THIN FILM MAGNETIC HEAD

Abstract: The present invention relates to a thin film magnetic head used in a magnetic reading and recording apparatus. The thin film magnetic head comprising a pair of yokes (2) made of magnetically permeable film, a thickness of said yokes (2) defining a track width of said thin film magnetic head, a space between first ends (2a) of said pair of yokes (2) defining a magnetic gap of said thin film magnetic head and second ends (2b) of said pair of yokes (2) being apart from each other, a pair of magneto-resistive ele­ ments (41, 42) magnetically connected to said second ends (2b) of said pair of yokes (2), respectively, and a return path (3) made of magnetically permeable film, said return path (3) magnetically connecting said pair of magneto-resistive elements (41,42).

Description: The present invention relates to a thin film magnetic head used in a magnetic reading and recording apparatus such as a magnetic disk drive, a magnetic tape drive, and so on, and more particularly to a thin film magnetic head employing a magneto-resistive (MR) element which is manufactured by the thin film forming technology. The thin film magnetic head employing the magneto-resistive (MR) element is disclosed in JP-A-150315/1976. The conventional thin film magnetic head includes a substrate on which a pair of yokes of a high permeability soft magnetic material are formed via a insulative layer by the thin film forming technology. One ends of the yokes form a gap which generates a magnetic flux to be applied to a magnetic medium. The other ends of the yokes are magnetically connected by a high permeability soft magnetic material (return path) and the MR element. The MR element is provided with contacts to supply a drive current thereto during a reading operation. The yokes are provided with a coil to which a recording current is applied. In the conventional thin film magnetic head, the track width thereof is determined by the thickness of the yoke. Accordingly, the track width can easily be reduced by decreasing the thickness of the yoke in order to obtain high recording density. However, the direction of the easy axis of magnetization of the MR element is the same as the longitudinal direction of the MR element. Since the magnetic flux flows along the longitudinal direction of the MR element, the domain walls are generated in the MR element so that Barkhausen noise is produced in the output signal of the MR element to degrade the signal/noise ratio of the output signal. Further, since the direction of the easy axis of magnetization of the yokes and the return path are arbitrary, the magnetic flux does not efficiently flow through the yokes and the return path. As a result, the output signal of the MR element is not sufficient. US-A-4,388,662 discloses a thin film magnetic head according to the preamble of claim 1. US-A-4,385,334 discloses a magnetic head with shield members for protecting the head against the magnetic flux from adjacent magnetic patterns. Accordingly, an object of the present invention is to provide a thin film magnetic head having a high electro-magnetic transducing efficiency and a reduced noise level of the output signal. This object is solved with the features of the claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a thin film magnetic head; Figs. 2 and 3 show an operation of MR elements used in the thin film magnetic head shown in Fig. 1; Fig. 4 is a perspective view schematically showing a thin film magnetic head; Figs. 5A to 5C are perspective view and cross-sectional views showing a thin film magnetic head according to a first embodiment of the present invention; and Fig. 6 is a perspective view schematically showing a thin film magnetic head according to a second embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 schematically shows a thin film magnetic head. The magnetic head includes a substrate 1 made of non-magnetic material such as Aℓ₂O₃ - TiC. An insulative layer 11 of silicon oxide of about 10 µm thick is formed on the substrate 1 by sputtering. A pair of yokes 2 is formed on the insulative layer 11. The yokes 2 are made or soft magnetic material having a high magnetic permeability such as Co₉₀Zr₁₀ (weight percent), whose thickness TW is 2 µm. The yokes 2 are formed by sputtering the Co-Zr alloy within the magnetic field having the x-direction in Fig. 1, and then, by etching the Co -Zr layer to form L-shaped configuration. Accordingly, the magnetic anisotropy (easy axis of magnetization) of the yokes 2 is directed to the x-direction. A distance between one ends 2a of the yokes 2 defines a magnetic gap whose value is about 0.5 µm. An U-shaped return path 3 is formed on the insulative layer 11 in a similar manner to the yokes 2 such that both ends of the return path 3 are faced to and apart from the other ends 2b of the yokes 2. The return path 3 is also made of Co₉₀Zr₁₀ alloy and the thickness thereof is 2 µm. It should be noted that the Co - Zr alloy is sputtered to form the return path 3 within a magnetic field having the y-direction of Fig. 1 so that the magnetic anisotropy of the return path 3 is directed to y-direction. The upper surface of the yokes 2 and the return path 3 and the spaces between the yokes 2 and the return path 3 