Multilayer MTJ Stack for Thermal Stability at Smaller MRAM Nodes
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Solution Overview
Problem
As magnetic memory devices, such as MRAM, advance towards smaller process nodes to increase density, the energy barrier of MTJ bits decreases, compromising data retention and thermal stability, and high critical currents lead to periodic damage during write and reset operations, while maintaining magnetic stability of fixed and free regions is crucial.
Innovation Solution
The use of multilayer synthetic antiferromagnetic structures with increased height and alternating ferromagnetic and coupling regions within the SAF region to enhance stability and anisotropy without increasing individual layer thickness, thereby maintaining magnetic stability and reducing critical currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of MTJ bits is reduced to increase density, then device density increases, but the energy barrier decreases compromising data retention and thermal stability
Solution Approach 1:
The patent transitions from lateral scaling to vertical scaling by increasing the height of the SAF fixed region. Instead of making MTJ bits smaller laterally, the invention grows the structure in the vertical dimension (height >= width), thereby maintaining lateral density while achieving the required magnetic stability through increased volume and energy barrier in the vertical direction.
Solution Approach 2:
The patent employs multilayer composite structures within the SAF fixed region, alternating between ferromagnetic layers and coupling regions. This composite architecture enables the structure to achieve both magnetic stability and high anisotropy through the combined properties of different materials, without requiring increased thickness of individual layers.
2Stability of the object's composition
If the perpendicular anisotropy or magnetic moment of the free region is increased to correct the decrease in energy barrier, then the energy barrier increases, but the critical current increases causing greater periodic damage
Solution Approach 1:
The patent segments the magnetic moment enhancement function across multiple components: the multilayer SAF fixed region provides stable reference magnetization, while the SyF free region provides controllable switching. This segmentation allows the system to achieve high energy barrier without concentrating all magnetic moment requirements in the free region, thereby reducing critical current and periodic damage.
Solution Approach 2:
The patent introduces a SyF (synthetic ferromagnetic) structure as an intermediary between the SAF fixed region and the traditional free region. This SyF structure acts as a mediator that provides the necessary magnetic moment and anisotropy while having lower critical current than directly enhancing the free region, thus reducing periodic damage during write operations.
3Stability of the object's composition
If the thickness of individual layers is increased to maintain magnetic stability, then magnetic stability is maintained, but the device complexity and fabrication difficulty increase
Solution Approach 1:
The patent resolves the thickness control issue by shifting from lateral expansion to vertical growth. Instead of increasing the lateral dimensions or thickness of individual layers, the invention achieves magnetic stability through increased height of the overall SAF fixed region, which can be controlled through the number of repeated bilayers rather than individual layer thickness.
Solution Approach 2:
The patent segments the total height requirement into multiple repeated bilayer units (ferromagnetic layer + coupling region). This segmentation allows precise control of the overall height through the number of repetitions, while each individual bilayer can be fabricated with standard thickness tolerances, thereby maintaining magnetic stability without excessive fabrication complexity.
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 maintains magnetic stability and thermal stability of MTJ bits at smaller sizes by increasing the energy barrier and reducing critical currents, ensuring reliable data retention and operation.
Implementation Method 1
The direction of the magnetization vectors of the free region may be switched and/or programmed (for example, through spin transfer torque (STT), spin-orbit-torque (SOT), etc.) by application of a write signal to the magnetoresistive memory stack
Implementation Method 2
The direction of the magnetization vectors of the free region may be switched and/or programmed (for example, through spin transfer torque (STT), spin-orbit-torque (SOT), etc.) by application of a write signal to the magnetoresistive memory stack
Implementation Method 3
magnetoresistive stack (for example, part of a magnetoresistive memory device, magnetoresistive sensor/transducer device, etc.)
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Aspects of the present disclosure are directed to magnetoresistive stacks including regions having increased height-to-diameter ratios. Exemplary magnetoresistive stacks - for example, used in a magnetic tunnel junction (MTJ) magnetoresistive device - of the present disclosure include one or more multilayer synthetic antiferromagnetic structures - SAFs - or synthetic ferromagnetic structures - SyFs - (A) in order to promote stability of the SAF or SyF, e.g., for smaller-sized MTJs (200).