Multi Level Magnetic Element for MRAM
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Solution Overview
Problem
Current magnetic random access memory (MRAM) cells with magnetic tunnel junctions are limited in writing multiple state levels and require complex configurations, such as multiple current lines, to achieve multilevel state operations, which increases complexity and power consumption.
Innovation Solution
A magnetic element with a dual magnetic tunnel junction structure, comprising a soft ferromagnetic layer between two tunnel barrier layers and two storage layers with different high temperature thresholds, allowing for writing four distinct state levels using a single current line and reducing heating current requirements, thereby enhancing endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single magnetic tunnel junction structure is used, then device complexity is reduced, but the ability to write multiple state levels is limited
Solution Approach 1:
The magnetic tunnel junction is segmented into two distinct storage layers (first storage layer and second storage layer) with different magnetization switching characteristics. This segmentation allows each layer to contribute to different state levels, enabling multilevel storage (0, 1, 2, 3) without increasing overall device complexity. The soft ferromagnetic layer is also segmented into regions with different magnetization orientations.
Solution Approach 2:
The patent adds a thermal dimension to the magnetic storage system by introducing temperature-dependent magnetization switching. The first storage layer switches at a first critical temperature while the second storage layer switches at a second critical temperature. This thermal dimension enables sequential writing of multiple states by controlling the temperature profile during write operations.
2Productivity
If multiple current lines are used for multilevel state writing, then storage capacity increases, but device complexity and power consumption increase
Solution Approach 1:
A single current line is designed to perform multiple functions: it can write all four state levels (0, 1, 2, 3) by controlling the temperature profile, and it can also perform read operations. The different write states are achieved by applying the current for different durations or with different amplitude profiles, making the single current line universal for both write and read operations.
Solution Approach 2:
The patent changes the temporal and amplitude parameters of the write current rather than adding more current lines. By varying the current pulse width and amplitude, the system can selectively switch the magnetization of the first and second storage layers to achieve different state combinations. This parameter-based control eliminates the need for multiple dedicated current lines.
3Productivity
If higher heating current is applied to achieve multilevel states, then storage capacity increases, but power consumption and endurance decrease
Solution Approach 1:
The heating function is segmented and distributed across two storage layers with different critical temperatures. The first storage layer requires lower heating current to switch at its first critical temperature, while the second storage layer requires higher heating current to switch at its second critical temperature. This segmentation allows progressive heating strategies that reduce peak power requirements compared to switching a single high-threshold layer.
Solution Approach 2:
The patent uses preliminary low-temperature switching of the first storage layer before attempting to switch the second storage layer. By first establishing the magnetization state of the lower-threshold layer at moderate temperatures, the system prepares the magnetic configuration to require less additional energy for subsequent high-threshold layer switching, reducing overall power consumption.
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 dual magnetic tunnel junction configuration enables writing four distinct state levels with reduced heating current and power consumption, increasing storage capacity to 2 bits per cell while maintaining high read margin and endurance.
Implementation Method 1
During a write operation of the MRAM cell, the magnetization direction of the first magnetic layer is switched, for example, by applying an external magnetic field. In a thermally assisted (TA) write operation, switching the magnetization direction of the first magnetic layer is performed when the magnetic tunnel junction has been heated to or above a critical temperature.
Implementation Method 2
The magnetic tunnel junction is then cooled down below the critical temperature where the first magnetic layer magnetization is 'frozen' in the written direction.
Implementation Method 3
A low measured junction resistance (or level state '0') corresponds to the magnetization direction of the second ferromagnetic layer being oriented parallel to the magnetization direction of the first ferromagnetic layer. A high measured junction resistance (or level state' 1 ') corresponds to the magnetization direction of the second ferromagnetic layer being oriented antiparallel to the magnetization direction of the first ferromagnetic layer.
Data Source
Figure 1
Figure 2(a)~2(d)
Figure 3
AI summary
The present disclosure concerns a multilevel magnetic element (2) comprising a first tunnel barrier layer (22) between a soft ferromagnetic layer (23) having a magnetization that can be freely aligned and a first hard ferromagnetic layer (21) having a magnetization that is fixed at a first high temperature threshold (Tw1) and freely alignable at a first low temperature threshold (Tw3). The magnetic element (2) further comprises a second tunnel barrier layer (24) and a second hard ferromagnetic layer (25) having a magnetization that is fixed at a second high temperature threshold (Tw2) and freely alignable at a first low temperature threshold (Tw3); the soft ferromagnetic layer (23) being comprised between the first and second tunnel barrier layers (22, 24). The magnetic element disclosed herein allows for writing four distinct levels using only a single current line.