Oxide Semiconductor TFT LDD Structure for Threshold Voltage Stability
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Solution Overview
Problem
In oxide semiconductor TFTs, high driving voltages lead to significant variation in threshold voltage due to hot carrier deterioration, which is not effectively mitigated by existing configurations.
Innovation Solution
A semiconductor device with an oxide semiconductor TFT featuring a transition region with lower resistivity than the channel and source/drain regions, and a gate electrode structure that includes a through hole over the transition region to enhance conductivity and reduce threshold voltage variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LDD region is formed in oxide semiconductor TFT, then hot carrier effects are reduced, but threshold voltage variation becomes significant at high driving voltages
Solution Approach 1:
The patent applies local quality by creating a transition region with specifically controlled resistivity that is higher than the channel region but lower than the drain region. This localized property gradient (achieved through controlled oxygen deficiency or specific doping) provides gradual electric field modulation exactly where needed - at the channel-drain interface - to suppress hot carrier generation while maintaining overall device reliability at high voltages
Solution Approach 2:
The patent changes physical parameters by controlling the resistivity of the transition region through oxygen deficiency or doping, creating a intermediate resistance state between the low-resistance channel and high-resistance drain. This parameter transformation (resistivity gradient) enables gradual electric field reduction, effectively mitigating hot carrier effects and threshold voltage variation without requiring extreme voltage reduction
2Object-affected harmful factors
If the transition region resistivity is increased to suppress hot carriers, then hot carrier effects are reduced, but OFF current increases
Solution Approach 1:
The transition region is designed with localized intermediate resistivity properties - higher than the channel but lower than the drain - creating a spatial gradient that suppresses hot carrier generation at the interface while maintaining sufficient conductivity to prevent excessive OFF current. This localized quality control allows simultaneous management of both harmful effects
Solution Approach 2:
The transition region's resistivity is dynamically optimized through controlled oxygen deficiency or doping levels, allowing the region to adapt its conductivity characteristics. This dynamic property adjustment enables the transition region to provide hot carrier suppression during operation while maintaining low enough resistance to prevent significant OFF current leakage
3Reliability
If the transition region thickness is increased to improve hot carrier suppression, then hot carrier effects are reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Rather than increasing transition region thickness, the patent achieves hot carrier suppression by changing the resistivity parameter through controlled oxygen deficiency or doping. This parameter-based approach (modifying electrical properties) is simpler and more controllable than geometric expansion, reducing manufacturing complexity while maintaining effective hot carrier suppression
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 effectively suppresses threshold voltage variation and OFF current increase by optimizing the thickness and length of the transition region, ensuring stable operation even at high voltages.
Implementation Method 1
In a TFT using an oxide semiconductor which has a wide band gap, impact ionization and avalanche breakdown hardly occur, and a problem of hot carriers hardly occurs.
Implementation Method 2
a transition region between the channel region and the source region and between the channel region and the drain region, in which a resistivity of the transition region is smaller than that of the channel region, and larger than that of the source region or the drain region
Data Source
AI summary
The purpose of the present invention is to suppress a variation in a threshold voltage (Δ Vth) in a Thin Film Transistor (TFT) using an oxide semiconductor. The present invention takes a structure as follows to attain this purpose. A semiconductor device having TFT using an oxide semiconductor including: a channel region, a source region, a drain region, and a transition region between the channel region and the source region and between the channel region and the drain region, in which a resistivity of the transition region is smaller than that of the channel region, and larger than that of the source region or the drain region; a source electrode is formed overlapping the source region, and a drain electrode is formed overlapping the drain region; and a thickness of the transition region of the oxide semiconductor is larger than a thickness of the channel region of the oxide semiconductor.