Sensor element and manufacturing method thereof

Abstract

[Problem] To electrically connect a lead layer and a protective film reliably even when the film thickness of a protective film that covers a functional film is extremely thin. [Solution] After the conductive protective film 51 is formed on the surface of the functional film 20, reverse sputtering is performed while a portion of the surface of the protective film 51 is covered with a mask 60, thereby physically restoring a natural oxide film 52 formed on the surface of the protective film 51 not covered by the mask 60. Thereafter, a lead layer 40 is formed on the surface of the protective film 51 not covered by the mask 60. Consequently, since the natural oxide film 52 formed on the surface of the protective film 51 can be removed without performing etching, the lead layer 40 and the protective film 51 can be connected electrically without damaging the functional layer 20 even when the film thickness of the protective film 51 is extremely thin.

Description

[Technical Field]

[0001] The present invention relates to a sensor element and a method for manufacturing the same, and more particularly to a sensor element having a conductive protective film covering the surface of a functional film, and a method for manufacturing the same. [Background technology]

[0002] Patent Document 1 discloses a GMR element covered with a protective film made of Ta, etc. Here, since a natural oxide film is formed on the surface of metals such as Ta, when a lead layer for applying voltage to a functional film constituting a GMR element, etc. is formed on the surface of the protective film made of Ta, etc., it is necessary to remove the natural oxide film formed on the surface of the protective film beforehand. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5971681 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the protective film is very thin, it is difficult to remove the native oxide film by etching so that the protective film remains. In other words, in this case, if the etching amount is excessive, the protective film at the etched portion will be completely removed, exposing the functional film to the etching, while if the etching amount is insufficient, the native oxide film will remain, resulting in a high resistance value between the lead layer and the protective film.

[0005] Therefore, an object of the present invention is to reliably electrically connect the lead layer and the protective film even when the protective film covering the functional film is very thin. [Means for solving the problem]

[0006] The sensor element according to the present invention comprises a conductive functional film whose electrical properties change based on a predetermined physical quantity to be detected, a conductive protective film covering the surface of the functional film, and a lead layer that applies a voltage to the functional film via the protective film, wherein the protective film has a connection area covered by the lead layer and a non-connection area not covered by the lead layer, the surface of the non-connection area of ​​the protective film is covered with an insulating film, the surface of the connection area of ​​the protective film is in contact with the lead layer without being covered by the insulating film, and the thickness of the protective film in the connection area is thicker than the thickness of the protective film in the non-connection area.

[0007] According to the present invention, the thickness of the protective film in the connection area is ensured, so that the lead layer and the protective film can be reliably electrically connected even if the thickness of the protective film covering the functional film is very thin.

[0008] In the present invention, the insulating film may be a natural oxide film formed by oxidizing the surface of the protective film, which prevents the natural oxide film from being interposed between the lead layer and the protective film, thereby enabling the resistance between them to be sufficiently reduced.

[0009] In the present invention, the protective film may be a single film, which allows the protective film to be formed in a single step.

[0010] In the present invention, the functional film may be a part of a magnetoresistive element whose resistance value changes in response to a magnetic field, the functional film may have first and second element pieces, a hard magnetic material may be provided between the first and second element pieces to apply a magnetic bias to the functional film, and the lead layer may cover the surface of the hard magnetic material and the connection region of the first element piece and the connection region of the second element piece to electrically connect the first element piece and the second element piece. This makes it possible to provide a magnetic sensor with little random noise.

[0011] The method for manufacturing a sensor element according to the present invention is characterized by comprising a first step of depositing a conductive functional film whose electrical properties change based on a predetermined physical quantity to be detected; a second step of depositing a conductive protective film on the surface of the functional film; a third step of covering a portion of the surface of the protective film with a mask; a fourth step of physically reducing a native oxide film formed on the surface of the protective film that is not covered by the mask by performing reverse sputtering through the mask; and a fifth step of depositing a lead layer on the connection area of ​​the protective film that is not covered by the mask after the fourth step.

[0012] According to the present invention, the natural oxide film formed on the surface of the protective film can be removed without etching, and therefore, even if the protective film is very thin, it is possible to electrically connect the lead layer and the protective film without damaging the functional film.

[0013] In the present invention, the fourth and fifth steps may be carried out consecutively without exposure to the atmosphere, which prevents a native oxide film from forming again on the surface of the physically reduced protective film. [Effects of the Invention]

[0014] As described above, according to the present invention, even if the protective film covering the functional film is very thin, the lead layer and the protective film can be reliably electrically connected. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic plan view illustrating the structure of a sensor element 10 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along the line AA shown in FIG. [Figure 3] FIG. 3 is a schematic enlarged cross-sectional view of region B shown in FIG. [Figure 4] FIG. 4 is a schematic enlarged cross-sectional view of an area C shown in FIG. [Figure 5] FIG. 5 is a process diagram for explaining a method for manufacturing the sensor element 10. [Figure 6] FIG. 6 is a process diagram for explaining a method for manufacturing the sensor element 10. [Figure 7] FIG. 7 is a process diagram for explaining the method of manufacturing the sensor element 10. [Figure 8] FIG. 8 is a process diagram for explaining the method of manufacturing the sensor element 10. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] Fig. 1 is a schematic plan view illustrating the structure of a sensor element 10 according to one embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view taken along line AA shown in Fig. 1.

