Back Gate Floating State for Semiconductor On-State Current
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Solution Overview
Problem
OS transistors with low off-state current require high threshold voltage control, leading to low on-state current and increased power consumption, which affects circuit reliability.
Innovation Solution
A semiconductor device with a memory cell and two circuits, where the first circuit controls the conduction state of a transistor and the second circuit controls the threshold voltage, with the back gate lines brought into an electrically floating state during writing and reading operations to increase on-state current while reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage for controlling threshold voltage is applied to the back gate electrode, then off-state current is reduced to extremely low levels, but on-state current becomes low and power consumption increases
Solution Approach 1:
The back gate electrode voltage is applied periodically rather than continuously. The voltage is supplied during specific periods (when the transistor should maintain low off-state current) and the back gate line is brought into an electrically floating state during other periods (when writing or reading operations are performed). This periodic application reduces overall power consumption while maintaining the low off-state current characteristic when needed.
Solution Approach 2:
The voltage state of the back gate electrode is dynamically changed based on operational requirements. The back gate line can be switched between a voltage-applied state (for maintaining low off-state current) and an electrically floating state (for allowing voltage changes during write/read operations). This dynamic adaptability resolves the contradiction by adjusting the back gate voltage according to the current operational phase.
2Power
If driving voltage of the gate electrode is increased to increase on-state current, then power consumption increases and electrical characteristics of the transistor may change, reducing circuit reliability
Solution Approach 1:
The back gate electrode acts as an intermediary that indirectly controls the transistor's electrical characteristics. Instead of directly increasing the gate electrode driving voltage (which would affect electrical characteristics stability), the back gate electrode supplies a voltage that controls the threshold voltage. This indirect control mechanism allows on-state current to be increased while maintaining the stability of the transistor's electrical characteristics, as the gate electrode voltage remains within its normal operating range.
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 solution effectively increases on-state current and reduces power consumption by lowering the driving voltage of the gate electrode, while maintaining low off-state current and improving circuit reliability.
Implementation Method 1
a structure in which a threshold voltage is controlled by supplying a voltage to a back gate electrode which is provided in addition to a gate electrode for controlling the conduction state
Implementation Method 2
the second circuit has a function of bringing the second wiring into an electrically floating state in a period in which a signal for controlling the conduction state of the first transistor is supplied to the first wiring
Data Source
AI summary
A semiconductor device is provided in which the power consumption can be reduced by reducing the driving voltage and the on-state current can be increased in a period in which a transistor having an extremely low off-state current is brought into an electrically floating state. The semiconductor device comprises a memory cell, a first circuit, and a second circuit. The memory cell includes a first transistor. The first transistor includes a first semiconductor layer, a first gate electrode, and a first back gate electrode. The first gate electrode is connected to a word line. The first back gate electrode is connected to a back gate line. The first circuit supplies a signal for controlling the conduction state of the first transistor to the word line. The second circuit supplies a voltage for controlling the threshold voltage of the first transistor to the back gate line. The second circuit has a function of bringing the back gate line into an electrically floating state in a period in which a signal for controlling the conduction state of the first transistor is supplied to the word line.