Oxide TFT Shift Register for Normally-On Driver Reliability
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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 transistor configurations and connections to manage clock signal amplitudes and power supply voltages, ensuring reliable operation even when all transistors are normally on.
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 transistors become normally-on (depletion mode) due to oxygen defects, causing malfunctions
Solution Approach 1:
The patent applies parameter changes by utilizing the naturally occurring depletion mode characteristic of oxide semiconductor transistors (caused by oxygen defects) as a functional feature rather than a defect. The circuit is designed to operate with all transistors in depletion mode, where the normally-on behavior is harnessed to achieve low power consumption while maintaining reliability through proper circuit configuration
Solution Approach 2:
The patent inverts the conventional approach by not trying to eliminate the normally-on characteristic but rather designing the circuit to exploit it. Instead of attempting to make transistors normally-off through additional processing or structures, the design accepts and utilizes the depletion mode operation of oxide semiconductor transistors as the basis for the driver circuit architecture
2Loss of energy
If all transistors are designed as depletion-mode with oxide semiconductor, then power consumption is reduced, but circuit control becomes more difficult due to normally-on behavior
Solution Approach 1:
The patent segments the driver circuit into functional blocks (shift register stage, inverter circuit, switch) where each segment is designed to work with depletion-mode transistors. The circuit is divided into multiple stages with controlled signal propagation, allowing manageable control of the normally-on transistors through structured signal routing and timing
Solution Approach 2:
The patent introduces clock signals as intermediary control mechanisms that mediate between the input and the normally-on transistors. The clock signals act as intermediaries to control the timing and propagation of signals through the depletion-mode transistors, making the circuit operation controllable despite the normally-on characteristic
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.