Trapezoidal back bias and trilayer reader geometry with predetermined magnetization shape

A magnetoresistive sensor is generally disclosed. Various embodiments of a sensor can have at least a trilayer sensor stack biased with a back biasing magnet adjacent a back of the trilayer sensor. The back biasing magnet, the trilayer sensor stack, or both have substantially trapezoidal shapes to enhance the biasing field and to minimize noise.

SUMMARY

A magnetoresistive sensor includes at least a trilayer sensor stack with a front width proximate an ABS, and a back width distal from an ABS and a back biasing magnet with a trapezoidal shape with a front width and a back width. The trapezoidal shape concentrates the magnetic field at the front of the biasing magnet in the vicinity of the sensor stack.

DETAILED DESCRIPTION

The various embodiments of shapes disclosed herein increase the performance of a reader by increasing the bias field at the front of a back bias magnet and by decreasing signal noise. The origin of these effects is shown inFIGS. 1A-1C.FIG. 1Aillustrates possible micromagnetic magnetization patterns in a rectangular magnetic sample under a magnetization oriented generally from the left to right. Magnetization vectors12′ and14′ originate at the corners of the sample and are directed to the center where they converge at magnetization vector10′. Magnetization vector10′ diverges into vectors16′ and18′ as it approaches the right side of the sample.FIG. 1shows all possible micromagnetic magnetization patterns. Two patterns are energetically favored.FIG. 1Billustrates a “C” pattern comprised of vectors12′,10′ and16′. An alternative “C” pattern comprises vectors14′,10′ and18′.FIG. 1Cillustrates an “S” pattern comprised of vectors12′,10′ and18′ or alternatively vectors14′,10′ and16′. The energy difference between the “C” state and the “S” state is very small and during magnetic switching, thermally activated transitions between both patterns contribute to measurable sensor noise.

By changing the geometry of a magnetic element, one or the other of the “C” and “S” states can be energetically favored.FIG. 1Dillustrates how the “C” state can be favored by a trapezoidal shape of the micromagnetic element. This shape will be used in what follows to tailor magnetization in the back bias permanent magnet of a trilayer reader as well as in the freelayers of the reader itself. Although trapezoidal geometries are discussed herein to favor “C” shape micromagnetic magnetization patterns, it should be noted that other geometries such as half moon shapes can be used to obtain similar beneficial results.

FIGS. 2 and 3illustrate one non-limiting aspect of an example trilayer reader.FIG. 2is a top view of an embodiment of the trilayer read head10, andFIG. 3is an ABS view of read head10. Read head10comprises rectangular trilayer reader stack20(comprising ferromagnetic freelayers22and24and spacer layer26) in front of trapezoidal back bias magnet30. Magnetic side shields40and42abut both sides of bias magnet30and trilayer reader stack20. Trilayer reader stack20, bias magnet30, and side shields40and42are separated from each other by insulating layer50. Side shields40and42may also be replaced by an insulator preferably an oxide of aluminum.

The ABS view of trilayer read head10inFIG. 3shows top shield60, bottom shield70and side shields40and42adjacent trilayer reader stack20and insulator layer50. Ferromagnetic freelayers22and24of trilayer reader stack20are separated by spacer layer26. If spacer layer26is a nonmagnetic electrical conductor, read head10is a GMR head. If spacer layer26is a nonmagnetic electrical insulator, read head10is a TGMR head. Read head10can be a current perpendicular to plane (CPP) head wherein electrical contact is made to trilayer reader stack20through top shield60and bottom shield70.

If spacer layer26is nonmagnetic, and electrically conducting, it may be fabricated from, for example, copper. If spacer layer26is nonconducting, it may be fabricated from, for example, aluminum oxide (Al2O3or AlxO where x may or may not be an integer) or magnesium oxide. Ferromagnetic layers22and24may be fabricated from magnetic material such as, for example, nickel-iron-cobalt (Ni—Fe—Co) compositions. The shield layers may be fabricated from, for example, a soft magnetic material such as nickel-iron (Ni—Fe). Back bias magnet30may be fabricated from a permanent magnet material such as, for example, a cobalt-platinum (Co—Pt) alloy.

The operation of read head10, according to one aspect of the invention is described in conjunction withFIGS. 4A-4C.FIGS. 4A,4B and4C show top views of read head10with magnetization vector30′ of back bias layer30oriented with respect to magnetization vectors22′ and24′ of freelayers22and24to achieve optimum response of freelayers22and24to external magnetic fields. In the absence of back bias magnetization, freelayer magnetization vectors22′ and24′ would be antiparallel and commonly parallel to the ABS. Under the bias of magnetization vector30′, they arrange in a scissor orientation for optimum sensitivity. One benefit of the trapezoidal shape of back bias magnet30is that the smaller base near the back of trilayer reader stack20results in magnetic flux concentration in that region resulting in deeper penetration of the biasing field into reader stack20in the direction of the ABS.

