Rounded Corner MTJ Free Layer for STTRAM Stability

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The practical implementation of magnets in semiconductor devices, such as spin transfer torque random access memory (STTRAM), is hindered by the difficulty in producing stable elliptical and rectangular nanomagnets due to limitations in modern lithography techniques, leading to inefficient switching currents and instability in magnetic states.

Innovation Solution

A magnetic tunnel junction (MTJ) with a free magnetic layer featuring a rectangular shape with rounded corners, which allows for easier manufacturing and stable magnetization states, is introduced, using a combination of two masks to pattern the nanomagnets, thereby reducing the complexity and cost of lithography processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If elliptical nanomagnets are used in STTRAM, then magnetic state stability is improved, but manufacturing complexity and lithography difficulty increase

Engineering Contradiction:

Improvemagnetic state stabilityVSAvoidlithography ease

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

The patent applies curvature by rounding the corners of rectangular nanomagnets rather than using sharp corners. This partial spheroidality (rounded corners) provides magnetic state stability similar to elliptical shapes while maintaining the manufacturing simplicity of rectangular patterns. The rounded corners eliminate magnetic field concentration at sharp edges, stabilizing the magnetic states without requiring complex elliptical lithography.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Ease of manufacture

If rectangular nanomagnets are used in STTRAM, then ease of manufacture is improved, but magnetic state stability deteriorates

Engineering Contradiction:

Improvelithography easeVSAvoidmagnetic state stability

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The patent modifies rectangular nanomagnets by adding rounded corners, combining the manufacturing ease of rectangles with the magnetic stability of curved shapes. The rounded corners prevent magnetic domain instability that occurs at sharp corners while preserving the simple rectangular fabrication process.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Manufacturing precision

If specialized masks are used for nanomagnet patterning, then manufacturing precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improvenanomagnet patterning precisionVSAvoidlithography process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Instead of using complex specialized masks to create elliptical shapes, the patent inverts the approach by using simple rectangular masks and achieving stability through rounded corners. This reversal of the conventional wisdom (that elliptical shapes require specialized masks) simplifies the lithography process while maintaining manufacturing precision for stable magnetic states.

Inventive Principle:

Principle #13The other way round (Inversion)

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 achieves stable magnetization states and efficient switching currents while maintaining manufacturability, enhancing the competitiveness of STTRAM memory by reducing the need for specialized masks and improving data fidelity.

Implementation Method 1

Some magnetic memories, such as a spin transfer torque memory (STTM), utilize a magnetic tunnel junction (MTJ) for switching and detection of the memory's magnetic state

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

Memory 100 is 'read' by assessing the change of resistance (e.g., tunneling magnetoresistance (TMR)) for different relative magnetizations of FM layers 125, 127

Methodology Applied

Scientific EffectTunneling magnetoresistance: Magnetoresistance

Implementation Method 3

The MTJ couples bit line (BL) 105 to selection switch 120 (e.g., transistor), word line (WL) 110, and sense line (SL) 115. Layer 127 is the 'reference layer' or 'fixed layer' because its magnetization direction is fixed. Layer 125 is the 'free layer' because its magnetization direction is changed

Methodology Applied

Scientific EffectFerromagnetism: Ferromagnetism

Data Source

PatentUS10483455B2Magnetic element for memory and logic

Publication Date: 2019.11.19 INTEL CORP

AI summary

An embodiment includes a magnetic tunnel junction (MTJ) having a non-elliptical free layer with rounded corners. For example, an embodiment includes a MTJ including a free magnetic layer, a fixed magnetic layer, and a tunnel barrier between the free and fixed layers; wherein the free magnetic layer includes a top surface, a bottom surface, and a sidewall circumnavigating the free magnetic layer and coupling the bottom surface to the top surface; wherein the top surface is rectangular with a plurality of rounded corners. In an embodiment, the aspect ratio of the top surface is between 4:1 and 8:1 (length to width). Such an embodiment provides ease of manufacture along with accept critical switching current (to reverse polarity of the free layer) and stability. Other embodiments are described herein.