MAGNETORESISTIVE SENSOR

Abstract: A magnetoresistance sensor which has magnetic sensing parts (2s) consisting of ferromagnetic thin films, at least two terminal electrode parts (3) and a wiring part (2w) on one of the two surfaces of a rectangular dielectric substrate. The substrate (1) has at least two corners (1A) whose surfaces are lower than the surface other than them on the surface, and at least two terminal electrode parts (3) are formed on the corners singly. Also, the magnetism sensing parts (2s) consisting of the ferromagnetic thin films are formed on the surface other than the corners. Since the terminal electrode parts (3) are formed on the corner parts of the substrate lower than the surface provided with the magnetism sensing parts (2s), when performing resin molds etc. intending to reinforce bonding parts, the surfaces of the molds can be formed on a level with the surface provided with the magnetic sensing parts.

Description: The present invention relates to a magnetoresistive sensor according to the pre-characterizing part of claim 1. This sensor includes a ferromagnetic thin film and is used in, for instance, a capstan motor for video cassette recorders (VCR) and a magnetic encoder. Recently, there has been used a magnetoresistive sensor comprising a ferromagnetic thin film for an accurate control of a magnetic encoder or an accurate control of a capstan motor for VCR and it is necessary to use such a sensor for controlling a motor with a high accuracy. Fig. 1 is a schematic cross sectional view of a capstan motor for VCR in which conventional magnetoresistive sensor is incorporated. In this capstan motor shown in Fig. 1, reference numerals 16, 17 and 10' respectively represent a rotor yoke, a rotor magnet and a frequency-generating magnet (FG magnet) in which N poles and S poles are alternatively magnetized at small pitches and these elements constitute a rotor part. Reference numeral 18 stands for a stator coil for driving the motor and reference numeral 19 represents a case. Reference numeral 15 represents a magnetoresistive sensor which is fixed to a holder 15H made of a resin, the magnetic field detecting portion 15S is arranged facing to the FG magnet 10' usually at a distance of about 100 µm and thus the rotation control of the motor is performed by the output signal from the magnetoresistive sensor. Reference numeral 7 stands for a lead portion of the magnetoresistive sensor for electrically connecting the magnetoresistive sensor 15 and a printed circuit board 20. The FG magnet is in general magnetized at small pitches and correspondingly the intensity of the generated magnetic field is small. For this reason, a desired output cannot be obtained if the gap between the magnetoresistive sensor 15 and the FG magnet 10' is large. Fig. 2A shows a plan view of a conventional magnetoresistive sensor before it is attached to the holder made of a resin and Fig. 2B shows a sectional view thereof taken along the line A-A of Fig. 2A. Reference numerals 15S, 15M and 7 represent a magnetic field detecting portion of the magnetoresistive sensor 15, a molded portion for reinforcing lead-bonding portion and a lead, respectively. In the structure as shown in Figs. 2A and 2B, the electrical connection between the lead and the sensor pellet is usually performed through the bonding with a solder. Moreover, electrical short often arises and the lead is sometimes peeled off from the lead-bonding portions when they are in the exposed state. Thus, the bonding portions are reinforced by molding for the purpose of eliminating such inconvenience. The reinforcement of the bonding portions are in general performed with the aid of a resin such as epoxy resin and so on and the thickness of the resin must be more than the thickness of the lead and more specifically it must be 200µm or thicker. This sensor is arranged facing to the FG magnet 10, which produces the magnetic field signals, as shown in Fig. 3A. Then, the minimum gap between the magnetic field detecting portion 15S and the surface of the FG magnet 10 becomes greater than 200µm even if the molded portion with a resin approaches the magnet to such an extent that the portion almost comes in contact with the latter. Recently, motors have been miniaturized and made highly precise and correspondingly the pitch of magnetization of the FG magnet has become smaller and hence the intensity of the magnetic field produced by such a magnet has very small value. Therefore, the desired output signal from the sensor cannot be obtained, as has been described above, if the gap between the magnetic field detecting portion 15S and the FG magnet 10 is as much as 200µm. As has been discussed above, a desired value of output signal from the sensor cannot be obtained unless the gap is in the order of 100µm or smaller. For this reason, in the conventional technology as shown in Fig. 3B, an element is arranged so that a molded portion 15'M is kept away from the FG magnet 10. However, if the element is arranged in such a manner, a large space is required below the rotor for avoiding the contact of the molded portion with the rotor. Therefore this makes it difficult to reduce the thickness of the motor. In order to obtain the maximum output signal of the magnetoresistive sensor, it is necessary to face the entire region of the magnetic field detecting portion 15'S to the magnetized surface of the rotor. In general, it is sometimes observed that the rotor is shifted up and down during rotating in the order of about several hundreds of micrometers. Accordingly, to prevent the reduction in the output of the sensor, it is inevitable to keep a large distance between the lower end of the magnetic field detecting portion 15'S and the upper end of molded portion 15'M reinforced with a resin because the magnetic field detecting portion and the magnetized surface always face each other even if the rotor position shifts up and down. This would be a major obstacle in the miniaturization of the sensor element. Another conventional magnetoresistive sensor is disclosed in Japanese Utility Model Application Laying-open No. 158966/1986. Fig. 4A is a plan view thereof and Fig. 4B is a sectional view taken along the line A-A in Fig. 4A. As shown