Manufacturing method for a magnetoresistive head

Abstract: In a magnetoresistive head capable of performing favorable magnetic recording and reproduction, an overlap amount (OV1) of a front yoke (25) and a magnetoresistive element (23) is always greater than an overlap amount (OV2) of a back yoke (26) and the magnetoresistive element (23). Generally, the magnetoresistive head varies in its reproduction efficiency by the overlap amount of the yoke and magnetoresistive element. In particular, the reproduction output is significantly affected by the overlap amount (OV1) of the front yoke and magnetoresistive element, and when the overlap amount of the front yoke becomes smaller than the overlap amount (OV2) of the back yoke, the reproduction output tends to decrease abruptly. Therefore, by keeping the overlap amount of the front yoke always greater than the other, a stable reproduction output can be achieved. In particular, an outstanding effect is obtained in a multi-channel magnetoresistive head containing multiple magnetoresistive elements in one head.

Description: The present invention relates to a manufacturing method for a thin film magnetic head used in magnetic recording and/or reproducing apparatus. Recently, to cope with the trend of higher recording density, higher data transfer speed and multiple channels in magnetic recording and/or reproducing apparatus, the thin-film magnetic head is noticed. In particular, in a magnetic recording and/or reproducing apparatus in which the recording medium runs at low speed, a magnetoresistive head of which reproduction output does not depend on the speed is used. A magnetoresistive head of a simplest structure is already known, for example, in the published paper, "A Magnetoresistive Readout Transducer," R.P. Hunt, IEEE Trans. Magn. Vol. 1, MAG-7, No. 1 (March 1971), pp.150-154. In this magnetoresistive head, a magnetoresistive element composed of Ni-Fe alloy thin film with film thickness of hundreds of Angströms is disposed vertically or horizontally on the recording medium, and a pair of electrodes are disposed at both ends of this magnetoresistive element. For signal detection, the resistance change of the magnetoresistive element due to the signal magnetic field generated by the recording medium is converted into a voltage change by the constant current in the magnetoresistive element flowing through the electrodes. However, in the magnetoresistive head in which the magnetoresistive element is disposed horizontally, since its reproduction resolution depends on the geometric shape of the magnetoresistive element, a signal recorded at high density of recording wavelength of several micrometers or less cannot be reproduced. Or, in the magnetoresistive head in which the magnetoresistive element is disposed vertically, since the intensity of the signal magnetic field from the recording medium attenuates in terms of exponential function with respect to the distance from the magnetoresistive element to the recording medium, and the signal magnetic field becomes smaller generally as the recording wavelength becomes shorter, the reproduction sensitivity is particularly poor in the short wavelength region of recording wavelength of several micrometers or less. Furthermore, in either magnetoresistive head, the wear of the magnetoresistive element is inevitable because it is kept in contact with the recording medium. A magnetoresistive head intended to solve the above problems of wear and lowering of reproduction capability in short wavelength region has been already known, for example, in the Japanese Laid-open Patent No. 52-9413. This magnetoresistive head comprises a bias conductor made of conductive material for applying a bias magnetic field to a magnetoresistive element, the magnetoresistive element, a pair of electrodes for passing a driving current to the magnetoresistive element, and two magnetic yokes, that is, front yoke and back yoke, which are sequentially formed on a magnetic substrate by way of insulation layer such as SiO₂. The front yoke and back yoke are disposed so that one ends thereof overlap the ends of the magnetoresistive element. Between the front yoke and the magnetic substrate, a magnetic gap is formed in order to lead the recording magnetic field generated from the recording medium into the magnetic head. At this time, mainly the thin-film forming technology such as vacuum deposition and sputtering, or fine pattern technology such as photolithography is employed. This magnetoresistive head possesses such advantages that the magnetoresistive element would not be worn because the magnetoresistive element does not directly contact the recording medium, and that signals with recording wavelength of 1 µm or less would be reproduced by setting the magnetic gap at 1 µm or less. Such conventional magnetoresistive head is designed generally so that the both ends of the magnetoresistive element overlap the front yoke and back yoke by the same overlapping amount. In fabrication of such magnetoresistive head, however, the position of the magnetoresistive element tends to be shifted longitudinally due to various causes including pattern matching precision in the process of photolithography. Accordingly, when a plurality