Toggle MRAM with Asymmetric SAF Free Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional MRAM technologies require a 'read before write' process, which increases write cycle time and makes MRAMs less efficient due to the need to determine the magnetic states of toggle memory cells before writing, leading to susceptibility of half-selected cells to unintended magnetic state changes.
Innovation Solution
An MRAM structure with a synthetic anti-ferromagnetic (SAF) free layer having sub-layers with equal magnetic moments but unequal anisotropies, allowing for direct writing of selected MTJ cells without prior reading, using a SAF free layer configuration with specific sub-layer materials and orientations to manage magnetic fields effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a read process is performed before writing to determine magnetic states of toggle memory cells, then the accuracy of write operation is improved, but the write cycle time is increased
Solution Approach 1:
The patent applies preliminary action by configuring the SAF free layer with unequal anisotropies before the write operation. This pre-configured asymmetric structure enables the write operation to directly achieve the desired magnetic state change without requiring a prior read operation to determine the initial state, thus eliminating the read-before-write requirement and reducing write cycle time while maintaining write accuracy
2Ease of manufacture
If conventional toggle memory cell structure with equal anisotropies is used, then the manufacturing simplicity is maintained, but the cell selectivity is reduced leading to unintended state changes in half-selected cells
Solution Approach 1:
The patent applies local quality by creating unequal anisotropies in different sub-layers of the SAF free layer. Specifically, the first sub-layer has a first uniaxial anisotropy and the second sub-layer has a second uniaxial anisotropy that is different from the first. This localized differentiation in magnetic properties within the free layer enables selective writing to targeted memory cells while preventing unintended state changes in half-selected cells, thereby improving cell selectivity without significantly complicating the manufacturing process
3Stability of the object's composition
If equal anisotropies are used in both sub-layers of SAF free layer, then the structural symmetry is maintained, but the write field requirement increases making writing less efficient
Solution Approach 1:
The patent applies asymmetry by intentionally creating unequal uniaxial anisotropies in the two sub-layers of the SAF free layer. The first sub-layer has a first uniaxial anisotropy while the second sub-layer has a second uniaxial anisotropy that is different from the first. This asymmetric configuration optimizes the magnetic switching characteristics, reducing the write field requirement and improving writing efficiency compared to symmetric structures with equal anisotropies
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 faster and more stable writing of MRAM cells by eliminating the need for a read process, reducing write cycle time and enhancing cell selectivity, thus improving the overall efficiency and speed of memory operations.
Implementation Method 1
a first sub-layer, a coupling layer, and a second sub-layer that are sequentially formed on the tunnel barrier. The coupling layer enables exchange coupling between the first and second sub-layers so that magnetic moments of the first and second sub-layers are anti-parallel aligned
Implementation Method 2
an electrical current I1 in bit line 12 and a current I2 in word line 10 yield two magnetic fields on the free layer 15. The magnetic fields conform to a right hand rule so that a first field is generated along a first axis (easy axis) in the plane of the free layer and a second field is produced in a direction orthogonal to the first axis and along a hard axis in the free layer
Data Source
AI summary
A toggle MTJ is disclosed that has a SAF free layer with two or more magnetic sub-layers having equal magnetic moments but different anisotropies which is achieved by selecting Ni˜0.8Fe˜0.2 for one sub-layer and CoFeB or the like with a uni-axial anisotropy of 10 to 30 Oe for the higher anisotropy sub-layer. When a field is applied at <10° angle from the easy axis, magnetic vectors for the two sub-layers rotate to form different angles from the easy axis. A method is also described for selectively writing to bits along a word line that is orthogonal to bit line segments and avoids the need to “read first”. A bipolar word line pulse with two opposite pulses separated by a no pulse interval is applied in the absence of a bit line pulse to write a “0”. A bit line pulse opposite the second word line pulse writes a “1”.