in Fig. 4B, this sensor is designed such that a terminal electrode portion 21T is formed on a lower portion of a linear step formed on a silicon substrate 21. Reference numerals 21S, 21M and 6 represent, respectively, a magnetic field detecting portion, a molded portion and a wiring portion for electrically connecting the terminal electrode portion 21T and a lead 7. By making the step larger, this sensor can be designed such that the resin molded surface is not projected over the level of the surface on which the magnetic field detecting portion is formed, unlike the foregoing conventional sensor, even when the terminal portion is reinforced through molding with a resin. If the sensor is designed so as to have such a construction, the distance between the magnetic signal source such as an FG magnet and the surface of the sensor, or the position at which the sensor is to be arranged can arbitrarily be established without the restrictions observed in the conventional ones explained with reference to Figs. 3A and 3B. First, the production of an element having such a structure requires extra steps to make the linear or band-like portion before processing a substrate and subsequently preparing the element. In addition, it is very difficult to practically produce an element having such a structure because of the following problems. A first problem relates to the structure of the substrate. The band-like stepped portion must have a difference of level in the order of at least 200µm for limiting the surface of the molded portion to a level lower than that of the surface on which the magnetic field detecting portion is formed. As a specific example, Japanese Utility Model Application Laying-open No. 158966/1986 discloses that the stepped portion may be formed by etching an Si substrate. However, the formation thereof is very difficult, such a stepped portion cannot be obtained through only one run of etching at all and thus it is necessary to repeat such an etching process over several tens of times. In other words, the etching process must be repeated over many times and accordingly the resulting substrate would be very expensive while taking the cost for the production thereof into consideration. Another problem is the difficulty in processing a substrate. In particular, it is very difficult to carry out the photolithography process and it is impossible to obtain a pattern at a high accuracy. When it is intended to prepare the sensor element having a band-like stepped portion as shown in Fig. 4B, a terminal electrode portion must be formed on the lower portion of the stepped portion. However, for having a large difference of level, it is impossible to form a pattern on the band-like portion of the lower step through the photolithography process. Therefore, a sufficient mass-production and productivity cannot be ensured. Moreover, as the terminal electrode portion cannot be formed through the photolithography process, a fine terminal pattern cannot be formed at a high accuracy, so that the distance between the terminals and the size thereof increase, therefore correspondingly the size of the sensor element is also increased. On the other hand, if the width of the sensor element is compulsorily reduced, this conventional sensor element having the foregoing structure suffers from the problems of electrical short arising between the terminals and of the contact with the bonded wires each other since terminal electrode portions are present on the same line (or band). JP-U-59-179320 discloses a magnetoresistive sensor structure in which the surface levels of two opposed side edges are lowered with respect to the central portion of the substrate surface. Two magnetic field detecting portions are formed as band-like stripes of ferromagnetic thin films which extend from the central protrusion portion to the lower opposed side edges of the substrate. The fine stripes are directly connected to electrodes disposed on each of said low edge portions of the substrate. This may cause a break of the fine stripes of the ferromagnetic thin film especially at the boundary between the flat surface and the inclined surface at the edges of the device. The object of the present invention is to solve the problems explained above and to provide a magnetoresistive sensor which is not attended by bad effects due to the projection of the mold on terminal portions, in which the distance between the surface of a magnetic signal source as an FG magnet and the magnetic field detecting portion of a sensor as well as the position, at which the sensor is arranged, can be freely established, in other words, in which the lead-taking out portion is not an obstacle in the detection of magnetic signals. Another object of the invention is to provide a magnetorestrictive sensor which can be miniaturized, which has high reliability and can be produced at low cost. These objects are achieved by the features of claim 1. The present invention provides a magnetoresistive sensor which has a structure whose electrical connection between terminal electrode portion of an element pellet and a lead can be performed through the wire-bonding method capable of ensuring high heat resistance and high reliability, and which can be produced according to a wafer process capable of achieving mass-production. According to the present invention, wiring portions are provided the width of which being larger than that of the lines of the magnetic field detecting portion. This ensures a good connection and a high reliability of the magnetoresistive sensor. Since the magnetic field detecting portion is only formed on the substrate surface other than the lower portion thereof, the sensitivity of the magnetoresistive sensor becomes high. In accordance with the present invention, the size of the magnetoresistive sensor can be reduced because the substrate surface area can be effectively used for disposing the magnetic field detecting portion. The foregoing at least two corner portions on the surface of the substrate may have stepped portions so that the surface level thereof is lower than the level of the other surface portion or alternatively the surface of the at least two corner portions may be inclined with respect to the other