High thermal stability free layer with high out-of-plane anisotropy for magnetic device applications

• US 8,946,834 B2
• Filed: 03/01/2012
• Issued: 02/03/2015
• Est. Priority Date: 03/01/2012
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Wang, Yu-Jen, Kula, Witold, Jan, Guenole
• Primary Examiner(s): BERNATZ, KEVIN M
• Application Number:
  US13/409,456
• Publication Number:
  US 20130230741A1
• Time in Patent Office: 1,069 Days
• Field of Search: None
• US Class Current: 257/421
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors
• CPC Class Codes: G11B 5/82 Disk carriers
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: H01F 10/123 having a L10 crystallographic structure, e.g. [Co,Fe][Pt,Pd] thin films
• CPC Class Codes: H01F 10/16 containing cobalt H01F10/126 , H01F10/13 take precedence
• CPC Class Codes: H01F 10/3231 via a non-magnetic spacer
• 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 10/3286 Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy
• CPC Class Codes: H01F 10/3295 Spin-exchange coupled multilayers wherein the magnetic pinned or free layers are laminated without anti-parallel coupling within the pinned and free layers
• CPC Class Codes: H01F 41/307 insulating or semiconductive spacer
• 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 428/1114 having tunnel junction effect
• CPC Class Codes: Y10T 428/1143 with defined structural feature

Abstract

A CoFeB or CoFeNiB magnetic layer wherein the boron content is 25 to 40 atomic % and with a thickness <20 Angstroms is used to achieve high perpendicular magnetic anisotropy and enhanced thermal stability in magnetic devices. A dusting layer made of Co, Ni, Fe or alloy thereof is added to top and bottom surfaces of the CoFeB layer to increase magnetoresistance as well as improve Hc and Hk. Another embodiment includes a non-magnetic metal insertion in the CoFeB free layer. The CoFeB layer with elevated B content may be incorporated as a free layer, dipole layer, or reference layer in STT-MRAM memory elements or in spintronic devices including a spin transfer oscillator. Thermal stability is increased such that substantial Hk is retained after annealing to at least 400° C. for 1 hour. Ku enhancement is achieved and the retention time of a memory cell for STT-MRAM designs is increased.

Claims

1. A multilayer stack in a magnetic device, comprising:

(a) a reference layer;

(b) a free layer containing at least a layer with a Co_RFe_SNi_WB_T composition wherein R, S, W, and T are the content of Co, Fe, Ni, and B respectively, R+S+W+T=100, S>

(R+W), W is greater than 0 but less than or equal to 2 atomic %, and T is from about 25 to 40 atomic %, and two dusting layers made of Co, Fe, Ni, or alloys thereof that are selected from CoFe, CoTa, CoZr, CoHf, CoMg, CoNb, CoB_V or FeB_V where v is from 0 to 40 atomic %, a first dusting layer (DL1) contacts a bottom surface of the Co_RFe_SNi_WB_T layer and a second dusting layer (DL2) contacts a top surface of the Co_RFe_SNi_WB_T layer to give a DL1/Co_RFe_SNi_WB_T/DL2 free layer configuration, the free layer maintains perpendicular magnetic anisotropy (PMA) after thermal treatment to above 400°

C.; and

(c) a tunnel barrier layer formed between the reference layer and free layer.

2. The multilayer stack of claim 1 wherein the layer with a Co_RFe_SNi_WB_T composition has a thickness from about 5 to 20 Angstroms.

3. The multilayer stack of claim 1 wherein each of the first and second dusting layers has a thickness from about 5 to 15 Angstroms.

4. The multilayer stack of claim 3 wherein one or both of the first and second dusting layers is a composite comprising a laminated structure of dusting layers.

5. The multilayer stack of claim 3 further comprised of a seed layer and a cap layer wherein the seed layer, first dusting layer, Co_RFe_SNi_WB_T layer, second dusting layer, tunnel barrier layer, reference layer, and cap layer are sequentially formed on a substrate to form a top spin valve structure.

6. The multilayer stack of claim 1 further comprised of a cap layer as an uppermost layer in the multilayer stack, the cap layer is a metal layer or a metal oxide layer that contacts a top surface of the free layer in a bottom spin valve configuration and thereby induces or enhances PMA in the free layer.

7. The multilayer stack of claim 1 wherein the reference layer exhibits PMA, a magnetization direction thereof is parallel or anti-parallel to the PMA in the free layer to establish either a 1 or 0 memory state in the magnetic device.

