TMR device with novel free layer structure
A TMR sensor that includes a free layer having at least one B-containing (BC) layer made of CoFeB, CoFeBM, CoB, COBM, or CoBLM, and a plurality of non-B containing (NBC) layers made of CoFe, CoFeM, or CoFeLM is disclosed where L and M are one of Ni, Ta, Ti, W, Zr, Hf, Tb, or Nb. One embodiment is represented by (NBC/BC) n where n≧2. A second embodiment is represented by (NBC/BC) n /NBC where n≧1. In every embodiment, a NBC layer contacts the tunnel barrier and NBC layers each with a thickness from 2 to 8 Angstroms are formed in alternating fashion with one or more BC layers each 10 to 80 Angstroms thick. Total free layer thickness is <100 Angstroms. The free layer configuration described herein enables a significant noise reduction (SNR enhancement) while realizing a high TMR ratio, low magnetostriction, low RA, and low Hc values.
1. A magnetoresistive element in a magnetic device, comprising:
(a) a synthetic anti-parallel (SyAP) pinned layer;
(b) a free layer consisting of (CoFeTb/CoFeB) n , (CoFeTb/CoFeBTb) n ,(CoFeTbL/CoFeB) n , or (CoFeTbL/CoFeBTb) n wherein n≧2, L is one of Ni, Ti, W, Zr, Hf, or Nb and has a content greater than 0 atomic %, and each of said CoFeB or CoFeBTb layers has a greater thickness than each of said CoFeTb, or CoFeTbL layers in the free layer wherein a boron containing layer alternates with a non-boron containing layer, and all layers in the free layer have at least one non-magnetic element, and;
(c) a tunnel barrier layer having a first surface that contacts the SyAP pinned layer and a second surface that contacts a CoFeTb, or CoFeTbL layer in said free layer wherein said second surface is opposite said first surface.
2. The magnetoresistive element of claim 1 wherein the boron content in each of said CoFeB layers is between about 10 and 40 atomic % and the boron content in each of said CoFeBTb layers is between about 5 and 40 atomic %.
3. The magnetoresistive element of claim 1 wherein each of said CoFeTb, or CoFeTbL layers has a thickness between about 2 and 8 Angstroms and each of said CoFeB or CoFeBTb layers has a thickness from about 10 to 80 Angstroms.
4. The magnetoresistive element of claim 1 wherein the tunnel barrier layer is comprised of MgO, MgZnO, ZnO, Al 2 O 3 , TiOx, AITiO, HfOx, ZrOx, or a combination of two or more of the aforementioned materials.
5. The magnetoresistive element of claim 1 wherein Tb in the CoFeTb or CoFeBTb layer is less than about 10 atomic %.
6. The magnetoresistive element of claim 1 wherein a total of L and Tb in the CoFeTbL layer is less than about 10 atomic %.
7. The magnetoresistive element of claim 1 wherein the free layer has a thickness less than about 100 Angstroms.
8. A magnetoresistive element in a magnetic device, comprising:
(a) a synthetic anti-parallel (SyAP) pinned layer;
(b) a free layer consisting of (CoFeTb/[Co (100-X) Fe X ] 100-Y B Y ) n , (CoFeTb/CoFeBTb) n , (CoFeTbL/[Co (100-X) Fe X ] 100-Y B Y ) n , or (CoFeTbL/CoFeBTb) n wherein n≧2, x=0 or 100 atomic %, y is from 10 to 40 atomic %, L is one of Ni, Ta, Ti, W, Zr, Hf, or Nb and has a content greater than 0 atomic %, and each of said [Co (100-X) Fe X ] 100-Y B Y or CoFeBTb layers has a greater thickness than each of said CoFeTb, or CoFeTbL layers in the free layer wherein a boron containing layer alternates with a non-boron containing layer, and all layers in the free layer have at least one non-magnetic element, and;
(c) a tunnel barrier layer having a first surface that contacts the SyAP pinned layer and a second surface that contacts a CoFeTb, or CoFeTbL layer in said free layer wherein said second surface is opposite said first surface.