GB2273292A - Ceramic board having glaze,manufacture method therefor,and electronic device using the ceramic board - Google Patents

Abstract

By providing protuding sections (3) on a ceramic board (1), the shape and the forming region of a glaze can be controlled precisely. By selecting the amount of the material of the glaze applied to the ceramic board (1), obtained are boards (101, 102, 103, 104, 105, 106, 108, 109, 110) whose glaze sections (2) are flat to the end parts of the glaze. Further, a board (107) in which the glaze section (2) has a arbitrary curvature is similarly obtained. Therefore, by forming functional sections on such an appropriate glaze, an electronic device of good characteristics is obtained. <IMAGE>

Description

CERAMIC BOARD HAVING GLAZE, MANUFACTURING METHOD THEREFOR, AND ELECTRONIC DEVICE USING THE CERAMIC BOARD TECHNICAL FIELD The present invention relates to glazed ceramic substrates and their manufacturing methods. Furthermore the present invention relates to electronic devices such as magnetoresistive element type magnetic sensors, thermal heads for printers, thin film resistors and condensers, which demonstrate excellent characteristics through the use of said ceramic substrates.

BACKGROUND ART Ceramic substrates have excellent quality stability and processability, and conventionally have been used in various forms in the field of electronic components.

Of these forms, glazed ceramic substrates have been mainly used for electronic devices which utilize a thin film as the functional element.

As an example of such conventional use is the disclosure in the publication of Japanese Patent Application Laying-open No. 954383/1986, of a magnetoresistive element which utilizes a strongly magnetic thin film. Figure 1A shows a plan view of the magnetoresistive element disclosed in this publication. Fig. 1B shows a cross sectional view along the line A-A of Fig.

1A which represents a cross sectional structure of a general glazed substrate which is -not-- however disclosed in the said official gazette.

In the figure, numeral 1 denotes the ceramic sheet and numeral 2 denotes the glazed portion.

A sensor portion 4S comprising a strongly magnetic thin film 4 is formed on the surface of the glazed portion 2. Symbol 4T denotes an electrode portion. Generally, magnetoresistive elements are formed with the sensor portion having a thin film of no more than 0.1 microns.

Consequently, the value of surface roughness, at least in the region forming the sensor, should be as small as possible. Normally, this value must be less than the value of the film thickness in order to obtain the required element properties.

With ceramics however, the surface roughness is normally of the order of several microns so that if the sensor portion is formed as is, the required element properties will not be obtained.

In order to obtain a small surface roughness in the region of the sensor portion 4S, this region is therefore glazed as shown in Fig.1. With glazing, in order to obtain a sufficiently small surface roughness and stable surface condition without pinholes, it is generally necessary for the thickness of the glazed portion 2 to be of the order of 25- 60 microns. In this case, a surface roughness of the glazed portion 2 of no more than 0.1 microns can be obtained. Normally, however the surface of the glazed portion 2 is curved over a length of lmm to 2mm inwards from the edge, forming a gentle step of 25-60 microns from the edge of the glazed portion 2.

Figure 2A shows a plan view of a substrate 112 prior to the formation of an element, while Fig. 2B shows a sectional view along the line A-A of Fig. 2A. The region indicated by the dotted line "a" in Fig. 2A corresponds to that for an element constructed as shown in Fig. 1.

Figure 3 gives an example of measurements of the surface shape of the glazed portion 2 for a ceramic substrate 112 having a glazed portion 2 approximately 30 microns thick and 2mm wide.

This figure shows that with a glaze width of approximately 2mrn, there is-practically no flat region on the surface of the glaze.

The sensor portion 4S of the magnetoresistive element shown in Fig. 1 is normally formed in a number of repeating patterns of fine lines approximately 10 microns in width. Consequently, a high patterning accuracy is required. It is therefore desirable to form the sensor portion on a region that is as flat as possible. However, since the glazed surface is narrow, and-as shown in Fig. 3, the whole of the glazed surface is curved, it is not generally possible to obtain a flat region for patterning. As a result, highly accurate patterning is not possible.To solve this problem, the glazed portion 2 on the substrate 112, as shown in Figs. 2A and 2B is made wide, for example of the order of Smm to 10mm, thereby forming a flat region of glaze in a central portion separated sufficiently from the edge of the glaze, and the sensor portion is formed on this flat region.

In this case, since the glazed portion is wide and the sensor portion must be formed in the region separated from the edge of the glaze, the element is necessarily large. Recently however, with the advent of thin type motors for use in electrical products, small sized components have become necessary. With conventional substrates however, due to the above reasons, the edge part of the glaze portion as shown in Fig. 2 is subject to a large curvature. The area of the glazed portion must therefore be large to ensure a suitable flat region for forming the sensor portion. Consequently, miniaturization of the element becomes difficult.

Furthermore, even if the glaze region is made as small as possible in order to miniaturize the element, the glaze surface curvature remains large as shown in Fig. 3, and since patterning is formed on this curved surface, an accurate pattern cannot be obtained. This results in a high offset voltage so that it becomes difficult to manufacture an element having properties of any practical use.

To address this problem, the glaze surface may be polished to obtain a flat surface.

However with polishing it is very difficult to obtain uniformity over the whole of the substrate surface, and due to the complexity of the process it is relatively expensive. Furthermore, even with polishing, the curvature of the glaze border portion cannot be removed.

Another example of a conventional device is the magnetic sensor disclosed in the publication of Japanese Patent Application Laying-open No.

293676/1989. Fig. 4A shows a cross sectional view of the magnetic sensor disclosed in this publication. As with the previous example, numeral 1 indicates a ceramic sheet and numeral 2 indicates a glazed portion. A diffusion layer 8 is formed on the substrate of the magnetic sensor between the glazed portion 2 and a thick film electrode 7. A nickel alloy film 4 is formed over the glazed portion 2, the diffusion- layer 8 and the thick film electrode 7, thereby finishing off the magnetic sensor. The protective film and lead etc. are not shown in the figure.

