Resistivity Changing Memory Cell Refresh Voltage Stabilization

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Solution Overview

Problem

PMC memory cells in CBRAM devices face challenges with data retention and reliability due to degradation of the programmed state over time, especially at higher temperatures, and the irreversible imprinting of the programmed state when repeatedly programmed, which reduces their reliability and requires time-consuming erasure before reprogramming.

Innovation Solution

A method is introduced that applies a refresh voltage to stabilize the programmed state of PMC memory cells, preventing imprinting and maintaining data retention by selecting a refresh voltage within specific voltage ranges that avoid altering the erased state, allowing for multi-level operation and reducing the need for frequent erasure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If programming voltage is applied repeatedly to write programmed state, then data can be stored, but irreversible imprinting occurs and reliability is reduced

Engineering Contradiction:

Improvememory cell reliabilityVSAvoidimprinting effect

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

An erase voltage is applied before programming to remove any existing conductive path in the solid electrolyte. This preliminary erasure prevents the imprinting effect that would occur from repeated programming attempts, ensuring the memory cell is in a known state before new data is written.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The memory operation follows a periodic sequence of erase and program cycles. By regularly erasing the cell before programming, the system prevents cumulative imprinting effects while maintaining the ability to store data reliably over multiple write operations.

Inventive Principle:

Principle #19Periodic action

2Reliability

If programming voltage is applied to develop conductive path, then programmed state is achieved, but resistance increases over time due to degradation

Engineering Contradiction:

Improvedata retentionVSAvoidprogrammed state retention time

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

An erase voltage is applied before programming to ensure the solid electrolyte starts in a high-resistance state. This preliminary erasure creates a stable baseline that prevents degradation-induced resistance drift during the programmed state, improving long-term data retention.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes the operational parameters by applying erase voltage at specific intervals before programming. This parameter change resets the resistance state of the solid electrolyte, preventing the gradual resistance increase that would otherwise occur during programmed state retention.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If erase voltage is applied to achieve high resistance state, then erased state is stored, but time is consumed for erasure process

Engineering Contradiction:

Improveprogramming speedVSAvoiderasure time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The erase voltage is applied as a preliminary step before programming only when necessary to prevent imprinting. This selective preliminary erasure reduces unnecessary erasure operations, thereby improving overall programming speed while maintaining data integrity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The memory cell's solid electrolyte material inherently maintains its state without continuous intervention. By erasing only when needed to prevent imprinting rather than continuously, the system allows the material to self-maintain its state, reducing the time loss from frequent erasure operations.

Inventive Principle:

Principle #25Self-service

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

This method enhances data retention and reliability by stabilizing the resistance window between programmed and erased states, preventing irreversible imprinting, and reducing the time required for programming and erasure processes, thereby improving the overall performance and access times of PMC memory cells.

Implementation Method 1

The storing of different states in a PMC memory cell is based on the developing or diminishing of a conductive path in the electrolyte material between electrodes based on an applied electrical field

Methodology Applied

Scientific EffectConductive path formation in solid electrolyte: Electrolysis

Implementation Method 2

A refresh voltage is applied to the PMC memory cell at a predetermined time to stabilize the programmed state of the PMC memory cell

Methodology Applied

Scientific EffectElectrical field stabilization: Electric Field

Implementation Method 3

the conductive path between electrodes has a low resistance. Thereby, the PMC memory cell can be set to different states depending on the set resistance of the PMC memory element

Methodology Applied

Scientific EffectElectrical conduction through solid electrolyte: Conduction (electrical)

Data Source

PatentUS8531863B2Method for operating an integrated circuit having a resistivity changing memory cell

Publication Date: 2013.09.10 GLOBALFOUNDRIES US INC

AI summary

A method for operating a resistivity changing memory including applying a programming voltage to a resistivity changing memory cell to define a programmed state and applying a refresh voltage to the resistivity changing memory cell for maintaining the programmed state of the resistivity changing memory cell. In one embodiment, the refresh voltage is less than the programming voltage.