Magnetoresistive transducer conductor configuration

Abstract: A magnetoresistive transducer has a conductor configuration (32, 34) in which magnetic fields in the conductors are oriented in the same direction to provide symmetric track profiles and improved track edge response. Conductor area at the transducer air bearing surface is also minimised to eliminate shorting and improve device yield and reliability. In one embodiment, inductive pickup is minimised by limiting the active width of magnetoresistive sensing elements through conductor placement. Another embodiment for dual stripe magnetoresistive transducers, minimises inductive pickup by providing relatively large conductors for each magnetoresistive stripe, arranged in parallel with each other and coupled differentially to cancel inductive pickup through common mode rejection.

Description: The present invention relates to magnetoresistive transducers. More particularly, the present invention relates to improvements in conductor configurations for magnetoresistive transducers. Continuing advances in magnetic media technology allow increasing data storage densities. One active area of development is that of reading transducers of high output. As such transducers are made smaller, data densities are increased. Magnetoresistive (MR) thin film technology has provided a particularly promising area of inquiry with regard to producing smaller reading transducers. In such technology, conductive thin films are formed on a substrate using techniques analogous to those of the semiconductor arts. The MR stripe or element in a single stripe MR transducer (or the two MR stripes or elements is a dual stripe MR transducer, such as is described in U.S. Patent No. 3,860,965, issued to Voegeli), must be long with respect to a magnetic medium track width. In this way, the transducer presents a stable domain state. Various configurations have been proposed for contacting the MR stripe to provide a source of current to the stripe and to sense flux (i.e. data) with the MR stripe arrangement. JP-A-60018811 discloses a magnetoresistive transducer having an air bearing surface comprising magnetoresistive elements and associated conductor pairs for carrying current to and from them. One prior art conductor arrangement, shown in Figs. la and lb, provides two conductors 12, 14 for contacting each MR stripe 16. In the Fig. current directions are indicated by the designation 'i', magnetic field directions by the designation 'H', and magnetization directions by the designation 'M'. These conventions shall be applied throughout the present application. The arrangement shown, referred to as a conductors-over arrangement because the conductors are arranged above an MR stripe, is used in barber-pole biased MR heads. The conductors-over arrangement is prone to shorting either to the transducer shields (not shown) or to the other MR stripe (in a dual stripe MR transducer). Such shorting is due to conductor smearing during the lapping process used to form the transducer air bearing surface, or as a consequence of encountering an asperity on the surface of a disk in an operating disk drive. The length of the conductor along the transducer air bearing surface is of critical importance. The length of the conductor in Fig. 1a can be as much as 400 µm and as little as 40 µm. The longer this dimension, the more likely a short can occur between transducer shields (not shown) and the MR conductors, or between the two MR conductors in a dual stripe transducer, as a consequence of lapping the transducer air bearing surface, or as a consequence of contacting disk asperities as previously described. Another arrangement discussed in the prior art, shown in Figs. 2a and 2b, is referred to, appropriately, as a tip arrangement. A tip transducer includes conductors 21,22 arranged to carry current to and from an MR element 26. It is generally acknowledged that this arrangement was developed by International Business Machines of Armonk, NY. It has been the experience of those working with transducers having a tip arrangement that such configuration leads to unequal track edge response, in part because of the way magnetic fields 'H' are imposed in different directions at the conductor (track edge) edges due to the electrical current 'i'. In Fig. 2a, the directions of the magnetic fields 'H' induced by the currents 'i' are not equivalent, even if the current does not bend as assumed at the track edges. Thus, the magnetization 'M' is rotated unequally at the track edges. Accordingly, different responses occur at the track edges and, as a result, track profiles become asymmetric. The length of the MR element (or elements in a dual stripe transducer configuration) must also be significantly larger than the track width to achieve high track density reproduction with a single domain MR transducer. One practice is to place the MR sensor portion of an MR transducer between two magnetic shields to obtain high resolution along the track. In an MR read element, the active area is defined as the area in which sense current flows in the MR element and typically results from the placement of the conductor leads which carry current to and from the MR element. The leads and MR element in combination constitute a single turn coil which gives rise to an undesirable inductive response to recorded information. The magnitude of this response is determined by the number of tracks over which such coil extends. Thus, the state of MR transducer art presents a technology that suffers from various problems associated with conductor arrangement, including low yields due to shorting, poor symmetry in track profiles due to a lack if uniform fields at the track edges, and inductive pickup which results in intertrack interference. The present invention provides an improved arrangement for current carrying conductors in a magnetoresistive transducer such that the problems of shorting, lack of symmetry in track edges, and inductive pickup are minimized, if not eliminated. According to the present invention, there is provided a magnetoresistive transducer having an air bearing surface, said transducer comprising at least one magneto-resistive element, a first conductor for carrying current to said magnetoresistive element, and a second conductor for carrying current from said magneto-resistive element, each of said conductors having a tapered configuration when viewed from said air bearing surface, and each of said conductors having an L-shaped configuration (or a mirrored version thereof) when viewed along said air bearing surface, the arrangement being such that the magnetic fields in the conductor along the tapered edge adjacent the transducer active area run in the same direction, characterised in that the portions of the conductors leading to and from the magnetoresistive element have a width of 5 µm to 25 µm and in that the dimension of the portions of the conductors in the same direction and extending along the magnetoresistive element is greater by 2 µm to 5 µm, whereby the conductors are arranged in a closely spaced configuration to encompass a minimal area necessary to confine the transducer active area to a defined track region. In the preferred embodiment of the invention, a conductor arrangement is provided for either single or dual stripe transducers in which magnetic fields in the conductors are oriented in the same direction to provide symmetric track profiles and thus improved track edge response. Conductor area at the air bearing surface is also minimized to mitigate shorting and thus improve device yield and reliability. Fig. 1a is a plan view of a conductors-over conductor arrangement according to the prior art; Fig. 1b is an air bearing surface view of a conductors-over conductor arrangement according to the prior art; Fig. 2a is a plan view of a tip conductor arrangement according to the prior art; Fig. 2b is an air bearing surface view of a tip conductor arrangement according to the prior art; Fig. 3a is a plan view of a conductor arrangement according to the present invention; and Fig. 3b is an air bearing surface view of a conductor arrangement according to the present invention. The present invention is best understood by referring to the Drawings in connection with review of this Description. The present invention provides a unique conductor configuration for a magnetoresistive (MR) transducer. By application of the teachings of the present invention, it is possible to produce various types of MR transducer, all exhibiting the properties of symmetric track profiles, immunity to inductive pickup, and low likelihood of shorting due to smearing during the lapping process. An MR transducer configuration is shown in Figs. 3a and 3b in which conductors 32,34 are arranged to contact an MR element 36 for carrying current to and from the MR element. The conductors are provided in a general L-shaped configuration with the wider portion of the 'L' contacting the MR element. The conductors shown in the Fig. have a conductor width of from 5 µm to 25 µm at a conductor portion leading to the MR element and a width of from 2 µm to 5 µm at a conductor portion overlaying the MR element. Current flow in the conductors 'i' is shown by arrows in the Fig. Thus, current is brought to the MR element by the conductor 32 and is taken from the MR element by the conductor 34 and uniform current injection into the MR elements is effected. As is shown in the Fig., an important property of the present invention is that the magnetic fields 'H' in the conductors run in the same direction due to the current in the conductors at each track edge. In this way, the invention provides uniform magnetic fields at the track edges. This is important in maintaining a symmetric track profile, without having a negative effect on track edge response. Magnetization 'M' is indicated as a diagonal across the transducer active area. Fig. 3b shows a transducer air bearing surface view of the present invention in which the conductors 32,34 have a narrow, tapered profile. It is significant to note that this narrow profile presents a minimal conductor surface to the air bearing surface of the transducer. Thus, when the transducer is lapped to create the air bearing surface, it is less likely that the conductor will smear and short to other transducer structures. Additionally, the small area presented by conductors fabricated in accordance with the present invention minimizes inductive pickup. It is important to note that the foregoing discussion has been with regard to a conductors-over transducer configuration in which magnetization direction is shown in a biased state. The invention is not limited to the exemplary embodiment discussed above and it is contemplated that conductors under the MR elements, as well as other types of elements may be provided in practising the invention. Additionally, the invention is not dependent upon the method used for biasing the MR element. This arrangement can also be used in dual stripe MR transducers.

