MRAM Initialization Process for Magnetic Domain Alignment
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Solution Overview
Problem
Perpendicularly magnetized magnetic tunnel junctions (p-MTJs) in MRAM and STT-MRAM devices often suffer from multiple domains in the pinned layer, leading to weak spin current during write processes, resulting in high switching error rates and power consumption, which hinders their competitiveness with other memory technologies.
Innovation Solution
A single initialization step involving the application of a magnetic field in either an in-plane or perpendicular-to-plane direction to align the magnetic domains of the pinned layers, inducing interfacial perpendicular magnetic anisotropy and antiferromagnetic coupling, thereby establishing a single domain in each layer, reducing switching current and error rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple domains are present in the pinned layer, then the device structure is formed as per standard fabrication process, but the spin current becomes weak and insufficient to switch the free layer magnetization
Solution Approach 1:
An initialization process is performed before the write operation to establish a single domain state in the pinned layer. This preliminary action eliminates multiple domains that would otherwise be present after standard fabrication, ensuring the pinned layer is in the desired single domain state before attempting to switch the free layer magnetization.
2Manufacturing precision
If multiple domains exist in the pinned layer, then the fabrication process is simpler, but the switching error rate increases and power consumption increases
Solution Approach 1:
The initialization process is integrated into the fabrication sequence as a preliminary step that establishes single domain pinned layers across all devices. This approach achieves high manufacturing precision for domain formation without requiring fundamental changes to the fabrication process, as the initialization can be performed using standard magnetic field application techniques.
3Reliability
If multiple domains are present in the pinned layer, then the device can be fabricated using standard processes, but the write performance is insufficient and error rate is high
Solution Approach 1:
The initialization process is performed as a preliminary step before write operations to ensure the pinned layer is in the correct single domain state. This preliminary action eliminates multiple domains that would cause weak spin current and high switching error rates, thereby improving write performance and reducing information loss.
4Power
If multiple domains are present in the pinned layer, then the standard fabrication process is used, but the spin current is insufficient for magnetization switching
Solution Approach 1:
The initialization process is performed beforehand to eliminate multiple domains in the pinned layer, establishing a single domain state that enables strong spin current generation. This preliminary action ensures that when write current is applied, the pinned layer can generate sufficient spin current to effectively switch the free layer magnetization.
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 significantly reduces the switching error rate to less than 10 ppm, enhances write performance, and lowers power consumption, making p-MTJs more competitive with other memory technologies while maintaining critical device properties like magnetoresistive ratio.
Implementation Method 1
an initialization step comprising the application of a magnetic field to temporarily set all magnetic domains in the free layer (FL), AP1 pinned layer, and AP2 pinned layer in a first direction
Implementation Method 2
After the applied field is removed, the tunnel barrier/AP1 interface induces interfacial perpendicular magnetic anisotropy (PMA) such that all AP1 domains have a magnetization in a vertical direction
Implementation Method 3
Because of AF coupling, all domains in the AP2 layer are aligned antiparallel to the AP1 domains
Data Source
AI summary
An initialization process is disclosed for a perpendicular magnetic tunnel junction (p-MTJ) wherein the switching error rate is reduced from a typical range of 30-100 ppm to less than 10 ppm. In one embodiment, an in-plane magnetic field is applied after a final anneal step is performed during memory device fabrication such that all magnetizations in the free layer, and AP1 and AP2 pinned layers are temporarily aligned “in-plane”. After the applied field is removed, interfacial perpendicular magnetic anisotropy (PMA) at a tunnel barrier/AP1 interface induces a single AP1 magnetic domain with a magnetization in a first vertical direction. Interfacial PMA at a FL/tunnel barrier interface affords a single FL domain with magnetization in the first direction or opposite thereto. AP2 magnetization is opposite to the first direction as a result of antiferromagnetic coupling with the AP1 layer. Alternatively, a perpendicular-to-plane magnetic field may be applied for initialization.