Magnetic memory devices having a low switching voltage

1 . A magnetic tunnel junction (MTJ) device, comprising:

a bottom electrode;

a bottom CoFeB fixed layer disposed above and in electrical communication with the bottom electrode;

a MgO layer disposed above the bottom CoFeB fixed layer;

a top CoFeB free layer disposed above the MgO layer;

a metal Mo capping layer disposed above the top CoFeB free layer; and

a top electrode disposed above and in electrical communication with the metal Mo capping layer.

2 . The MTJ device of claim 1 , wherein:

the bottom CoFeB fixed layer comprises Co 20 Fe 60 B 20 ; and

the top CoFeB free layer comprises Co 17.5 Fe 52.5 B 30 .

3 . The MTJ device of claim 2 , wherein:

the bottom CoFeB fixed layer has a thickness of about 0.8 nm;

the MgO layer has a thickness of about 1.5 nm;

the top CoFeB free layer has a thickness of about 1.6 nm; and

the metal Mo capping layer has a thickness of about 5 nm.

4 . The MTJ device of claim 1 , wherein the bottom CoFeB fixed layer, the MgO layer, the top CoFeB free layer, and the metal Mo capping layer are patterned into a circular vertically-oriented pillar.

5 . The MTJ device of claim 4 , wherein the circular vertically-oriented pillar has a diameter within a range from about 50 nm to about 70 nm.

6 . The MTJ device of claim 4 , wherein the circular vertically-oriented pillar has a diameter within a range from about 30 nm to about 50 nm.

7 . The MTJ device of claim 1 , wherein the bottom electrode includes a Co/Pt-based synthetic antiferromagnetic (SAF) multilayer.

8 . The MTJ device of claim 1 , wherein the bottom CoFeB fixed layer and the top CoFeB free layer each have a composition ratio of 1:3 between Co and Fe, and the top CoFeB free layer has a higher B concentration than the bottom CoFeB fixed layer.

9 . The MTJ device of claim 1 , further comprising a plurality of MTJ devices and electronic circuitry coupled with the plurality of MTJ devices and the MTJ device of claim 1 and configured as a complementary metal oxide semiconductor (CMOS)-compatible magnetic random-access memory (MRAM).

10 . A method of fabricating a voltage-controlled magnetic anisotropy (VCMA) magnetic tunnel junction (MTJ) device, comprising:

forming a plurality of layers in a perpendicularly rising sequence above a bottom electrode, the plurality of layers comprising a bottom CoFeB fixed layer disposed above and in electrical communication with the bottom electrode, a MgO layer disposed above the bottom CoFeB fixed layer, a top CoFeB free layer disposed above the MgO layer, a metal Mo capping layer disposed above the top CoFeB free layer, and a top electrode disposed above and in electrical communication with the metal Mo capping layer;

performing thermal annealing; and

patterning the plurality of layers into a circular pillar.

11 . The method of claim 10 , wherein the plurality of layers further comprises a pinning layer between the bottom electrode and the bottom CoFeB fixed layer.

12 . The method of claim 10 , wherein forming the plurality of layers comprises sputter depositing using physical vapor deposition.

13 . The method of claim 10 , wherein the circular pillar is patterned with a diameter within a range of about 30 nm to about 50 nm.

14 . The method of claim 10 , wherein the circular pillar is patterned with a diameter within a range of about 50 nm to about 70 nm.

15 . The method of claim 10 , wherein the circular pillar is patterned using electron beam lithography.

16 . The method of claim 10 , wherein the MgO layer is deposited by radio-frequency (RF) sputtering.

17 . The method of claim 10 , wherein layers comprising metallic compounds are deposited by DC sputtering.

18 . A method of switching a free-layer magnetization state of a voltage-controlled magnetic anisotropy (VCMA) magnetic tunnel junction (MTJ) device patterned as a circular pillar comprising a plurality of layers in arranged in a perpendicularly rising sequence above a bottom electrode, the plurality of layers including a bottom CoFeB fixed layer disposed above and in electrical communication with the bottom electrode, a MgO layer disposed above the bottom CoFeB fixed layer, a top CoFeB free layer disposed above the MgO layer, a metal Mo capping layer disposed above the top CoFeB free layer and in electrical communication with a top electrode thereabove, the method comprising:

applying a magnetic field H across the top CoFeB free layer of the MTJ device along an axis;

applying a switching voltage V SW between the top electrode and the bottom electrode of the MTJ device, where V SW =4t MgO E b (V=0)/(πξD 2 ), t MgO is a thickness of the MgO layer, E b is an energy barrier between two free-layer magnetization states, ξ is a VCMA coefficient, and D is a diameter of the MTJ device; and

removing the switching voltage V SW after the switching voltage V SW has been applied for a switching time t SW corresponding to a half period of a magnetic moment precession of the top CoFeB free layer.

19 . The method of claim 18 , wherein the axis, along which the magnetic field H is applied, is offset by an angle θ H from normal to a plane of the plurality of layers of the MTJ device.