Spin Transfer MRAM with Magnetic Biasing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional magnetic random access memories (MRAMs) face challenges in sustaining the required electric current for magnetization switching due to increased coercive force and power consumption as devices are microminiaturized, and spin-transfer induced switching requires precise control of current pulses and high current densities, which is difficult to integrate with CMOS technology.
Innovation Solution
A hybrid MRAM structure is introduced that combines spin-transfer with magnetic biasing, using a write word line to bias the free layer magnetization and reduce the spin current required for switching, allowing for segmented word line layouts where multiple bits share the same write word line and individual bit lines apply spin currents for desired magnetic states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional MRAM uses external magnetic fields for magnetization switching, then switching can be achieved, but the required electric current becomes excessively large and power consumption increases
Solution Approach 1:
The patent introduces a magnetic biasing layer as an intermediary component that generates a bias magnetic field to assist the spin-polarized current in switching the free layer magnetization. This mediator enables switching at lower current densities by providing the additional magnetic field component needed to overcome the energy barrier, thus reducing power consumption while maintaining switching reliability.
Solution Approach 2:
The patent changes the magnetic field parameter by introducing a bias field from the magnetic biasing layer. This bias field modifies the effective anisotropy field and reduces the switching field requirement, allowing spin-transfer torque to achieve switching at lower current densities and reduced power consumption.
2Area of moving object
If devices are microminiaturized to increase density, then area is reduced, but coercive force increases making switching more difficult
Solution Approach 1:
The magnetic biasing layer acts as an intermediary that provides a bias magnetic field to counteract the increased coercive force in miniaturized devices. This bias field assists the spin-polarized current in overcoming the higher energy barrier associated with smaller device dimensions, enabling reliable switching despite increased coercivity.
Solution Approach 2:
The patent employs a composite magnetic structure consisting of multiple layers including the magnetic biasing layer, free layer, and reference layer. This composite structure allows the biasing layer to provide the necessary magnetic field assistance while the other layers maintain data storage functionality, effectively managing the increased coercive force in miniaturized devices.
3Reliability
If spin-transfer switching uses high current densities for reliable switching, then switching reliability improves, but integration with CMOS technology becomes difficult
Solution Approach 1:
The magnetic biasing layer serves as an intermediary that reduces the current density requirement for switching. By providing a bias magnetic field that assists the spin-polarized current, it enables reliable switching at lower current densities that are compatible with standard CMOS technology processes and transistor current-carrying capabilities.
Solution Approach 2:
The patent changes the switching parameter by reducing the required current density through the introduction of magnetic biasing. This parameter change makes the switching mechanism compatible with CMOS technology, which cannot sustain the very high current densities required by conventional spin-transfer switching schemes.
4Reliability
If segmented word line architecture is used to reduce disturb conditions, then cell disturb is reduced, but larger magnetic fields are required for rewriting
Solution Approach 1:
The magnetic biasing layer acts as an intermediary that provides a bias field to assist switching in segmented word line architectures. This bias field reduces the additional magnetic field burden on bit lines, enabling rewriting with lower currents despite the segmented architecture requirements, thus reducing write power while maintaining data stability.
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 reduces the spin and bit line currents needed for magnetization switching, improving power efficiency and reliability, enabling ultra-high density MRAMs with reduced transistor size and enhanced MTJ reliability.
Implementation Method 1
the electric current flowing in a write word line generates a magnetic field 31 to bias the magnetization 32 of the free layer
Implementation Method 2
the spin current generates torque 34 to help switch the magnetization of the free layer
Data Source
AI summary
The addition of segmented write word lines to a spin-transfer MRAM structure serves to magnetically bias the free layer so that the precessional motion of the magnetization vector that is set in play by the flow of spin polarized electrons into the free layer allows said magnetic vector to be switched rather than to oscillate between two easy axis directions.