connection, while the drain electrode is positioned to overlap only with the inner edge portion to prevent parasitic channels. This local differentiation of electrode positioning strategies resolves the contradiction between manufacturing ease and device reliability.
2Power
If the gate voltage is increased to improve current drive capability, then the first channel conducts better, but the parasitic channel forms at lower threshold voltage causing two-stage current increase and unstable operation
Solution Approach 1:
The patent removes the parasitic channel formation mechanism by preventing electrical connection at the end portion where parasitic channels form. This eliminates the harmful two-stage current increase effect, allowing the transistor to operate with a single well-defined threshold voltage corresponding to the first channel, thus stabilizing the gate voltage control.
3Use of energy by moving object
If the oxide semiconductor film is used to form the channel, then low-power operation is achieved, but impurity entry and oxygen release at end portions cause electric characteristic changes
Solution Approach 1:
The patent extracts the problematic end portion region from the electrical conduction path by positioning the drain electrode to overlap only with the inner edge portion of the gate electrode. This prevents impurity entry and oxygen release at the end portion from affecting the channel characteristics, maintaining the low-power operation benefits while ensuring composition stability.
Data Source
AI summary
To provide a highly reliable semiconductor device in which a transistor including an oxide semiconductor film has stable electric characteristics. The semiconductor device includes a gate electrode layer over a substrate, a gate insulating film over the gate electrode layer, an oxide semiconductor film over the gate insulating film, a drain electrode layer which is over the oxide semiconductor film so as to overlap with the gate electrode layer, and a source electrode layer provided so as to cover part of an outer edge portion of the oxide semiconductor film. An outer edge portion of the drain electrode layer is on an inner side than an outer edge portion of the gate electrode layer.