Picosecond Optospintronic Tunnel Junctions for Non-volatile Photonic Memories

Abstract

Perpendicular magnetic tunnel junctions are one of the building blocks for spintronic memories, which allow fast nonvolatile data access, offering substantial potentials to revolutionize the mainstream computing architecture. However, conventional switching mechanisms of such devices are fundamentally hindered by spin polarized currents, either spin transfer torque or spin orbit torque with spin precession time limitation and excessive power dissipation. These physical constraints significantly stimulate the advancement of modern spintronics. Here, we report an optospintronic tunnel junction using a photonic-spintronic combination. This composite device incorporates an all-optically switchable Co/Gd bilayer coupled to a CoFeB/MgO-based perpendicular magnetic tunnel junction by the Ruderman-Kittel-Kasuya-Yosida interaction. A picosecond all-optical operation of the optospintronic tunnel junction is explicitly confirmed by time-resolved measurements. Moreover, the device shows a considerable tunnel magnetoresistance and thermal stability. This proof-of-concept device represents an essential step towards ultrafast photonic memories with THz data access, as well as ultralow power consumption.

Progress toward picosecond on-chip magnetic memory

“…We have modified the existing M3TM model to explain the observed ultrafast switching in such complex structures. A working opto-MTJ cell with relatively high TMR employing an optically switchable FM-FEM heterostructure as the free layer of an MTJ has now been demonstrated 58 with time-resolved magnetization reversal in ~10 ps (for 3 m diameter memory cell). We have also demonstrated SOT-induced magnetization reversal in a conventional FM using ~6 ps pure charge-current pulses 32 .…”

“…The ultrafast laser-induced toggle-switchable HI-AOS phenomenon is already being explored and integrated into MTJ cells which offers enhanced energy efficiency and much faster switching compared to conventional MRAM devices 58 . Applications for this technology will likely involve integration with silicon photonics.…”

“…Instead of using a conventional ferromagnet as the free layer of the MTJ building block, researchers have studied a toggle-switchable ferrimagnet exhibiting HI-AOS as the free layer. The free layer in such an optospintronic device is switched optically and then the TMR across the MTJ is measured to read the corresponding magnetization state 54,55,57,58 . However, the TMR ratio of an MTJ device tends to be small when only a ferrimagnet is used as the free layer 57 due to its low spin-polarization.…”