Magnetoresistive memory device including a high dielectric constant capping layer and methods of making the same
View Patent ↗Magnetoelectric or magnetoresistive memory cells include at least one of a high dielectric constant dielectric capping layer and/or a nonmagnetic metal dust layer located between the free layer and the dielectric capping layer.
1. A voltage controlled magnetic anisotropy (VCMA) magnetoelectric memory device comprising a VCMA magnetoelectric memory cell, wherein the VCMA magnetoelectric memory cell comprises: a first electrode; a second electrode that is spaced from the first electrode; a magnetic tunnel junction located between the first electrode and the second electrode, the magnetic tunnel junction comprising a reference layer having a fixed magnetization direction, a free layer, and a nonmagnetic tunnel barrier layer located between the reference layer and the free layer; a voltage controlled magnetic anisotropy (VCMA) dielectric capping layer having a dielectric constant greater than 10 and located between the free layer and the second electrode; and wherein the VCMA dielectric capping layer is thicker than the nonmagnetic tunnel barrier layer and has a higher dielectric constant than the nonmagnetic tunnel barrier layer, such that an electric field is generated in the VCMA dielectric capping layer during the application of a voltage between the first electrode and the second electrode.
2. The VCMA magnetoelectric memory device of claim 1 , wherein the VCMA dielectric capping layer consists essentially of at least one transition-metal-containing dielectric metal oxide material.
3. The VCMA magnetoelectric memory device of claim 2 , wherein the at least one transition-metal-containing dielectric metal oxide material comprises at least one ternary dielectric oxide material including two transition metal elements.
4. The VCMA magnetoelectric memory device of claim 3 , wherein the at least one ternary dielectric oxide material comprises SrTiO 3 , BaTiO 3 , or BiFeO 3 .
5. The VCMA magnetoelectric memory device of claim 2 , wherein the at least one transition-metal-containing dielectric metal oxide material consists essentially of hafnium oxide.
6. The VCMA magnetoelectric memory device of claim 1 , wherein the VCMA dielectric capping layer has a thickness in a range from 1.0 nm to 10 nm.
7. The VCMA magnetoelectric memory device of claim 1 , wherein the VCMA dielectric capping layer has a thickness in a range from 1 nm to 5 nm and a dielectric constant of 25 or greater.
8. The VCMA magnetoelectric memory device of claim 7 , wherein the nonmagnetic tunnel barrier layer comprises magnesium oxide having a thickness in a range from 0.5 nm to 1.5 nm.
9. The VCMA magnetoelectric memory device of claim 1 , further comprising an external magnetic field source configured to apply an ancillary magnetic field to the free layer.
10. The VCMA magnetoelectric memory device of claim 1 , further comprising a synthetic antiferromagnet (SAF) structure comprising a stack of a hard ferromagnetic layer, an antiferromagnetic coupling layer, and the reference layer, the SAF structure being located between the first electrode and the nonmagnetic tunnel barrier layer.
11. The VCMA magnetoelectric memory device of claim 1 , wherein the VCMA dielectric capping layer directly physically contacts the free layer.
12. The VCMA magnetoelectric memory device of claim 1 , further comprising a nonmagnetic metal dust layer located between the VCMA dielectric capping layer and the free layer.
13. The VCMA magnetoelectric memory device of claim 1 , further comprising a control circuit that is configured to perform a programming operation by applying a programming voltage between the first electrode and the second electrode, wherein the programming voltage has a same polarity for a first magnetization state in which the free layer and the reference layer have parallel magnetization directions and for a second magnetization state in which the free layer and the reference layer have antiparallel magnetization directions.
14. A method of programming the VCMA magnetoelectric memory device of claim 1 , comprising applying a first programming voltage of a first polarity between the first electrode and the second electrode to switch a first magnetization state of the free layer in which the free layer and the reference layer have parallel magnetization directions to a second magnetization state of the free layer in which the free layer and the reference layer have antiparallel magnetization directions.
15. The method of claim 14 , further comprising applying a second programming voltage of the first polarity between the first and the second electrodes to switch the second magnetization state of the free layer to the first magnetization state of the free layer.
16. The method of claim 15 , wherein:
the first programming voltage and the second programming voltage generate an electric field in the VCMA dielectric capping layer which induces precession in the free layer; and
the first programming voltage has a magnitude in a range from 500 mV to 3 V.
17. The method of claim 16 , further comprising terminating the first programming voltage when the free layer has the first magnetization direction.
18. The method of claim 17 , further comprising terminating the second programming voltage when the free layer has the second magnetization direction.
19. The method of claim 14 , further comprising applying an external magnetic field during the step of applying the first programming voltage.