Abstract:
Process for producing a planar structure thin film magnetic head wherein a recess is etched in a substrate and is filled by a magnetic film. A coil is formed in an insulating film and magnetic contact pads are formed. Two magnetic films are formed in an insulating film and then in a hard film are formed two pole pieces separated by a magnetic spacer.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a process for the production of planar structure thin film magnetic heads and to a head obtained by this process. 
     Two types of thin film magnetic heads are known, namely those mounted perpendicular to the magnetic film to be read or recorded and those mounted parallel to said film. 
     FIG. 1 shows a head formed from two pole pieces P1 and P2 defining an air gap E, a coil B surrounding said pole pieces. The recording film C passes in front of air gap E. Such a head is described in Japan patent abstracts, vol. 5, No. 150, P-81, 822 of 22.9.1981. 
     The field gradient produced by such a head is high and produces intense demagnetizing fields in the recording film, which makes writing difficult. Moreover, on reading, a signal V is obtained like that of FIG. 2. Perpendicular to the external angles of the pole pieces voltage polarity reversals appear, which leads to serious problems in connection with the processing of the information read. 
     For these reasons, preferance is given to the use of horizontally mounted heads, like that shown in FIG. 3. Such a head is described in European patent application 85400136.9, published under No. 0 152 326. It is possible to see a first magnetic film 1, in which is formed a coil 2 and a second magnetic film 3 subdivided into two parts by an amagnetic spacer 4. A hard film 5 protects the assembly and ensures the planarity of the film. 
     FIG. 4 illustrates a known process for the production of a horizontal head. This process is produced in Japan patent abstracts, vol. 5, No. 5, P-44, 677, of 14.1.1981. On a substrate 6 is deposited a first magnetic film M1, followed by an insulating film 7 and a coil B (part a). This is followed by the depositing of an insulating film 8 and the etching of two wells P1, P2 (part b). This is followed by the deposition of a second magnetic film M2, which comes into contact with the first as a result of the two wells P1 and P2 (part c). This is followed by the formation of an air gap, the deposition of a glass layer (part d) and the planification of the assembly (part e). 
     Although satisfactory in certain respects, these prior art processes and means suffer from disadvantages. In the case of the head of FIG. 3, there are still outer ends of pole pieces which can lead to reversing of the reading signal. In the process illustrated in FIG. 4, the fineness or thinness of the end of the pole pieces is avoided, but the air gap is open and relatively wide, being gradually filled with magnetic particles, which magnetically short-circuit the head. Finally, the magnetic flux produced by the coil follows a quasi-constant section circuit and consequently there is no flux concentration of the air gap. Moreover, in the process of FIG. 4, coil B is not in a single plane, instead being in two separate planes, one corresponding to the central part above the first pole piece and another lower plane corresponding to the two side parts (only one of which is shown to the right in FIG. 4, i.e. part a). The lateral parts make is possible to close the winding around the pole pieces. Moreover, it can be seen that pole piece M1 is not buried in the substrate 6, which leads to a head having a large relief. Finally, the parts of the pole piece M2 not covered by the protective film 9 are very wide (because they are substantially as wide as the coil), which makes the head very fragile. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to obviate these disadvantages. It therefore proposes a production process making it possible to obtain a narrow air gap formed from an amagnetic film and pole pieces such that a flux concentration occurs in the vicinity of the air gap and giving only a small unprotected surface. Moreover, the inventive process makes it possible to obtain a structure buried or embedded in a substrate, i.e. without relief. It can also be added that the inventive process does not require the final polishing operation required by the prior art process. 
     The inventive process involves conventional thin film deposition and etching operations in connection with the technology of integrated circuits, as well as electrolytic deposition operations with respect to the various magnetic films. 
     The invention also relates to a magnetic head obtained by the inventive process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in greater detail hereinafter relative to non-limiting embodiments and the attached drawings, wherein show: 
     FIG. 1, already described, a vertically mounted known magnetic head. 
     FIG. 2, already described, the configuration of the signal obtained by the preceding head. 
