Tunneling magnetoresistance (TMR) read sensor with a long diffusion path and ex-situ interfaces in a sense layer structure
The invention provides a tunneling magnetoresistance (TMR) read sensor with a long diffusion path and ex-situ interfaces in a sense layer structure. The sense layer structure comprises a first sense layer preferably formed of a ferromagnetic Co—Fe film, a second sense layer preferably formed of a ferromagnetic Co—Fe—B film, and a third sense layer preferably formed of a ferromagnetic Ni—Fe film. The sense layer structure has a long diffusion path (defined as a total thickness of the first and second sense layers) and ex-situ interfaces for suppressing unwanted diffusions of Ni atoms. Alternatively, the sense layer structure comprises a first sense layer preferably formed of a ferromagnetic Co—Fe film, a second sense layer preferably formed of a ferromagnetic Co—Fe—B film, a third sense layer preferably formed of a ferromagnetic Co—Fe—B—Hf film, and a fourth sense layer preferably formed of a ferromagnetic Ni—Fe film.
1. A read sensor, comprising:
a barrier layer sandwiched between a lower sensor stack and an upper sensor stack;
the lower sensor stack comprising:
a pinning layer;
a keeper layer structure on the pinning layer;
an antiparallel-coupling layer on the keeper layer structure; and
a reference layer structure on the antiparallel-coupling layer;
the upper sensor stack comprising:
a sense layer structure that includes a first layer comprising CoFe formed on the barrier layer, a second layer consisting of CoFeB having a thickness of 2 to 4.8 nm and formed directly on the first layer and a third layer consisting of NiFe formed directly on the second layer, wherein the total thickness of the first sense layer and the second sense layer is large enough to form a sufficiently long diffusion path to trap Ni atoms thereby preventing Ni atoms from migrating from the third layer to the barrier layer; wherein the sense structure has a diffusion path (defined as the total thickness of the first and second sense layers) of at least 3.2 nm; and
a cap layer structure on the sense layer structure.
2. The read sensor as in claim 1 further comprising:
a first interface between the first and second sense layers; and
second interface between the second and third sense layers, wherein the first and second interfaces form diffusion barriers to inhibit the migration of Ni therethrough.
3. The read sensor as in claim 2 wherein the first interface between the first and second sense layers is formed by deferring the deposition of the second sense layer after the deposition of the first sense layer by transferring a wafer on which the first sense layers is deposited through a transfer module, and exposing the wafer to vacuum for an exposure time ranging from 1 to 20 minutes.
4. The read sensor as in claim 2 , wherein the second interface between the second and third sense layers is formed by deferring the deposition of the third sense layer after the deposition of the second sense layer by transferring a wafer on which the first and second sense layers are deposited through a transfer module, and exposing the wafer to vacuum for exposure time ranging from 1 to 20 minutes.
5. The read sensor as in claim 1 , wherein the first sense layer has:
a Co content ranging from 40 to 80 at %;
an Fe content ranging from 20 to 60 at %; and
a thickness ranging from 0.6 to 1.2 nm.
6. The read sensor as in claim 1 , wherein the second sense layer has:
a Co content ranging from 68 to 84 at %;
an Fe content not greater than 8 at %;
a B content ranging from 16 to 24 at %.
7. The read sensor as in claim 1 , wherein the third sense layer has:
a Ni content ranging from 92 to 100 at %;
an Fe content not greater than 8 at %; and
a thickness ranging from 2 to 8 nm.
8. The read sensor as in claim 1 , wherein the sense layer structure has a diffusion path (defined as the total thickness of the first and second sense layers) ranging from 3.2 to 4.8 nm.