surface portion so that the surface level thereof is lower than the level of the other surface portion. The external shape of the substrate may be a regular square. The longitudinal direction of the sensor pattern of the magnetic field detecting portion may be formed parallel to a diagonal line of the regularly square substrate. The terminal electrode portions for input and that for output may be formed on symmetrical positions with one another with respect to the center of the surface of the substrate. On the surface of the substrate, the level of the corner portions on which the terminal electrode portions are formed may be at least 50µm lower than that for the portion on the substrate on which the magnetic field detecting portion is formed. On one side of the substrate, the level of a part of the peripheral portion other than the corner portions may be lower than that for the surface on which the magnetic field detecting portion is formed. An electric resistance element may be formed and further other functional elements may also be formed on the surface of the substrate. In the magnetoresistive sensor according to the present invention, the terminal electrode portions are formed at the corner portions on the substrate whose level is lower than that for the surface on which the magnetic field detecting portion is formed. Accordingly, it is easy to miniaturize the element and when a resin mold is applied for the purpose of reinforcing the bonded portions, the resin mold can be formed so that the surface of the molded portion is almost equal to that for the surface on which the magnetic field detecting portion is formed. Moreover, the wire bonding technique can be adopted in the sensor of the present invention and, therefore, the sensor element having high reliability can be produced at low cost. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic sectional view of a motor for VCR in which a conventional magnetoresistive sensor is incorporated; Figs. 2A and 2B are a plan view and a sectional view of a conventional magnetoresistive sensor, respectively; Figs. 3A and 3B are, respectively, sectional views, each illustrating a condition wherein a conventional magnetoresistive sensor and the surface of a rotor facing one another; Fig. 4A is a plan view of another conventional magnetoresistive sensor and Fig. 4B is a sectional view taken along the line A-A in Fig. 4A; Figs. 5A, 5B and 5C are, respectively, a plan view, a side view and a sectional view taken along the line A-A in Fig. 5A for illustrating a first embodiment of the magnetoresistive sensor pellet according to the present invention; Fig. 6A is a plan view of the structure of a substrate prior to the production of the first embodiment of the magnetoresistive sensor according to the present invention and Fig. 6B is a cross sectional view taken along the line A-A in Fig. 6A; Fig. 7A is a plan view for showing the first embodiment of the magnetoresistive sensor according to the present invention which is subjected to the wire bonding and the transfer molding to thus form a final element and Fig. 7B is a sectional view taken along the line A-A in Fig. 7A; Fig. 8 is a sectional view for showing the first embodiment of the magnetoresistive sensor pellet according to the present invention which is subjected to the wire bonding and the injection molding to thus form a final element; Fig. 9 is a sectional view for illustrating a condition in which the surface of a rotor and the element shown in Fig. 7B or Fig. 8 facing each other; Figs. 10A and 10B are a plan view and a sectional view showing a ceramic green sheet through which holes are made, respectively; Figs. 11A and 11B are a plan view and a sectional view showing a plate-like ceramic green sheet, respectively; Figs. 12A to 12E are sectional views for illustrating the structure of a substrate (corresponding to one chip) which can be used for fabricating the magnetoresistive sensor according to the present invention; Fig. 13A is a plan view showing a second embodiment of the magnetoresistive sensor according to the present invention and Fig. 13B is a cross sectional view taken along the line A-A in Fig. 13A; Fig. 14 is a plan view showing a third embodiment of the magnetoresistive sensor according to the present invention; Fig. 15 is a plan view showing a fourth embodiment of the magnetoresistive sensor according to the present invention; Fig. 16 is a plan view showing a fifth embodiment of the magnetoresistive sensor according to the present invention; Fig. 17 is a plan view showing a sixth embodiment of the magnetoresistive sensor according to the present invention; Fig. 18A is a plan view showing a seventh embodiment of the magnetoresistive sensor according to the present invention and Fig. 18B is a sectional view taken along the line A-A in Fig. 18A; Fig. 19A is a plan view of an element which is obtained to electrically connect on the terminal electrode portions of the magnetoresistive sensor pellet shown in Figs. 18A and 18B by the lead bonding with a solder and Fig. 19B is a sectional view taken along the line A-A in Fig. 19A; Fig. 20A is a plan view showing a eighth embodiment of the magnetoresistive sensor according to the present invention and Fig. 20B is a sectional view taken along the line A-A in Fig. 20A; Fig. 21 is a sectional view showing a ninth embodiment of the magnetoresistive sensor according to the present invention; Figs. 22 and 23 are plan views showing tenth and eleventh embodiments of the magnetoresistive sensor according to the present invention, respectively; and Figs. 24A and 24B are, respectively, a plan view and a sectional view of a twelfth embodiment of the magnetoresistive sensor according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will hereunder be explained with reference to the attached drawings. In the following description, the term "magnetoresistive sensor" means one in which terminals are electrically connected to lead portions and desired portions are molded and the term "magnetoresistive sensor pellet" means a principal component which has function as a magnetoresistive sensor. Accordingly, the magnetoresistive sensor and the magnetoresistive sensor pellet are handled as being identical with one another