In the publication of Japanese Patent Application Laying-open No. 293676/1989 the substrate for the magnetic sensor, as shown in Fig. 4B, comprises an insulated substrate sheet 1 of alumina and the like with a thick film electrode material 7' and glaze material 2' applied on top so that a portion overlaps, the materials then being fired together at the same time. The overlapping portion X coincides with the formation region of the diffusion layer 8 of Fig. 4A, and due to mutual diffusion in this region a smooth intermixing results. In the figure of the publication (Fig. 4A), the glazed portion 2, the diffusion layer 8, and the thick film electrode 7 appear to be the same height.

That is to say, they are drawn as if formed -flat.

However, in reality, the region encircled by the dotted line "a" in Fig. 4A, that is to say the region surrounding the diffusion layer 8 has a gentle sloping shape, as shown magnified in Fig.

4C. This gives rise to an undulation approximately equal to the film thickness of the electrode material 7' with respect to the glazed portion 2, so that the diffusion layer 8 cannot be flat. In order to produce a flat region, a higher than normal firing temperature may be used, with the addition of vibration during the firing process. However, with this method, the glaze and electrode material are diffused over a wide area so that the utilization value of the substrate is reduced. Furthermore, as shown in Fig. 4B, where the glaze material 2' overlaps the thick film electrode material 7', since the materials are fired at the same time, it is difficult to control the formation and extent of diffusion in the diffusion layer 8.Also, since the diffusion layer 8 is not an insulative layer, then if the sensor portion of the magnetic sensor is formed at this location, there is a drop in sensitivity and an increase in offset voltage.

This has a negative influence on the characteristics of the element. Accordingly, in this case also, it is necessary to have the sensor portion sufficiently inside the glaze region, away from the diffusion layer 8, thereby detracting from miniaturization of the element.

Also, since materials for the thick film electrode and for the glaze portion which have a large difference in coefficient of linear expansion are overlapped and fired, there is a possibility of fracturing between them.

Another conventional example disclosed in publication of Japanese Patent Application Laying-open No. 34986/1988 cites a magnetoresistive element with a ceramic substrate having through holes.

Figure 5 shows the structure of a ceramic substrate 113 disclosed in this publication, prior to formation of the magnetoresistive element. Fig. 5A is a plan view, and Fig. 5B shows a sectional view along the line A-A of the region indicated by dotted line "a" in Fig. 5A.

In the publication, the glazed portion 2 is drawn flat. However, in fact as with the previous first conventional example, the edge portion is curved significantly. The region surrounded by dotted line "b" in Fig. 5A corresponds to a single sensor chip when used in the manufacture of a magnetoresistive element. Through holes are formed at predetermined spacing in the substrate 113, and the front and rear faces of the substrate are electrically connected by a conducting material 7. The other regions on the front surface of the substrate 113 have a glaze 2.

Figure 6A shows a plan view of a magnetoresistive element chip formed using a through hole substrate made from a substrate such as that of Fig. 5 having a through hole pitch of the order of 2 mm. Fig. 6B is a sectional view along the line A-A of Fig.6A. The structure of this substrate, as with the previously mentioned substrate, has a curved glazed portion 2.

Consequently, in this case also, the pitch of the holes in the substrate, as shown in Fig. 5, must be large as also must the area of the glazed region in the single chip surrounded by the dotted line "b" in order to form a sensor on a flat portion thereof. Accordingly, as with the previously mentioned example, miniaturization of the element becomes extremely difficult.

Conventionally, with substrates having a narrow glazed region and holes of fine pitch it has not been possible to obtain a flat glazed surface without polishing. Consequently, when using this type of substrate, element miniaturization has been difficult. Also with the method involving overlapping the thick film electrode material with glaze material and firing together to obtain a smooth transition at the boundary of the glazed surface and the electrode material, the diffusion layer formed between the glazed portion and the electrode has an indistinct boundary. Hence, although there may be a smooth shape, undulations of the order of the film thickness of the electrode material occur. Consequently, as with the previous example, since effective utilization of the element up to the edge of the glaze is not possible, miniaturization is made difficult.

The present invention is not in a technical field directly related to the above situation, but is concerned with the beforementioned high accuracy positioning of the resistive film on substrates wherein corresponding electrodes and several resistive films are provided between these electrodes such as is disclosed in publication of Japanese Patent Application Laying-open No. 35506/1991. An object of the invention of this publication was to achieve high accuracy positioning of the resistive film by preventing an electrode paste and resistive paste from running together during printing. To achieve this, glaze was printed beforehand-on the insulating substrate and fired. The glaze formed a zone to prevent the running together of the electrode paste and resistive paste of a subsequent formation.In this case, as disclosed in this publication, the glaze was not for forming a functional portion, but acted merely as a zone to prevent the running together of the electrode paste and resistive paste.

Furthermore, after printing the glaze itself on the substrate, it was fired in this condition.

Consequently, in this invention also, the problem of preventing the curvature at the edge of the glaze has not been addressed.

There is also the reverse situation where it is required to form the glazed portion as a curved protuberance, such as for the case where the substrate is used for a thermal head. In this application, a heat generating layer is formed on a curved protruding glazed portion to give a convex shaped heat generating body. Heat generated by the heat generating portion can then be efficiently transferred to recording paper.

With the conventional substrate however, even though a curved protruding glazed portion is obtained, it is difficult to stably form this glazed portion to a uniform shape.

