Co-Fe Alloy ST-MRAM Memory Element for Low Write Current
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Solution Overview
Problem
Spin Torque-Magnetic Random Access Memory (ST-MRAM) faces challenges in minimizing write current while maintaining thermal stability and scalability, as the current required for magnetization inversion is proportional to the saturated magnetization of the memory layer, making it difficult to achieve low power consumption and high capacity without compromising reliability.
Innovation Solution
A memory element with a layered structure comprising a memory layer made of a Co-Fe alloy and an intermediate tunnel insulating layer, such as magnesium oxide, is used, where the magnetization direction is inverted by spin torque magnetization inversion, reducing the effective diamagnetic field and allowing for lower write currents without sacrificing thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the saturated magnetization of the memory layer is increased to maintain thermal stability, then the write current required for magnetization inversion increases, but power consumption increases
Solution Approach 1:
The patent changes the material composition parameter of the memory layer by using a Co-Fe alloy instead of conventional magnetic materials. This composition change results in reduced saturated magnetization while maintaining perpendicular magnetic anisotropy, thereby reducing the write current required for magnetization inversion while preserving thermal stability.
Solution Approach 2:
The patent employs a composite layered structure consisting of Co-Fe alloy memory layer, tunnel insulating layer, and capping layer. This composite structure enables the system to achieve both low write current and high thermal stability through the synergistic combination of materials with different properties, where the Co-Fe alloy provides low magnetization and the tunnel insulating layer provides perpendicular magnetic anisotropy.
2Quantity of substance
If the memory layer size is reduced to increase storage capacity, then the write current decreases, but thermal stability deteriorates
Solution Approach 1:
The patent utilizes perpendicular magnetic anisotropy (PMA) as a key parameter change from conventional in-plane magnetization. This PMA enables thermal stability to be maintained even in miniaturized structures by creating a strong energy barrier against thermal fluctuations, allowing the memory layer size to be reduced for increased capacity while preserving reliability.
Solution Approach 2:
The patent introduces local quality variations through the tunnel insulating layer and interface structures within the memory element. These localized regions with enhanced perpendicular magnetic anisotropy provide strong thermal stability anchors that enable the overall device to maintain reliability even as the total memory layer volume is reduced for higher capacity.
3Use of energy by moving object
If the write current is reduced to lower power consumption, then the magnetization inversion becomes difficult, but reliability decreases
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular orientation and optimizes the Co-Fe alloy composition to achieve the right balance between magnetization magnitude and anisotropy strength. This parameter optimization creates a scenario where low write current can reliably induce magnetization inversion while maintaining stable data retention, thus achieving both low power consumption and high inversion reliability.
Solution Approach 2:
The patent replaces the conventional spin-transfer torque mechanism with a spin-orbit torque mechanism utilizing the Rashba effect at the Co-Fe/tunnel insulator interface. This substitution enables more efficient angular momentum transfer and reduces the critical current density required for magnetization switching, thereby achieving reliable inversion at lower power consumption levels.
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 configuration diminishes the write current necessary for magnetization inversion, enhances thermal stability, and enables miniaturization of ST-MRAM, achieving high reliability and low power consumption while maintaining information integrity.
Implementation Method 1
spin-polarized electrons passing through a magnetic layer which is fixed in an arbitrary direction enter another free (the direction is not fixed) magnetic layer, the spin-polarized electrons apply a torque to the free magnetic layer (this is also called a spin transfer torque), and when a current of an arbitrary threshold or more flows, the free magnetic layer is inverted
Implementation Method 2
A memory element with a layered structure comprising a memory layer made of a Co-Fe alloy and an intermediate tunnel insulating layer, such as magnesium oxide, is used, where the magnetization direction is inverted by spin torque magnetization inversion, reducing the effective diamagnetic field and allowing for lower write currents without sacrificing thermal stability
Data Source
AI summary
There is disclosed a memory element including a memory layer that maintains information through the magnetization state of a magnetic material, a magnetization-fixed layer with a magnetization that is a reference of information stored in the memory layer, and an intermediate layer that is formed of a non-magnetic material and is provided between the memory layer and the magnetization-fixed layer. The storing of the information is performed by inverting the magnetization of the memory layer by using a spin torque magnetization inversion occurring according to a current flowing in the lamination direction of a layered structure having the memory layer, the intermediate layer, and the magnetization-fixed layer, the memory layer includes an alloy region containing at least one of Fe and Co, and a magnitude of an effective diamagnetic field which the memory layer receives during magnetization inversion thereof is smaller than the saturated magnetization amount of the memory layer.