in embodiments according to the present invention. Embodiment 1 Fig. 5A is a plan view of a magnetoresistive sensor pellet which is a principal component of the magnetoresistive sensor according to the first embodiment of the present invention, Fig. 5B is a side view thereof and Fig. 5C is a sectional view taken along the line A-A in Fig. 5A. This embodiment relates to a magnetoresistive sensor pellet with four terminals which comprises an insulating rectangular substrate 1 made of a ceramic such as alumina having rectangular recesses 1A at the four corners. Reference numeral 2 represents a ferromagnetic thin film of, for instance, an iron-nickel alloy (Fe-Ni), 2S a magnetic field detecting portion, 2W wiring portions, 3 terminal electrode portions formed in the recesses 1A and 4 a passivation film. The sensor pattern of the magnetic field detecting portion in this sensor pellet is formed such that the longitudinal direction of the pattern is parallel to the side of the pellet. Further, in this embodiment, patterns of the wiring portions 2W are formed symmetrically, in other words they are designed to have such a structure that any offset voltage is hardly generated. The method for manufacturing this embodiment will now be described below. Figs. 6A and 6B show the structure of a substrate prior to the production of the element according to this embodiment. Fig. 6A is a plan view of the substrate. In Fig. 6A, the shadowed region 1B enclosed with broken lines corresponds to the region of one unitary sensor pellet. Fig. 6B is a sectional view taken along the line A-A in Fig. 6A. The recessed structure on the substrate is formed by depressing a metal mold against a green sheet prior to firing thereof during the processes for producing the ceramic substrate so that each step has a difference in level of the order of 200µm. A ferromagnetic material such as an Fe-Ni alloy which shows an magnetoresistive effect was deposited on the whole surface of the substrate to thus give a ferromagnetic thin film (Fig. 5A). Subsequently, a photoresist pattern was formed onto the substrate according to the photolithography technique so that the surface of the substrate other than the recessed portions shown in Fig. 6A was covered and terminal electrode portions 3 (Fig. 5A) were formed on the recessed portions according to a means such as a plating or vapor deposition technique. In this respect, the most upper layer was formed from a material which makes it possible to perform wire bonding with, for instance, gold (Au). Thereafter, photoresist patterns for the magnetic field detecting portions 2S and the wiring portions 2W were again formed according to the photolithography technique and then the unnecessary portions thereof were removed by etching to thus form a sensor pattern. The desired portion was covered with a passivation film 4. Then the resulting product was cut into unitary sensor pellets (chips), i.e., sensor pellets each corresponding to the shadowed region 1B as shown in Fig. 6A with a cutting means such as a dicing. As has been described above, the magnetoresistive sensor according to the present invention can be produced while making use of the usual semiconductor processes. Figs. 7A and 7B show an element obtained by fixing the magnetoresistive sensor pellet shown in Fig. 5A to a lead frame through die bonding, electrically connecting between terminals of the sensor pellet and a lead by bonding with an Au wire 6 and subjecting the connected element to transfer molding with a thermoset epoxy resin 5. Fig. 7A is a plan view thereof and Fig. 7B is a sectional view taken along the line A-A in Fig. 7A. In this case, the structure of the pellet was formed in such a manner that terminal electrode portions for input and for output and the sensor patterns each was formed in a 180° point symmetrical relation as shown in Figs. 5A and 5B. For this reason, the fixing of the pellet through the die bonding can be performed according to two ways. In other words, a pattern having a certain orientation is geometrically identical with a pattern which is obtained by rotating the former at an angle of 180°. Thus, if the fixing through the die bonding is performed in either of the orientations to prepare a sensor element, the resulting element makes it possible to detect the same magnetic signal source and to give the same output signal. Moreover, in the element having such a structure, the sensor pellet and the lead 7 are electrically connected through a wire 6 and, therefore, the element has very high reliability in "test for heat resistance during soldering". The following table 1 shows the results (variation in properties) obtained by examining the embodiment of the element according to the present invention and the comparative embodiment which was obtained by bonding with a solder as shown in Fig. 2B through a "test for heat resistance during soldering" which was performed at 260°C for 30 seconds. The element according to the present invention never caused any change in its properties even after the test. Change in Resistance (%) Change in Sensitivity (%) Embodiment of the Invention ±0.2 ±0.6 Comparative Embodiment +2.5 -9.3 In addition, the element as shown in Fig. 7A and 7B in which the electrical connection is performed by the wire bonding has a structure suitable for automatic production inclusive of the molding process to thus simplify the manufacturing processes and thus such a structure makes it possible to reduce the production cost thereof since the element has very high reliability and can be assembled in a high efficiency compared with the those obtained by assembling through bonding with a solder. In order to make the level of the surface of the magnetic field detecting portion identical with that for the molded resin surface as shown in Fig. 7B, the difference in level between the terminal electrode portions and the other portion on a substrate must be at least 50µm while taking the height of the wire and the accuracy of the metal mold for molding into consideration. The practical difference in level is preferably not less than 100µm and more preferably not less than 200µm. When the transfer molding is performed, the surface of the magnetic field detecting portion