Oxide Semiconductor Memory Structure for Refresh-Free Data Retention
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Solution Overview
Problem
Existing semiconductor memory devices, such as DRAM and flash memory, face challenges with power consumption, data retention time, and the limitations of the number of writing operations due to leakage currents and tunneling effects.
Innovation Solution
A semiconductor device is developed using a highly purified oxide semiconductor, which includes a layered structure of transistors using both oxide and non-oxide semiconductor materials. This structure minimizes leakage current, allowing for long-term data storage without the need for frequent refresh operations or high voltage for data writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a floating gate structure is used to achieve non-volatile storage, then data retention time is improved, but the gate insulating layer deteriorates due to tunneling current limiting the number of writing operations
Solution Approach 1:
The patent changes the material parameter of the semiconductor layer from conventional silicon-based semiconductor to oxide semiconductor, which fundamentally alters the electrical characteristics and enables non-volatile storage without tunneling current damage. This material parameter change resolves the contradiction by providing both long data retention and unlimited write operations.
Solution Approach 2:
The patent employs a composite structure combining oxide semiconductor layer with conventional semiconductor substrates and insulating layers. This composite approach integrates the advantages of oxide semiconductors (low leakage, non-volatile storage) with the maturity of conventional semiconductor manufacturing, achieving both long-term data retention and high reliability for repeated writing operations.
2Speed
If DRAM structure is used for volatile memory, then writing speed is improved, but power consumption increases due to frequent refresh operations
Solution Approach 1:
The oxide semiconductor transistor inherently maintains charge in the capacitor without requiring external refresh operations. The extremely low leakage current of the oxide semiconductor transistor automatically preserves data, making the memory system self-maintaining and eliminating the power-consuming refresh cycle needed in conventional DRAM.
3Duration of action of stationary object
If flash memory structure is used for non-volatile storage, then data retention time is improved, but writing speed deteriorates due to high voltage requirements and charge holding time
Solution Approach 1:
The patent changes the material parameter to oxide semiconductor, which eliminates the need for high voltage charge injection mechanisms used in flash memory. The oxide semiconductor's inherent low leakage current enables simple voltage-based switching for fast writing while maintaining non-volatile storage capabilities, resolving the speed-retention tradeoff.
Data Source
AI summary
An object of one embodiment of the present invention is to provide a semiconductor device with a novel structure in which stored data can be stored even when power is not supplied in a data storing time and there is no limitation on the number of times of writing. The semiconductor device includes a first transistor which includes a first channel formation region using a semiconductor material other than an oxide semiconductor, a second transistor which includes a second channel formation region using an oxide semiconductor material, and a capacitor. One of a second source electrode and a second drain electrode of the second transistor is electrically connected to one electrode of the capacitor.