JP2002033559A - Electronic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic circuit board which prevents the breakdown voltage of a capacitor element from falling and has superior high-frequency characteristics. SOLUTION: Positive photoresist is formed by spin coating on the top surface of an alumina substrate 1, and then exposed and developed to partially form an insulating layer 6. A thin-film capacitor element 2 is formed on the insulating layer 6 by laminating a lower electrode 7, a dielectric layer 8, and an upper electrode 9 in order. A low-resistance element 3, an inductor element 4, and a transmission line 5 are formed into a thin film on the top surface of the alumina substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electronic circuit board having a thin film circuit element such as a capacitor element and an inductor element formed on an alumina substrate, and more particularly to an electronic circuit board suitable for use as a high-frequency device.

[0002]

2. Description of the Related Art In recent years, electronic circuits have been increasingly miniaturized with the development of integrated circuit technology, and small electronic circuit boards in which capacitors, resistors, inductors, and the like as circuit elements are formed as thin films on the boards have been developed. Have been.

In such an electronic circuit board, a single crystal substrate such as sapphire or a sintered substrate such as alumina can be used as a material of the substrate. Among them, alumina is relatively inexpensive and has excellent high frequency characteristics. Material
In general, an alumina substrate is used in a high-frequency device. Various necessary circuit elements are formed in a thin film shape on the alumina substrate. For example, a capacitor element is formed by sequentially laminating a lower electrode, a dielectric layer, and an upper electrode on the alumina substrate. The resistance element is formed by forming a thin film of a desired shape on an alumina substrate and forming thin electrodes on both ends thereof.The inductor element is formed by forming a thin metal film of a desired shape on an alumina substrate. It is formed by forming electrodes on both ends as thin films. Further, a transmission line as a conductive pattern is formed as a thin film on the alumina substrate, and the transmission line is connected to each electrode of the capacitor element, the resistance element, and the inductor element.

In the electronic circuit board having such a schematic configuration, the capacitance value of a capacitor element having a laminated structure of a lower electrode, a dielectric layer, and an upper electrode is determined by the dielectric constant and the film thickness of the dielectric layer and the opposition of both electrodes. Determined by area. Here, since the capacitance value per unit area increases as the dielectric constant is increased and the film thickness is reduced, the element shape of the capacitor element can be reduced, and the device can be downsized. However, when a material having a high dielectric constant is used, the dielectric loss of the dielectric layer tends to increase, which causes a problem that the Q value of the capacitor is reduced. There is a problem that the breakdown voltage decreases and the lower electrode and the upper electrode are broken at a low voltage. For these reasons, the dielectric constant of the dielectric layer is generally set to about 3 to 200, and the thickness of the dielectric layer is set to about 10 nm to 1 μm.

[0005]

The alumina substrate used for this type of electronic circuit board has the above-mentioned advantages, but has a smoother surface than a single crystal substrate such as sapphire. Poor, eg 99.5 purity
% Of the alumina substrate has a surface roughness (Ra) of 30 to 1
It has an uneven surface of about 00 nm. Therefore, when a capacitor element is formed as a thin film on an alumina substrate having a poor surface smoothness, the thickness of a dielectric layer formed on the lower electrode is partially reduced, and the breakdown voltage is significantly reduced. Occurs.

Conventionally, in order to smooth the surface of the alumina substrate, a method of mirror polishing the entire surface of the alumina substrate and a method of coating the entire surface of the alumina substrate with an insulating film such as a polymer film or a glass film are known. Are known. However, the former polishing method has a drawback that minute recesses remain between the crystals in the alumina substrate, and the alumina substrate is hard, so that much time is required for the polishing step.
On the other hand, in the latter method of coating an insulating film, since the dielectric loss of the insulating film such as a polymer film or a glass film is large, of the various circuit elements and transmission lines formed as a thin film on the insulating film,
Capacitor elements, which are capacitive elements, do not pose a major problem, but other resistive elements, inductor elements, or dielectric layers under the transmission line may have a large dielectric loss, thereby deteriorating the high frequency characteristics of the high frequency device. is there.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances of the prior art, and has as its object to provide an electronic circuit board which prevents a reduction in breakdown voltage of a capacitor element and has excellent high frequency characteristics. It is in.

[0008]

In order to achieve the above object, in an electronic circuit board according to the present invention, an insulating layer is partially formed on the surface of an alumina substrate, and a lower electrode and a dielectric layer are formed on the insulating layer. The capacitor element in which the upper electrode and the upper electrode were sequentially laminated was formed in a thin film shape, and at least the inductor element and the transmission line were formed in a thin film shape on the surface of the alumina substrate.

