Oxide Semiconductor Memory Device Low Voltage Threshold Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing flash memory devices face challenges with high power consumption, limited data storage period due to charge leakage, and limited number of data rewriting cycles due to gate insulating film deterioration.
Innovation Solution
A non-volatile memory device is developed using a transistor with a second gate electrode for controlling threshold voltage, along with a capacitor for holding the potential of the second gate electrode. This device uses a highly-purified oxide semiconductor film with extremely low off-state current, reducing power consumption and enhancing data storage capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high voltage is applied to accumulate electric charge in a floating gate for data writing, then data storage capability is improved, but power consumption increases
Solution Approach 1:
The patent changes the voltage parameter from high voltage (20V) to low voltage (5V or less) by introducing a second gate electrode that controls threshold voltage. This allows data writing to be performed at low voltage while maintaining storage capability through threshold voltage modulation rather than charge accumulation requiring high voltage.
Solution Approach 2:
The patent extracts the high voltage requirement by separating the data storage function (achieved through threshold voltage control via second gate) from the charge accumulation function. The floating gate structure is retained but the need for high voltage charge injection is eliminated through the alternative threshold voltage control mechanism.
2Reliability
If electric charge is accumulated in a floating gate for data storage, then non-volatile memory function is achieved, but data storage period is limited due to charge leakage
Solution Approach 1:
The patent changes the storage mechanism parameter from electric charge accumulation to threshold voltage control. By using the second gate electrode to modulate threshold voltage, the system achieves non-volatile storage without relying on trapped charge, thereby eliminating leakage-related degradation and extending storage period.
3Reliability
If electric charge is accumulated in a floating gate for data storage, then data writing capability is achieved, but gate insulating film deteriorates due to tunnel current
Solution Approach 1:
The patent extracts the tunnel current harmful effect by removing the charge accumulation mechanism that causes it. The floating gate structure is kept for potential use, but the high voltage charge injection process that generates damaging tunnel current is replaced with low voltage threshold voltage control via the second gate, eliminating the root cause of insulating film deterioration.
4Reliability
If a transistor with floating gate is used for memory element, then data storage function is achieved, but device complexity increases due to additional electrode structures
Solution Approach 1:
The second gate electrode is designed to serve multiple functions: controlling threshold voltage for data storage, enabling low voltage operation, and extending retention time. This multi-functionality reduces the need for separate dedicated structures, effectively managing device complexity while achieving multiple performance goals simultaneously.
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 proposed memory device achieves reduced power consumption, extended data storage period, and increased number of data rewriting cycles, addressing the limitations of conventional flash memory technologies.
Implementation Method 1
a transistor which serves as a memory element and includes a second gate electrode for controlling threshold voltage... a capacitor for holding a potential of the second gate electrode... a transistor used as a switching element for controlling charging and discharging of the capacitor
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.