SOT-MTJ Probabilistic Bit Cell for Controlled 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 random numbers efficiently.
Innovation Solution
A probabilistic bit device incorporating a spin orbit torque (SOT) 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 number 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 functionality is achieved, but random number generation capability is lacking
Solution Approach 1:
The magnetic memory device is designed to perform both data storage and random number generation functions using the same memory cell structure. By controlling the magnetization state of the free layer through spin-orbit torque, the device can operate as either a conventional memory storing deterministic data or a random number generator producing unpredictable bits, thereby achieving multi-functionality without increasing structural complexity
Solution Approach 2:
The invention changes the operational parameters of the magnetic memory device to enable random number generation. Specifically, it applies spin-orbit torque with controlled current magnitude and duration to manipulate the magnetization switching probability of the free layer. By adjusting these parameters, the device transitions from deterministic switching (for memory) to probabilistic switching (for random number generation), enabling the new function without structural modification
2Speed
If spin orbit torque is used to determine magnetization direction, then operation speed improves to 10 nanoseconds, but the ability to generate random numbers is not provided
Solution Approach 1:
The invention introduces dynamic control of the spin-orbit torque parameters (current magnitude, pulse width, and amplitude) to enable probabilistic magnetization switching. By dynamically adjusting these parameters during operation, the device can exploit the transient magnetic states and switching probabilities to generate random bits while maintaining the fast 10 nanosecond operation speed characteristic of SOT-MRAM
3Reliability
If deterministic magnetization switching is used for memory storage, then data retention is stable, but randomness required for random number generation is insufficient
Solution Approach 1:
The invention changes the operational parameters from deterministic to probabilistic control. By applying spin-orbit torque with specific current magnitudes and pulse durations that result in switching probabilities between 0 and 1 (rather than deterministic switching), the device generates random bits. The underlying magnetic tunnel junction maintains its stable data retention characteristics while the switching behavior becomes probabilistic, enabling both reliability and randomness
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 numbers with high speed and stability, operating efficiently at low power and compatible with semiconductor processes, ensuring complete randomness and fast operation.
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
A 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. The resistance of the magnetic tunnel junction element depends on a magnetization direction of a free layer.
Implementation Method 4
A spin polarization direction is perpendicular to the magnetization direction in the SOT-MRAM
Implementation Method 5
a controller configured to provide an in-plane current with a predetermined first magnitude and a magnetic field with a predetermined second magnitude to the spin orbit torque pattern in an in-plane direction parallel to an upper surface of the ferromagnetic pattern
Data Source
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.