Multiferroic Layer Enables Deterministic VCMA Memory Switching
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Solution Overview
Problem
Magnetoresistive memory devices face non-deterministic programming due to voltage-controlled magnetic anisotropy (VCMA) requiring precise control of voltage pulses for magnetization direction switching, which is challenging to achieve with existing technologies.
Innovation Solution
Incorporating a magnetoelectric multiferroic layer with crystalline grains having an easy axis of magnetization along a specific direction, allowing for deterministic programming through specific voltage patterns that switch the magnetization direction of the free layer relative to the reference layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage-controlled magnetic anisotropy (VCMA) is used to switch magnetization direction, then programming of magnetoresistive memory device is achieved, but the programming becomes non-deterministic and requires precise control of voltage pulse timing
Solution Approach 1:
A magnetoelectric multiferroic layer is introduced as an intermediary between the voltage control mechanism and the free layer magnetization. This multiferroic layer converts the applied voltage into a magnetization switch through voltage-controlled magnetic anisotropy, which then provides a deterministic magnetic field to switch the free layer magnetization direction. This intermediary mechanism eliminates the non-deterministic behavior of direct VCMA switching.
Solution Approach 2:
The patent replaces the direct electrical voltage control mechanism with a magnetoelectric coupling mechanism. Instead of using voltage pulses to directly control magnetization (which is non-deterministic), the system uses voltage to control the magnetic anisotropy of the multiferroic layer, which then deterministically switches magnetization through magnetic field coupling to the free layer.
2Loss of energy
If the dielectric tunnel barrier layer thickness is increased to at least 1 nm to reduce tunneling current, then tunneling current flow below critical current is achieved, but the VCMA programming requires even more precise voltage pulse control
Solution Approach 1:
The magnetoelectric multiferroic layer serves as an intermediary that decouples the tunneling current reduction requirement from the magnetization switching mechanism. The multiferroic layer's voltage-controlled magnetic anisotropy provides deterministic switching without requiring thin tunnel barriers, allowing the use of thicker dielectric layers for reduced tunneling current while maintaining simple voltage pulse control.
3Manufacturing precision
If precise control of voltage pulse timing is implemented to achieve desired magnetization direction, then programming accuracy is improved, but the device operation becomes more complex and difficult to control
Solution Approach 1:
The patent substitutes the complex timing-controlled voltage pulse system with a magnetoelectric multiferroic layer that provides deterministic magnetization switching. The multiferroic layer's intrinsic magnetic anisotropy switching behavior, controlled by simple voltage polarity reversal, replaces the need for precise timing control, thereby simplifying device operation while maintaining high programming accuracy.
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 solution enables deterministic programming of magnetization directions in magnetoresistive memory devices, improving the reliability and precision of switching between resistance states without relying on precise pulse duration control.
Implementation Method 1
Voltage controlled magnetic anisotropy (VCMA) refers to an effect in which the perpendicular magnetic anisotropy of the free layer has a first-order dependence on the externally applied voltage across the free layer
Implementation Method 2
a magnetoelectric multiferroic layer including at least one crystalline grain having an easy axis of magnetization
Implementation Method 3
The thickness of the dielectric tunnel barrier layer may be at least 1 nm, which reduces tunneling current flow through the dielectric tunnel barrier layer below a critical current required to switch the magnetization direction
Implementation Method 4
A magnetoresistive memory device can store information employing the difference in electrical resistance of a first configuration in which a ferromagnetic free layer has a magnetization direction that is parallel to the magnetization of a ferromagnetic reference layer and a second configuration in which the free layer has a magnetization direction that is antiparallel to the magnetization of the reference layer
Data Source
AI summary
A magnetic memory device includes a first electrode, a second electrode, and a layer stack located between the first electrode and the second electrode. The layer stack includes a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectric multiferroic layer including at least one crystalline grain. The magnetization of the magnetoelectric multiferroic layer may be axial, canted, or in-plane. For axial or canted magnetization of the magnetoelectric multiferroic layer, a deterministic switching of the free layer may be achieved through coupling with the axial component of magnetization of the magnetoelectric multiferroic layer. Alternatively, the in-plane magnetization of the magnetoelectric multiferroic layer may be employed to induce precession of the magnetization angle of the free layer.