Oxide Semiconductor Memory Cell With Capacitor for Nonvolatile Rewriting
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Solution Overview
Problem
Existing volatile memory devices require frequent refresh operations due to leakage currents and power loss, while non-volatile memory devices face limitations in rewrite cycles and high voltage requirements, making them unsuitable for frequent data rewriting.
Innovation Solution
A semiconductor device using a highly purified oxide semiconductor transistor with extremely low off-current, integrated with a capacitor, allowing data storage without power supply and unlimited rewrite cycles, eliminating the need for high voltage and refresh operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a volatile memory device (DRAM) is used to store data, then data can be accessed quickly, but leakage current causes charge loss requiring frequent refresh operations and limiting data storing time
Solution Approach 1:
The invention changes the material parameter of the transistor from conventional semiconductor to highly purified oxide semiconductor, which fundamentally alters the electrical characteristics to achieve extremely low off-state current (1×10^-21 to 1×10^-24 A), enabling long-term data retention without refresh operations while maintaining fast access speeds
2Duration of action of stationary object
If a non-volatile memory device (flash memory) is used to store data for long time, then data storing time is extremely long, but tunneling current deteriorates the gate insulating layer after predetermined writing operations
Solution Approach 1:
The invention changes the transistor material to highly purified oxide semiconductor, which eliminates the tunneling current problem that causes gate insulating layer deterioration in flash memory, while maintaining non-volatile data storage capability through extremely low leakage current
Solution Approach 2:
The invention uses a composite structure combining oxide semiconductor transistor with floating gate and control gates, integrating the advantages of both volatile and non-volatile memory technologies to achieve unlimited rewrite cycles with long data retention
3Use of energy by stationary object
If flash memory is used for non-volatile storage, then refresh operation is not needed, but high voltage is necessary for charge holding and removal requiring additional circuitry
Solution Approach 1:
The invention changes the transistor material to highly purified oxide semiconductor with extremely low off-state current, which enables charge retention without high voltage, eliminating the need for complex high voltage generation circuits while maintaining non-volatile storage functionality
4Ease of manufacture
If conventional semiconductor transistor is used, then manufacturing is straightforward, but leakage current limits data storing time and requires refresh operations
Solution Approach 1:
The invention changes the semiconductor material to highly purified oxide semiconductor, which can be manufactured using existing semiconductor fabrication processes (sputtering, CVD, ALD) while achieving fundamentally different electrical characteristics with extremely low leakage current for long-term data storage
Data Source
AI summary
An object of the present invention is to provide a semiconductor device having a novel structure in which in a data storing time, stored data can be stored even when power is not supplied, and there is no limitation on the number of writing. A semiconductor device includes a first transistor including a first source electrode and a first drain electrode; a first channel formation region for which an oxide semiconductor material is used and to which the first source electrode and the first drain electrode are electrically connected; a first gate insulating layer over the first channel formation region; and a first gate electrode over the first gate insulating layer. One of the first source electrode and the first drain electrode of the first transistor and one electrode of a capacitor are electrically connected to each other.