Magnetoresistance Element Thermal Stability via Junction Thickness Ratio
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Solution Overview
Problem
Current magnetic memory technologies face challenges in achieving high thermal stability with finer junction sizes, which is essential for increasing integration density and retaining bit information over time, as the thermal stability factor of existing perpendicular magnetic anisotropy magnetoresistance effect elements does not exceed 70 with finer junction sizes.
Innovation Solution
The solution involves optimizing the junction size and layer thickness relationship in the magnetoresistance effect element, where the junction size is set to be less than 0.9 times the layer thickness plus 13, to enhance thermal stability, allowing for a thermal stability factor of 70 or more, even with smaller junction sizes, without relying on materials with high magnetic anisotropy energy density or high magnetic damping constants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the junction size of the ferromagnetic layer is reduced to increase integration density, then the integration density is improved, but the thermal stability factor decreases below 70
Solution Approach 1:
The patent changes the geometric parameters of the ferromagnetic layer, specifically setting the thickness t to be greater than the junction size D (t > D), which is opposite to conventional designs where D > t. This parameter inversion modifies the magnetic anisotropy energy density Keff through the relationship Keff = Kb + Ki/t + (1/2)μ0Ms²(D/t - 1), enabling thermal stability factor E/kBT of 70 or more even with fine junction sizes of 30 nm or less.
Solution Approach 2:
The patent inverts the conventional design relationship between junction size and layer thickness. Instead of making the junction size larger than the thickness (D > t) as in existing perpendicular magnetic anisotropy magnetoresistance effect elements, the patent makes the thickness greater than the junction size (t > D). This inversion fundamentally changes the magnetic shape anisotropy contribution, allowing perpendicular magnetization to become the easy axis while achieving high thermal stability with fine junction sizes.
2Reliability
If materials with high magnetic anisotropy energy density or high magnetic damping constants are used to enhance thermal stability, then the thermal stability factor is improved, but the writing current increases
Solution Approach 1:
The patent changes the thickness parameter t of the ferromagnetic layer to be greater than the junction size D, which modifies the magnetic anisotropy energy density Keff through the term Ki/t. This parameter change enhances thermal stability without requiring materials with high magnetic damping constants, thereby avoiding the increase in writing current that would otherwise be necessary.
Solution Approach 2:
The patent utilizes the interface between the ferromagnetic layer and adjacent layers to generate interface magnetic anisotropy energy density Ki. This interface effect, analogous to utilizing surface properties, provides enhanced magnetic anisotropy without requiring bulk material changes, thus avoiding the need for high-damping materials that would increase writing current.
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 enables the achievement of thermal stability factors of 70 or more with reduced junction sizes, minimizing writing current and maintaining high thermal stability, thereby supporting the development of high-capacity magnetic memory with improved integration density.
Implementation Method 1
a magnetoresistance effect element which includes a first magnetic layer of a fixed magnetization direction that is either an upward direction or a downward direction in a thickness direction, a second magnetic layer of a variable magnetization direction that can be varied upwardly or downwardly in a thickness direction
Implementation Method 2
The resistance value of the magnetoresistance effect element 110 is reduced if the respective magnetizations of the first and second ferromagnetic layers 111 and 112 are parallel and is increased if these magnetizations are antiparallel
Implementation Method 3
it has become increasingly important to make the junction size D of a ferromagnetic layer smaller than its layer thickness t in order to make magnetization point in a perpendicular direction by means of magnetic shape anisotropy
Data Source
AI summary
A magnetoresistance effect element and a magnetic memory having thermal stability expressed by a thermal stability factor of 70 or more even with a fine junction size. The magnetoresistance effect element includes a first magnetic layer of an invariable magnetization direction forming a reference layer, a second magnetic layer of a variable magnetization direction forming a recording layer, and a first non-magnetic layer disposed between the first and second magnetic layers in a thickness direction of the first and second magnetic layers. At least one of the first and second magnetic layers has the following relationship between D (nm) and t (nm): D<0.9t+13, where D is a junction size corresponding to the length of a longest straight line on an end surface perpendicular to the thickness direction, and t is a layer thickness. The junction size is 30 nm or less.