CoFeB Storage Layer Composite for STT-MRAM Scalability
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Solution Overview
Problem
Conventional magnetic memory technologies, such as MRAM and STT-MRAM, face scalability issues due to the increasing magnetic fields required for switching smaller bit cells, leading to higher current density and power consumption, and the use of Cobalt-Iron-Boron (CoFeB) as a storage layer material introduces uncontrollable switching fields and currents due to its large magnetostriction property.
Innovation Solution
A novel magnetic tunnel junction (MTJ) element design incorporating a storage ferromagnetic layer with a CoFeB sub-layer coupled to a CoFe or NiFe sub-layer through a non-magnetic sub-layer, such as Ruthenium, to reduce magnetostriction and critical switching current, thereby improving scalability and stability of STT-MRAM cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the bit cell size is reduced to increase storage density, then the storage density is improved, but the magnetic field required for switching increases leading to higher current density and power consumption
Solution Approach 1:
The patent changes the material composition parameters of the storage layer from conventional CoFeB to a CoFeB/CoFe or CoFeB/NiFe composite structure. This material parameter change reduces the magnetostriction coefficient and allows switching at lower magnetic fields, thereby reducing the current density and power consumption required for switching even in scaled-down bit cells.
Solution Approach 2:
The patent employs a composite ferromagnetic layer structure combining CoFeB with CoFe or NiFe sub-layers. This composite material approach leverages the advantageous properties of each material: CoFeB provides high spin polarization while the CoFe or NiFe sub-layers contribute to reduced magnetostriction and lower switching fields, enabling energy-efficient switching in high-density configurations.
2Reliability
If CoFeB is used as the storage layer material to achieve high spin polarization, then the magnetoresistive effect is improved, but the large magnetostriction property causes uncontrollable switching fields and currents
Solution Approach 1:
The patent modifies the material composition parameters by introducing CoFe or NiFe sub-layers alongside CoFeB. This changes the overall magnetostriction coefficient of the storage layer from large (in pure CoFeB) to controlled and reduced, enabling precise control over switching fields and currents while preserving the high spin polarization necessary for strong magnetoresistive effects.
Solution Approach 2:
The patent creates a composite ferromagnetic layer where CoFeB is combined with CoFe or NiFe materials. This composite structure maintains the high spin polarization of CoFeB for strong magnetoresistive effects while the CoFe or NiFe components provide controlled magnetocrystalline anisotropy and reduced magnetostriction, achieving both high reliability and ease of operation.
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 proposed design decreases the critical switching current and mitigates magnetostriction-induced switching field variations, enhancing the scalability and stability of STT-MRAM cells while maintaining reliable data storage and retrieval capabilities.
Implementation Method 1
During the write operation, the spin-polarized electrons exert a torque on the free layer, which can switch the polarity of the free layer
Implementation Method 2
a magnetic tunnel junction (MTJ) element 100 can be formed from two magnetic layers 110 and 130, each of which can hold a magnetic field, separated by an insulating (tunnel barrier) layer 120
Implementation Method 3
the use of Cobalt-Iron-Boron (CoFeB) as a storage layer material introduces uncontrollable switching fields and currents due to its large magnetostriction property
Data Source
AI summary
According to an embodiment of the invention, a magnetic tunnel junction (MTJ) element includes a reference ferromagnetic layer, a storage ferromagnetic layer, and an insulating layer. The storage ferromagnetic layer includes a CoFeB sub-layer coupled to a CoFe sub-layer and/or a NiFe sub-layer through a non-magnetic sub-layer. The insulating layer is disposed between the reference and storage ferromagnetic layers.