Patent Publication Number: US-7218103-B2

Title: Methods for manufacturing a thin film magnetic sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a Divisional application of application Ser. No. 10/853,619 filed May 24, 2004. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a thin film magnetic sensor and a method of manufacturing the same, and particularly to a thin film magnetic sensor suitable for detection of information on the rotation of an axle of a car, a rotary encoder, and an industrial gear, etc., suitable for detection of information on the stroke position of a hydraulic cylinder or an air type cylinder, and on the position and speed of a slide of a machine tool, suitable for detection of information on the arc current of the industrial welding robot, and suitable for use in a geomagnetism direction sensor, and to a method of manufacturing the particular thin film magnetic sensor. 
   2. Description of the Related Art 
   A magnetic sensor is an electronic device for converting the detected value of an electromagnetic force such as current, voltage, an electric power, a magnetic field, or a magnetic flux, the detected value of a dynamic quantity such as a position, speed, acceleration, displacement, distance, tension, pressure, torque, temperature, or humidity, and the detected value of the biochemical quantity, into voltage via a magnetic field. A magnetic sensor is classified into, for example, a hole sensor, an anisotropic magnetoresistance (AMR) sensor, and a giant magnetoresistance (GMR) sensor in accordance with the detecting method of a magnetic field. 
   Among the magnetic sensors noted above, the GMR sensor is advantageous in that: 
   (1) The GMR sensor has the maximum value in the rate of change of the electrical resistivity, i.e., MR ratio given below, which is markedly larger than that of any of the hole sensor and the AMR sensor: 
   MR ratio=Δρ/ρ o , where Δρ=ρ H −ρ o , in which ρ H  denotes the electrical resistivity under the external magnetic field H, and ρ o  denotes the electrical resistivity under the condition that the external magnetic field is zero. 
   (2) The GMR sensor has a change with temperature in the resistance value, which is smaller than that of the hole sensor. 
   (3) Since the material producing the giant magnetoresistance effect is a thin film material the GMR sensor is suitable for miniaturization of the magnetic sensor. 
   Such being the situation, it is expected for the GMR sensor to be used as a high sensitivity micro magnetic sensor in a computer, a power generator, a car, a household electrical appliance, and a portable device. 
   The materials that are known to exhibit the GMR effect include, for example, (1) a metallic artificial lattice, which is a multilayer film including a ferromagnetic layer such as a layer of Permalloy and a nonmagnetic layer such as a layer of Cu, Ag, or Au, or a multilayer film having a four layer structure, which called a spin valve, the spin valve including an antiferromagnetic layer, a ferromagnetic layer (pinned layer), a nonmagnetic layer, and a ferromagnetic layer (free layer), (2) a metal-metal system nano granular material provided with particulates of a nanometer size formed of a ferromagnetic metal such as Permalloy and with a intergranule consisting of a nonmagnetic metal such as Cu, Ag, or Au, (3) a tunnel junction film that is allowed to exhibit the MR effect by the spin-dependent tunneling effect, and (4) a metal-insulator system nano granular material provided with particulates of a nanometer size formed of an alloy of a ferromagnetic metal and with a intergranule consisting of a nonmagnetic and insulating material. 
   Among the materials producing the GMR effect pointed out above, the multilayer film represented by the spin valve is featured in its high sensitivity under a low magnetic field. However, for preparing the multilayer film, it is necessary to laminate thin films made of various materials at a high precision, leading to a poor stability and a low manufacturing yield of the multilayer film. Such being the situation, reduction of the manufacturing cost is limited. Under the circumstances, the multilayer film of this kind is used exclusively in a high value-added device such as a magnetic head for a hard disk. It is considered difficult to use the particular multilayer film in a magnetic sensor that is forced to make competition in price with, for example, the AMR sensor or the hole sensor having a low unit price. It should also be noted that diffusion tends to be generated among the layers forming the multilayer film, and the GMR effect tends to disappear, with the result that the multilayer film is poor in its heat resistance. 
   On the other hand, the nano granular material can be manufactured easily and has a high reproducibility in general. Therefore, the manufacturing cost of the magnetic sensor can be lowered when the nano granular material is used for the manufacture of the magnetic sensor. Particularly, the metal-insulator system nano granular material is advantageous in that (1) if the composition is optimized, the metal-insulator system nano granular material is allowed to exhibit a high MR ratio exceeding 10% under room temperature, (2) since the metal-insulator system nano granular material exhibits an extremely high electrical resistivity, it is possible to miniaturize markedly the magnetic sensor and to save the power consumption of the magnetic sensor, and (3) the metal-insulator system nano granular material can be used even under a high temperature environment unlike the spin valve films comprising an antiferromagnetic film that is poor in its heat resistance. However, the metal-insulator system nano granular material is defective in that the sensitivity to the magnetic field is very low under a low magnetic field. 
   A measure for overcoming the problems pointed out above is disclosed in Japanese Patent Disclosure (Kokai) No. 11-087804. Specifically, it is disclosed that soft magnetic thin films are arranged on both sides of a giant magnetoresistance effect thin film in order to increase the sensitivity of the giant magnetoresistance effect thin film to the magnetic field. Also disclosed in the patent document quoted above is a method of manufacturing a thin film magnetic sensor, comprising the steps of forming a permalloy thin film (soft magnetic film) in a thickness of 2 μm on a substrate, forming a gap having a width of about 9 μm in the permalloy thin film by using an ion beam etching apparatus, and forming a nano granular GMR film having a composition of Co 38.6 Y 14.0 O 47.4  in the gap portion. 
   Japanese Patent Disclosure No. 11-274599 is also directed to a thin film magnetoresistance element in which soft magnetic thin films are arranged on both sides of a giant magnetoresistance thin film. It is taught that, in order to further improve the sensitivity of the magnetoresistance element to the magnetic field, the giant magnetoresistance thin film is made thinner than the soft magnetic thin film. 
   A soft magnetic material having a large saturation magnetization and a high magnetic permeability has a very high sensitivity to the magnetic field and exhibits a very large magnetization under a relatively weak external magnetic field. Therefore, when an external magnetic field is allowed to act on a thin film magnetic sensor constructed such that a thin film having a high electrical resistivity and producing a giant magnetoresistance effect (GMR film) is arranged in a small gap formed between thin film yokes formed of a soft magnetic material such that the GMR film is electrically connected to the thin film yokes, the thin film yokes are magnetized by a weak external magnetic field, and a magnetic field having an intensity 100 to 10,000 times as high as that of the external magnetic field is exerted on the GMR film. As a result, it is possible to markedly increase the sensitivity of the GMR film to the magnetic field. Incidentally, a metal-insulator system nano granular thin film is known nowadays as the GMR film. 
     FIG. 1  is a plan view schematically showing the construction of a conventional thin film magnetic sensor  10 , and  FIG. 2  is a cross sectional view along the line II—II shown in  FIG. 1 . As shown in  FIGS. 1 and 2 , the conventional thin film magnetic sensor  10  comprises an insulating substrate  12  made of an insulating and nonmagnetic material, a pair of thin film yokes  14  each formed of a soft magnetic material, the thin film yokes  14  being arranged to face each other with a gap  14   a  formed therebetween, a GMR film  16  formed within the gap  14   a , electrodes  18 ,  18  formed at the edge portions of the thin film yokes  14 , and a protective film  19  for protecting the thin film yokes  14  and the GMR film  16 . 
   The conventional thin film magnetic sensor  10  of the construction described above is formed by the method comprising the steps of forming the pair of the thin film yokes  14  arranged to face each other with the gap  14   a  (concave groove) interposed therebetween by removing the unnecessary portion of the soft magnetic thin film formed on the surface of the insulating substrate  12 , and depositing the GMR film  16  with a mask formed to cover the insulating substrate  12  except the regions in the vicinity of the gap  14   a.    
   However, the thin film magnetic sensor  10  manufactured by the method described above gives rise to the problem that the electrical characteristics and the magnetic characteristics of the sensor  10  greatly varies. The difficulty is brought about by the situation that, in the conventional manufacturing method described above, for example, the electrical contact between the thin film yokes  14  and the GMR film  16  is rendered insufficient, or the thickness of the GMR film  16  is made nonuniform within the gap  14   a , with the result that the manufactured sensor  10  is rendered unstable. 
     FIG. 3  shows the difficulty accompanying the conventional method of manufacturing the thin film magnetic sensor. To be more specific, if the GMR film  16  is deposited from above the thin film yokes  14  positioned to face each other with the small gap  14   a  interposed therebetween, the thickness in the side wall portions  16   c  of the GMR film  16 , which are formed on the side walls of the thin film yokes  14  having a large height, is gradually increased in accordance with increase in the thickness of the upper portions  16   a  of the GMR film  16  deposited on the upper surfaces of the thin film yokes  14 , as shown in  FIG. 3 . As a result, the corner portions at the bottom of the gap  14   a  are shaded by the side wall portions  16   c  of the GMR film  16  deposited on the side walls of the thin film yokes  14 . It follows that the deposition of the GMR film  16  is inhibited at the corner portions in the bottom portion  16   b  of the GMR film  16 , which is deposited on the bottom surface of the gap  14   a . Such being the situation, the bottom portion  16   b  of the GMR film  16  is rendered triangular or trapezoid in its cross sectional shape so as to cause the contact electrical resistance between the bottom portion  16   b  of the GMR film  16  and the thin film yokes  14  to greatly vary. Particularly, this undesirable phenomenon is rendered prominent in the high performance type thin film magnetic sensor in which the thin film yokes have a large height and the gap between the paired thin film yokes is small. In the worst case, the electrical resistance is rendered infinitely high so as to give rise to a serious obstacle that must be eliminated for putting the thin film magnetic sensor to the practical use. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a thin film magnetic sensor comprising a GMR film having a high electrical resistivity and thin film yokes arranged on both sides of the GMR film and formed of a soft magnetic material so as to permit the thin film yokes to be electrically connected to the GMR film, the thin film magnetic sensor being capable of suppressing the variation in the electrical contact state between the GMR film and the thin film yokes, the GMR film having a uniform thickness, the thin film magnetic sensor exhibiting stable magnetic characteristics, and a method of manufacturing the particular thin film magnetic sensor. 
