Oxide Semiconductor Logic Circuit With Floating Capacitor Retention
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Solution Overview
Problem
Thin film transistors using oxide semiconductors exhibit low on-off ratios due to high off-state currents, leading to unstable circuit operation and increased power consumption, primarily because of excess oxygen and hydrogen impurities affecting electrical conductivity.
Innovation Solution
A logic circuit with a thin film transistor featuring a channel formation region made from an oxide semiconductor with reduced hydrogen concentration (≤5×10^19 atoms/cm^3) and an energy gap ≥2 eV, minimizing impurities and off-state current, thereby stabilizing the transistor's operation and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oxide semiconductor is used with conventional impurity levels, then manufacturing is easier, but off-state current increases and on-off ratio decreases
Solution Approach 1:
The patent applies parameter changes by strictly controlling the hydrogen concentration in the oxide semiconductor to be 5×10^19/cm³ or less, and setting the carrier density to 5×10^14/cm³ or less. These parameter specifications transform the oxide semiconductor from a conventional high-impurity state to a highly purified state, achieving an on-off ratio of 10⁸ or more while maintaining manufacturing feasibility through defined process parameters.
Solution Approach 2:
The patent employs inert atmosphere techniques by forming the oxide semiconductor film in a highly purified environment and using protective films to prevent contamination. The manufacturing process maintains an inert environment throughout film formation and heat treatment steps, preventing hydrogen and water ingress that would otherwise increase off-state current and degrade the on-off ratio.
2Power
If oxide semiconductor has high carrier density, then conductivity is improved, but off-state current increases
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the carrier density parameter to be 5×10^14/cm³ or less, which is significantly lower than conventional oxide semiconductors. This parameter change reduces off-state current to extremely low levels while maintaining sufficient on-state conductivity through the purified oxide semiconductor channel, achieving the desired balance between power and harmful off-state current.
Solution Approach 2:
The patent references and improves upon conventional oxide semiconductor structures by copying the basic thin film transistor architecture while fundamentally changing the material purity and carrier density characteristics. The invention maintains the familiar TFT structure but replicates it with ultra-purified oxide semiconductor, achieving superior electrical characteristics without altering the fundamental device design.
3Ease of manufacture
If hydrogen concentration is high in oxide semiconductor, then film formation is easier, but transistor operation becomes unstable
Solution Approach 1:
The patent employs inert atmosphere techniques throughout the film formation process, using highly purified environments and protective films to prevent hydrogen contamination. The oxide semiconductor is formed and processed in controlled atmospheric conditions that exclude hydrogen and water, ensuring stable transistor operation while maintaining ease of manufacture through standardized inert environment processes.
Solution Approach 2:
The patent specifies hydrogen concentration should be 5×10^19/cm³ or less, transforming the oxide semiconductor from a hydrogen-containing state to a highly purified state. This parameter change stabilizes the transistor operation by eliminating hydrogen-related instability mechanisms while maintaining manufacturability through defined purification parameters and protective processing techniques.
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 reduced hydrogen concentration in the oxide semiconductor transistors significantly decreases off-state current, preventing malfunction and extending the floating state of capacitors, which in turn reduces power consumption and enhances the reliability of logic circuits.
Implementation Method 1
an oxide semiconductor which is made intrinsic or substantially intrinsic by removing impurities (e.g., hydrogen and water) having possibilities of being electron donors
Data Source
AI summary
A logic circuit includes a thin film transistor having a channel formation region formed using an oxide semiconductor, and a capacitor having terminals one of which is brought into a floating state by turning off the thin film transistor. The oxide semiconductor has a hydrogen concentration of 5×1019 (atoms/cm3) or less and thus substantially serves as an insulator in a state where an electric field is not generated. Therefore, off-state current of a thin film transistor can be reduced, leading to suppressing the leakage of electric charge stored in a capacitor, through the thin film transistor. Accordingly, a malfunction of the logic circuit can be prevented. Further, the excessive amount of current which flows in the logic circuit can be reduced through the reduction of off-state current of the thin film transistor, resulting in low power consumption of the logic circuit.