DISCLOSURE OF THE INVENTION It is an object of the present invention to address the above mentioned problems and provide a substrate structure which enables the production of a functional element with high reliability and suitability for mass production, wherein high patterning accuracy may be achieved in spite of the small size. That is to say, to provide a glazed ceramic substrate for electronic devices, wherein the glazed surface is flat up to the edge of the glaze even with substrates having a narrow glaze region or a small hole pitch, and to provide a manufacturing method for such a ceramic substrate, as well as electronic devices using said ceramic substrate.

It is another object of the present invention to provide a ceramic substrate wherein the curvature of the glazed portion can be optionally set by adjusting the quantity of glaze material, and to provide a manufacturing method for such a ceramic substrate, and an electronic device utilizing said ceramic substrate.

In order to achieve the above mentioned objectives, the ceramic substrate of the present invention has a raised portion formed on a surface of the ceramic sheet, and a glazed portion formed on the ceramic sheet adjacent to at least a portion of the raised portion, wherein the material of the raised portion and the material of the glazed portion are different.

In this case the raised portion may be formed along an entire edge region of the glazed portion.

Furthermore, the raised portion may be formed as a plurality of line shaped raised portions, or as a plurality of right angled parallelepiped shaped raised portions.

Preferably, the previously mentioned glazed portion and adjacent raised portion may be formed with approximately the same height, with the surface of the glazed portion flat.

Alternatively, the glazed portion may have a curved surface protruding uniformly over its whole area.

Furthermore, the ceramic sheet may have through holes or recessed portions, and the raised portion may be formed around the periphery of the through holes or recessed portions. The surface of the glazed portion formed on the ceramic sheet having recessed portions should preferably be at least 50 microns above the bottom surface of the recessed portion, and the average surface roughness of the glazed portion no greater than 0.2 microns.

Furthermore, the raised portion may be formed of a ceramic material substantially the same as the ceramic material making up the main body of the substrate. Alternatively it may be formed from a ceramic material different from that making up the main body of the substrate. It may also be formed from an electrical- conducting material.

The method of manufacture of the ceramic substrate of the present invention comprises at least the steps of: (1) Printing a heat bakeable material in the form of a paste at a predetermined position on the surface of a smooth ceramic green sheet, then firing the sheet and paste together to give a ceramic sheet with a raised portion formed on its surface; (2) Subsequently printing a glass paste on the ceramic sheet at predetermined positions which include an edge of the raised portion, and then firing to form a glazed portion.

Here, the green sheet may be one with through holes or recessed portions disposed at a predetermined pitch, and the raised portions may be formed around the periphery of the through holes or recessed portions. In this case, the green sheet having recessed portions may be formed from a green sheet having holes formed at a predetermined pitch which is adhered to a flat green sheet. Furthermore, the green sheet having recessed portions may be formed by using a- glass layer to adhere a green sheet having holes formed at a predetermined pitch to a flat green sheet.

The raised portion may be made from a ceramic paste of the same material as that used for making the green sheet, or may be made from a ceramic paste of a different material to that used for making the green sheet. It may also be made from a paste comprising an electrical conducting material.

Furthermore, the ceramic sheet may be fired prior to printing the paste material used for making the raised portion.

With regards to the electronic devices of the present invention, this may be a magnetoresistive element. This is constructed with a raised portion formed on a ceramic sheet, and a flat glazed portion formed on the ceramic sheet adjacent to the raised portion. The material forming the raised portion is different from that forming the glazed portion. A strongly magnetic thin film is then formed on the surface of the flat glazed portion and the ceramic sheet. Then a sensor portion is formed on the glazed portion, and a terminal electrode is formed on the ceramic sheet.

Another electronic device according to the present invention may be a chip resistor--element.

With this element a conducting raised portion is formed on the ceramic sheet, and a flat glazed portion is formed on the ceramic sheet adjacent to the raised portion. A resistor is formed on the flat glazed portion, with the conducting raised portion connected to the resistor.

Another electronic device according to the present invention may be a thermal head. In this case, a raised portion is formed on the ceramic sheet and a curved protruding glazed portion is formed on the surface of the ceramic sheet adjacent to the raised portion. The material forming the raised portion is different from that forming the glazed portion. A heat generating layer is formed on the curved protruding face of the glazed portion, and a terminal electrode is formed connected to the heat generating layer.

BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B show a magnetoresistive element made with a conventional ceramic substrate. Fig. 1A is a plan view showing the element, while Fig. 1B is a sectional view along the line A-A of Fig. 1A.

Figs. 2A and 2B show a conventional glass glazed ceramic substrate. Fig. 2A is a plan view showing the substrate, while Fig. 2B is a sectional view along the line A-A of Fig. 2A.

Fig. 3 is a characteristic diagram showing typical measurements of the glazed surface condition for a conventional substrate having a glaze width of approximately 2mm.

Figs. 4A, 4B and 4C show a conventional ceramic substrate having a thick film electrode.

Fig. 4A is a side sectional view showing the ceramic substrate. Fig. 4B is a side sectional view of the substrate showing a formation process of the glaze on the ceramic substrate during manufacture. Fig. 4C is an enlarged sectional view showing the portion indicated by "a" in Fig.

4A.

Figs. 5A and 5B show a conventional ceramic substrate with through holes. Fig. 5A is a plan view showing the conventional ceramic substrate, while Fig. 5B is a sectional view along the line A-A of Fig. SA.

Figs. 6A and 6B show a magnetoresistive element formed using the conventional through hole substrate shown in Fig. 5. Fig. 6A is a plan view showing the conventional through hole substrate, while Fig. 6B is a sectional view along the line A-A of Fig. 6A.

Figs. 7A and 7B show a first example- of a ceramic substrate according to the present invention. Fig. 7A is a plan view showing the ceramic substrate, while Fig. 7B is a sectional view along the line A-A of Fig. 7A.

Figs. 8A to 8D are views showing the method of manufacture of the ceramic substrate according to the first example of the present invention.

Fig. 8A is a plan view showing the ceramic sheet used for manufacture of the ceramic substrate.