8. A magnetic device including a stack of layers, comprising:

(a) a reference layer with perpendicular magnetic anisotropy (PMA);

(b) a composite free layer with a Co_RFe_SNi_WB_T/M/Co_RFe_SNi_WB_T structure wherein R, S, W, and T are the content of Co, Fe, Ni, and B respectively, R+S+W+T=100, S>

(R+W), T is from about 25 to 40 atomic %, and M is a non-magnetic metal layer that is one of Cu, Al, Zr, or Mg, and further comprised of two dusting layers made of Co, Fe, Ni, or alloys thereof that are selected from NiFe, CoFe, CoTa, CoZr, CoHf, CoMg, CoNb, CoB_V, or FeB_V where v is from 0 to 40 atomic %, a first dusting layer (DL1) contacts a bottom surface of the Co_RFe_SNi_WB_T/M/Co_RFe_SNi_WB_T structure, and a second dusting layer (DL2) contacts a top surface of the Co_RFe_SNi_WB_T/M/Co_RFe_SNi_WB_T structure to give a DL1/Co_RFe_SNi_WB_T/M/Co_RFe_SNi_WB_T/DL2 composite free layer configuration wherein each of the Co_RFe_SNi_WB_T layers has perpendicular magnetic anisotropy; and

(c) a tunnel barrier layer formed between the reference layer and composite free layer.

9. The magnetic device of claim 8 wherein the stack of layers further comprises a seed layer formed on a substrate and a cap layer, the stack of layers has a bottom spin valve structure in which the seed layer, reference layer, tunnel barrier, composite free layer, and cap layer are sequentially formed on the substrate, and the cap layer is made of a metal oxide.

10. The magnetic device of claim 9 wherein the metal oxide cap layer is one of MgTaOx, MgO, SiOx, SrTiOx, BaTiOx, CaTiOx, LaAlOx, MnOx, VOx, Al₂O₃, TiOx, BOx, and HfOx, or a lamination of one or more of the aforementioned oxides.

11. The magnetic device of claim 8 wherein the metal (M) layer has a thickness between about 5 and 10 Angstroms.

12. The magnetic device of claim 8 wherein each of the Co_RFe_SNi_WB_T layers has a thickness between about 5 and 14 Angstroms.

13. The magnetic device of claim 8 wherein the composite free layer has a thickness from about 15 to 38 Angstroms.

14. The magnetic device of claim 8 wherein the first and second dusting layers each have a thickness from about 2 to 10 Angstroms.

15. The magnetic device of claim 8 wherein the reference layer exhibits PMA, a magnetization direction thereof is parallel or anti-parallel to the PMA in the composite free layer to establish either a 1 or 0 memory state in the magnetic device.

16. The magnetic device of claim 8 further comprised of a seed layer and a cap layer wherein the seed layer, the DL1/Co_RFe_SNi_WB_T/M/Co_RFe_SNi_WB_T/DL2 composite free layer, tunnel barrier layer, reference layer, and cap layer are sequentially formed on a substrate to give a top spin valve structure.

17. A magnetic device including a stack of layers, comprising:

(a) a seed layer formed on a substrate;

(b) a reference layer with perpendicular magnetic anisotropy (PMA);

(c) a composite free layer with a Co_RFe_SNi_WB_T/M/Co_RFe_SNi_WB_T configuration wherein each of the Co_RFe_SNi_WB_T layers has PMA, R, S, W, and T are the content of Co, Fe, Ni, and B respectively, R+S+W+T=100, S>

R, W is from 0 to about 2 atomic %, T is from about 25 to 40 atomic %, and M is a non-magnetic metal layer that is one of Cu, or Al;

(d) a tunnel barrier layer formed between the reference layer and composite free layer; and

(e) a cap layer as the uppermost layer in the stack of layers.

18. The magnetic device of claim 17 wherein the stack of layers is a bottom spin valve structure in which the seed layer, reference layer, tunnel barrier, composite free layer, and cap layer are sequentially formed on the substrate, and the cap layer is made of a metal oxide.

19. The magnetic device of claim 18 wherein the metal oxide cap layer is one of MgTaOx, MgO, SiOx, SrTiOx, BaTiOx, CaTiOx, LaAlOx, MnOx, VOx, Al₂O₃, TiOx, BOx, and HfOx, or a laminate of one or more of the aforementioned oxides.

20. The magnetic device of claim 17 wherein the metal (M) layer has a thickness between about 5 and 10 Angstroms.

21. The magnetic device of claim 17 wherein each of the Co_RFe_SNi_WB_T layers has a thickness between about 5 and 14 Angstroms.

22. A magnetic device including a stack of layers, comprising:

(a) a seed layer formed on a substrate;

(b) a reference layer with perpendicular magnetic anisotropy (PMA);

(c) a composite free layer with a Co_RFe_SNi_WB_T/M/Co_RFe_SNi_WB_T configuration wherein each of the Co_RFe_SNi_WB_T layers has PMA, R, S, W, and T are the content of Co, Fe, Ni, and B respectively, R+S+W+T=100, S>

R, W is from 0 to about 2 atomic %, T is from about 25 to 40 atomic %, and M is a non-magnetic metal layer that is one of Cu, Al, Zr, or Mg;

(d) a tunnel barrier layer formed between the reference layer and composite free layer; and

(e) a MgTaOx cap layer as the uppermost layer in the stack of layers.