Devices and circuits based on magnetic tunnel junctions utilizing a multilayer barrier

• US 20080061388A1
• Filed: 09/13/2006
• Published: 03/13/2008
• Est. Priority Date: 09/13/2006
• Status: Active Grant

• Current Assignee: Samsung Semiconductor Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Grandis, Inc. (Samsung Electronics Co. Ltd.)
• Inventors: Huai, Yiming, Diao, Zhitao
• Granted Patent: US 7,851,840 B2
• Time in Patent Office: Days
• US Class Current: 257/421
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

Devices having magnetic or magnetoresistive tunnel junctions (MTJS) have a multilayer insulator barrier layer to produce balanced write switching currents in the device circuitry, or to produce the magnetic devices with balanced critical spin currents required for spin torque transfer induced switching of the magnetization, or both for the MTJs under both the forward and reversed bias directions.

Claims

1. A device, comprising:

a magnetoresistive tunnel junction (MTJ) which comprises;

a free ferromagnetic layer having a magnetization direction that is changeable;

a pinned ferromagnetic layer having a magnetization direction fixed along a predetermined direction; and

an insulator barrier structure formed between the free and pinned ferromagnetic layers and configured to comprise at least first and second insulator barrier layers that have different dielectric constants.

2. The device as in claim 1, wherein the insulator barrier structure has a multilayer structure which comprises more than two insulator barrier layers.

3. The device as in claim 1, wherein at least one of the first and the second insulator barrier layers comprises at least one of an oxide, a nitride and a nitridoxide.

4. The device as in claim 3, wherein at least one of the first and the second insulator layers comprises an oxide of Al, Ti, Zn, Zr, Hf, Nb, Zn, Ce, Ta and Mg.

5. The device as in claim 3, wherein at least one of the first and the second insulator layers comprises AlN, TiN, or TaN.

6. The device as in claim 1, wherein at least one of the first and second insulator barrier layers is made of an amorphous material.

7. The device as in claim 6, wherein both the first and the second insulator barrier layers are made of amorphous materials.

8. The device as in claim 1, wherein at least one of the first and second insulator barrier layers is made of a crystalline material.

9. The device as in claim 8, wherein both the first and the second insulator barrier layers are made of crystalline materials.

10. The device as in claim 1, wherein at least one of the first and the second insulator barrier layers comprises a composite layer that comprises at least two different insulator barrier layers.

11. The device as in claim 1, wherein either of the first and second insulator barrier layers has a thickness between 5 Å

and 50 Å

.

12. The device as in claim 1, further comprising:

a substrate on which the MTJ is formed;

wherein the pinned ferromagnetic layer is formed above the substrate and below the first and second insulator barrier layers, and the free ferromagnetic layer,

wherein the first insulator barrier layer is adjacent to the free ferromagnetic layer and the second insulator barrier layer is adjacent to the pinned ferromagnetic layer, and

wherein the first insulator barrier layer has a smaller dielectric constant than the second insulator barrier layer.

13. The device as in claim 12, further comprising:

a spacer layer, which is non-magnetic and electrically conductive, formed on top of the free ferromagnetic layer; and

a second pinned ferromagnetic layer formed on top of the spacer layer to construct a spin valve with the spacer layer and the free ferromagnetic layer.

14. The device as in claim 12, further comprising:

a third insulator barrier layer formed on top of the free ferromagnetic layer; and

a second pinned ferromagnetic layer formed on top of the spacer layer to construct a second MTJ with the third insulator barrier layer and the free ferromagnetic layer.

15. The device as in claim 14, wherein the third insulator barrier layer includes a material used for one of the first and second insulator barrier layers.

16. The device as in claim 14, wherein the third insulator barrier material includes an oxide, a nitride, or a nitrioxide.

17. The device as in claim 1, further comprising:

a substrate on which the MTJ is formed;

wherein the free ferromagnetic layer is formed above the substrate and below the first and second insulator barrier layers, and the pinned ferromagnetic layer,

wherein the first insulator barrier layer is adjacent to the pinned ferromagnetic layer and the second insulator barrier layer is adjacent to the free ferromagnetic layer, and

wherein the first insulator barrier layer has a smaller dielectric constant than the second insulator barrier layer.

18. The device as in claim 17, further comprising:

a spacer layer, which is non-magnetic and electrically conductive, formed above the substrate and below the MTJ; and

a second pinned ferromagnetic layer formed above the substrate and below the spacer layer to construct a spin valve with the spacer layer and the free ferromagnetic layer.

19. The device as in claim 18, wherein the spacer layer comprises two nonmagnetic metal layers and an oxide layer between the two nonmagnetic metal layers.