Fig. 8B is a sectional view along the line A-A of Fig. 8A. Fig. 8C is a plan view showing the ceramic sheet with the raised portion in the formed condition. Fig. 8D is a sectional view along the line A-A of Fig. 8C.

Figs. 9A and 9B show a second example of the present invention. Fig. 9A is a plan view showing a magnetoresistive element manufactured from the ceramic substrate of the first example, while Fig. 9B is a sectional view along the line A-A of Fig. 9A.

Figs. 10A and 10B show a third example of the present invention. Fig. 10A is a plan view showing the ceramic substrate of the present invention, while Fig. 10B is a sectional view along the line A-A of Fig. 10A.

Fig. 11 is a characteristic diagram showing typical measurements of the glazed surfacecondition for a ceramic substrate of the third example having a glaze width of approximately 2mm.

Figs. 12A to 12C show a fourth example of the present invention. Fig. 12A is a plan view showing a ceramic substrate of the present invention having a conducting portion. Fig. 12B is a sectional view along the line A-A of Fig.

12A, and Fig. 12C is a sectional view along the line B-B of Fig. 12A.

Figs. 13A to 13F are respective sectional views showing the region near the glaze edge of the ceramic substrate, and modified examples of the present invention.

Fig. 14 shows a fifth example of the present invention, being a plan view showing the essential portion of the ceramic substrate wherein the whole of the glazed portion is formed as a curved protrusion.

Figs. 15A and 15B show a sixth example of the present invention. Fig. 15A is a plan view showing a ceramic substrate having through holes, while Fig. 15B is a sectional view along the line A-A of Fig. 15A.

Figs 16A to 16D are views showing the method of manufacture of the ceramic substrate shown in Fig. 15 according to the present inventio, Fig.

16A is a plan view showing the ceramic sheet used for manufacture of the ceramic substrate. Fig.

16B is a sectional view along the line A-A of Fig. 16A. Fig. 16C is a plan view showing the ceramic substrate after application of through hole conducting material, and Fig. 16D is a sectional view along the line A-A of Fig. 16C.

Figs. 17A and 17B show a seventh example of the present invention. Fig. 17A is a plan view showing a magnetoresistive element formed using a ceramic substrate having through holes, while Fig. 17B is a sectional view along the line A-A of Fig. 17A.

Figs. 18A and 18B show an eight example of the present invention. Fig. 18A is a plan view showing a chip resistance element manufactured using the ceramic substrate having through holes, while-Fig. 18B is a sectional view along the line A-A of Fig. 18A.

Figs. 19A and 19B show a ninth example of the present invention. Fig. 19A is a plan view showing a ceramic substrate having through holes of a different form to that of the previously mentioned through holes, while Fig. 19B is a sectional view along the line A-A of Fig. l9A.

Figs. 20A and 20B show a tenth example of the present invention. Fig. 20A is a plan view showing a ceramic substrate having recessed portions, while Fig. 20B is a sectional view along the line A-A of Fig. 20A.

Figs. 21A and 21B show an eleventh example of the present invention. Fig. 21A is a plan view showing a magnetoresistive head manufactured using a ceramic substrate having recessed portions, while Fig. 21B is a sectional view along the line A-A of Fig. 21A.

Fig. 22 shows a twelfth example of the present invention, being a sectional view showing a thermal head manufactured using a ceramic substrate having a curved convex shape glazed portion as shown in Fig. 14.

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the present invention will be described below with reference to the drawings.

Example 1 Figure 7 shows a first example of the present invention. A substrate 101 of this example comprises a ceramic sheet 1 as the principal component, and is made up with linear shaped glazed portions 2 provided at a uniform spacing.

Fig. 7A is a plan view, while Fig. 7B is a sectional view along the line A-A of Fig. 7A. In this example, the surface of the ceramic sheet 1 is raised at locations apart from those where the glazed portions 2 are formed. These raised portions 3 are formed with approximately the same height as the region near the boundary of the glazed portions 2 adjacent to the raised portions 3. The raised portions 3 adjacent to the edges of the glazed portions 2 are made to act as a dam to the glaze material. The surface of the glazed portions 2 is formed flat at the same level as that of the raised portions 3. The glazed portions 2 have an approximate thickness of 40 microns and an average surface roughness of approximately 0.02 microns.

The manufacturing method of the substrate of the present invention will be described with reference to Fig. 8.

At first a flat ceramic green sheet 1 as shown in Figs. 8A and 8B is manufactured. Then as shown in Figs. 8C and 8D, a ceramic paste 3 (raised portion) of the same material as that of the green sheet 1 is printed onto the green sheet 1 at an even pitch, and a thickness of approximately 40 microns by a screen printing process. Subsequently the green sheet 1 and raised portions 3 are fired together to fuse the ceramic, resulting in the ceramic sheet 1 with raised portions 3. Then a glass paste is printed on the ceramic surface formed by the above process except on that of the raised portions 3.

This is then fired to give the ceramic substrate 101 with linear sections of glaze as shown in Fig. 7. After firing, the surface of the glazed portion 2 may be brought up to the same level as that of the raised portion 3 and made flat by applying an appropriate amount of the glaze material (glass paste).

There are no particular requirements for the material of the ceramic sheet 1 making up the principal component of the substrate 101.

However this material may preferably be alumina, nitrided aluminum or carbonized silicon.

In the present example, the raised portion 3 is formed of a similar material to that of the principal material of the substrate, however there are no particular restrictions on this material. Furthermore, with the present example, the firing of the raised portion 3 is carried out at the same time as that of the principal ceramic sheet 1. It is however possible for theapplication and firing of the raised portion 3 to be done after firing of the ceramic sheet 1. In this case, the firing temperature would preferably be approximately the same as or less than that of the firing temperature of the principal ceramic sheet 1.

