Oxide Semiconductor Memory Cell Capacitive Voltage Boosting
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Solution Overview
Problem
Current storage devices, such as DRAM and flash memory, face limitations in data retention, power consumption, and the number of write operations, with DRAM requiring frequent refresh and flash memory experiencing degradation due to tunneling current and high voltage requirements.
Innovation Solution
A storage device utilizing a transistor with a wide-gap semiconductor material, like oxide semiconductor, that minimizes off-state current, allowing data to be stored without power and read quickly by boosting voltage through capacitive coupling, eliminating the need for frequent refresh and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a DRAM storage element is used, then writing operation is simple, but refresh operation is needed frequently and power consumption increases
Solution Approach 1:
The patent changes the fundamental parameter of charge storage by using a floating gate structure that can retain charge without power supply. The floating gate is isolated by tunnel insulating films, creating a parameter change from volatile to non-volatile storage, eliminating refresh operations and reducing power consumption while maintaining simple writing capability.
2Duration of action of stationary object
If a flash memory is used, then data holding period is long and refresh operation is not needed, but the number of writing operations is limited due to gate insulating layer deterioration
Solution Approach 1:
The patent segments the storage structure into distinct functional layers: a channel formation region, a floating gate region separated by first and second tunnel insulating films, and a gate insulating layer. This segmentation isolates the charge storage function in the floating gate from the control function, protecting the gate insulating layer from tunneling current damage and enabling unlimited write operations while maintaining long data retention.
3Duration of action of stationary object
If a flash memory is used, then data retention is improved, but high voltage is needed for charge injection and power consumption increases
Solution Approach 1:
The patent introduces tunnel insulating films as intermediary layers between the channel formation region and the floating gate. These intermediary layers enable charge transfer through quantum tunneling at lower voltages compared to direct charge injection, reducing the high voltage requirement while achieving effective charge storage for long data retention.
4Reliability
If a transistor with oxide semiconductor is used, then off-state current is decreased and data retention is improved, but device structure becomes more complex
Solution Approach 1:
The oxide semiconductor layer serves multiple functions simultaneously: it forms the channel formation region for transistor operation and provides the semiconductor material for the memory element. This multi-functionality reduces device complexity by eliminating the need for separate structures to achieve low off-state current and data retention, as the oxide semiconductor inherently provides both capabilities.
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 enables long-term data retention without power, low power consumption, and unlimited write cycles, enhancing storage capacity and speed while simplifying the device structure.
Implementation Method 1
a transistor included in a storage element is selected and charge is stored in a capacitor... since leakage current (off-state current) or the like flows between a source and a drain of a transistor included in a storage element when the transistor is in an off-state... a transistor used for a memory cell is formed using a semiconductor material which can decrease off-state current sufficiently, for example, a wide-gap semiconductor material (such as an oxide semiconductor material) as a channel region
Implementation Method 2
charge is stored in a capacitor... a memory cell including the transistor and a storage capacitor is electrically connected to a capacitor to form a node. The voltage of the node is boosted up in accordance with stored data by capacitive coupling
Implementation Method 3
the potential is read with an amplifier circuit to distinguish data
Data Source
AI summary
A storage device in which stored data can be held even when power is not supplied, and stored data can be read at high speed without turning on a transistor included in a storage element is provided. In the storage device, a memory cell having a transistor including an oxide semiconductor layer as a channel region and a storage capacitor is electrically connected to a capacitor to form a node. The voltage of the node is boosted up in accordance with stored data by capacitive coupling through a storage capacitor and the potential is read with an amplifier circuit to distinguish data.