Spin Transfer MRAM Cell Structure for Microminiaturization

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Solution Overview

Problem

Magnetic Random Access Memory (MRAM) faces challenges in microminiaturization due to high power consumption and difficulty in applying sufficient electric current, leading to increased coercive force and power consumption, which hinders the microminiaturization of memory cells.

Innovation Solution

The development of a Spin Transfer Random Access Memory (SpRAM) structure that uses spin injection current to invert magnetization without relying on current magnetic fields, allowing for magnetization inversion with a smaller electric current and simplifying the memory cell structure by eliminating the need for write address wiring.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional MRAM structure with current magnetic field is used to invert magnetization, then magnetization inversion can be achieved, but power consumption increases and microminiaturization becomes difficult

Engineering Contradiction:

Improvemagnetization inversion capabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces the conventional current magnetic field method (electromagnetic mechanism) with spin transfer torque mechanism. By applying spin-polarized current directly through the tunnel magnetoresistance element, magnetization inversion is achieved through spin transfer rather than external magnetic fields, reducing power consumption and enabling microminiaturization.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operational parameters by using spin transfer torque with threshold current characteristics. The magnetization inversion occurs when spin-polarized current exceeds a threshold value, allowing precise control of magnetization state switching with lower power consumption compared to conventional methods.

Inventive Principle:

Principle #35Parameter changes

2Area of moving object

If memory cell size is reduced for microminiaturization, then integration density increases, but sufficient electric current cannot be applied leading to increased coercive force

Engineering Contradiction:

Improvememory cell areaVSAvoidcoercive force

Core Design Contradiction:

Area of moving objectVSForce

Solution Approach 1:

The patent replaces external current magnetic field application with direct spin transfer torque through the tunnel magnetoresistance element. This substitution allows magnetization inversion in miniaturized cells where external field application becomes difficult, as the spin transfer effect occurs internally within the element structure itself.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent transitions from planar current flow to vertical current flow through the tunnel magnetoresistance element structure. By applying current in the laminating direction through the stacked layers (storage layer, tunnel insulating layer, magnetization fixed layer), the spin transfer torque acts vertically, enabling effective magnetization inversion in miniaturized vertical structures.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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

SpRAM achieves stable and efficient information recording with reduced power consumption, enabling high-speed operation and nearly limitless rewriting capabilities while maintaining thermal stability and scalability, even in small memory cells.

Implementation Method 1

Magnetization inversion based on spin transfer is such as to cause magnetization to be inverted in another magnetic material by injecting electrons spin-polarized by passing through a magnetic material into the magnetic material

Methodology Applied

Scientific EffectSpin transfer:

Implementation Method 2

a tunnel magnetoresistance effect that a resistance value relative to a tunnel current flowing through the tunnel insulating film changes in response to an angle formed by the direction of magnetization of the storage layer and the direction of magnetization of the magnetization fixed layer takes place

Methodology Applied

Scientific EffectTunnel magnetoresistance effect: Magnetoresistance

Data Source

PatentUS7633796B2Storage element and memory

Publication Date: 2009.12.15 SONY GROUP CORP

AI summary

A storage element includes a storage layer for holding information depending on a magnetization state of a magnetic material; and a magnetization fixed layer in which magnetization direction is fixed, that is arranged relative to the storage layer through a nonmagnetic layer. The magnetization direction of the storage layer is changed with application of an electric current in a laminating direction to enable information to be recorded to the storage layer. A plurality of magnetization regions respectively having magnetization components in laminating directions and having magnetizations in different directions from each other are formed in the magnetization fixed layer or on an opposite side of the magnetization fixed layer relative to the storage layer.