[0018] The sensor element according to this embodiment is a magnetic sensor for detecting magnetic fields. As shown in FIGS. 1 and 2 , it includes functional films 20 and hard magnetic materials 30 arranged alternately in the X direction, and a lead layer 40 that electrically connects two element pieces of the functional film 20 adjacent in the X direction. The functional films 20 and hard magnetic materials 30 are formed on a sensor substrate 11 via an insulating film 12. The functional film 20 is a magnetoresistive element whose resistance changes depending on the direction and strength of a magnetic field. The functional film 20 is essentially converted into a single magnetic domain by a magnetic bias applied by the hard magnetic materials 30. This reduces random noise caused by magnetic domain disturbance. The magnetic sensing direction of the functional film 20 is, for example, the Y direction. The hard magnetic materials 30 are made of a material with high resistance. The lead layer 40 covers the surface of the hard magnetic materials 30 and also covers the ends of the two element pieces of the functional film 20 that sandwich the hard magnetic materials 30, thereby electrically connecting the two element pieces of the functional film 20 adjacent in the X direction. As a result, the resistance value of the magnetoresistive strip made up of element pieces of multiple functional films 20 arranged in the X direction changes depending on the magnetic field strength in the Y direction, for example. Therefore, by applying a voltage to the magnetoresistive strip via the lead layer 40, it becomes possible to detect a magnetic field.

[0019] FIG. 3 is a schematic enlarged cross-sectional view of region B shown in FIG.

[0020] 3, the surface of the functional film 20 is covered with a protective film 51. The protective film 51 is provided to protect the functional film 20, and is made of a conductive material such as Ta, Ti, or nichrome, which is excellent in terms of cost, solvent resistance, and resistance value. The protective film 51 made of such a conductive material is easily oxidized in the atmosphere, and therefore a natural oxide film 52 is formed on the surface not covered by the lead layer 40.

[0021] FIG. 4 is a schematic enlarged cross-sectional view of an area C shown in FIG.

[0022] In the example shown in FIG. 4 , the functional film 20 includes a pinned layer 21, a nonmagnetic layer 22, and a free layer 23, and the surface of the free layer 23 is covered with a protective film 51. With this configuration, the functional film 20 functions as a GMR element. The thickness of the protective film 51 is not uniform. If T1 is the thickness in the connection region S1 covered with the lead layer 40 and T2 is the thickness in the non-connection region S2 not covered with the lead layer 40, then T1 > T2. Here, the surface of the non-connection region S2 of the protective film 51 is covered with a native oxide film 52, whereas the surface of the connection region S1 of the protective film 51 is not covered with the native oxide film 52 and is in contact with the lead layer 40 directly or via an adhesive layer such as Ti. Although the thickness of the protective film 51 varies depending on the planar position, it is a single film formed in a single film formation process.

[0023] As described above, in the sensor element 10 according to this embodiment, the thickness T1 of the protective film 51 in the connection region S1 covered with the lead layer 40 is sufficiently ensured, and the lead layer 40 and the protective film 51 are not insulated by the natural oxide film 52, so that the functional film 20 is reliably protected and a voltage can be applied from the lead layer 40 to the functional film 20 via the protective film 51. Note that another insulating film formed by a subsequent chemical treatment or the like may be present on the surface of the natural oxide film 52 present in the non-connection region S2.

[0024] Next, a method for manufacturing the sensor element 10 according to this embodiment will be described.

[0025] 5 to 8 are process diagrams illustrating a method for manufacturing the sensor element 10 according to this embodiment.

[0026] First, as shown in Fig. 5, a functional film 20 is formed, and then a protective film 51 is formed on the surface of the functional film 20 by a method such as sputtering. Immediately after the formation, the surface of the protective film 51 is exposed, but when the protective film 51 is removed from the chamber and exposed to the atmosphere, a natural oxide film 52 is formed on the surface of the protective film 51. The thickness of the protective film 51 immediately after the formation is the thickness T1 shown in Fig. 4, and the thickness of the protective film 51 after the natural oxide film 52 is formed is the thickness T2 shown in Fig. 4.

[0027] Next, as shown in FIG. 6, a photosensitive resist is formed on the surface of the protective film 51 on which the native oxide film 52 has been formed, followed by exposure and development to form a mask 60. As a result, a portion of the protective film 51 is covered with the mask 60. By performing reverse sputtering in this state, the native oxide film 52 formed on the surface of the protective film 51 that is not covered with the mask 60 is physically reduced. Specifically, sputtering gas such as Ar is bombarded onto the native oxide film 52 to drive out the oxygen contained in the native oxide film 52. To achieve this, it is necessary to adjust the applied voltage and gas pressure so that only oxygen atoms are driven out without driving out the metal elements contained in the native oxide film 52. As a result, the portion of the native oxide film 52 not covered with the mask 60 is reduced, returning to the protective film 51 made of metal, as shown in FIG. 7.

