Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1994-09-13
1998-01-27
O'Shea, Sandra L.
Electricity: measuring and testing
Magnetic
Magnetometers
360113, G01R 3302
Patent
active
057125651
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is a magnetoresistive (MR) sensor. More specifically, the present invention is an MR sensor having an MR layer with recessed regions and permanent magnet material contained therein.
MR sensors are used to detect magnetic flux levels stored on magnetic media. In an MR sensor, the resistivity of the sensor varies with the magnitude of the flux passing through the sensor. Typically, a constant current is passed through the sensor and the magnitude of the flux passing through the sensor is represented by a change in the voltage across the sensor, which of course is a function of the resistance of the sensor. Likewise, a constant voltage source can be applied to the MR sensor, in which case the magnetic flux magnitude is represented by a change in the current through the sensor.
In an MR sensor, a linear response is achieved when the active region of the MR sensor is magnetized at approximately 45.degree. with respect to the direction of current flow through the MR sensor. The output voltage of the MR sensor for any given input current is proportional to COS.sup.2.theta., where .theta. is the angle between the static magnetization vector and the current vector. At 45.degree., this function, in conjunction with the saturation effects in the sensor, provides maximum equal and opposite changes in output for corresponding equal and opposite deviations in magnetic flux.
While Permalloy will naturally tend to form a magnetization vector along its long axis when it is formed into a long narrow strip, it is prone to fracturing into multiple magnetic domains when exposed to an external magnetic field. This causes Barkhausen noise. In addition, some MR sensors are not formed from long narrow strips of Permalloy. Accordingly, it is known in the art to stabilize an MR sensor to a single domain state using permanent magnets.
In the prior art, sensor stabilization is typically achieved by hard biasing or by exchange coupling. Generally, hard biasing is accomplished by positioning a boundary of a permanent magnet proximate a boundary of a magnetoresistive layer. The magnetic flux emanating from the permanent magnet boundary flows into the magnetoresistive layer, thereby stabilizing the magnetoresistive layer in a single domain state.
Exchange coupling is generally achieved by depositing an antiferromagnetic layer or a permanent magnet layer over part of the magnetoresistive layer. The magnetic characteristics of added layer are exchange coupled into the magnetoresistive layer, thereby stabilizing the magnetoresistive layer. In prior an exchange coupling configurations, it is common for the permanent magnet material to form part of the current contact structure.
SUMMARY OF THE INVENTION
The present invention is a single domain magnetoresistive sensor. The sensor is comprised of a magnetoresistive layer, at least one permanent magnet, and first and second current contacts. The magnetoresistive layer is comprised of an active sensing region having a first thickness, and at least one under layer region, with each under layer region having a second thickness that is less than the first thickness. Each permanent magnet is formed upon an under layer region of the magnetoresistive layer, and the first and second contacts are electrically coupled to the active region.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a magnetoresistive (MR) sensor constructed in accordance with the present invention.
FIGS. 2-7 are sectional views showing the method of forming the sensor of FIG. 1 from the perspective of line 2--2 in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a magnetoresistive (MR) sensor 10 constructed in accordance with the present invention. Sensor 10 is comprised of MR layer 12 (typically Permalloy), permanent magnets 14a and 14b, and canted contacts 16a and 16b. MR layer 12 is comprised of active region 18 and two inactive under layer regions 26a and 26b under permanent magnets 14a and 14b. Contacts 16a and 16b overlay a portion of active region
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Bonyhard Peter I.
Calderon Arthur
Fernandez-De Castro Juan J.
George Peter K.
Longworth Leroy L.
O'Shea Sandra L.
Patidar Jay M.
Seagate Technology Inc.
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