Spin Transfer Torque Magnetic Memory Cell Architecture

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Solution Overview

Problem

Conventional magnetic random access memory (MRAM) faces issues with write disturbances due to non-localized magnetic fields affecting nearby memory cells, leading to increased power consumption and longer access times, especially in high-density applications.

Innovation Solution

The implementation of spin transfer torque magnetic random access memory (STT-MRAM) uses localized current-driven switching to program magnetic memory cells, reducing write disturbances and power consumption by employing local and global word lines with different resistivities and a common source line for efficient data writing and reading.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional magnetic fields are used for writing, then magnetic memory cells can be programmed, but write disturbances occur due to non-localized magnetic fields affecting nearby cells

Engineering Contradiction:

Improvewrite disturbanceVSAvoidmagnetic field spread

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the conventional magnetic field-based writing mechanism with a current-driven spin transfer torque mechanism. Current pulses are applied through the bit line and word line to generate localized magnetic fields via the spin transfer effect, enabling precise writing without the non-localized magnetic field spread that causes write disturbances in conventional MRAM.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If conventional magnetic field writing is used, then memory cells can be programmed, but power consumption increases

Engineering Contradiction:

Improveprogramming capabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent substitutes the conventional magnetic field writing method with spin transfer torque writing using current pulses. This mechanism allows for more efficient energy utilization by directly manipulating the magnetic state through spin-polarized current flow, reducing the power consumption required for writing operations compared to conventional magnetic field approaches.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If conventional magnetic field writing is used, then memory cells can be programmed, but access time increases

Engineering Contradiction:

Improveprogramming capabilityVSAvoidaccess time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the conventional magnetic field writing mechanism with a current-driven spin transfer torque system. This substitution enables faster writing operations by utilizing the direct spin transfer effect, which operates on shorter timescales compared to conventional magnetic field-based writing, thereby reducing access time.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If conventional magnetic field writing is used, then memory cells can be programmed, but memory density decreases

Engineering Contradiction:

Improveprogramming capabilityVSAvoidmemory density

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent substitutes the conventional magnetic field writing method with spin transfer torque writing using current pulses. This mechanism enables more memory cells to be packed into a smaller area by allowing for more precise and localized writing operations, thereby increasing memory density while maintaining reliable programming capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 approach enhances memory cell scalability, reduces area usage, minimizes write disturbances, and enables faster access times while maintaining high memory density and speed, making it suitable for high-density applications.

Implementation Method 1

The magnetic element is programmed by a first write current driven through the magnetic element in a first direction and a second write current driven through the magnetic element in a second direction

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

a magnetic field is typically used. This magnetic field (switching field) is sufficient to switch the conventional MTJ 12 between the high and low resistance states

Methodology Applied

Scientific EffectMagnetic field generation: Magnetic Field

Data Source

PatentUS7623369B2Method and system for providing a magnetic memory structure utilizing spin transfer

Publication Date: 2009.11.24 SAMSUNG SEMICONDUCTOR INC

AI summary

A method and system for providing a magnetic memory is described. The method and system include providing magnetic memory cells, local and global word lines, bit lines, and source lines. Each magnetic memory cell includes a magnetic element and a selection device connected with the magnetic element. The magnetic element is programed by first and second write currents driven through the magnetic element in first and second directions. The local word lines are connected with the selection device of and have a first resistivity. Each global word line corresponds to a portion of the local word lines and has a resistivity lower than the first resistivity. The bit lines are connected with the magnetic element. The source lines are connected with the selection device. Each source line corresponds to a more than one of the magnetic memory cells and carries the first and second write currents.