   According to a first aspect of the present invention, there is provided a thin film magnetic sensor, comprising: 
   a pair of thin film yokes each formed of a soft magnetic material, the thin film yokes being arranged to face each other with a gap interposed therebetween; 
   a GMR film electrically connected to the pair of the thin film yokes and having an electrical resistivity higher than that of the soft magnetic material; and 
   an insulating substrate supporting the thin film yokes and the GMR film and formed of an insulating nonmagnetic material; 
   wherein a gap column of a multilayer structure including a layer formed of an insulating nonmagnetic material and a layer of the GMR film is arranged within the gap, and the thickness of the GMR film is uniform over the gap length. 
   According to a second aspect of the present invention, there is provided a method of manufacturing a thin film magnetic sensor, comprising the steps of: 
   forming a projection on a surface of an insulating substrate formed of an insulating nonmagnetic material by removing the unnecessary portion of the insulating substrate from a surface region thereof or by depositing a thin film formed of an insulating nonmagnetic material on the surface of the insulating substrate; 
   forming a pair of thin film yokes positioned to face each other with the projection interposed therebetween and electrically separated from each other completely, the thin film yokes being formed by depositing a thin film formed of a soft magnetic material on the surface of the insulating substrate having the projection formed thereon, followed by partially removing the thin film formed of the soft magnetic material until at least the tip surface of the projection is exposed to the outside; and 
   depositing a GMR film having an electrical resistivity higher than that of the soft magnetic material on the tip surface of the projection and on the upper surfaces of the thin film yokes contiguous to the projection such that the GMR film is electrically connected to the upper surfaces of the thin film yokes. 
   According to a third aspect of the present invention, there is provided a method of manufacturing a thin film magnetic sensor, comprising the steps of: 
   depositing a GMR film on a surface of an insulating substrate formed of an insulating nonmagnetic material; 
   forming a projection by depositing a thin film formed of an insulating nonmagnetic material on the GMR film, followed by entirely removing the thin film formed of the insulating nonmagnetic material and removing partly or entirely the GMR film, with the region forming the projection left unremoved, until the GMR film is exposed partly or entirely to at least a side wall surface of the projection; and 
   forming a pair of thin film yokes positioned to face each other with the projection interposed therebetween and electrically connected to the GMR film alone, the thin film yokes being formed by depositing a thin film formed of a soft magnetic material having an electrical resistivity lower than that of the GMR film on the surface of the insulating substrate having the projection formed thereon such that the deposited thin film is electrically connected to the GMR film exposed in advance to the side wall surface of the projection, followed by partially removing the thin film formed of the soft magnetic material until at least a tip surface of the projection is exposed to the outside. 
   According to a fourth aspect of the present invention, there is provided a method of manufacturing a thin film magnetic sensor, comprising the steps of: 
   depositing a GMR film on a surface of an insulating substrate formed of an insulating nonmagnetic material; 
   forming a projection by depositing a thin film formed of an insulating nonmagnetic material on the GMR film, followed by partially removing the thin film formed of the insulating nonmagnetic material, with a region forming the projection left unremoved, until a surface of at least the GMR film is exposed to the outside; and 
   forming a pair of thin film yokes positioned to face each other with the projection interposed therebetween and connected electrically to the GMR film alone, the thin film yokes being formed by depositing a thin film formed of a soft magnetic material having an electrical resistivity lower than that of the GMR film on the surface of the insulating substrate having the projection formed thereon such that the deposited thin film is electrically connected to the GMR film exposed in advance to the outside, followed by partially removing the thin film formed of the soft magnetic material until at least a tip surface of the projection is exposed to the outside. 
   According to the first aspect of the present invention, a gap column of a multilayer structure comprising a layer of an insulating nonmagnetic material and a layer of the GMR film is arranged in the gap between the thin film yokes each of the soft magnetic material. Since the thickness of the GMR film is uniform over the gap length, it is possible to connect electrically the GMR film to the thin film yokes without fail. It follows that the electrical characteristics and the magnetic characteristics of the thin film magnetic sensor are rendered highly stable because of a precise electrical resistivity. 
   According to the second aspect of the present invention, the thin film yokes are formed on both sides of a projection formed on the surface of the insulating substrate, followed by forming a GMR film on the plane including the tip surface of the projection and the upper surfaces of the thin film yokes. It follows that it is unnecessary to carry out the step of depositing a GMR film within a small gap formed between the thin film yokes each having a large height so as to make it possible to obtain a GMR film having a uniform thickness over at least the gap length. In addition, since a metallic face contact can be achieved without fail between the GMR film and the thin film yokes, the electric and magnetic characteristics of the thin film magnetic sensor are stabilized. 
   Further, according to the third and fourth aspects of the present invention, a GMR film and a thin film of an insulating nonmagnetic material are formed in advance on the surface of an insulating substrate, followed by forming a projection in a manner to permit the GMR film to be exposed to the outside on the side wall surface or in the vicinity of the bottom surface of the projection. It follows that it is unnecessary to carry out the step of forming a GMR film within a small gap formed between the thin film yokes each having a large height so as to make it possible to obtain a GMR film having a uniform thickness over at least the gap length. Also, if the thin film yokes are formed on both sides of the projection, a face contact can be achieved without fail between the GMR film and the thin film yokes so as to stabilize the electric and magnetic characteristics of the thin film magnetic sensor. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a plan view schematically showing the construction of the conventional thin film magnetic field sensor; 
       FIG. 2  is a cross sectional view along the line II—II shown in  FIG. 1 ; 
       FIG. 3  is a cross sectional view showing in a magnified fashion the region in the vicinity of the gap included in the conventional thin film magnetic field sensor; 
       FIG. 4  is a plan view schematically showing the construction of a thin film magnetic sensor according to a first embodiment of the present invention; 
       FIG. 5  is a cross sectional view along the line V—V shown in  FIG. 4 ; 
       FIG. 6  is a cross sectional view showing in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the first embodiment of the present invention; 
       FIGS. 7A and 7B  are plan views showing in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the first embodiment of the present invention; 
       FIGS. 8A to 8Q  are cross sectional views collectively showing the manufacturing process of the thin film magnetic sensor according to the first embodiment of the present invention; 
       FIG. 9  is a plan view schematically showing the construction of a thin film magnetic sensor according to a second embodiment of the present invention; 
       FIG. 10  is a cross sectional view along the line X—X shown in  FIG. 9 ; 
       FIG. 11  is a cross sectional view showing the construction of a thin film magnetic sensor in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the second embodiment of the present invention; 
       FIG. 12  is a cross sectional view showing another construction of a thin film magnetic sensor in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the second embodiment of the present invention; 
       FIGS. 13A to 13P  are cross sectional views collectively showing the manufacturing process of the thin film magnetic sensor according to the second embodiment of the present invention; 
       FIG. 14  is a plan view schematically showing the construction of a thin film magnetic sensor according to a third embodiment of the present invention; 
       FIG. 15  is a cross sectional view along the line XV—XV shown in  FIG. 14 ; 
       FIG. 16  is a cross sectional view showing in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the third embodiment of the present invention; and 
       FIGS. 17A to 17O  are cross sectional views collectively showing the manufacturing process of the thin film magnetic sensor according to the third embodiment of the present invention. 
       FIG. 18  is a graph showing the relationship between the electrical resistance and the frequency in respect of the thin film magnetic sensor obtained in each of Examples 1, 2 and Comparative Example 1; 
       FIG. 19  is a graph showing the relationship between the variation in resistance of the thin film magnetic sensors formed in a single chip and the frequency in respect of the thin film magnetic sensor obtained in each of Examples 1, 2 and Comparative Example 1; and 
       FIGS. 20A and 20B  collectively show the arrangement of the unit elements within the chip manufactured in Example 1 of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Some embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
   First Embodiment 
   A first embodiment of the present invention will now be described first. 
     FIG. 4  is a plan view schematically showing the construction of a thin film magnetic sensor  20  according to a first embodiment of the present invention,  FIG. 5  is a cross sectional view along the line V—V shown in  FIG. 4 , and  FIG. 6  is a cross sectional view showing in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the first embodiment of the present invention. 
   As shown in the drawings, the thin film magnetic sensor  20  according to the first embodiment of the present invention comprises an insulating substrate  22 , a pair of thin film yokes  24   b ,  24   c , and a GMR film  26 . The thin film yokes  24   b  and  24   c  are arranged to face each other with a gap  24   a  interposed therebetween. Also, the GMR film  26  is formed in the gap  24   a  in a manner to permit the GMR film  26  to be electrically connected to the thin film yokes  24   b ,  24   c . Electrodes  28   b ,  28   c  are formed in the edge portions of the thin film-yokes  24   b ,  24   c , respectively. Also, first protective films  30   b ,  30   c  are formed on the upper surfaces of the thin film yokes  24   b ,  24   c , respectively. Further, the uppermost surface of the insulating substrate  22  is covered with a second protective film  32 . 
   The insulating substrate  22 , which serves to support the first and second thin film yokes  24   b ,  24   c  and the GMR film  26 , is formed of an insulating nonmagnetic material. To be more specific, the insulating substrate  22  is formed of a high rigidity material, for example, a glass, an alumina, a silicon covered with a thermally-oxidized film, and an alumina titanium carbide, which have flattened surface with a insulating film. 
   A gap column  23  is formed in a gap  24   a  formed in an optional portion on the surface of the insulating substrate  22  so as to separate the thin film yokes  24   b  and  24   c , which are positioned to face each, from each other. The term “gap column” denotes a multilayer structure layered within the gap  24   a  formed between the thin film yokes  24   b  and  24   c  positioned to face each other and including an insulating nonmagnetic layer and the GMR film  26 . To be more specific, the gap column  23  extends upward from the lowest plane of the surface of the insulating substrate  22 . In the first embodiment of the present invention, the gap column  23  is formed of a multilayer structure comprising a projection  22   a  formed on the surface of the insulating substrate  22 , and a layered structure deposited on the projection  22   a  and including the GMR film  26  and the second protective film  32 . Also, in the first embodiment of the present invention, the gap length, i.e., the length of the gap  24   a , denotes the distance between the thin film yokes  24   b  and  24   c , which is the shortest distance of the region in which the thin film yokes  24   b  and  24   c  are brought into contact with the GMR film  26 . Also, the term “gap width” denotes the length in a direction perpendicular to the direction of the gap length of the region sandwiched between the tips of the thin film yokes  24   b  and  24   c  which are positioned to face each other, as shown in  FIG. 7A . Incidentally, if the thin film yokes  24   b  and  24   c , which are positioned to face each other, are arranged in symmetry, the gap width coincides with the width of the thin film yoke  24  at the tip, as shown in  FIG. 7B . 
