Oxide Semiconductor Driver Circuit for Display Devices
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Solution Overview
Problem
Driver circuits using thin film transistors with oxide semiconductor channels often malfunction due to their normally-on depletion mode, leading to increased power consumption and reliability issues.
Innovation Solution
A driver circuit design incorporating a static shift register with inverter circuits and demultiplexer circuits, where all transistors are depletion-mode and made of oxide semiconductors, with specific voltage and L/W ratio configurations to manage the on/off states effectively, reducing power consumption and malfunctions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If thin film transistors with oxide semiconductor channels are used in the driver circuit, then field-effect mobility is improved, but the threshold voltage fluctuates due to oxygen defects causing normally-on depletion mode
Solution Approach 1:
The patent applies parameter changes by using different voltage amplitudes for clock signals compared to power supply voltages. Specifically, clock signals have higher voltage amplitudes to ensure proper switching of depletion-mode transistors, while power supply voltages are controlled to maintain stable threshold voltages. This resolves the contradiction by adjusting electrical parameters to accommodate both high mobility and stable threshold voltage requirements.
2Ease of operation
If all transistors are configured as depletion-mode transistors, then circuit operation is simplified, but malfunctions increase due to inability to properly control on/off states
Solution Approach 1:
The patent applies dynamics by making the voltage amplitudes of clock signals variable and higher than the power supply voltages. This dynamic voltage control allows depletion-mode transistors to be properly switched on and off despite their normally-on characteristic, reducing malfunctions while maintaining the simplicity of using all depletion-mode transistors in the circuit.
3Reliability
If higher voltage amplitudes are applied to clock signals, then switching control of depletion-mode transistors is improved, but power consumption increases
Solution Approach 1:
The patent optimizes power consumption by carefully controlling the voltage amplitudes of clock signals to be higher than power supply voltages only when necessary for switching, and by using the inherent low power consumption characteristic of depletion-mode transistors. This balanced approach ensures reliable switching control while minimizing overall power consumption in the driver circuit.
Data Source
AI summary
An object of the present invention is to provide a driver circuit including a normally-on thin film transistor, which driver circuit ensures a small malfunction and highly reliable operation. The driver circuit includes a static shift register including an inverter circuit having a first transistor and a second transistor, and a switch including a third transistor. The first to third transistors each include a semiconductor layer of an oxide semiconductor and are depletion-mode transistors. An amplitude voltage of clock signals for driving the third transistor is higher than a power supply voltage for driving the inverter circuit.