Spin-valve magnetoresistance sensor having minimal hysteresis problems

• US 5,747,997 A
• Filed: 06/05/1996
• Issued: 05/05/1998
• Est. Priority Date: 06/05/1996
• Status: Expired due to Fees

• Current Assignee: Regents of The University of Minnesota (University of Minnesota)
• Original Assignee: Regents of The University of Minnesota (University of Minnesota)
• Inventors: Moran, Timothy J., Dahlberg, E. Dan
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): Patidar, Jay M.
• Application Number:
  US08/655,222
• Time in Patent Office: 699 Days
• Field of Search: 324/207.21, 324/244, 324/249, 324/252, 324/260, 324/253, 338/32 R, 360/113, 360/111, 33/318, 33/355 R, 33/361, 33/352, 33/354, 368/14
• US Class Current: 324/252
• 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: G01C 17/30 Earth-inductor compasses
• CPC Class Codes: G01R 33/04 using the flux-gate principle
• CPC Class Codes: G01R 33/09 Magnetoresistive devices
• CPC Class Codes: G11B 2005/0016 of magnetoresistive transducers
• 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 5/012 Recording on, or reproducing or erasing from, magnetic disks G11B17/00, G11B19/00 take precedence
• CPC Class Codes: G11B 5/3903 using magnetic thin film layers or their effects, the films being part of integrated structures
• CPC Class Codes: G11B 5/3932 Magnetic biasing films
• CPC Class Codes: G11B 5/399 with intrinsic biasing, e.g. provided by equipotential strips
• CPC Class Codes: G11B 5/465 Arrangements for demagnetisation of heads
• CPC Class Codes: H01F 10/32 Spin-exchange-coupled multilayers, e.g. nanostructured superlattices applying spin-exchange-coupled multilayers to substrates H01F41/302
• CPC Class Codes: H01F 10/324 Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer
• CPC Class Codes: H01F 10/3295 Spin-exchange coupled multilayers wherein the magnetic pinned or free layers are laminated without anti-parallel coupling within the pinned and free layers
• CPC Class Codes: H10N 50/85 Magnetic active materials

Abstract

The present invention provides a method and apparatus for utilizing spin valve magnetoresistance devices for the measurement of weak magnetic fields. The magnetoresistive element consists of a pinned ferromagnetic layer and a soft ferromagnetic layer separated by a thin spacer layer. The pinned layer may be pinned by high intrinsic coercivity, or by a neighboring antiferromagnet or high coercivity ferromagnet layer. An oscillating magnetic field is applied to the device. The amplitude of the excitation field is large enough to reverse the magnetization of the soft layer during each cycle, but small enough that the magnetization direction of the pinned layer is not much affected. In one embodiment, the applied field is applied using a current strip deposited onto the top of the other layers, so that the entire device can be produced on a single chip.

Claims

1. A thin film magnetic compass comprising;

a substrate;

a pinned-layer spin-valve magnetoresistive device on the substrate forming a magnetic core;

an excitation strip on the magnetoresistive device;

a driving circuit coupled to the excitation strip that provides a drive signal for producing an oscillating magnetic field that drives the magnetic core into magnetic saturation using the excitation strip and then allows the magnetic core to come out of saturation;

a sensing circuit that measures a sensor output signal from the magnetoresistive device the sensor output signal including a signal component representative of an external applied magnetic field.

2. The magnetic-field sensor of claim 1, wherein the excitation strip includes a conducting strip separated from the magnetoresistive device by an insulating layer.

3. The magnetic-field sensor of claim 1, wherein the drive signal oscillates as substantially a triangle wave.

4. The magnetic-field sensor of claim 1, wherein the drive signal oscillates about a total bias value.

5. The magnetic-field sensor of claim 4, wherein a feedback signal is coupled to the driving circuit to provide a feedback component that varies the total bias value so as to keep the sensing element in a range chosen to achieve sensitivity and/or linearity.

6. The magnetic-field sensor of claim 1, wherein the drive signal oscillates as substantially a triangle wave about the total bias value.

7. The magnetic field sensor of claim 6, wherein a feedback signal is coupled to the driving circuit to provide a feedback component that varies the total bias value so as to keep the sensing element in a range chosen to achieve sensitivity and/or linearity.

8. The magnetic-field sensor of claim 1, wherein the sensing circuit measures a time proportion representative of a ratio of a time that the magnetic-field sensor is in a first saturated state to a time that the magnetic-field sensor is in a second saturated state, and generates an output signal representative of the external applied magnetic field.

9. The magnetic-field sensor of claim 1, wherein the sensing circuit comprises a two-omega mixer.

10. The magnetic-field sensor of claim 1, further comprising an output circuit coupled to the drive signal, the output circuit including a low-pass filter that removes an oscillating signal component of the drive signal, and generates an output signal representative of the external applied magnetic field.