Gate Driver Circuit With Oxide Pull-Down TFTs for Threshold Stability
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Solution Overview
Problem
Conventional gate driver circuits using amorphous silicon transistors face issues with transistor threshold voltage shifts, leading to malfunctions and limitations in circuit size and drive capability due to the need for repeated on-off cycles and off-state current losses.
Innovation Solution
Employing oxide semiconductors with high purity to reduce impurities, which suppress hot carrier degradation and off-state current, allowing for smaller circuit sizes and improved drive capability by using transistors with channel regions made of oxide semiconductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon transistors are used in gate driver circuits, then the circuit can be manufactured with conventional processes, but the transistor threshold voltage shifts causing malfunctions and requiring repeated on-off cycles
Solution Approach 1:
The patent changes the material parameter of the transistor from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical characteristics including threshold voltage stability, off-state current, and resistance to hot carrier degradation while maintaining compatibility with existing manufacturing processes
Solution Approach 2:
The patent employs oxide semiconductor materials (such as In-Ga-Zn-O) as a composite material system that combines the advantages of low-cost fabrication with superior electrical stability, creating a transistor structure that resists threshold voltage shifts and hot carrier effects
2Duration of action of stationary object
If pull down transistor is repeatedly turned on and off to suppress deterioration, then transistor lifespan is extended, but circuit size cannot be reduced and drive frequency range is limited
Solution Approach 1:
The patent changes the transistor material to oxide semiconductor, which inherently suppresses deterioration mechanisms (hot carrier degradation, threshold voltage shifts), allowing the transistor to operate continuously without repeated on-off cycling while maintaining small circuit size and broad drive frequency range
3Power
If all transistors connected to pull up transistor gate are turned off to maintain floating state, then capacitive coupling can raise gate potential above clock high voltage, but off-state current causes charge loss over time limiting drive frequency
Solution Approach 1:
The patent changes the transistor material to oxide semiconductor, which has extremely low off-state current (1 aA/μm or less), enabling the floating gate of the pull-up transistor to retain charge indefinitely without degradation, thus allowing drive frequencies to be lowered and operational frequency range to be broadened while maintaining the ability to raise gate potential above clock high voltage through capacitive coupling
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 use of oxide semiconductors reduces off-state current to 1 aA/μm, enabling smaller circuit sizes and broader operational frequency ranges, thus enhancing the drive capability and reducing transistor deterioration.
Implementation Method 1
Employing oxide semiconductors with high purity to reduce impurities, which suppress hot carrier degradation and off-state current
Data Source
AI summary
A transistor whose channel region includes an oxide semiconductor is used as a pull down transistor. The band gap of the oxide semiconductor is 2.0 eV or more, preferably 2.5 eV or more, more preferably 3.0 eV or more. Thus, hot carrier degradation in the transistor can be suppressed. Accordingly, the circuit size of the semiconductor device including the pull down transistor can be made small. Further, a gate of a pull up transistor is made to be in a floating state by switching of on/off of the transistor whose channel region includes an oxide semiconductor. Note that when the oxide semiconductor is highly purified, the off-state current of the transistor can be 1 aA/μm (1×10−18 A/μm) or less. Therefore, the drive capability of the semiconductor device can be improved.