Sub-volt switching of nanoscale voltage-controlled perpendicular magnetic tunnel junctions

Abstract

Magnetic random-access memory (MRAM) based on voltage-controlled magnetic anisotropy in magnetic tunnel junctions (MTJs) is a promising candidate for high-performance computing applications, due to its lower power consumption, higher bit density, and the ability to reduce the access transistor size when compared to conventional current-controlled spin-transfer torque MRAM. The key to realizing these advantages is to have a low MTJ switching voltage. Here, we report a perpendicular MTJ structure with a high voltage-controlled magnetic anisotropy coefficient ~130 fJ/Vm and high tunnel magnetoresistance exceeding 150%. Owing to the high voltage-controlled magnetic anisotropy coefficient, we demonstrate sub-nanosecond precessional switching of nanoscale MTJs with diameters of 50 and 70 nm, using a voltage lower than 1 V. We also show scaling of this switching mechanism down to 30 nm MTJs, with voltages close to 2 V. The results pave the path for the future development and application of voltage-controlled MRAMs and spintronic devices in emerging computing systems.

Magneto-ionic Control of Ferrimagnetic Order by Oxygen Gating

“…The relatively high power consumption of these mechanisms has created a need for novel low-dissipation alternatives such as voltage control of magnetism (VCM). It has been reported that applying voltage can lead to significant changes in magnetic properties including magnetic anisotropy, − SOT efficiency, , and Curie temperature. , Furthermore, researchers have even realized voltage-controlled 180-degree magnetization switching in piezoelectric or multiferroic ferromagnetic devices where the time reversal symmetry is broken. , However, most of the current VCM efforts have been focused on ferromagnetic materials.…”

Reconfigurable Physically Unclonable Functions Based on Nanoscale Voltage‐Controlled Magnetic Tunnel Junctions

“…VCMA has been previously proposed as a writing mechanism for MRAM due to its potential high density and low power consumption, [53][54][55][56][57][58] where switching can be realized by tuning the width of a voltage pulse across the VC-MTJ. [53,56,58]- [71] On the other hand, Figure 1c depicts the writing operation principle for the VCMA-based reconfigurable PUF which is based on the idea of stochastic switching. At zero bias voltage, there are two minima in the energy landscape which are the two stable out-of-plane directions of the free layer magnetization.…”

“…If the voltage is removed at half period, the magnetic moment will settle in the opposite direction. [53,56,[58][59][60][61][62][63][64][65][66][67][68][69][70][71] However, if the voltage is applied for a longer time, the precession will continue with a reducing amplitude due to damping, and the free layer will settle into an in-plane direction within a few nanoseconds. If the voltage pulse is removed at this point, the easy-axis is changed to perpendicular again and the magnetic moment reorients to one of the perpendicular states with equal probability.…”

Progress and Application Perspectives of Voltage‐Controlled Magnetic Tunnel Junctions

“…In precessional VCMA switching, the switching voltage, noted as V sw , is the value at which the energy barrier between the free layer states is eliminated. The switching voltage can be expressed as $${V}_{sw} = {t}_{{\mathrm{MgO}}}\ {t}_{{\mathrm{free}}}( {{K}_i( {V\ = \ 0} )/{t}_{{\mathrm{free}}} - 2\pi {M}_{\mathrm{S}}^2} )/\xi ,$$ [ 65,83,92 ] where t MgO is the thickness of the MgO tunnel barrier, t free is the thickness of the free layer, K i is the PMA, M S is the saturation magnetization, and ξ is the VCMA coefficient that quantifies the magnetic anisotropy's sensitivity to electric fields. As the switching voltage is inversely proportional to ξ , a sufficiently large VCMA coefficient is necessary for low write voltages and to achieve switching of nanoscale MTJs.…”

“…On the other hand, a large enough energy barrier is needed to maintain sufficient thermal stability. The energy barrier can be written as $${E}_{\mathrm{b}} = \ \pi {D}^2{t}_{{\mathrm{free}}}( {{K}_{\mathrm{i}}( {V\ = \ 0} )/{t}_{{\mathrm{free}}} - 2\pi {M}_S^2} )/4,$$ [ 65,83,92 ] where D is the diameter of the device. For smaller devices, to have the same thermal stability coefficient Δ = E b / kT , a higher PMA is needed, imposing an even higher demand for the VCMA coefficient.…”