Spin-Orbit Torque MTJ Cell for Tunable Random Bit Generation
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Solution Overview
Problem
Existing magnetic memory devices, such as STT-MRAM and SOT-MRAM, lack the capability to generate truly random bits efficiently, limiting their applications in random number generation and secure data storage.
Innovation Solution
A probabilistic bit device is developed using a spin orbit torque-based memory cell with a ferromagnetic pattern, conductive pattern, and magnetic tunnel junction pattern, controlled by an in-plane current and magnetic field to manipulate the magnetization direction of the free magnetic pattern, allowing for random bit generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional magnetic memory devices (STT-MRAM or SOT-MRAM) are used, then data storage capability is achieved, but random bit generation capability is lacking
Solution Approach 1:
The magnetic memory device is designed to perform both data storage and random bit generation functions using the same core structure. The memory cell can operate in deterministic mode for storage or in probabilistic mode for random number generation, achieving multi-functionality without requiring separate dedicated hardware components.
Solution Approach 2:
The device transitions from deterministic operation to probabilistic operation by changing the magnitude of the write current applied to the ferromagnetic layer. By controlling the current magnitude to be below the threshold required for deterministic magnetization switching, the system exploits stochastic thermal fluctuations to generate random bits, thereby achieving random bit generation capability through parameter adjustment.
2Reliability
If deterministic magnetization switching is used in magnetic memory, then data storage reliability is improved, but random bit generation efficiency deteriorates
Solution Approach 1:
The system dynamically adjusts its operating mode by varying the write current magnitude. For data storage, a high current above the switching threshold is applied to achieve deterministic magnetization reversal. For random bit generation, a lower current below the threshold is applied to allow stochastic switching, thereby optimizing both data storage reliability and random bit generation efficiency through dynamic parameter control.
3Reliability
If high current magnitude is applied for deterministic switching, then write operation reliability is improved, but energy consumption increases
Solution Approach 1:
The device uses parameter changes in current magnitude to switch between operational modes. Deterministic writing uses high current for reliable switching, while random bit generation uses lower current to reduce energy consumption. This parameter-based mode switching allows the system to optimize energy efficiency for random number generation operations compared to conventional high-current approaches.
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 device generates genuinely random bits with high probability control, operating faster and more efficiently than conventional methods, suitable for low-power random number generation and secure data storage.
Implementation Method 1
A magnetic memory element that uses a spin orbit torque for a write operation that determines the magnetization direction of the free layer is referred to as a SOT-MRAM (Spin Orbit Torque MRAM)
Implementation Method 2
the spin polarization direction is perpendicular to the magnetization direction in the SOT-MRAM
Implementation Method 3
A magnetic memory device such as MRAM (Magnetic Random Access Memory) is a memory device that stores data therein using change in a resistance of a magnetic tunnel junction element
Implementation Method 4
The ferromagnetic pattern can have an in-plane magnetic anisotropy
Implementation Method 5
each of the pinned magnetic pattern and the free magnetic pattern may have perpendicular magnetic anisotropy
Data Source
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AI summary
A probabilistic bit device includes a spin orbit torque (SOT) pattern, which contains a stacked combination of a ferromagnetic pattern having in-plane magnetic anisotropy and a conductive pattern on the ferromagnetic pattern, and a magnetic tunnel junction (MTJ) pattern on the SOT pattern. The MTJ pattern contains a stacked combination of a free magnetic pattern having perpendicular magnetic anisotropy, a barrier pattern, and a pinned magnetic pattern having perpendicular magnetic anisotropy. A controller is provided, which is configured to supply an in-plane current having a first magnitude and a magnetic field having a second magnitude to the SOT pattern, such that a desired probability that a magnetization direction of the free magnetic pattern is in a predetermined direction is achieved.