Low resistance tunneling magnetoresistive sensor with composite inner pinned layer
A high performance TMR sensor is fabricated by employing a composite inner pinned (AP 1 ) layer in an AP 2 /Ru/AP 1 pinned layer configuration. In one embodiment, there is a 10 to 80 Angstrom thick lower CoFeB or CoFeB alloy layer on the Ru coupling layer, a and 5 to 50 Angstrom thick Fe or Fe alloy layer on the CoFeB or CoFeB alloy, and a 5 to 30 Angstrom thick Co or Co rich alloy layer formed on the Fe or Fe alloy. A MR ratio of about 48% with a RA of <2 ohm-um 2 is achieved when a CoFe AP 2 layer, MgO (NOX) tunnel barrier, and CoFe/NiFe free layer are used in the TMR stack. Improved RA uniformity and less head noise are observed. Optionally, a CoFe layer may be inserted between the coupling layer and CoFeB or CoFeB alloy layer to improve pinning strength and enhance crystallization.
1. A pinned layer in a magnetoresistive element of a magnetic device, comprising:
(a) an outer pinned (AP 2 ) layer;
(b) a coupling layer having one side formed on the AP 2 layer; and
(c) an inner pinned (AP 1 ) layer formed on a side of the coupling layer opposite the AP 2 layer, said AP 1 layer has a composite configuration comprised of at least a
(1) a CoFeB or CoFeB alloy layer;
(2) a Fe or Fe alloy layer formed on the CoFeB or CoFeB alloy layer; and
(3) a Co or Co alloy layer formed on the Fe or Fe alloy layer wherein said Co or Co alloy layer contacts a tunnel barrier layer in the magnetoresistive element.
2. The pinned layer of claim 1 wherein said magnetoresistive element is a tunneling magnetoresistive (TMR) sensor further comprised of a seed layer formed on a substrate, an anti-ferromagnetic (AFM) layer on the seed layer, a free layer formed on the tunnel barrier layer, and a capping layer on the free layer, said AP 2 layer contacts the AFM layer.
3. The pinned layer of claim 1 wherein the CoFeB or CoFeB alloy has a thickness between about 10 and 80 Angstroms, the Fe or Fe alloy layer has a thickness from about 5 to 50 Angstroms, and the Co or Co alloy layer has a thickness between about 5 and 30 Angstroms.
4. The pinned layer of claim 1 wherein the CoFeB layer has a composition represented by Co (100-X-Y) Fe X B Y where x is from about 5 to 95 atomic % and y is from about 5 to 40 atomic %.
5. The pinned layer of claim 1 wherein the Fe alloy comprises Co, Ni, or B and has a Fe content of at least 25 atomic %, the Co alloy has a Co content of greater than 90 atomic %, and the CoFeB alloy has a composition represented by CoFeBM where M is one or more of Ni, Zr, Hf, Ta, Mo, Nb, Pt, Cr, Si, and V.
6. The pinned layer of claim 1 wherein the AP 1 layer is further comprised of a CoFe layer formed between the coupling layer and the CoFeB or CoFeB alloy layer.
7. The pinned layer of claim 1 wherein the tunnel barrier layer is comprised of MgO, AlOx, TiOx, TiAlOx, MgZnOx, or any combination of the aforementioned materials.
8. A TMR sensor in a magnetic device, comprising:
a seed layer, AFM layer, pinned layer, tunnel barrier layer, free layer, and capping layer that are sequentially formed on a substrate, said pinned layer is comprised of
(a) an outer pinned (AP 2 ) layer formed on the AFM layer;
(b) a coupling layer having one side formed on the AP 2 layer; and
(c) an inner pinned (AP 1 ) layer formed on a side of the coupling layer opposite the AP 2 layer, said AP 1 layer has a composite configuration comprised of at least
(1) a CoFeB or CoFeB alloy layer;
(2) a Fe or Fe alloy layer formed on the CoFeB or CoFeB alloy layer; and
(3) a Co or Co alloy layer formed on the Fe or Fe alloy layer wherein said Co or Co alloy layer contacts the tunnel barrier layer.
