TMR device with novel free layer structure

• US 8,259,420 B2
• Filed: 02/01/2010
• Issued: 09/04/2012
• Est. Priority Date: 02/01/2010
• Status: Active Grant

• Current Assignee: Headway Technologies Incorporated
• Original Assignee: Headway Technologies Incorporated
• Inventors: Zhao, Tong, Wang, Hui Chuan, Li, Min, Zhang, Kunliang
• Primary Examiner(s): Klimowicz, Will J
• Application Number:
  US12/658,005
• Publication Number:
  US 20110188157A1
• Time in Patent Office: 946 Days
• Field of Search: 360324-3242, 148/108, 148/121, 296/030.7, 296/030.8, 296/031.3, 296/031.4
• US Class Current: 360/324.12
• CPC Class Codes: G01R 33/09 Magnetoresistive devices
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors
• CPC Class Codes: G11B 2005/3996 large or giant magnetoresistive effects [GMR], e.g. as generated in spin-valve [SV] devices
• 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: H01F 10/3254 the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
• CPC Class Codes: H01F 10/3272 by use of anti-parallel coupled [APC] ferromagnetic layers, e.g. artificial ferrimagnets [AFI], artificial [AAF] or synthetic [SAF] anti-ferromagnets
• CPC Class Codes: H01F 41/303 with exchange coupling adjustment of magnetic film pairs, e.g. interface modifications by reduction, oxidation
• CPC Class Codes: H10N 50/01 Manufacture or treatment
• CPC Class Codes: H10N 50/10 Magnetoresistive devices
• CPC Class Codes: H10N 50/85 Magnetic active materials
• CPC Class Codes: Y10T 29/49034 Treating to affect magnetic properties
• CPC Class Codes: Y10T 29/49052 by etching

Abstract

A composite free layer having a FL1/insertion/FL2 configuration where a top surface of FL1 is treated with a weak plasma etch is disclosed for achieving enhanced dR/R while maintaining low RA, and low λ in TMR or GMR sensors. The weak plasma etch removes less than about 0.2 Angstroms of FL1 and is believed to modify surface structure and possibly increase surface energy. FL1 may be CoFe, CoFe/CoFeB, or alloys thereof with Ni, Ta, Mn, Ti, W, Zr, Hf, Tb, or Nb having a (+) λ value. FL2 may be CoFe, NiFe, or alloys thereof having a (−) λ value. The thin insertion layer includes at least one magnetic element such as Co, Fe, and Ni, and at least one non-magnetic element selected from Ta, Ti, W, Zr, Hf, Nb, Mo, V, Cr, or B. When CoFeBTa is selected as insertion layer, the CoFeB:Ta ratio is from 1:1 to 4:1.

Claims

1. A magnetoresistive element in a magnetic device, comprising:

(a) a pinned layer formed on a substrate;

(b) a non-magnetic spacer with a first surface contacting the pinned layer and a second surface opposite the first surface wherein both first and second surfaces are parallel to the substrate; and

(c) a composite free layer contacting the second surface of the non-magnetic spacer;

said composite free layer is comprised of;

(1) a first ferromagnetic layer including one or more of CO_WFe_(100-W), [CO_WFe_(100-W)]_(100-Y)B_Y where w is from 0 to about 100% and y is from 10 atomic % to about 40 atomic %, and an alloy of one of the aforementioned compositions comprised of one or more additional elements including Ni, Ta, Mn, Ti, W, Zr, Hf, Tb, and Nb, said first ferromagnetic layer has a positive magnetostriction, an inner surface contacting the second surface of the non-magnetic spacer, and an outer surface opposite the inner surface that has one or both of a modified structure and increased surface energy with respect to other portions of the first ferromagnetic layer;

(2) an insertion layer with a first side contacting the outer surface of the first ferromagnetic layer, and a second side contacting a second ferromagnetic layer, said insertion layer includes at least one magnetic element selected from Fe, Co, and Ni and at least one non-magnetic element selected from Ta, Ti, W, Zr, Hf, Nb, Mo, V, Mg, or Cr; and

(3) the second ferromagnetic layer comprised of one or more of CO_WFe_(100-W) where w is from 0 to about 100 atomic %, Ni_ZFe_(100-Z) where z is from about 70% to 100%, and an alloy wherein CoFe or NiFe are combined with one or more elements selected from Ni, Ta, Mn, Ti, W, Zr, Hf, Tb, Nb, and B, said second ferromagnetic layer has a negative magnetostriction or a small positive magnetostriction (λ

) so that overall λ

for the composite free layer is less than about 5×

10<sup>−

6</sup>.