are covered by an insulative layer 12 of silicon oxide by sputtering. The surface of the insulative layer 12 is made plane. A pair of magneto- resistive (MR) elements 41 and 42 are formed on the insulative layer 12 at the position above the other ends 2b of the yokes 2 and ends of the return path 3 by evaporating so that the MR elements 41 and 42 are magnetically connected to the yokes 2 and the return path 3. The MR elements 41 and 42 are made of Ni₈₁Fe₁₉ (atomic percent) alloy and their thickness is 0.03 µm. A pair of hard magnetic materials 43 and 44 made off Co₇₀Pt₃₀ (atomic percent) alloy are formed on the MR elements 41 and 42 far magnetically biasing the MR elements 41 and 42. The hard magnetic materials 43 and 44 enable the magnetic vector of the MR elements 41 and 42 to have an angle of 45° with respect to the flowing direction of the bias current applied to the MR elements 41 and 42. The thickness of the hard magnetic materials 43 and 44 is favorably about 0.045 µm. As schematically shown, the MR elements 41 and 42 are connected to respective electrical contacts T B and T A to which the bias current is supplied. Further, the MR elements 41 and 42 are electrically connected one another by a conductor 45 such as Au and Cu, and an intermediate terminal T c is connected to the conductor 45. As shown in Fig. 2, a positive voltage is applied to the contact T A and a negative voltage is applied to the contact T B so that the constant bias or sense current I is supplied to the MR elements 41 and 42. The intermediate terminal T C is grounded. The magnetic vectors 41v and 42v in the MR elements 41 and 42 have an angle of 45° with respect to the direction of the current I as shown in the solid arrow. When the magnetic flux from a magnetic recording medium, such as a magnetic disk or a magnetic tape, is applied to the one ends 2a of the yokes 2, the magnetic flux flows through the right side yoke 2, the return path 3 and the left side yoke 2. Accordingly, the MR element 41 is supplied with a magnetic field He₁ so that the magnetic vector 41v is rotated counterclockwise by an angle Δϑ as shown in dotted arrow in Fig. 2. That is, the resistance of the MR element 41 is decreased by ΔR. On the other hand, the MR element 42 is supplied with a magnetic field He₂ whose direction is opposite to the magnetic field He₁. Accordingly, the magnetic vector 42v is rotated clockwise by an angle Δϑ as shown in dotted arrow and the resistance of the MR element 42 is increased by ΔR. In response to the change of the resistance of the MR elements 41 and 42, the voltages V AC and V BC between the contact T A and the terminal T C and between the terminal T C and the contact T B , respectively, are reversely changed. A differential amplifier 46 detects the difference voltage between the voltages V AC and V BC to produce an output signal (- reading signal) having a value of 2 · ΔR · I which is twice the value obtained by only one MR element. Even if undesired magnetic flux is applied to the MR elements 41 and 42, the changes of the voltages V AC and V BC due to the undesired magnetic flux have the same polarity, and therefore, the changes are cancelled each other by the differential amplifier 46. Additionally, even if the resistance of the MR elements 41 and 42 is changed due to thermal change, the changes of the voltages V AC and V BC due to the thermal change are also cancelled each other. Accordingly, the noise in the output signal is greatly reduced. Fig. 3 shows another example of the electrical connection in the case that the bias current I is applied to the MR elements 41 and 42 in the opposite direction from each other. The constant bias current I flows from the contacts T A and T B to the terminal T C via the MR elements 42 and 41, respectively. In this case, a differential amplifier 46' is directly connected to the contacts T A and T B . Since the magnetic anisotropy of the yokes 2 is directed to the x-direction and that of the return path 3 is directed to the y-direction in Fig. 1, the magnetic flux flows through the yokes 2 and the return path 3 perpendicularly to the magnetic anisotropy. Accordingly, the movement of the magnetic flux is carried out by the rotation of magnetic vector so that the magnetic head can operate in relatively high frequency and high electro-magnetic efficiency. In other words, the output signal of the magnetic head is not degraded. For the purpose of illustration, the substrate 1, the insulative layers 11 and 12 and the hard magnetic materials 43 and 44 are omitted in Fig. 4. Around the return path 3, there is provided a coil 7 made of about 1 µm thick Cu. The coil 7 is formed by plating using a photoresist pattern. As is well known in the art, the coil 7 includes a lower portion and an upper portion relative to the return path 3. Each ends of the coil 7 are connected to respective terminals T D and T E to which recording current is applied. When the recording current is applied, the magnetic flux is generated along the yokes 2 and the return path 3. The magnetic flux is used for recording information to a recording medium at the ends 2a of the yokes 2 as disclosed in previously described JP-A-150315/1976. Fig. 5A schematically shows a first embodiment of the present invention. The