MRAM Reference Voltage Stability via MTJ String Merging

Solution Overview

Problem

Current magnetoresistive random access memory (MRAM) devices face issues such as high chip area, high cost, high power consumption, and sensitivity to temperature variations, limiting their effectiveness in magnetic field sensing applications.

Innovation Solution

The proposed MRAM design includes device strings with magnetic tunnel junctions (MTJs) coupled in parallel, where each string has an equivalent resistance calculated as the average of high and low resistance MTJs, and a reference array with specific connections between MTJs to stabilize the resistance and improve read margin.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional magnetic field sensor technologies (AMR, GMR, MTJ sensors) are used, then magnetic field sensing capability is achieved, but chip area increases, cost increases, power consumption increases, and temperature stability deteriorates

Engineering Contradiction:

Improvetemperature stabilityVSAvoidchip area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent combines multiple MTJs in series within device strings and connects multiple device strings in parallel, merging their resistance characteristics to achieve a reference voltage that averages out temperature variations and outlier effects, thereby improving temperature stability while maintaining compact chip area

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the resistance parameter configuration by selecting MTJs with specific high and low resistance values and arranging them in series/parallel configurations, creating an equivalent resistance that is less sensitive to temperature changes and reduces the impact of manufacturing variations

Inventive Principle:

Principle #35Parameter changes

2Reliability

If conventional magnetic field sensor technologies are used, then magnetic field sensing capability is achieved, but power consumption increases

Engineering Contradiction:

Improvetemperature stabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent combines multiple MTJs in series within device strings and connects multiple device strings in parallel, merging their resistance characteristics to achieve a reference voltage that averages out temperature variations and outlier effects, thereby improving temperature stability while maintaining compact chip area

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the resistance parameter configuration by selecting MTJs with specific high and low resistance values and arranging them in series/parallel configurations, creating an equivalent resistance that is less sensitive to temperature changes and reduces the impact of manufacturing variations

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If conventional magnetic field sensor technologies are used, then magnetic field sensing capability is achieved, but sensitivity to temperature variations increases

Engineering Contradiction:

ImprovesensibilityVSAvoidtemperature variation sensitivity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent combines multiple MTJs in series within device strings and connects multiple device strings in parallel, merging their resistance characteristics to achieve a reference voltage that averages out temperature variations and outlier effects, thereby improving temperature stability while maintaining compact chip area

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the resistance parameter configuration by selecting MTJs with specific high and low resistance values and arranging them in series/parallel configurations, creating an equivalent resistance that is less sensitive to temperature changes and reduces the impact of manufacturing variations

Inventive Principle:

Principle #35Parameter changes

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 design reduces the influence of outliers, achieving a more stable reference voltage output and enhancing the performance of MRAM devices by optimizing chip area, cost, and power consumption while improving temperature stability.

Implementation Method 1

Magnetoresistance (MR) effect has been known as a kind of effect caused by altering the resistance of a material through variation of outside magnetic field

Methodology Applied

Scientific EffectMagnetoresistance (MR) effect: Magnetoresistance

Implementation Method 2

magnetic tunneling junction (MTJ) sensors have been widely developed in the market

Methodology Applied

Scientific EffectMagnetic tunneling junction (MTJ):

Data Source

PatentUS10700126B2Magnetoresistive random access memory wherein number of memory cells in each string is equal to number of strings connected in parallel

Publication Date: 2020.06.30 UNITED MICROELECTRONICS CORP

AI summary

A magnetic random access memory (MRAM) includes device strings coupled in parallel, each comprising magnetic tunnel junctions (MTJs) coupled in serial, wherein a quantity of the MTJs of each of the device strings is equal to a quantity of the device strings, and an equivalent resistance (Req) of the MTJs is equal to an average of the sum of a high resistance of one of the MTJs and a low resistance of another MTJ.