Oxide Semiconductor TFT With Protective Insulation Layer
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Solution Overview
Problem
The manufacturing process of thin film transistors (TFTs) using oxide semiconductors faces challenges such as damage to the semiconductor channel layer during the formation of source and drain electrodes, leading to degraded TFT characteristics, and a short channel effect due to the direct deposition of metal films, which affects the reliability and display quality of liquid crystal display devices.
Innovation Solution
A TFT structure is implemented with a gate electrode, first and second insulating films, and a semiconductor channel layer connected via contact holes in the second insulating film, where the source and drain electrodes are formed as a lower layer under a protective insulation layer, preventing damage to the channel layer and reducing the short channel effect by increasing the channel length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the source electrode and drain electrode are directly deposited on the oxide semiconductor film, then the TFT structure can be simplified and manufacturing process can be reduced, but the oxide semiconductor film is damaged by the acid solution used to etch the metal film, resulting in degradation of TFT characteristics
Solution Approach 1:
The patent divides the electrode structure into multiple segments: a first electrode (source/drain) deposited on the oxide semiconductor film, and a second electrode (gate electrode) deposited on the first electrode. This segmentation allows the etching process to be performed on the first electrode without directly exposing the oxide semiconductor film to the acid solution, thus preventing damage while maintaining structural complexity at an acceptable level.
Solution Approach 2:
The first electrode acts as an intermediary layer between the etching process and the oxide semiconductor film. By performing the etching process on the first electrode rather than directly on the oxide semiconductor film, the harmful acid solution is blocked from damaging the channel layer, thus protecting the TFT characteristics while still allowing effective electrode formation.
2Ease of manufacture
If the source electrode and drain electrode are formed as an upper layer on the oxide semiconductor film, then the TFT can be manufactured using conventional processes, but the oxide semiconductor film is damaged by the acid solution during etching of the metal film, causing characteristics degradation
Solution Approach 1:
The patent performs the etching process on the first electrode before depositing the oxide semiconductor film in the channel formation region. This preliminary etching action allows the metal electrode pattern to be formed with high precision while preventing subsequent damage to the oxide semiconductor film during the etching process, thus maintaining both manufacturing ease and film integrity.
Solution Approach 2:
Instead of the conventional approach of depositing the oxide semiconductor film first and then forming the electrode on top, the patent inverts the sequence by first forming the metal electrode (first electrode) and then depositing the oxide semiconductor film. This inversion allows the etching process to be performed on the metal electrode without exposing the oxide semiconductor film to damaging acid solutions, thus preserving film integrity while maintaining manufacturing feasibility.
3Productivity
If the channel length is short to improve device integration, then productivity increases, but the short channel effect occurs, affecting reliability
Solution Approach 1:
The patent introduces a vertical dimension to the electrode structure by stacking the second electrode (gate electrode) on top of the first electrode (source/drain electrode). This three-dimensional arrangement allows for shorter horizontal channel lengths that improve integration density while the vertical gate control maintains effective electrostatic control over the channel, suppressing short channel effects and preserving device reliability.
Data Source
AI summary
It is an object to provide a technique capable of suppressing a damage on a semiconductor channel layer due to a process of forming a source electrode and a drain electrode and also suppressing a short channel effect. A thin film transistor includes a gate electrode, a first insulating film, a source electrode, a drain electrode, a second insulating film, and a semiconductor channel layer that includes an oxide semiconductor. The second insulating film is disposed on the first insulating film, the source electrode, and the drain electrode. The semiconductor channel layer is electrically connected to the source electrode and the drain electrode via a first contact hole and a second contact hole provided in the second insulating film.