9. The TMR sensor of claim 8 wherein said AP 2 layer is CoFe, the coupling layer is Ru, and the AP 1 layer has a CoFeB/Fe/Co configuration in which the CoFeB layer has a thickness between about 5 and 50 Angstroms and a composition represented by Co (100-X-Y) Fe X B Y where x is from about 5 to 95 atomic % and y is from about 5 to 40 atomic %, the Fe layer has a thickness from about 5 to 50 Angstroms, and the Co layer has a thickness from about 5 to 30 Angstroms.
10. The TMR sensor of claim 8 wherein the AP 1 layer is further comprised of a CoFe layer formed between the CoFeB or CoFeB alloy layer and the coupling layer.
11. The TMR sensor of claim 8 wherein the Fe alloy comprises Co, Ni, or B and has a Fe content of at least 25 atomic %, the Co alloy has a Co content of greater than 90 atomic %, and the CoFeB alloy has a composition represented by CoFeBM where M is one or more of Ni, Zr, Hf, Ta, Mo, Nb, Pt, Cr, Si, and V.
12. The TMR sensor of claim 9 wherein the seed layer is Ta/Ru, the AFM layer is IrMn, the tunnel barrier layer is comprised of MgO, the free layer is made of CoFe/NiFe, and the capping layer has a Ta/Ru configuration.
13. A method of forming a pinned layer in a TMR sensor in a magnetic device, comprising:
(a) forming an outer (AP 2 ) layer;
(b) forming a coupling layer having one side on the AP 2 layer; and
(c) forming an inner (AP 1 ) layer on a side of the coupling layer opposite the AP 2 layer, said AP 1 layer has a composite configuration comprised of
(1) a CoFeB or CoFeB alloy layer;
(2) a Fe or Fe alloy layer formed on the CoFeB or CoFeB alloy layer; and
(3) a Co or Co alloy layer formed on the Fe or Fe alloy layer wherein said Co or Co alloy layer contacts a tunnel barrier layer in the TMR sensor.
14. The method of claim 13 wherein said TMR sensor is further comprised of a seed layer formed on a substrate, an anti-ferromagnetic (AFM) layer on the seed layer, a free layer formed on the tunnel barrier layer, and a capping layer on the free layer, said AP 2 layer contacts the AFM layer.
15. The method of claim 13 further comprised of forming an additional AP 1 layer made of CoFe between the CoFeB or CoFeB alloy layer and coupling layer.
16. The method of claim 13 wherein the CoFeB or CoFeB alloy layer has a thickness between about 10 and 80 Angstroms and a composition represented by Co (100-X-Y) Fe X B Y where x is from about 5 to 95 atomic % and y is from about 5 to 40 atomic %, or a composition represented by CoFeBM where M is one or more of Ni, Zr, Hf, Ta, Mo, Nb, Pt, Cr, Si, and V.
17. The method of claim 13 wherein the Co or Co alloy layer has a thickness between about 5 and 30 Angstroms and the Co alloy has a Co content greater than 90 atomic %, and said Fe or Fe alloy layer has a thickness of about 5 to 50 Angstroms and the Fe alloy comprises Co, Ni, or B and has a Fe content of at least 25 atomic %.
18. The method of claim 13 further comprised of annealing the TMR sensor comprising said pinned layer at a temperature between about 240° C. and 340° C.
19. The method of claim 13 further comprising the formation of a surfactant layer between the CoFeB or CoFeB alloy layer and the Co or Co alloy layer, or forming a surfactant layer between the Co or Co alloy layer and the tunnel barrier layer.
20. The method of claim 13 further comprising a plasma treatment of the CoFeB or CoFeB alloy layer prior to forming the Co or Co alloy layer, or a plasma treatment of the Co or Co alloy layer prior to forming the tunnel barrier layer.