Multiferroic-assisted voltage controlled magnetic anisotropy memory device and methods of manufacturing the same
A magnetic memory device includes a first electrode, a second electrode, and a layer stack located between the first electrode and the second electrode. The layer stack includes a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectric multiferroic layer including at least one crystalline grain. The magnetization of the magnetoelectric multiferroic layer may be axial, canted, or in-plane. For axial or canted magnetization of the magnetoelectric multiferroic layer, a deterministic switching of the free layer may be achieved through coupling with the axial component of magnetization of the magnetoelectric multiferroic layer. Alternatively, the in-plane magnetization of the magnetoelectric multiferroic layer may be employed to induce precession of the magnetization angle of the free layer.
1. A magnetic memory device, comprising:
a first electrode;
a second electrode; and
a layer stack located between the first electrode and the second electrode and comprising, from one side to another, a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectric multiferroic layer including at least one crystalline grain having an easy axis of magnetization along an axial direction or along a first tilted direction having a first tilt angle less than 90 degrees relative to the axial direction, the axial direction being perpendicular to an interface between the free layer and the tunnel barrier layer.
2. The magnetic memory device of claim 1 , wherein the at least one crystalline grain of the magnetoelectric multiferroic layer has an easy axis of ferroelectric polarization along the axial direction or along a second tilted direction having a second tilt angle less than 90 degrees relative to the axial direction.
3. The magnetic memory device of claim 1 , further comprising a programming circuit configured to apply programming voltage patterns between the first electrode and the second electrode, wherein the programming voltage patterns comprise:
a first programming voltage pattern comprising a first voltage having a first polarity and having a magnitude greater than a coercive voltage sufficient to switch a magnetization direction of the magnetoelectric multiferroic layer; and
a second programming voltage pattern comprising a second voltage having a second polarity opposite to the first polarity and having a magnitude greater than the coercive voltage followed by a third voltage having the first polarity and having a magnitude less than the coercive voltage.
4. The magnetic memory device of claim 3 , wherein:
the first voltage comprises a first positive voltage deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be parallel to a magnetization direction of the reference layer; and
the first positive voltage has a sufficient magnitude to lower a perpendicular magnetic anisotropy of the free layer that allows the free layer to deterministically switch its magnetization direction to be parallel to the magnetization direction of the reference layer.
5. The magnetic memory device of claim 4 , wherein:
the second voltage comprises a negative voltage which deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be antiparallel to the magnetization direction of the reference layer; and
the negative voltage increases the perpendicular magnetic anisotropy of the free layer such that the free layer cannot switch its magnetization direction.
6. The magnetic memory device of claim 5 , wherein:
the third voltage comprises a second positive voltage which does not have a sufficient magnitude to switch the magnetization direction of the magnetoelectric multiferroic layer; and
the second positive voltage has a sufficient magnitude to lower the perpendicular magnetic anisotropy at the interface between the tunnel barrier layer and the free layer to allow the free layer to deterministically switch its magnetization direction to be antiparallel to magnetization direction of the reference layer.
7. The magnetic memory device of claim 6 , wherein:
the first positive voltage pulse has a magnitude between 0.5 V and 2 V;
the negative voltage pulse has a magnitude between −0.5 V and −2 V; and
the second positive voltage pulse has a magnitude between 0.3 V and 1 V, and has an absolute value which is less than an absolute value of the negative voltage pulse.
8. The magnetic memory device of claim 6 , wherein the magnetization direction of the free layer is coupled to the magnetization direction of the magnetoelectric multiferroic layer.
9. The magnetic memory device of claim 6 , wherein:
the magnetic memory device is programmed into a lower resistance state by the first programming voltage pattern; and
the magnetic memory device is programmed into a higher resistance state by the second programming voltage pattern.
10. The magnetic memory device of claim 1 , wherein the easy axis of magnetization of the at least one crystalline grain of the magnetoelectric multiferroic layer is along the axial direction.
11. The magnetic memory device of claim 1 , wherein the easy axis of magnetization of the at least one crystalline grain of the magnetoelectric multiferroic layer is along the first tilted direction.
12. The magnetic memory device of claim 1 , wherein the layer stack further comprises a SAF structure located adjacent to the reference layer.
13. The magnetic memory device of claim 1 , wherein the layer stack further comprises a nonmagnetic electrically conductive capping layer contacting the magnetoelectric multiferroic layer and one of the electrode and the second electrode.
14. The magnetic memory device of claim 1 , wherein:
the tunnel barrier layer comprises a dielectric layer having a thickness of 1 nm to 2 nm; and
the magnetoelectric multiferroic layer comprises a material selected from BiFeO 3 , h-YMnO 3 , BaNiF 4 , PbVO 3 , BiMnO 3 , LuFe 2 O 4 , HoMn 2 O 5 , h-HoMnO 3 , h-ScMnO 3 , h-ErMnO 3 , h-TmMnO 3 , h-YbMnO 3 , h-LuMnO 3 , K 2 SeO 4 , Cs 2 CdI 4 , TbMnO 3 , Ni 3 V 2 O 8 , MnWO 4 , CuO, ZnCr 2 Se 4 , LiCu 2 O 2 , or Ni 3 B 7 O 13 I.
15. The magnetic memory device of claim 14 , wherein the magnetoelectric multiferroic layer comprises a BiFeO 3 layer having a thickness of 1 nm or less.
16. A method of programming the magnetic memory device of claim 1 , comprising:
applying a first programming voltage pattern comprising a first voltage having a first polarity and having a magnitude greater than a coercive voltage sufficient to switch a magnetization direction of the magnetoelectric multiferroic layer; and
applying a second programming voltage pattern comprising a second voltage having a second polarity opposite to the first polarity and having a magnitude greater than the coercive voltage followed by a third voltage having the first polarity and having a magnitude less than the coercive voltage.
17. The method of claim 16 , wherein:
the first voltage comprises a first positive voltage which deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be parallel to a magnetization direction of the reference layer; and
the first positive voltage has a sufficient magnitude to lower a perpendicular magnetic anisotropy at an interface between the tunnel barrier layer and the free layer to allow the free layer to deterministically switch its magnetization direction to be parallel to the magnetization direction of the reference layer.
18. The method of claim 17 , wherein:
the second voltage comprises a negative voltage which deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be antiparallel to the magnetization direction of the reference layer;
the negative voltage increases the perpendicular magnetic anisotropy of the free layer such that the free layer cannot switch its magnetization direction;
the third voltage comprises a second positive voltage which does not have a sufficient magnitude to switch the magnetization direction of the magnetoelectric multiferroic layer; and
the second positive voltage has a sufficient magnitude to lower the perpendicular magnetic anisotropy at the interface between the tunnel barrier layer and the free layer to allow the free layer to deterministically switch its magnetization direction to be antiparallel to magnetization direction of the reference layer.
19. The method of claim 18 , wherein:
the first positive voltage pulse has a magnitude between 0.5 V and 2 V;
the negative voltage pulse has a magnitude between −0.5 V and −2 V; and
the second positive voltage pulse has a magnitude between 0.3 V and 1 V, and has an absolute value which is less than an absolute value of the negative voltage pulse.
20. The method of claim 18 , wherein:
the magnetization direction of the free layer is coupled to the magnetization direction of the magnetoelectric multiferroic layer;
the magnetic memory device is deterministically programmed into a lower resistance state by the first programming voltage pattern; and
the magnetic memory device is deterministically programmed into a higher resistance state by the second programming voltage pattern.