WO1998016921A1 - Magnetoresistive head having shorted shield configuration for inductive pickup minimization - Google Patents

Abstract

A transducing head (70) has a magnetoresistive read head with an air-bearing surface. The magnetoresistive read head includes a magnetoresistive sensor (77) having an active area (79) and a shield (76, 94, 96, 98) encircling the active area (79) of the magnetoresistive sensor (77) in a plane substantially parallel to the air-bearing surface of the read head.

Description

MAGNETORESISTIVE HEAD HAVING SHORTED SHIELD CONFIGURATION FOR INDUCTIVE PICKUP MINIMIZATION

BACKGROUND OF THE INVENTION The present invention relates to a magnetoresistive disc drive head for high frequency and high data rate applications, and in particular to a magnetoresistive disc drive read head configured to reduce inductive pickup of the head to improve its signal-to-noise ratio.

Magnetoresistive (MR) sensors are used in magnetic storage systems to detect magnetically encoded information. A time dependent magnetic field from a magnetic storage medium or disc directly modulates the resistivity of the MR sensor. The change in resistance of the MR sensor can be detected by passing a sense current through the MR sensor and measuring the voltage across the MR sensor. The resulting signal can be used to recover information from a magnetic storage medium or disc.

Practical MR sensors are typically formed using ferromagnetic metal alloys because of their high magnetic permeability. A ferromagnetic metal alloy is deposited in a thin film upon an electrically insulated substrate or wafer. Changing magnetic fields originating from the magnetic storage medium produce a change in the magnetization direction of the MR sensor and thereby change the resistance of the sensor. This phenomenon is called an MR effect.

MR sensors have a maximum signal-to-noise ratio when the active region of the sensor has no movable magnetic domain boundaries or no domain boundaries. In other words, the active sense area of the MR sensor should be a single domain. The presence of domain boundaries in the sensor active area that move when a field is applied gives rise to Barkhausen noise, a phenomenon caused by the irreversible motion of a magnetic domain in the presence of an applied magnetic field. Barkhausen noise cannot occur if no domain boundaries exist. Typically, a single magnetic domain MR sensor is achieved by either utilizing geometry, via boundary control stabilization, inherent longitudinal magnetic fields, or any combination thereof.

During a read operation, an MR sensor transduces the data field of a medium directly by virtue of an MR effect and produces an MR voltage signal. However, the MR sensor also couples an ideally 90° out of phase voltage signal due to the inductive pickup from the contact loop configuration of the sensor current path providing current to the MR sensor (neglecting capacitance). The out of phase signal is undesired because it adds a coherent signal that is phase shifted away from the real MR signal attempting to be detected through use of the MR effect. Therefore, the MR sensor is detecting two different signals from a single medium. First, the MR sensor detects the MR signal representing the magnetic field directly. Second, the extended MR sensor contact structure detects the inductive pickup signal from the time rate of change of magnetic flux of the medium linked by the single-loop contact configuration of the current path. The purpose of the MR sensor is to detect the MR signal representative of the magnetic field of the medium directly, and not the inductive pickup signal from the time rate of change of the magnetic flux.

Inductive voltage signal detection is not normally associated with MR sensor operations due to the fact that most applications utilizing MR sensors have a relatively low disc velocity. The single-loop contact configuration of a conventional MR sensor current path (wherein the single loop is encompassed by the MR sensor, bond pads, and the electrical contacts connection the MR sensor to the bond pads) will not produce significant inductive time rate of change signals from a disc since its inductive output is directly proportional to a disc velocity, which itself is relatively small.

In MR sensor operations having a relatively small head disc velocity, the inductive pickup signal induced by the single-loop contact configuration of a conventional MR sensor current path is often more than 40 dB down in magnitude from the MR signal itself. As a result, induced noise does not substantially affect the MR signal due to its relatively small magnitude as compared to the MR signal. However, as the relative head disc velocity increases, the inductive pickup signal transduced by the single-loop contact configuration of the MR sensor current path can within 20 dB below the MR signal. This induced signal can represent a serious signal-to-noise ratio problem.