2. The magnetoresistive element of claim 1 wherein the first ferromagnetic layer has a thickness from about 2 to 40 Angstroms and is comprised of CoFeB, CoFe/CoFeB, or CoFe/CoFeB/CoFe.

3. The magnetoresistive element of claim 1 further comprised of a capping layer formed on a side of the second ferromagnetic layer that is opposite the insertion layer, and said magnetoresistive element has a bottom spin valve configuration.

4. The magnetoresistive element of claim 1 wherein the insertion layer has a thickness from about 2 to 10 Angstroms and has a CoFeBTa composition wherein the ratio of CoFeB to Ta is from about 1:

1 to 4;

1.

5. The magnetoresistive element of claim 1 wherein the second ferromagnetic layer has a thickness from about 2 to 50 Angstroms and is comprised of CoFe, NiFe, or CoFe/NiFe/CoFe.

6. The magnetoresistive element of claim 1 wherein the non-magnetic spacer is a tunnel barrier layer comprised of MgO, MgZnO, ZnO, Al₂O₃, TiOx, AlTiO, HfOx, or ZrOx, to provide a TMR sensor configuration, or is comprised of a metal to give a GMR sensor configuration.

7. The magnetoresistive element of claim 1 wherein the substrate is comprised of a seed layer and an AFM layer formed on the seed layer, said AFM layer has a surface contacting the pinned layer.

8. A magnetoresistive element in a magnetic device, comprising:

(a) a seed layer formed on a substrate;

(b) a composite free layer contacting a top surface of the seed layer;

said composite free layer is comprised of;

(1) a FL2 ferromagnetic layer comprised of one or more of CO_WFe_(100-W) where w is from 0 to about 100 atomic %, Ni_ZFe_(100-Z) where z is from 0 to 100%, and an alloy wherein CoFe or NiFe are combined with one or more elements selected from Ni, Ta, Mn, Ti, W, Zr, Hf, Tb, Nb, and B, said FL2 ferromagnetic layer has a top surface facing away from the seed layer;

(2) an insertion layer with a first side contacting the top surface of the FL2 ferromagnetic layer, and a second side contacting a FL1 ferromagnetic layer, said insertion layer includes at least one magnetic element selected from Fe, Co, and Ni and at least one non-magnetic element selected from Ta, Ti, W, Zr, Hf, Nb, Mo, V, Mg, or Cr; and

(3) a FL1 ferromagnetic layer including one or more of CO_WFe_(100-W), [CO_WFe_(100-W)]_(100-y)B_Y where w is from 0 to about 100% and y is from 10 atomic % to about 40 atomic %, and an alloy of one of the aforementioned compositions comprised of one or more additional elements including Ni, Ta, Mn, Ti, W, Zr, Hf, Tb, and Nb, said FL1 ferromagnetic layer has a positive magnetostriction, an inner surface contacting the bottom surface of a non-magnetic spacer, and an outer surface opposite the inner surface that contacts the insertion layer wherein the inner surface has one or both of a modified structure and increased surface energy with respect to other portions of the FL1 ferromagnetic layer;

(c) the non-magnetic spacer with a top surface opposite said bottom surface;

(d) a pinned layer contacting the top surface of the non-magnetic spacer;

(e) an AFM layer contacting a side of the pinned layer opposite the non-magnetic spacer; and

(f) a capping layer formed on the AFM layer.

9. The magnetoresistive element of claim 8 wherein the non-magnetic spacer is comprised of a metal and the magnetic device is a GMR-CPP sensor or a GMR-CIP sensor, or the non-magnetic spacer is a tunnel barrier layer and the magnetic device is a TMR sensor.

10. The magnetoresistive element of claim 8 wherein the FL1 ferromagnetic layer has a thickness from about 2 to 40 Angstroms and is comprised of CoFeB, CoFe/CoFeB, or CoFe/CoFeB/CoFe.