In the electronic circuit board configured as described above,
Since minute irregularities on the surface of the alumina substrate are smoothed by the insulating layer, the breakdown voltage of the capacitor element formed in a thin film on the insulating layer can be prevented from lowering,
Further, since the insulating film having a large dielectric loss does not adversely affect the inductor element and the transmission line, it is possible to prevent the high-frequency characteristics from deteriorating.

[0010] In the above structure, it is preferable that the lower electrode and the upper electrode of the capacitor element are overlapped within the contour of the insulating layer, so that the breakdown voltage of the capacitor element is reliably prevented from lowering. Can be.

In the above structure, as a means for partially forming the insulating layer on the alumina substrate, a glass film coated on the entire surface of the alumina substrate can be patterned into a desired shape. Preferably, a photosensitive polymer film such as a photoresist is exposed / developed to form an insulating layer. In this case, an insulating layer having a desired shape can be formed easily and with high precision.

In the above configuration, when the circuit element includes a resistance element in addition to the capacitor element and the inductor element, particularly, when a material having a large specific resistance such as TaSiO ₂ is used as a resistance layer of the resistance element. It is preferable to form this resistance layer in a thin film form on the surface of the alumina substrate, similarly to the inductor element and the transmission line, from the viewpoint of preventing deterioration of high frequency characteristics. On the other hand, when a material having a low specific resistance, such as Ta ₂ N, is used for the resistance layer of the resistance element, it is preferable that this resistance layer be formed in a thin film on the insulating layer similarly to the capacitor element. Although the high-frequency characteristics are slightly degraded by the insulating layer below the resistive element, the fine irregularities on the surface of the alumina substrate are smoothed by the insulating layer, so that the resistance value of the resistive element formed in a thin film on the insulating layer is reduced. Can be prevented from significantly changing.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of an electronic circuit board according to a first embodiment of the present invention, and FIG. FIGS. 3 and 4 are cross-sectional views taken along line A, and are explanatory views showing the steps of manufacturing the electronic circuit board.

The electronic circuit board according to the present embodiment is used as various high-frequency devices. As shown in FIGS.
A 5% alumina substrate 1 is provided, on which a capacitor element 2, a resistor element 3, a circuit element such as an inductor element 4, and a transmission line 5 that conducts between these circuit elements are formed as a thin film. Incidentally, a large number of these circuit elements 2, 3, 4 and the transmission line 5 are formed in an effective area on the alumina substrate 1 according to a required circuit configuration, and FIGS. It shows.

The surface roughness (Ra) of the surface of the alumina substrate 1 is an irregular surface of about 30 to 100 nm. This is a substrate in which the alumina substrate 1 is a porous sintered body, and the surface of the substrate has many fine depressions. Because it exists. An insulating layer 6 is formed on a part of the alumina substrate 1, and the insulating layer 6 is filled in minute recesses on the surface of the alumina substrate 1, so that the surface roughness of the surface of the insulating layer 6 ( Ra) is flattened to 10 nm or less. The insulating layer 6 is made of a photosensitive polymer film such as a positive photoresist, and is formed by exposing / developing a desired pattern shape using a mask.

The capacitor element 2 is composed of a lower electrode 7, a dielectric layer 8 and an upper electrode 9 which are sequentially laminated on the insulating layer 6, and the lower electrode 7 and the upper electrode 9 inside the contour of the insulating layer 6. Are overlapped to form an effective area of the capacitor. Here, if the contour of the insulating layer 6 is too large with respect to the effective area of the capacitor, the area ratio of the insulating layer 6 occupying a limited space on the alumina substrate 1 increases, so that the insulating layer 6 is formed on the alumina substrate 1. As a result, the effective area of the circuit element that can be obtained is reduced, and the area efficiency is reduced.
Conversely, when the contour of the insulating layer 6 is reduced to the last minute of the effective area of the capacitor, the insulating layer 6 may not be formed due to variations in mask accuracy used in each step described later.
There is a concern that the effective area of the capacitor cannot be formed within the outline of the capacitor. Therefore, in the present embodiment, in consideration of these points, the contour of the insulating layer 6 is set to be larger than the design value of the effective area of the capacitor by about 10 to 100 μm.