may be pressed against the surface of the metal mold for the purpose of exposing the surface of the sensor. In such a case, a resin such as a polyimide, a photosolder resist or a solder mask resist may further be coated on the passivation film 4 for preventing the breakage of the surface of the magnetic field detecting portion. Fig. 8 shows a section of an element which is molded with a thermoplastic resin 8 through the injection molding. In respect of the rationilization of assembling or the like, the foregoings may apply to this case. As to the heat resistance during soldering, this element is unfavorable as compared with the thermosetting resin used in the transfer molding, but this problem can be solved by the use of a resin having high heat resistance such as polyphenylene sulfide or polybutylene terephthalate. Fig. 9 shows a condition in which the magnetoresistive element 10 having a structure as show in Fig. 7B or Fig. 8 and an FG magnet 9 facing each other. Since the surface of the resin mold and the magnetic field detecting portion 10S can be formed such that the level of the former is approximately equal to that for the latter and, therefore, the miniaturization of the element can be ensured. Moreover, it is not necessary to secure any space below the rotor for avoiding the contact with the projected portion of the molded resin. This serves to reduce the thickness of the motor. The following Table 2 shows the ratio of the smallest required area of the sensor pellet according to the embodiment of the present invention to that for the comparative element as shown in Fig. 2B when these elements are designed so as to have the same electrical properties. As seen from the results listed in Table 2, the present invention can reduce the size of the sensor pellet to not more than 1/3 time that for the conventional one. Size of Sensor Pellet Area Ratio Embodiment of the Invention 2mm×2mm 1 Comparative Embodiment 3mm×4mm 3 Although it is practically difficult to obtain an element as shown in Figs. 4A and 4B, the ratio of the size of the sensor pellets becomes more greater than that obtained with respect to the foregoing comparative element while taking large pitches between wiring portions to avoid the electrical short into consideration even if the elements are designed so as to have the same electrical properties. In this embodiment, the formation of the terminal electrode portions is performed after depositing the ferromagnetic thin film, but it is also possible to form the terminal electrode portions in advance before the deposition of the ferromagnetic material to give a ferromagnetic thin film. In other words, there is no restriction in the order of the formation thereof. In this embodiment, the recessed portions on the substrate are formed by depressing a metal mold against a green sheet of a ceramic prior to firing, but there is also no restriction in the method for manufacturing these recessed portions. For instance, a substrate having the same structure can also be obtained by pasting a green sheet 11 of a ceramic having holes made at desired pitches whose plan view and sectional view are shown in Figs. 10A and 10B respectively to a usual plate-like green sheet 11' of a ceramic having no hole whose plan view and sectional view are shown in Figs. 11A and 11B respectively and then firing the resulting assembly. The holes as shown in Figs. 10A and 10B can easily be formed by pressing a ceramic while it is still in the green sheet state in a metal mold or the like. A ceramic substrate having a structure similar to that shown in Figs. 6A and 6B can be prepared by pasting this green sheet in which holes are made in the manner explained above to a green sheet with no holes as shown in Figs. 11A and 11B and then firing the assembly. The recessed portions can also be formed after the firing of the substrate through a means such as a laser processing technique. Figs. 12A to 12E show sectional views of substrates which are cut into chips and which can be used in the present invention. Fig. 12A is a sectional view of a ceramic substrate 1 in which a part of a ceramic substrate, i.e., regions 1A for forming the terminal electrode portions are recessed as exemplified in this embodiment, and Fig. 12B is a sectional view of a ceramic substrate having recessed portions 1A and a glazed layer 12 applied on the surface other than recessed portions. Fig. 12C is a sectional view of a substrate 1 which is prepared by applying a glazed layer 12' onto the surface of a ceramic substrate 1' except for the surface regions 1A for forming the terminal electrode portions to thus project the surface area except for the region 1A. Fig. 12D is a sectional view of the structure of a substrate whose regions 1A for forming the terminal electrode portions are tapered. Fig. 12E is a sectional view of the structure of a substrate whose stepped portions are almost vertically formed and in which a glazed layer 12 is applied to the region for forming the magnetic field detecting portion. In order to make the most use of the magnetic properties of the magnetoresistive sensor, the surface roughness of the region for forming the magnetic field detecting portion is desirably as small as possible. Therefore, a glazed layer is preferably applied onto the surface of the region for forming the magnetic field detecting portion as shown in Figs. 12B, 12C and 12E because of the small surface roughness thereof. However, if the glazed layer is too thick, the surface of the glazed layer is greatly curved. As a result, if such a substrate as such is processed to form a sensor element, the magnetic field detecting portion is thus formed on such a curved surface. In such a sensor element, the gap between a magnetic signal source and the magnetic field detecting portion is not uniform and accordingly, the output signal from the sensor element is also unstable. The glazed surface may be polished in order to eliminate such a disadvantage. Thus, the magnetic field detecting portion can be formed on a flat surface by polishing the glazed surface. Embodiment 2 Fig. 13A is a plan view of a second embodiment of the magnetoresistive sensor pellet according to the present invention and Fig. 13B is a sectional view taken