Multi-bit MRAM Cell with Tilted Anisotropy Axis
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Solution Overview
Problem
Conventional MRAM devices with single-bit cells face limitations in storage density, power consumption, and manufacturing costs, necessitating an increase in storage capacity while maintaining performance.
Innovation Solution
The implementation of multi-bit MRAM cells with a magnetic tunnel junction structure, including a first and second magnetic layer, a spacer layer, and a field line that induces a write magnetic field, allowing magnetization direction switching to store multiple logic states by tilting the magnetic anisotropy axis relative to the magnetic field axis, and using thermally assisted switching to align magnetizations during write operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional single-bit MRAM cells are used, then device simplicity and ease of manufacture are maintained, but storage density is limited
Solution Approach 1:
The patent introduces a tilted magnetic anisotropy axis at an angle θ (0° < θ < 90°) relative to the magnetic field axis, adding a dimensional parameter to the conventional binary magnetization switching. This angular dimension enables continuous magnetization orientation control, allowing a single cell to represent multiple logic states (m > 2) based on the number of discrete angular positions, thereby increasing storage density without multiplying the physical cell count.
Solution Approach 2:
The patent changes the magnetic anisotropy axis orientation from the conventional parallel alignment with the magnetic field axis to a tilted configuration. This parameter change enables the storage layer magnetization to assume multiple stable equilibrium positions at different angles relative to the field axis, creating multiple distinguishable logic states within a single cell while maintaining the same physical structure.
2Quantity of substance
If multiple field lines are used to achieve multi-bit storage, then storage density increases, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent makes a single field line multi-functional by utilizing the angular dimension of magnetization switching. Instead of requiring one field line per bit, the same field line can induce magnetization switching to multiple discrete angular positions, enabling the storage of m logic states (where m > 2) with a single field line, thus reducing device complexity while increasing storage capacity.
Solution Approach 2:
The patent introduces dynamic control of magnetization orientation through angular positioning. The storage layer magnetization can be dynamically switched between multiple angular positions relative to the field axis by controlling the write current magnitude and direction, enabling flexible multi-state storage without additional static structural elements.
3Quantity of substance
If multi-bit cells are implemented, then storage density increases, but power consumption increases
Solution Approach 1:
The patent employs partial switching action where the magnetization is switched to intermediate angular positions rather than requiring full 180-degree reversal for each logic state. By utilizing angular positions between 0° and 90° relative to the field axis, the required switching energy is reduced compared to conventional binary switching, as the magnetization follows a lower energy path through angular adjustment rather than complete reversal.
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 enhances storage density, reduces power consumption, and lowers manufacturing costs by encoding multiple logic states per cell using a single field line, while maintaining efficient data storage and retrieval.
Implementation Method 1
a field line magnetically coupled to the MRAM cell and configured to induce a write magnetic field along a magnetic field axis
Implementation Method 2
the magnetic anisotropy axis is tilted relative to the magnetic field axis
Implementation Method 3
heating the MRAM cell above the threshold temperature, such that the storage magnetization direction is temporarily unpinned
Implementation Method 4
discovery of magnetic tunnel junctions having a strong magnetoresistance at ambient temperatures
Data Source
AI summary
A magnetic random access memory (“MRAM”) cell includes: (1) a first magnetic layer having a first magnetization direction and a magnetic anisotropy axis; (2) a second magnetic layer having a second magnetization direction; and (3) a spacer layer disposed between the first magnetic layer and the second magnetic layer. The MRAM cell also includes a field line magnetically coupled to the MRAM cell and configured to induce a write magnetic field along a magnetic field axis, and the magnetic anisotropy axis is tilted relative to the magnetic field axis. During a write operation, the first magnetization direction is switchable between m directions to store data corresponding to one of m logic states, with m>2, at least one of the m directions is aligned relative to the magnetic anisotropy axis, and at least another one of the m directions is aligned relative to the magnetic field axis.