Gate Driver Circuit Using Oxide TFTs for Low Off-State Current
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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 and processes, but the transistors suffer from threshold voltage shifts and high off-state current that limit circuit size reduction and drive frequency improvement
Solution Approach 1:
The patent changes the material parameter of the semiconductor from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical characteristics including off-state current and threshold voltage stability. This material parameter change enables both improved reliability and higher drive frequency by achieving off-state currents of 1aA/μm or less while maintaining stable threshold voltages
Solution Approach 2:
The patent employs oxide semiconductor materials with specific compositional characteristics (high purity, large band gap) to create transistors that combine the benefits of low off-state current with stable electrical characteristics, resolving the contradiction between reliability and productivity
2Productivity
If oxide semiconductors are used to reduce off-state current, then circuit size can be reduced and drive frequency increased, but the manufacturing process becomes more complex
Solution Approach 1:
By changing the semiconductor material parameter to oxide semiconductor with specific properties (high purity, large band gap), the patent achieves dramatically reduced off-state current (1aA/μm or less) enabling smaller circuits and higher drive frequencies, while the manufacturing complexity is managed through established oxide semiconductor fabrication techniques
3Power
If the gate of the pull up transistor is kept in floating state to enable capacitive coupling, then high voltage can be output to the gate line, but all transistors connected to the gate must be turned off which limits drive frequency
Solution Approach 1:
The patent changes the off-state current parameter of the pull-up transistor to extremely low levels (1aA/μm or less) by using oxide semiconductor material. This enables the gate to maintain floating state for longer periods while minimizing charge leakage, thus allowing high voltage output capability to be maintained at higher drive frequencies where conventional transistors would fail
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 results in reduced off-state current, suppressed threshold voltage fluctuations, and improved drive frequency range, enabling smaller circuit sizes and enhanced semiconductor device performance.
Implementation Method 1
Incorporating oxide semiconductors with high purity and large band gaps in the channel region of transistors to reduce off-state current
Implementation Method 2
fluctuations in the threshold voltage of the transistor due to injection of carriers (electrons) into a gate insulating layer (so-called hot carrier degradation) can be suppressed
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.