Method of producing a dielectric layer magnetoresistive stripes for a read head

Abstract: Materials for use as a dielectric to separate various metallic layers (10/11, 12/13) within a magnetoresistive transducer include oxides of Ta, Hf, Zr, Y, Ti, or Nb. Thin films of these materials constitute dielectric films which maintain their integrity as insulators at thickness of down to 5 nm.

Description: The present invention relates to a method of producing thin dielectric films separating various metallic layers within a magnetoresistive transducer. Magnetoresistive (MR) transducers for sensing a magnetic flux produced by a moving medium are known. A dual stripe MR transducer is described in U.S. Patent No. 3,860,965, issued to Voegeli. Such dual stripe MR transducer design is currently considered state of the art because it produces the largest output per unit track width, has a low noise level due to common mode rejection, and provides linear and symmetric off-track response. In a transducer constructed in accordance with such design, two closely spaced MR stripes are sensed differentially. The close spacing of the MR stripes is desirable as it allows greater storage capacity on a magnetic medium that is to be read by the transducer. In addition, the proximity of the two stripes is required so that the proper biasing condition can be established without exceeding the current density limit of the magnetoresistive stripes. If the dual stripe MR design is to function properly the two MR stripes must be electrically isolated from one another, at least at one end of the pair. Otherwise, the stripes would be shorted together, thereby rendering the transducer inoperable. In some MR transducer designs it is also useful to employ equally small distances between the MR stripes and adjacent ferromagnetic shields. Again, to produce a useful MR transducer, the MR stripes must be close to the shields and yet remain electrically isolated from the shields. Fig. 1 shows a perspective view of a dual stripe MR transducer of the type disclosed in the '965 patent. In Fig. 1, a first MR device is shown, consisting of conductive leads 10,11 which are spaced apart along an axis of the first MR stripe 14 to provide a gap 15. The gap defines an active area corresponding to the read track width of the media to be read by the transducer. In dual stripe MR transducer designs, a second device having conductive leads 12,13 spaced apart along an axis of the second MR stripe 18 to form a gap 15a is provided in parallel with the first element. Fig. 2 is a cross-sectional view of a dual stripe MR transducer showing the active area of the transducer. Thus, portions of the two MR stripes 14,18 are shown in a parallel spaced relation to one another. The spacing 16 between the stripes is maintained by an interMR dielectric 20. Additional dielectrics 22,24 space the MR stripes from ferromagnetic shields 25,26. An air bearing surface 27 is provided by which the transducer floats over a magnetic storage medium that is being read by the transducer. In operation, current is introduced into the conductors in the direction indicated by the arrows i 1 , i 2 . These currents are propagated along the MR stripes and serve as both sense and bias currents. An instantaneous value of the magnetic flux from the portion of the medium which is moving proximate to the gap 15 at any given time is measured by the dual stripe transducer. Such flux value corresponds to bits of data stored on the medium. While the '965 patent teaches a 30 nm separation between the MR stripes, there is no indication that such device was actually fabricated. In fact, maintaining electrical isolation across such small dielectric thicknesses has been a major impediment to the implementation of the dual stripe MR design. It has been the experience of researchers in the relevant art that reliably and reproducibly fabricating dual stripe MR heads with spacings of less than about 70 nm is exceedingly difficult. This is due to shorting between the two MR stripes, primarily as a result of process and material limitations. All of the teachings to date concerning dual stripe MR heads pertain to the use of sputtered Al 2 O 3 , SiO 2 , or SiO as the inter-MR dielectric. Nonetheless, in practice these materials provide unacceptable isolation between the metallic layers within the MR head for dielectric thicknesses less than about 70 nm. There is also some teaching in the semiconductor art to perform post-deposition processing of a thin film to improve the film dielectric properties. In such cases, gate dielectrics of SiO x N y have been fabricated by exposing 5-10 nm SiO 2 films to nitrogen ambients at elevated temperatures for short periods of time. See, for example, Process dependence of breakdown field in thermally nitrided silicon dioxide , Ramesh et al , J. Appl. Phys. 70 (4), 1991. It has also been proposed to use Ta oxide as a gate dielectric in 64 Mbit DRAMs. See, for example, THERMCO INTERNATIONAL LABORATORY , DR212.06, Japanese Daily Report, 12 November 1991. In addition, it has been taught that Ta 2 O 5 can be used as a capacitive dielectric in integrated circuit structures. See, for example, Highly Stable Tantalum Thin Film CR Circuit on a Single Substrate , Yamazaki et al, FUJITSU Scientific and Technical Journal, December 1970. Such teachings are not particularly useful, by way of analogy, to the fabrication of MR stripes, which are generally formed of an NiFe film. JP-A-3-268216 (Hitachi Seisakusho KK) discloses a magnetoresistive effect device incorporating a 20 nm niobium layer which may be oxidised. Thus, the full advantage of dual stripe MR transducer technology, i.e. extremely dense data storage on a magnetic medium, cannot be realised unless MR stripe spacings can be minimised. This, in turn, requires a new class of dielectric. According to the present invention there is provided a method of forming a thin layer of dielectric material in a multilayer magnetoresistive transducer structure having two closely spaced magnetoresistive stripes, separated