Claims: A magnetoresistive transducer having an air bearing surface, said transducer comprising at least one magneto-resistive element (36), a first conductor (32) for carrying current to said magnetoresistive element, and a second conductor (34) for carrying current from said magneto-resistive element, each of said conductors having a tapered configuration when viewed from said air bearing surface, and each of said conductors having an L-shaped configuration, or a mirrored version thereof, when viewed along said air bearing surface, the arrangement being such that the magnetic fields in the conductor along the tapered edge adjacent the transducer active area run in the same direction, characterised in that the portions of the conductors leading to and from the magnetoresistive element have a width of 5 µm to 25 µm and in that the dimension of the portions of the conductors in the same direction and extending along the magnetoresistive element is greater by 2 µm to 5 µm, whereby the conductors are arranged in a closely spaced configuration to encompass a minimal area necessary to confine the transducer active area to a defined track region. A transducer according to claim 1, wherein said conductors (32, 34) are each arranged in a conductors-over configuration. A transducer according to claim 1 or 2, comprising at least two magnetoresistive elements, and a conductor pair associated with each magnetoresistive element for carrying current to and from said magnetoresistive elements, said conductor pairs being arranged coincident to each other.

Inventors: DAVIDSON ROBERT J, HESTERMAN VICTOR W, NABERHUIS STEVEN L, SIMMONS RALPH, TARNOPOLSKY GIORIA J, TRAN LUNG THE, DAVIDSON, ROBERT J., HESTERMAN, VICTOR W., NABERHUIS, STEVEN L., SIMMONS, RALPH, TARNOPOLSKY, GIORIA J., TRAN, LUNG THE
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1993
Main classification: G11B5
IPC codes: H01F10, G01D5, G01R33, H01L43, G11B5