of magnetic heads are fabricated, the reproduction output by them vary largely. This is a fatal problem for fabricating a multi-channel magnetoresistive head. This invention provides a method of manufacturing a magnetoresistive head which comprises a magnetoresistive element formed on a magnetic substrate, a magnetic gap for leading a signal magnetic field generated from a recording medium into the head, a pair of front and back magnetic yokes having opposing ends respectively overlapping with front and rear ends of the magneto-resistive element for leading the signal magnetic flux from the recording medium, and a current supply means for supplying a drive current to the magneto-resistive element, the method being characterized in that a photo mask used in a step of forming the front and back magnetic yokes is disposed in that step at a position shifted in a direction from the back magnetic yoke side toward the front magnetic yoke side by shift amount larger than a maximum patterning error from a position where areas of opposing ends of the photo mask overlapping front and rear ends of a photo mask for forming the magnetoresistive elements are the same. A magnetoresistive head manufacturing according to the invention is thus capable of magnetically recording and reproducing favourably by solving the problems of the conventional magnetoresistive head mentioned above. This is achieved in a magnetoresistive head made according to the invention, by the overlap amount of the front yoke and a magnetoresistive element always having greater than the overlap amount of the back yoke and the magnetoresistive element. By this constitution, a magnetoresistive head generating a stable reproduction output can be obtained. The reason is described below. That is, the magnetoresistive head varies in its reproduction efficiency depending on the overlap amount. In particular, the reproduction output is largely affected by the overlap amount of the front yoke and the magnetoresistive element, and when the overlap amount of the front yoke becomes smaller than the overlap amount of the back yoke, the reproduction output tends to decline sharply. Therefore, by setting the overlap amount of the front yoke always greater than that of the back yoke, a stable reproduction output can be obtained. Fig. 1 is an outline view of a magnetoresistive head made according to the invention; Fig. 2 is a sectional view along a line A-A in Fig. 1; Fig. 3 shows an overlapped pattern of a photo mask for a magnetoresistive element and a photo mask for magnetic yokes used in fabrication of the magnetoresistive head in Fig. 1; Fig. 4 shows a magnetic density flux distribution in the magnetoresistive element when the position of the magnetoresistive element is changed in the magnetoresistive head in Fig.1; and Fig. 5.is an outline view of a multi-channel magnetoresistive head made according to the invention. A preferred embodiment of the invention is described below firstly by referring to Fig. 1 and Fig. 2. The magnetoresistive head of the embodiment is fabricated in the following manner. In the first place, on a magnetic substrate 21 made of Ni-Zn ferrite, Mn-Zn ferrite or the like, a first insulation layer 29 of SiO₂, Al₂O₃ or the like is formed by sputtering or other method. On the first insulation layer 29, a conductive thin film of copper, aluminum, gold or the like is formed by vacuum deposition or other method, and is formed into a desired shape by photolithography or other method, so that a bias conductor 22 is formed. The bias conductor 22 is for applying a bias magnetic field to the magnetoresistive element in a direction perpendicular to the track width direction of the track formed on the recording medium. On the bias conductor 22, a second insulation layer 30 of SiO₂, Al₂O₃ or the like is formed. On the second insulation layer 30, a magnetoresistive element 23 composed of Ni-Fe alloy thin film or Ni-Co alloy thin film is formed by vacuum deposition in the magnetic field or sputtering in the magnetic field so that the easy magnetization axis becomes parallel to the longitudinal direction of the magnetoresistive element 23, and it is patterned in a stripe of 10 µm in width by photolithographic technology. Next, a pair of electrodes 24a, 24b for passing a driving current into the magnetoresistive element 23 are formed so as to be connected to both ends of the magnetoresistive element 23. On the magnetoresistive element 23, a third insulation layer 31 of SiO₂ or Al₂O₃ is formed. Afterwards, of the first, second and third insulation films, the magnetic gap 27 and the junction 33 of the back yoke 26 and magnetic substrate 21 are removed by etching photolithographically. In particular, the magnetic gap 27 is etched so that the first insulation layer 27 may be left over. Consequently, an Ni-Fe alloy thin film, a sendust thin film or a Co-Nb-Zr amorphous alloy thin film is formed by vacuum deposition or sputtering, and a magnetic yoke 34 divided into a front yoke 25 and a back yoke 26 in the portion of magneto-resistive element 23 is formed by photolithography. In particular, the front yoke 25 and back yoke 26 are formed so that one ends thereof respectively overlap the front and rear ends of the magnetoresistive