Magnetic Junction With Interleaved Free Layers For High Density STT-RAM

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Solution Overview

Problem

Conventional spin transfer torque random access memories (STT-RAMs) face challenges in achieving high density due to the areal requirements and fabrication complexities of magnetic tunneling junctions (MTJs) and associated circuitry, leading to poor yield and high aspect ratios in memory cell stacks.

Innovation Solution

A magnetic junction design featuring a pinned layer and multiple interleaved free layers with nonmagnetic spacer layers, where each free layer has a distinct critical switching current density, allowing for multiple bits to be stored in a single stack with reduced stack height and simplified fabrication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If conventional MTJ stacks are used to increase memory density, then memory density is improved, but aspect ratio increases and fabrication yield deteriorates

Engineering Contradiction:

Improvememory densityVSAvoidfabrication yield

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent transitions from storing multiple bits horizontally (in-plane) to storing multiple bits vertically (out-of-plane) within a single MTJ stack. By utilizing the vertical dimension with multiple free layers having different magnetization orientations, the design achieves higher memory density without increasing the lateral footprint, thereby maintaining acceptable aspect ratios and fabrication yield.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Quantity of substance

If conventional MTJ stacks are used to increase memory density, then memory density is improved, but device complexity increases

Engineering Contradiction:

Improvememory densityVSAvoidstack structure complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent segments the magnetic functionality into multiple free layers (first free layer, second free layer, etc.), each with distinct magnetization orientations (in-plane, out-of-plane, or canted). This segmentation allows multiple bits to be stored in a single stack by independently controlling the magnetization state of each layer, increasing memory density while maintaining a unified stack structure rather than requiring multiple separate MTJ cells.

Inventive Principle:

Principle #1Segmentation

3Quantity of substance

If higher switching current densities are used to switch deeper free layers, then multiple bits can be stored in single stack, but energy consumption increases

Engineering Contradiction:

Improvememory capacity per stackVSAvoidwrite energy consumption

Core Design Contradiction:

Quantity of substanceVSUse of energy by moving object

Solution Approach 1:

The patent applies local quality by giving different magnetization orientations to different free layers based on their position and switching requirements. The first free layer has in-plane magnetization requiring lower switching current, while the second free layer has out-of-plane or canted magnetization requiring higher switching current. This local differentiation allows the stack to store multiple bits with optimized energy consumption for each layer rather than uniformly high energy for all layers.

Inventive Principle:

Principle #3Local quality

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 design enables improved memory density, reduced stack height, and enhanced fabrication yield by allowing multiple bits to be stored in a single stack with lower aspect ratios, simplifying the fabrication process and improving performance.

Implementation Method 1

STT-RAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction.

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

The magnetization 17 of the conventional pinned layer 16 is fixed, or pinned, in a particular direction, typically by an exchange-bias interaction with the AFM layer 14.

Methodology Applied

Scientific EffectExchange-bias interaction:

Implementation Method 3

the conventional pinned layer 16 may be a synthetic antiferromagnetic (SAF) layer including magnetic layers antiferromagnetically coupled through thin conductive layers, such as Ru.

Methodology Applied

Scientific EffectMagnetic coupling:

Data Source

PatentUS8446761B2Method and system for providing multiple logic cells in a single stack

Publication Date: 2013.05.21 SAMSUNG SEMICONDUCTOR INC

AI summary

A method and system for providing a magnetic junction usable in a magnetic device are described. The magnetic junction includes a pinned layer, a plurality of nonmagnetic spacer layers, and a plurality of free layers. The free layers are interleaved with the nonmagnetic spacer layers. A first nonmagnetic spacer layer of the nonmagnetic spacer layers is between the free layers and the pinned layer. Each of the free layers is configured to be switchable between stable magnetic states when a write current is passed through the magnetic junction. Each of the free layers has a critical switching current density. The critical switching current density of one of the free layers changes monotonically from the critical switching current density of an adjacent free layer. The adjacent free layer is between the pinned layer and the one of the plurality of free layers.