There are no particular restrictions on the material properties of the glazed portion 2.

However, since the glazed portion must be dammed up by the raised portion, the melting point and firing temperature should preferably be lower than that for the ceramic and raised portion materials. Perhaps of most importance is that since a thin film is formed on the surface of the glazed portion, the material for the glazed portion should preferably be of a non alkali type. If an alkali is present, the material is susceptible to pattern erosion in a high humidity atmosphere, with a resulting loss in reliability.

Furthermore, in order to avoid cracking at the boundary of the glaze, the difference in coefficient of linear expansion of the materials for the ceramic 1 and the glaze portion 2 should be as small as possible.

Example 2 An example of a magnetoresistive element manufactured from the substrate 101 of example 1 is shown in Fig. 9. An alumina is used for the ceramic material of the substrate, and a non alkali material is used for the glaze material.

The glaze material is applied in an appropriate amount and fired to give a flat level glazed portion on the substrate. Fig. 9A is a plan view showing the magnetoresistive element, while Fig.

9B is a sectional view along the line A-A of Fig.

9A. Symbol 4S denotes the sensor portion and numeral 5 denotes the terminal electrode. The dotted area marked "a" in Fig. 7A corresponds to the region of one element of Fig. 9. In fabricating the magnetoresistive element of the present example, a magnetic thin film 4 having a magnetoresistive effect is vapor deposited over the whole surface of the ceramic substrate 101 to a film thickness of approximately 500 angstroms.

The terminal electrode 5 is then formed by printing or plating a conducting material over the thin film 4. Subsequently the element is made to a prescribed shape by patterning using a photoresist process. Normally, though not shown in the figure, a protective film is then formed over the element.

The construction of the ceramic substrate 101 is such that the glazed surface edge is flat up to the ceramic region, unlike the curved edge of the conventional example. Consequently, the glazed surface can be used effectively up to the vicinity of the boundary. Accordingly, with this type of ceramic substrate 101, the sensor portion 4S can be formed up to the edge of the glazed portion 2 thereby facilitating miniaturization of the element. Furthermore, since the glaze portion 2 is flat, then as well as enabling miniaturization, highly accurate patterning is possible so that the value of the offset voltage being a negative factor of the element properties can be kept to a low level.

Example 3 Figure 10 shows a third example of the present invention. The ceramic substrate- 102 of this example has a raised portion 3 of a thin line shaped ceramic at the edge of the glazed portion 2, with the glazed portion 2 formed as uniformly spaced strips. Fig. 10A is a plan view, while Fig. 10B is a sectional view along the line A-A of Fig. 10A. In this example also, the surface of the glazed portion 2 is formed flat and at approximately the same height as that of the line shaped ceramic raised portion 3 adjacent to the edge of the glazed portion 2.

Figure 11 shows typical measurements of the glazed surface condition for a ceramic substrate 102 having a glazed portion 2 approximately 25 microns thick and 2 mm wide, and a raised portion 3 approximately 25 microns thick and 0.1mum wide.

The substrate for these measurements was not polished. As shown in Fig. 11 the glazed surface up to the edge of the glazed portion is flat, and the step at the edge of the glazed portion from the level of the lower portion 1B on the substrate to the raised portion 3 is formed abruptly. Compared to the measured examples for the conventional substrate shown in Fig. 3, the glazed region of the substrate of the present invention is extremely flat and even.

Accordingly, by forming the electrode on top of the glaze portion 2 as with the previous example, in this case also miniaturization of the element is facilitated.

The substrate structure is obtained by printing a ceramic paste of the same material as that of the ceramic green sheet 1, in lines at predetermined positions on the flat and even surface of the ceramic green sheet 1, thereby forming linear raised portions 3. Then after firing together, a glass paste is printed at predetermined positions including the edge portions of the raised portion 3, and fired to give the resultant substrate.

Example 4 Figure 12 shows a fourth example of the present invention. In this example, the substrate 103 is made up with rectangular shaped raised portions 3 formed on the ceramic green sheet 1 at predetermined positions and uniform spacing. Fig.

12A shows a plan view, Fig. 12B shows a sectional view along the line A-A of Fig. 12A, and Fig. 12C shows a sectional view along the line B-B of Fig.

12A. In this example also, the edge portion of the glazed portion 2 and the raised portion 3 are formed at approximately the same height and the glazed surface is formed flat.

The substrate structure is obtained by printing a paste of different material to the ceramic, in rectangular shapes at predetermined positions on the even surfaced ceramic green sheet 1 using a process such as screen printing.

After firing together, a glass paste is printed at predetermined positions including the edge face of the raised portion 3 formed by the- above process, and the whole is again fired. In this way the raised portion 3 may be formed of a different material to that for the main material of the ceramic green sheet 1 without any difficulty. In this case also, as before, the formation of the raised portion 3 may be carried out after firing of the ceramic green sheet 1.

The material of the raised portion 3 in this example is a ceramic, however a conducting material may also be used. When a conducting material is used, it is preferable to have a material which is not susceptible to diffusion with the glaze material. Hence this should have a melting point and firing temperature higher than that of the glaze material. If a material such as platinum is used, since this has a high firing temperature and high heat resistance, the ceramic and conducting materials may be fired together.

If a material having a melting point and firing temperature lower than that of the raised portion 3 is used for the glazed material, then Ag and Pd type materials may be used as conductors which also form the raised portion 3 to act as a dam against the glaze.

Figure 13 shows sectional structural diagrams of the edge portion of the glazed portion -2 of ceramic substrates used in electronic devices of the present invention. Figs. 13A to 13C are sectional magnified views showing the region near the glaze edge portion of the ceramic substrate of the previously described examples. Fig. 13A is a sectional view of the substrate 101 of the first example, Fig. 13B is a sectional view of the substrate 102 of the third example, and Fig.

