Two step annealing process for TMR device with amorphous free layer

• US 20090229111A1
• Filed: 03/12/2008
• Published: 09/17/2009
• Est. Priority Date: 03/12/2008
• Status: Active Grant

• Current Assignee: Headway Technologies Incorporated (TDK Corporation)
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Zhang, Kunliang, Li, Min, Wang, Hui-Chuan, Zhao, Tong
• Granted Patent: US 9,021,685 B2
• Time in Patent Office: Days
• US Class Current: 29/603.80
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors
• CPC Class Codes: G11B 5/3163 Fabrication methods or processes specially adapted for a particular head structure, e.g. using base layers for electroplating, using functional layers for masking, using energy or particle beams for shaping the structure or modifying the properties of the basic layers
• CPC Class Codes: G11B 5/3906 Details related to the use of magnetic thin film layers or to their effects
• CPC Class Codes: G11B 5/3909 Arrangements using a magnetic tunnel junction
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: H10N 50/01 Manufacture or treatment
• CPC Class Codes: Y10T 29/49034 Treating to affect magnetic properties

Abstract

An annealing process for a TMR or GMR sensor having an amorphous free layer is disclosed and employs at least two annealing steps. A first anneal at a temperature T1 of 200° C. to 270° C. and for a t1 of 0.5 to 15 hours is employed to develop the pinning in the AFM and pinned layers. A second anneal at a temperature T2 of 260° C. to 400° C. where T2>T1 and t1>t2 is used to crystallize the amorphous free layer and complete the pinning. An applied magnetic field of about 8000 Oe is used during both anneal steps. The mechanism for forming a sensor with high MR and robust pinning may involve structural change in the tunnel barrier or at an interface between two of the layers in the spin valve stack. A MgO tunnel barrier and a CoFe/CoB free layer are preferred.

Claims

1. An annealing process for a spin valve in a magnetic read head, said spin valve is comprised of a plurality of layers including at least one AFM layer and at least one pinned layer, and has a free layer that includes at least one amorphous layer, comprising:

(a) a first anneal step comprised of applying a first temperature and a magnetic field along a certain direction for a first period of time; and

(b) a second anneal step comprised of applying a second temperature and a magnetic field along said certain direction for a second period of time wherein said second temperature is greater than said first temperature and said first period of time is longer than said second period of time.

2. The annealing process of claim 1 wherein said spin valve is a MTJ element in a TMR sensor or a magnetoresistive element in a GMR-CPP, GMR-CIP sensor, or STT-RAM device.

3. The annealing process of claim 2 wherein the MTJ element includes a tunnel barrier layer comprised of one or more of MgO, MgZnO, ZnO, Al₂O₃, TiOx, TiAlOx, HfOx, and ZrOx.

4. The annealing process of claim 3 wherein the MTJ further includes a free layer formed on the tunnel barrier layer, said free layer is a single layer comprised of Co_ZFe_XB_Y where x is from 0 to about 90 atomic %, y is about 10 to 40 atomic %, and x+y+z=100 atomic %, or is a bilayer having a Co_ZFe_(100-Z)/Co_ZFe_XB_Y, CoFe/CoB, CoNiFe/CoFeB, or CoFe/CoNiFeB configuration where z is from 0 to about 100 atomic %, or is a multilayer structure comprised of at least one CoFeB or CoNiFeB layer.

5. The annealing process of claim 1 wherein said magnetic field is from about 1000 to 20000 Oe, said first temperature is between about 200°

C. to 270°

C., said first time period is from about 0.5 to 15 hours, said second temperature is between about 260°

C. and 400°

C., and said second time period is from about 0.1 to 3 hours.

