Abstract:
A shorted DMR reproduce head includes two substantially identical MR elements, separated by a thin film of titanium nitride having a resistivity of 1000 μΩ-cm. Signal loss due to current shunting in the shorted DMR head is significantly reduced by use of the titanium nitride film.

Description:
FIELD OF THE INVENTION 
     This invention relates to a magnetoresistive reproduce head and in particular to a shorted dual element magnetoresistive (DMR) head. 
     BACKGROUND OF THE INVENTION 
     A shorted DMR reproduce head for reproducing signals recorded in a magnetic recording medium is disclosed in U.S. Pat. No. 5,193,038 issued Mar. 9, 1993 to Smith. The shorted DMR head includes a pair of identical magnetoresistive (MR) stripes separated by a non-magnetic conductive spacer. Sputtered titanium has been employed as the conductive spacer material. The resistivity of sputtered titanium is about 100 μΩ-cm and the resulting shorted DMR reproduce head suffers from a roughly 40% signal loss due to current shunting in the head. The problem to be solved by the present invention is to provide a shorted DMR reproduce head with reduced signal loss. 
     SUMMARY OF THE INVENTION 
     The problem is solved according to the present invention by providing a shorted DMR reproduce head wherein the spacer between the magnetoresistive stripes is a layer of titanium nitride having a resistivity value of between 200 μΩ-cm and 2,000 μΩ-cm. The titanium nitride is a high melting point metallic compound with high thermal and electrical conductivity and low grain boundary and bulk diffusivity. Generally, the resistivity of stoichiometric titanium nitride film is lower than that of pure titanium films. However, we have discovered that deposited titanium nitride films can have a wide range of resistivity values depending on the deposition conditions. Particularly, when depositing titanium nitride films by reactive sputtering, increasing the nitrogen gas flow or reducing the deposition rate by lowering the sputtering power, in the presence of some ambient oxygen, results in higher resistivity titanium nitride films. By controlling the deposition conditions of the titanium nitride films to produce a film having resistivity between 200 μΩ-cm and 2,000 μΩ-cm and preferably 1,000 μΩ-cm, the signal loss due to current shunting in the resulting shorted DMR may be reduced to less than 5%. In addition, the titanium nitride layer is easy to prepare and can be deposited in sequence with the MR elements in the same sputtering chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view of a shorted DMR reproduce head according to the present invention; 
     FIG. 2 is a flow chart showing the steps of making a shorted DMR head according to the present invention; 
     FIG. 3 is a graph showing the resistivity of titanium nitride film vs. nitrogen partial pressure during sputtering; 
     FIG. 4 is a graph showing the resistivity of titanium nitride film vs. the DC power employed in the sputtering apparatus; and 
     FIG. 5 is an Auger spectrometer profile of a titanium nitride film prepared according to the present invention, showing the presence of a few percent of oxygen in the film. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a shorted DMR reproduce head 10 according to the present invention, includes a pair of sensing and mutually biasing magnetoresistive (MR) elements 12, 14 matched for magnetoresistive characteristics, electrical resistivity, and geometrical shape and dimensions. The MR elements 12, 14 are separated by an electrically conductive, non-magnetic layer 16 of titanium nitride having a resistivity of between 200 μΩ-cm to 2,000 μΩ-cm. A current 22 which is the sense current and the excitation current for biasing the MR elements 12, 14 flows into two leads 18, 20 connected to the shorted DMR head. 
     The MR elements 12, 14 are in electrical contact over their entire length with the titanium nitride layer 16 and will therefor share any current flowing in the DMR depending on the relative resistances of the MR elements and the titanium nitride layer. Because the MR elements 12, 14 are matched for electrical characteristics (as well as magnetic characteristics) and because of the symmetry of the DMR head, the current will divide into current components 24, 26, 28 where the currents 24, 26 flowing in the same direction through the MR elements 12, 14 are equal in magnitude and the remainder of the current, i.e. current 28, flows in the spacer 16. 
     Turning now to FIG. 2, the shorted DMR reproduce head according to the present invention is produced as follows. The first MR element 12 is formed (30) for example by sputtering 250Å of permalloy under conditions well known in the art for forming MR elements. Next the film 16 of titanium nitride is deposited (32) over the first MR element 12. FIG. 3 is a plot of empirical data showing the resistivity of the deposited film as a function of partial pressure of nitrogen and FIG. 4 is a plot of empirical data showing the resistivity of the titanium nitride as a function of sputtering power. In a preferred embodiment, titanium nitride is sputtered at a temperature of 120° C. using a pure titanium target at a sputtering pressure of 4 m Torr with an argon:nitrogen gas flow ratio=60:40. Not all of the ambient atmosphere is purged from the sputtering chamber so that sufficient oxygen remains in the chamber to contribute a small atomic percentage (e.g., 3-12 atomic percent) of oxygen to the resulting titanium nitride layer. The titanium nitride layer was deposited at approximately 0.6Å/second with an applied DC power of 700 W to a thickness of 1,000Å. The measured resistivity of the deposited titanium nitride film was 1,000 μΩ-cm. This high film resistivity was mainly attributed to the low deposition rate which resulted in a microstructure that accommodated a significant amount of trapped oxygen. 
     FIG. 5 is a plot of an Auger analysis of the finished DMR structure, showing about 7% trapped oxygen in the titanium nitride layer. 
     After the titanium nitride layer 16 is deposited, the surface of the titanium nitride layer is conditioned (34) to remove the columnar structure of the titanium nitride film, which if left untreated would adversely affect the properties of the magnetoresistive element 14. A preferred method of conditioning the surface of the titanium nitride layer 16 is to sputter etch or ion-mill the deposited titanium nitride layer to remove about 200Å from the surface thereof. Finally, the second MR element 14 is formed (36) on top of the titanium nitride film under the same conditions that were employed for forming the first MR element 12. 
     Measured DMR properties for a shorted DMR reproduce head prepared as described above were as follows: Hk=4.03 Oe; Hch=0.565 Oe; Hce=0.481 Oe; Rs=5.094 Ω/□ and δρ/ρ=2.10%. Where: 
     Hk is anisotropy field; 
     Hch is hard axis coercivity; 
     Hce is easy axis coercivity; 
     Rs is sheet resistance; and 
     δρ/ρ is magnetoresistance coefficient. 
     The signal loss due to current shunting in the resulting shorted DMR head was less than 5%. To determine the stability of the titanium nitride spacer material, the DMR head structure was subjected to anneal at 275° C. for twenty hours in air. The annealing resulted in only a minor change in film properties that did not degrade the performance of the shorted DMR head. 
     While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention. 
     PARTS LIST 
     10 Shorted DMR head 
     12 MR element 
     14 MR element 
     16 titanium nitride spacer 
     18 lead 
     20 lead 
     24, 26, 28 currents