All-electrical control of nanoscale domain wall devices using magnetic tunnel junction read and write INVITED

Abstract

Fast domain wall (DW) motion in magnetic nanostructures is crucial for future spintronic devices, such as racetrack memory [1], spin logic [2] and neuromorphic computing [3]. The discovery of fast DW transport governed by spin-orbit torque (SOT) and the Dzyaloshinskii-Moriya interaction (DMI) in ultrathin magnetic layers on heavy metals was a breakthrough in the development of low energy devices based on DW motion. However, a lack of all-electrical control of DWs in nanoscale devices impedes to bring these advanced materials to practical applications. Therefore, finding energy-efficient ways to electrically write, read and transport DWs is a necessity. As demonstrated in STT-MRAM technology, the magnetic tunnel junction (MTJ) based on a CoFeB/MgO free layer (FL) [4], which offers efficient spin-transfer torque (STT) write and a high tunneling magnetoresistance (TMR) readout signal, could be a potential solution to electrically operate a full functional DW device. However, such an MTJ stack poses significant challenges to realize a DW device, which particularly relate to low DW speed and poor manufacturability of a CoFeB/MgO based DW conduit using industrial integration platforms [5].Here, we propose and develop a new type of MTJ stack that incorporates typical high DW velocity materials (i.e., Pt/Co) as the second FL into a conventional MTJ with a CoFeB/MgO based FL. We firstly demonstrate that the fundamental properties of a standard MTJ device are not compromised by the integration of DW conduit materials. Complete functional DW devices, consisting of multiple MTJ pillars connected by a common FL, have been fully integrated using such novel MTJ stack, Figure 1 (a). We then demonstrate that all-electrical control of a DW in a nanoscale device, i.e., STT write, TMR read and SOT driven DW motion, can be achieved. As an example, figure 1 (b) presents field-driven domain expansion from P2 through the whole track, after the domain was nucleated by STT in P2. Figure 1 (c) demonstrates the current-driven DW transport from P2 to P1, with small field assistance. No change in resistance was observed in P3, as expected from directional current-driven DW motion.Finally, we show that these DW devices can be used to investigate the SOT driven DW dynamics in nanoscale devices where conventional magnetic imaging techniques become ineffective. Our DW devices show good TMR read-out and efficient STT writing, comparable to current STT-MRAM devices. The devices are fabricated in imec’s 300 mm CMOS fab on full wafers which clears the path for large scale integration. This proof-of-concept thus offers potential solutions for high performance and low-power DW-based devices for logic and neuromorphic applications [5,6]. **