6. The annealing process of claim 4 wherein the tunnel barrier layer is comprised of MgO, the free layer is comprised of a CoFe/CoB composite, the first step includes a temperature of about 250°

C. for about 3 hours with a magnetic field of about 8000 Oe, and the second step includes a temperature of about 280°

C. for about 1.5 hours with a magnetic field of about 8000 Oe.

7. The annealing process of claim 4 wherein the free layer includes one or more layers made of CoFe, CoFeB, CoB, FeB, CoNiFe, CoNiFeB, or alloys thereof wherein the B content is at least 10 atomic %.

8. The annealing process of claim 3 wherein the two step annealing process results in a high MR ratio with robust pinning of the AFM and pinned layers because of a mechanism that involves structural change in the tunnel barrier layer or at an interface between two of the plurality of layers.

9. The annealing process of claim 1 wherein said AFM layer is comprised of IrMn, PtMn, NiMn, OsMn, RuMn, RhMn, PdMn, RuRhMn, or MnPtPd and requires annealing to enhance pinning of the AFM and pinned layers.

10. The annealing process of claim 1 further comprised of a third annealing step after the second annealing step.

11. A method of forming a sensor element in a read head, said sensor element is comprised of a plurality of layers including at least one AFM and at least one pinned layer, a tunnel barrier layer, and has a free layer that includes at least one amorphous layer, comprising:

(a) forming a stack comprised of said plurality of layers on a substrate;

(b) performing a first anneal step comprised of applying a first temperature and a magnetic field along a certain direction for a first period of time;

(c) performing a second anneal step comprised of applying a second temperature and a magnetic field along said certain direction for a second period of time wherein said second temperature is greater than said first temperature and said first period of time is longer than said second period of time; and

(d) patterning said plurality of layers.

12. The method of claim 11 wherein said sensor element is a MTJ in a TMR sensor or a magnetoresistive element in a GMR-CPP, GMR-CIP sensor, or STT-RAM device.

13. The method of claim 11 wherein the sensor element includes a tunnel barrier layer comprised of one or more of MgO, MgZnO, ZnO, Al₂O₃, TiOx, TiAlOx, HfOx, and ZrOx.

14. The method of claim 11 wherein the sensor element further includes a free layer formed on the tunnel barrier layer, said free layer is a single layer comprised of Co_ZFe_XB_Y where x is from 0 to about 90 atomic %, y is about 10 to 40 atomic %, and x+y+z=100 atomic %, or is a bilayer having a Co_ZFe_(100-Z)/Co_ZFe_XB_Y, CoFe/CoB, CoNiFe/CoFeB, or CoFe/CoNiFeB configuration where z is from 0 to about 100 atomic %, or is a multilayer structure comprised of at least one CoFeB or CoNiFeB layer.

15. The method of claim 11 where said magnetic field is from about 1000 to 20000 Oe, said first temperature is between about 200°

C. to 270°

C., said first time period is from about 0.5 to 15 hours, said second temperature is between about 260°

C. and 400°

C., and said second time period is from about 0.1 to 3 hours.

16. The method of claim 15 wherein the tunnel barrier layer is comprised of MgO, the free layer is comprised of a CoFe/CoB composite, the first step includes a temperature of about 250°

C. for about 3 hours with a magnetic field of about 8000 Oe, and the second step includes a temperature of about 280°

C. for about 1.5 hours with a magnetic field of about 8000 Oe.

17. The method of claim 11 wherein the free layer includes one or more layers made of CoFe, CoFeB, CoB, FeB, CoNiFe, CoNiFeB, or alloys thereof wherein the B content is at least 10 atomic %.

18. The method of claim 11 wherein the two step annealing process results in a high MR ratio with robust pinning of the AFM and pinned layers because of a mechanism that involves structural change in the tunnel barrier layer or at an interface between two of the plurality of layers.

19. The method of claim 11 wherein said AFM layer is comprised of IrMn, PtMn, NiMn, OsMn, RuMn, RhMn, PdMn, RuRhMn, or MnPtPd and requires annealing to enhance pinning of the AFM layer and at least one pinned layer.

20. The method of claim 11 further comprised of at least one additional annealing step after the second anneal step and before patterning said plurality of layers.