Oxide Semiconductor TFT Substrate with Protective Insulating Layer
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Solution Overview
Problem
The existing manufacturing processes for thin film transistor (TFT) substrates using oxide semiconductors face challenges such as damage to the semiconductor film during the formation of source and drain electrodes due to acid etching, leading to degradation of TFT characteristics and increased manufacturing costs due to the need for additional photolithography processes for etch stopper layers.
Innovation Solution
A TFT substrate configuration that includes a semiconductor film made of an oxide semiconductor with a protective insulating layer, where the source and drain electrodes are formed using conductors other than oxide conductors, and oxide conductors are used for the second source and drain electrodes, connected through contact holes, reducing the risk of oxidation-reduction reactions and eliminating the need for additional photolithography steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If acid etching is used to form source and drain electrodes on oxide semiconductor films, then the electrodes can be formed, but the semiconductor film is damaged and TFT characteristics are degraded
Solution Approach 1:
A protective film is introduced as an intermediary layer between the oxide semiconductor film and the acid etching solution. This protective film allows acid etching to proceed for electrode formation while preventing direct contact between the acid and the semiconductor film, thus avoiding damage to the TFT characteristics.
Solution Approach 2:
The electrode formation process is segmented into multiple steps: first forming a protective film on the semiconductor film, then forming the electrode pattern on top of the protective film, and finally removing the protective film. This segmentation allows the acid etching to affect only the protective film and electrode materials, not the semiconductor film.
2Reliability
If additional photolithography processes are added to prevent semiconductor film damage, then TFT characteristics are protected, but manufacturing cost increases
Solution Approach 1:
The protective film serves multiple functions: it protects the semiconductor film during acid etching, acts as a mask for electrode pattern formation, and can be removed selectively. This multi-functionality eliminates the need for separate etch stopper layers and additional photolithography processes, reducing manufacturing complexity while maintaining TFT characteristics.
3Reliability
If oxide conductors are used for source and drain electrodes, then contact properties improve, but oxidation-reduction reactions occur at the interface
Solution Approach 1:
The protective film acts as an intermediary barrier between the oxide conductor and the oxide semiconductor film, preventing direct chemical interaction. This allows oxide conductors to maintain their excellent contact properties while avoiding oxidation-reduction reactions at the interface that would degrade TFT characteristics.
Data Source
AI summary
A thin film transistor substrate includes a semiconductor channel layer made of an oxide semiconductor, protective insulating layers that cover the semiconductor channel layer, a first source electrode, a first drain electrode, a second source electrode, and a second drain electrode. The second source electrode is located on the first source electrode and connected with the semiconductor channel layer through a first contact hole. The second drain electrode is located on the first drain electrode and connected with the semiconductor channel layer through a second contact hole.