11. The magnetoresistive element of claim 8 wherein the insertion layer has a thickness from about 2 to 10 Angstroms and has a CoFeBTa composition wherein the ratio of CoFeB to Ta is about 1:

1 to 4;

1.

12. The magnetoresistive element of claim 8 wherein the FL2 ferromagnetic layer has a thickness from about 2 to 50 Angstroms and is comprised of CoFe, NiFe, or CoFe/NiFe/CoFe.

13. The magnetoresistive element of claim 8 wherein the inner surface of the FL2 ferromagnetic layer has one or both of a modified structure and increased surface energy with respect to other portions of the FL2 ferromagnetic layer.

14. A method of forming a magnetoresistive element in a TMR sensor, comprising:

(a) sequentially forming a seed layer, AFM layer, and a pinned layer on a substrate;

(b) forming a tunnel barrier layer with a top surface on said pinned layer;

(c) depositing a first ferromagnetic layer FL1 on the tunnel barrier layer, said ferromagnetic layer (FL1) free layer has an inner surface contacting the tunnel barrier layer, an outer surface facing away from the tunnel barrier layer, and is comprised of one or more of CO_WFe_(100-W), [CO_WFe_(100-W)]_(100-Y)B_Y where w is from 0 to about 100% and y is from 10 atomic % to about 40 atomic %, and an alloy of one of the aforementioned compositions comprised of one or more additional elements including Ni, Ta, Mn, Ti, W, Zr, Hf, Tb, and Nb;

(d) performing a weak plasma etch treatment (PT) on the outer surface of said first ferromagnetic layer (FL1) thereby forming a modified FL1 that has one or both of a modified structure and increased surface energy with respect to other portions of the (FL1) layer;

(e) sequentially depositing an insertion layer (INS) and a second ferromagnetic layer (FL2) on the modified surface of the first ferromagnetic layer (FL1) to give a composite free layer with a FL1(PT)/INS/FL2 configuration, said insertion layer has at least one magnetic element selected from Fe, Co, and Ni and at least one non-magnetic element selected from Ta, Ti, W, Zr, Hf, Nb, Mo, V, Mg, and Cr, and said second ferromagnetic layer is comprised of one or more of CO_WFe_(100-W) where w is from 0 to about 100 atomic %, Ni_ZFe_(100-Z) where z is from about 70% to 100%, and an alloy wherein CoFe or NiFe are combined with one or more elements selected from Ni, Ta, Mn, Ti, W, Zr, Hf, Tb, Nb, and B; and

(f) forming a capping layer on the composite free layer.

15. The method of claim 14 wherein the tunnel barrier layer is comprised of one or more of MgO, MgZnO, ZnO, Al₂O₃, TiOx, AlTiO, HfOx and ZrOx.

16. The method of claim 15 wherein formation of the MgO tunnel barrier layer is comprised of depositing a first Mg layer, performing a natural oxidation process to form a MgO layer, and then depositing a second Mg layer on the MgO layer.

17. The method of claim 14 further comprised of performing an annealing step after step (f) wherein the annealing conditions comprise a temperature between about 240°

C. and 440°

C. with an applied magnetic field of at least 2000 Oe for about 30 minutes to 10 hours.

18. The method of claim 14 wherein the first ferromagnetic layer has a thickness from about 2 to 40 Angstroms and is comprised CoFeB, CoFe/CoFeB, or CoFe/CoFeB/CoFe.

19. The method of claim 14 wherein the insertion layer has a thickness from about 2 to 10 Angstroms and has a CoFeBTa composition wherein the ratio of CoFeB to Ta is from about 1:

1 to 4;

1.

20. The method of claim 14 wherein the second ferromagnetic layer has a thickness from about 2 to 50 Angstroms and is comprised of CoFe, NiFe, or CoFe/NiFe/CoFe.

21. The method of claim 14 wherein the weak plasma etch comprises Ar or another inert gas at a pressure greater than about 0.01 Torr and with a power less than about 20 Watts.

22. The method of claim 21 wherein the weak plasma etch results in an etch rate of less than about 0.01 Angstroms per second and removes less than about 0.2 Angstroms from the outer surface of the first ferromagnetic layer.