Of the constituent elements of the capacitor element 2, the lower electrode 7 has a two-layer structure of a first lower electrode layer 7a and a second lower electrode layer 7b. It is set in the range of 0.5 to 5 μm. The first lower electrode layer 7a is formed of a metal film such as Ti / Cu formed on the insulating layer 6 by sputtering, and the second lower electrode layer 7b is formed on the first lower electrode layer 7a by plating. And a metal film such as Cu / Ni. The dielectric layer 8 is formed of a dielectric film such as SiO ₂ formed as a thin film on the first lower electrode layer 7a of the lower electrode 7 by a sputtering method or a CVD method, and the dielectric layer 8 is formed of the lower electrode 7 (first lower electrode 7). The step portion between the electrode layer 7a and the second lower electrode layer 7b) is covered. The upper electrode 9 also has a two-layer structure of the first upper electrode layer 9a and the second upper electrode layer 9b, and has a total thickness of 0.5 to increase the Q value.
It is set in the range of ５5 μm. First upper electrode layer 9a
Is a thin film formed on the dielectric layer 8 by sputtering.
/ Cu or the like, and the second upper electrode layer 9b
Cu formed as a thin film on the upper electrode layer 9a by a plating method
/ Ni or other metal film.

The resistance element 3 is composed of a resistance layer 10 and an insulating protective layer 11 sequentially laminated on the alumina substrate 1, and both ends of the resistance layer 10 are connected to the transmission line 5.
The resistance layer 10 is made of a resistance material having a large specific resistance, such as TaSiO ₂ , and is formed as a thin film on the surface of the alumina substrate 1 by a sputtering method. The insulating protective layer 11 is made of a photosensitive polymer film such as a positive photoresist,
It is formed so as to cover the surface of the resistance layer 10. As described later, the insulating layer 6 below the capacitor element 2 and the insulating protective layer 11 are formed in the same step.

The inductor element 4 comprises a conductor film 12 formed on the alumina substrate 1 as a thin film and bonding wires 13 connecting both ends thereof. Both ends of the conductor film 12 are connected to the transmission line 5. The conductor film 12 is formed in a rectangular spiral shape, and has a two-layer structure of a first conductor layer 12a and a second conductor layer 12b. The transmission line 5 also has a two-layer structure of a first conductor layer 5a and a second conductor layer 5b.
The conductor film 12 and the transmission line 5 are made of the same material as the lower electrode 7 and the upper electrode 9 of the capacitor element 2 described above. That is, the first conductor layers 5a and 12a are made of a metal film such as Ti / Cu formed on the alumina substrate 1 by a sputtering method, and the second conductor layers 5b and 12b are formed on the first conductor layers 5a and 12a, respectively. It is made of a metal film such as Cu / Ni formed as a thin film by a plating method.

Next, the steps of manufacturing the electronic circuit board configured as described above will be described mainly with reference to FIG. 3 and FIG.

First, a film of TaSiO ₂ is formed on the surface of the alumina substrate 1 by a sputtering method, and the film is etched by a RIE method after patterning a photoresist to form a film on the alumina substrate 1 as shown in FIG. Then, a rectangular resistance layer 10 is formed. In this case, TaSiO ₂ is a resistance material having a relatively large specific resistance, and a desired resistance value can be obtained even if the thickness of the resistance layer 10 is sufficiently large. Therefore, it is assumed that the resistance layer 10 is directly formed on the alumina substrate 1. Also, the resistance value does not fluctuate significantly due to minute irregularities on the surface of the alumina substrate 1.

Next, a positive type photoresist (AZ-P4620, manufactured by Clariant) is spin-coated on the entire surface of the alumina substrate 1 from above the resistance layer 10, and this is exposed / developed using a mask to obtain a desired shape. After patterning, a further curing treatment (240 ° C.-60 minutes) forms an insulating layer 6 on a predetermined portion of the alumina substrate 1 and an insulating layer on the resistance layer 10 as shown in FIG. The protection layer 11 is formed.

Next, as shown in FIG. 3C, Ti (0.1 μm) and Cu (0.1 μm) are formed on the entire surface of the alumina substrate 1 from above the insulating layer 6 and the insulating protective layer 11 by sputtering.
m) are sequentially formed to form a Ti / Cu layer.
A positive photoresist (AZ-P4620, manufactured by Clariant) is spin-coated on the i / Cu layer, and the photoresist is exposed / developed using a mask to obtain a desired photoresist as shown in FIG. A resist pattern having a shape is formed. Further, as shown in FIG.
/ Cu (3 μm) and Ni on the Cu layer by electrolytic plating
(0.3 μm) is sequentially formed to form a Cu / Ni layer, and then the resist pattern is peeled off as shown in FIG. 3F. Thereafter, the Ti / Cu layer is formed by dry etching (milling method). Etch. As a result, FIG.
As shown in (g), a lower electrode 7 composed of a first lower electrode layer 7a and a second lower electrode layer 7b is formed on an alumina substrate 1, and a transmission line 5 (the The first conductor layer 5a and the second conductor layer 5b) are simultaneously formed.

