Shift Register Back Gate Control for TFT Leakage Reduction
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Solution Overview
Problem
The existing shift register circuits for liquid crystal display devices using amorphous semiconductor TFTs face issues with increased power consumption and signal malfunctions due to transistor leakage currents caused by threshold voltage fluctuations, and the complexity of power supply circuits for controlling back gate voltages adds to the cost and complexity.
Innovation Solution
A shift register circuit with a back gate voltage generation circuit that adjusts the back gate voltage of transistors based on the gate electrode voltage, using the same power supply as the unit shift register, allowing for stable on/off control of transistors without the need for additional power supplies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a back gate voltage is commonly input into all the TFTs constituting a shift register to control threshold voltage, then the threshold voltage can be controlled, but the on-resistance of the TFT increases when another TFT is turned on at the timing of applying negative voltage
Solution Approach 1:
The patent divides the shift register into multiple unit shift registers, each with independent back gate voltage control. This segmentation allows each transistor to have its back gate voltage controlled independently based on its own operating state, preventing the conflict where one transistor's negative back gate voltage increases another transistor's on-resistance.
Solution Approach 2:
The patent applies different back gate voltages to different transistors based on their local operating conditions. Each transistor receives a back gate voltage appropriate to its specific state (on or off), rather than a uniform voltage applied to all transistors. This local optimization maintains low on-resistance for active transistors while providing threshold control for inactive ones.
2Reliability
If a signal source for controlling the voltage of the back gate electrode is added to control threshold voltage, then the threshold voltage can be controlled, but the power supply circuit becomes complicated, resulting in an increase in cost
Solution Approach 1:
The patent merges the back gate voltage control function with the existing power supply circuit by having the power supply unit provide both the drive voltage for the transistor gate and the back gate voltage. This integration eliminates the need for separate back gate voltage signal sources, simplifying the power supply circuit while maintaining effective threshold voltage control.
Solution Approach 2:
The power supply unit is designed to perform multiple functions: it provides the drive voltage to the gate electrode and simultaneously provides the back gate voltage to the back gate electrode. This multi-functionality reduces the overall circuit complexity by eliminating dedicated back gate voltage generation circuits.
3Ease of manufacture
If amorphous semiconductor TFT is used for unipolar drive circuit, then the manufacturing process can be simplified, but the transistor may become depletion type due to manufacturing variation and threshold voltage fluctuation, causing leakage current
Solution Approach 1:
The patent changes the electrical parameters of the amorphous semiconductor TFT by applying a back gate voltage. This shifts the threshold voltage to a more appropriate level and stabilizes the transistor's operating characteristics, preventing the depletion type behavior and reducing leakage current while maintaining the manufacturing simplicity of amorphous semiconductor materials.
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
This configuration compensates for threshold voltage shifts, reduces leakage currents, and simplifies the power supply, enabling stable operation and cost-effective manufacturing by using existing power supply lines for back gate voltage control.
Implementation Method 1
a back gate voltage generation circuit which changes a voltage of the back gate electrode according to a voltage of the gate electrode
Data Source
AI summary
A shift register circuit that controls back gate voltage of a transistor with a simple configuration and at a low cost, and a display panel. In the shift register circuit, shift registers include: an output circuit, a charge and discharge circuit, a first power supply terminal, and at least one back gate voltage generation circuit. The output circuit or the charge and discharge circuit includes at least one transistor. The back gate voltage generation circuit includes a back gate node. The back gate node is connected to the back gate electrode of the transistor. The back gate voltage generation circuit changes a voltage of the back gate node according to a voltage of a gate electrode of the transistor. The back gate voltage generation circuit is supplied with a drive voltage from the first power supply terminal.