Method for Making Magnetic Heads

The present invention relates to a method for making magnetic heads.

In recent years advances in high coercive metalized tape have stimulated research into magnetic heads which comprises high magnetic density core material. Promising materials for such magnetic cores can be found in Sendust (Tradename) and amorphous alloys. However, the method currently used in forming magnetic gaps in ferrite cores cannot readily be applied to the formation of magnetic gaps in such high magnetic density core materials. More specifically, in the current method use is made of glass which is sandwiched between ferrite core halves and bonded thereto by fusion at elevated temperatures. Advantages reside in the fact that in the fusion process the glass partially diffuses into the core material and increases the bonding strength and that a suitable glass material can be easily found to match the thermal expansion coefficient of the core material used. However, Sendust and amorphous alloys have a considerably low bonding strength to glass, and in addition the thermal expansion coefficient of Sendust is typically 170.times.10.sup.-7 which is considerably greater than that of glass that ranges between 50.times.10.sup.-7 and 120.times.10.sup.-7. Mismatch in thermal expansion coefficient presents a serious problem. The low bonding strength is considered to arise from the fact that glass is less capable of diffusing into such materials than it is with ferrite materials. In the case of amorphous alloys, the difficulty is that their crystalization temperature, which is around 500.degree. C., requires that glass fusion be effected at temperatures lower than this crystalization temperature. Otherwise, amorphous alloys would lose their required magnetic properties. Thus, fusion bonding is more difficult to achieve in the case of amorphous alloys than in the case of Sendust. Although the use of resinous materials can be considered as a gap filling material, their pronounced characteristic in thermal expansion and contraction renders them unsuitable for such applications where the gap length is required to meet the tolerance range of .+-.0.1 micrometers.

The present invention is therefore to eliminate the above-mentioned problems and has for its object the provision of a method whereby a magnetic gap is formed with a higher degree of precision.

According to the present invention, a magnetic gap is formed by the use of a sputtering method and supplementarily with the use of a bonding method in which glass or resin is employed as a strengthening material. The method of the present invention ensures high precision and ease with which magnetic heads are fabricated.

FIGS. 1a-1h and 2a-2c are perspective views illustrating a method for making a magnetic head according to the present invention; and

FIGS. 3a-3f and 4a-4e are perspective views illustrating another method of the present invention which is an improvement over the method of FIGS. 1 and 2.

FIG. 1 illustrates the steps 1a to 1h of making a magnetic head according to an embodiment of the present invention.

A substrate 1 is cut off along a central portion 2, forming substrate halves 3 and 7. On the surface of a substrate half 3 a magnetic layer 4 is formed by a sputtering method as shown in FIG. 1. An end face 5 is polished to a mirror finish and a nonmagnetic gap filling layer 6 is sputtered thereon. The substrate half, thus obtained, is aligned end-to-end with the other substrate half 7 as shown in FIG. 1d and bonded together. This bonding can be effectively made by cutting out a portion 8 as indicated by a broken line in the step d and pouring fused low-melting-point glass into the cut-out portion 8. On the upper surface of the recombined subtrate 9 is a magnetic layer 10 which is similar in material to layer 4 and which is formed by the sputtering technique, as illustrated in FIG. 1e. Since the subtrate halves 3 and 7 are magnetically short-circuited by layer 10, this short circuit must be removed by lapping it directly or by coating it with a layer 11 formed of resin or low-melting-point glass as shown in FIG. 1f and then lapping the overlying layers until the coplanar surface of magnetic layers 4 and 10 is reached, thus forming a core 11a as indicated in FIG. 1g. The core 11a has its amorphous layers 4 and 10 bonded to a side core 13 which is formed of a soft magnetic material and on which is wound a coil 12, as shown at h. An essential part of a magnetic head is thus fabricated. The above process is followed by a number of known processes to complete a head assembly. Numeral 14 indicates a nonmagnetic body. It is also possible to use a nonmagnetic substrate instead of the side core to sandwich the magnetic layer by forming a hole through which the coil is wound.

FIGS. 2a-2c illustrate the steps a to c respectively of another embodiment which is a modification of the FIG. 1 embodiment in which the essential parts are similar to those shown in FIG. 1.

A composite substrate 23 comprises a central section 21 formed of a nonmagnetic material and a pair of opposite side sections 22 of ferrite. The substrate 23 is cut off along a center line 24. On one end face of one of the substrate halves is formed a magnetic layer by sputtering technique, which was followed by the steps a to f of FIG. 1 so that a head structure shown in FIG. 2b, is fabricated. In this step, 25 represents a nonmagnetic layer, numerals 26 and 27 represent said magnetic layers, 28 indicating a moulded material. Next, the glass layer 28 is lapped so that it presents a curved surface. A front core 29 having a magnetic gap as shown in FIG. 2c is obtained. A head assembly is completed by having the front core 29 cemented to a ferrite back core 31 having a coil 30.

