TMR device with novel free layer structure

• US 9,437,812 B2
• Filed: 05/15/2015
• Issued: 09/06/2016
• 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
• Primary Examiner(s): Bernatz, Kevin
• Application Number:
  US14/712,943
• Publication Number:
  US 20150249210A1
• Time in Patent Office: 480 Days
• Field of Search: None
• 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, CoFeBTb, CoB, CoBTb, or CoBTbL layer having a first thickness and where L is one of Ni, Ta, Ti, W, Zr, Hf, or Nb, and said at least one CoFeB, CoFeBTb, CoB, CoBTb, or CoBTbL layer is formed in an alternating configuration with the plurality of CoFeTb, or CoFeTbL layers; and

(2) the plurality of CoFeTb, or CoFeTbL layers each having a second thickness less than the first thickness, and one of the CoFeTb, or CoFeTbL 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, CoFeBTb, CoB, CoBTb, and CoBTbL 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.