Magnetoresistive memory device and method of operating same using ferroelectric-controlled exchange coupling
A magnetoresistive memory cell includes a magnetoresistive layer stack containing a reference layer, a nonmagnetic spacer layer, and a free layer. A ferroelectric material layer having two stable ferroelectric states is coupled to a strain-modulated ferromagnetic layer to alter a sign of magnetic exchange coupling between the strain-modulated ferromagnetic layer and the free layer. The strain-modulated ferromagnetic layer may be the reference layer or a perpendicular magnetic anisotropy layer that is located proximate to the ferroelectric material layer. The magnetoresistive memory cell may be configured as a three-terminal device or as a two-terminal device, and may be configured as a tunneling magnetoresistance (TMR) device or as a giant magnetoresistance (GMR) device.
1. A memory device comprising at least one magnetoresistive memory cell which comprises:
a first terminal electrode;
a second terminal electrode;
a magnetoresistive layer stack comprising a reference layer, a free layer and a dielectric tunnel barrier layer located between the reference layer and the free layer, wherein the magnetoresistive layer stack is located between the first terminal electrode and the second terminal electrode;
a perpendicular magnetic anisotropy (PMA) layer having a higher PMA than a PMA of the free layer, wherein the PMA layer is located between the second terminal electrode and the magnetoresistive layer stack;
a nonmagnetic electrically conductive layer located between the PMA layer and the free layer; and
a ferroelectric material layer located between the PMA layer and the second terminal electrode;
wherein the PMA layer and the free layer are magnetically exchange-coupled across the nonmagnetic electrically conductive layer; and
wherein a magnetic coupling between the PMA layer and the free layer is modulated by strain within the PMA layer.
2. The memory device of claim 1 , wherein a sign of an interlayer exchange coupling coefficient of the magnetic coupling between the PMA layer and the free layer changes based on a strain applied to the PMA layer by the ferroelectric material layer.
3. The memory device of claim 2 , wherein the ferroelectric material layer has two stable ferroelectric states having two different states of lattice deformation.
4. The memory device of claim 3 , wherein the two different states of lattice deformation have different average in-plane lattice constants within a horizontal plane that is parallel to an interface between the ferroelectric material layer and the PMA layer.
5. The memory device of claim 4 , wherein:
the two stable ferroelectric states of the ferroelectric material layer apply different first and second in-plane stresses to the PMA layer across the middle electrode;
a change between the first and the second in-plane stresses applied to the PMA layer changes the sign of the interlayer coupling coefficient between the PMA layer and the free layer; and
the change of the sign of the interlayer coupling coefficient changes a magnetization direction of the free layer.
6. The memory device of claim 5 , further comprising a programming circuit electrically connected to the first terminal electrode and the second terminal electrode and configured to apply two types of programming voltages between the first terminal electrode and the second terminal electrode.
7. The memory device of claim 6 , wherein the two types of programming voltages have two different polarities and have magnitudes that induce a ferroelectric transition of the ferroelectric material layer between the two ferroelectric states.
8. The memory device of claim 7 , further comprising a sensing circuit electrically connected to the first terminal electrode and the second terminal electrode and configured to apply a sensing voltage between the first terminal electrode and the second terminal electrode.
9. The memory device of claim 8 , wherein the sensing circuit is configured to measure a tunneling magnetoresistance (TMR) of the magnetoresistive layer stack.
10. A memory device comprising at least one magnetoresistive memory cell which comprises:
a first terminal electrode;
a second terminal electrode;
a magnetoresistive layer stack comprising a reference layer, a free layer and a dielectric tunnel barrier layer located between the reference layer and the free layer, wherein the magnetoresistive layer stack is located between the first terminal electrode and the second terminal electrode;
a perpendicular magnetic anisotropy (PMA) layer having a higher PMA than a PMA of the free layer, wherein the PMA layer is located between the second terminal electrode and the magnetoresistive layer stack;
a nonmagnetic electrically conductive layer located between the PMA layer and the free layer; and
a ferroelectric material layer located between the PMA layer and the second terminal electrode;
wherein the ferroelectric material layer comprises a transition metal oxide material that is selected from a hafnium oxide based material or a perovskite material, and wherein the ferroelectric material layer is single crystalline or polycrystalline with a predominant crystallographic orientation that is aligned along a vertical direction.
11. A memory device comprising at least one magnetoresistive memory cell which comprises:
a first terminal electrode;
a second terminal electrode;
a magnetoresistive layer stack comprising a reference layer, a free layer and a dielectric tunnel barrier layer located between the reference layer and the free layer, wherein the magnetoresistive layer stack is located between the first terminal electrode and the second terminal electrode;
a perpendicular magnetic anisotropy (PMA) layer having a higher PMA than a PMA of the free layer, wherein the PMA layer is located between the second terminal electrode and the magnetoresistive layer stack;
a nonmagnetic electrically conductive layer located between the PMA layer and the free layer; and
a ferroelectric material layer located between the PMA layer and the second terminal electrode;
wherein:
the free layer comprises a CoFe or CoFeB ferromagnetic layer; and
the PMA layer comprises a FePt or FePd ferromagnetic layer or a Co/Pt multilayer.
12. A memory device comprising at least one magnetoresistive memory cell which comprises:
a first terminal electrode;
a second terminal electrode;
a magnetoresistive layer stack comprising a reference layer, a free layer and a dielectric tunnel barrier layer located between the reference layer and the free layer, wherein the magnetoresistive layer stack is located between the first terminal electrode and the second terminal electrode;
a perpendicular magnetic anisotropy (PMA) layer having a higher PMA than a PMA of the free layer, wherein the PMA layer is located between the second terminal electrode and the magnetoresistive layer stack;
a nonmagnetic electrically conductive layer located between the PMA layer and the free layer;
a ferroelectric material layer located between the PMA layer and the second terminal electrode;
a middle electrode located between the ferroelectric material layer and the PMA layer;
a programming circuit electrically connected to the middle electrode and the second terminal electrode and configured to apply two types of programming voltages between the middle electrode and the second terminal electrode, wherein the two types of programming voltages have two different polarities and have magnitudes that induce a ferroelectric transition of the ferroelectric material layer between the two stable ferroelectric states; and
a sensing circuit electrically connected to the first terminal electrode and the middle electrode and configured to apply a sensing voltage between the first terminal electrode and the middle electrode to determine a tunneling magnetoresistance across the magnetoresistive layer stack.