Gate Driver Circuit Using Oxide TFTs for Stable Floating Gates
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Solution Overview
Problem
Conventional gate driver circuits using amorphous silicon transistors face issues with transistor malfunction due to threshold voltage shifts and high off-state current, limiting circuit size reduction and drive frequency improvement.
Innovation Solution
Incorporating oxide semiconductors with high purity and large band gaps in the channel region of transistors to reduce off-state current and prevent hot carrier degradation, allowing for smaller circuit sizes and increased drive capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amorphous silicon transistors are used in gate driver circuits, then the circuit can be implemented with conventional materials, but the transistor threshold voltage shifts leading to malfunctions and limited drive capability
Solution Approach 1:
The patent changes the material parameter of the transistor channel from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical characteristics including threshold voltage stability and off-state current levels, thereby resolving the contradiction between reliability and drive capability
Solution Approach 2:
The patent employs oxide semiconductor materials (such as In-Ga-Zn-O) as a composite material system that combines high purity semiconductor properties with insulating characteristics, enabling both stable threshold voltage and low off-state current for improved drive capability
2Reliability
If the pull down transistor is repeatedly turned on and off to suppress threshold voltage shift, then the threshold voltage stability is improved, but the circuit size cannot be decreased
Solution Approach 1:
By changing the material parameter to oxide semiconductor, the patent achieves threshold voltage stability without requiring repeated on-off cycles, thereby eliminating the need for additional control circuitry and reducing overall circuit size
Solution Approach 2:
The patent extracts the requirement for repeated on-off control by using oxide semiconductor transistors that inherently maintain stable threshold voltage, removing the need for complex control mechanisms and reducing circuit complexity
3Ease of operation
If all transistors connected to the pull up transistor gate are turned off to maintain floating state, then the capacitive coupling driving method can be realized, but off-state current causes charge loss over time
Solution Approach 1:
The patent changes the material parameter to oxide semiconductor, which provides extremely low off-state current (1 aA/μm or less), enabling the gate to maintain floating state and retain charge indefinitely, thereby resolving the charge loss problem while maintaining ease of operation
Solution Approach 2:
The patent achieves continuous charge retention in the floating gate by using oxide semiconductor's near-zero off-state current, allowing the capacitive coupling driving method to operate continuously without charge loss over time
4Speed
If conventional transistors are used, then the circuit can operate at higher drive frequencies, but the off-state current increases causing charge loss and limiting frequency range
Solution Approach 1:
The patent changes the material parameter to oxide semiconductor, which reduces off-state current to 1 aA/μm or less, enabling broader operational frequency ranges by eliminating the energy loss that previously limited frequency operation
Solution Approach 2:
The patent achieves excessive reduction in off-state current (to levels 1000 times lower than conventional transistors), which provides a large margin for operating across a broad frequency range without energy loss concerns
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 in transistors significantly reduces off-state current, suppresses threshold voltage fluctuations, and enhances drive frequency and operational range, leading to improved semiconductor device performance.
Implementation Method 1
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.