Abstract
A heat-assisted multiferroic solid-state memory design is proposed and analysed, based on a PbNbZrSnTiO3 antiferroelectric layer and Ni81Fe19 magnetic free layer. Information is stored as magnetisation direction in the free layer of a magnetic tunnel junction element. The bit writing process is contactless and relies on triggering thermally activated magnetisation switching of the free layer towards a strain-induced anisotropy easy axis. A stress is generated using the antiferroelectric layer by voltage-induced antiferroelectric to ferroelectric phase change, and this is transmitted to the magnetic free layer by strain-mediated coupling. The thermally activated strain-induced magnetisation switching is analysed here using a three-dimensional, temperature-dependent magnetisation dynamics model, based on simultaneous evaluation of the stochastic Landau-Lifshitz-Bloch equation and heat flow equation, together with stochastic thermal fields and magnetoelastic contributions. The magnetisation switching probability is calculated as a function of stress magnitude and maximum heat pulse temperature. An operating region is identified, where magnetisation switching always occurs, with stress values ranging from 80 to 180 MPa, and maximum temperatures normalised to the Curie temperature ranging from 0.65 to 0.99.
Highlights
Non-volatile memories for primary storage are potential candidates for a universal memory, promising both long-term storage and reliability, as well as speeds comparable to volatile memory such as dynamic random access memory (RAM)
In the heat-assisted multiferroic memory (HAMM) array design introduced here, bits are stored in magnetic tunnel junction (MTJ) elements as with MRAM; the writing process uses a low power contactless method, based on triggering thermally activated magnetisation switching towards a strain-induced anisotropy easy axis
In order to investigate the operation of a HAMM element, the magnetisation switching processes are investigated using a three-dimensional coupled micromagnetics model based on the stochastic
Summary
Non-volatile memories for primary storage are potential candidates for a universal memory, promising both long-term storage and reliability, as well as speeds comparable to volatile memory such as dynamic random access memory (RAM). The most widely researched magnetic RAM is the spin transfer torque magnetic RAM (STT-MRAM) [2,3,4], based on switching the magnetisation direction of a free magnetic layer in a magnetic tunnel junction (MTJ) using spin-polarised currents Whilst this is commercially available, offering lower power consumption, faster speeds and comparable bit densities to dynamic RAM, the high manufacturing cost required to achieve large bit densities currently prevents it from being widely adopted. In the HAMM array design introduced here, bits are stored in MTJ elements as with MRAM; the writing process uses a low power contactless method, based on triggering thermally activated magnetisation switching towards a strain-induced anisotropy easy axis This avoids the difficulties encountered with STT-MRAM due to the high tunnel current densities required to induce magnetisation switching, allowing for the simplest possible MTJ stacks to be used
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