Oxide Semiconductor Memory Cell for Non-Volatile Data Retention
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Solution Overview
Problem
Conventional semiconductor memory devices face challenges such as short data holding periods, high power consumption, and limited write cycles due to leakage currents and gate insulating layer deterioration, making them unsuitable for frequent data rewriting applications.
Innovation Solution
A semiconductor device utilizing an oxide semiconductor material with significantly reduced off-state current, combined with a delayed potential change mechanism in signal lines relative to write word lines, to minimize data loss and eliminate the need for high voltage charge injection, thereby enabling long-term data retention and unlimited write cycles without refreshing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a DRAM structure with transistor and capacitor is used, then writing operation is simple, but data holding period becomes short due to leakage current
Solution Approach 1:
The patent changes the material parameter of the transistor from conventional semiconductor to oxide semiconductor, which fundamentally alters the off-state current characteristics. This material parameter change enables the transistor to maintain extremely low leakage current while preserving the simple DRAM writing operation structure.
Solution Approach 2:
The patent employs a composite structure combining oxide semiconductor material with conventional DRAM components (capacitor, word lines, bit lines). This composite approach integrates the low-leakage property of oxide semiconductor into the established DRAM architecture, achieving extended data holding period without complicating the basic writing operation.
2Duration of action of moving object
If refresh operation is performed at predetermined intervals, then data holding is maintained, but power consumption increases
Solution Approach 1:
The oxide semiconductor transistor inherently maintains extremely low off-state current without requiring external refresh operations. The material's physical properties automatically prevent charge leakage, enabling the memory to hold data indefinitely without power consumption for refreshing, thus achieving self-sustaining data retention.
3Duration of action of moving object
If flash memory with floating gate is used, then data holding period becomes extremely long, but gate insulating layer deteriorates after predetermined number of writing operations
Solution Approach 1:
The patent extracts and eliminates the floating gate structure from the memory cell, replacing it with a simple transistor-capacitor configuration using oxide semiconductor. This removal of the floating gate eliminates the source of write cycle degradation (tunneling current effects) while preserving long data holding capability through the oxide semiconductor's low leakage properties.
Solution Approach 2:
The patent converts the typically harmful tunneling current that causes flash memory degradation into a beneficial feature by using oxide semiconductor's ability to block current flow. The same physical mechanism that would normally degrade flash memory (current blocking) becomes the advantage that enables unlimited write cycles in the oxide semiconductor memory.
4Productivity
If high voltage is applied for charge injection in flash memory, then data writing is achieved, but element lifetime is reduced due to gate insulating layer deterioration
Solution Approach 1:
The patent changes the voltage parameter from high voltage (required for flash memory charge injection) to low voltage operation. The oxide semiconductor transistor enables effective charge control at low voltages due to its superior off-state characteristics, eliminating the need for high voltage stress that degrades gate insulating layers and extends element lifetime.
5Speed
If conventional semiconductor material is used, then transistor operation speed is high, but off-state current is large causing short data holding period
Solution Approach 1:
The patent uses a composite material approach by selecting oxide semiconductor, which combines the dual benefits of high carrier mobility (enabling fast operation) and extremely low off-state current (enabling long data holding). This material selection integrates both speed and low leakage properties into a single transistor structure.
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 semiconductor device achieves long-term data storage with low power consumption, high-speed operation, and extended write cycle life by using oxide semiconductors and delayed potential changes, eliminating the need for high voltage and reducing gate insulating layer deterioration.
Implementation Method 1
a semiconductor device using a material capable of sufficiently reducing the off-state current of a transistor, such as an oxide semiconductor material that is a widegap semiconductor
Data Source
AI summary
An object is to provide a semiconductor device with a novel structure, which can hold stored data even when not powered and which has an unlimited number of write cycles. A semiconductor device is formed using a material capable of sufficiently reducing the off-state current of a transistor, such as an oxide semiconductor material that is a widegap semiconductor. The use of a semiconductor material capable of sufficiently reducing the off-state current of a transistor allows data to be held for a long time. In addition, the timing of potential change in a signal line is delayed relative to the timing of potential change in a write word line. This makes it possible to prevent a data writing error.