13C is a sectional view showing the substrate 103 of the fourth example. Fig. 13D shows the sectional structure of the ceramic substrate 104 for the case where the raised portion 3 of Fig.

13B is formed from a ceramic or conducting material which differs from that of the base material 1. Fig. 13E shows a sectional construction of a ceramic substrate 105 wherein a ceramic exposed portion 105B on the substrate surface of Fig. 13B is lower than the lower face If of the glazed portion, and the glaze material 2 is dammed by the raised portion 3.

In fabrication of this substrate, a ceramic green sheet lb in which holes have been formed at predetermined positions is placed on the flat ceramic green sheet la. The raised portion 3 is then formed by applying a ceramic paste at predetermined positions on the ceramic green sheet la, and the whole is fired together.- Glass paste 2 is then printed on the surface if and fired to produce the substrate. Figure 13F shows the sectional structure of a substrate 106 formed with the raised portion 3 of Fig. 13E made of a magnetic or ceramic material different to that of the base material 1. The substrates 105 and 106 of Figs. 13E and 13F are fabricated in the same way as the substrate of example 10 to be discussed later.

With the substrates 101 to 106 shown in Fig.

13, the surface of the glazed portion 2 is at the same level as the raised portion 3, and the whole surface of the glazed portion 2 is flat. This is achieved by provision of the raised portion 3 and by applying the glaze material in an appropriate amount and then firing.

Example 5 Figure 14 shows a fifth example of the present invention. The substrate 107 of this example has a glaze material printed onto a ceramic sheet comprising raised portions 3 as shown in Fig. 7 and Fig. 8. The glaze material is printed to a thickness greater than that of the raised portions 3 and then fired. Since the glaze material generally has a high surface tension, the material of the protruding portion does not tend to flow outside of the dammed up region even when melted. A glazed portion having a large curved protrusion can therefore be formed. The curvature of the protrusion can be generally set to within a required range of values by the amount of glaze applied and the firing temperature.

In this way, with the above method of construction, the curvature of the glazed portion can be optionally set in a prescribed region by appropriate selection of the amount of glaze material.

Example 6 Figure 15 is an example of ceramic substrate 108 of the present invention having through holes. Fig. 15A is a plan view, while Fig. 15B is a sectional view along the line A-A of the region outlined by dotted line "a" of Fig. 15A.

In this example, the ceramic sheet 1 has through holes, and an electrical conducting path is formed by printing a conducting material 3' on the front and rear faces of the ceramic sheet 1, and on the side faces of the through holes-. The conducting material 3' extends along the upper face of the ceramic sheet 1, and protrudes from the surface. A glazed portion 2 is formed up to the edge of the conducting raised portion 3. An appropriate amount of glaze material is applied so that the surface of the glazed portion 2 is flat up to the edge.

The method of construction of the substrate 108 will now be described with reference to Fig.

16. First a flat ceramic green sheet 1 is produced. Then through holes as shown in Figs.

16A and 16B are formed by for example punching with a die. Subsequently, as shown in Figs. 16C and 16D, a paste 3' of a conducting material is printed on and around the through holes by a method such as screen printing. In this case, a Pt type high temperature resistant material which can be fired at the same time as the ceramic is used as the conducting material. The ceramic sheet 1 and conducting material 3' are then fused by firing together. A glass paste is then printed on the exposed portion of the ceramic sheet 1 surrounding the raised portion 3 of the conducting material 3', and fired to complete the ceramic substrate 108 shown in Fig. 15. In this case the raised portion 3 formed on the upper surface of the sheet 1 is made of the conducting material 3'. This makes up a through hole thick film electrode and also acts as a barrier to the glazed portion 2.

Example 7 Figure 17 shows an example of magnetoresistive element made from the ceramic substrate 108 of example 6. Fig. 17A is a plan view, while 7B is a sectional view along the line A-A of Fig. 17A. Symbol 4S in the figure denotes a sensor portion while numeral 5 denotes a terminal electrode. The dotted area marked "b" in Fig. 15A corresponds to the region of one element of Fig. 17.

In fabricating the magnetoresistive element of this example, a strongly magnetic thin film having a magnetoresistive effect is vapor deposited over the whole surface of the ceramic substrate 108 as with example 2. A terminal electrode portion 5 is then formed by printing or plating a conducting material over the thin film.

Subsequently the element is made to a predetermined shape by patterning using a photoresist process. A protective film (not shown in the Figure) is then formed over the element.

With the substrate 108 or this construction also, in to obtain a flat glazed portion 2, a raised portion 3 is provided and the glaze material is applied in an appropriate amount so that the surface height is the same as that of the raised portion 3. Consequently, as with example 2, the glaze surface is not curved as with the conventional example. Accordingly, since the surface is flat up to the ceramic boundary (raised portion) it is easy to miniaturize the element, and even with a small sized element, highly accurate patterning is possible. Consequently, problems such as those due to the occurrence of offset voltage are less likely.

Table 1 shows a comparative example of the surface areas required to make magnetoresistive elements having the same characteristics including offset voltage, using either the conventional substrate of Fig. 5, or the substrate of the present examples. As shown in table 1, by using the substrate of the present invention, it is possible to make an element exhibiting the same properties as those of the conventional element, but having approximately 1/4 the surface area.

This is because when using the conventional substrate, the element size must be large due to the following reasons. In order to obtain a sensor portion which exhibits similar desirable characteristic to those of an element of the present invention, the sensor portion must be formed on a flat surface. However with the conventional substrate, since the edge of the glazed portion is curved, a wide glazed portion is required in order to obtain a flat glaze region.