[0028] Next, as shown in FIG. 8 , the lead layer 40 is formed by sputtering or the like on the protective film 51 in the portion not covered by the mask 60. This allows the protective film 51 and the lead layer 40 to come into direct contact with each other without the intermediary of the native oxide film 52. An adhesive layer such as Ti may be formed before forming the lead layer 40. The mask 60 is then removed by ashing or the like to complete the sensor element 10 according to this embodiment. Here, the physical reduction of the native oxide film 52 by reverse sputtering and the subsequent formation of the lead layer 40 are performed consecutively without exposure to the atmosphere. Specifically, after processing using a chamber for reverse sputtering, the substrate may be transferred to a separate chamber for forming the lead layer 40 while maintaining a reduced pressure, or the reverse sputtering and sputtering of the lead layer 40 may be performed consecutively using the same chamber.

[0029] As described above, in this embodiment, the native oxide film 52 is physically reduced by reverse sputtering, and then the lead layer 40 is formed using the same mask 60, so that it is possible to adhere the protective film 51 and the lead layer 40 to each other without the native oxide film 52. Furthermore, if a chemical treatment or the like is performed after the lead layer 40 is formed, another insulating film may be formed on the surface of the native oxide film 52, but at this point, the connection region S1 of the protective film 51 is in contact with the lead layer 40, so that such an insulating film is not formed at the interface between them.

[0030] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0031] For example, in the above embodiment, an example in which the present invention is applied to a magnetic sensor has been described, but the application of the present invention is not limited to this, and the present invention can be widely applied to sensor elements that use a conductive functional film whose electrical characteristics change based on a predetermined physical quantity that is the object of detection, such as an infrared sensor or a gyro sensor. [Explanation of symbols]

[0032] 10 Sensor element 11 Sensor board 12 insulating film 20 Functional membrane 21 pin layer 22 Non-magnetic layer 23 Free Tier 30 Hard magnetic material 40 Lead Layer 51 Protective film 52 Native oxide film 60 Mask S1 Connection Area S2 disconnected area

Claims

1. a conductive functional film whose electrical characteristics change based on a predetermined physical quantity to be detected; a conductive protective film covering the surface of the functional film; a lead layer that applies a voltage to the functional film through the protective film, the protective film has a connection region covered with the lead layer and a non-connection region not covered with the lead layer, a surface of the non-connection region of the protective film is covered with an insulating film; a surface of the connection region of the protective film is in contact with the lead layer without being covered with an insulating film; the thickness of the protective film in the connection region is greater than the thickness of the protective film in the non-connection region; The sensor element is characterized in that the insulating film is a natural oxide film formed by oxidizing the surface of the protective film.

2. a conductive functional film whose electrical characteristics change based on a predetermined physical quantity to be detected; a conductive protective film covering the surface of the functional film; a lead layer that applies a voltage to the functional film through the protective film, the protective film has a connection region covered with the lead layer and a non-connection region not covered with the lead layer, a surface of the non-connection region of the protective film is covered with an insulating film; a surface of the connection region of the protective film is in contact with the lead layer without being covered with an insulating film; the thickness of the protective film in the connection region is greater than the thickness of the protective film in the non-connection region; The sensor element, wherein the protective film is a single film.

3. a conductive functional film whose electrical characteristics change based on a predetermined physical quantity to be detected; a conductive protective film covering the surface of the functional film; a lead layer that applies a voltage to the functional film through the protective film, the protective film has a connection region covered with the lead layer and a non-connection region not covered with the lead layer, a surface of the non-connection region of the protective film is covered with an insulating film; a surface of the connection region of the protective film is in contact with the lead layer without being covered with an insulating film; the thickness of the protective film in the connection region is greater than the thickness of the protective film in the non-connection region; the functional film is a part of a magnetoresistive element whose resistance value changes based on a magnetic field; the functional film has first and second element pieces, a hard magnetic material that applies a magnetic bias to the functional film is provided between the first element piece and the second element piece; A sensor element characterized in that the lead layer electrically connects the first element piece and the second element piece by covering the surface of the hard magnetic material, the connection area of ​​the first element piece, and the connection area of ​​the second element piece.

4. a first step of depositing a conductive functional film whose electrical characteristics change based on a predetermined physical quantity to be detected; a second step of forming a conductive protective film on the surface of the functional film; a third step of covering a portion of the surface of the protective film with a mask; a fourth step of physically reducing a native oxide film formed on a surface of the protective film that is not covered by the mask by performing reverse sputtering through the mask; a fifth step of forming a lead layer on the connection area of ​​the protective film that is not covered by the mask after the fourth step is performed.

5. 5. The method for manufacturing a sensor element according to claim 4, wherein the fourth step and the fifth step are carried out successively without exposure to the atmosphere.

Images