   It is desirable for the cross section of the projection  22   a  constituting the gap column  23  to include a parallel portion extending over a prescribed distance on the side of the upper surfaces of at least the thin film yokes  24   b ,  24   c . It is possible for the proximal end portion of the projection  22   a  to be tapered as shown in  FIG. 5 . Alternatively, it is possible for the entire region of the projection  22   a  to have a columnar shape. 
   The method of forming the projection  22   a  is not particularly limited. For example, the projection  22   a  can be formed by partially removing by way of, for example, the etching the unnecessary portion of a flat surface region of the insulating substrate  22 , as described herein later. Alternatively, the projection  22   a  can be formed by depositing a thin film of an insulating nonmagnetic material on a flat surface of the insulating substrate  22 , followed by partially removing the unnecessary portion of the thin film. 
   The shapes in other portions of the insulating substrate  22  are not particularly limited. It is possible to select optimum shapes in accordance with the use and the required properties of the thin film magnetic sensor  20 . Also, only one element comprising the thin film yokes  24   b ,  24   c  and the GMR film  26 , which is formed on the insulating substrate  22 , is shown in each of  FIGS. 4 to 6 . However, these drawings are simply intended to exemplify the construction of the thin film magnetic sensor  20 . In the case of the mass production of the thin film magnetic sensors  20 , a plurality of elements are formed simultaneously on one insulating substrate  22 . 
   In order to prevent the fluctuation of the standard potential caused by the temperature, the thin film magnetic sensor generally comprises two elements that are connected in series, and the external magnetic field is detected by measuring the midpoint potential. Also, the thin film magnetic sensor is classified into a perpendicular type in which the two elements are arranged such that the sensitive axes of these two elements are perpendicular to each other, and a parallel type in which the two elements are arranged such that the sensitive axes of these two elements are parallel to each other. Also, in order to double the output, a bridge circuit is formed in some cases by using four elements. In this case, it is possible to form only one element on the insulating substrate  22  and to prepare a magnetic sensor by combining a plurality of the elements each formed on the single insulating substrate  22 . Alternatively, it is also possible to form a plurality of elements on the single insulating substrate  22  such that these plural elements are electrically connected to each other. 
   Each of the thin film yokes  24   b  and  24   c , which are intended to increase the sensitivity of the GMR film  26  to the magnetic field, is formed of a soft magnetic material. In order to obtain a high sensitivity to the magnetic field under a weak magnetic field, it is desirable to use a material having a high magnetic permeability μ and/or a high saturation magnetization Ms for forming the thin film yokes  24   b  and  24   c . To be more specific, it is desirable for the yoke-forming material to have a magnetic permeability μ not lower than 100, preferably not lower than 1,000. It is also desirable for the yoke-forming material to have a saturation magnetization Ms not lower than 5 kilo Gauss, preferably not lower than 10 kilo Gauss. 
   The specific materials preferably used for forming the thin film yokes  24   b  and  24   c  include, for example, permalloy (40 to 90% Ni—Fe alloy), Sendust (Fe 74 Si 9 Al 17 ), Hardperm (Fe 12 Ni 82 Nb 6 ), Co 88 Nb 6 Zr 6  amorphous alloy, (Co 94 Fe 6 ) 70 Si 15 B 15  amorphous alloy, Finemet (Fe 75.6 Si 13.2 B 8.5 Nb 1.9 Cu 0.8 ), Nanomax (Fe 83 HF 6 C 11 ), Fe 85 Zr 10 B 5  alloy, Fe 93 Si 3 N 4  alloy, Fe 71 B 11 N 18  alloy, Fe 71.3 Nd 9.6 O 19.1  nano granular alloy, Co 70 Al 10 O 20  nano granular alloy, and Co 65 Fe 5 Al 10 O 20  alloy. 
   The thin film yokes  24   b  and  24   c  are formed of the material deposited on both sides of the projection  22   a  formed on the surface of the insulating substrate  22 . The shape of the thin film yokes  24   b ,  24   c  is not particularly limited. However, in order to increase the sensitivity of the GMR film  26  to the magnetic field, it is desirable for the thin film yokes  24   b ,  24   c  to satisfy the conditions described in the following. 
   First of all, it is desirable that the cross sectional area each of the thin film yokes  24   b  and  24   c  on the side of the gap  24   a  is smaller than that on the each side of the electrodes  28   b  and  28   c  each of which acts inflow edge or outflow edge of the external magnetic field. If the cross sectional area of the thin film yoke is made smaller on the side of the gap  24   a , the magnetic flux density is increased at the tip of the gap  24   a  thereby permitting a stronger magnetic field to act on the GMR film  26 . 
   What should also be noted is that it is desirable for each of the thin film yokes  24   b  and  24   c  to have an appropriately large L/W ratio, i.e., the ratio of the length L in the gap length direction to the width W on the side of the electrode. Since the demagnetizing field generated in the gap length direction is weakened as the length of each of the thin film yokes  24   b  and  24   c  is relatively increased in the gap length direction, it is possible to allow the facing surfaces of the thin film yokes  24   b  and  24   c  on the side of the electrodes  28   b  and  28   c  to perform effectively the function as the inflow and outflow edge of the external magnetic field. 
   Further, it is desirable for the thin film yokes  24   b  and  24   c  to be shaped in symmetry with respect to the gap  24   a . It is undesirable for the thin film yokes  24   b  and  24   c  to be shaped in asymmetry because the characteristics of the thin film magnetic sensor  20  are governed by the thin film yoke having bad magnetic properties. 
   In addition, it is desirable for the shortest distance between the thin film yokes  24   b  and  24   c , which are positioned to face each other in contact with the GMR film  26  with the gap  24   a  interposed therebetween, i.e., the gap length, to be short. With decrease in the gap length, the dispersion into the air atmosphere of the magnetic flux leaking from the tips of the thin film yokes  24   b  and  24   c  is suppressed more effectively so as to allow a stronger magnetic field to act on the GMR film  26 . It should be noted, however, that the gap length should be determined appropriately in view of, for example, the magnitude of the magnetic field acting on the GMR film  26 , the easiness of formation of the projection  22   a , and the specification of the electrical resistance. 
   Incidentally, the thickness of each of the thin film yokes  24   b  and  24   c  is not particularly limited. It is possible to determine appropriately the thickness of the thin film yoke in accordance with, for example, the material of each of the thin film yokes  24   b ,  24   c  and the characteristics required for the thin film magnetic sensor  20 . Also, in the example shown in  FIG. 4 , the planar shape of each of the thin film yokes  24   b  and  24   c  is tapered on the side of the tip (on the side of the gap  24   a ). However, it is also possible to form a parallel portion at the tip of each of the thin film yokes  24   b  and  24   c . If a parallel portion is formed at the tip of each of the thin film yokes  24   b  and  24   c , it is possible to suppress the dispersion of the magnetic flux at the tip of each of the thin film yokes  24   b  and  24   c  so as to allow a stronger magnetic field to act on the GMR film  26 . 
   The GMR film  26  will now be described. The GMR film  26 , which is sensitive to the change of the external magnetic field as the change of the electrical resistance thereby detecting the change of the external magnetic field as a change of the voltage, is formed of a material exhibiting giant magnetoresistance effect. In order to allow the GMR film  26  to detect the change of the external magnetic field with a high sensitivity, it is desirable for the GMR film  26  to have an absolute value of the MR ratio not smaller than 5%, preferably not smaller than 10%, under the condition that the external magnetic field H is not higher than several ten thousand oersteds (Oe). 
   Also, in the present invention, the GMR film  26  is directly connected electrically to the thin film yokes  24   b  and  24   c . Therefore, a material having an electrical resistivity higher than that of the thin film yokes  24   b  and  24   c  is used for forming the GMR film  26 . It is undesirable to use a material having an excessively low electrical resistivity for forming the GMR film  26  because, in this case, an electrical short circuit is formed in general between the thin film yokes  24   b  and  24   c . On the other hand, in the case of using a material having an excessively high electrical resistance for forming the GMR film  26 , a noise is increased so as to make it difficult to detect the change of the external magnetic field as the change of voltage. It is desirable for the GMR film  26  to exhibit an electrical resistivity falling within a range of between 10 3  μΩcm and 10 12  μΩcm, preferably between 10 4  μΩcm and 10 11  μΩcm. 
   The condition given above can be satisfied by various materials. Particularly, the metal-insulator system nano granular material can be used suitably for forming the GMR film  26 . In the metal-insulator system nano granular material which exhibits a high MR ratio and a high electrical resistivity, the MR ratio is not greatly changed by a slight change in the composition. It follows that the metal-insulator system nano granular material is advantageous in that it is possible to manufacture a thin film having stable magnetic characteristics with a high reproducibility at a low cost. 
   The metal-insulator system nano granular materials producing a giant magnetoresistance effect and used for forming the GMR film  26  include, for example, Co—Y 2 O 3  system nano granular alloy, Co—Al 2 O 3  system nano granular alloy, Co—Sm 2 O 3  system nano granular alloy, Co—Dy 2 O 3  system nano granular alloy, FeCo—Y 2 O 3  system nano granular alloy, and fluoride system nano granular alloys such as Fe—MgF 2 , FeCo—MgF 2  and Fe—CaF 2 . 
   The thin film magnetic sensor according to the first embodiment of the present invention differs from the conventional thin film magnetic sensor in that the GMR film  26  is formed on a surface (hereinafter referred to as a “GMR film-forming surface”) consist of the tip surface of the projection  22   a  made of an insulating nonmagnetic material and the upper surfaces of the thin film yokes  24   b ,  24   c  deposited on both sides of the projection  22   a.    
   The GMR film-forming surface can be formed by the steps of (1) forming the projection  22   a  on the surface of the insulating substrate  22 , (2) depositing the thin film yokes  24   b  and  24   c  each of a soft magnetic material on both sides of the projection  22   a , and (3) partially removing the thin film yokes  24   b ,  24   c  formed of the soft magnetic material by, for example, polishing or etching until at least the tip surface of the projection  22   a  is exposed to the outside. 
