Display Device TFT Stack with Nitride Barrier for Film Adhesion
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Solution Overview
Problem
In TFTs with a bottom-contact structure, the adhesion between a molybdenum layer and an oxide semiconductor layer is compromised due to oxygen desorption from silicon oxide films, leading to film peeling and display failures, while silicon nitride films cause hydrogen desorption affecting threshold voltage shifts.
Innovation Solution
A display device with a stack of inorganic insulating films, including a silicon oxide and silicon nitride layer, is used to improve adhesion between a molybdenum-containing metal layer and a substrate, with the silicon nitride layer positioned under the source and drain electrodes to prevent hydrogen diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxide film is provided directly under the oxide semiconductor layer to prevent electrical continuity, then electrical isolation is improved, but oxygen desorption during annealing causes molybdenum layer oxidation and adhesion deterioration
Solution Approach 1:
A nitrogen-containing inorganic insulating film (silicon nitride film) is introduced as an intermediary layer between the silicon oxide film and the molybdenum layer. This intermediary film acts as a barrier to prevent oxygen diffusion from the silicon oxide film to the molybdenum layer during annealing, while also serving as an effective adhesion layer. The nitrogen-containing film has low oxygen permeability and provides strong bonding interfaces with both the silicon oxide film and the molybdenum layer, thereby resolving the contradiction between electrical isolation and adhesion strength.
2Strength
If a silicon nitride film is provided under the oxide semiconductor layer to improve adhesion to molybdenum, then adhesion is improved, but hydrogen desorption causes threshold voltage shift
Solution Approach 1:
The nitrogen-containing inorganic insulating film is selectively positioned only in regions where strong adhesion is required (under the source and drain electrodes), while allowing other regions to maintain their original structure. This localized application provides adhesion enhancement exactly where needed (at the molybdenum-inorganic insulating film interface) without causing widespread hydrogen diffusion effects that would affect threshold voltage stability in the channel region.
3Ease of manufacture
If the molybdenum layer is formed in the same layer as the oxide semiconductor layer in a bottom-contact structure, then manufacturing simplicity is improved, but film peeling occurs due to adhesion deterioration
Solution Approach 1:
The nitrogen-containing inorganic insulating film serves as a mediator between the molybdenum layer and the underlying silicon oxide film in the bottom-contact structure. This intermediary layer prevents oxygen-induced adhesion deterioration while maintaining the simple bottom-contact architecture, thereby enabling reliable film stacking without peeling issues.
4Reliability
If annealing is performed after silicon oxide film formation to activate the semiconductor, then semiconductor activation is improved, but oxygen desorption causes molybdenum oxidation
Solution Approach 1:
The nitrogen-containing inorganic insulating film acts as a protective barrier during the annealing process. It allows the annealing to proceed for semiconductor activation while blocking the oxygen desorption pathway from the silicon oxide film to the molybdenum layer, thereby preventing molybdenum oxidation despite the necessary thermal treatment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This structure enhances adhesion and prevents depression shifts in the TFTs, thereby reducing film peeling and display failures.
Implementation Method 1
the silicon nitride film and the oxide semiconductor layer are in contact together. In this case, hydrogen desorbed from the silicon nitride film reaches the oxide semiconductor layer, thereby possibly causing a depression shift
Implementation Method 2
a nitrogen-containing inorganic insulating film (a silicon nitride film)... has low permeability to oxygen and effectively prevents oxygen from reaching a molybdenum layer
Data Source
AI summary
A display device includes a TFT layer having a stack of, in sequence, a first inorganic insulating film composed of a first inorganic material, a second inorganic insulating film composed of a second inorganic material different from the first inorganic material, a first metal film composed of a metal material containing molybdenum a principal component, an oxide semiconductor film composed of an oxide semiconductor, a gate insulating film, and a second metal film. The second inorganic insulating film is provided between the first inorganic insulating film and a first electrode formed from the first metal film, and between the first inorganic insulating film and a second electrode formed from the first metal film.