Oxide TFT Buffer Layer Structure for Low-Resistance Contacts
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Solution Overview
Problem
Thin film transistors using oxide semiconductor films for channel formation regions face challenges with high contact resistance and low frequency characteristics due to direct contact with metal electrode layers, leading to signal delay and display unevenness in large-area display devices.
Innovation Solution
An inverted-staggered thin film transistor structure is implemented with an oxide semiconductor layer containing indium (In), gallium (Ga), and zinc (Zn), where a buffer layer with higher carrier concentration than the semiconductor layer is introduced between the oxide semiconductor layer and the source and drain electrode layers to reduce contact resistance and parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If metal material with low resistance is used for source and drain electrode layers, then wiring resistance is reduced, but contact resistance between oxide semiconductor film and electrode layers increases due to Schottky junction formation
Solution Approach 1:
A buffer layer made of oxide semiconductor is introduced between the metal electrode layer and the oxide semiconductor film. This buffer layer acts as an intermediary that prevents direct contact between the metal and the semiconductor, thereby avoiding Schottky junction formation and reducing contact resistance while still allowing efficient electrical connection.
Solution Approach 2:
The carrier concentration of the buffer layer is controlled to be higher than that of the oxide semiconductor film. By changing the electrical parameters (carrier concentration) of the buffer layer, it achieves low resistance contact with both the metal electrode and the oxide semiconductor film, resolving the contradiction between low wiring resistance and low contact resistance.
2Ease of manufacture
If oxide semiconductor film is directly contacted with source and drain electrode layers, then manufacturing process is simplified, but frequency characteristics deteriorate due to increased parasitic capacitance
Solution Approach 1:
The buffer layer serves as an intermediary structure between the oxide semiconductor film and the electrode layers. While it adds an additional layer, it significantly reduces parasitic capacitance by preventing direct large-area contact, thereby improving frequency characteristics with minimal impact on manufacturing complexity.
Solution Approach 2:
The buffer layer is selectively formed only in regions where electrode contacts are needed, rather than throughout the entire device. This localized approach maintains process simplicity while achieving the desired reduction in parasitic capacitance at critical contact points.
Data Source
AI summary
To offer a semiconductor device including a thin film transistor having excellent characteristics and high reliability and a method for manufacturing the semiconductor device without variation. The summary is to include an inverted-staggered (bottom-gate structure) thin film transistor in which an oxide semiconductor film containing In, Ga, and Zn is used for a semiconductor layer and a buffer layer is provided between the semiconductor layer and source and drain electrode layers. An ohmic contact is formed by intentionally providing a buffer layer containing In, Ga, and Zn and having a higher carrier concentration than the semiconductor layer between the semiconductor layer and the source and drain electrode layers.