ST-MRAM Storage Element Laminate Structure for Thermal Stability
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Solution Overview
Problem
Spin torque magnetic random access memory (ST-MRAM) faces challenges in reducing the reverse current for magnetization reversal while ensuring thermal stability and maintaining a high rate of change in magnetoresistance, which is crucial for reliable and efficient data storage as the device miniaturizes.
Innovation Solution
The storage element incorporates a laminate structure with magnetic layers and conductive oxide layers, featuring a perpendicular magnetic anisotropy film, where the storage layer is formed by alternately laminating magnetic layers containing Co and Fe with oxide layers, and an insulating layer is used between the storage and magnetization fixed layers to reduce the writing current and enhance thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the device is miniaturized to increase integration density, then the degree of integration is improved, but the reverse current for magnetization reversal increases and thermal stability deteriorates
Solution Approach 1:
The storage layer is constructed as a composite laminate structure alternating magnetic layers (containing Co and Fe) and oxide layers. This composite structure provides perpendicular magnetic anisotropy that enhances thermal stability while maintaining miniaturization. The interface between magnetic and oxide layers generates the necessary magnetic anisotropy energy to prevent superparamagnetic effects in small-scale devices.
Solution Approach 2:
The invention transitions from in-plane magnetization to perpendicular magnetization by changing the orientation of magnetic anisotropy to the vertical dimension. This perpendicular magnetic anisotropy, achieved through the laminate structure, provides stronger thermal stability for miniaturized devices by increasing the energy barrier for magnetization reversal, thus preventing data loss due to thermal fluctuations.
2Area of moving object
If the device is miniaturized, then the degree of integration is improved, but the reading signal intensity decreases due to increased series resistance
Solution Approach 1:
The invention changes the electrical parameter of the storage layer by using conductive oxide layers in the laminate structure. This reduces the series resistance of the storage layer, maintaining high reading signal intensity even in miniaturized devices. The conductive oxide layers provide low-resistance pathways that compensate for the increased resistance effects caused by device scaling.
3Ease of manufacture
If a conventional magnetic layer structure is used, then the manufacturing process is simple, but the writing current is high and power consumption is high
Solution Approach 1:
The invention changes the magnetic parameter of the storage layer by introducing perpendicular magnetic anisotropy through the laminate structure. This parameter change enables spin torque magnetization reversal to occur at lower current densities, reducing writing current and power consumption. The perpendicular anisotropy allows for more efficient spin transfer torque effects compared to conventional in-plane magnetization structures.
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 allows for stable data retention with reduced power consumption, improved reliability, and minimized series resistance, preventing a decrease in the reading signal intensity and maintaining high thermal stability even as the device is miniaturized.
Implementation Method 1
a phenomenon is used in which when a spin-polarized electron passing through a magnetic layer in which the magnetization is fixed in a certain direction enters another free magnetic layer (the direction of the magnetization is not fixed), a torque (this is referred to as 'spin transfer torque') is imparted to the free magnetic layer, and when a current equivalent to or more than a certain threshold value is supplied, the magnetization of the free magnetic layer is reversed
Implementation Method 2
the storage element has a magnetization fixed layer having magnetization perpendicular to a film surface and an insulating layer of a nonmagnetic substance between the storage layer and the magnetization fixed layer
Data Source
AI summary
A storage element includes: a storage layer which has magnetization perpendicular to a film surface, the direction of the magnetization being changed in accordance with information; a magnetization fixed layer which has magnetization perpendicular to a film surface used as a base of information stored in the storage layer; and an insulating layer of a nonmagnetic substance provided between the storage layer and the magnetization fixed layer. In the storage element described above, the magnetization of the storage layer is reversed using a spin torque magnetization reversal generated by a current flowing in a lamination direction of a layer structure including the storage layer, the insulating layer, and the magnetization fixed layer to store information, and the storage layer has a laminate structure including a magnetic layer and a conductive oxide.