FIGS. 4A-4Cillustrate an example effect of varying bit magnetization on recorded media on the magnetization directions22′ and24′ of first freelayer22and second freelayer24respectively.FIG. 4Ashows an example trilayer reader stack10in a quiescent magnetic state when it is not under the influence of magnetic flux emanating from recording media. The angle of magnetization between first ferromagnetic freelayer22and second ferromagnetic freelayer24at the ABS is in a scissors relation for optimum sensor response.FIG. 4Bis a top view of an embodiment of the read head10showing trilayer reader stack20under the influence of a first state of data D1corresponding to a positive bit. This first state of data causes the angle of magnetization between first freelayer22and second freelayer24to increase at the ABS. When this occurs, the resistance across trilayer reader stack20changes and is detected when a sense current is passed through trilayer reader stack20.FIG. 4Cis a top view of an example read head10showing trilayer reader stack20under the influence of a second state of data D2corresponding to a negative bit. This second state of data causes the angle of magnetization between first freelayer22and second freelayer24to decrease at the ABS. As with the first state of data, the second state of data causes a change in resistance across trilayer reader stack20and is detected when a sense current is passed through trilayer reader stack20.

FIGS. 5 and 6illustrate another non-limiting embodiment.FIG. 5is a top view of trilayer reader head110, andFIG. 6is an ABS view of read head110. Read head110comprises trapezoidal trilayer reader stack120comprising ferromagnetic freelayers122and124and spacer layer126in front of trapezoidal back bias magnet130. Magnetic side shields140and142are adjacent both sides of back bias magnet130and freelayer stack120. Trilayer reader stack120, back bias magnet130, and side shields140and142are separated from each other by insulating layer150. Side shields140and142may also be replaced by an insulator, preferably an oxide of aluminum. In this aspect of the invention, trilayer reader stack120has a trapezoidal shape. A benefit of the trapezoidal shape is that a “C” pattern of micromagnetic magnetization in reader stack120is preferred. The ABS view of trilayer read head110inFIG. 6shows top shield160, bottom shield170and side shields140and142adjacent trilayer reader stack120and insulator layer150. Ferromagnetic freelayers122and124of trilayer reader stack120are separated by spacer layer126. If spacer layer126is nonmagnetic, read head110is a GMR head. If spacer layer126is an insulator, read head110is a TGMR head. Read head110can be a current perpendicular to plane (CPP) head wherein electrical contact is made to trilayer reader stack120through top shield160and bottom shield170.

If spacer layer126is nonmagnetic and electrically conducting, it may be fabricated from, for example, copper. If spacer layer126is nonconducting, it may be fabricated from, for example, aluminum oxide (Al2O3or AlxO where x may be not be an integer) or magnesium oxide. Ferromagnetic layers122and124may be fabricated from magnetic materials, such as, for example, nickel-iron-cobalt (Ni—Fe—Co) compositions. The shield layers may be fabricated from, for example, a soft magnetic material such as nickel-iron (Ni—Fe). Back bias magnet130may be fabricated from a permanent magnet material such as, for example, a cobalt-platinum (Co—Pt) alloy.

The operation of read head110according to one embodiment is described in conjunction withFIGS. 7A-7C.FIGS. 7A,7B and7C show top views of read head110with magnetization vector130′ of back bias layer130oriented with respect to magnetization vectors122′ and124′ of freelayers122and124to achieve optimum response of freelayers122and124to external magnetic fields. In the absence of back bias magnetization130′, freelayer magnetization vectors122′ and124′ would be antiparallel and parallel to ABS160. Under the back bias of magnetization130′, they arrange in a scissor orientation for optimum sensitivity. A benefit of the trapezoidal shape of back bias magnet130is that the smaller base at trilayer reader stack120results in magnetic flux concentration in that region resulting in deeper penetration of the biasing field into reader stack120in the direction of the ABS.

FIGS. 7A-7Cillustrate the effect of varying bit magnetizations on recorded media on the magnetization directions122′ and124′ of first freelayer122and second freelayer124respectively.FIG. 7Ashows trilayer reader stack120in a quiescent magnetic state when it is not under the influence of magnetic flux emanating from recording media. The angle of magnetization between first ferromagnetic freelayer122and second ferromagnetic freelayer124at the ABS is in a scissors relation for optimum sensor response.FIG. 7Bis a front view of read head110showing trilayer reader stack120under the influence of a first state of data D1corresponding to a positive bit. This first state of data causes the angle of magnetization between first freelayer122′ and second freelayer124′ to increase at the ABS. When this occurs, the resistance across trilayer reader stack120changes and is detected when a sense current is passed through trilayer reader stack120.FIG. 7Cis a top view of read head110showing trilayer reader stack120under the influence of a second state of data D2corresponding to a negative bit. This second state of data causes the angle of magnetization between first freelayer122′ and second freelayer124′ to decrease at the ABS. As with the first state of data, the second state of data causes a change in resistance across trilayer reader stack120and is detected when a sense current is passed through trilayer reader stack120.

