Magnetic pre-conditioning of magnetic sensors
View Patent ↗Methods, systems and apparatus are provided to apply a magnetic pre-conditioning to magnetic tunneling junction (MTJ) sensors and other micro-magnetic devices after fabrication but before testing, trimming or other subsequent processing. The fabricated sensor device is passed through a magnetic field that has a known direction and orientation relative to the device so that the device is placed into a known state prior to final testing and trimming. Various embodiments allow the field to be applied in situ by a permanent magnet or electromagnet as the devices are being processed by a conventional device handler or similar processing system.
1. A method executable by a handler apparatus to process a fabricated sensor device that comprises a magnetic sensing element and a flux guide aligned to direct magnetic flux toward the magnetic sensing element, the method comprising:
passing the fabricated sensor device through an externally applied magnetic field applied by an external magnetic field source that is outside of the fabricated sensor device by the handler apparatus, the externally applied magnetic field having a component aligned along a long axis of the flux guide, the component of the externally applied magnetic field having a magnitude along the long axis of the flux guide sufficient to place the flux guide of the fabricated sensor device into a known magnetic state;
prior to passing the fabricated sensor device through the externally applied magnetic field, the handler apparatus aligning the fabricated sensor device to the externally applied magnetic field so that the long axis of the flux guide is aligned to the component of the externally applied magnetic field while the fabricated sensor device passes through the externally applied magnetic field to thereby magnetically pre-condition the fabricated sensor device prior to testing and operation of the fabricated sensor device; and
after passing the fabricated sensor device through the externally applied magnetic field, the handler apparatus providing the fabricated and pre-conditioned sensor device for subsequent testing and operation of the fabricated sensor device.
2. The method of claim 1 wherein the component of the externally applied magnetic field magnetically preconditions the fabricated sensor device by making alignment of magnetic domains uniform along substantially an entirety of the long axis of the flux guide, thereby placing the flux guide into a known magnetic state.
3. The method of claim 1 wherein the external magnetic field source that applies the externally applied magnetic field is a stationary magnet.
4. The method of claim 3 wherein the passing comprises directing a moveable member of the handler apparatus to pass through the externally applied magnetic field produced by the stationary magnet, wherein the fabricated sensor device is coupled to the moveable member.
5. The method of claim 1 wherein the external magnetic field source that applies the externally applied magnetic field is an electromagnet, and wherein the method comprises activating the electromagnet as the fabricated sensor device approaches to thereby apply the externally applied magnetic field.
6. The method of claim 1 wherein the externally applied magnetic field is produced by a magnetic yoke assembly comprising a single magnet.
7. The method of claim 1 wherein the externally applied magnetic field is produced by a magnetic yoke assembly comprising two permanent magnets.
8. The method of claim 1 wherein the magnitude of the component of the externally applied magnetic field exceeds about 75 Gauss.
9. The method of claim 1 wherein the magnitude of the component of the externally applied magnetic field is about 100 Gauss.
10. A handler system for processing sensing devices, each sensing device comprising a magnetic sensing element and a flux guide aligned to direct magnetic flux toward the magnetic sensing element, the handler system comprising:
a supply source configured to receive the sensing devices after fabrication of the sensing devices;
a movable member configured to obtain the sensing devices from the supply source, to align the sensing device to an externally-applied magnetic field prior to testing and operation of the sensing device so that at least a component of the externally applied magnetic field is aligned along a long axis of the flux guide, and to move the sensing devices along a path from the supply source toward at least one test station; and
a magnetic field source external to the sensing devices that is located proximate to the path of the sensing devices to thereby apply the externally applied magnetic field to the aligned sensing devices as the movable member moves the sensing devices along the path toward the at least one test station to thereby magnetically pre-condition the sensing devices prior to testing and operation of the sensing devices.
11. The handler system of claim 10 comprising a machine vision system configured to recognize orientations of the sensing devices and to adjust the orientations of the sensing devices through actuation of the movable member.
12. The handler system of claim 10 wherein the magnetic field source comprises a magnetic yoke, the magnetic yoke comprising a crosspiece member having opposing ends and two permanent magnets each located at one of the opposing ends of the crosspiece member to thereby apply the externally applied magnetic field as the sensing devices pass between the two permanent magnets of the magnetic yoke.
13. The handler system of claim 10 wherein the magnetic field source comprises a yoke, the yoke comprising a single magnet and a region proximate the single magnet that is configured to receive the sensing devices during application of the externally applied magnetic field.
14. The handler system of claim 10 further comprising a magnetic shield between the magnetic field source and the at least one test station.
15. A magnetic yoke apparatus for providing a magnetic field to a sensing device that comprises a magnetic sensing element and a flux guide having a long axis aligned to direct magnetic flux toward the magnetic sensing element, the magnetic yoke apparatus comprising:
a crosspiece member comprising a region configured to accept the sensing device; and
a magnet disposed on the crosspiece member to thereby produce an externally applied magnetic field in the region configured to accept the sensing device, wherein the magnet is external to the sensing device and is configured to apply the externally applied magnetic field as an externally-applied field that is aligned along the long axis of the sensing device as the sensing device is placed in the region configured to accept the sensing device and to thereby magnetically pre-condition the sensing device prior to testing and operation of the sensing device.
16. The magnetic yoke apparatus of claim 15 further comprising a second magnet, wherein the crosspiece member is substantially C-shaped so that first and second ends of the crosspiece member face toward each other, and wherein the magnet and the second magnet are located near the first and second ends of the crosspiece member.
17. The magnetic yoke apparatus of claim 16 further comprising two extender members each located proximate to one of the magnets, wherein the two extender members are separated from each other by a gap corresponding to the region configured to accept the sensing device, and wherein the gap allows the sensing device to pass therethrough.
18. The magnetic yoke apparatus of claim 17 further comprising a mount coupled to the crosspiece member, wherein the mount is configured to couple the magnetic yoke apparatus to a handler system so that the magnetic yoke apparatus remains stationary with respect to the handler system, and wherein the handler system aligns the sensing device and moves the sensing device through the gap separating the two extender members to thereby apply the magnetic field to the long axis of the sensing device.