along the line A-A in Fig. 13A. This embodiment relates to a magnetoresistive sensor with four terminals which comprises fan-shaped recesses 101A at the four corners on a regular square substrate 101. In this case, a glazed layer 12 is applied below the magnetic field detecting portion and a substrate having a sectional structure as shown in Fig. 12B is employed. The recess may have a fan-shaped form as in this embodiment or may have any other shape. Reference numeral 101 represents a ceramic substrate, 201 a ferromagnetic thin film, 201S a magnetic field detecting portion, 201W wiring portions and 301 terminal electrode portions, respectively. The magnetoresistive sensor pellet of this embodiment can be produced in the same manner used in Embodiment 1 except for the formation of the glazed layer, the shape of the recesses and the pitches thereof. The glazed layer 12 was formed by coating a glass paste on a ceramic substrate after preparing the same and then firing the coated layer. Moreover, in this case, the sensor pattern of the magnetic field detecting portion is formed such that the longitudinal direction of the pattern is parallel to the diagonal of the regular square substrate. This structure is favorable for elongating the length of the sensor in comparison with that of Embodiment 1. In addition, the input terminals, the output terminals or the like each are formed symmetrically as in Embodiment 1 and correspondingly the element can be fixed through the die bonding technique according to two ways as is Embodiment 1. Further, the layout of the wiring portions are also symmetrical as in the case shown in Fig. 5A. This structure is likewise designed so that the offset voltage is never generated. Embodiment 3 Fig. 14 is a plan view of a third embodiment which is a magnetoresistive sensor pellet with three terminals which comprises fan-shaped recesses 102A at three corners among the four corners of a substrate. This sensor pellet can be produced according to the same manner as used in Embodiment 1 except for the shape of the recess and the pitches thereof formed. In Fig. 14, reference numeral 102 represents a ceramic substrate, 202 a ferromagnetic thin film, 202S a magnetic field detecting portion, 202W wiring portions and 302 terminal electrode portions, respectively. In case of elements with three terminals, at least three recesses must be formed on the substrate, but the number of recesses may be more than 3. Embodiment 4 Fig. 15 is a plan view of an embodiment of the magnetoresistive sensor pellet according to the present invention. This embodiment is a magnetoresistive sensor with three terminals in which the sensor pattern is formed such that the longitudinal direction thereof is parallel to the diagonal of a regular square substrate as in Embodiment 2. The element can be produced according to the same method used in Embodiment 1 except for the shape of the recess and the pitches thereof formed. In Fig. 15, reference numeral 103 represents a ceramic substrate, 103A recessed portions, 203 a ferromagnetic thin film, 203S a magnetic field detecting portion and 203W wiring portions. Reference numeral 303 stands for terminal electrode portions. When this embodiment is compared with the embodiment shown in Fig. 14, the element has a structure which hardly causes the offset voltage from the viewpoint of its design since the layout of the wiring portions are symmetrical. The offset voltage is preferably as low as possible from the practical point of view. Therefore, the shape shown in Fig. 15 is more preferred than that shown in Fig. 14 so far as the element with three terminals is concerned. Embodiment 5 Fig. 16 is a plan view of a fifth embodiment of the magnetoresistive sensor pellet according to the present invention. This embodiment relates to a magnetoresistive sensor with four terminals having single-phase output signal which comprises terminal electrode portions formed a the four corners on a substrate and has a point symmetrical pattern. In Fig. 16, reference numeral 104 represents a ceramic substrate, 104A recessed portions, 204 a ferromagnetic thin film, 204S a magnetic field detecting portion and 204W wiring portions, respectively. Reference numerals 304a to 304d each represents a terminal electrode portion. In the pellet shown in Fig. 16, input terminals and output terminals each are disposed on the diagonal of the rectangular substrate. Reference numerals 304a and 304c represent the input terminals. The output terminals represented by 304b and 304d are electrically connected through the common wiring portion so that the same output signal can be obtained through either of the terminals. As has been explained above, the input terminals and the output terminals are formed on the positions which are in a 180° point symmetrical relation, respectively in this element. Accordingly, the degree of freedom for fixing the pellet through the die bonding technique is 2 as in Embodiments 1 and 2. Embodiment 6 Fig. 17 is a plan view of a sixth embodiment of the magnetoresistive sensor pellet according to the present invention. As in Embodiment 2 or 4, this embodiment comprises a substrate having a regular square appearance and is a magnetoresistive sensor with four terminals having single-phase output signal in which a sensor pattern is formed such that the longitudinal direction thereof is parallel to the diagonal of the regular square substrate. In Fig. 17, reference numeral 105 represents a ceramic substrate, 105A recessed portions, 205 a ferromagnetic thin film, 205S a magnetic field detecting portion and 205W wiring portions, respectively. Reference numerals 305a to 305d each represents a terminal electrode portion. Reference numerals 305a and 305c represent the input terminals. In this case, the output terminals represented by 305b and 305d are likewise electrically connected through common wiring portion as in Embodiment 5 so that the same output signal can be obtained through either of the terminals. In this case, the input terminals and the output terminals are likewise formed on the positions which are in a 180° point symmetrical relation, respectively. Accordingly, the degree of freedom for fixing the pellet through the die bonding technique