The operation of read head110is similar to that discussed for read head10and schematically illustrated inFIG. 4A-4C, with one exception. The trapezoidal shape of trilayer reader stack120encourages a “C” type of micromagnetic magnetization in freelayers124and126. This forces the magnetization vectors into orientations parallel to the ABS and discourages the formation of “S” type micromagnetic magnetization patterns in the freelayers, thereby minimizing noise resulting from “C” type to “S” type switching behavior during operation.

The formation of reader10with trapezoidal back bias magnet30shown inFIGS. 2 and 3is schematically illustrated inFIGS. 8A-8K.FIG. 8Ashows a substrate coated with reader stack220. The reader stack can be a GMR or a TGMR stack. In the next step, photoresist (PR) layer260, covering the center portion of reader stack220, is deposited as shown inFIG. 8B. In the next step, shown inFIG. 8C, exposed reader stack220has been removed by ion beam machining or etching or by other means known in the art. Following removal of exposed reader stack220, insulating layer250is deposited on each side of reader stack220and PR layer260as shown inFIG. 8D. Insulating layer250, as mentioned earlier, is preferably aluminum oxide and is preferably deposited by atomic layer deposition (ALD). In the next step permanent bias magnet230is then deposited as shown inFIG. 8Ecomprising reader stack220with bias magnets230above and below reader stack220separated from reader stack220by insulating layers250. The structure inFIG. 8Eis then covered with PR layer260bwith a narrow center width and wider ends as shown inFIG. 8F. The exposed structure not covered with PR layer260bis then removed by ion beam machining or etching or other means known in the art as shown inFIG. 8G. Insulator layer250is then deposited on each side of the structure covered with PR layer260bas shown inFIG. 8H. Side shields240and242are deposited to form the structure shown inFIG. 8I. Side shields240and242could be replaced with insulator layer250if needed. Removing PR layer260binFIG. 8Ireveals the structure shown inFIG. 8Jcomprising rectangular reader stack220separated from side shields240and242and trapezoidal bias magnets230by insulating layer250. Masking the top half of the structure shown inFIG. 8Jand removing the remainder creates reader structure10shown inFIG. 8Kcomprising rectangular reader stack220, side shields240and242and trapezoidal back bias magnet230separated from each other by insulating layer250. Air bearing surface ABS is indicated inFIG. 8K.

The formation of reader110with trapezoidal back bias magnet130and trapezoidal reader stack120shown inFIGS. 5 and 6is schematically illustrated inFIGS. 9A-9K.FIG. 9Ashows a substrate coated with reader stack320. The reader stack can be a GMR or a TGMR stack. Photoresist (PR) layer360, covering the center portion of reader stack320, is deposited as shown inFIG. 9B. In the next step, shown inFIG. 9C, exposed reader stack320has been removed by ion beam machining or etching or by other means known in the art. Following removal of exposed reader stack320, insulating layer350is deposited on each side of reader stack320and PR layer360as shown inFIG. 9D. Insulating layer350, as mentioned earlier, is preferably aluminum oxide and is preferably deposited by atomic layer deposition (ALD). In the next step, permanent bias magnet330is then deposited as shown inFIG. 9Ecomprising reader stack320with bias magnets330above and below reader stack320separated from reader stack320by insulating layer350. The structure inFIG. 9Eis then covered with PR layer360bwith a narrow center width and asymmetrically wider ends as shown inFIG. 9H. The exposed structure not covered with PR layer360bis then removed by ion beam machining or etching or other means known to produce the structure shown inFIG. 9G. Insulator layer350is then deposited on each side of the structure inFIG. 9Gto produce the structure shown inFIG. 9H. Side shields340and342are deposited on each side to form the structure shown inFIG. 9I. Side shields340and342could be replaced with insulator layer350if needed. Removing PR layer360binFIG. 9Kreveals the structure shown inFIG. 9Jcomprising trapezoidal reader stack320, side shields340and342and trapezoidal bias magnet330. All are separated by insulating layer350. Masking the top half of the structure shown inFIG. 9Jand removing the remainder creates reader structure110shown inFIG. 9Kcomprising trapezoidal trilayer reader stack320, side shields340and342, and trapezoidal back bias magnet330separated from each other by insulating layer350. Air bearing surface ABS is indicated inFIG. 9K.

While the present disclosure has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the technology. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the provided technology not be limited to the particular embodiment(s) disclosed, but will include all embodiments falling within the scope of the appended claims.