Self-Referenced MRAM Cell Using Thermal-Assisted Write
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Solution Overview
Problem
Conventional magnetic random access memory (MRAM) cells face challenges with high power consumption and limited writing speed due to large magnetic field requirements and small operating temperature windows, especially in varying environmental conditions, which restrict their application in extreme environments.
Innovation Solution
The MRAM cell design includes a magnetic tunnel junction with a sense layer and a storage layer, where a selection transistor heats the junction to a high temperature for writing, allowing a small read field current to align the sense layer's magnetization, enabling low power consumption and faster operations, and uses a spin transfer torque effect for magnetization switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large magnetic field is applied to switch the storage layer magnetization, then the writing speed is improved, but the power consumption increases due to high heating current requirements
Solution Approach 1:
The patent applies preliminary thermal heating to the magnetic tunnel junction before applying the write current. By pre-heating the junction to a temperature above the blocking temperature of the antiferromagnetic layer, the storage layer magnetization becomes free and can be switched more easily. This preliminary thermal action reduces the magnitude of the subsequent write current needed, thereby reducing power consumption while maintaining writing speed.
Solution Approach 2:
The patent changes the temperature parameter of the magnetic tunnel junction during the write operation. By dynamically adjusting the temperature above the blocking temperature threshold, the magnetic properties of the storage layer are modified to enable easier magnetization switching. This parameter change allows for lower write currents and reduced power consumption while achieving the desired writing speed.
2Adaptability or versatility
If the operating temperature window is made larger to accommodate environmental variations, then the adaptability is improved, but the blocking temperature difference between reference and storage layers must be increased
Solution Approach 1:
The patent employs dynamic temperature control during write operations, heating the magnetic tunnel junction to a temperature above the blocking temperature of the antiferromagnetic storage layer. This dynamic adjustment allows the system to adapt to different environmental conditions by temporarily modifying the operating temperature during writing, while maintaining a smaller permanent temperature window between reference and storage layers.
Solution Approach 2:
The patent changes the operating temperature parameter dynamically during write operations to achieve adaptability. By temporarily raising the junction temperature above the blocking temperature threshold during writing and then cooling it down for reading, the system can accommodate environmental variations without requiring a permanently large temperature window between reference and storage layers.
3Manufacturing precision
If tight process control is implemented to maintain high performance, then the manufacturing precision is improved, but the production cost increases
Solution Approach 1:
The patent employs a self-referenced read operation where the sense layer magnetization is aligned by a read field current and then compared with the storage layer magnetization. This self-comparison mechanism inherently compensates for variations in magnetic tunnel junction resistance caused by fabrication process fluctuations, eliminating the need for tight process control and external reference cells, thereby reducing production costs.
Solution Approach 2:
The self-referenced read operation provides inherent feedback compensation for process variations. By comparing the sense layer magnetization (aligned by read field) with the storage layer magnetization, the system automatically compensates for resistance variations due to fabrication fluctuations, reducing the need for tight process control and associated costs.
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 reduces power consumption and increases writing speed, enabling MRAM cells to function effectively in high-temperature environments, such as automotive and military applications, with improved process control and reduced production costs.
Implementation Method 1
heating the magnetic tunnel junction above TBS but below TBR, preferably but not limited to by sending a heating current through the magnetic tunnel junction
Implementation Method 2
or by the so-called spin transfer torque (STT) effect, where a spin transfer torque current, in which the spin is polarized, is passed through the magnetic tunnel junction
Implementation Method 3
a first read field current having a first polarity is passed in said field line to align the magnetization of the sense layer in a first aligned magnetization direction according to said first polarity
Implementation Method 4
When the respective magnetizations of the reference layers and the storage layer are antiparallel, the resistance of the magnetic tunnel junction is high (Rmax)... when the respective magnetizations are parallel, the resistance of the magnetic tunnel junction becomes low (Rmin)
Implementation Method 5
the reference layer is 'exchange biased' to an adjacent antiferromagnetic reference layer characterized by a critical temperature (above which the exchange bias vanishes) known as the blocking temperature TBR
Data Source
AI summary
The present disclosure concerns a magnetic random access memory cell containing a magnetic tunnel junction formed from an insulating layer comprised between a sense layer and a storage layer. The present disclosure also concerns a method for writing and reading the memory cell comprising, during a write operation, switching a magnetization direction of said storage layer to write data to said storage layer and, during a read operation, aligning magnetization direction of said sense layer in a first aligned direction and comparing said write data with said first aligned direction by measuring a first resistance value of said magnetic tunnel junction. The disclosed memory cell and method allow for performing the write and read operations with low power consumption and an increased speed.