Self-Referenced MRAM Cell Writing Reliability and Power
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Solution Overview
Problem
Self-referenced MRAM cells face reduced reproducibility in writing operations due to storage magnetization not fully aligning with the easy axis of the storage layer after cooling, leading to magnetically frustrated configurations and reduced reliability.
Innovation Solution
A method involving a write magnetic field to switch the sense magnetization and a subsequent heating current pulse to induce a local sense stray field that switches the storage magnetization, with the heating current applied after turning off the write magnetic field, allowing the storage magnetization to relax into a stable configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a write magnetic field is applied to switch the sense magnetization and heating is performed simultaneously, then the storage magnetization can be switched during the write operation, but the storage magnetization may not be fully recovered after cooling, leading to magnetically frustrated configurations and reduced reliability
Solution Approach 1:
The write magnetic field is applied first to switch the sense magnetization to the desired state before heating the magnetic tunnel junction. This preliminary action ensures that when heating occurs and the storage magnetization becomes switchable, the sense layer is already in the correct configuration to guide the storage magnetization to the proper aligned state, preventing magnetic frustration upon cooling
Solution Approach 2:
The write operation uses a two-stage periodic process: first applying the write magnetic field to configure the sense layer, then applying heating to enable storage layer switching. This sequential periodic action separates the sense layer configuration from the storage layer switching, ensuring proper magnetization recovery and alignment after cooling
2Reliability
If a high magnitude write magnetic field is used to ensure complete storage magnetization switching, then writing reliability improves, but power consumption increases
Solution Approach 1:
The invention changes the operational parameters by using heating to temporarily modify the magnetic properties of the storage layer, reducing its coercivity and making it more susceptible to switching. This parameter change allows the use of a lower magnitude write magnetic field while still achieving reliable storage magnetization switching, thereby reducing power consumption
Solution Approach 2:
Heating acts as an intermediary that facilitates the switching process. By temporarily raising the temperature to above the critical temperature of the antiferromagnetic layer, the storage magnetization becomes more easily switchable, allowing the write magnetic field to achieve complete switching with lower magnitude, thus reducing power consumption while maintaining reliability
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 method enhances the reliability of the writing operation by ensuring the storage magnetization aligns stably and reduces power consumption by minimizing the magnitude of the write magnetic field needed, allowing the same field to be used for both writing and reading.
Implementation Method 1
applying a write magnetic field in order to switch the sense magnetization (210) from the first stable direction to said another stable direction
Implementation Method 2
the switched sense magnetization generating a local sense stray field being large enough for switching the storage magnetization
Implementation Method 3
passing a heating current pulse in the magnetic tunnel junction (2) for heating the magnetic tunnel junction at the writing temperature
Implementation Method 4
heating the magnetic tunnel junction (2) at a writing temperature which is at or above the critical temperature of an antiferromagnetic layer
Implementation Method 5
an antiferromagnetic layer exchange-coupling the storage layer such that the storage magnetization can be pinned when the antiferromagnetic layer is below a critical temperature
Implementation Method 6
the storage magnetization can be pinned when the antiferromagnetic layer is below a critical temperature
Implementation Method 7
The magnetic tunnel junction is then cooled below the critical temperature such as to pin the storage magnetization in its written state
Implementation Method 8
once the magnetic tunnel junction has been cooled below the critical temperature
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
MRAM cell (1) comprising a magnetic tunnel junction (2) including a sense layer (21), a storage layer (23, 231), a tunnel barrier layer (22) and an antiferromagnetic layer (24) exchange- coupling the storage layer (23, 231) such that the storage magnetization (234) can be pinned when the antiferromagnetic layer (24) is below a critical temperature and freely varied when the antiferromagnetic layer (24) is heated at or above the critical temperature; said sense layer (21) being arranged such that the sense magnetization (210) can be switched from a first stable direction to another stable direction opposed to the first direction; the switched sense magnetization (210) generating generating a sense stray field (60) being large enough for switching the storage magnetization (234) according to 15 the switched sense magnetization (210), when the magnetic tunnel junction (2) is heated at the writing temperature. The disclosure also relates to a method for writing to the MRAM cell with increased reliability and reduced power consumption.