STTMRAM Reference Bit Thermal Stability via Local Quality
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Solution Overview
Problem
Perpendicular MRAM devices face challenges with thermal stability, particularly in reference bits, which affects their ability to maintain data integrity over time without requiring costly refresh mechanisms, impacting operational speed and usability in high-data-rate applications.
Innovation Solution
A spin-transfer-torque magnetic random access memory (STTMRAM) device is developed using a perpendicular magnetic tunnel junction (MTJ) structure with a magnetic free layer, reference layer, and pinned layer, where the magnetization directions are perpendicular to the film plane, allowing for stable magnetization orientation changes in the reference bit without external refresh, while maintaining lower thermal stability for data bits for fast write operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the reference bit is made of identical MRAM cell structure as data bit to simplify fabrication and circuit design, then manufacturing precision and ease of manufacture are improved, but thermal stability deteriorates causing reference bit errors that require costly refresh mechanisms
Solution Approach 1:
The patent applies local quality by making the reference bit structure locally different from data bits. Specifically, the reference bit uses a fictitious TMR element with a fixed magnetization state, while data bits use switchable magnetization states. This local structural differentiation allows the reference bit to have enhanced thermal stability without affecting the manufacturing process for data bits, resolving the contradiction between manufacturing simplicity and reference bit reliability.
2Reliability
If refresh mechanisms are implemented to ensure reference bit correctness, then reliability is improved, but device complexity and operational speed deteriorate due to costly refresh operations
Solution Approach 1:
The patent applies preliminary action by pre-establishing the reference bit in a fixed, thermally stable magnetization state during initialization. This preliminary configuration ensures the reference bit maintains its correctness without requiring ongoing refresh operations. The fixed magnetization state is set once and persists throughout operation, eliminating the need for complex refresh mechanisms and their associated overhead.
3Reliability
If thermal stability is increased for reference bits to ensure long-term data integrity, then reliability is improved, but write operation speed and energy efficiency deteriorate
Solution Approach 1:
The patent applies local quality by creating distinct magnetic properties in different parts of the memory device. The reference bit has high thermal stability with fixed magnetization, while data bits have lower thermal stability barriers enabling efficient switching. This local differentiation allows reference bits to maintain integrity over time without requiring data bits to have similarly high energy barriers, thus preserving write operation efficiency.
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
The proposed solution enhances the thermal stability of reference bits, ensuring reliable long-term operations without the need for special refresh mechanisms, while allowing data bits to maintain lower thermal stability for efficient and low-power write operations, thus improving overall device performance.
Implementation Method 1
A spin-transfer-torque magnetic random access memory (STTMRAM) device is developed using a perpendicular magnetic tunnel junction (MTJ) structure
Implementation Method 2
with the at least one MJT including, a magnetic free layer (FL) having a switchable magnetization with a direction that is perpendicular to a film plane
Implementation Method 3
The direction of magnetization the RL and the PL remain the same... The direction of magnetization of the RL and the PL are anti-parallel relative to each other
Data Source
AI summary
A magnetic random access memory (MRAM) element is configured to store a state when electric current flows therethrough. The MRAM element includes a first magnetic tunnel junction (MTJ) for storing a data bit and a reference bit MTJ for storing a reference bit. The data bit MTJ and reference bit MTJ are preferred to be of identical structure that includes a magnetic free layer (FL) having a switchable magnetization with a direction that is perpendicular to a film plane. The direction of magnetization of the FL is determinative of the data bit stored in the at least one MTJ. The identical structure further includes a magnetic reference layer (RL) having a magnetization with a direction that is perpendicular to the film plane, and a magnetic pinned layer (PL) having a magnetization with a direction that is perpendicular to the film plane. The direction of magnetization of the RL and the PL are anti-parallel relative to each other in the data bit MTJ for storing data bit, wherein when electric current is applied to the first MTJ, the magnetization orientation of the FL switches during a write operation, whereas, the direction of magnetization the RL and the PL remain the same. The direction of magnetization of the FL, the RL and the PL are parallel relative to each other in the reference bit MTJ for storing reference bit, the magnetization orientation of the FL does not switch under normal read operations.