Perpendicular Magnetization MRAM Element with Amorphous Crystallinity Dividing Layer
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Solution Overview
Problem
Magnetoresistance effect elements with perpendicular magnetization face challenges in downsizing due to increased coercive force and thermal disturbance, making it difficult to maintain magnetization direction and achieve both small element size and low electric current requirements.
Innovation Solution
Incorporating crystallinity dividing layers with an amorphous structure between the perpendicular magnetization magnetic layers and interface magnetic layers to maintain crystal structure integrity during annealing, reducing anisotropic axis dispersion and enhancing thermal stability, while using materials with high magnetocrystalline anisotropy to support spin transfer torque writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the element size is decreased to achieve large-capacity memory, then the storage capacity increases, but the coercive force increases and write current increases
Solution Approach 1:
The patent changes the magnetization direction from in-plane to perpendicular magnetization, fundamentally altering the magnetic anisotropy parameter. This enables the storage layer to maintain stable magnetization at smaller sizes with lower write currents, as perpendicular magnetization provides stronger magnetic anisotropy energy that is less sensitive to size reduction
Solution Approach 2:
The patent employs composite material structures including CoFeB (cobalt-iron-boron) alloy for the storage layer and CoFe (cobalt-iron) alloy for the reference layer, combined with specific interface structures. These composite materials provide optimized magnetic properties that enable both small element size and low write current operation
2Productivity
If the element size is decreased to achieve large-capacity memory, then the storage capacity increases, but thermal disturbance increases and magnetization stability decreases
Solution Approach 1:
The patent changes the magnetization orientation to perpendicular direction, which increases the magnetic anisotropy energy barrier. This higher energy barrier prevents thermal fluctuations from randomly switching magnetization directions, thereby maintaining data stability even in highly miniaturized elements
Solution Approach 2:
The patent introduces specific interface structures between magnetic layers, including gradient composition interfaces and controlled interdiffusion zones. These localized structural features at the interfaces enhance the overall magnetic stability by creating pinning effects that resist thermal disturbance
3Reliability
If materials with high magnetic anisotropy constant are selected to resist thermal disturbance, then the thermal stability improves, but the reversal current increases
Solution Approach 1:
The patent utilizes spin transfer torque (STT) mechanism to reverse magnetization, which fundamentally changes the switching mechanism from field-driven to current-driven at the nanoscale. This allows efficient magnetization reversal with low currents even in materials with high perpendicular magnetic anisotropy, resolving the contradiction between thermal stability and write current
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 solution enables thermally stable spin transfer torque writing with high heat resistance, maintaining desired storage characteristics and achieving a high TMR effect, even after annealing, by suppressing crystallinity deterioration and anisotropic axis variation, thus supporting both downsizing and low electric current needs.
Implementation Method 1
a writing (spin transfer torque writing) method using spin-momentum-transfer (SMT) has recently been proposed. This method reverses the magnetization direction in the storage layer by supplying a spin polarization current to the magnetoresistance effect element
Implementation Method 2
the resistance of the junction portion changes in accordance with the relative angle between the magnetization directions of the storage layer and reference layer. This resistance change is called a tunneling magneto-resistance effect (to be referred to as a TMR effect hereinafter)
Implementation Method 3
Incorporating crystallinity dividing layers with an amorphous structure between the perpendicular magnetization magnetic layers and interface magnetic layers to maintain crystal structure integrity during annealing
Data Source
AI summary
According to one embodiment, a magnetoresistance effect element includes first and second magnetic layers having an axis of easy magnetization in a direction perpendicular to a film surface, a first nonmagnetic layer formed between the first and second magnetic layers, a first interface magnetic layer formed between the first magnetic layer and the first nonmagnetic layer, and a second nonmagnetic layer formed in the first interface magnetic layer and having an amorphous structure. An electric current flowing through the first magnetic layer, the first nonmagnetic layer, and the second magnetic layer makes a magnetization direction in the first magnetic layer variable.