     FIG. 3, already described, a known horizontally mounted magnetic head. 
     FIGS. 4a-4e, already described, a known process for producing a horizontal head. 
     FIGS. 5a-5m 13 stages (a to m) of the production process according to the invention. 
     FIG. 6 The magnetic head which is obtained. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 shows the main stages of the inventive process. The invention involves the following operations. 
     On an e.g. silicon insulating substrate 10 is formed a first insulating film 12 (e.g. of silicon oxide constituting part a). Insulating film 12 and substrate 10 are etched to form a first recess 13 (part b). On the entity is deposited a first conductive film 14, which is then selectively etched in such a way that it only remains at the bottom of the first recess 13 (part b). By a first electrolysis using conductive film 14 as the electrode, a first magnetic film 16 is deposited which fills the recess 13, said first magnetic film 16 being level with the surface of the first insulating film 12 (part c). Thus, said magnetic film is buried or embedded in the substrate. 
     On the entity is deposited a second insulating film 18 (part d). In said second insulating film 18 is formed an electric coil 20 (part e). Such an operation is described in the aforementioned European patent application (FIGS. 3 and 4 thereof). This coil is closed by side parts (only one being shown) 20&#39;, which are in the same plane as the central part 20. On either side of the coil 20, two openings 21, 22 are etched in the second insulating film 18 and they reach the first magnetic film 16 (part f). 
     By a second electrolysis using the first conductive film 14 as the electrode, these openings are filled to constitute magnetic contact pads 23, 24, which are in good magnetic continuity with the first magnetic film 16 and are level with the second insulating film 18 (part g). On the entity is deposited a third insulating film 26 (part h), e.g. of SiO 2 , Al 2  O 3 , polyimide resin, etc. Second and third recesses 27, 28 are etched in said third insulating film 26 above the magnetic contact pads 23, 24 leaving between the second and third recesses a central insulating island 32 (part h). On the entity is deposited a second conductive film 33, which is then selectively etched so as to only leave it at the bottom of the second and third recesses 27, 28 (part h). 
     By a third electrolysis using the second conductive film 33 as the electrode, the second and third recesses are filled by a second magnetic film subdivided into two parts 30, 31 and located on either side of the central insulating island 32, said film being level with the surface of the third insulating film 26 (part i). On the entity is deposited a fourth hard protective insulating film 34 (part j). In said fourth recess 36 is produced a thin amagnetic spacer centered on the central insulating island 32. Such a spacer can be obtained in the manner described in the aforementioned European patent application by the depostion of an insulant 38, etching of the latter to give it the shape of a step, deposition of an amagnetic film 40 (part k), etching horizontal portions and maintaining the vertical wall 42 (part l). On the entity is deposited a third conductive film 43, which is then selectively etched so as to only leave it at the bottom of the fourth recess 36 on either side of spacer 42 (part l). 
     By a fourth electrolysis taking the third conductive film 43 as the electrode, the fourth recess 36 is filled by a third magnetic film subdivided into two parts 46, 48 located on either side of amagnetic spacer 42, said third magnetic film being level with the surface of the hard protective film 34 (part m). There is consequently no need to polish the part as in the prior art. 
     In this process, the conductive films 14, 33, 43 can e.g. be of copper, chromium or tungsten. The magnetic films 16, 23, 24, 30, 31, 46, 48 can be of Fe:Ni in a ratio of e.g. 80:20 in order to obtain a high magnetic permeability. The thickness of magnetic film 16 can be 1 to 5 μm. The vertical wall 42 can have a width between 0.05 and 1 μm. The width X of the central contact pad 32 (part i) is between 1 and 5 μm. The thickness of hard film 34 can be between 1 and 5 μm. The etching width Y is between 5 and 15 μm (part j). 
     In section, FIG. 6 shows the complete head obtained, with the magnetic field lines making it possible to distinguish the concentration of the flux close to the air gap. The width U of parts 46 and 48 is approximately 10 μm, whereas coil 18 has a width between 120 and 200 μm. Thus, the unprotected path of the pole pieces is very narrow.