The head manufacturing methods as taught by the present invention defines a magnetic gap with a high degree of precision not attainable with the prior art method. When using the steps of the FIG. 1 embodiment, misalignment tends to occur between substrate halves 3 and 7 in the step d. If track width is 30 micrometers, such misalignment is not immaterial, but if track width is less than 10 micrometers, the misregistration is problematic.

FIG. 3 is an illustration of another embodiment which is suitable for making a head assembly having a narrow track width.

As shown in FIG. 3a, a magnetic layer 41 is formed on the upper surface of a substrate 42 using a sputtering or evaporation technique and one end of which is mirror-finished. This is followed by the step of forming a nonmagnetic layer 43 on the mirror-finished end face as shown in FIG. 3b, by sputtering. The sputtering is continued until the layer 43 has attained a desired thickness. Next, the substrate 42 is placed on the upper surface of a second substrate 44 with the magnetic layer 41 facing downward as shown in FIG. 3c, and bonded together. This bonding can be made by initially coating the surface of the substrate 44 with a layer of a low-melting-point glass with a thickness of 500 to 1000 Angstrom units using sputtering method and subsequently raising the temperature. A composite body can be obtained by sputtering a magnetic layer 41' over the upper surface of the bonded substrates, as shown in FIG. 3d. The composite body of is then cut off along a chain-dot line indicated at d, FIG. 3, and the cut-off plane is polished to obtain a structure shown in FIG. 3e, which a vertical edge of the nonmagnetic layer 43 forming a magnetic gap. Magnetic layers 41 and 41' are precisely aligned horizontally with each other. Side edges of the aligned layers 41 and 41' can be used as a tape contact face and define a narrow track. In a preferred embodiment, a side core 44' is formed on the aligned layers 41 and 41' as shown, in FIG. 3f to render the whole unit into a symmetrical configuration to prevent the head from being worn nonuniformly by contact with a tape and to prevent the tape from being worn by the upper edge of the layers 41, 41'. Resin is sufficient to assure bonding between the side core 44' and the layers 41, 41'. Although FIG. 3 shows only the front elevation of the core structure, the head assembly is complete when a coil is wound through a hole provided in the core.

The process can be simplified by eliminating the cutting step d, FIG. 3, by forming the substrate 42 with a material that can be easily etched and the other parts of the unit with materials which are resistant to etching solution.

FIG. 4 illustrates another embodiment which is an improvement over the FIG. 3 embodiment.

In FIG. 4, the steps shown at a and b are identical to the steps a and b of FIG. 3, respectively. The magnetic layer 41' is effectively sputter-formed using a mask 5 over the magnetic layer 41 as shown at c, since it only requires a lapping process to remove a raised portion of the magnetic layer 41' that overlaps the layer 41 as shown at e, FIG. 4. As shown at e, FIG. 4, by lapping the raised portion, the magnetic layers 41, 41' can be separated by the nonmagnetic gap filling layer which serves as a magnetic gap.

This method is suitable for making narrow-width magnetic hands.

The following is a description of the specific embodiments of the present invention.

A magnetic head was manufactured according to the steps of FIG. 1. Crystallized glass having a thermal expansion coefficient 104.times.10.sup.-7 was used for the substrate 1. Amorphous alloy Co.sub.88 Nb.sub.8 Z.sub.4 was sputtered on the substrate 1 under the pressure of 2.times.10.sup.-2 Torr within the environment of argon gas to form magnetic layers 4 and 10. The magnetic gap 6 was created by sputtering SiO.sub.2. A front core 11 a manufactured in this way was bonded to the side core comprising ferrite 13 and glass body 14, followed by the provision of a coil.

Example 2 is similar to Example 1 with the exception that use was made of amorphous alloy Fe.sub.80 Zr.sub.10 Nb.sub.10 and SiO.sub.2 for a gap material to form a magnetic gap in the same manner as in Example 1.

Forsterite was used for the central portion 21 of FIG. 2 and ferrite was used for the side portions 22 to form a composite substrate 23 having a thickness of 300 micrometers. The substrate was cut along the line 24 and amorphous alloy Co.sub.81 Mo.sub.3 Cr.sub.7 Zr.sub.9 was sputtered on one end face of one of the substrate halves to form a magnetic layer until it attains a thickness of 20 micrometers. This was followed by the steps as in Example 1 and the structure shown at b in FIG. 2 was manufactured. The nonmagnetic layer 25 comprised SiO.sub.2. The magnetic layers 26 and 27 each comprised the above noted amorphous alloy and the layer 28 comprised glass. The glass layer 28 was next lapped to present a curved surface as shown at c in FIG. 2. The front core 29 was bonded to the back core 31 with coil 30.

