Progress toward picosecond on-chip magnetic memory

Abstract

We offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ∼3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ∼6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed to accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.

Picosecond spin-orbit torque–induced coherent magnetization switching in a ferromagnet

“…In recent years, spintronics (1-3) has gained considerable attention and shows great promise for low-power, nonvolatile memory technology. While magnetic memory devices based on spin-transfer torque (STT) have already been introduced to the market (4)(5)(6), they still present some challenges such as device lifetime (10 10 write cycles limited by tunnel barrier breakdown), relatively slow switching speed and the write error rate (due to the stochastic thermal fluctuation induced switching initiation), which are affecting its performance compared to the state-of-the-art semiconductor memory devices (3,4). Spin-orbit torque (SOT)-based devices, on the other hand, are expected to largely overcome these problems.…”

“…2 Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720, USA. 3 Department of Physics and Nanotechnology, SRM Institute of Science and Technology, Kattankulathur-603 203, Tamil Nadu, India. 4 Department of Engineering, University of San Francisco, San Francisco CA 94117, USA.…”

Helicity-independent all-optical switching of magnetization in ferrimagnetic alloys

“…In 2012, it was even established that the circular polarization could be disregarded completely, leading to the process of helicity-independent all-optical switching [9,10]. These seemingly paradoxical results -disproving the long-held notion that magnetic fields must be at least somewhat involved to reverse magnetization -has since triggered intense research efforts [11] aimed at engineering ever-faster switching capabilities under non-equilibrium conditions in a wide array of materials, ultimately targeting practical application within ultrafast memory technologies [12,13].…”

Enhancing All-Optical Switching of Magnetization by He Ion Irradiation

“…It is well-known that single pulse all-optical switching (AOS) of the magnetization in 3d-4f ferrimagnets is the fastest and one of the least dissipative ways of magnetization switching [1][2][3][4][5] . This mechanism not only offers means for ultrafast memory operations, but also gives rise to integration between integrated photonics and spintronics 2,6 , in which the 3d-4f ferrimagnets should prevail 7 .…”

“…It is well-known that single pulse all-optical switching (AOS) of the magnetization in 3d-4f ferrimagnets is the fastest and one of the least dissipative ways of magnetization switching [1][2][3][4][5] . This mechanism not only offers means for ultrafast memory operations, but also gives rise to integration between integrated photonics and spintronics 2,6 , in which the 3d-4f ferrimagnets should prevail 7 . Initially observed in a 3d-4f alloy systems 4 , recently, it was found that the Co/Gd bilayer 8,9 based synthetic ferrimagnets exhibit likewise this ultrafast (ps switching time scale 10,11 ) single pulse AOS process.…”