In high performance disc drive applications having large relative head disc velocity, the single loop contact configuration of a conventional MR sensor can transduce an inductive pickup signal which is 90° out of phase with a desired MR signal and with a magnitude that causes error by peak shifting the information away from the desired timing windows of the information channel. The inductive pickup signal results in head disc channel performance errors.

One approach to reducing the induced inductive signal picked up from the disc medium involves reconfiguring the MR sensor contact geometry. An example of this approach is disclosed in U.S. Patent No. 5,563,753 to G. Mowry et al., assigned to Seagate Technology, Inc. , showing a "figure-eight" configuration of the leads connecting the MR element to bond pads on the trailing edge surface of the disc drive slider. Even further reduction of the inductive pickup signal is desirable for high data rate applications, to maximize the signal-to-noise ratio of the MR read head.

Thus, there is a need for a disc drive head for reading an MR voltage signal representing the magnetic flux from a magnetic storage medium directly while minimizing any induced inductive pickup signal representing time rate of change of magnetic flux from the medium.

BRIEF SUMMARY OF THE INVENTION The present invention is a transducing head having a magnetoresistive read head with an air-bearing surface. The read head includes a magnetoresistive sensor having an active area and a shield encircling the active area of the magnetoresistive sensor in a plane substantially parallel to the air-bearing surface of the read head. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a disc drive slider showing the rear of the slider as it flies over a rotating disc.

FIG. 2 is a sectional view of a prior art MR sensor configuration.

FIG. 3 is a sectional view of an MR sensor configuration according to a first embodiment of the present invention. FIG. 4 is a sectional view of an MR sensor configuration according to a second embodiment of the present invention.

FIG. 5 is a graph illustrating the relative performance of the prior art MR sensor and the MR sensor of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of disc drive slider 10 showing the rear of slider 10 incorporating an MR head positioned above disc 35, which is a magnetic storage medium. Slider 10 includes head 12, rear surface 14, rails 16, pads 18, 20, 22, and 24, contacts 26, 28, 30, and 32, and recessed area 34. Rails 16 extend from rear surface 14 of slider 10 to the front surface of slider 10 (not shown in FIG. 1). Rails 16 form recessed area 34 between them. Pads 18, 20, 22, and 24 provide electrical connections to circuitry exterior to slider 10 not shown. Disc 35 includes a plurality of concentric data tracks 36 recorded on its surface.

Contacts 26, 28, 30, and 32 provide electrical connection to a pair of magnetoresistive (MR) sensors (not shown in FIG. 1) at the bottom surface of rail 16 on rear surface 14. Contacts 26, 28, 30, and 32, also known as electrical leads or electrical contacts, are formed from a high conductivity metal to ensure a proper electrical connection. Contacts 26 and 28, as well as contacts 30 and 32, are routed as close together as possible, consistent with sense current carrying capabilities and photolithography constraints.

FIG. 2 is a frontal schematic view of a prior art magnetic device 40 constructed as is known in the art to include an inductive write head and an MR read sensor 47. The sectional view shown in FIG. 2 is taken from a plane parallel to the air bearing surface of the device. In other words, the air bearing surface of device 40 is parallel to the plane of the page. The inductive write head is formed from top pole 42, shared pole 46 and insulator 44 between the two poles forming the write gap. A write coil (not shown) encircles top pole 42 through insulator layer 44 at a region set back from the air bearing surface.

MR sensor 47 is formed between shared pole 46 and bottom pole 64. Insulator 62 is formed on bottom pole 64. A soft magnetic film layer 60, also known as a soft adjacent layer (SAL), is formed on insulator 62. Spacer layer 59 and hard bias magnetic layers 56 and 58 are formed on SAL 60. MR element 50 is formed as a layer over the resulting surface, with conductors 52 and 54 formed on MR element 50 to provide electrical contacts for connection to bond pads on a disc drive slider. Alternatively, MR element 50 (contacted by conductors 52 and 54) may be formed on insulator 62, with SAL 60 being formed over hard bias layers 56 and 58 and spacer layer 59; in either case spacer layer 59 remains between MR element 50 and SAL 60 in the active region 49 between hard bias magnetic layers 56 and 58. Insulator 48 is formed between the MR sensor structure and shared pole 46. Insulators 48 and 62 may be formed of an oxide such as aluminum oxide or silicon dioxide, for example.