element 23. Fig. 3 shows patterns of a photo mask 53 for the magnetoresistive element and a photo mask 51, 52 for the magnetic yoke used in fabrication according to the preferred embodiment of the invention, in which the pattern of the magnetic yoke and the pattern of the magnetoresistive element are combined. The photo masks in the preferred embodiment are designed in the width W of the magnetoresistive element photo mask 53 of 10 µm, the overlap amount OV1 of the magnetoresistive element photo mask with the front yoke photo mask 51 of 3 µm, and the overlap amount OV2 with the back yoke photo mask 52 of 1 µm. In the actual fabrication of the head, a pattern matching error of about 1 µm at maximum occurs. Therefore, in the magnetoresistive head which is actually fabricated in this embodiment of the invention, the overlap amount of the front yoke may vary in the range of 2 to 4 µm, and the overlap amount with the back yoke may vary in the range of 0 to 2 µm. That is, the photo mask for forming the front and back yokes is shifted toward the front side by a shift amount larger than a maximum patterning error amount from a position where OV1 and OV2 are the same. Thus, in the magnetoresistive head made according to this embodiment, the overlap amount of the magnetoresistive element with the front yoke is set always greater than the overlap amount with the back yoke. Fig. 4 shows the result of calculation of the magnetic flux density distribution in the width direction in the magnetoresistive element when the position of the magnetoresistive element is changed in a magnetoresistive head of a preferred embodiment. The X-axis denotes the width-wise position in the magnetoresistive element, and 0 represents the center of the magnetoresistive element. The Y-axis expresses the ratio of magnetic flux density distribution in the magnetoresistive element. In the diagram, A is the case of overlapping of the magnetoresistive element 23 with the front yoke 25 and the back yoke 26 by 2 µm each; B is the case of overlapping of the magnetoresistive element 23 with the front yoke 25 by 4 µm, and C is the case of overlapping of the magnetoresistive element 23 with the back yoke 26 by 4 µm. As clear from the diagram, the magnetic flux density distribution of C is lowered notably as compared with the cases A and B. Therefore, in order to suppress the variations of the reproduction output, it is important to keep the front side overlap amount always greater than that at the back yoke side. In fact, in the conventional magnetoresistive head fabricated by using the photo masks designed at the same overlap amount of 2 µm for the front yoke and back yoke, the overlap amount of the front yoke varied from 1 to 3 µm, and the overlap amount of the back yoke varied from 3 to 1 µm, and the reproduction output varied in a range of ±25%. On the other hand, in the case of the magnetoresistive head fabricated by using photo masks designed at the overlap of 3 µm at the front side and the overlap of 1 µm at the back yoke side according to the embodiment of the invention, the variations of reproduction output settled within a range of ±5%. As described herein, in the magnetoresistive head manufacturing method of the invention, since the overlap amount of the magnetoresistive element with the front yoke is always greater than the overlap amount with the back yoke, a stable reproduction output is obtained. Fig. 5 shows a multi-channel magnetoresistive head 60 having three magnetoresistive head units 61, 62, 63 disposed on a magnetic substrate 21 in the track widthwise direction. In each magnetoresistive head units, it is designed so that the overlap amount at the front yoke side is greater than the overlap amount at the back yoke side. Therefore, it is effective to keep the variations of reproduction outputs of the three channels within ±5%. Thus, the effect is great in the multi-channel magnetoresistive head conforming to the magnetoresistive head and its manufacturing method of the invention.

Claims: A method of manufacturing a magnetoresistive head which comprising a magnetoresistive element (23) formed on a magnetic substrate (21), a magnetic gap for leading a signal magnetic field generated from a recording medium into the head, a pair of front and back magnetic yokes (25,26) having opposing ends respectively overlapping with front and rear ends of the magnetoresistive element for leading the signal magnetic flux from the recording medium, and a current supply means (24a,24b) for supplying a drive current to the magnetoresistive element, the method being characterized in that a photo mask used in a step of forming the front and back magnetic yokes is disposed in that step at a position shifted in a direction from the back magnetic yoke side toward the front magnetic yoke side by a shift amount larger than a maximum patterning error from a position where areas of opposing ends of the photo mask overlapping front and rear ends of a photo mask for forming the magnetoresistive elements are the same.

Inventors: FUKAZAWA TOSHIO, NAGATA YUJI, TOSAKI YOSHIHIRO, WADA KUMIKO, FUKAZAWA, TOSHIO, NAGATA, YUJI, TOSAKI, YOSHIHIRO, WADA, KUMIKO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G11B5
IPC codes: G11B5