   It is not absolutely necessary for the GMR film-forming surface not to include a stepped region. It is possible for the GMR film-forming surface to include a slightly stepped region. If the unnecessary portions of the projection  22   a  and the thin film yokes  24   b ,  24   c , which differ from each other in the material, are partially removed simultaneously as in the first embodiment of the present invention, it is possible for the difference in the polishing rate or the etching rate between the material of the projection  22   a  and the material of the thin film yokes  24   b ,  24   c  to cause a step “d” to be formed between the tip surface of the projection  22   a  and the upper surfaces of the thin film yokes  24   b ,  24   c , as shown in  FIG. 6 . 
   In order to permit a sound GMR film  26  to be deposited on the GMR film-forming surface and to stabilize the state of the electrical contact between the GMR film  26  and the thin film yokes  24   b ,  24   c , it is desirable for the step “d” on the GMR film-forming surface in the direction of the gap length to be not larger than at least the thickness of the GMR film  26 , more preferably to be not larger than ½ of the thickness of the GMR film  26 . The step “d” on the GMR film-forming surface should be as small as possible. 
   Where a small step is formed on the GMR film-forming surface, it is desirable for the inclination angle θ of the side wall of the step in the direction of the gap length, i.e., the inclination angle θ of the edge surfaces of the thin film yokes  24   b ,  24   c  in  FIGS. 4 to 6 , to be as small as possible. With increase in the inclination angle θ of the side wall of the step, the shading is formed by the side wall of the step on the GMR film-forming surface, with the result that the deposition of the GMR film  26  is inhibited in the shaded portion. Such being the situation, the inclination angle θ noted above should be as small as possible. 
   In order to permit a sound GMR film  26  to be deposited on the GMR film-forming surface, it is desirable for the inclination angle θ of the side wall of the step to be not larger than 80° relative to the horizontal plane, more preferably not larger than 60° relative to the horizontal plane. Incidentally, in the case where the removing treatment such as an etching is applied simultaneously to the projection  22   a  and the thin film yokes  24   b ,  24   c , it is possible to set the inclination angle θ of the side wall of the step relative to the horizontal plane at 80° or less by optimizing the conditions of the removing treatment. 
   Further, it is necessary for the length of the GMR film-forming surface in the gap length direction to be equal to or larger than the gap length. On the other hand, it is possible for the length of the GMR film-forming surface in its width direction, i.e., the length in a direction perpendicular to the gap length direction, to be larger or smaller than the gap width. It should be noted, however, that it is necessary for the length of the GMR film-forming surface in its width direction to be larger than the lateral width of the GMR film  26 . 
   Also, in order to improve the sensitivity of the GMR film  26  to the magnetic field, it is desirable for the shape of the GMR film  26  deposited on the GMR film-forming surface to satisfy the conditions described in the following. 
   First of all, it is desirable for the lateral width of the GMR film  26  to be smaller than the gap width. It is undesirable for the GMR film  26  to have a large lateral width because, if the lateral width of the GMR film  26  is increased, that region of the GMR film  26  which is sensitive to the weak magnetic flux leaking from the thin film yokes  24   b ,  24   c  in the direction of the lateral width is increased so as to lower the sensitivity of the GMR film  26  to the magnetic field. It should be noted, however, that it is acceptable for the lateral width of the GMR film  26  to be increased to a level about 1.1 times as much as the gap width. 
   It is also desirable for the thickness of the GMR film  26  to be larger than the step “d” between the tip surface of the projection  22   a  and the upper surfaces of the thin film yokes  24   b  and  24   c . Incidentally, the thickness of the GMR film  26  can be determined in accordance with the specification of the electrical resistance of the thin film magnetic sensor. 
   Incidentally, in the first embodiment of the present invention, the length of the GMR film  26  in the direction of the gap length is not particularly limited. The length of the GMR film  26  in the direction of the gap length may be markedly larger than the gap length. It should be noted in this connection that the electric current supplied into the electrodes  28   b ,  28   c  of the thin film magnetic sensor  20  flows mainly into only that region of the GMR film  26  which is positioned within the gap  24   a  having the lowest electrical resistance, and only a very small current alone flows into the other region. Such being the situation, it is possible for the length of the GMR film  26  in the direction of the gap length to be markedly larger than the gap length as pointed out above. 
   Each of the electrodes  28   b  and  28   c , which serves to take out the output, is formed of a conductive material. To be more specific, it is desirable to use, for example, Cu, Ag or Au for forming the electrodes  28   b  and  28   c . It should be noted, however, that an underlayer formed of, for example, Cr, Ti or Ni is formed below the electrode for improving the bonding strength of the electrode and for preventing the diffusion. The shapes of the electrodes  28   b  and  28   c  are not particularly limited. It is possible to select an appropriate shape in accordance with, for example, the size of the thin film magnetic sensor  20  and the shapes of the thin film yokes  24   b  and  24   c.    
   The first protective films  30   b  and  30   c  serve to protect the thin film yokes  24   b  and  24   c  in the step of exposing the projection  22   a  to the outside after deposition of the thin film yokes  24   b  and  24   c  on both sides of the projection  22   a . It follows that the first protective films  30   b ,  30   c , which are required in the removing process, are not absolutely required in the thin film magnetic sensor  20 . On the other hand, the second protective film  32  serves to shield the GMR film  26  and the thin film yokes  24   b ,  24   c  exposed to the surface of the insulating substrate  22  from the air atmosphere so as to protect the GMR film  26 , etc. noted above. 
   An insulating nonmagnetic material is used for forming each of the first protective films  30   b ,  30   c  and the second protective film  32 . To be more specific, a material selected from the group consisting of Al 2 O 3 , SiO 2 , Si 3 N 4  and photoresist hard-baked under temperatures not lower than 200° C. is used for forming the first protective films  30   b ,  30   c  and the second protective film  32 . 
   The manufacturing process of the thin film magnetic sensor  20  according to the first embodiment of the present invention will now be described. 
     FIGS. 8A to 8Q  are cross sectional views collectively showing the manufacturing process of the thin film magnetic sensor according to the first embodiment of the present invention. The manufacturing process for this embodiment comprises the step of forming a projection, the step of forming thin film yokes, the step of forming a GMR film, the step of forming electrodes, and the step of forming a surface protective film. 
   The step of forming a projection will now be described first. The projection  22   a  consisting of an insulating nonmagnetic material is formed on the surface of the insulating substrate  22  in the step of forming the projection. To be more specific, it is desirable for the step of forming the projection to be carried out as follows. 
   In the first step, a penetration preventing film  34  is formed on the surface of the insulating substrate  22 , as shown in  FIG. 8A . The penetration preventing film  34  serves to enhance the pattern accuracy in the patterning step with photoresist, which is described herein later. In general, the penetration preventing film  34  is formed of, for example, a Cr thin film or a Ti thin film. 
   In the next step, the penetration preventing film  34  is coated with photoresist  37 , followed by arranging a mask  36  having a prescribed open portion above the insulating substrate  22 , as shown in  FIG. 8B , followed by exposing to light. Then, the sensitized portion is removed by the development so as to form a photoresist film  38   a  in the portion forming the projection  22   a  and a photoresist film  38   b  in the portion where the thin film yokes  24   b ,  24   c  are not formed, as shown in  FIG. 8C . 
   In this case, it is desirable to carry out a post baking at 80 to 120° C. for 0.05 to 1 hour after formation of the photoresist films  38   a ,  38   b . If the post baking is applied, the solvent is evaporated from the photoresist film  38   b  so as to permit the photoresist film  38   b  to be shrunk to some extent, with the result that a gradient is imparted to the side surface of the photoresist film  38   b . If the side surface of the photoresist film  38   b  is slightly inclined, the shading is unlikely to be generated in the subsequent etching step of the insulating substrate  22  and, thus, the etching can be performed efficiently. Also, if the etching condition is optimized, it is possible to etch the insulating substrate  22  along the boundary line of the photoresist film  38   b  in a direction substantially perpendicular to the surface of the insulating substrate  22 . Incidentally, the photoresist film  38   a  formed in the portion of the projection  22   a  has a small volume and, thus, even if a post baking is applied to the photoresist film  38   a , the shape of the photoresist film  38   a  in the stage of the development is held substantially unchanged. In other words, the side surface of the photoresist film  38   a  is held substantially perpendicular to the upper surface of the insulating substrate  22 . 
   In the next step, an Ar ion beam etching is performed while rotating the insulating substrate  22 , as shown in  FIG. 8D . In this stage, it is possible to etch the surface region of the insulating substrate  22  in a direction substantially perpendicular to the upper surface of the insulating substrate  22  along the boundary lines of the photoresist films  38   a  and  38   b  as shown in the drawing, if the irradiating conditions such as the rotating speed of the insulating substrate  22  and the irradiating angle of the Ar ion beam are optimized. Particularly, in the case of applying the post baking, the depth of the perpendicular portion of the insulating substrate  22  which is formed by etching along the boundary line of the photoresist film  38   b  can be made larger than the depth on the side of the photoresist film  38   a.    
   After completion of the Ar ion beam etching, the photoresist films  38   a  and  38   b  remaining on the surface of the insulating substrate  22  are removed (peeled off) so as to form the projection  22   a  on the surface of the insulating substrate  22 , as shown in  FIG. 8E . It should be noted that the side wall of the projection  22   a  is substantially perpendicular to the upper surface of the insulating substrate  22 , and the projection  22   a  has a prescribed width (gap length) and a prescribed height. It should also be noted that two concavities positioned to face each other with the projection  22   a  interposed therebetween are formed in the surface region of the insulating substrate  22 . 
   The method of forming the projection  22   a  is not limited to the method described above, and another method can be employed for forming the projection  22   a . For example, it is possible to employ a wet etching that uses a chemical liquid or a reactive ion etching in place of the Ar ion beam etching. Alternatively, the projection  22   a  can be formed by depositing a thin film of an insulating nonmagnetic material on the entire surface of the insulating substrate  22 , followed by selectively removing the thin film of the insulating nonmagnetic material except the portion where the projection  22   a  is to be formed. 
