Oxide Semiconductor Memory Cell Structure for Low Leakage
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Solution Overview
Problem
Conventional memory devices, such as DRAM and flash memory, face limitations in data retention, power consumption, and durability due to high leakage currents and the need for frequent rewriting, which restricts their application in scenarios requiring long-term data storage and high-speed data access.
Innovation Solution
A semiconductor device utilizing purified oxide semiconductors with a unique structure comprising multiple transistors and a capacitor, where the transistors have different channel materials and overlapping electrodes, reducing off-state current and eliminating the need for high voltage writing, thereby enhancing data retention and operational speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a transistor is used in a memory element to store data by accumulating charge in a capacitor, then data can be stored in a volatile memory device, but leakage current flows between source and drain when the transistor is in off state, causing charge to flow in or out and making the data holding period short
Solution Approach 1:
The invention changes the material parameter of the transistor from conventional semiconductor to oxide semiconductor, which fundamentally alters the electrical characteristics to achieve extremely low off-state current and extended data retention without refresh operations
Solution Approach 2:
The invention uses a composite structure combining oxide semiconductor material with conventional semiconductor materials in different transistors within the same memory cell, leveraging the unique properties of oxide semiconductor for data retention while maintaining compatibility with existing manufacturing processes
2Duration of action of moving object
If a flip-flop circuit is used in an SRAM to hold stored data, then refresh operation is not needed, but cost per memory capacity is increased
Solution Approach 1:
The invention extracts and eliminates the need for complex flip-flop circuits by using oxide semiconductor transistors whose inherent low leakage current properties enable data retention through simpler capacitor-based storage, reducing circuit complexity while maintaining non-volatile characteristics
Solution Approach 2:
The oxide semiconductor transistor serves multiple functions: it acts as both the switching element and the data retention element, eliminating the need for separate flip-flop circuitry while enabling refresh-free operation through its extremely low off-state current
3Duration of action of moving object
If a floating gate is used in a flash memory to store data by holding charge, then data holding period becomes extremely long and refresh operation is not needed, but the memory element becomes unable to function after a predetermined number of writings due to gate insulating layer deterioration
Solution Approach 1:
The invention changes the transistor material from conventional semiconductor to oxide semiconductor, which eliminates the tunneling current-induced gate insulating layer deterioration problem while maintaining long-term charge retention capabilities, thereby enabling unlimited rewrite cycles
Solution Approach 2:
The invention replaces the fragile floating gate structure with a more robust oxide semiconductor transistor and capacitor combination that does not suffer from tunneling current damage, effectively creating a wear-free memory element that can be rewritten indefinitely
4Reliability
If high voltage is used to inject charge in the floating gate or removing the charge, then data can be written or erased, but it takes a relatively long time and it is not easy to increase the speed of writing and erasing data
Solution Approach 1:
The invention changes the material system from conventional semiconductor with floating gate to oxide semiconductor with capacitor-based storage, which eliminates the need for high-voltage charge injection and enables fast writing and erasing operations through conventional low-voltage transistor switching
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 retention with low power consumption, high-speed operation, and increased integration density, eliminating the limitations of conventional memory devices by minimizing off-state current and eliminating the need for frequent refresh operations.
Implementation Method 1
A transistor formed using a purified oxide semiconductor can hold data for a long time because leakage current thereof is extremely small
Data Source
AI summary
A semiconductor device with a novel structure is provided in which stored data can be held even when power is not supplied and the number of writing is not limited. The semiconductor includes a second transistor and a capacitor over a first transistor. The capacitor includes a source or drain electrode and a gate insulating layer of the second transistor and a capacitor electrode over an insulating layer which covers the second transistor. The gate electrode of the second transistor and the capacitor electrode overlap at least partly with each other with the insulating layer interposed therebetween. By forming the gate electrode of the second transistor and the capacitor electrode using different layers, an integration degree of the semiconductor device can be improved.