Thin Film Transistor With Oxide Buffer Layer
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Solution Overview
Problem
Thin film transistors with oxide semiconductor layers, such as those using zinc oxide, face reliability issues due to sensitive electrical characteristics that vary with structure and process conditions, leading to low reliability.
Innovation Solution
A thin film transistor structure is developed with an oxide semiconductor layer, an oxide buffer layer having a lower carrier concentration, and a protective layer with contact holes exposing the buffer layer in source and drain regions, allowing for source and drain electrodes to be coupled without overlapping with the gate electrode, thereby improving reliability and electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If oxide semiconductor layer is used as semiconductor layer, then fabrication temperature can be reduced and ion injection process can be omitted, but electrical characteristics are easily changed depending on structure and process conditions leading to low reliability
Solution Approach 1:
An oxide buffer layer is introduced as an intermediary between the oxide semiconductor layer and the source/drain electrodes. This buffer layer has a carrier concentration lower than that of the oxide semiconductor layer, serving as a transition region that stabilizes the interface and prevents direct harmful interactions between the electrodes and the semiconductor channel, thereby improving reliability while maintaining low-temperature fabrication
Solution Approach 2:
The oxide buffer layer is selectively positioned only in the source and drain regions, creating a local quality change. The buffer layer has different electrical properties (lower carrier concentration) compared to the oxide semiconductor layer, allowing the structure to have optimal characteristics in different regions: stable interface bonding at the electrodes and good channel performance in the middle
2Reliability
If source and drain electrodes are formed to couple with oxide semiconductor layer, then electrical connection is achieved, but damage occurs to oxide semiconductor layer during electrode formation process
Solution Approach 1:
The oxide buffer layer acts as a protective intermediary that enables the source and drain electrodes to be formed without directly contacting and damaging the oxide semiconductor layer. The buffer layer can withstand the electrode formation process while maintaining the integrity of the underlying semiconductor layer
Solution Approach 2:
The oxide buffer layer is formed in advance on the oxide semiconductor layer before the source and drain electrodes are deposited. This preliminary action prepares a protective interface that prevents damage during subsequent electrode formation processes
3Reliability
If gate electrode overlaps with source and drain electrodes, then standard transistor structure is achieved, but parasitic capacitance increases reducing signal transmission quality
Solution Approach 1:
The oxide buffer layer is selectively formed only in the source and drain regions, creating a local quality change that allows non-overlapping electrode configuration. This local modification enables reduced parasitic capacitance without requiring a complete redesign of the overall transistor structure
Data Source
AI summary
A thin film transistor includes a gate electrode, a gate insulating layer, an oxide semiconductor layer, an oxide buffer layer, a protective layer, and source and drain electrodes. The gate electrode is formed on a substrate. The gate insulating layer is formed on the substrate. The oxide semiconductor layer is formed on the gate insulating layer and includes a source, a channel and a drain region. The oxide buffer layer is formed on the oxide semiconductor layer, and has a carrier concentration lower than that of the oxide semiconductor layer. The protective layer is formed on the oxide buffer layer and the gate insulating layer, and has contact holes formed therein so that the oxide buffer layer in the source and drain regions are exposed therethrough. The source and drain electrodes are coupled with the oxide buffer layer in the source and drain regions through the contact holes.