   The step of forming the thin film yokes will now be described. A pair of thin film yokes  24   b  and  24   c  positioned to face each other with the projection  22   a  interposed therebetween and electrically separated from each other completely are formed in the step of forming the thin film yokes. The thin film yokes  24   b  and  24   c  noted above are formed by depositing a thin film of a soft magnetic material on both sides of the projection  22   a  formed on the surface of the insulating substrate  22 , followed by partially removing the thin film of the soft magnetic material until at least the tip surface of the projection  22   a  is exposed to the outside. 
   To be more specific, a soft magnetic thin film  24   d  is deposited in a prescribed thickness on the entire surface of the insulating substrate  22  as shown in  FIG. 8F . Then, a first protective film  30  of an insulating nonmagnetic material is deposited in a prescribed thickness on the surface of the soft magnetic thin film  24   d , as shown in  FIG. 8G . As described previously, the first protective film  30  serves to protect the soft magnetic thin film  24   d , i.e., the thin film yokes  24   b  and  24   c , in the step of planarizing the surface of the insulating substrate  22 . Also, the material of the first protective film  30  is selected appropriately in accordance with the planarizing method. 
   In the next step, the first protective film  30  and the soft magnetic thin film  24   d  are partially removed until at least the tip surface of the projection  22   a  is exposed to the outside so as to form the thin film yokes  24   b  and  24   c , which are separated from each other, on both sides of the projection  22   a , as shown in  FIG. 8H . As a result, formed on the surface of the insulating substrate  22  is a GMR film-forming surface including the tip surface of the projection  22   a  and the upper surfaces of the thin film yokes  24   b  and  24   c  contiguous to the tip surface of the projection  22   a . It should also be noted that the length of the GMR film-forming surface in the direction of the gap length is larger than the gap length, and the length of the GMR film-forming surface in the width direction is larger than the gap width. Also, the first protective layer  30  is separated in this stage into right and left first protective layers  30   b  and  30   c.    
   The method of removing the unnecessary portion of the soft magnetic thin film  24   d  for forming the GMR film-forming surface is not particularly limited so as to make it possible to employ various methods. To be more specific, it is desirable to employ the methods described in the following. 
   A first method is a mechanical polishing method in which the first protective film  30  is formed on the entire surface of the insulating substrate  22 , followed by mechanically polishing the surface of the first protective film  30  formed on the insulating substrate  22 . In this case, it is desirable for the first protective film  30  to be formed of, for example, a Al 2 O 3  film, a SiO 2  film, a Si 3 N 4  film, or a photoresist film hard-baked under temperatures not lower than 200° C. 
   A second method is an etch back method, in which the first protective film  30  is formed on the entire surface of the insulating substrate  22  so as to moderate the irregularity on the surface of the insulating substrate  22 , followed by etching the surface of the first protective film  30  formed on the insulating substrate  22  by utilizing an ion beam. In this case, it is desirable for the first protective film  30  to be formed of a photoresist film post-baked at 90 to 120° C. 
   If the photoresist film (first protective film  30 ) formed on the surface of the insulating substrate  22 , i.e., on the surface of the soft magnetic thin film  24   d  formed on the insulating substrate  22 , is etched, the photoresist film alone is etched first. With progress of the etching, the convex portion of the soft magnetic thin film  24   d  comes to be exposed in the surface of the photoresist film. Then, the photoresist film and the convex portion of the soft magnetic thin film  24   d  are etched simultaneously. 
   In general, the uppermost surface of the photoresist film is not rendered completely flat. In addition, there is a difference in the etching rate between the soft magnetic thin film  24   d  and the photoresist film. It follows that it is difficult to planarize completely the surface of the insulating substrate  22  by a single etching. Such being the situation, the etching is once stopped before the photoresist film is completely etched away, and the photoresist film is removed (peeled off). In this fashion, the operations including (1) formation of the photoresist film and application of the post baking at 90 to 120° C., (2) etching, and (3) removing (peeling off) are repeated a prescribed number of times until the surface of the insulating substrate  22  is planarized substantially completely. 
   Incidentally, it suffices to remove partially the soft magnetic thin film  24   d  until at least the tip surface of the projection  22   a  is exposed to the outside and, thus, it is unnecessary to remove completely the first protective film  30 , as shown in  FIG. 8H . However, where the projection  22   a  has an allowance in height, it is possible to remove partially the soft magnetic thin film  24   d  until the first protective film  30  is removed completely. 
   The step of forming the GMR film will now be described. In the step of forming the GMR film, a GMR film  26  is deposited on the GMR film-forming surface formed on the surface of the insulating substrate  22 , followed by processing the deposited GMR film  26  into a prescribed shape. To be more specific, it is desirable for the step of forming the GMR film to be carried out as follows. 
   In the first step, a photoresist film  38  is newly formed on the surface of the insulating substrate  22  except the region in which the GMR film  26  is to be formed, as shown in  FIG. 8I . The photoresist film  38  is formed by a method similar to that described previously in conjunction with the step for forming the projection  22   a . In this stage, the length of the region for forming the GMR film  26 , i.e., the region in which the photoresist film  38  is not formed, in the direction of the gap length is set sufficiently larger than the gap length. Also, where a high sensitivity is required, it is desirable for the length of the region for forming the GMR film  26  in the direction of the gap width to be smaller than the gap width, though the length of the particular region noted above is determined in accordance with, for example, the required sensitivity to the magnetic field and the electrical resistance. 
   In the next step, the GMR film  26  having a prescribed composition is deposited on the entire surface of the insulating substrate  22 , as shown in  FIG. 8J . As a result, a sound GMR film  26  having a prescribed thickness is formed in the region longer than the gap length in the direction of the gap length. At the same time, the GMR film  26  formed in the gap  24   a  is electrically connected to the thin film yokes  24   b  and  24   c . After formation of the GMR film  26 , the photoresist film  38  is removed by the lift-off method from the surface of the insulating substrate  22 , as shown in  FIG. 8K . 
   Incidentally, another method can be employed in place of the method described above for forming the GMR film  26 . To be more specific, the GMR film  26  can be formed in the gap  24   a  by the method comprising the steps of (1) depositing the GMR film  26  directly on the entire planarized surface of the insulating substrate  22 , (2) masking only the region in the vicinity of the projection  22   a  with, for example, a photoresist film, and (3) removing by etching that region alone of the GMR film  26  which is not covered with, for example, the photoresist film. 
   The step of forming the electrode will now be described. The electrodes  28   b  and  28   c  are formed in the edge portions of the thin film yokes  24   b  and  24   c  in the step of forming the electrode. To be more specific, a photoresist film  38  is newly formed on the insulating substrate  22  excluding the regions in which the electrodes  28   b ,  28   c  are to be formed, as shown in  FIG. 8L . The photoresist film  38  is formed by the method similar to that described previously in conjunction with the step of forming the projection. Then, a thin film  28   a  having a prescribed thickness and formed of an electrically conductive material is deposited from above the photoresist film  38 , as shown in  FIG. 8M , followed by removing (lifting off) the photoresist film  38 . As a result, it is possible to form the electrodes  28   b  and  28   c  in the edge portions of the thin film yoke s  24   b  and  24   c , respectively, as shown in  FIG. 8N . Incidentally, the electrode  28   b  alone is shown in  FIG. 8N . 
   Incidentally, the method of forming the electrodes  28   b  and  28   c  is not limited to the method described above. For example, it is possible to form the electrodes  28   b  and  28   c  by the method comprising the step of depositing a thin film  28   a  consisting of an electrically conductive material directly on the entire surface of the insulating substrate  22  except the region in the vicinity of the GMR film  26 , the step of covering the required portion with a photoresist film, and the step of removing the unnecessary portion by, for example, an Ar ion beam etching, a wet etching utilizing a chemical liquid, or a reactive ion etching. In the case of employing the particular method, however, it is necessary to form in advance a protective film for protecting the GMR film and the thin film yokes positioned below that portion of the thin film  28   a  which is to be removed. 
   The step of forming the surface protective film will now be described. A second protective film  32  serving to protect the thin film yokes  24   b ,  24   c , and the GMR film  26  is formed on the uppermost surface of the insulating substrate  22  in the step of forming the surface protective film. To be more specific, a photoresist film  38  is newly formed on the insulating substrate  22  excluding the region in which the second protective film  32  is to be formed, as shown in  FIG. 80 . The photoresist film  38  is formed by the method described previously in conjunction with the step of forming the projection. In this case, it is advisable to form the photoresist film  38  such that the electrodes  28   b ,  28   c  (the electrode  28   b  alone is shown in  FIG. 8O ) are partly covered with the second protective film  32 . Then, a second protective film  32  is deposited in a prescribed thickness from above the photoresist film  38  as shown in  FIG. 8P , followed by removing (lifting off) the photoresist film  38 . As a result, obtained is the thin film magnetic sensor  20  according to the first embodiment of the present invention, as shown in  FIG. 8Q . 
   Incidentally, the method of forming the second protective film  32  is not limited to the method described above. Alternatively, the second protective film  32  can be formed by the method comprising the step of, for example, depositing the second protective film  32  directly on the entire surface of the insulating substrate  22 , the step of forming a photoresist film in a manner to cover the required portion of the second protective film  32 , and the step of removing the unnecessary portion of the second protective film  32  by an Ar ion beam etching, a wet etching utilizing a chemical liquid, or a reactive ion etching. 
   The function and effect of the thin film magnetic sensor  20  according to the first embodiment of the present invention will now be described. 
   The conventional method of manufacturing the thin film magnetic sensor comprises depositing a soft magnetic thin film on the surface of an insulating substrate, forming a concave groove (gap) having a small width in the soft magnetic thin film thus formed so as to obtain thin film yokes positioned to face each other with the small gap interposed therebetween, and depositing a GMR film on the thin film yokes including the gap. 
   In the conventional method described above, however, the cross sectional shape of bottom portion of the GMR film formed within the gap is rendered triangular or trapezoid. As a result, the contact area between the side wall portion of the GMR film and the bottom portion of the GMR film is rendered markedly smaller than the average cross sectional area in the thickness direction of the GMR film. In the extreme case, the side wall portion and the bottom portion of the GMR film are brought into a linear contact. It follows that the contact electrical resistance between the thin film yoke and the GMR film is markedly changed by a slight change in the manufacturing conditions. In addition, the magnetic characteristics of the thin film magnetic sensor are rendered unstable. 