by said dielectric material layer, characterised in that it comprises the steps of providing a thin metal film selected from a group including Ta, Hf, Zr, Y, Ti, or Nb, and oxidising said metal film by exposure of said film to oxygen at elevated temperatures, in a plasma, and/or in the presence of UV light to form a layer of dielectric material having a thickness of down to 5 nm. In embodiments of the present invention, a class of materials is used as a dielectric that separates various metallic layers within a multilayer magnetoresistive transducer structure. The present invention allows the production of extremely fine, high quality dielectric films having good reproducibility. These results are achieved by the deposition of a thin metal film upon a substrate. The film thus deposited provides a surface upon which an oxide is formed. Oxidised thin films of Ti, Ta, Hf, Zr, Y, or Nb, when fabricated in accordance with the teachings of the invention, constitute dielectric films which maintain their integrity as insulators at thicknesses down to 5 nm. Fig. 1 is a perspective view of a prior art dual stripe MR transducer; and Fig. 2 is a cross-sectional view of a prior art dual stripe MR transducer, showing a section taken in the active area of the transducer. The present invention is best understood by referring to the drawings in connection with review of this description. The present invention employs a class of materials useful as a dielectric that separates various metallic layers within a multilayer magnetoresistive transducer structure. It is recognised in the art that certain metal films are highly susceptible to oxidation when exposed to air. In many cases, the thin layer of oxide formed in this manner is sufficient to create an effective (albeit often unintentional) insulating layer between the oxidized metal film and a subsequently deposited metal layer. The present invention exploits this property in providing a dielectric composed of an oxidized metallic film. Example Nickel-iron(25 nm)/tantalum(15nm) - NiFe/Ta - films, were deposited onto a silicon wafer. The films were patterned into rectangles about 14 X 200 micrometers in size. After exposure to air for thirteen days, followed by a two-minute exposure to an oxygen plasma, tantalum/gold - Ta/Au - leads were deposited on either end of the rectangles by a lift-off process. Three other silicon wafers were processed in a like manner, except that prior to Ta/Au lead deposition, the patterned NiFe/Ta film was argon ion etched for several minutes to remove any oxide layer on the surface of the Ta. Resistances of the NiFe/Ta stripes having Ta/Au leads were then measured. NiFe/Ta stripes from the wafer that had not been argon ion etched had resistances that were uniformly greater than 10,000 Ohms, whereas the wafers that had been argon ion etched produced stripes that had resistances of about 15 Ohms. Thus, the present invention teaches that ultrathin dielectrics (of no more than 5 nm in the preferred embodiment of the invention) may be created through oxidation of thin metal films. That is, the present invention exploits to good advantage the problem of oxidation in various metals that has plagued the industry for some time. Thus, where current teachings are to avoid such oxidation and to provide methods for such avoidance, the present invention relies on such oxidation to produce very thin dielectrics. These dielectrics, surprisingly, may be used to isolate the MR stripes in a dual stripe MR head. The present invention provides a vast improvement in dielectric integrity of post-processed metal over that for traditional deposited dielectrics for at least the following reasons: improved surface coverage of deposited metal vs. deposited dielectric films; and increase in effective volume of the deposited metal film upon subsequent oxidation. provides for the use of oxides of tantalum (Ta), hafnium (Hf), zirconium (Zr), niobium (Nb), titanium (Ti), or Yttrium (Y), none of which have heretofore been identified in the art as potential dielectrics for MR heads. The metals of the present invention have a strong affinity for oxygen and form stable, strongly adhered oxides. While these oxides could be deposited directly by known thin film deposition techniques, the present invention provides for fabricating the oxide by oxidizing a previously deposited thin metal film by exposure to oxygen either at elevated temperature, in a plasma, in the presence of UV light, or in any combination of these three. Experiments have shown that 5 nm of Ta can be effectively oxidized by either exposure to air at 300°C or by exposure to an oxygen plasma.

Claims: A method of forming a thin layer (20) of dielectric material in a multilayer magnetoresistive transducer structure having two closely spaced magnetoresistive stripes (14, 18), separated by said dielectric material layer, characterised in that it comprises the steps of providing a thin metal film selected from a group including Ta, Hf, Zr, Y, Ti, or Nb, and oxidising said metal film by exposure of said film to oxygen at elevated temperatures, in a plasma, and/or in the presence of UV light to form a layer of dielectric material having a thickness down to 5 nm. A method according to claim 1, wherein said thin metal film is a deposited film. A method according to claim 1 or 2, wherein said dielectric material is also formed between conductive layers (10/11, 12/13) serving to supply current (i 1 , i 2 ) through said magnetoresistive stripes (14, 18). A method according to claim 3, wherein said magnetoresistive transducer is part of a dual-stripe magnetoresistive head comprising a first magnetoresistive stripe (14) connected between a first pair of conductive layers (10, 11) arranged axially thereof, and a second magnetoresistive stripe (18) connected between a second pair of conductive layers (12, 13) arranged axially thereof.

Inventors: ANTHONY THOMAS C, ANTHONY, THOMAS C.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1993
Main classification: H01L43
IPC codes: G11B5, H01B3, H01L43