Double-Fixed-Layer MTJ Structure for Lower Write Current
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Solution Overview
Problem
The challenge in existing magnetic tunnel junctions (MTJs) is the high information writing current required for changing the state from parallel (P) to antiparallel (AP) and vice versa, which can damage the tunneling layer, and there is an imbalance in the spin polarization rates leading to increased durability issues.
Innovation Solution
A double-fixed-layer structure is introduced, with ferromagnetic materials having high spin polarization rates and different coercivity strengths, where the spin directions of the fixed layers are opposite, and a specific magnetization process is applied to reduce the information writing current and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the spin polarization rate of the ferromagnetic material for the fixed layer is increased to reduce information writing current from AP to P state, then the information writing current for AP to P transition decreases, but the information writing current for P to AP transition increases, causing tunneling layer damage
Solution Approach 1:
The patent divides the single fixed layer into two separate fixed layers with different spin polarization rates. The first fixed layer has higher spin polarization rate (η1 > 0.4) for reducing AP to P transition current, while the second fixed layer has lower spin polarization rate (η2 < 0.4) for reducing P to AP transition current. This segmentation allows each layer to optimize for its specific transition direction, resolving the contradiction between lowering writing current and maintaining tunneling layer durability.
Solution Approach 2:
The patent applies different spin polarization rates to different fixed layers based on their specific functions. The first fixed layer is optimized with high spin polarization for one transition direction, while the second fixed layer is optimized with low spin polarization for the opposite transition direction. This local optimization of material properties allows the system to achieve low current requirements for both transition types without compromising tunneling layer integrity.
2Productivity
If a single fixed layer with high spin polarization rate is used, then information writing current for one state transition decreases, but the imbalance in spin polarization rates leads to increased durability issues
Solution Approach 1:
The patent segments the fixed layer function into two distinct layers with different spin polarization characteristics. This segmentation eliminates the imbalance problem by ensuring that each transition direction has access to a fixed layer optimized for that direction, thereby maintaining both high writing efficiency and durability.
Solution Approach 2:
The patent changes the spin polarization rate parameter between the two fixed layers. By setting the first fixed layer with η1 > 0.4 and the second fixed layer with η2 < 0.4, the system optimizes current requirements for different transition directions while maintaining balanced durability characteristics across both transitions.
3Ease of operation
If the information writing current is increased to change spin state, then the spin direction of the free layer can be reversed, but the tunneling layer may be damaged by the voltage
Solution Approach 1:
The patent segments the current path by introducing two fixed layers that provide alternative current routes for different spin transition directions. This allows the system to achieve spin state switching with lower current requirements in each direction, thereby reducing the harmful voltage stress on the tunneling layer while maintaining ease of operation.
Solution Approach 2:
The patent changes the magnetic resistance parameters by using fixed layers with different spin polarization rates. This parameter optimization allows spin state switching to be achieved at lower current levels, reducing the voltage stress that would otherwise damage the tunneling layer while preserving the ability to reliably switch spin states.
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 double-fixed-layer structure reduces the information writing current and enhances the durability of the insulating tunneling layer, ensuring stable operation and improved resistance signals for data storage.
Implementation Method 1
The principle is that spin electrons, as they travel from the fixed layer, pass through the insulating tunneling layer and enter the free layer or travel from the free layer, pass through the insulating tunneling layer and enter the fixed layer, may generate a magnetic moment that changes the spin direction of the free layer.
Implementation Method 2
The difference between the up and down spins is determined by the electron spin polarization rate η as shown in equation (1) below: where s+ denotes the number of up spins, and s− denotes the number of down spins.
Implementation Method 3
The MTJ forming the MRAM is formed by sandwiching a layer of ferromagnetic film with a fixed spin direction (called a fixed layer or pined layer) and a layer of ferromagnetic film with a spin direction that can be controlled to be flipped (called a free layer or reference layer) with an insulating tunneling layer (usually MgO).
Implementation Method 4
The spin directions of the two layers of magnetic films being antiparallel and parallel will form high and low resistance states through the MTJ for storing numerical information 0 and 1 (or 1 and 0) respectively.
Data Source
AI summary
The present disclosure relates to a fixed layer of a magnetic tunnel junction, a magnetic storage chip, and a method for manufacturing the magnetic tunnel junction, and particularly provides a new MTJ device structure and a method for manufacturing the same. Specifically, fixed layers are prepared on both sides of a free layer of a conventional MTJ, i.e., forming a double-fixed-layer structure. The double-fixed-layer MTJ is made of ferromagnetic materials with high spin polarization rates that are subject to certain magnetization treatment, have a certain difference in coercivity strength and have opposite spin directions. The structure can realize for the first time that information writing energy can be reduced when spins of the fixed layers and the free layer of the MTJ change from parallel state to antiparallel state and from antiparallel state to parallel state.