Asymmetric Write Current Waveform for MRAM Thermal Stability
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Solution Overview
Problem
In magnetoresistive random access memory (MRAM) using the spin transfer magnetization reversal scheme, excessive write current can lead to erroneous writing due to thermal disturbances, especially in elements with small threshold reversing currents, causing data loss and unintended data storage.
Innovation Solution
A data writing method that generates a write current with a falling period longer than the rising period, which helps in maintaining a thermally stable state during data writing, reducing erroneous writing occurrences by ensuring a normal write state is maintained even with excessive currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If excessive write current is supplied to the MTJ element to ensure reliable magnetization reversal, then the data writing reliability is improved, but thermal disturbances occur causing erroneous writing and data loss
Solution Approach 1:
The patent applies periodic pulsed current action with specific timing characteristics. A write current pulse is applied with a controlled duration where the falling period is longer than the rising period. This periodic action allows the magnetization to reverse during the current pulse while providing a longer decay period for thermal stabilization, thus preventing erroneous writing caused by excessive current while ensuring reliable magnetization reversal.
Solution Approach 2:
The patent changes the temporal parameters of the write current pulse, specifically setting the falling period longer than the rising period. This parameter modification optimizes the balance between achieving sufficient current magnitude for reliable magnetization reversal and limiting thermal disturbance duration to prevent erroneous writing, thereby resolving the contradiction between reliability and thermal stability.
2Duration of action of moving object
If the write current duration is extended to ensure complete magnetization reversal, then the writing completeness is improved, but the element remains in a thermally unstable state longer increasing erroneous writing risk
Solution Approach 1:
The patent uses a pulsed current waveform with asymmetric rise and fall times. The current rises quickly to achieve magnetization reversal and then falls more slowly to allow thermal stabilization. This periodic action ensures complete reversal while minimizing the duration of thermal instability, thus preventing erroneous writing.
Solution Approach 2:
The patent applies a preliminary current rise phase that quickly establishes the necessary current magnitude for magnetization reversal, followed by a controlled fall phase. This preliminary action ensures the reversal is initiated and completed efficiently, while the subsequent slower decay phase allows the element to return to a stable state, preventing writing errors.
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 effectively reduces the frequency of erroneous writing and stabilizes the data writing process in MRAM, ensuring reliable data storage by suppressing thermally unstable states during the falling edge of the write current.
Implementation Method 1
there is a spin transfer magnetization reversal scheme. According to the spin transfer magnetization reversal scheme, directly flowing a current through an element enables reversing the magnetization of the magnetization variable layer based on a spin torque injected from the magnetization invariable layer
Implementation Method 2
A junction resistance value of the MTJ element varies in accordance with a cosine of a relative angle of the magnetizations of the first and second ferromagnetic layers. Therefore, the junction resistance value becomes a minimal value when the magnetizations of the first and second ferromagnetic layers are parallel, and it becomes a maximal value when they are anti-parallel. This is called a TMR effect.
Data Source
AI summary
A data writing method for a magnetoresistive effect element of an aspect of the present invention including generating a write current in which a falling period from the start of a falling edge to the end of the falling edge is longer than a rising period from the start of a rising edge to the end of the rising edge, and flowing the write current through the magnetoresistive effect element which comprises a first magnetic layer having an invariable magnetizing direction, a second magnetic layer having a variable magnetizing direction, and a tunnel barrier layer provided between the first magnetic layer and the second magnetic layer, to change the magnetizing direction of the second magnetic layer.