IGZO Thin Film Transistor Buffer Layer Contact Resistance
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Solution Overview
Problem
Thin film transistors using oxide semiconductor films face challenges with high contact resistance between the oxide semiconductor layer and metal source and drain electrodes, leading to signal delay and reduced frequency characteristics, which hinder high-speed operation and cause display unevenness in large-area display devices.
Innovation Solution
A buffer layer with higher carrier concentration than the oxide semiconductor layer is introduced between the oxide semiconductor layer and the source and drain electrodes to reduce contact resistance, and a second buffer layer is used to further optimize carrier concentration, ensuring reliable ohmic contact and improved electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a metal material with low electric resistance is used for source and drain electrodes, then wiring resistance is reduced, but contact resistance between the oxide semiconductor film and electrodes increases due to Schottky junction formation
Solution Approach 1:
An oxide semiconductor layer with higher carrier concentration is introduced as an intermediary between the metal source/drain electrodes and the oxide semiconductor film. This intermediate layer acts as a buffer that prevents direct contact between the metal electrodes and the semiconductor film, thereby avoiding Schottky junction formation while maintaining low resistance electrical pathways. The intermediate layer has carrier concentration of 1×10^18 to 1×10^21 atoms/cm³, which is higher than the channel-forming oxide semiconductor layer, enabling ohmic contact with the metal electrodes while still providing good interface with the semiconductor film.
2Ease of manufacture
If the oxide semiconductor film directly contacts source and drain electrodes, then manufacturing is simplified, but capacitance increases at the contact portion, lowering frequency characteristics
Solution Approach 1:
The structure is segmented into distinct functional layers: a channel-forming oxide semiconductor layer with lower carrier concentration (1×10^16 to 1×10^18 atoms/cm³) and an oxide semiconductor layer with higher carrier concentration (1×10^18 to 1×10^21 atoms/cm³) positioned between the metal electrodes and the channel layer. This segmentation allows the channel layer to maintain low capacitance for high-frequency operation while the higher-concentration layer provides the necessary electrical contact functionality, thus improving frequency characteristics without significantly complicating manufacturing.
3Reliability
If carrier concentration in the oxide semiconductor layer is increased to reduce contact resistance, then electrical connection improves, but variations in electrical properties increase, causing display unevenness
Solution Approach 1:
Different regions of the oxide semiconductor structure are assigned different carrier concentrations to fulfill different functional requirements. The channel-forming region maintains lower carrier concentration (1×10^16 to 1×10^18 atoms/cm³) to ensure uniform electrical properties and reduce display unevenness, while the region positioned between the metal electrodes and the channel layer has higher carrier concentration (1×10^18 to 1×10^21 atoms/cm³) to ensure low contact resistance. This local differentiation of material properties allows simultaneous optimization of both electrical connection and manufacturing precision.
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
The solution results in a thin film transistor with reduced contact resistance, low parasitic capacitance, and improved dynamic characteristics, enhancing the reliability and performance of display devices by minimizing variations in electrical properties and maintaining optimal oxygen concentration.
Implementation Method 1
A buffer layer with higher carrier concentration than the oxide semiconductor layer is introduced between the oxide semiconductor layer and the source and drain electrodes to reduce contact resistance
Data Source
AI summary
One of the objects of the present invention is to provide a thin film transistor using an oxide semiconductor film containing indium (In), gallium (Ga), and zinc (Zn), in which the contact resistance between the oxide semiconductor layer and a source and drain electrodes is reduced, and to provide a method for manufacturing the thin film transistor. An ohmic contact is formed by intentionally providing a buffer layer having a higher carrier concentration than the IGZO semiconductor layer between the IGZO semiconductor layer and the source and drain electrode layers.