Annular STT Memory Cell With Soft Magnetic Field Confinement
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Solution Overview
Problem
As semiconductor MRAM cells shrink, the distance between adjacent cells decreases, leading to increased cell disturb from current-carrying lines, which results in higher power consumption and thermal profiles, and existing STT RAM cells still require significant currents for magnetic moment switching.
Innovation Solution
The introduction of a ferromagnetic coupling material between the soft magnetic material and the first ferromagnetic material in an annular STT stack, which reduces cross-talk and programming current requirements while maintaining thermal stability by confining the Oersted field within the soft magnetic material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of MRAM cells decreases, then the integration density increases, but the cell disturb from current carrying lines increases and power consumption increases
Solution Approach 1:
The patent extracts the magnetic field confinement function into a dedicated soft magnetic material layer surrounding the MTJ stack. This layer captures and confines the Oersted field generated by write current, preventing it from spreading to adjacent cells. By separating the field confinement function from the general cell structure, the patent reduces cell disturb and power consumption while maintaining small cell size for high integration density.
Solution Approach 2:
The soft magnetic material layer provides localized magnetic field confinement exactly where needed - surrounding the MTJ stack in the regions where Oersted field leakage would affect adjacent cells. This local quality enhancement ensures that field confinement is applied precisely at the cell boundaries without affecting the overall cell size or requiring global structural changes.
2Length of moving object
If the width of current carrying lines decreases, then the cell size decreases, but greater currents are required to produce switching fields
Solution Approach 1:
The patent extracts the magnetic field amplification and confinement function into the soft magnetic material layer, which concentrates the Oersted field generated by the write current. This allows narrower current carrying lines to produce sufficient switching fields because the soft magnetic material amplifies and directs the field efficiently to the free layer, reducing the required write current despite smaller line widths.
Solution Approach 2:
The introduction of soft magnetic material changes the magnetic permeability parameter in the region surrounding the MTJ stack. This parameter change enhances the magnetic field generation efficiency, allowing smaller current carrying lines to produce the necessary switching fields with lower currents, thereby resolving the contradiction between line width reduction and write current requirements.
3Volume of moving object
If the distance between adjacent cells decreases, then the integration density increases, but cell disturb from current carrying lines increases
Solution Approach 1:
The patent extracts the field confinement function into the soft magnetic material layer that surrounds each MTJ stack. This layer acts as a magnetic shield that captures Oersted field leakage, preventing it from reaching adjacent cells. By implementing this dedicated confinement mechanism, the patent enables smaller cell spacing while maintaining cell integrity and reducing mutual disturbance between neighboring cells.
Solution Approach 2:
The soft magnetic material layer provides localized magnetic field management at each cell boundary, creating a magnetic confinement zone that prevents field leakage to adjacent cells. This local quality enhancement ensures that even with reduced cell spacing, each cell maintains its magnetic isolation, thereby preserving cell integrity while enabling higher integration density.
4Power
If write current increases, then magnetic moment switching is achieved, but thermal profile and energy consumption increase
Solution Approach 1:
The patent extracts the magnetic field confinement and amplification function into the soft magnetic material layer, which efficiently directs the Oersted field to the free layer. This reduces the required write current magnitude, thereby decreasing the thermal profile and energy consumption associated with magnetic moment switching while still achieving reliable switching.
Solution Approach 2:
The soft magnetic material layer changes the magnetic permeability parameter, enhancing the efficiency of magnetic field generation from write current. This parameter change reduces the required write current to achieve magnetic moment switching, thereby lowering the thermal profile and energy consumption without sacrificing switching reliability.
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 decreases the programming current needed for magnetic moment switching, reduces energy consumption, and enhances cell integrity and reliability by minimizing cross-talk and thermal disturbances.
Implementation Method 1
switching of the free material magnetic moment (e.g., the write process) can be produced by passage of the spin polarized current itself
Implementation Method 2
unpolarized conduction electrons passing through a first magnetic material having its magnetic moment oriented in a given direction (e.g. a 'fixed' material) are preferentially polarized by their passage through that material by a quantum mechanical exchange interaction with the polarized bound electrons in the material
Implementation Method 3
the write current associated with a MRAM device can be about 10 mA, which can be problematic as the size of the MRAM cells and current carrying lines decreases
Implementation Method 4
a ferromagnetic coupling material formed between the soft magnetic material and the first ferromagnetic material
Data Source
Figure 1A~1B
Figure 1C
Figure 2
AI summary
Spin Torque Transfer (STT) memory cell structures and methods are described herein. One or more STT memory cell structures comprise an annular STT stack including a nonmagnetic material between a first ferromagnetic material and a second ferromagnetic material and a soft magnetic material surrounding at least a portion of the annular STT stack.