MRAM Free Layer Segmentation for Low Write Current
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Solution Overview
Problem
Current magnetic random access memory (MRAM) technologies face challenges in achieving high-speed operation with low write current while maintaining thermal stability, as the write current is proportional to the anisotropic magnetic field, and reducing this field compromises thermal stability.
Innovation Solution
The magnetic random access memory employs a multilayer structure for the magnetization free layer, comprising a sense layer with small magnetic anisotropy and a storage layer with large magnetic anisotropy, coupled through a bonding layer, allowing for magnetization reversal with a small magnetic field and low write current, while ensuring thermal stability by optimizing the magnetic volume and anisotropic magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the anisotropic magnetic field is reduced to lower write current, then write current decreases, but thermal stability deteriorates
Solution Approach 1:
The magnetization free layer is segmented into two distinct ferromagnetic layers: a sense layer with small magnetic anisotropy and a storage layer with large magnetic anisotropy. This segmentation allows each layer to fulfill different functions - the sense layer responds to small magnetic fields for low-current writing, while the storage layer provides thermal stability through its large anisotropic magnetic field.
Solution Approach 2:
Different regions (layers) of the magnetization free layer are assigned different magnetic properties. The sense layer has small magnetic anisotropy optimized for sensitivity to write fields, while the storage layer has large magnetic anisotropy optimized for thermal stability. This local differentiation resolves the contradiction between low write current and thermal stability.
2Speed
If the magnetic field write method is used to achieve high-speed operation, then operation speed increases, but write current increases
Solution Approach 1:
By segmenting the magnetization free layer into sense and storage layers with different anisotropic magnetic fields, the invention enables magnetic field write method to operate at high speeds while using low current. The sense layer's small anisotropic magnetic field allows efficient magnetic field writing without requiring large currents.
3Use of energy by moving object
If the spin injection write method is used to reduce write current, then write current decreases, but operation speed decreases
Solution Approach 1:
Instead of using spin injection to reverse magnetization (which is slow), the invention uses the sense layer's small anisotropic magnetic field to enable efficient magnetic field writing. This inverts the conventional approach by making the layer with small anisotropy (sense layer) the primary target for magnetic field writing, achieving both low current and high speed.
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 a magnetic random access memory that reduces the write current to 1 mA or less while maintaining sufficient thermal stability, preventing intermediate states and ensuring stable '0' or '1' states, and allows for a larger reading margin due to the use of materials with high polarizability.
Implementation Method 1
To read the information in the magnetic random access memory, a magnetoresistive effect is utilized. That is, the information is read by passing a current passing through the MTJ and detecting a difference between resistance values of MTJ due to a difference between magnetization of the magnetization free layer and magnetization of the magnetization fixed layer in relative angle.
Implementation Method 2
According to the spin injection write method, by changing a direction of the current passing through the MTJ, the magnetization of the magnetization free layer is reversed through spin torque transfer with respect to the magnetization of the magnetization fixed layer.
Implementation Method 3
Generally, according to the magnetic field write method in the magnetic random access memory, a magnetic field induced when a current passes to a write interconnection disposed in a vicinity of the MTJ is utilized.
Data Source
AI summary
A magnetic random access memory has a laminating structure including: a magnetization free layer; an insulating layer; and a magnetization fixed layer. The magnetization free layer includes: a sense layer; a first bonding layer being adjacent to the sense layer; and a storage layer being adjacent to the first bonding layer on an opposite side to the sense layer. At least a part of the sense layer and the storage layer is magnetically coupled to one another through the first bonding layer. A magnetic anisotropy of the storage layer is larger than that of the sense layer. A product of a saturation magnetization and a volume of the sense layer is larger than that of the storage layer. According to such a structure, a magnetic random access memory can be provided in which a current for writing is reduced while enough thermal stability is maintained.