Heusler MRAM Layer Stack for Lower STT Switching Current
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Solution Overview
Problem
Current magnetic random access memory (MRAM) devices with Heusler storage layers thicker than 20 nm face challenges in being switched by spin transfer torque (STT) due to high coercivity (Hc) and anisotropy field (Hk) values.
Innovation Solution
A multi-layered structure comprising alternating layers of Co and E, where E includes at least one element from Ge, Ga, Sn, or Al, with a composition of Co1−xEx, and a combined layer with an insertion layer of Co, Fe, Mn, or Al in contact with a Heusler compound, is used to lower the Hc and Hk of the Heusler compound, enabling STT switching even in devices with Heusler storage layers thicker than 20 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the Heusler storage layer is increased to enhance memory storage, then the storage capacity is improved, but the coercivity and anisotropy field increase making STT switching difficult
Solution Approach 1:
The patent employs a composite material structure consisting of a Heusler storage layer combined with a multi-layered Co-E alloy structure. This composite approach allows the system to achieve both high storage capacity (through thicker Heusler layers) and low coercivity (through the Co-E alloy's magnetic properties), resolving the contradiction between storage capacity and switching reliability
Solution Approach 2:
The patent utilizes parameter changes by adjusting the composition (Co1−xEx with x from 0.42 to 0.55) and thickness of the Co-E alloy layers to optimize the magnetic properties. By changing the concentration parameter x and layer thickness, the system achieves the desired balance between storage capacity and switching characteristics
2Quantity of substance
If the thickness of the Heusler storage layer is increased beyond 20 nm, then memory storage is enhanced, but the switching current density increases making STT switching inefficient
Solution Approach 1:
The composite structure of Heusler layer + Co-E alloy layers enables the system to maintain low switching current density even with thick storage layers. The Co-E alloy acts as a magnetic moment layer that facilitates efficient spin transfer torque, reducing the energy required for switching while preserving high storage capacity
Solution Approach 2:
The patent applies local quality by creating distinct functional zones: the Heusler layer provides high storage capacity with perpendicular magnetic anisotropy, while the adjacent Co-E alloy layers provide enhanced spin polarization and reduced damping. Each layer has optimized local properties that contribute to overall system performance
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 solution effectively reduces the coercivity and anisotropy field of the Heusler compound, allowing for successful STT switching in MRAM devices with thicker Heusler storage layers, thereby enhancing memory storage and reducing switching current densities.
Implementation Method 1
The magnetization of the so-called storage or memory layer is toggled between being parallel or anti-parallel to the magnetization of the reference magnetic layer. Currently, the change in magnetic state of the MTJ device is achieved via the spin transfer torque (STT) effect by passing an electric current through the device.
Implementation Method 2
Currently, the change in magnetic state of the MTJ device is achieved via the spin transfer torque (STT) effect by passing an electric current through the device.
Implementation Method 3
Some Heusler compounds have a tetragonal structure such that thin films may exhibit perpendicular magnetic anisotropy along their tetragonal axis at room temperature (RT).
Data Source
AI summary
A device is provided. The device includes a multi-layered structure that is non-magnetic at room temperature, the multi-layered structure comprising alternating layers of Co and E, wherein E comprises at least one other element selected from the group consisting of Ge, Ga, Sn and Al, wherein a composition of the multi-layered structure is represented by Co1−xEx, with x being in a range from 0.42 to 0.55. The device also includes a combined layer provided in contact with the multi-layered structure, the combined layer including an insertion layer comprising Co or Fe or Mn or Al in contact with a Heusler compound.