TMR Device with Novel Free Layer Structure

• US 20150249210A1
• Filed: 05/15/2015
• Published: 09/03/2015
• Est. Priority Date: 09/22/2008
• Status: Active Grant

• Current Assignee: Headway Technologies Incorporated (TDK Corporation)
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Zhao, Tong, Wang, Hui-Chuan, Zhou, Yu-Chen, Li, Min, Zhang, Kunliang
• Granted Patent: US 9,437,812 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• 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 5/3909 Arrangements using a magnetic tunnel junction
• CPC Class Codes: G11B 5/3929 Disposition of magnetic thin films not used for directly coupling magnetic flux from the track to the MR film or for shielding
• 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 428/1121 Multilayer
• CPC Class Codes: Y10T 428/1143 with defined structural feature

Abstract

A method of fabricating 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. 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 TMR sensor may be annealed with a one step or two step process. 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.

Claims

1. A method of forming a sensor element in a magnetic device, comprising:

(a) sequentially forming a stack of layers comprised of a seed layer, anti-ferromagnetic (AFM) layer, and a SyAP pinned layer having an AP2/coupling/AP1 configuration on a substrate wherein the AP2 layer contacts said AFM layer;

(b) forming a tunnel barrier having a first surface that contacts the AP1 layer and a second surface opposite the first surface;

(c) forming a composite free layer on the tunnel barrier, the composite free layer is comprised of;

(1) at least one CoFeB, CoFeBM, CoB, CoBM, or CoBLM layer having a first thickness and where L and M are one of Ni, Ta, Ti, W, Zr, Hf, Tb, or Nb, L is unequal to M, and said at least one CoFeB, CoFeBM, CoB, CoBM, or CoBLM layer is formed in an alternating configuration with the plurality of CoFe, CoFeM, or CoFeLM layers; and

(2) a plurality of CoFe, CoFeM, or CoFeLM layers each having a second thickness less than the first thickness, and one of the CoFe, CoFeM, or CoFeLM layers contacts said second surface of the tunnel barrier; and

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

2. The method of claim 1 wherein the first thickness of each of the at least one CoFeB, CoFeBM, CoB, CoBM, and CoBLM layers is about 10 Angstroms to 80 Angstroms.

3. The method of claim 1 wherein the second thickness is from about 2 to 8 Angstroms.

4. The method of claim 1 wherein the tunnel barrier is comprised of MgO, MgZnO, ZnO, Al₂O₃, TiOx, AlTiO, HfOx, ZrOx, or a combination of two or more of the aforementioned materials.

5. The method of claim 1 wherein the tunnel barrier is MgO and is formed by a process of DC sputter depositing a first Mg layer, performing a natural oxidation process to yield a MgO layer, and then DC sputter depositing a second Mg layer on said MgO layer.

6. The method of claim 1 further comprised of annealing the sensor element in a vacuum oven within a temperature range of about 240°

C. to 340°

C. with an applied magnetic field of 2000 Oe to 8000 Oe for about 2 to 10 hours.

7. The method of claim 1 further comprised of a two step annealing process wherein a first anneal is performed at a temperature of about 250°

C. for 3 hours, and a second anneal is performed at a temperature of about 280°

C. for 1.5 hours with an applied field of 8000 Oe.