Oxide Semiconductor Transistor for CMOS Direct-Path Current Reduction
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Solution Overview
Problem
CMOS circuits face challenges in reducing direct-path current due to concurrent turning on of n-channel and p-channel transistors when gate voltage is changed slowly, leading to insufficient reduction in direct-path current.
Innovation Solution
Incorporating transistors with lower off-state current, specifically those with channel formation regions in oxide semiconductor layers, between power supply lines and CMOS circuits, and controlling these transistors to turn off during voltage changes, thereby reducing direct-path current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If transistors in CMOS circuit are turned on slowly to change voltage, then the transistors can be controlled smoothly, but direct-path current cannot be sufficiently reduced due to concurrent turning on of n-channel and p-channel transistors
Solution Approach 1:
An oxide semiconductor transistor is introduced as an intermediary switch between the power supply lines and the CMOS circuit. This intermediary transistor has superior off-state current characteristics compared to conventional silicon-based transistors, enabling it to block direct-path current effectively while the CMOS circuit transistors change voltage smoothly. The oxide semiconductor transistor acts as a gatekeeper that prevents the harmful direct-path current even when the CMOS transistors are in transition.
2Ease of manufacture
If a transistor with silicon layer channel formation region is used to prevent direct-path current, then the transistor can be integrated with CMOS circuit, but off-state current flows and direct-path current cannot be reduced
Solution Approach 1:
The patent changes the material parameter of the transistor channel from conventional silicon-based semiconductor to oxide semiconductor. This material parameter change fundamentally alters the off-state current characteristics, reducing it by several orders of magnitude compared to silicon-based transistors. The oxide semiconductor's unique electronic properties enable extremely low off-state current while maintaining compatibility with CMOS fabrication processes.
3Power
If transistor gate size is increased to improve voltage control, then voltage can be changed more effectively, but direct-path current increases due to concurrent turning on of transistors
Solution Approach 1:
The patent segments the current control function into two independent parts: (1) the CMOS circuit transistors handle voltage control and signal processing, and (2) the oxide semiconductor transistor handles direct-path current blocking. This segmentation allows each component to optimize its function without compromising the other, enabling effective voltage control while preventing direct-path current through the superior off-state characteristics of the oxide semiconductor transistor.
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
Significantly reduces direct-path current and power consumption by effectively managing the off-state of transistors, allowing for reduced charging and discharging of electric charge.
Implementation Method 1
the first transistor and the second transistor each have lower off-state current than a transistor included in the first CMOS circuit
Data Source
AI summary
Direct-path current is reduced in a semiconductor device including CMOS circuits. One embodiment of the present invention is a method for driving a semiconductor device that includes a first CMOS circuit between power supply lines, a first transistor between the power supply lines, a second CMOS circuit between the power supply lines, and a second transistor between an output terminal of the first CMOS circuit and an input terminal of the second CMOS circuit. The first transistor and the second transistor each have lower off-state current than a transistor included in the first CMOS circuit. In a period during which the voltage of a first signal input to the first CMOS circuit is changed, a second signal is input to the first transistor and the second transistor to turn off the first transistor and the second transistor.