STT-MRAM Cylindrical Stack with Conical Top Electrode

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Solution Overview

Problem

Conventional spin-transfer torque magnetoresistive random access memory (STT-MRAM) cell structures face challenges in optimizing the magnetic tunneling junction (MTJ) layer configuration and electrode design for improved performance and reliability, particularly in achieving efficient magnetic switching and reduced power consumption.

Innovation Solution

The proposed STT-MRAM cell structure incorporates a cylindrical stack with a bottom electrode, a magnetic tunneling junction (MTJ) layer, and a top electrode comprising ruthenium (Ru) and tantalum (Ta) or titanium nitride (TiN) layers, with a conical or convex curved top surface profile, and a spacer layer on the sidewall, enhancing the MTJ layer configuration and electrode design for improved performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If conventional planar MTJ structure is used, then manufacturing process is simple, but magnetic switching efficiency is insufficient and power consumption is high

Engineering Contradiction:

Improvepower consumptionVSAvoidelectrode structure complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent applies curvature by designing the top electrode with a conical shape instead of a flat planar structure. This conical configuration concentrates the spin-polarized current through the MTJ tunnel barrier more effectively, enhancing the spin-transfer torque and improving magnetic switching efficiency while reducing the current required for switching, thus lowering power consumption.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The top electrode is constructed as a composite structure comprising multiple material layers (e.g., Ru, Ta, CoFeB) with distinct magnetic and electrical properties. This composite configuration optimizes both the spin polarization efficiency and the electrical conductivity, enabling effective magnetic switching with reduced power consumption while managing the increased structural complexity through systematic material selection.

Inventive Principle:

Principle #40Composite materials

2Reliability

If MTJ layer configuration is optimized for better magnetic switching, then switching efficiency improves, but device structure becomes more complex

Engineering Contradiction:

Improvemagnetic switching characteristicsVSAvoidMTJ layer structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements local quality by creating a conical top electrode with spatially varying thickness and material composition. The electrode structure transitions from a wider base to a narrower apex, concentrating the current density locally at the MTJ interface where it is most needed for effective magnetic switching, while maintaining simpler structures in other regions of the device.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The top electrode is designed with an asymmetric conical shape rather than a symmetric planar structure. This asymmetry allows for optimized current flow paths and enhanced spin-transfer torque generation at the MTJ interface, improving magnetic switching reliability while the asymmetric geometry itself becomes a defining characteristic of the device architecture.

Inventive Principle:

Principle #4Asymmetry

3Speed

If electrode design is enhanced for faster switching speed, then operating speed increases, but manufacturing precision requirements increase

Engineering Contradiction:

Improveoperating speedVSAvoidelectrode profile precision

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The conical curvature of the top electrode is designed to achieve faster switching speeds by concentrating spin-polarized current through the MTJ barrier. The curved geometry naturally guides current flow and enhances the spin-transfer torque effect, enabling faster magnetic switching. The curvature can be fabricated using standard semiconductor processing techniques such as angled sputtering or focused ion beam milling, balancing performance gains with manufacturing feasibility.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 configuration enhances the magnetic switching characteristics and reduces power consumption, leading to improved endurance and faster operating speeds in STT-MRAM cells, addressing the limitations of conventional designs.

Implementation Method 1

magnetic elements (MTJ elements) having MTJs utilizing a tunnel magneto resistance (TMR) effect

Methodology Applied

Scientific EffectTunnel magneto resistance (TMR) effect: Magnetoresistance

Implementation Method 2

spin-transfer torque magnetoresistive random access memory (STT-MRAM)

Methodology Applied

Scientific EffectSpin-transfer torque:

Data Source

PatentUS10727397B1Magnetoresistive random access memory cell

Publication Date: 2020.07.28 UNITED MICROELECTRONICS CORP

AI summary

A magneto-resistive random access memory (MRAM) cell includes a substrate having a dielectric layer disposed thereon, a conductive via disposed in the dielectric layer, and a cylindrical stack disposed on the conductive via. The cylindrical stack includes a bottom electrode, a magnetic tunneling junction (MTJ) layer on the bottom electrode, and a top electrode on the MTJ layer. A spacer layer is disposed on a sidewall of the cylindrical stack. The top electrode protrudes from a top surface of the spacer layer.