Heating Strap MRAM Reduces Junction Stress
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Solution Overview
Problem
Conventional MRAM devices with thermally assisted switching suffer from stress on insulating layers due to high currents required for writing, leading to reduced operational life, as they need to heat magnetic tunnel junctions above 120°C, which degrades the insulating layer with repeated writing operations.
Innovation Solution
The implementation of heating straps that partially heat the magnetic tunnel junctions during write operations, reducing the magnitude of current passing through the junctions and alleviating stress, while also allowing for efficient magnetic field induction for switching, thereby increasing durability and operational life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a current of sufficient magnitude is passed through the magnetic tunnel junction to heat it above the threshold temperature, then the storage layer can be written, but the insulating layer is stressed and degraded, reducing operational life
Solution Approach 1:
The heating function is segmented from the magnetic tunnel junction itself and assigned to a separate heating strap structure. The strap is positioned adjacent to the magnetic tunnel junction and carries the heating current, while the magnetic tunnel junction only carries the read current. This segmentation allows the heating current to flow through a dedicated path that does not stress the insulating layer of the magnetic tunnel junction, while still achieving the necessary temperature increase for thermal assisted switching.
Solution Approach 2:
The heating strap acts as an intermediary structure that mediates between the current source and the magnetic tunnel junction. Instead of passing high-magnitude current directly through the magnetic tunnel junction, the heating strap serves as an intermediate conductor that generates heat through resistive heating, which then thermally couples to the magnetic tunnel junction. This intermediary approach allows heating without direct high-current stress on the delicate insulating layer.
2Force
If a current is passed through the magnetic tunnel junction to induce a magnetic field for switching, then writing is achieved, but the insulating layer degrades due to repeated high-current operations
Solution Approach 1:
The magnetic field induction function is segmented from the magnetic tunnel junction and assigned to the heating strap. The heating strap is positioned and dimensioned to serve as a write magnet, inducing the necessary magnetic field for switching the storage layer magnetization. This segmentation separates the write function (performed by the strap carrying heating current) from the read function (performed by the magnetic tunnel junction), eliminating the need for high-current operations through the magnetic tunnel junction during writing.
Solution Approach 2:
The heating strap is designed to serve multiple functions: it provides thermal assistance for lowering the switching threshold, it induces the magnetic field for writing through its current flow, and it can be used for both write and read operations. This multi-functionality consolidates what would otherwise require separate structures, with the strap handling both heating and magnetic field induction while the magnetic tunnel junction handles only sensing.
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 the stress on the magnetic tunnel junctions, enhances switching efficiency, and extends the operational life of MRAM devices by allowing lower-intensity magnetic fields and reduced power consumption, while maintaining effective heating to above the threshold temperature.
Implementation Method 1
Writing is carried out by passing a current through the magnetic tunnel junction, thereby heating the magnetic tunnel junction above the threshold temperature
Implementation Method 2
The magnetic tunnel junction is then cooled to below the threshold temperature with a magnetic field applied, such that the magnetization of the storage layer is 'frozen' in the written direction
Implementation Method 3
MRAM devices have become the subject of increasing interest, in view of the discovery of magnetic tunnel junctions having a strong magnetoresistance at ambient temperatures
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A memory device includes at least one magnetic random access memory cell, which includes: (1) a magnetic tunnel junction having a first end and a second end; and (2) a strap electrically coupled to the second end of the magnetic tunnel junction. The memory device also includes a bit line electrically coupled to the first end of the magnetic tunnel junction. During a write operation, the bit line is configured to apply a first heating current through the magnetic tunnel junction, and the strap is configured to apply a second heating current through the strap, such that the magnetic tunnel junction is heated to at least a threshold temperature according to the first heating current and the second heating current.