Table 1

Outer dimensions Surface area ratio Made with substrate 2 mm x 2 mm of present invention Made with 4 mm x 4 mm 4 conventional substrate Example 8 Figure 18 shows an example of a chip resistance element made from a substrate 108 having a structure as shown in Fig. 15. Fig. 18A is plan view, while Fig. 18B is a sectional view along the line A-A of Fig. 18A. Numeral 6 denotes a resistor made of a resistive material such as NiCr or Ta2N disposed on the glaze portion 2, and connected to the raised portion 3 of the through hole electrode conducting material 3'. The region surrounded by the dotted line "c" in Fig. 15A corresponds to the region of one element of Fig. 18.The substrate of the present invention may thus be used in this way to make a chip resistance element.

Example 9 Figure 19 shows a different example of a glazed ceramic substrate of the present invention formed with through holes. Fig. 19A is a plan view, while Fig. 19B is a sectional view along the line A-A of Fig.19A. In this case, construction is such that the glaze material of the glazed portion 2 on the ceramic substrate 109, is dammed by the ceramic raised portion 3.

The method of construction of the substrate of this example is as follows. The method is the same as for the previous example up to the stage where the through holes are die punched in the flat ceramic green sheet 1. Subsequently, a ceramic paste is printed around the periphery of the through holes (later to become the raised portion 3), and fused with the ceramic by firing.

Glass paste is then applied on the ceramic surface, excluding the ceramic raised portion 3 and the through hole portion, in an appropriate amount to give a height equal to that of the raised portion 3 after firing. The element is then fired to give the glazed substrate of Fig.

19.

In this case also, since the glaze surface is flat as with the previous examples of manufacture, then when the substrate is used for the manufacture of magnetoresistive elements, element miniaturization is possible without detracting from the element characteristics.

Example 10 Figure 20 shows an example of a glazed ceramic substrate 110 of the present invention having a sectional structure as shown in Fig.

13E. Fig. 20A is a plan view, while Fig. 20B is a sectional view along the line A-A of Fig. 20A.

In this example, the recessed portion is square in shape. The shape of the recessed portion may also be rectangular.

One example of the manufacturing method of the substrate 110 is given below.

At first an even flat ceramic green sheet la is laminated together with a ceramic green sheet lb in which uniformly space square holes have been formed at predetermined positions by a die press. A ceramic paste of the same material is then printed at predetermined positions, that is, around the square holes, to form the raised portion 3, and the whole is then fired together.

A glass paste 2 is then printed over the surface of the ceramic sheet 1, excluding inside the square holes and on the raised portion 3, and fired to give the substrate 110 of the present example.

With the above manufacturing method, the flat ceramic green sheet la is laminated with the ceramic green sheet lb in which evenly spaced square shaped holes have been formed with a die press at predetermined positions, to form the ceramic sheet 1. The lamination of the green sheets la and lb may also be joined together by crystallized glass.

Example 11 An example of a magnetoresistive head made using the substrate 110 of the previous example is given in Fig. 21. Fig. 21A is a plan view, while Fig. 21B is a sectional view along the line A-A of Fig. 21A. Symbol 4S in the figure denotes a sensor portion, symbol 5' denotes the wiring, and numeral 5 denotes a terminal electrode. The region outlined by dotted line "a" in Fig. 20A corresponds to the region of one element of Fig.

21. Terminal electrode 5 is positioned inside the rectangular hole of the substrate 110.

With the magnetoresistive head constructed in this way, even if the terminal 5 is connected to a lead and molded, the mold surface will still be formed lower than the surface of the sensor portion 4S. Hence flat surface opposed type magnetoresistive heads can be manufactured.

With electronic devices of this type, the functional portion of the sensor may be provided on the glaze, and the terminal portion formed in the recess and molded to st#rengthen the terminal portion. With a ceramic substrate using an element wherein the resin does not protrude past the functional portion of the sensor, the distance from the uppermost surface of the glazed portion to the lower face of the recess should be not less than 50 microns and preferably not less than 100 microns.

Furthermore, since the film thickness of the functional portion of the sensor is generally be not more than 1 micron, it is desirable to have a glazed portion surface roughness of no more than 0.2 microns. In this case, an excellent sensor may be obtained. The flat glazed portion of the substrate of the present invention matches these conditions.

Example 12 Figure 22 is a sectional view of a thermal head using a glazed ceramic substrate 111 of the present invention having the sectional construction of Fig. 14.

With the thermal head of this example, a heat generating resistance film 6 is printed as a continuous film over the top of the glazed portion 2 of the ceramic substrate 111 and over the surface of ceramic sheet 1. A terminal electrode film 5 is then formed over the whole of the heat generating resistance film 6 with the exception of the central portion on the glazed portion 2. An anti wear protective film 10 is then formed as an uppermost layer so as to cover the glazed portion 2.

With the thermal head of the above construction, since the heat generating portion is formed with a convex shape due to the curved protruding glazed portion 2, heat generated by the heat generating portion can be efficiently transferred to recording paper.

Since the substrate of the present invention is constructed as described above with the glazed portion dammed by the raised portion, the glazed portion may be made extremely flat up to the edge of the raised portion by appropriate selection of the amount of applied glaze material.

Furthermore, with the present invention, by forming a line shaped raised portion, a flat glazed surface can be achieved without polishing, this glazed surface having a sharp step at the edge portion.

Furthermore, the curvatureof the glazed portion in a predetermined glaze region may be optionally set by setting a large value for the amount of glaze material to be applied.

Using a substrate of the present invention wherein the glaze portion is flat up to the edge, enables miniaturization of electronic devices such as magnetoresistive elements which require the sensor portion to be formed on the glaze face. Furthermore, as well as miniaturization, accurate patterning is also possible. The substrate of the present invention is applicable to electronic components such as thin film magnetoresistive heads, and it is also applicable to various electronic devices which require the formation of highly accurate patterning on the substrate surface.

The substrate of the present invention wherein the glazed portion is curved is applicable to electronic devices such as thermal heads where it is desirable to have a convex glazed portion.