   Also, the metal-insulator system nano granular material, which is excellent in the magnetic characteristics, is brittle and, thus, when deposited within the gap so as to form a thin film, the film tends to be cracked along the boundary line between the thin film portion growing from the planar bottom portion of the gap and the thin film portion growing from the side wall of the gap. It follows that, in the case of using the metal insulator system nano granular material as the GMR film of the thin film magnetic sensor and deposited the material within the gap, the thin film magnetic sensor tends to be rendered unstable both electrically and magnetically. 
   On the other hand, the thin film magnetic sensor  20  according to the first embodiment of the present invention is constructed such that the projection  22   a  is formed on the surface of the insulating substrate  22  and the thin film yokes  24   b  and  24   c  are deposited on both sides of the projection  22   a . It follows that the gap  24   a  is under the state of being loaded with the projection  22   a  formed of an insulating nonmagnetic material. Such being the situation, if the GMR film  26  is deposited on the surface of the insulating substrate  22  after planarization of the tip surface of the projection  22   a , the deposition of the GMR film  26  is not impaired by the side walls of the thin film yokes  24   b  and  24   c.    
   Also, since the tip surface of the projection  22   a  and the region in the vicinity of the tip surface of the projection  22   a  acts as a relatively flat GMR film-forming surface longer than the gap length in the direction of the gap length, and the GMR film  26  is formed on the GMR film-forming surface, it is possible to form a sound GMR film  26  having a substantially uniform thickness in at least the gap  24   a . Also, the lower surface of the GMR film  26  can be electrically connected without fail to the upper surfaces of the thin film yokes  24   b  and  24   c . In addition, even in the case where a relatively brittle material is used for forming the GMR film  26 , the GMR film  26  is unlikely to be cracked. It follows that the contact electrical resistance between the GMR film  26  and the thin film yokes  24   b ,  24   c  is not significantly changed even if the manufacturing conditions are slightly changed so as to stabilize the magnetic characteristics of the thin film magnetic sensor. 
   Second Embodiment 
   A thin film magnetic sensor according to a second embodiment of the present invention will now be described.  FIG. 9  is a plan view schematically showing the construction of a thin film magnetic sensor  40  according to a second embodiment of the present invention,  FIG. 10  is a cross sectional view along the line X—X shown in  FIG. 9 ,  FIG. 11  is a cross sectional view showing the construction of a thin film magnetic sensor in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the second embodiment of the present invention, and  FIG. 12  is a cross sectional view showing another construction of a thin film magnetic sensor in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the second embodiment of the present invention. 
   As shown in the drawings, the thin film magnetic sensor  40  according to the second embodiment of the present invention comprises an insulating substrate  42 , a pair of thin film yokes  44   b ,  44   c , and a GMR film  46 . The thin film yokes  44   b  and  44   c  are positioned to face each other with a gap  44   a  interposed therebetween. Also, the GMR film  46  is formed in the gap  44   a  so as to be electrically connected to the thin film yokes  44   b  and  44   c . Also, electrodes  48   b  and  48   c  are connected to the edge portions of the thin film yokes  44   b  and  44   c , respectively. Further, the uppermost surface of the insulating substrate  42  is covered with a second protective film  52 . 
   The thin film yokes  44   b  and  44   c  are deposited on both sides of a projection  43   a  formed on the surface of the insulating substrate  42 . Also, the projection  43   a  includes a tapered convex portion  42   a  of the insulating substrate  42 , which is formed by etching the insulating substrate  42 , the GMR film  46  layered on the upper surface of the tapered convex portion  42   a  of the insulating substrate  42 , and a third protective film  50  layered on the GMR film  46 . Further, in the second embodiment of the present invention, a gap column  43  includes the projection  43   a  and a second protective film  52  layered on the projection  43   a . In other words, in the second embodiment of the present invention, that surface of the GMR film  46  which is exposed to the side surface and/or the lower inclined surface of the gap column  43  is electrically connected to the side surfaces and/or the lower inclined surfaces of the thin film yokes  44   b  and  44   c.    
   The gap column  43  of the particular construction can be formed by the method, comprising the steps of (1) depositing the GMR film  46  and the third protective film  50  in the order mentioned on the surface of the insulating substrate  42 , (2) removing the third protective film  50  entirely and removing the GMR film  46  partly or entirely until the GMR film  46  is exposed partly or entirely to the side wall surface of the projection  43   a  with the region forming the tip portion of the projection  43   a  left unremoved, and (3) forming the thin film yokes  44   b  and  44   c  on both sides of the projection  43   a , followed by depositing the second protective film  52  on the entire surface. 
   It is possible for that portion of the projection  43   a  which is perpendicular to the upper surface of the insulating substrate  42 , i.e., the side wall surface of the projection  43   a , to be formed of the third protective film  50  alone. In this case, those portions of the GMR film  46  which are exposed to the inclined side surfaces of the projection  43   a  can be connected to the thin film yokes  44   b  and  44   c  without fail, though the sensitivity is somewhat lowered. Further, in order to obtain a high sensitivity to the magnetic field, it is desirable for the GMR film  46  to be included in the side wall surface of the projection  43   a , as shown in  FIG. 12 . It is desirable for the thickness “t” of that portion of the GMR film  46  which constitutes a part of the side wall surface of the projection  43   a  to be not smaller than ½ of the thickness of the GMR film  46 . The sensitivity to the magnetic field can be increased with increase in the thickness “t” of that portion of the GMR film  46  which constitutes a part of the side wall surface of the projection  43   a.    
   Any kind of an insulating nonmagnetic material can be used for forming the third protective film  50  constituting the tip portion of the projection  43   a . To be more specific, the third protective film  50  can be formed of, for example, Al 2 O 3 , SiO 2 , Si 3 N 4  or a photoresist hard-baked under temperatures not lower than 200° C. 
   Incidentally, the insulating substrate  42 , the projection  43   a , thin film yokes  44   b ,  44   c , the GMR film  46 , the electrodes  48   b  and  48   c , the second protective film  52  and the other members are equal to the insulating substrate  22 , the projection  22   a , the thin film yokes  24   b ,  24   c , the GMR film  26 , the electrodes  28   b  and  28   c , the second protective film  32  and the other members included in the thin film magnetic sensor  20  according to the first embodiment of the present invention and, thus, the description of the insulating substrate  42 , etc. is omitted. 
   A method of manufacturing the thin film magnetic sensor  40  according to the second embodiment of the present invention will now be described. 
     FIGS. 13A to 13P  are cross sectional views collectively showing the manufacturing process of the thin film magnetic sensor according to the second embodiment of the present invention. The manufacturing process according to the second embodiment of the present invention comprises the step of forming the GMR film, the step of forming the projection, the step of forming the thin film yokes, the step of forming the electrodes, and the step of forming the surface protective film. 
   First of all, the step of forming the GMR film will now be described. In the step of forming the GMR film, a GMR film  46  is deposited on the surface of the insulating substrate  42 . To be more specific, it is desirable for the step of forming the GMR film to be carried out as follows. 
   In the first step, a photoresist film  38  is formed on the planarized surface of the insulating substrate  42  except the region in which the GMR film  46  is to be formed, as shown in  FIG. 13A . In this stage, the length of the region, in which the GMR film  46  is to be formed, in the direction of the gap length is set sufficiently larger than the gap length, and the width of the particular region noted above is defined in accordance with, for example, the required sensitivity to the magnetic field and the electrical resistance. In the next step, a GMR film  46  is formed on the entire surface of the insulating substrate  42  as shown in  FIG. 13B , followed by lifting off the photoresist film  38  so as to form the GMR film  46  in the region in which the gap  44   a  is to be formed, as shown in  FIG. 13C . 
   Incidentally, it is possible to employ another method for forming the GMR film  46  in place of the method described above. To be more specific, the GMR film  46  can also be formed by the method, comprising the steps of (1) depositing the GMR film  46  directly on the planarized entire surface of the insulating substrate  42 , (2) masking only the region in which the projection  43   a  is to be formed and the region in the vicinity of the particular region noted above with, for example, a photoresist film, and (3) removing-by etching that region alone of the GMR film  46  which is not covered with, for example, the photoresist film, as in the first embodiment described previously. 
   The step of forming the projection will now be described. In the step of forming the projection, the projection  43   a  is formed by the method, comprising the step of further depositing a third protective film  50  on the GMR film  46 , and the step of removing entirely the third protective film  50  and removing partly or entirely the GMR film  46 , with the region forming the projection  43   a  left unremoved, until the GMR film  46  is exposed partly or entirely to the side wall surface of the projection  43   a  so as to form the projection  43   a . To be more specific, it is desirable for the step of forming the projection to be carried out as follows. 
   In the first step, the third protective film  50  is deposited in a prescribed thickness on the entire surface of the insulating substrate  42  as shown in  FIG. 13D . Incidentally, the accuracy in the shape of the projection  43   a  formed by the etching tends to be rendered poor with increase in the thickness of the third protective film  50 . Such being the situation, it is desirable for the third protective film  50  to be formed as thin as possible. 
   In the next step, a penetration preventing film  34  consisting of, for example, a Cr thin film or a Ti thin film is formed on the third protective film  50 , as shown in  FIG. 13E , followed by forming a photoresist film  38   a  in the region in which the projection  43   a  is to be formed and another photoresist film  38   b  in the region in which the thin film yokes  44   b ,  44   c  are not formed, as shown in  FIG. 13F . Incidentally, it is desirable to apply the post baking to the photoresist films  38   a  and  38   b  as in the first embodiment of the present invention described previously. 
   In the next step, an Ar ion beam etching is performed under prescribed conditions while rotating the insulating substrate  42  so as to form the projection  43   a  on the surface of the insulating substrate  42 , as shown in  FIG. 13G . The side walls in the tip portion of the projection  43   a  are perpendicular to the upper surface of the insulating substrate  42 . Also, the projection  43   a  has a prescribed width (gap length) and a height. If the irradiating conditions are optimized, it is possible to permit the GMR film  46  to be exposed partly or entirely to the side wall surfaces, which are perpendicular to the upper surface of the insulating substrate  42 , of the projection  43   a . Further, the insulating substrate  42  is also etched simultaneously along the boundary line of the photoresist film  38   b . The insulating substrate  42  is etched in this step in a direction substantially perpendicular to the upper surface of the insulating substrate  42  so as to form two concavities in the surface region of the insulating substrate  42  such that these two concavities are positioned to face each other with the projection  43   a  interposed therebetween. After completion of the etching, the photoresist film remaining on the surface of the insulating substrate  42  is removed (peeled off), as shown in  FIG. 13H . 