is 2 as in Embodiment 5. Embodiment 7 Fig. 18A is a plan view of the magnetoresistive sensor pellet according to the present invention and Fig. 18B is a sectional view taken along the line A-A in Fig. 18A. This embodiment relates to a magnetoresistive sensor with two terminals which comprises rectangular recesses 106A on two positions among the four corners on the rectangular substrate. In Figs. 18A and 18B, reference numeral 106 represents a ceramic substrate, 206 a ferromagnetic thin film, 206S a magnetic field detecting portion, 206W wiring portion, 306 terminal electrode portions disposed on recessed portions and 4 a passivation film. In this sensor pellet, the sensor pattern is formed such that the longitudinal direction thereof is parallel to one side of the pellet. Fig. 19A is a plan view of a magnetoresistive sensor with two terminals obtained by electrically connecting the terminal portions of the foregoing sensor pellet to a lead 7 through the bonding with a solder 21. Fig. 19B is a sectional view taken along the line A-A in Fig. 19A. Reference numeral 5' stands for a portion reinforced by molding with resin on a connected portion. In this case, the mold is formed such that the level of the mold surface is approximately equal to that for the magnetic field detecting portion. As in this embodiment, even if the connection is performed through the bonding with a solder, the molded surface can be formed so as not to project over the level of the surface on which the magnetic field detecting portion is formed. Incidentally, in the element with two terminals shown in Fig. 19A, two recessed portions are formed on the two corners of the rectangular substrate, the recessed portions may be formed on three or four corners on the substrate. Moreover, the recessed portions may also be formed on a peripheral portion in addition to the corners. If a part of the corners of the rectangular substrate is missing, the foregoings may apply in this case, so far as desired recessed portions are formed and the desired terminal electrode portions are formed on the recesses. Embodiment 8 Fig. 20A is a plan view of an eighth embodiment of the magnetoresistive sensor pellet according to the present invention and Fig. 20B is a sectional view taken along the line A-A in Fig. 20A. This embodiment is a magnetoresistive sensor pellet with two terminals in which the difference of level is a almost vertically formed on a substrate as shown in Fig. 12E. In Figs. 20A and 20B, reference numeral 107 represents a ceramic substrate, 107A recessed portions, 207 a ferromagnetic thin film, 207S a magnetic field detecting portion and 207W wiring portions. Reference numeral 307 represents terminal electrode portions composed of Au. In this embodiment, the substrate can be manufactured according to the method used in Embodiment 2 with a minor modification except that the shape of the recessed portions and the pitches thereof formed. Reference numeral 12 stands for a glazed layer. Since the stepped portions are approximately vertically formed on the substrate, it is very difficult to apply a material for electrodes to the side wall of the stepped portions through a means such as the vapor deposition. For this reason, a conductive paste 3' is coated on the side wall thereof, then fired, thereafter a layer of a material for electrodes is formed on the side wall by plating and to thus simultaneously form the terminal electrode portions. The electrodes may be formed by coating a conductive paste and then firing, or by plating alone. Moreover, the materials for electrodes are not restricted to specific ones so far as they are electrically conductive. As shown in Fig. 20B, if the stepped portions are approximately vertically formed on the substrate, the wiring portions 207W can be shortened and accordingly the size of the sensor element can further be miniaturized. Embodiment 9 Fig. 21 is a sectional view of a ninth embodiment of the magnetoresistive sensor according to the present invention. This embodiment relates to a magnetoresistive sensor in which the corners 108A of a substrate are tapered as shown in Fig. 12D. Further, Fig. 21 shows a condition in which the magnetoresistive sensor pellet is electrically connected to a lead 7 by a conductive resin 21'. The region surrounded by the broken line in Fig. 21 corresponds to the region to be molded with resin when the pellet is formed into a final element. Reference numeral 108 represents a ceramic substrate, 208 a ferromagnetic thin film, 208S a magnetic field detecting portion and 308 terminal electrode portions. As has been described above, the corners of the substrate on which the terminal electrode portions are to be formed are tapered. Therefore, the electrical connection between the terminal electrode portion 308 and the lead 7 can be performed using the conductive resin 21' without using any wires. The materials for the conductive resin 21' is not restricted to specific ones so far as they are electrically conductive. Embodiment 10 Fig. 22 is a plan view of a tenth embodiment of the magnetoresistive sensor pellet according to the present invention. This embodiment is a magnetoresistive sensor with six terminals in which two hemicircular recesses 109A are formed on two peripheral portions of a substrate in addition to four recesses formed at the four corners of the substrate. In this figure, reference numeral 109 represents a ceramic substrate, 209 a ferromagnetic thin film, 209S a magnetic field detecting portion, 209W wiring portions and 309 terminal electrode portions, respectively. As in Embodiment 10, elements provided with more than 4 terminals can be obtained by forming recesses on peripheral portions on the substrate in addition to the four corners thereof. Embodiment 11 Fig. 23 is a plan view of an eleventh embodiment of the magnetoresistive sensor pellet according to the present invention. This embodiment relates to a sensor in which a pattern for magnetoresistive sensor is formed on the same substrate used in Embodiment 10 and further a pattern for resistive element comprising, for instance, an NiCr alloy is also formed on the surface of the same substrate. In Fig. 23, reference numeral 110 represents a ceramic substrate, 110A