Vertical Superconducting Memory Cell With Magnetic Junction
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Solution Overview
Problem
Existing hybrid superconducting and magnetic memory cells face challenges in achieving high access speed, small size, high integration density, low power consumption, and efficient operation, particularly in scaling down to small dimensions while maintaining effective magnetic field coupling.
Innovation Solution
The proposed memory cell integrates a superconductive Josephson junction and a magnetic junction vertically, with the magnetic junction comprising two magnetic layers of different coercive forces and a non-magnetic layer, allowing for controlled magnetization rotation and significant variation in the Josephson critical current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the magnetic junction is positioned close to the Josephson junction to achieve high integration density, then the area is reduced, but the magnetic field coupling efficiency may be compromised
Solution Approach 1:
The patent transitions from lateral placement to vertical stacking of the magnetic junction relative to the Josephson junction. This vertical arrangement allows the magnetic junction to be positioned directly above the Josephson junction, maximizing magnetic field coupling through the thin non-superconducting layer while minimizing the lateral footprint of the memory cell, thereby achieving both high integration density and effective magnetic coupling.
2Measurement precision
If the critical current variation is increased to improve logic state discrimination, then the signal detection becomes easier, but the power consumption may increase
Solution Approach 1:
The patent utilizes changes in magnetic field parameters (strength and direction) produced by the magnetic junction to modulate the critical current of the Josephson junction. By controlling the magnetization orientation of the magnetic layer, the system achieves at least 15% critical current depression to distinguish logic states, while the superconducting nature of the Josephson junction maintains low power consumption during read operations.
3Adaptability or versatility
If the magnetic junction uses multiple magnetic layers with different coercive forces to enable controlled magnetization rotation, then the device functionality is improved, but the device complexity increases
Solution Approach 1:
The magnetic junction is divided into multiple magnetic layers with different coercive forces, allowing independent control of each layer's magnetization. This segmentation enables the soft magnetic layer to be switched by lower fields while the hard magnetic layer maintains stable reference magnetization, providing versatile magnetization control capabilities while keeping each layer's fabrication and control relatively simple.
4Measurement precision
If the Josephson junction critical current is significantly depressed to represent logic '1' state, then the readout signal becomes stronger, but the energy barrier between states may be reduced
Solution Approach 1:
The non-superconducting layer acts as an intermediary between the magnetic junction and the Josephson junction, allowing magnetic field coupling while maintaining electrical isolation. This intermediary structure enables strong readout signals through critical current modulation while preserving the superconducting energy gap and maintaining stable energy barriers between logic states through proper layer thickness and material selection.
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 configuration enables reliable discrimination between logic states with a critical current depression of at least 15%, allowing for high-density memory arrays with efficient READ and WRITE operations, while maintaining low power consumption and compact size.
Implementation Method 1
a magnetic junction in close proximity to the Josephson junction... The magnetic junction produces magnetic fields of different strength and direction which lead to two distinct values of the Josephson critical current
Implementation Method 2
The Josephson junction comprises two superposed superconductive layers with a non-superconductive layer therebetween... a two-terminal device, which when biased above its critical current Ic, can generate a time-series of SFQ pulses
Implementation Method 3
Because the barrier of an MJJ contains a ferromagnetic material, which being a permanent magnet material has hysteresis, the stable magnetic flux in the junction may have (at least) two different values
Implementation Method 4
The rotation can be accomplished either by magnetic fields produced by appropriately configured control lines carrying electric current, or by spin-polarized current through the magnetic junction
Data Source
AI summary
A memory cell having a Josephson junction and a magnetic junction in close proximity. The two junctions may be vertically integrated. The magnetic junction has at least two magnetic layers with different coercive forces and a non-magnetic layer therebetween, to form a spin valve or pseudo-spin valve. A magnetization direction of a magnetic layer with lower coercive force can be rotated with respect to the larger coercive force magnetic layer(s). Magnetic fields produced by appropriately configured control lines carrying electric current, or spin-polarized current through the magnetic junction, can result in rotation. The magnetic junction influences the Josephson critical current of the Josephson junction, leading to distinct values of critical current which can serve as digital logic states. The memory cell can be integrated into large arrays containing a plurality of the cells, to enable the selective READ and WRITE operations.