Oxide Semiconductor Memory Cell With Second-Gate Threshold Control
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Solution Overview
Problem
Flash memory devices face high power consumption during data writing and erasing, short data storage periods, and limited rewrite cycles due to high voltage requirements and gate insulating film deterioration.
Innovation Solution
A non-volatile memory device with a transistor having a second gate electrode for controlling threshold voltage, using a highly purified oxide semiconductor with low off-state current, which reduces power consumption and extends data storage periods by eliminating the need for high voltage and minimizing gate insulating film deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage is applied to accumulate electric charge in a floating gate for data writing and erasing, then data storage capability is achieved, but power consumption becomes high
Solution Approach 1:
The patent changes the operating voltage parameter from high voltage (20V) to low voltage (5V or less) by replacing the floating gate mechanism with a threshold voltage control mechanism using a second gate electrode, thereby resolving the contradiction between data storage capability and power consumption
Solution Approach 2:
The patent extracts and removes the floating gate structure entirely, replacing it with a conventional gate electrode and a second gate electrode system that controls threshold voltage without requiring charge accumulation, thus eliminating the need for high voltage operation
2Productivity
If high voltage is applied repeatedly for data writing and erasing, then data rewrite capability is achieved, but gate insulating film deteriorates rapidly
Solution Approach 1:
The patent changes the operating mechanism from high voltage charge injection to low voltage threshold control, eliminating the tunnel current that causes gate insulating film deterioration, thereby enabling repeated rewrites without film degradation
Solution Approach 2:
The patent converts the potentially harmful high voltage tunnel current mechanism into a beneficial low voltage threshold control mechanism, where the second gate electrode safely adjusts transistor characteristics without causing insulating film damage
3Reliability
If electric charge is accumulated in a floating gate surrounded by insulating film, then data storage is achieved, but data storage period is limited to five to ten years due to charge leakage
Solution Approach 1:
The patent removes the floating gate and its surrounding insulating film structure that causes charge leakage, replacing it with a threshold voltage control system that does not rely on trapped charge, thereby extending data storage period indefinitely
Solution Approach 2:
The patent replaces the fragile charge accumulation mechanism with a robust threshold voltage control mechanism that does not depend on maintaining trapped charge, effectively creating a more durable storage mechanism
4Use of energy by moving object
If a transistor with low off-state current is used to control the second gate electrode, then power consumption is reduced and data storage period is extended, but device complexity increases
Solution Approach 1:
The patent adds a second gate electrode dimension to the conventional transistor structure, enabling independent threshold voltage control without affecting the basic transistor operation, thereby managing complexity through functional separation
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 significantly reduces power consumption, extends data storage periods, and increases the number of rewrite cycles, while maintaining low off-state current and temperature independence.
Implementation Method 1
a channel formation region which includes a semiconductor material with a wide band gap compared to that of silicon and low intrinsic carrier density compared to that of silicon
Implementation Method 2
a channel formation region which includes a semiconductor material with a wide band gap compared to that of silicon and low intrinsic carrier density compared to that of silicon
Implementation Method 3
a capacitor for holding a potential of the second gate electrode
Implementation Method 4
a transistor having extremely low off-state current
Data Source
AI summary
It is an object to provide a memory device whose power consumption can be suppressed and a semiconductor device including the memory device. As a switching element for holding electric charge accumulated in a transistor which functions as a memory element, a transistor including an oxide semiconductor film as an active layer is provided for each memory cell in the memory device. The transistor which is used as a memory element has a first gate electrode, a second gate electrode, a semiconductor film located between the first gate electrode and the second gate electrode, a first insulating film located between the first gate electrode and the semiconductor film, a second insulating film located between the second gate electrode and the semiconductor film, and a source electrode and a drain electrode in contact with the semiconductor film.