Next, a film of SiO ₂ (0.3 μm) is formed on the lower electrode 7 and the insulating protective layer 11 by sputtering.
This SiO ₂ layer is etched by RIE after patterning a positive type photoresist (OFPR-7450 manufactured by Tokyo Ohka Co., Ltd.), and as shown in FIG. A continuous dielectric layer 8 is formed over the substrate 1.

Next, as shown in FIG. 4B, a Ti layer is formed on the dielectric layer 8 and the insulating protective layer 11 by sputtering.
(0.1 μm) and Cu (0.1 μm) are sequentially formed and T
After forming the i / Cu layer, a positive photoresist (AZ-P462, manufactured by Clariant) is formed on the Ti / Cu layer.
0), and the photoresist is exposed / developed to form a resist pattern having a desired shape as shown in FIG. 4 (c). Further, as shown in FIG. 4 (d), Cu
(3 μm) and Ni (0.3 μm) are sequentially formed to form Cu /
After forming the Ni layer, the resist pattern is peeled off as shown in FIG. Finally, by etching the Ti / Cu layer by dry etching (milling method), the first upper electrode layer 9a and the second upper electrode layer 9a are etched as shown in FIG.
The upper electrode 9 composed of the upper electrode layer 9b is formed, and the transmission line 5 (the first conductor layer 5a and the second conductor layer 5b), which is a routing pattern of the upper electrode 9 and the resistance layer 10, is formed at the same time.

In the above description, the manufacturing process of the inductor element 3 is omitted, but the conductor film 12 of the inductor element 3 can be formed in the same process as the upper electrode 9 and the transmission line 5. That is, FIGS.
In each step shown in (f), the Ti / Cu layer and the Cu /
If the Ni layer is patterned into a desired shape using a resist pattern or the like, the conductor film 12 of the inductor element 3 composed of the first conductor layer 12a and the second conductor layer 12b is
Can be formed on. Therefore, after forming these various circuit elements 2 to 4 and the transmission line 5 on the alumina substrate 1 as a thin film, the bonding wire 13 is connected to the conductor film 12 of the inductor element 3 as shown in FIGS. A simple electronic circuit board can be obtained.

As described above, according to the electronic circuit board of the first embodiment, the insulating layer 6 formed on a part of the alumina substrate 1 smoothes out minute irregularities on the surface of the alumina substrate 1, Since the capacitor element 2 in which the lower electrode 7, the dielectric layer 8, and the upper electrode 9 are sequentially laminated on the layer 6 is formed as a thin film, the dielectric layer 8 can be formed on the lower electrode 7 with a uniform film thickness. It is possible to prevent the breakdown voltage of the capacitor element 2 from lowering. On the other hand, the resistive layer 10 of the resistive element 3, the conductive film 12 of the inductor element 4, and the transmission line 5 are formed on the surface of the alumina substrate 1 where the insulating layer 6 is not formed. These resistance element 3 and inductor element 4
In addition, it is possible to prevent high-frequency characteristics from deteriorating without adversely affecting the transmission line 5.

FIG. 5 is a plan view of a main part of an electronic circuit board according to the second embodiment, and FIG. 6 is a cross-sectional view taken along the line BB of FIG. 5, showing portions corresponding to FIGS. Are denoted by the same reference numerals.

This embodiment is different from the first embodiment in that Ta _{2 is used} as the resistance layer 10 of the resistance element 3.
A material having a small specific resistance, such as N, is used.
This is because the insulating layer 6 is also formed below 0, and the other configuration is basically the same. That is, the lower electrode 7 of the capacitor element 2 and the resistance layer 10 of the resistance element 3 are respectively formed by the insulating layer 6 partially formed on the surface of the alumina substrate 1.
The other inductor elements 4 are formed on the thin film.
The transmission line 5 is formed on the alumina substrate 1 as a thin film. The resistive layer 10 of the resistive element 3 is made of a resistive material having a small specific resistance such as Ta ₂ N. After the insulating layer 6 is partially formed on the surface of the alumina substrate 1, the insulating layer 6 is sputtered from above. It is formed by forming a Ta ₂ N film, etching the film by a RIE method after patterning a photoresist. In this case, the specific resistance of Ta ₂ N is much smaller than that of TaSiO _{2, and} the thickness of the resistance layer 10 is made extremely thin in order to obtain a desired resistance value. 6, the fine irregularities on the surface of the alumina substrate 1 are flattened, so that the resistance value does not fluctuate significantly. Since the resistance layer 10 is formed as a thin film on the insulating layer 6, the insulating protective layer 11 covering the surface of the resistance layer 10 needs to be formed in a step different from that of the insulating layer 6.