   The step of forming the thin film yokes will now be described. In the step of forming the thin film yokes, a soft magnetic material is deposited on both sides of the projection  43   a  so as to form a pair of thin film yokes  44   b  and  44   c  positioned to face each other with the projection  43   a  interposed therebetween and electrically separated from each other completely. The thin film yokes  44   b  and  44   c  can be formed by the process substantially equal to the process described previously in conjunction with the first embodiment of the present invention. 
   Specifically, for forming the thin film yokes  44   b  and  44   c , a photoresist film  38  is newly formed first on the surface of the insulating substrate  42  excluding the regions in which the thin film yokes  44   b  and  44   c  are to be formed, as shown in  FIG. 13I . Then, a soft magnetic thin film  44   d  is deposited in a prescribed thickness on the entire surface of the insulating substrate  42 , as shown in  FIG. 13J , followed by removing the photoresist film  38  by the lift-off method as shown in  FIG. 13K . 
   In the next step, a first protective film  30  is formed on the entire surface of the insulating substrate  42  as shown in  FIG. 13L . Then, the first protective film  30  and the soft magnetic thin film  44   d  are partially removed by the mechanical polishing method or the etch back method described previously until the soft magnetic thin film  44   d  is removed completely from at least the tip surface of the projection  43   a . As a result, the thin film yokes  44   b  and  44   c  are formed to face each other with the projection  43   a  interposed therebetween, as shown in  FIG. 13M . 
   Incidentally,  FIG. 13M  shows that the first protective film  30  remaining on the thin film yokes  44   b ,  44   c  is removed (peeled off) completely after formation of the thin film yokes  44   b  and  44   c . However, it is possible for the first protective film  30  to be partly left unremoved on the thin film yokes  44   b  and  44   c . Also, the mechanical polishing method or the etch back method employed for removing the unnecessary portion of the soft magnetic thin film  44   d  can be replaced by a method (hereinafter referred to as an “extra film removing method), comprising the steps of (1) masking the soft magnetic thin film  44   d  with, for example, a photoresist film except the portion deposited on the tip surface of the projection  43   a , and (2) removing by etching that portion of the soft magnetic thin film  44   d  which is not covered with, for example, the photoresist film. 
   The electrode forming step will now be described. The electrode forming step is carried out by the procedures equal to those described previously in conjunction with the first embodiment of the present invention. Specifically, a photoresist film  38  is newly formed on the surface of the insulating substrate  42  except the regions in which the electrodes  48   b  and  48   c  are to be formed as shown in  FIG. 13N , followed by depositing a thin film  48   a  consisting of an electrically conductive material on the surface of the insulating substrate  22 , as shown in  FIG. 13O , and subsequently removing (lifting off) the photoresist film  38 , as shown in  FIG. 13P . As a result, the electrodes  48   b  and  48   c  can be formed on the edge portions of the thin film yokes  44   b  and  44   c , respectively. Incidentally, the electrode  48   b  alone is shown in  FIG. 13P . 
   Further, the second protective film  52  is formed on the surface of the insulating substrate  42  by carrying out the step of forming the surface protective film by the procedures similar to those described previously in conjunction with the first embodiment of the present invention so as to obtain the thin film magnetic sensor  40  according to the second embodiment of the present invention. 
   The function and effect of the thin film magnetic sensor  40  according to the second embodiment of the present invention will now be described. In the second embodiment of the present invention, the GMR film  46  and the third protective film  50  are deposited in the order mentioned on the surface of the insulating substrate  42 , followed by etching the surface of the insulating substrate  42  under prescribed conditions. As a result, it is possible to form the projection  43   a  having the GMR film  46  exposed partly or entirely to the side wall surface thereof. 
   When depositing the soft magnetic thin film  44   d , the shading is scarcely formed around the projection  43   a  projecting upward from the surface of the insulating substrate  42  unlike the case of depositing the soft magnetic thin film within a small groove. It follows that the soft magnetic thin film  44   d  is deposited in the second embodiment of the present invention such that the soft magnetic thin film  44   d  is in direct contact strongly with the side wall surface of the projection  43   a . As a result, a face contact is achieved without fail between the thin film yokes  44   b ,  44   c  each formed of the soft magnetic thin film  44   d  and the GMR film  46  exposed to the side wall surfaces of the projection  43   a . Also, the contact electrical resistance between the thin film yokes  44   b ,  44   c  and the GMR film  46  is not appreciably changed even if the manufacturing conditions are slightly changed so as to stabilize the magnetic characteristics of the thin film magnetic sensor. 
   It should be noted that, if the thin film yokes  44   b  and  44   c  are magnetized by the external magnetic field, the magnetic flux leaking from the thin film yokes  44   b ,  44   c  run mainly through the region between the side wall surfaces of the projection  43   a . It follows that, where the GMR film  46  is exposed to the side wall surfaces of the projection  43   a , a stronger magnetic field acts on the GMR film  46  so as to further improve the sensitivity of the thin film magnetic sensor to the magnetic field. 
   Third Embodiment 
   A thin film magnetic sensor according to a third embodiment of the present invention will now be described.  FIG. 14  is a plan view schematically showing the construction of a thin film magnetic sensor  60  according to a third embodiment of the present invention,  FIG. 15  is a cross sectional view along the line XV—XV shown in  FIG. 14 , and  FIG. 16  is a cross sectional view showing in a magnified fashion the region in the vicinity of the gap included in the thin film magnetic sensor according to the third embodiment of the present invention. 
   As shown in the drawings, the thin film magnetic sensor  60  according to the third embodiment of the present invention comprises an insulating substrate  62 , a pair of thin film yokes  64   b ,  64   c , and a GMR film  66 . The thin film yokes  64   b  and  64   c  are positioned to face each other with a gap  64   a  interposed therebetween. Also, the GMR film  66  is formed in the gap  64   a  so as to be electrically connected to the thin film yokes  64   b  and  64   c . Further, electrodes  68   b  and  68   c  are connected to the edge portions of the thin film yokes  64   b  and  64   c , respectively, and the uppermost surface of the insulating substrate  62  is covered with a second protective film  72 . 
   The GMR film  66  is deposited on the surface of the insulating substrate  62 . Also, a projection  63   a  consisting of the GMR film  66  and a fourth protective film  70  is formed in the gap  64   a , and the thin film yokes  64   b ,  64   c  are formed on both sides of the projection  63   a . To be more specific, in the third embodiment of the present invention, the upper surface of the GMR film  66  is in an electric face contact with the lower surfaces of the thin film yokes  64   b ,  64   c . Further, in the third embodiment of the present invention, a gap column  63  consists of the projection  63   a  and the second protective film  72 . 
   In forming the projection  63   a , the GMR film  66  and the fourth protective film  70  formed of an insulating nonmagnetic material are successively deposited in the order mentioned on the surface of the insulating substrate  62 , followed by partially removing the fourth protective film  70  until at least the surface of the GMR film  66  is exposed to the outside. In this stage, the fourth protective film  70  in the region forming the projection  63   a  is left unremoved. The materials suitable for use as the material of the fourth protective film  70  include, for example, Al 2 O 3 , SiO 2 , Si 3 N 4  and photoresist hard-baked under temperatures not lower than 200° C. 
   Incidentally, the insulating substrate  62 , the projection  63   a , the thin film yokes  64   b  and  64   c , the GMR film  66 , the electrodes  68   b  and  68   c , the second protective film  72  and the other members are equal to the insulating substrate  22 , the projection  22   a , the thin film yokes  24   b  and  24   c , the GMR film  26 , the electrodes  28   b  and  28   c , the second protective film  32  and the other members included in the thin film magnetic sensor  20  according to the first embodiment of the present invention and, thus, the description of the insulating substrate  62 , etc. is omitted. 
   The manufacturing process of the thin film magnetic sensor  60  according to the third embodiment of the present invention will now be described. 
     FIGS. 17A to 17O  are cross sectional views collectively showing the manufacturing process of the thin film magnetic sensor according to the third embodiment of the present invention. The manufacturing process for this embodiment comprises the step of forming a GMR film, the step of forming a projection, the step of forming thin film yokes, the step of forming electrodes, and the step of forming a surface protective film. 
   The step for forming the GMR film in the third embodiment of the present invention is substantially equal to that in the second embodiment of the present invention described previously. To be more specific, a photoresist film  38  is formed first on the planarized surface of the insulating substrate  62  except the region in which the GMR film  66  is to be formed, as shown in  FIG. 17A . Then, the GMR film  66  having a prescribed composition is deposited in a prescribed thickness on the photoresist film  38 , as shown in  FIG. 17B , followed by removing (lifting off) the photoresist film  38  as shown in  FIG. 17C . In this fashion, it is possible to form the GMR film  66  that is longer than the gap length in the direction of the gap length. 
   The step for forming the projection will now be described. In the step for forming the projection, the fourth protective film  70  is further deposited on the GMR film  66  formed on the surface of the insulating substrate  62 , followed by partially removing the fourth protective film  70  until at least the surface of the GMR film  66  is exposed to the outside. In this stage, that region of the fourth protective film  70  which forms the projection  63   a  is left unremoved. To be more specific, it is desirable for the step of forming the projection to be carried out as follows. 
   To be more specific, a fourth protective film  70  is deposited in a prescribed thickness on the entire surface of the insulating substrate  62 , as shown in  FIG. 17D . Incidentally, the accuracy of the shape of the projection  63   a  formed by the etching in the subsequent step tends to be lowered with increase in the thickness of the fourth protective film  70 . Such being the situation, it is desirable for the fourth protective film  70  to be formed as thin as possible, as in the first embodiment of the present invention described previously. 
   In the next step, a penetration preventing film  34  consisting of, for example, a Cr thin film or a Ti thin film is formed on the fourth protective film  70 , as shown in  FIG. 17E , followed by forming a photoresist film  38  in the portion where the projection  63   a  is to be formed, as shown in  FIG. 17F . 
