Perpendicular MRAM Element with Sacrificial Boron Diffusion Layer
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Solution Overview
Problem
Conventional perpendicular magnetoresistive memory technologies face challenges in achieving low write currents and thermal stability due to high damping constants and material diffusion issues during device manufacturing, which hinder the miniaturization and power efficiency of spin-transfer-torque magnetic-random-access memory (MRAM) devices.
Innovation Solution
The formation of perpendicular magnetoresistive elements involves a reference layer with perpendicular magnetic anisotropy, a tunnel barrier layer, a recording layer of amorphous CoFeB alloy, an oxide buffer layer, and a sacrificial layer with boron-absorbing composition, where thermal annealing diffuses boron atoms to transform the recording layer into a crystalline CoFe alloy with low damping constants, maintaining perpendicular anisotropy and reducing write current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional perpendicular magnetization layers are added to achieve thermal stability, then thermal stability is improved, but damping constant increases and write current cannot be reduced
Solution Approach 1:
The patent changes the material composition parameter by using CoFeB alloy with specific boron content (10-30 at%) and controlling the crystalline structure to achieve perpendicular magnetic anisotropy. This allows obtaining thermal stability through material composition optimization rather than adding more layers, thus avoiding the increase in damping constant and write current
Solution Approach 2:
The patent employs composite material structure with CoFeB alloy combined with specific buffer layers and cap layers. The CoFeB alloy itself is a composite material system where boron atoms substitute into the CoFe lattice, creating a composite structure that achieves both thermal stability and low damping constant through the synergistic effect of different elements
2Volume of moving object
If device miniaturization is pursued to reduce write current, then device size is reduced, but thermal stability becomes difficult to maintain
Solution Approach 1:
The patent changes the magnetic anisotropy parameter by optimizing the CoFeB alloy composition and crystalline structure. The perpendicular magnetic anisotropy energy density is enhanced through material composition control, allowing miniaturized devices to maintain sufficient thermal stability (high energy barrier) even at reduced volume
Solution Approach 2:
The patent applies local quality optimization by creating specific interface structures between CoFeB alloy and buffer/cap layers. The perpendicular magnetic anisotropy is primarily generated at these interfaces through spin-orbit coupling and magnetostatic coupling effects, concentrating the thermal stability mechanism at critical locations rather than requiring uniform distribution throughout the entire device volume
3Use of energy by moving object
If amorphous CoFeB alloy is used for low damping constant, then write current is reduced, but crystallization is insufficient and thermal stability is compromised
Solution Approach 1:
The patent utilizes controlled phase transition from amorphous to crystalline state through heat treatment. The CoFeB alloy is initially deposited in amorphous state for low damping constant, then undergoes controlled crystallization to form (100)-oriented BCC structure that provides perpendicular magnetic anisotropy and thermal stability. This phase transition allows the material to exhibit both low damping and high thermal stability properties at different stages
Solution Approach 2:
The patent changes the crystalline structure parameter by controlling the heat treatment process to achieve specific (100)-oriented BCC crystal structure. This crystalline structure transformation from amorphous state enhances the perpendicular magnetic anisotropy while maintaining the low damping constant property, thereby achieving both reduced write current and improved thermal stability
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 enables the reduction of write current while maintaining thermal stability and miniaturization, achieving efficient power usage and non-volatility in MRAM devices by inducing low-damping perpendicular magnetization with epitaxial growth of BCC CoFe grains.
Implementation Method 1
thermal annealing diffuses boron atoms to transform the recording layer into a crystalline CoFe alloy
Implementation Method 2
sacrificial layer with boron-absorbing composition
Implementation Method 3
inducing low-damping perpendicular magnetization with epitaxial growth of BCC CoFe grains
Implementation Method 4
transform the recording layer into a crystalline CoFe alloy
Implementation Method 5
a write method (spin torque transfer switching technique) using spin momentum transfers
Implementation Method 6
magnetic random access memories (hereinafter referred to as MRAMs) using the magnetoresistive effect of ferromagnetic tunnel junctions
Data Source
AI summary
A perpendicular magnetoresistive element comprises (counting from the element bottom): a reference layer having magnetic anisotropy in a direction perpendicular to a film surface and having an invariable magnetization direction; a tunnel barrier layer; a crystalline recording layer having magnetic anisotropy in a direction perpendicular to a film surface and having a variable magnetization direction; an oxide buffer layer; and a cap layer, wherein the crystalline recording layer consists of a CoFe alloy that is substantially free of boron and has BCC (body-centered cubic) CoFe grains having epitaxial growth with (100) plane parallel to a film surface.