Hard bias layers 56 and 58 define active region 49 of MR sensor 47 between them, constituting the region where spacer layer 59 is formed. It is generally desirable for active region 49 to have a width equal to the width of a data track 36 (FIG. 1). MR element 50 is typically a layer of Permalloy. Permalloy is a name commonly used to identify any of a large number of highly magnetically permeable alloys containing a combination of nickel (Ni) and iron (Fe). It should be noted that other magnetoresistive materials may be used instead of Permalloy. The resistivity of MR element 50 is typically less than about 100 μ Ω - cm. MR element 50 may have a thickness of between 50 and 400 angstroms (A).

Hard bias magnetic layers 56 and 58 are preferably formed from a layer of high coercivity cobalt-platinum (CoPt), although other ferromagnetic materials may be used as well. The resistivity of hard bias layers 56 and 58 is preferably between 30 and 60 μ Ω - cm. Hard bias layers 56 and 58 may have a thickness between 200 and 600 angstroms (A).

Spacer layer 59 is a non-magnetic layer of high resistivity material which is positioned between SAL 60 and the active region of MR element 50 to prevent magnetic exchange coupling between these two layers. The resistivity of spacer layer 59 is higher than that of MR element 50, so that it does not shunt current away from the active region of MR element 50. Spacer layer 59 may be a layer of tantalum (Ta) having a resistivity several times greater than the resistivity of MR element 50, preferably at least 10 times greater, and in all cases greater than 50 μ Ω - cm. Spacer layer 59 has a thickness of between 100 and 300 angstroms (A).

SAL 60 is a layer of ferromagnetic material such as nickel-iron- rhodium (NiFeRh), nickel-iron-rhenium (NiFeRe), or nickel-iron-chromium (NiFeCr). The resistivity of SAL 60 is typically several times greater than the resistivity of MR element 50, preferably at least 10 times greater, to reduce the shunting of current away from the active region of MR element 50, and preferably at least 100 μ Ω - cm in all cases. SAL 60 typically has a thickness of between 100 and 300 angstroms (A).

During a high-performance read application, magnetic flux radiates from a track 36 of disc 35 (shown in FIG. 1) located directly beneath active region 49 of MR sensor 47 in a generally perpendicular direction from disc 35. Thus, most of the magnetic flux coming from the disc radiates generally perpendicular to disc 35 through active region 49 of MR element 50 between hard bias layers 56 and 58. MR element 50 detects magnetically encoded information on data tracks 36 of disc 35 (FIG. 1) as a selected data track 36 passes directly beneath active region 49 of MR element 50. A change in the magnetic field radiating from disc 35 modulates the resistivity of MR element 50. The changing resistance is detected by passing a sense current through conductor 52, MR element 50 and conductor 54. The resulting voltage measured across MR element 50 is used to recover information for data stored on the selected track 36 of disc 35.

In the prior art configuration shown in FIG. 2, magnetic device 40 detected two distinct signals from disc 35. First, MR element 50 detected an MR signal representing the magnetic flux directly by virtue of an MR effect. An MR effect is the ability to fundamentally vary the resistivity of a ferromagnetic material as a function of an applied field, such as magnetic flux, to the magnetic material. Second, magnetic device 40 detected an inductive pickup signal based on the time rate of change of the magnetic flux from disc 35 caused by various factors such as the data encoded on adjacent tracks, for example. Shared pole 46 and bottom pole 64 extended horizontally in FIG. 2 proximate data tracks adjacent the central desired track, and did not fully enclose MR sensor 49, allowing a path for the inductive signal to be picked up by MR element 50. This inductive signal could induce a current through MR element 50 which affected the voltage measured across MR element 50, giving the appearance that the resistivity of MR element 50 had changed in response to a magnetic field radiating from a central selected data track 36 when in fact it had not. These undesired voltage fluctuations were effectively noise to the MR signal, reducing the signal-to-noise ratio and sensitivity of MR sensor 47 in recovering data from the disc. Therefore, it is desirable to minimize the inductive pickup signal in magnetic device 40. FIG. 3 is a frontal schematic view of magnetic device 70 according to a first embodiment the present invention, including an inductive write head and an MR read sensor 77. The sectional view in FIG. 3 is taken from a plane parallel to the air bearing surface (ABS) of the device. In other words, the ABS of device 70 is parallel to the plane of the page. The inductive write head is formed from top pole 72, shared pole 76 and insulator 74 between the two poles. A write coil (not shown) encircles top pole 72 through insulator layer 74 at a region set back from the air bearing surface.

