Spintronic Free Layer with Oxidation Control and Moment Tuning
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Solution Overview
Problem
Current perpendicular magnetic tunnel junctions (p-MTJs) face challenges in achieving high thermal stability and low switching voltage while maintaining a high magnetoresistive ratio and resistance-area product, especially at reduced free layer thicknesses, which is crucial for spin-transfer torque magnetic random access memory (STT-MRAM) applications.
Innovation Solution
Incorporating an oxidation control layer (OCL) and a magnetic moment tuning layer (MMTL) within the free layer to prevent unwanted oxidation and tune the saturation magnetization, respectively, enabling a free layer thickness ≤10 Angstroms with substantial perpendicular magnetic anisotropy, thereby enhancing thermal stability and reducing switching voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the free layer thickness is reduced to improve switching voltage and write margin, then the switching voltage decreases and write capability improves, but thermal stability deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the free layer by incorporating specific elements (Ta, W, Mo, Nb) that modify the magnetic anisotropy and saturation magnetization. This allows achieving both thin thickness (5-15 Å) for low switching voltage and sufficient thermal stability through compositional optimization rather than relying solely on thickness control
Solution Approach 2:
The patent creates a composite free layer structure combining multiple materials (CoFeB, Ta, W, Mo, Nb, or other magnetic/non-magnetic materials) to achieve properties that cannot be obtained with single materials. The composite structure provides both the thin thickness needed for low switching voltage and the thermal stability required for reliable operation
2Productivity
If the free layer thickness is reduced to improve device scaling and switching performance, then the switching voltage decreases and device density increases, but the magnetoresistive ratio deteriorates
Solution Approach 1:
The patent optimizes compositional parameters within the free layer (adding 1-10% Ta, W, Mo, Nb or other elements) to enhance spin polarization and TMR ratio. This compositional tuning allows maintaining high magnetoresistive ratio even when thickness is reduced for higher device density
Solution Approach 2:
The patent creates local compositional variations within the free layer structure, with different regions having optimized compositions for specific functions. The free layer may have gradient compositions or localized regions with different element concentrations to simultaneously achieve high TMR ratio and low switching voltage in a scaled-down structure
3Speed
If the free layer thickness is reduced to improve switching speed and reduce pulse length, then the switching speed increases and pulse length decreases, but thermal stability deteriorates
Solution Approach 1:
The patent modifies magnetic parameters (saturation magnetization Ms, perpendicular magnetic anisotropy Ku) through compositional changes in the free layer. This enables achieving fast switching speeds (sub-10ns pulse lengths) with thin layers while maintaining adequate thermal stability through optimized material composition rather than thickness alone
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 achieves thermal stability up to 400°C, a switching voltage below 500 mV, and maintains a magnetoresistive ratio of at least 1 and a resistance-area product less than 5 ohm-μm², improving the performance of STT-MRAM devices.
Implementation Method 1
the free layer has an oxidation control layer (OCL) to prevent unwanted oxidation of boron in the free layer
Implementation Method 2
a magnetic moment tuning layer (MMTL) for tuning the saturation magnetization (Ms) value of the free layer thereby enabling a free layer thickness ≤10 Angstroms that provides substantial perpendicular magnetic anisotropy (PMA)
Implementation Method 3
STT-MRAM is based on a p-MTJ element having a tunneling magneto-resistance (TMR) effect and wherein a stack of layers has a configuration in which two ferromagnetic (FM) layers are separated by a thin non-magnetic dielectric layer
Implementation Method 4
When a spin-polarized current traverses a magnetic multilayer in a current perpendicular to plane (CPP) direction, the spin angular moment of electrons incident on a FL interact with the magnetic moment of the FL near the interface between the FL and non-magnetic spacer that is typically a tunnel barrier layer. Through this interaction, the electrons transfer a portion of their angular momentum to the FL. As a result, spin-polarized current can switch the magnetization direction of the FL
Data Source
AI summary
A perpendicular magnetic tunnel junction is disclosed wherein first and second interfaces of a free layer (FL) with a first metal oxide (Hk enhancing layer) and second metal oxide (tunnel barrier), respectively, produce perpendicular magnetic anisotropy (PMA) to provide thermal stability to 400° C. Insertion of an oxidation control layer (OCL) such as Mg and a magnetic moment tuning layer (MMTL) like Mo or W enables FL thickness to be reduced below 10 Angstroms while providing sufficient PMA for a switching voltage substantially less than 500 mV at a 10 ns pulse width and 1 ppm defect rate. Magnetoresistive ratio is ≥1, and resistance×area (RA) product is below 5 ohm-μm2. Embodiments are provided where MMTL and OCL materials interface with each other, or do not contact each other. Each of the MMTL and OCL materials may be deposited separately, or at least one is co-deposited with the FL.