News Column

Patent Issued for CPP-GMR Sensor with Corrosion Resistent Spacer Layer and Higher Signal/Noise Ratio

June 18, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Childress, Jeffrey R. (San Jose, CA); Read, John C. (San Jose, CA); Smith, Neil (San Jose, CA), filed on August 31, 2011, was published online on June 3, 2014.

The assignee for this patent, patent number 8743511, is HGST Netherlands B.V. (Amsterdam, NL).

Reporters obtained the following quote from the background information supplied by the inventors: "Embodiments of the present invention generally relate to giant magnetoresistive (GMR) sensors. More particularly, the invention relates to current-perpendicular-to the-plane (CPP) magnetoresistive sensors.

"Magnetic read heads in modern magnetic disk drives operate on the basis of the tunneling magnetoresistive (TMR) effect in which a component of the read element resistance varies as the cosine of the angle between the magnetization in free and reference magnetic layers which sandwich an insulating tunnel barrier layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (i.e., the signal field) causes a change in the direction of magnetization in the free layer, which in turn causes a change in resistance across the tunnel barrier in the TMR and a corresponding change in the sensing electrical current or voltage. As read head sizes scale down to accommodate increasing areal storage densities, the device resistance of TMR read heads is projected to increase beyond levels that are easily accommodated using standard detection electronics.

"A GMR sensor is an alternative to a TMR read head. A GMR read head has a resistance that varies according to the angle between the free and reference magnetic layers. Further, a GMR read head uses a sense CPP of these magnetic layers. CPP-GMR sensors primarily differ in structure from TMR read heads in that the high resistance tunnel barrier layer is replaced by a low resistance metallic spacer. Accordingly, the resistance of a CPP-GMR sensor is primarily determined by stack structure of the free layer, the reference layer, and the low resistance metallic space. Rather than spin-dependent tunneling of electrons across a barrier layer as used in a TMR sensor, the CPP-GMR sensor uses spin-dependent scattering of the conduction electrons at both the interface between the magnetic and spacer layers as well as in the magnetic layers themselves. For a given cross-section area, the device resistance of a CPP-GMR sensor will be 10-20 times smaller than for a TMR sensor.

"Because of the much lower device resistance, CPP-GMR sensors operate at much higher sense current densities if the bias voltage applied is comparable to that used in TMR sensors (e.g., 100 mV). At these higher current densities, the output signal and signal/noise ratio for a CPP-GMR sensor is limited by spin-torque effects, which originate from the torque induced on either the free or reference magnetic layers by the spin-polarized electron current density applied during operation. If too large, the spin-torque can introduce oscillatory instability of the magnetization in either the free or reference layers. Accordingly, reducing the susceptibility of a CPP-GMR read sensor to spin-torque induced instability improves its performance in magnetic recording applications.

"Moreover, during processing of a read head, a CPP-GMR sensor may be subjected to lapping or chemical mechanical polishing/planarization (CMP) during which exposed layers may begin to corrode. The metallic spacer layer may be particularly susceptible to oxidizing during this process. For example, common spacer layer materials are known to easily corrode or tarnish. During a mechanical lapping process to form the air bearing surface (ABS), these materials may oxidize and hamper the electrical current flowing between the different layers of the CPP-GMR sensor."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "One embodiment of the present invention provides a read head sensor that includes a first magnetic layer and a second magnetic layer with a spacer layer deposited in between. The spacer layer comprises an alloy, of which at least one metal of the alloy is electrically conductive. Further, the spacer layer is (i) more resistant to corrosion and (ii) increases the electrical resistivity of the read head sensor relative to a spacer layer consisting entirely of the at least one metal.

"One embodiment of the present invention provides a read head sensor that includes a first magnetic layer and a second magnetic layer with a spacer layer disposed in between. The spacer layer comprises a silver alloy.

"Another embodiment of the present invention provides a method of fabricating a read head sensor. The method includes depositing a first magnetic layer onto a substrate. The method also includes depositing a spacer layer above the first magnetic layer. The spacer layer comprises a metallic alloy, of which at least one metal in the alloy is electrically conductive. Further, the spacer layer is (i) more resistant to corrosion and (ii) increases the electrical resistivity of the read head sensor, relative to a spacer layer consisting entirely of the at least one metal. The method includes depositing a second magnetic layer above the spacer layer."

For more information, see this patent: Childress, Jeffrey R.; Read, John C.; Smith, Neil. CPP-GMR Sensor with Corrosion Resistent Spacer Layer and Higher Signal/Noise Ratio. U.S. Patent Number 8743511, filed August 31, 2011, and published online on June 3, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8743511.PN.&OS=PN/8743511RS=PN/8743511

Keywords for this news article include: HGST Netherlands B.V.

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Source: Journal of Engineering


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