   In the next step, an Ar ion beam etching is carried out while rotating the insulating substrate  62  so as to remove partially the penetration preventing film  34  and the fourth protective film  70 . The ion beam etching is carried out under the conditions which permit the ion beam to run in a direction relatively close to the vertical direction. As a result, formed is the projection  63   a  on the surface of the GMR film  66 , as shown in  FIG. 17G . The projection  63   a  thus formed has a side wall having an optional angle relative to the upper surface of the insulating substrate  62 . Also, the projection  63   a  has a prescribed width (gap length) and a prescribed height. Incidentally, if the etching conditions are optimized, it is possible for the projection  63   a  to be shaped like a column free from the tapered portion and substantially perpendicular to the upper surface of the insulating substrate  62 . After completion of the etching, the photoresist film  38  remaining on the tip surface of the projection  63   a  is removed (peeled off), as shown in  FIG. 17H . 
   The step of forming the thin film yokes will now be described. In the step of forming the thin film yokes, a soft magnetic thin film  64   d  is deposited on both sides of the projection  63   a  so as to form a pair of thin film yokes  64   b ,  64   c  positioned to face each other with the projection  63   a  interposed therebetween and electrically separated from each other completely. The thin film yokes  64   b  and  64   c  can be formed by the method substantially equal to the method employed in the first embodiment of the present invention described previously. 
   To be more specific, a photoresist film  38  is newly formed on the surface of the insulating substrate  62  except the regions where the thin film yokes  64   b ,  64   c  are to be formed, as shown in  FIG. 17I . Then, a soft magnetic thin film  64   d  is deposited in a prescribed thickness on the entire surface of the insulating substrate  62  as shown in  FIG. 17J , followed by removing (lifting off) the photoresist film  38  as shown in  FIG. 17K . 
   In the next step, a first protective film  30  is formed on the entire surface of the insulating substrate  62  as shown in  FIG. 17L , followed by partially removing the soft magnetic thin film  64   d  by the mechanical polishing method or the etch back method until the soft magnetic thin film  64   d  is removed completely from at least the tip surface of the projection  63   a . As a result, formed are the thin film yokes  64   b ,  64   c  positioned to face each other with the projection  63   a  interposed therebetween as shown in  FIG. 17M . Incidentally, after formation of the thin film yokes  64   b ,  64   c , the first protective film  30  remaining on the thin film yokes  64   b ,  64   c  is completely removed in the step shown in  FIG. 17M . However, it is possible for the first protective film  30  to be partly left unremoved on the thin film yokes  64   b ,  64   c . Also, it is possible to employ the extra film removing method in place of the mechanical polishing method or the etch back method. 
   The step for forming the electrode will now be described. The step for forming the electrode is carried out by the procedures similar to those in the first embodiment of the present invention described previously. Specifically, a photoresist film  38  is newly formed on the surface of the insulating substrate  62  except the regions where the electrodes  68   b ,  68   c  are to be formed, followed by depositing an electrode material  68   a  on the photoresist film  38  as shown in  FIG. 17N  and subsequently removing (lifting off) the photoresist film  38  as shown in  FIG. 17O . By the procedures described above, it is possible to form the electrodes  68   b  and  68   c  in the edge portions of the thin film yokes  64   b  and  64   c , respectively. Incidentally, the electrode  68   b  alone is shown in  FIG. 17O . 
   Then, the second protective film  72  is formed on the surface of the insulating substrate  62  by carrying out the step for forming the surface protective layer by the procedures similar to those in the first embodiment of the present invention described previously so as to obtain the thin film magnetic sensor  60  according to the third embodiment of the present invention. 
   The function and effect of the thin film magnetic sensor  60  according to the third embodiment of the present invention will now be described. The thin film magnetic sensor  60  according to the third embodiment of the present invention is prepared by forming the GMR film  66 , which is longer than the gap length in the direction of the gap length, on the surface of the insulating substrate  62 , followed by depositing the fourth protective film  70  on the GMR film  66  and subsequently forming the projection  63   a  and, then, depositing the soft magnetic thin film  64   d . It should be noted that, in the thin film magnetic sensor  60  for this embodiment, an electric area-to-area contact can be achieved without fail between the upper surface of the GMR film  66  and the lower surfaces of the thin film yokes  64   b ,  64   c . It follows that the contact electrical resistance between the thin film yokes  64   b ,  64   c  and the GMR film  66  is not appreciably changed even if the manufacturing conditions are slightly changed so as to stabilize the magnetic characteristics of the thin film magnetic sensor  60 . 
   EXAMPLES 
   Example 1 
   A thin film magnetic sensor  40  that was constructed as shown in  FIGS. 9 to 11  was manufactured by the method shown in  FIGS. 13A to 13P . In this Example, 25 element groups (chips)  41  were formed on a single insulating substrate  42 , as shown in  FIG. 20B . Each element group (chip)  41  included  4  unit elements  40   a  each consisting of a single GMR film  46  and a pair of thin film yokes  44   b ,  44   c  arranged on both sides of the GMR film  46  as shown in  FIG. 20A . It follows that  100  unit elements  40   a  in total were formed on the single insulating substrate  42 . 
   A nonalkali glass substrate was used as the insulating substrate  42 . The GMR film  46  was formed of a metal-insulator system nano granular material having a composition of FeCo—MgF 2 . Further, a CoFeSiB amorphous film was used as each of the thin film yokes  44   b  and  44   c . The thickness of each of the thin film yokes  44   b  and  44   c  was set at 1.0 μm. The thickness of the GMR film  46  was set at 0.5 μm. Further, the gap length was set at 2.0 μm. Also, after deposition of the soft magnetic thin film  44   d , the soft magnetic thin film  44   d  was partially removed by the extra film removing method so as to expose the tip surface of the projection  43   a  to the outside. 
   Example 2 
   Twenty-five chips (or 100 unit elements in total) were formed on the insulating substrate  42  by the procedures equal to those for Example 1, except that the etch back method was employed for partially removing the deposited soft magnetic thin film  44   d  until the tip surface of the projection  43   a  was exposed to the outside. 
   Comparative Example 1 
   Sixteen chips each including 4 thin film magnetic sensors  10  as unit elements, i.e., 64 unit elements (thin film magnetic sensors  10 ) in total, which were constructed as shown in  FIGS. 1 to 3 , were manufactured as follows. Specifically, a soft magnetic thin film consisting of a CoFeSiB amorphous was deposited in a thickness of 1.0 μm on the surface of an insulating substrate  12  of a no-alkali glass substrate. Then, the soft magnetic thin film was partially etched so as to form thin film yokes  14 ,  14 , which were positioned to face each other with a gap (groove)  14   a  having a gap length of 2.0 μm interposed therebetween. 
   In the next step, a GMR film  16  consisting of a metal-insulator system nano granular material having a composition of FeCo—MgF 2  was deposited in a thickness of 0.5 μm on the surface of the insulating substrate  12  with a mask arranged to cover the surface of the insulating substrate  12  except the region of the gap  14   a . Further, electrodes  18 ,  18  were formed on the edge portions of the thin film yokes  14 ,  14 , followed by forming a protective film  19  in a manner to cover the surfaces of the thin film yokes  14 ,  14  and the GMR film  16  so as to obtain the thin film magnetic sensor  10 . 
   The thin film magnetic sensor obtained in each of Examples 1, 2 and Comparative Example 1 was subjected to a heat treatment at 200° C. for 1.0 hour in order to eliminate the internal strain of each of the multilayer films, followed by measuring the electrical resistance (kΩ) and the MR ratio (%) under the magnetic field of 100 (Oe) for each of the unit elements. Further, the variation ΔR in the resistance values of elements within the chip was calculated in accordance with the formula given below by using the electrical resistance values measured for the four adjacent unit elements within the chip
 
Δ R=|R   i   −R   j |×100/ R   m  (%)
 
   where R i  and R j  denote the electrical resistance values of the i-th unit element and the j-th unit element, respectively, i and j denote integers of 1 to 4, the values of i and j differing from each other, and R m  denotes the average value of the electrical resistance values of the four unit elements within the same chip. 
     FIGS. 18 and 19  show the distribution of the electrical resistance values of the unit elements and the distribution of the variation ΔR in the resistance values of the elements within the chip, respectively. In the case of the thin film magnetic sensor  10  obtained in Comparative Example 1, the electrical resistance values of the unit elements were distributed over a range of between 100 kΩ and 1600 kΩ. In other words, the largest resistance value was found to be more than 10 times as large as the smallest resistance value. On the other hand, the variation ΔR in the resistance values of the elements within the chip for Comparative Example 1 was found to fall within a range of between 2% and 40%. Further, the variation in the MR ratios of the unit elements for Comparative Example 1 was found to fall within a range of between 0% and 6%. It should be noted that only about 10% of all the unit elements exhibited the MR ratio not smaller than 5%, indicating that the yield of the thin film magnetic sensor was very low in Comparative Example 1. 
   On the other hand, in the case of the thin film magnetic sensors  40  obtained in each of Examples 1 and 2, the electrical resistance values of the unit elements were stable, which were found to fall within a range of between 400 kΩ and 1000 kΩ. In other words, the variation in the electrical resistance values was very small, compared with Comparative Example 1. Also, the variation ΔR in the resistance values of the elements within the chip was not larger than 6% in Examples 1 and 2 of the present invention, which was markedly smaller than that for Comparative Example 1. Further, the MR ratio of the unit element was found to fall within a range of 5% and 7% in each of Examples 1 and 2 of the present invention. In addition, the thin film magnetic sensors  40  for the Examples of the present invention exhibited a high MR ratio with a high stability such that each of the unit elements exhibited an MR ratio not lower than 5%. 
   The embodiments described above are simply intended to clarify the technical concept of the present invention. Of course, the present invention should not be limited to the embodiments described above in interpreting the technical scope of the present invention. The present invention can be worked in variously modified fashions within the spirit of the present invention and within the scope defined by the accompanying claims. 
   For example, although the element of the present invention having the GMR film and the thin film yokes arranged on both sides of the GMR film is suitable for a magnetic sensor, application of the present invention is not limited to a magnetic sensor. The element of the present invention can also be applied to, for example, a magnetic memory and a magnetic head.