Engineered Free Layer Magnetic Memory Elements
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Solution Overview
Problem
Conventional magnetic tunneling junctions (MTJs) used in magnetic recording and memory systems face challenges with poor soft magnetic performance due to high magnetostriction, which limits their applicability in high-density HDD and MRAM applications, especially when attempting to achieve high magnetoresistance and low resistance-area (RA) products.
Innovation Solution
A magnetic element is designed with a free layer comprising ferromagnetic layers having different crystalline orientations, separated by an intermediate layer that maintains high magnetoresistance while improving soft magnetic properties, utilizing a crystalline MgO barrier layer and ferromagnetic materials like CoFeB and NiFe, with an intermediate layer configured to prevent texture growth and atomic interdiffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional antiferromagnetic layers and pinned layers are used in magnetic tunneling junctions, then the magnetization state can be changed by external fields or spin transfer effect, but the soft magnetic performance is poor due to high magnetostriction
Solution Approach 1:
The patent employs composite material structures including synthetic antiferromagnetic (SAF) layers combining CoFeB and Ru, and engineered free layers with CoFeB/NiFe combinations. These composite structures reduce magnetostriction while maintaining reliable magnetization switching through exchange coupling and interfacial effects.
Solution Approach 2:
The patent modifies material composition parameters by varying the atomic percent of B (5-30%) in CoFeB layers and adjusting layer thicknesses (e.g., Ru layer 3-8 Angstroms). These parameter changes optimize the balance between magnetostriction reduction and magnetic switching performance.
2Reliability
If high magnetoresistance is achieved in magnetic tunneling junctions, then the signal is large, but the resistance-area (RA) product increases which is critical for reducing noise and impedance matching
Solution Approach 1:
The patent optimizes the barrier layer thickness parameter to achieve the desired balance between magnetoresistance and RA product. By precisely controlling the barrier thickness, the patent enables high signal strength while maintaining low enough RA for acceptable noise levels and impedance matching.
Solution Approach 2:
The use of CoFeB-based ferromagnetic layers combined with MgO barrier layers creates a composite structure that achieves both high magnetoresistance (150%) and low RA (3 Ωμm2), resolving the contradiction between signal strength and energy loss.
3Productivity
If spin transfer switching current density is reduced for high density MRAM applications, then the switching efficiency improves, but the process control of switching current distribution becomes more difficult
Solution Approach 1:
The patent reduces spin transfer switching current density by modifying material composition (CoFeB with 5-30% B), layer thicknesses, and crystalline orientation. These parameter changes improve switching efficiency while the engineered structure provides more uniform switching characteristics that facilitate process control.
Solution Approach 2:
The composite CoFeB/NiFe free layer structure with controlled crystalline orientations creates more uniform magnetic properties throughout the layer, leading to better process control of switching current distribution while maintaining high switching efficiency.
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 magnetic elements with high magnetoresistance and low RA, enhancing soft magnetic performance, reducing spin transfer switching current, and improving thermal stability, making them suitable for high-density recording applications.
Implementation Method 1
an intermediate layer configured to prevent texture growth and atomic interdiffusion
Implementation Method 2
The first ferromagnetic layer resides between the barrier layer and the intermediate layer and is ferromagnetically coupled with the second ferromagnetic layer
Implementation Method 3
The magnetization state of the conventional MTJ 10 may also be changed using the spin transfer effect, for example in applications such as microwave generators
Implementation Method 4
a magnetoresistance (AR/R) of 150% with an RA as low as 3 Ωμm2 can be realized for such a conventional MTJ 10 that uses an MgO for the conventional barrier layer 16
Implementation Method 5
amorphous layers of CoFeB exhibit a large magnetostriction. This magnetostriction results in poor soft magnetic performance
Data Source
AI summary
A method and system for providing a magnetic memory are described. The method and system include providing a plurality of magnetic storage cells. Each of the magnetic storage cells includes at least one magnetic element. The magnetic element(s) includes a pinned layer, a barrier layer that is a crystalline insulator and has a first crystalline orientation, and a free layer. The free layer includes a first ferromagnetic layer, a second ferromagnetic layer, and an intermediate layer between the first and second ferromagnetic layer. The barrier layer resides between the pinned and free layers. The first ferromagnetic layer resides between the barrier layer and the intermediate layer and is ferromagnetically coupled with the second ferromagnetic layer. The intermediate layer is configured such that the first ferromagnetic layer has the first crystalline orientation and the second ferromagnetic layer has a second crystalline orientation different from the first ferromagnetic layer. The magnetic element is configured to allow the free layer to be switched utilizing spin transfer when a write current is passed through the magnetic element.