Example 4 differs from Example 3 in that high-melting-point glass with a thermal expansion coefficient 120.times.10.sup.-7 was used for the center portion 21 instead of forsterite, and permalloy was used instead of ferrite for the side portions 22 having a thickness of 300 micrometers. Same steps as employed in Example 1 were used in sputtering amorphous alloy Fe.sub.2 CO.sub.83 Nb.sub.15 in the manufacture of a front core which was bonded to a permalloy back core as shown at c, FIG. 2.

Example 5 is similar to Example 1 with the exception that high-melting-point glass with a thermal expansion coefficient of 120.times.10.sup.-7 instead of 104.times.10.sup.-7 was used for the substrate which was cut into halves one of which was coated with a 10-micrometer thick Sendust alloy. This was followed by steps similar to those in Example 1 to obtain the head shown at h, FIG. 1.

Life tests were conducted between those made in accordance with Examples 1 through 5 and two magnetic heads made in accordance with a prior art method. In one of the prior art magnetic heads, glass was fused between Sendust core halves to form a magnetic gap therebetween. In the other prior art head, use was made of Co.sub.81 Mo.sub.3 Cr.sub.7 Zr.sub.9 which is an amorphous alloy of zero-magnetic distortion ribbon having a thickness of 20 micrometers, sandwiched between glass plates 300 micrometers thick each to obtain a total thickness of about 620 micrometers and was cut in half and was processed according the method currently used to make a magnetic gap.

One test cycle consisted of placing the test pieces in an environment of 30.degree. C. with a relative humidity of 90% for a period of 7 days and thereafter subjecting them to a tape contact test for 8 hours on a commercially available video tape recorder. The test cycle was repeated four times for each test piece and the magnetic gap of each tested piece was observed. The results of the observation are listed in the Table below.

As is seen from the test results given above, the magnetic heads made according to the present invention proves high precision in comparison with the prior art heads. While substantial changes in gap length were not observed in the present invention, considerable changes were observed in the prior art gap lengths.

Amorphous alloy Co.sub.86 Nb.sub.10 Zr.sub.4 was sputtered on the surface of a ferrite substrate 42 of FIG. 3 to a thickness of 10 micrometers. One end face of the substrate was mirror-finished and SiO.sub.2 was used to form layer 43 having a thickness of 0.3 micrometers. The amorphous alloy surface of the composite body was bonded to a substrate 44 of glass having a thermal expansion coefficient 120.times.10.sup.-7 as shown at c, FIG. 3. The composite body was cut along the chain-and-dot line and lapped to obtain the core shown at e. A second glass substrate was bonded to the amorphous layers 41, 41'. The reason for using ferrite for the substrate 42 is that it is easier than glass to be machined.

Amorphous alloy Co.sub.84 Fe.sub.2 Nb.sub.14 was sputtered on a copper substrate 42, FIG. 3, until a thickness of 10 micrometers was attained to form a magnetic layer 41, which was followed by steps as in Example 7 to obtain a composite body as shown at d in FIG. 3 in which the substrate 44 is composed of glass having a thermal expansion coefficent of 120.times.10.sup.-7 and the gap material 43 was composed of SiO.sub.2. The same amorphous alloy was used for layer 41' as in layer 41. The copper substrate 42 was removed by the use of an etching liquid whose main composition is HCl. It is not neccessary to use a mask since the glass substrate, SiO.sub.2 layer and amorphous layers are resistant to such liquid. The etching was followed by lapping to obtain the structure shown at e.

Amorphous alloy Co.sub.85 Nb.sub.10 ti.sub.5 was sputtered on an NaCl single crystalline body which was used as the substrate 42 of FIG. 3 to form the layer 41. The same process as used in Example 7 was followed to obtain a structure as shown at d, FIG. 3, using the same materials for layer 43 and substrate 44 as used in Example 8. The structure was then immersed in water to remove the NaCl composition, which was then followed by lapping to obtain a flat surface as shown at e, FIG. 3.

Comparison was made between those manufactured according to Examples 7-9 and a ferrite head having glass fused magnetic gap and the head manufactured according to the steps shown at FIG. 1. The test results are illustrated in the Table below.

As is seen from the Table given above, the magnetic head manufactured according to the invention ensures a high degree of precision in determining magnetic gap length in comparison with the prior art head having a glass-fused magnetic gap and ensures against track misalignement. The invention thus allows manufacture of magnetic heads having narrow track width suitable for high density magnetic recording.

As is understood from the foregoing description, the magnetic head made according to the invention ensures a significantly smaller gap length variation over the lifetime than those made according to prior art methods as well as a high degree of precision in gap length.