recessed portions, 210S a magnetic field detecting portion of the magnetoresistive sensor composed of a ferromagnetic thin film and 210W wiring portions, respectively. Reference numeral 13 represents a resistance portion which is formed by, for instance, depositing an NiCr thin film on the surface of the substrate and then forming the film into a desired pattern. Reference numeral 310 stands for terminal electrode portions. As has been explained above, if a pattern for magnetoresistive sensor and a pattern for resistance element are formed on the same surface of a substrate, a proper electrical voltage can be applied to the magnetoresistive sensor through the resistance element when a high electrical voltage must be inputted to the magnetoresistive sensor. Likewise, other functional elements other than resistance elements may be formed on the same surface of a substrate. Embodiment 12 A twelfth embodiment of the present invention is shown in Figs. 24A and 24B. This embodiment relates to a magnetoresistive sensor pellet 1 and an integrated circuit element 14 which are electrically connected to one another through wires 6 and which are molded in a package. Fig. 24A is a plan view of these elements prior to the molding and Fig. 24B is a sectional view of these elements after the molding taken along the line A-A in Fig. 24A. As shown in Fig. 24B, there can be obtained a magnetoresistive sensor having a function for processing output signals of sensor pellet in which the level of the mold is not projected over the surface of the sensor if the thickness of the substrate for an integrated circuit element is thinner than that for the magnetoresistive sensor pellet. INDUSTRIAL APPLICABILITY As has been described above, in the magnetoresistive sensor pellet of the present invention, a difference in level is established between the surface on which the magnetic field detecting portion is formed and the surface of the terminal electrode portions at the corners or further at the periphery of the substrate and, therefore, when a resin mold is applied to the sensor for the purpose of reinforcing the bonding portions, the mold can be formed such that the surface of the mold is equal to that for the magnetic field detecting portion. Moreover, the sensor of the present invention can be electrically connected through the wire bonding technique, and so elements having high heat resistance can be obtained. In addition, the process for assembling elements can be rationalized and accordingly the cost for the assembling can be reduced. Furthermore, the production cost can be reduced by miniaturizing the sensor pellet and simultaneously the thickness of motors can be reduced.

Claims: A magnetoresistive sensor comprising a magnetic field detecting portion (2S) composed of a band-like pattern of a ferromagnetic thin film (2), formed on one surface of a rectangular substrate (1), said one surface of said substrate (1) having at least two corner portions or said at least two corner portions and further portions at the periphery of the substrate the surface level of which being lower than that of the upper portion other than said at least two corner portions or further periphery portions, at least two terminal electrode portions (3, 309) being separately formed on said corner portions or on said at least two corner portions and further periphery portions and connected to said magnetic field detecting portion (2S), said magnetic field detecting portion (2S) being formed on said upper portion, wherein said ferromagnetic thin film (2) comprises besides said band-like pattern of said magnetic field detecting portion (2S) wiring portions (2W) which connect said magnetic field detecting portion (2S) to said at least two terminal electrode portions (3, 309), the width of the wiring portions (2W) being larger than that of the lines of the pattern of said magnetic field detecting portion (2S). A magnetoresistive sensor as claimed in claim 1, wherein said at least two corner portions (1A) on said surface of said substrate (1) have stepped portions. A magnetoresistive sensor as claimed in claim 1, wherein said at least two corner portions (1A) on said surface of said substrate (1) are inclined with respect to the other surface portions. A magnetoresistive sensor as claimed in any of claims 1 to 3, wherein the external shape of the substrate (1) is a regular square. A magnetoresistive sensor as claimed in claim 4, wherein the longitudinal direction of the band-like pattern of said magnetic field detecting portion (2S) is formed parallel to a diagonal line of said regularly square substrate (1). A magnetoresistive sensor as claimed in any of claims 1 to 5, wherein terminal electrode portions (3) for input and those for output among the terminal electrode portions (3) are formed on symmetrical positions with one another with respect to the center of the surface of said substrate (1). A magnetoresistive sensor as claimed in any of claims 1 to 6, wherein the level of the corner portions (1A) on which said terminal electrode portions (2) are formed is at least 50 µm lower than that for the surface portion of said substrate (1) on which said magnetic field detecting portion (2S) is formed. A magnetoresistive sensor as claimed in any of claims 1 to 7, wherein on said one surface of said substrate (1), the surface level of a part of a peripheral portion other than said corner portions (1A) is lower than that for the surface on which said magnetic field detecting portion (2S) is formed. A magnetoresistive sensor as claimed in any of claims 1 to 8, wherein an electric resistance element is formed on the surface of said substrate (1). A magnetoresistive sensor as claimed in any of claims 1 to 8, wherein other functional elements are further formed on the surface of said substrate (1). A magnetoresistive sensor as claimed in any of claims 1 to 10, comprising a magnetic signal processing part (14) which comprises an integral circuit element disposed on a semiconductor substrate.

Inventors: SHIBASAKI ICHIRO, SUGIMOTO YOSHIYASU, SHIBASAKI, ICHIRO, SUGIMOTO, YOSHIYASU
Applicants: ASAHI CHEMICAL IND, ASAHI KASEI KOGYO KABUSHIKI KAISHA
Application year: 1991
Main classification: G01R33
IPC codes: G01R33, H01L43, G01D5