Stacked Oxide Semiconductor Layer for TFT Stability
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Solution Overview
Problem
Oxide semiconductor layers in TFTs face damage and hydrogen introduction during the deposition of upper layers, leading to deteriorated TFT characteristics, such as conductive surfaces, shifted threshold voltages, and reduced mobility and stability, which are exacerbated by the need for additional oxidatively-treated layers and increased production costs.
Innovation Solution
A thin-film transistor structure featuring a stacked oxide semiconductor layer configuration, where a first oxide semiconductor layer with high Zn content (50% or more) is directly in contact with the source-drain electrode and passivation/etch stop layer, preventing plasma damage and hydrogen introduction without the need for an oxidatively-treated layer, and a second oxide semiconductor layer containing Sn and other elements is formed on the substrate side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If upper layers are deposited on the oxide semiconductor layer using plasma CVD method, then the TFT structure is completed with necessary functional layers, but the surface of the oxide semiconductor layer is damaged and hydrogen is introduced, causing oxygen vacancies and deteriorated TFT characteristics
Solution Approach 1:
A protective layer is introduced as an intermediary between the oxide semiconductor layer and the upper layers. This protective layer serves as a barrier that prevents plasma damage and hydrogen introduction from the upper layer deposition process while still allowing the TFT structure to be completed with all necessary functional layers.
Solution Approach 2:
The protective layer is formed in advance before the upper layers are deposited. This preliminary action prepares the oxide semiconductor layer surface by covering it with a protective barrier that will prevent damage during the subsequent deposition process, eliminating the need for post-processing oxidation steps.
2Reliability
If an oxidatively-treated layer is deposited to protect the oxide semiconductor layer surface, then surface damage and hydrogen introduction are prevented, but mobility deteriorates and stress stability lowers
Solution Approach 1:
The protective layer is designed as a temporary, disposable layer that serves its protection function during the deposition process and then is removed. This disposable approach prevents the need for permanent oxidatively-treated layers that would deteriorate mobility and stress stability, allowing the oxide semiconductor layer to maintain its excellent electrical characteristics.
3Reliability
If N2O plasma irradiation is used to excessively oxidize the surface before deposition, then defect occurrence and hydrogen introduction are reduced, but additional process steps are required, lowering productivity and increasing production cost
Solution Approach 1:
The protective layer is formed as a preliminary barrier before the upper layers are deposited, eliminating the need for post-deposition N2O plasma irradiation steps. This preliminary protection approach integrates defect prevention into the deposition process itself, maintaining high productivity and reducing production costs by avoiding additional process steps.
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 configuration ensures stable TFT characteristics and reduces production costs by eliminating the need for additional plasma treatments, maintaining high mobility and stress stability while preventing surface damage and hydrogen introduction during upper layer deposition.
Implementation Method 1
when a passivation layer is formed by a plasma CVD (Chemical Vapor Deposition) method, radicals and molecules made to have high speed by plasma will collide to the surface of an oxide semiconductor
Implementation Method 2
the oxide semiconductor is required not only to have high carrier concentration, but also to provide the TFT with excellent switching properties
Data Source
AI summary
There is provided an oxide semiconductor layer capable of making stable the electric characteristics of a thin-film transistor without requiring an oxidatively-treated layer when depositing a passivation layer or the like in display devices such as organic EL displays and liquid crystal displays. The thin-film transistor structure of the present invention at least having, on a substrate, an oxide semiconductor layer, a source-drain electrode, and a passivation layer in order from the substrate side, wherein the oxide semiconductor layer is a stacked product of a first oxide semiconductor layer and a second oxide semiconductor layer; the first oxide semiconductor layer has a Zn content of 50 atomic % or more as a percentage of all metal elements contained therein, and the first oxide semiconductor layer is formed on the source-drain electrode and passivation layer side; the second oxide semiconductor layer contains Sn and at least one element selected from the group consisting of In, Ga, and Zn, and the second oxide semiconductor layer is formed on the substrate side; and the first oxide semiconductor layer is in direct contact both with the source-drain electrode and with the passivation layer.