In the electronic circuit board configured as described above, the capacitor element 2 and the resistor element 3 are formed on the insulating layer 6 partially formed on the surface of the alumina substrate 1 so that the capacitor element 2 breaks. The down voltage can be prevented from lowering, and the resistance value can be prevented from varying even though a resistance material having a small specific resistance such as Ta ₂ N is used for the resistance layer 10 of the resistance element 3. .
Although the high-frequency characteristics are slightly degraded by the insulating layer 6 below the resistance element 3, the other inductor element 4 and the transmission line 5 are formed on the alumina substrate 1 in a thin film, so that the insulating film 6 having a large dielectric loss is formed by the inductor element. 4 and the transmission line 5 are not adversely affected, and remarkable deterioration of high-frequency characteristics can be prevented.

In each of the above embodiments, the insulating layer 6 is partially formed on the surface of the alumina substrate 1 by exposing / developing a photosensitive polymer film such as a positive photoresist. However, the insulating layer 6 can be formed by coating the entire surface of the alumina substrate 1 with a glass film and patterning the glass film into a desired shape.

[0032]

The present invention is embodied in the form described above and has the following effects.

An insulating layer is partially formed on the surface of the alumina substrate, and a capacitor element in which a lower electrode, a dielectric layer and an upper electrode are sequentially laminated on the insulating layer is formed in a thin film shape. If at least the inductor element and the transmission line are each formed in a thin film, the minute unevenness on the surface of the alumina substrate is smoothed by the insulating layer, so that the breakdown voltage of the capacitor element formed in a thin film on the insulating layer is reduced. In addition, since the insulating film having a large dielectric loss does not adversely affect the inductor element and the transmission line, it is possible to prevent the high-frequency characteristics from deteriorating.

[Brief description of the drawings]

FIG. 1 is a plan view of a main part of an electronic circuit board according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram illustrating a manufacturing process of the electronic circuit board.

FIG. 4 is an explanatory view illustrating a manufacturing process of the electronic circuit board.

FIG. 5 is a plan view of a main part of an electronic circuit board according to a second embodiment of the present invention.

FIG. 6 is a sectional view taken along line BB of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Alumina substrate 2 Capacitor element 3 Resistance element 4 Inductor element 5 Transmission line 5a First conductor layer 5b Second conductor layer 6 Insulating layer 7 Lower electrode 7a First lower electrode layer 7b Second lower electrode layer 8 Dielectric layer 9 Upper electrode 9a first upper electrode layer 9b second upper electrode layer 10 resistive layer 11 insulating protective layer 12 conductive film 12a first conductive layer 12b second conductive layer 13 bonding wire

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuru Tokuda 1-7 Yukitani Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. F-term (reference) 4E351 AA07 BB03 BB05 BB09 BB32 CC03 CC16 DD01 GG07 5E033 AA05 AA08 5E070 AA01 AB03 AB07 CB12 5E082 AB03 BB05 BC35 EE05 EE18 EE19 EE26 EE37 FG03 FG22 FG27 FG42 KK01

Claims (5)

[Claims] An insulating layer is partially formed on a surface of an alumina substrate, and a capacitor element in which a lower electrode, a dielectric layer, and an upper electrode are sequentially laminated on the insulating layer is formed in a thin film shape. An electronic circuit board, wherein at least an inductor element and a transmission line are respectively formed in a thin film shape on a surface of the board. 2. The electronic circuit board according to claim 1, wherein the lower electrode and the upper electrode are overlapped within the contour of the insulating layer. 3. The electronic circuit board according to claim 1, wherein the insulating layer is made of a photosensitive polymer film. 4. The electronic circuit board according to claim 1, wherein a resistance element is formed in a thin film shape on the surface of the alumina substrate in addition to the inductor element and the transmission line. 5. The electronic circuit board according to claim 1, wherein a resistance element is formed in a thin film shape on the insulating layer in addition to the capacitor element.