difference between the magnetic heads desribed in conjunction with Fig. 1 and 4 on the one hand and the first embodiment on the other hand is that the return path 3 is formed on the plane different from the plane where the yokes 2 are formed. In Fig. 5A, the substrate 1, the insulative layers 11 and 12 and the hard magnetic materials 43 and 44 are omitted for the purpose of illustration. Referring to Fig. 5B which is a cross-sectional view taken alone a line B-B of Fig. 5A, the yoke 2 is formed on the insulative layer 11. The yoke 2 is covered by the next insulative layer 12, and then the MR element 41 and the hard magnetic material 43 are formed such that one edge of the MR element 41 is overlapped to the yoke 2. The MR element 41 and the material 43 are covered by an insulative layer 13 made of 0.5 µm thick silicon oxide (SiO₂). Referring also to Fig. 5C which is a cross-sectional view taken along a line C-C of Fig. 5A, a lower coil pattern 7ℓ is formed on the insulative layer 13 at the position where the central portion of the return path 3 is to be formed. The lower coil pattern 7ℓ is made of Cu and formed by through hall plating method by a thickness of 2 µm. Then, an insulative layer 14 of silicon oxide is formed on the lower coil pattern 7ℓ about 0.5 µm thick enough to insulate an electrical connection between the lower coil pattern 7ℓ and the return path 3. Next, the return path 3 is formed in a similar manner to the head according to Fig. 1 such that the central portion thereof is on the insulative layer 14 and both ends thereof are on the insulative layer 13. The both ends of the return path 3 are overlapped to the MR element 41 so that the yoke 2, the MR elements 41 and 42 and the return path 3 are magnetically connected as shown in Fig. 5B. The upper surface of the return path 3 is covered by an insulative layer 15 made of silicon oxide of 0.5 µm thickness. The insulative layers 14 and 15 located above the both ends of the lower coil pattern 7ℓ are removed by etching method using a desired resist pattern in order to obtain an electrical contact between the lower and an upper coil patterns 7ℓ and 7u. The upper coil pattern 7u made of Cu is then formed on the insulative layer 15 in the same manner as the lower coil pattern 7ℓ so that the lower and upper coil patterns 7ℓ and 7u forms a continuous coil wound around the return path 3. In the first embodiment, both ends of the lower coil pattern 7ℓ are covered by the insulative layers 14 and 15 each having a thickness of 0.5 µm. Accordingly, the etching for exposing the both ends of the lower coil pattern 7ℓ is required to remove only the 1 µm thickness of the insulative layers 14 and 15. In contrast, in the head according to Fig. 4, the etching is required to remove the insulative layer of about 3 µm thickness since the return path 3 is embedded in the insulative layer 12 of 2.5 µm thickness and the insulative layer of 0.5 µm thickness provided between the lower coil pattern and the return path 3. Specifically, about 18 to 40 minutes are required for the etching in the first embodiment while 50 to 120 minutes are required in the head according to Fig. 4. Fig. 6 schematically shows a second embodiment of the present invention in which the substrate 1, the insulative layers 11, 13, 14 and 15 and the hard magnetic materials 42 and 43 are omitted for the purpose of illustration. The difference to the first embodiment is that first and second shield layers 16 and 17 are additionally provided on lower and upper portions of the yokes 2. The first shield layer 16 is made of 3 µm thick Cu-Aℓ alloy and formed on the insulative layer 11 by sputtering before the yokes 2 are formed. The Co-Zr alloy layer is formed directly on the first shield layer 16 and etched together with the first shield layer 16 so as to form the yokes 2. The first shield layer 16 and the yokes 2 are embedded in the insulative layer 12, and then, the surface of the insulative layer 12 is made plane by etching back within an atmosphere of argon gas. After that, the second shield layer 17 of Cu-Aℓ alloy is formed on the insulative layer 12 by sputtering by about 3 µm thickness. The second shield layer 17 is shaped to trapezoid to cover the front portion of the yokes 2. Subsequently, the MR elements 41 and 42, the lower coil pattern 7ℓ, the return path 3, the upper coil pattern 7u, the insulative layers therebetween, and so on are formed in the same manner as the first embodiment. In the second embodiment, the first and second shield layers 16 and 17 made of conductive material prevent the yokes 2 from being subjected to magnetic flux from the adjacent tracks in the reading operation. Similarly, the shield layers 16 and 17 prevent the magnetic flux generated by the yokes 2 from being affected to the adjacent tracks in the recording operation. Accordingly, a higher track density can surely be obtained than the previous embodiment. In the first embodiment, the coil 7 is formed around the return path 3. However, the coil 7 may be formed around the yokes 2. Further, although Co-Zr alloy is used for the yokes 2 and the return path, the other soft magnetic material can also be used. Moreover, aluminum oxide or other insulative material can be used as the insulative layers.

