Perpendicular MRAM Permanent Magnet Offset Field
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Solution Overview
Problem
Existing perpendicular magnetic tunnel junction (MTJ) memory elements in STT-MRAM devices face asymmetric switching behavior due to stray magnetic fields, which complicates manufacturing and increases the propensity for electrical shunting during etching processes.
Innovation Solution
Incorporating a sheet of permanent magnet with a fixed magnetization direction perpendicular to the MTJ memory elements to cancel or minimize the stray magnetic field, thereby achieving symmetric switching behavior and simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If perpendicular MTJ memory elements are used in STT-MRAM devices, then non-volatile memory functionality is achieved, but asymmetric switching behavior occurs due to stray magnetic fields
Solution Approach 1:
A sheet of permanent magnet is introduced as an intermediary component between the magnetic reference layer and the magnetic free layer. This permanent magnet generates a compensating magnetic field that counteracts the stray magnetic field from the magnetic reference layer, thereby eliminating the offset field and achieving symmetric switching behavior without modifying the fundamental perpendicular MTJ structure.
2Productivity
If perpendicular MTJ memory elements are used, then high-density storage is achieved, but manufacturing complexity increases due to asymmetric switching requirements
Solution Approach 1:
The permanent magnet sheet serves as a manufacturing-friendly intermediary that provides the necessary magnetic field compensation during the fabrication process. By placing the permanent magnet in close proximity to the MTJ memory elements, the system achieves symmetric switching behavior without requiring complex multi-layer magnetic structures or additional processing steps, thereby maintaining manufacturing simplicity while enabling high-density storage.
3Reliability
If perpendicular MTJ memory elements are used, then non-volatile storage is achieved, but electrical shunting risk increases during etching processes
Solution Approach 1:
The permanent magnet sheet acts as a protective intermediary that eliminates the offset field during the etching process. By compensating for the stray magnetic field, the permanent magnet prevents the asymmetric switching behavior that would otherwise cause electrical shunting between the magnetic reference layer and the magnetic free layer, thereby improving manufacturing precision and reducing defect rates during etching.
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 ensures symmetric switching behavior in STT-MRAM devices, reduces manufacturing complexity, and minimizes the risk of electrical shunting, while allowing for cost-effective and high-yield production.
Implementation Method 1
The sheet of permanent magnet has a fixed or permanent magnetization direction substantially perpendicular to the sheet surface facing the MRAM die and exerts a magnetic field that cancels or counter-balances the stray magnetic field exerted on the magnetic free layer
Implementation Method 2
Each of the plurality of perpendicular MTJ memory elements may comprise a magnetic reference layer having an invariable or fixed magnetization direction substantially perpendicular to a layer plane thereof, a magnetic free layer having a variable magnetization direction substantially perpendicular to the layer plane
Implementation Method 3
As electrons that pass through the magnetic reference layer 84 are being spin-polarized, the spin-polarized electrons exert a spin transfer torque on the magnetic free layer 88. When the spin-polarized current or parallelizing current (ip) 98 exceeds a threshold level, the magnetic free layer 88 switches from the anti-parallel to parallel magnetization direction 90
Implementation Method 4
When the magnetization directions of the magnetic free and reference layers are substantially parallel, electrons polarized by the magnetic reference layer can tunnel through the insulating tunnel junction layer, thereby decreasing the electrical resistance of the MTJ
Data Source
AI summary
The present invention is directed to a magnetic random access memory (MRAM) comprising an MRAM die having a front side that includes therein a plurality of perpendicular magnetic tunnel junction (MTJ) memory elements and a back side; and a sheet of permanent magnet disposed in close proximity to the MRAM die with a sheet surface facing the front side or back side of the MRAM die. The sheet of permanent magnet has a permanent magnetization direction substantially perpendicular to the sheet surface facing the MRAM die and exerts a magnetic field that eliminate or minimize the offset field of the magnetic free layer. The MRAM die and the sheet of permanent magnet may be encapsulated by a package case. The MRAM may further comprise a soft magnetic shield disposed on a side of the MRAM die opposite the sheet of permanent magnet.