FM/NM/FM Multilayer Memory Using Unidirectional Spin Hall Magnetoresistance
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Solution Overview
Problem
Conventional magnetoresistive memory devices can only distinguish between two resistance states, limiting their ability to store multiple bits of information effectively, as they require a fixed reference layer and struggle with scalable bit densities.
Innovation Solution
The use of a unidirectional spin Hall magnetoresistance (USMR) effect in a FM/NM/FM trilayer structure allows for the detection of multiple magnetic states without an auxiliary magnetic layer, enabling the creation of a multi-bit-per-cell memory device by controlling individual ferromagnetic layers with spin-orbit torques and reading magnetic configurations electrically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional magnetoresistive memory devices use a fixed reference layer to store one bit, then the device structure is simple and easy to manufacture, but the information storage density is limited to one bit per cell
Solution Approach 1:
The patent divides the single ferromagnetic layer into multiple independent ferromagnetic layers (first FM layer, second FM layer, etc.), each capable of independent magnetization switching. This segmentation allows each layer to store one bit of information, enabling multi-bit storage per cell while maintaining the basic magnetoresistive memory structure
Solution Approach 2:
The patent makes all ferromagnetic layers functional storage elements rather than having one fixed reference layer and one free layer. Each FM layer can be independently switched and read, giving the device multi-functionality where n ferromagnetic layers can store n bits of information using the same basic readout mechanism
2Quantity of substance
If conventional magnetoresistive devices distinguish only two resistance states, then the device operation is simple, but the information storage capacity is limited
Solution Approach 1:
The patent transitions from distinguishing only two resistance states (parallel/antiparallel) to detecting multiple resistance states by adding the dimension of multiple ferromagnetic layers. Each layer's magnetization state contributes to the overall resistance, creating a multi-dimensional state space where 2^n states are possible with n layers
3Measurement precision
If auxiliary magnetic layers are used to detect in-plane magnetization reversal, then the detection capability is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent makes the ferromagnetic layers themselves serve the dual function of storing information and enabling detection. The magnetoresistive effect inherently provides the detection mechanism, eliminating the need for separate auxiliary magnetic layers. The system is self-sufficient, using its own magnetic layers for both storage and readout functions
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 enables the storage of more information per unit volume, scalable bit densities, and eliminates the need for a reference layer, allowing for efficient switching and reading of multiple bits using in-plane currents, enhancing memory device performance.
Implementation Method 1
a unidirectional spin Hall magnetoresistance (USMR) effect in a FM/NM/FM trilayer structure allows for the detection of multiple magnetic states
Implementation Method 2
spin currents can be more efficiently injected by utilizing the spin Hall effect (SHE) in a nonmagnetic metal (NM) layer 120 adjacent a ferromagnetic (FM) free layer 110
Data Source
AI summary
A multilayer structure comprising FM/NM/FM layers enhances the amplitude of the unidirectional spin Hall magnetoresistance (USMR) thanks to an additional FM/NM layer interface. The USMR can be used to detect the in-plane magnetization direction of each FM layer perpendicular to the current injection. Detection relies on second harmonic resistance measurements driven by the USMR with possible contribution of Joule heating-induced magnetothermal effects (ANE and SSE). The four different magnetization states (, , , ), of the FM/NM/FM layers give rise to four unique resistance levels, which can be read out by a simple two-terminal electric measurement. As a result, this FM/NM/FM multilayer structure can be used in a lateral, two-terminal device to store multiple magnetic bits. Moreover, the magnetic states can be manipulated by spin-orbit torques, opening the possibility for all-electrical operation.