Claims: A thin film magnetic head for reading recorded information from a magnetic recording medium moving relative to said thin film magnetic head in a first direction (x), said thin film magnetic head comprising: a pair of yokes (2, 2) made of a magnetically permeable film having a predetermined thickness (Tw), said thickness of said yokes defining a track width of said thin film magnetic head, a space (GL) between first ends of said pair of yokes defining a magnetic gap of said thin film magnetic head, second ends of said pair of yokes being spaced apart from each other; a pair of magneto-resistive elements (41, 42) magnetically connected to said second ends of said pair of yokes, respectively; first and second contacts (T A and T B ) electrically connected to said pair of magneto-resistive elements (42 and 41, respectively), for being supplied with bias current, a conductor electrically connected to said pair of magneto-resistive elements (41, 42) and an intermediate contact T C connected to said conductor for generating a first voltage (V AC ) between said first contact (T A ) and said intermediate contact (T C ) and a second voltage (V BC ) between said second contact (T B ) and said intermediate contact (T C ) whereby a difference between said first and second voltages (V AC and V BC , resp.) is detectable, means for applying a voltage across said serially connected magnetoresistive elements (41, 42); and a return path (3) made of a magnetically permeable film, said return path magnetically connecting said pair of magneto-resistive elements, characterized in that a magnetic anisotropy of said pair of yokes (2, 2) is directed substantially in said first direction (x) and a magnetic anisotropy of said return path (3) is directed in a second direction (y) substantially perpendicular to said first direction (x) and within the plane of the film of the return path (3), and that said pair of yokes (2, 2) are formed on a substrate (1) and covered by a first insulative layer (12), said pair of magneto-resistive elements (41, 42) are formed on said first insulative layer (12) and covered by a second insulative layer (13), and said return path (3) is formed on said second insulative layer (13). The thin film magnetic head as claimed in claim 1 further comprising a coil (7) provided around said return path (3) for being supplied with recording current, said coil including a lower coil pattern (7ℓ) and an upper coil pattern (7u), said lower coil pattern (7ℓ) being formed on said second insulative layer (13) and covered by a third insulative layer (14), a portion of said return path (3) around which said coil (7) is provided being formed on said third insulative layer (14) and covered by a fourth insulative layer (15), said upper coil pattern (7u) being formed on said fourth insulative layer (15), both ends of said upper coil pattern (7u) being connected to both ends of said lower coil pattern (7ℓ) at portions where said third and fourth insulative layers (14 and 15, resp.) are removed. The thin film magnetic head as claimed in Claims 1 to 2, wherein said magneto-resistive elements (41, 42) are piled on said yokes (2, 2) and said return path (3) is piled on said magnetro-resistive elements (41, 42). The thin film magnetic head as claimed in Claims 1 to 3, further comprising first and second shield layers (16, 17) provided on upper and lower surfaces of said yokes (2, 2), said first and second shield layers being made of conductive material. The thin film magnetic head as claimed in Claims 1 to 4, further comprising a pair of hard magnetic material layers (43) provided on a surface of said pair of said magnetro-resistive elements (41, 42).

Inventors: MARUYAMA, TAKAO C/O NEC CORPORATION, YAMADA, KAZUHIKO C/O NEC CORPORATION
Applicants: NEC CORPORATION
Application year: 1987
Main classification: G11B5
IPC codes: G11B5