Coupled MTJ Free Layer Structure for Low-Write-Energy MRAM
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Solution Overview
Problem
Magnetic random access memories (MRAMs) face a contradiction between low information writing energy consumption and high thermal stability, limiting their large-scale application due to the use of spin transfer torque (STT) in the free layer of magnetic tunnel junctions (MTJs).
Innovation Solution
The free layer of the MTJ is designed with a plurality of coupled ferromagnetic film layers, each separated by a coupling superposition layer, comprising oxide coupling layers and a magnetic insertion layer, to reduce information writing energy while maintaining thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a single ferromagnetic film layer is used in the free layer of MTJ with STT writing mode, then the structure is simple, but the information writing energy consumption is high and thermal stability is insufficient
Solution Approach 1:
The free layer is divided into multiple ferromagnetic film layers (first ferromagnetic film layer and second ferromagnetic film layer) separated by a coupling superposition layer. This segmentation allows each layer to be reversed independently during writing operations, reducing the energy required for magnetization reversal while maintaining thermal stability through the coupled structure.
2Use of energy by moving object
If multiple ferromagnetic film layers are used in the free layer to reduce writing energy, then information writing energy consumption decreases, but the device structure becomes more complex
Solution Approach 1:
A coupling superposition layer consisting of two oxide coupling layers and a magnetic insertion layer is introduced between the ferromagnetic film layers. This intermediary structure enables controlled magnetic coupling that facilitates independent reversal of each ferromagnetic layer during writing, thereby reducing energy consumption while maintaining a manageable device architecture through the mediating coupling mechanism.
3Reliability
If a coupling superposition layer with magnetic insertion layer is introduced between ferromagnetic film layers, then thermal stability and writing energy are improved, but the manufacturing process becomes more complex
Solution Approach 1:
The magnetic insertion layer uses specific materials (CoFeB, CoFe, or Co) with controlled thickness (0.3-1.0 nm) to achieve optimal magnetic coupling parameters. By precisely controlling the thickness and material composition of the insertion layer, the patent optimizes the coupling strength between ferromagnetic layers to maintain thermal stability while enabling energy-efficient writing operations.
4Force
If the magnetic insertion layer thickness is increased to strengthen coupling between ferromagnetic layers, then the coupling strength increases, but the separate reversal capability during writing is reduced
Solution Approach 1:
The patent precisely controls the thickness of the magnetic insertion layer within 0.3-1.0 nm to achieve optimal coupling strength. This parameter optimization ensures that the ferromagnetic layers are coupled sufficiently to maintain thermal stability while remaining weakly coupled enough to allow independent reversal during writing operations, thereby reducing energy 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
This design significantly reduces information writing energy and improves the endurance of the MTJ by ensuring separate magnetic reversals of the ferromagnetic film layers, enhancing thermal stability and insulating tunneling layer endurance.
Implementation Method 1
a coupling superposition layer sandwiched between all adjacent ferromagnetic film layers to couple the adjacent ferromagnetic film layers
Implementation Method 2
The principle thereof is that spin electrons, as they are transferred from the fixed layer, pass through the insulating tunneling layer and enter the free layer or transferred from the free layer, pass through the insulating tunneling layer and enter the fixed layer, may generate a spin transfer torque that changes the spin direction of the free layer
Implementation Method 3
an insulating tunneling layer (usually MgO)
Data Source
AI summary
The present disclosure provides a structure of a free layer of a magnetic tunnel junction (MTJ), the core device of a magnetic random access memory (MRAM) chip, and a method for manufacturing the same. The free layer provided by the present disclosure includes one or more ferromagnetic film layers and a coupling superposition layer sandwiched between all the adjacent ferromagnetic film layers. During information writing, the ferromagnetic films can carry out spin reversal separately to reduce information writing energy; at the same time, because of a coupling effect of the ferromagnetic film layers, the free layer can maintain high thermal stability. Therefore, the contradiction between low information writing energy and high thermal stability, which is the current main contradiction in the large-scale application of MTJ-based MRAMs is overcome.