Voltage-controlled Magnetic Anisotropy Coefficient Research Articles

Source Line Sensing in Magneto-Electric Random-Access Memory to Reduce Read Disturbance and Improve Sensing Margin

A source line sensing (SLS) scheme is presented, along with a corresponding memory core circuit architecture, for the sensing operation of magneto-electric random-access memory (MeRAM). Compared to a conventional bit-line sensing (BLS) scheme, the proposed SLS, which exploits the voltage-controlled magnetic anisotropy (VCMA) effect, applies a voltage across the magneto-electric tunnel junction (MEJ) with an opposite polarity. The SLS significantly reduces read disturbance and increases the sensing margin due to the enhanced coercivity of the bit during the read operation. Experimental data demonstrate that the thermal stability of nanoscale MEJs increases up to 2 times during the SLS operation compared with conventional BLS. An MEJ compact model based the SLS simulation shows that read disturbance improves by a factor greater than 10 ${}^{9}$ fJ/V $\cdot $ m and the sensing margin increases up to 3 times in the MEJ with the large VCMA coefficient $\left(>\text{100} \text{fJ}/\text{V}\cdot\text{m}\right)$ .

Thermally stable voltage-controlled perpendicular magnetic anisotropy in Mo|CoFeB|MgO structures

We study voltage-controlled magnetic anisotropy (VCMA) and other magnetic properties in annealed Mo|CoFeB|MgO layered structures. The interfacial perpendicular magnetic anisotropy (PMA) is observed to increase with annealing over the studied temperature range, and a VCMA coefficient of about 40 fJ/V-m is sustained after annealing at temperatures as high as 430 °C. Ab initio electronic structure calculations of interfacial PMA as a function of strain further show that strain relaxation may lead to the increase of interfacial PMA at higher annealing temperatures. Measurements also show that there is no significant VCMA and interfacial PMA dependence on the CoFeB thickness over the studied range, which illustrates the interfacial origin of the anisotropy and its voltage dependence, i.e., the VCMA effect. The high thermal annealing stability of Mo|CoFeB|MgO structures makes them compatible with advanced CMOS back-end-of-line processes, and will be important for integration of magnetoelectric random access memory into on-chip embedded applications.

Giant voltage modulation of magnetic anisotropy in strained heavy metal/magnet/insulator heterostructures

Ab initio electronic structure calculations reveal that epitaxial strain has a dramatic effect on the voltage-controlled magnetic anisotropy (VCMA) in Ta/FeCo/MgO junctions. Strain can give rise to a wide range of novel VCMA behaviors where the MA can change from a $\ensuremath{\vee}$- to a $\ensuremath{\wedge}$-shape electric-field dependence with giant VCMA coefficients which are asymmetric under voltage reversal. The underlying mechanism is the interplay of the strain- and electric-field-induced changes in the spin-orbit coupled $d$ states at the interfaces and the strain-induced modification of the dielectric constant of MgO. These findings demonstrate the feasibility of highly sensitive VCMA through strain engineering, which may provide a viable avenue for tailoring magnetoelectric properties for spintronic applications.

Temperature dependence of the voltage-controlled perpendicular anisotropy in nanoscale MgO|CoFeB|Ta magnetic tunnel junctions

In this work, we experimentally study the temperature dependence of the perpendicular magnetic anisotropy (PMA) and of the voltage-controlled magnetic anisotropy (VCMA) in nanoscale MgO|CoFeB|Ta-based magnetic tunnel junctions. We demonstrate that the temperature dependences of both the PMA and the VCMA coefficient follow power laws of the saturation magnetization, but with different exponents. We also find that the linear dependence of the PMA on electric field is maintained over a wide temperature range, although the VCMA strength decreases faster as a function of temperature as compared to the PMA. Possible mechanisms leading to the different exponents are discussed.