STTMRAM Free Layer Alloy for Low-Temperature Processing

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Solution Overview

Problem

Current spin-transfer torque magnetic random access memory (STTMRAM) technologies face challenges in achieving smaller cell sizes and low-cost, high-volume manufacturing due to high processing temperatures and complex cell architectures, which limit scalability and increase manufacturing costs.

Innovation Solution

Incorporating a low-crystallization temperature alloy of CoFeB with additives like Ti, Zr, Y, and V into the free layer of the magnetic tunnel junction (MTJ) to reduce saturation magnetization and damping, allowing for lower annealing temperatures while maintaining high thermal stability and tunnel magnetoresistance (TMR) ratios.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If conventional STTMRAM uses standard CoFeB free layer, then thermal stability is maintained, but processing temperature must be above 300°C which increases manufacturing cost and reduces scalability

Engineering Contradiction:
Improveprocessing temperatureVSAvoidmanufacturing cost
Core Design Contradiction:
TemperatureVSEase of manufacture

Solution Approach 1:

The patent modifies the compositional parameters of the CoFeB alloy by incorporating specific elements (Ti, Zr, Y, V) at controlled concentrations to change the crystallization temperature parameter, enabling low-temperature processing while maintaining thermal stability

Inventive Principle:
Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite magnetic alloy by combining CoFeB with additional elements (Ti, Zr, Y, V) to achieve both low crystallization temperature and high thermal stability simultaneously

Inventive Principle:
Principle #40Composite materials

2Productivity

If MTJ size is reduced for smaller cell architecture, then scalability improves, but switching current density increases making manufacturing difficult

Engineering Contradiction:
ImprovescalabilityVSAvoidswitching current density
Core Design Contradiction:
ProductivityVSPower

Solution Approach 1:

The patent changes the magnetic properties parameters of the free layer by adjusting alloy composition, specifically reducing saturation magnetization through element addition, which lowers switching current density and enables scaling

Inventive Principle:
Principle #35Parameter changes

3Power

If saturation magnetization is reduced to lower switching current, then cell size can be reduced, but thermal stability may be compromised

Engineering Contradiction:
Improveswitching current densityVSAvoidthermal stability
Core Design Contradiction:
PowerVSReliability

Solution Approach 1:

The patent develops a composite alloy where the added elements (Ti, Zr, Y, V) contribute to reducing saturation magnetization while their specific properties maintain thermal stability through enhanced magnetocrystalline anisotropy

Inventive Principle:
Principle #40Composite materials

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 approach results in a lower switching current density and reduced manufacturing costs, enabling smaller cell sizes and improved scalability with high thermal stability, making STTMRAM more suitable for integration into CMOS processes and logic devices.

Implementation Method 1

writing magnetic bits is achieved by using a spin polarized current through the magnetic tunnel junction (MTJ), instead of using a magnetic field

Methodology Applied
Scientific EffectSpin transfer torque:

Implementation Method 2

Incorporating a low-crystallization temperature alloy of CoFeB with additives like Ti, Zr, Y, and V into the free layer to reduce saturation magnetization and damping

Methodology Applied
Scientific EffectMagnetization reduction through alloying:

Implementation Method 3

high thermal stability and tunnel magnetoresistance (TMR) ratios

Methodology Applied
Scientific EffectTunnel magnetoresistance: Magnetoresistance

Data Source

PatentUS8611147B2Spin-transfer torque magnetic random access memory (STTMRAM) using a synthetic free layer
Publication Date: 2013.12.17 AVALANCHE TECHNOLOGY INC
  • US8611147B2 patent drawing
  • US8611147B2 patent drawing
  • US8611147B2 patent drawing

AI summary

A spin-torque transfer memory random access memory (STTMRAM) element, employed in a STTMRAM array, receives electric current for storage of digital information, the STTMRAM element has a magnetic tunnel junction (MTJ). The MTJ includes an anti-ferromagnetic (AF) layer, a fixed layer having a magnetization that is substantially fixed in one direction and that comprises a first magnetic layer, an AF coupling layer and a second magnetic layer, a barrier layer formed upon the fixed layer, and a free layer. The free layer is synthetic and has a high-polarization magnetic layer, a low-crystallization magnetic layer, a non-magnetic separation layer, and a magnetic layer, wherein during a write operation, a bidirectional electric current is applied across the STTMRAM element to switch the magnetization of the free layer between parallel and anti-parallel states relative to the magnetization of the fixed layer.