Magnetic field sensor with magnetoresistance elements and conductive trace magnetic source

• US 9,605,979 B2
• Filed: 03/25/2016
• Issued: 03/28/2017
• Est. Priority Date: 12/01/2014
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Eagen, Jeffrey, David, Paul A.
• Primary Examiner(s): Renner, Craig A.
• Application Number:
  US15/080,966
• Publication Number:
  US 20160209239A1
• Time in Patent Office: 368 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G01D 5/147 influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other
• CPC Class Codes: G01D 5/16 by varying resistance
• CPC Class Codes: G01R 15/205 using magneto-resistance devices, e.g. field plates
• CPC Class Codes: G01R 33/0082 Compensation, e.g. compensating for temperature changes
• CPC Class Codes: G01R 33/091 Constructional adaptation of the sensor to specific applications
• CPC Class Codes: G11B 5/3958 the active elements being arranged in a single plane, e.g. "matrix" disposition
• CPC Class Codes: H01F 1/055 and magnetic transition metals, e.g. SmCo5

Abstract

In an embodiment, a magnetic field sensor comprises a substrate and a first magnetoresistive element supported by the substrate. The magnetic field sensor also includes a second magnetoresistive element supported by the substrate and coupled in series with the first magnetoresistive element to form a voltage node between the first and second magnetoresistive elements, and at which an output voltage is provided that changes in response to an external magnetic field. The magnetic field sensor also includes a magnetic source that produces a local magnetic field having a strength sufficient to bias the first magnetoresistive element to a resistive value that is substantially resistant to changing in response to the external magnetic field. In embodiments, additional magnetoresistive elements are included to form an H-bridge circuit.

Claims

1. A magnetic field sensor comprising:

a substrate;

a first magnetoresistive element supported by the substrate;

a second magnetoresistive element supported by the substrate and coupled in series with the first magnetoresistive element to form a voltage node between the first and second magnetoresistive elements and at which an output voltage is provided that changes in response to an external magnetic field; and

a magnetic source producing a local magnetic field having a strength sufficient to bias the first magnetoresistive element to a resistive value that is substantially resistant to changing in response to the external magnetic field;

wherein the magnetic source comprises a conductive trace supported by the substrate and configured to carry a current to provide the local magnetic field and the first magnetoresistive element is disposed atop the conductive trace.

2. The magnetic field sensor of claim 1 wherein the first and second magnetoresistive elements have a temperature coefficient that is substantially the same.

3. The magnetic field sensor of claim 1 further comprising:

a third magnetoresistive element supported by the substrate;

a fourth magnetoresistive element supported by the substrate and coupled in series with the third magnetoresistive element to form a second voltage node between the third and fourth magnetoresistive elements and at which an output voltage is provided that changes in response to an external magnetic field; and

a magnetic source producing a second local magnetic field having a strength sufficient to bias the third magnetoresistive element to a resistive value that is substantially resistant to changing in response to the external magnetic field.

4. The magnetic field sensor of claim 3 wherein the first, second, third, and fourth magnetoresistive elements form a bridge circuit.

5. The magnetic field sensor of claim 1 wherein the first and second magnetoresistive elements comprise giant-magnetoresistive elements, TMR elements, AMR elements, MTJ elements, and/or spin valve elements.

6. The magnetic field sensor of claim 1 further comprising an oxide, nitride, and/or polymer layer disposed between the first magnetoresistive element and the conductive trace.

7. The magnetic field sensor of claim 1 further comprising a current source to provide the current, wherein the current source is capable of switching a direction of flow of the current to control the resistive value of the first magnetoresistive element.

8. The magnetic field sensor of claim 1 further comprising a current source to provide the current, wherein the current source is a variable current source capable of varying a magnitude of the current to control the resistive value of the first magnetoresistive element.

9. The magnetic field sensor of claim 1 wherein the first magnetoresistive element is arranged substantially parallel to the conductive trace.

10. The magnetic field sensor of claim 1 wherein the substrate comprises an integrated circuit.

11. The magnetic field sensor of claim 1 further comprising a circuit to measure a voltage across at least one of the magnetoresistive elements to detect the external magnetic field.

12. The magnetic field sensor of claim 1 wherein the first and second magnetoresistive elements comprise spin-valves.

13. The magnetic field sensor of claim 1 wherein the resistive value corresponds to a maximum resistance or a minimum resistance of the first magnetoresistive element.

14. The magnetic field sensor of claim 1 wherein the resistive value corresponds to a saturation resistance of the first magnetoresistive element.