Orthogonal STT-MRAM with Shared STNO for Low-Current Switching

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing spin-transfer torque magnetic random access memory (MRAM) devices require high switching currents and are limited by precessional modes, which affect switching efficiency and determinism, especially in in-plane structures, and previous solutions like precessional spin current layers enhance switching in one direction but hinder it in the other.

Innovation Solution

The implementation of orthogonal spin transfer magnetic tunnel junctions (OST-MTJs) with an in-plane polarization magnetic layer, a non-magnetic spacer, a reference magnetic layer, and a free magnetic layer, along with a spin torque nano oscillator (STNO) that generates a switching current pulse alternating between maximum and minimum values synchronized with the precession frequency of the free magnetic layer, improving switching efficiency in both directions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If spin transfer torque is used to switch magnetization direction in MRAM devices, then data storage and non-volatility are achieved, but high switching currents are required and switching efficiency is limited

Engineering Contradiction:

Improvedata storage reliabilityVSAvoidswitching current

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies periodic oscillating current at the precession frequency of the free layer magnetization to assist switching. The STNO generates an oscillating spin-polarized current that resonates with the natural precession frequency of the free layer, enabling switching at lower current amplitudes through resonant enhancement rather than requiring high DC currents.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent introduces dynamic control by using an oscillating current whose frequency matches the precession frequency of the free layer magnetization. This dynamic approach allows the system to exploit the natural precessional motion of magnetization, reducing the energy barrier for switching compared to static DC current application.

Inventive Principle:

Principle #15Dynamics

2Productivity

If precessional spin current layers are used to enhance switching in one direction, then switching efficiency improves for that direction, but switching is hindered in the opposite direction

Engineering Contradiction:

Improveswitching speedVSAvoidbidirectional switching capability

Core Design Contradiction:

ProductivityVSAdaptability or versatility

Solution Approach 1:

The STNO-based oscillating current source provides a universal switching mechanism that works effectively for both writing directions (0 to 1 and 1 to 0). The oscillating spin-polarized current from the STNO can drive magnetization switching in either direction by adjusting the phase and polarity of the oscillation, eliminating the directional limitation of precessional spin current layers.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

Instead of using a fixed polarizer layer that inherently favors one switching direction, the patent uses an STNO that generates oscillating current. By inverting the approach from static unidirectional enhancement to dynamic bidirectional control, the system achieves equal switching efficiency in both directions through resonant excitation.

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If high switching currents are applied to overcome precessional modes, then magnetization switching is achieved, but switching determinism and precision are reduced

Engineering Contradiction:

Improveswitching determinismVSAvoidswitching current amplitude

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent uses periodic oscillating current at the precise precession frequency to achieve deterministic switching. The resonant frequency matching ensures that the oscillating torque constructively interferes with the magnetization precession, leading to reliable and predictable switching outcomes at lower current amplitudes compared to high DC currents that cause erratic behavior.

Inventive Principle:

Principle #19Periodic action

4Adaptability or versatility

If in-plane polarization layers are used in OST-MTJs, then orthogonal spin transfer effect is achieved, but large spin currents are still required for switching

Engineering Contradiction:

Improveorthogonal spin transfer capabilityVSAvoidspin current magnitude

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent combines in-plane polarization layers with STNO-based oscillating current. The oscillating spin-polarized current from the STNO resonates with the precession frequency of the free layer, providing orthogonal spin transfer effect with enhanced efficiency. This resonant mechanism reduces the required spin current magnitude compared to using in-plane polarization layers with DC current.

Inventive Principle:

Principle #19Periodic action

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 significantly reduces switching currents and times while maintaining high-speed switching for both magnetization direction changes, enhancing the operational window and determinism of the free layer's magnetization switching.

Implementation Method 1

Spin transfer torque or spin transfer switching, uses spin-aligned ('polarized') electrons to change the magnetization orientation of the free layer in the magnetic tunnel junction ('MTJ'). If a spin-polarized current is passed to the magnetic region of a free layer in the MTJ device, the electrons will transfer a portion of their spin-angular momentum to the magnetization layer to produce a torque on the magnetization of the free layer.

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

The magnetization vector of the free magnetic layer has a predetermined precession frequency. The first frequency is synchronized with the predetermined precession frequency of the free magnetic layer, thereby causing the spin transfer torque to be at the maximum magnitude when the spin transfer torque increases the precession radius of the magnetization vector

Methodology Applied

Scientific EffectPrecession: Precession

Implementation Method 3

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 4

Due to the spin-polarized electron tunneling effect, the electrical resistance of the cell changes due to the orientation of the magnetic fields of the two layers. The cell's resistance will be different for the parallel and anti-parallel states and thus the cell's resistance can be used to distinguish between a '1' and a '0'.

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS10236047B1Shared oscillator (STNO) for MRAM array write-assist in orthogonal STT-MRAM

Publication Date: 2019.03.19 INTEGRATED SILICON SOLUTION CAYMAN INC

AI summary

Methods and structures useful for magnetoresistive random-access memory (MRAM) are disclosed. The MRAM device has plurality of magnetic tunnel junction (MTJ) stack having significantly improved performance of the free layers in the MTJ structures. The MRAM device utilizes a spin torque nano-oscillator (STNO), a metallic bit line and a plurality of orthogonal spin transfer magnetic tunnel junctions (OST-MTJs), each OST-MTJ comprising an in-plane polarizer, and a perpendicular MTJ.