Multi-Layered Free Layer MTJ for Perpendicular Magnetization Stability
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Solution Overview
Problem
Existing memory devices face challenges in maintaining a perpendicular magnetization direction of the free layer while preventing metal diffusion through the layer, which can lead to leakage paths and affect the performance of Magnetic Tunnel Junction (MTJ) structures.
Innovation Solution
The implementation of a semiconductor memory device with a free layer comprising a first ferromagnetic material of hard type and a second ferromagnetic material of soft type, where the second material has a coercive force smaller than the first, and an amorphous spacer, allowing for exchange coupling to maintain a perpendicular magnetization direction and reduce damping constants, thereby improving switching characteristics and interface characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer ferromagnetic material is used in the free layer, then the structure is simple, but it is difficult to maintain perpendicular magnetization direction and prevent metal diffusion
Solution Approach 1:
The free layer is divided into two separate ferromagnetic material layers (first and second ferromagnetic materials) with different coercive forces. The first ferromagnetic material layer provides perpendicular magnetization anisotropy, while the second ferromagnetic material layer has higher saturation magnetization to stabilize the perpendicular magnetization direction and prevent metal diffusion, thereby resolving the contradiction between structural simplicity and reliability.
2Reliability
If the thickness of the ferromagnetic material is increased to prevent metal diffusion, then diffusion protection improves, but the perpendicular magnetization direction becomes difficult to maintain
Solution Approach 1:
The free layer is segmented into two ferromagnetic material layers with distinct functions: the first layer (closer to the tunnel barrier layer) has thickness optimized for perpendicular magnetization anisotropy, while the second layer (closer to the capping layer) has greater thickness to prevent metal diffusion. This segmentation allows each layer to optimize its thickness for its specific function, resolving the contradiction between diffusion protection and perpendicular magnetization maintenance.
Solution Approach 2:
Different regions of the free layer are assigned different material properties and thicknesses: the first ferromagnetic material layer has smaller thickness with perpendicular magnetization anisotropy, while the second ferromagnetic material layer has larger thickness for diffusion barrier functionality. This local quality differentiation allows simultaneous optimization of both perpendicular magnetization and metal diffusion prevention.
3Reliability
If a multi-layered ferromagnetic structure is implemented, then perpendicular magnetization and diffusion prevention are improved, but the device complexity increases
Solution Approach 1:
The free layer is segmented into two ferromagnetic material layers with a non-magnetic spacer layer between them, creating a multi-layered structure that improves both perpendicular magnetization maintenance and metal diffusion prevention. The segmentation allows each sub-layer to be optimized for its specific function while working together as an integrated system.
Solution Approach 2:
A non-magnetic spacer layer is introduced as an intermediary between the two ferromagnetic material layers. This spacer layer facilitates exchange coupling between the layers while preventing direct metal diffusion, and allows the multi-layered structure to achieve improved reliability without excessive complexity by providing a clear functional interface between layers.
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 perpendicular magnetization characteristics, reduces damping constants, and prevents metal diffusion, leading to improved Tunnel Magnetoresistance (TMR) and High Resistance Depth (HRD) performance, while maintaining stability and endurance.
Implementation Method 1
exchange coupling between the first and second ferromagnetic materials is allowed so that a magnetization of the second ferromagnetic material is aligned to a magnetization of the first ferromagnetic material
Implementation Method 2
a first ferromagnetic material having a first magnetization that can be switched by spin torque transfer
Implementation Method 3
a tunnel barrier layer interposed between the pinned layer and the free layer
Data Source
AI summary
This technology provides an electronic device. An electronic device in accordance with an implementation of this document includes semiconductor memory, and the semiconductor memory includes a free layer having a variable magnetization direction; a pinned layer having a pinned magnetization direction; and a tunnel barrier layer interposed between the pinned layer and the free layer, wherein the free layer includes: a first ferromagnetic material; a second ferromagnetic material having a coercive force smaller than that of the first ferromagnetic material; and an amorphous spacer interposed between the first ferromagnetic material and the second ferromagnetic material.