20. The device as in claim 19, wherein one of the two nonmagnetic metal layers comprises at least one of or an alloy of Cu, Ag, Pt, Ru, Re, Rh, Ta and Ti.

21. The device as in claim 17, further comprising:

a third insulator barrier layer formed above the substrate and below the free ferromagnetic layer; and

a second pinned ferromagnetic layer formed above the substrate and below the third insulator barrier layer to construct a second MTJ with the third insulator barrier layer and the free ferromagnetic layer.

22. The device as in claim 21, wherein the third insulator barrier layer includes a material used for one of the first and second insulator barrier layers.

23. The device as in claim 21, wherein the third insulator barrier material includes an oxide, a nitride, or a nitrioxide.

24. The device as in claim, 1, further comprising:

a transistor electrically connected to the MTJ in series to supply a current to the MTJ to switch the magnetization of the free ferromagnetic layer.

25. The device as in claim 24, further comprising:

a plurality of MTJs similarly constructed as the MTJ to form an MTJ array with the MTJ; and

a plurality of transistors, each electrically connected to a respective one of the plurality of MTJs in series to supply a current to the respective MTJ to switch the magnetization of the free ferromagnetic layer.

26. The device as in claim 1, wherein the free ferromagnetic layer comprises a non-magnetic middle layer, a first ferromagnetic layer on one side of the non-magnetic middle layer and second ferromagnetic layer on the other side of the non-magnetic middle layer.

27. A device, comprising:

a magnetoresistive tunnel junction (MTJ) which comprises;

a free ferromagnetic layer having a magnetization direction that is changeable,

a pinned ferromagnetic layer having a magnetization direction fixed along a predetermined direction, and

an insulator barrier structure between the free and pinned ferromagnetic layers to comprise at least first and second insulator barrier layers that have different electrical barrier energies to provide different electrical properties when two opposite electrical bias voltages are applied between the free ferromagnetic layer and the pinned ferromagnetic layer.

28. The device as in claim 27, wherein at least one of the first and the second insulator barrier layers comprises at least one of an oxide, a nitride and a nitridoxide.

29. The device as in claim 27, wherein at least one of the first and the second insulator barrier layers comprises a composite layer comprising at least two different insulator layers.

30. The device as in claim 27, wherein the free ferromagnetic layer comprises a non-magnetic middle layer, a first ferromagnetic layer on one side of the non-magnetic middle layer and second ferromagnetic layer on the other side of the non-magnetic middle layer.

31. The device as in claim 27, further comprising:

a spacer layer, which is non-magnetic and electrically conductive, formed adjacent to the free ferromagnetic layer on one side of the free ferromagnetic layer that is opposite to another side where the first and second insulator barrier layers are located; and

a second pinned ferromagnetic layer formed adjacent to the spacer layer to construct a spin valve with the spacer layer and the free ferromagnetic layer which is shared by the spin valve and the MTJ.

32. The device as in claim 27, further comprising:

a third insulator barrier layer formed adjacent to the free ferromagnetic layer on one side of the free ferromagnetic layer that is opposite to another side where the first and second insulator barrier layers are located; and

a second pinned ferromagnetic layer formed adjacent to the third insulator barrier layer to construct a second MTJ with the third insulator barrier layer and the free ferromagnetic layer which is shared by the second MTJ and the MTJ.

33. A method, comprising:

providing a control circuit for a magnetoresistive tunnel junction (MTJ) to apply a forward electrical bias or a reversed electrical bias across the MTJ to effectuate a switching of a magnetization direction in the MTJ via a spin torque transfer is effect, wherein the control circuit has an electrical asymmetry in applying the forward electrical bias and the reversed electrical bias; and

providing a multilayer structure as the MTJ to include a free ferromagnetic layer having a magnetization direction that is changeable, a pinned ferromagnetic layer having a magnetization direction fixed along a predetermined direction, and an insulator barrier structure between the free and pinned ferromagnetic layers to comprise at least first and second insulator barrier layers that have different electrical properties of the MTJ under the forward electrical bias and the reversed electrical bias to negate the electrical asymmetry of the control circuit in applying the forward electrical bias and the reversed electrical bias at the MTJ.

34. The method as in claim 33, further comprising:

making the first and second insulator barrier layers to have different dielectric constants; and

connecting the MTJ to the control circuit to reversely bias the MTJ when applying a current to switch the MTJ from a state when the magnetization of the free ferromagnetic layer is parallel to the magnetization of the pinned ferromagnetic layer to a state when the magnetizations of the free ferromagnetic layer and the pinned ferromagnetic layer are anti-parallel, to negate an asymmetry of a critical spin current for switching the magnetization direction of the free ferromagnetic layer in applying the forward electrical bias and the reversed electrical bias at the bi-layer MTJ.