MR sensor 77 is formed between shared pole 76 and bottom pole 94. Insulator 92 is formed on bottom pole 94. Soft adjacent layer (SAL) 90 is formed on insulator 92. Spacer layer 85 and hard bias magnetic layers 86 and 88 are formed on SAL 90. MR element 80 is formed over the resulting surface, with conductor 82 and 84 formed on MR element 80 to provide electrical contacts for connection to bond pads on a disc drive slider. Alternatively, MR element 80 (contacted by conductors 82 and 84) may be formed on insulator 92, with SAL 90 being formed over hard bias layers 86 and 88 and spacer layer 85; in either case spacer layer 85 remains between MR element 80 and SAL 90 in the active region 79 between hard bias magnetic layers 86 and 88. Insulator 78 is formed between the MR sensor structure and shared pole 46. MR element 80, spacer layer 85, SAL 90 and insulators 78 and 92 are composed of the same or similar materials as described above with respect to FIG. 2.

Hard bias layers 86 and 88 define active region 79 of MR sensor 77 between them, constituting the region where spacer layer 85 is formed. It is generally desirable for active region 79 to have a width equal to the width of a data track 36 (FIG. 1).

Shared pole 76 and bottom pole 94 are connected on one side by magnetic via 96 and on the other side by magnetic via 98, to form a shorted-shield configuration, such as a toroid, surrounding MR sensor 77 between poles 76 and 94 in a plane substantially parallel to the ABS of device 70. Vias 96 and 98 are preferably formed of the same material as poles 76 and 94. Providing vias 96 and 98 to encircle MR element 80 and the other layers of MR sensor 77 in the plane of the ABS shields the sensor from inductive pickup signals, which improves the signal-to-noise ratio of the MR sensor. In particular, data encoded on adjacent data tracks tend to induce current through MR element 80, affecting the voltage measured across the element and the apparent resistivity of the element, which is effectively noise to the MR signal. The shorted-shield configuration encircling the sensor prevents induction of current through MR element 80 from neighboring tracks adjacent to the head/shield which could affect the voltage measured across MR element 80, by physically shielding MR sensor 77 from those tracks. Thus, MR sensor 77 is able to better distinguish the MR signal from the undesired voltage fluctuations due to the inductive pickup signal.

In a high performance read application, the shorted-shield pole configuration of the sensor shown in FIG. 3 enables MR element 80 to detect magnetically encoded information on a selected data track 36 passing directly beneath MR element 80, while minimizing the inductive pickup signal that potentially induces current through MR element 80.

FIG. 4 is a frontal schematic view of magnetic device 70 according to a second embodiment of the present invention, including an inductive write head and an. MR read sensor 77. The sectional view in FIG. 4 is taken from a plane parallel to the ABS of the device. In other words, the ABS of device 70 is parallel to the plane of the page. The inductive write head is formed from top pole 72, shared pole 76 and insulator 74 between the two poles. All of the elements of FIG. 4 which are similar in material and design to those of FIG. 3 have been similarly labeled.

In the embodiment shown in FIG. 4, SAL 90, spacer layer 85 and MR element 80 (forming active region 79 of MR sensor 77) are formed within a space defined by shared pole 76, bottom pole 94, and vias 96 and 98 in a plane substantially parallel to the ABS of the read head. This configuration positions vias 96 and 98 directly adjacent to active region 79 of MR sensor 77, which is desirable to minimize signals picked up from adjacent tracks. The remaining layers of MR sensor 77 are formed in other planes, such as by constructing vias extending away from the ABS of the device, for example, and are composed of the same or similar materials as described above with respect to FIGS. 2 and 3. It will be understood to one skilled in the art that many configurations of MR sensor 77 are possible to implement the present invention, provided that active area 79 of sensor 77 is encircled by shielding elements in a plane substantially parallel to the ABS of the device. Providing vias 96 and 98 directly adjacent to active region 79 of MR sensor 77 results in improved shielding of the active region from off-track signals, narrowing the track area from which signals are picked up toward the ideal one track width.

