Oxide TFT Contact Layer Threshold Voltage Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current oxide thin film transistors (TFTs) face challenges in achieving stable operation and uniform characteristics for large-scale OLED displays due to limitations in source and drain electrode materials, contact characteristics, and parasitic resistance, which affect threshold voltage and the integration of driver ICs.
Innovation Solution
The use of a contact layer made of a different metal or conductivity than the source and drain electrodes, specifically employing amorphous zinc oxide semiconductor with a-IGZO, to adjust the threshold voltage and improve contact characteristics between the active layer and electrodes, allowing for high mobility and constant current conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If amorphous silicon thin film transistor is used for LCD, then low temperature fabrication is achieved, but mobility is very small and constant current bias condition cannot be satisfied
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor (such as IGZO), which fundamentally alters the electrical characteristics to achieve high mobility and constant current bias condition while maintaining low temperature fabrication capability
Solution Approach 2:
The patent employs composite material structure with multiple oxide semiconductor layers having different compositions and properties, where each layer serves specific functions to collectively achieve high mobility, uniform characteristics, and stable operation
2Reliability
If polycrystalline silicon TFT is used, then high mobility and constant current bias condition are achieved, but uniform characteristics cannot be secured and large area fabrication is difficult requiring high temperature process
Solution Approach 1:
The patent changes the material from polycrystalline silicon to oxide semiconductor, which enables high mobility and constant current bias condition while simultaneously achieving uniform characteristics across large areas at low temperatures
Solution Approach 2:
The patent applies different oxide semiconductor compositions and structures in different regions (such as channel region vs. source/drain region) to optimize local characteristics while maintaining overall uniformity across the device
3Ease of manufacture
If oxide TFT with general bottom gate structure is fabricated without n+ layer, then fabrication is simplified, but threshold voltage control and contact characteristics are affected due to n-type characteristics of oxide semiconductor
Solution Approach 1:
The patent applies different oxide semiconductor compositions specifically in the channel region versus source/drain regions, where the channel region uses composition optimized for threshold voltage control while source/drain regions use composition optimized for contact characteristics
Solution Approach 2:
The patent introduces an intermediate oxide semiconductor layer between the gate insulating layer and the active oxide semiconductor layer, which acts as a mediator to improve interface characteristics and enable better threshold voltage control without requiring additional n+ doping layers
Data Source
AI summary
An oxide thin film transistor (TFT) and a fabrication method thereof are provided. The method for fabricating an oxide thin film transistor (TFT) comprises: forming a gate electrode on a substrate; forming a gate insulating layer on the substrate with the gate electrode formed thereon; forming an active layer made of oxide semiconductor on the gate insulating layer; forming a contact layer on the substrate with the active layer formed thereon and forming source and drain electrodes, which are electrically connected with source and drain regions of the active layer through the contact layer, on the contact layer; forming a protective layer on the substrate with the source and drain electrodes formed thereon; forming a contact hole by removing the protective layer to expose the drain electrode; and forming a pixel electrode electrically connected with the drain electrode through the contact hole, wherein the contact layer is made of oxide including a different metal or conductivity with that of the source and drain electrodes, to adjust a threshold voltage according to the difference in a work function.