INDUSTRIAL APPLICABILITY As explained above, with the present invention, a raised portion is formed on the substrate surface. Since this raised portion is positioned at the edge of the glazed portion, then by appropriate selection of the amount of applied glaze material, the glazed surface may be formed flat right up to its edge without the need for polishing. Furthermore, a substrate may be formed with a flat glazed surface, and a sharp step at the interface of the glaze portion and the base ceramic portion. Accordingly, functional devices such as thin film chip elements comprising thin film resistors and the like, or magnetic sensors such as magnetoresistive element, wherein the functional portions are formed on a substrate surface, may be easily miniaturized without degrading their characteristics.

Also with the present invention, a substrate having a curved glazed portion in a predetermined glaze region may be obtained by applying the glaze material so the thickness is greater than that of the raised portion and then firing. In this case, the curved shape may be optionally set by appropriate selection of the amount of glaze material. A substrate of this construction may be suitable for electronic devices such as thermal heads.

Claims (22)

What is claimed is:

1. A glazed ceramic substrate having a raised portion formed on a surface of a ceramic sheet, and a glazed portion formed on said ceramic sheet adjacent to at least a portion of said raised portion, wherein the material of said raised portion and the material of said glazed portion are different.

2. A glazed ceramic substrate as claimed in claim 1, wherein said raised portion is formed along an entire edge region of said glazed portion.

3. A glazed ceramic substrate as claimed in claim 1 or claim 2, wherein said raised portion is formed as a plurality of line shaped raised portions.

4. A glazed ceramic substrate as claimed in claim 1 or claim 2, wherein said raised portion is formed as a plurality of right angled parallelepiped shaped raised portions.

5. A glazed ceramic substrate as claimed in any one of claims 1 through claim 4, wherein said glazed portion and said raised portion adjacent to said glazed portion are formed with substantially the same height, with the surface of said glazed portion substantially flat.

6. A glazed ceramic substrate as claimed in any one of claims 1 through claim 4, wherein the surface of said glazed portion is curved and protrudes uniformly over substantially its whole area.

7. A glazed ceramic substrate as claimed in claim 1, wherein said ceramic sheet has a through hole or recessed portion, and said raised portion is formed around the periphery of said through hole or recessed portion.

8. A glazed ceramic substrate as claimed in claim 7, wherein the surface of the glazed portion formed on said ceramic sheet having a recessed portion is at least 50 microns above the bottom surface of said recessed portion, and the average surface roughness of said glazed portion is not greater than 0.2 microns.

9. A glazed ceramic substrate as claimed in any one of claims 1 through claim 8, wherein said raised portion is formed of a ceramic material substantially the same as the ceramic material making up the main body of the substrate.

10. A glazed ceramic substrate as claimed in any one of claims 1 through claim 8, wherein said raised portion is formed from a ceramic material different from the ceramic material making up the main body of the substrate.

11. A glazed ceramic substrate as claimed in any one of claims 1 through claim 8, wherein said raised portion is formed from an electrical conducting material.

12. A method of manufacture of a glazed ceramic substrate, the method comprising at least the steps of: (a) Printing a heat bakeable material in the form of a paste at a predetermined position on the surface of a smooth ceramic green sheet, then firing the sheet and paste together to give a ceramic sheet with a raised portion formed on its surface; (b) Subsequently printing a glass paste on the ceramic sheet at predetermined positions which include an edge of the raised portion, and then firing to form a glazed portion.

13. A method of manufacture of a glazed ceramic substrate as claimed in claim 12, wherein said green sheet comprises a green sheet having through holes or recessed portions disposed at a predetermined pitch, and said raised portion is formed around the periphery of said through holes or recessed portions.

14. A method of manufacture of a glazed ceramic substrate as claimed in claim 13, wherein said green sheet having recessed portions is formed from a green sheet having holes formed at a predetermined pitch, which is adhered to a flat green sheet.

15. A method of manufacture of a glazed ceramic substrate as claimed in claim 13, wherein said green sheet having recessed portions is formed by using a glass layer to adhere a green sheet having holes formed at a predetermined pitch, to a flat green sheet.

16. A method of manufacture of a glazed ceramic substrate as claimed in any one of claim 12 through claim 15, wherein said raised portion is made from a ceramic paste of the same material as that used for making said green sheet.

17. A method of manufacture of a glazed ceramic substrate as claimed in any one of claim 12 through claim 15, wherein said raised portion is made from a ceramic paste of a different material to that used for making said green sheet.

18. A method of manufacture of a glazed ceramic substrate as claimed in any one of claim 12 through claim 15, wherein said raised portion is made from a paste comprising an electrical conducting material.

19. A method of manufacture of a glazed ceramic substrate as claimed in any one of claim 12 through claim 18, wherein said ceramic sheet is fired prior to printing said paste material used for making said raised portion.

20. A magnetoresistive element comprising: a raised portion formed on a ceramic sheet, and a flat glazed portion formed on said ceramic sheet adjacent to said raised portion, the material forming said raised portion being different from that forming said glazed portion, a strongly magnetic thin film formed on the surface of said flat glazed portion and said ceramic sheet, a sensor portion formed on said glazed portion, and a terminal electrode formed on said ceramic sheet.

21. A chip resistor element comprising: a conducting raised portion formed on a ceramic sheet, a flat glazed portion formed on said ceramic sheet adjacent to said raised portion, and a resistor formed on said flat glazed portion, with said conducting raised portion connected to said resistor.

22. A thermal head comprising: a raised portion formed on a ceramic sheet, a curved protruding glazed portion formed on a surface of said ceramic sheet adjacent to said raised portion, the material forming the raised portion being different from that forming the glazed portion, a heat generating layer formed on the curved protruding surface of said glazed portion, and a terminal electrode connected to said heat generating layer.