SOT MRAM Cell Density via Selector Structures

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Solution Overview

Problem

Spin Orbit Torque (SOT) MRAM devices have a low device per area density due to their three-terminal configuration, which results in a large surface area requirement for each magnetoresistive random-access memory (MRAM) cell, limiting their packing density and efficiency.

Innovation Solution

Incorporating selector structures between the Source Line (SL), Write Word Line (WWL), and Read Word Line (RWL) to control current direction and pathways for each MRAM cell, allowing independent selection and operation of each cell while sharing terminals, thereby increasing device per area density.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a three-terminal configuration is used for SOT MRAM devices, then the device structure is simple and easy to manufacture, but the device per area density is low and surface area requirement is large

Engineering Contradiction:

Improveease of manufactureVSAvoiddevice per area density

Core Design Contradiction:

Ease of manufactureVSQuantity of substance

Solution Approach 1:

The patent divides the SOT MRAM device into separate functional components: a magnetic tunnel junction (MTJ) structure for data storage and selector structures for cell selection. This segmentation allows the MTJ to be shared among multiple cells while selector structures enable individual cell addressing, thereby increasing device density without complicating the core storage element fabrication

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transitions from a planar three-terminal configuration to a vertically stacked multi-terminal architecture. By stacking selector structures above and below the MTJ and extending conductive wires in multiple dimensions, the device achieves higher packing density in the vertical dimension while maintaining manufacturability through standard semiconductor stacking processes

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Quantity of substance

If selector structures are incorporated between SL, WWL, and RWL to control current pathways, then device per area density increases, but device complexity increases

Engineering Contradiction:

Improvedevice per area densityVSAvoiddevice complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The selector structures serve multiple functions: they enable individual cell selection, control current direction through the MTJ, and facilitate both read and write operations. This multi-functionality reduces the need for separate dedicated structures for each operation, thereby increasing device density without proportionally increasing complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The selector structures act as intermediary components between the conductive wires (SL, WWL, RWL) and the MTJ structure. These selectors mediate current flow, allowing complex selection logic to be implemented through simple threshold-switching behavior rather than requiring complex circuitry directly at the MTJ

Inventive Principle:

Principle #24Intermediary (Mediator)

3Area of stationary object

If selector structures are used to enable independent operation of each cell, then surface area required is reduced, but manufacturing precision requirements increase

Engineering Contradiction:

Improvesurface area requiredVSAvoidmanufacturing precision

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The patent merges multiple selector structures with the MTJ in a stacked configuration, where shared conductive wires and overlapping selector-MTJ assemblies reduce the overall surface footprint. This merging consolidates multiple functions into a compact vertical stack, decreasing surface area while using standard alignment tolerances in vertical stacking

Inventive Principle:

Principle #5Merging (Combining)

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 use of selector structures enables higher device per area density in SOT MRAM arrays by allowing independent operation of each cell, reducing the overall surface area required and enhancing storage density.

Implementation Method 1

A spin orbit torque (SOT) MRAM device uses an SOT layer to reduce power consumption and increase endurance

Methodology Applied

Scientific EffectSpin orbit torque:

Implementation Method 2

A magnetoresistive random access memory (MRAM) is a type of non-volatile memory that stores information according to the direction of magnetic moments in magnetic films layers

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS11903326B2SOT-MRAM cell in high density applications

Publication Date: 2024.02.13 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

In some embodiments, the present disclosure relates to a memory device that includes a spin orbit torque (SOT) layer arranged over a substrate. A magnetic tunnel junction (MTJ) structure may be arranged over the SOT layer. The MTJ structure includes a free layer, a reference layer, and a diffusion barrier layer disposed between the free layer and the reference layer. A first conductive wire is arranged below the SOT layer and coupled to the SOT layer. A second conductive wire is arranged below the SOT layer and coupled to the SOT layer. A third conductive wire is arranged over the MTJ structure. The memory device further includes a first selector structure arranged between the first conductive wire and the SOT layer.