FIG. 5 is a graph illustrating the relative performance of prior art MR sensor 47 in device 40 shown in FIG. 2 and MR sensor 77 of the present invention in device 70 shown in FIGS. 3 and 4. Curve 102 (shown as a dashed line) shows the signal read by prior art sensor 47 from information encoded on a desired track and its adjacent tracks, with '0' denoting the center of the desired track over which the head is directly positioned. A significant inductive signal is picked up by sensor 47 from adjacent tracks, shown by portions 106 and 108 of curve 102. This relatively high amplitude of inductive pickup signal forces the noise threshold of prior art MR sensor 47 to be high, reducing the sensitivity of the sensor.

Curve 104 shows the improved performance of MR sensor 77 of the present invention in device 70, utilizing the shorted-shield pole configuration shown in FIG. 3. The peak signal picked up by sensor 77 is limited to the region of the desired track (denoted by '0' on the graph), blocking the inductive signal originating from adjacent tracks that is picked up in the prior art. Thus, the noise threshold of MR sensor 77 of the present invention can be made much lower, significantly improving the sensitivity of the sensor. The improved sensitivity and signal-to-noise ratio reduces the possibility of data errors in reading the MR signal from the disc.

The present invention therefore improves the performance of an MR sensor by reducing the inductive pickup signal from adjacent tracks. The shared pole and bottom pole are connected by magnetic vias surrounding the MR sensor structure, forming a shorted-shield configuration which effectively blocks the inductive signal picked up from adjacent tracks. As a result, the MR sensor has a higher signal-to-noise ratio, and is able to employ a lower noise threshold, improving the sensitivity of the sensor. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

CLAIM(S):

1. A transducing head having a magnetoresistive read head with an air-bearing surface, the read head comprising: a magnetoresistive sensor having an active area; and a shield encircling the active area of the magnetoresistive sensor in a plane substantially parallel to the air -bearing surface of the read head.

2. The transducing head of claim 1, further comprising an inductive write head having a top pole, a shared pole and a write gap between the top pole and the shared pole.

3. The transducing head of claim 2, wherein the shared pole comprises a portion of the shield.

4. The transducing head of claim 3, wherein the shield of the magnetoresistive read head is made up of the shared pole, a bottom pole, a first magnetic via connecting a first side of the shared pole to a first side of the bottom pole, and a second magnetic via connecting a second side of the shared pole to a second side of the bottom pole.

5. The magnetoresistive read head of claim 4, wherein the magnetoresistive sensor comprises: a soft adjacent layer between the shared pole and the bottom pole; a magnetoresistive element between the shared pole and the bottom pole; a spacer layer between the soft adjacent layer and the magnetoresistive element in the active area of the magnetoresistive sensor; first and second hard bias layers between the soft adjacent layer and the magnetoresistive element, the first hard bias layer being positioned adjacent a first end of the spacer layer and the second hard bias layer being positioned adjacent a second end opposite the first end of the spacer layer; a first conductor on a first end of the magnetoresistive element to provide a first electrical contact to the magnetoresistive element; and a second conductor on a second end opposite the first end of the magnetoresistive element to provide a second electrical contact to the magnetoresistive element.

6. The magnetoresistive read head of claim 5, wherein the magnetoresistive element has a resistivity of less than about 100 μ Ω - centimeter.

7. The magnetoresistive read head of claim 5, wherein the spacer layer is composed of tantalum.

8. The magnetoresistive read head of claim 4, wherein the shared pole, the bottom pole, the first magnetic via and the second magnetic via are all composed of the same magnetic material.

9. The magnetoresistive read head of claim 1, wherein the shield is shaped as a toroid encircling the active region of the magnetoresistive sensor in a plane substantially parallel to the air-bearing surface of the read head.

10. The magnetoresistive read head of claim 1, wherein the active region of the magnetoresistive sensor has a width equal to a data track width on a rotatable disc.