JPH11195909A - Thin film multi-layer electrode, high frequency transmission line, high frequency resonator and high frequency filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the thin film multi-layer electrode where each film of the thin film multi-layer electrode is formed flat and the thin film conductor layers are not short-circuited with each other without being affected by an uneven surface of a dielectric substrate even in the case that the thin film multi-layer electrodes are formed on the dielectric substrate whose surface is rugged. SOLUTION: A thin film dielectric layer placed around the surface of a dielectric substrate 2, in the thin film multi-layer electrode 3 that is placed on the dielectric substrate 2 and that is structured by stacking alternately thin film conductors layers 4a-4d and thin film dielectric layers 5a-5c, is formed thick in a degree of absorbing the unevenness of the dielectric substrate 2, and the thin film dielectric layers 5a-5c are made of a dielectric material having a specific dielectric constant derived from a prescribed equation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film multilayer electrode, a high-frequency transmission line using the same, a high-frequency resonator, a high-frequency filter, and the like.

[0002]

2. Description of the Related Art In recent years, as electronic components have been miniaturized, devices have been miniaturized by using high dielectric constant materials even in high frequency bands such as microwaves, quasi-millimeter waves or millimeter waves. However, when the shape is reduced by using the high dielectric constant material, there is a problem that the energy loss increases in inverse proportion to the cubic root of the volume. The energy loss of this high-frequency device can be broadly classified into a conductor loss due to the skin effect and a dielectric loss due to a dielectric material. In recent years, a dielectric material having a high dielectric constant and having a low loss characteristic has been developed. Has been put into practical use, and therefore, conductor loss occupies a more dominant proportion in energy loss than dielectric loss.

Under the circumstances described above, the applicant of the present application has proposed in International Patent Application Publication No. WO95 / 06336 a thin-film multilayer electrode as an electrode capable of reducing conductor loss in a high-frequency band. A method for designing the optimum thickness of each layer of the thin film multilayer electrode has been disclosed. FIG. 4 is a perspective view of a half-wavelength line resonator 101 constituted by using a thin-film multilayer electrode 103 formed by using the design method disclosed in International Publication No. WO95 / 06336.

As shown in FIG. 4, a half-wavelength line resonator 101 has a longitudinal length of λg / 2 (λg) on a dielectric substrate 102 on which a ground conductor 106 is formed on the entire back surface.
(In-tube wavelength) is arranged and arranged.

As shown in FIG. 5, a thin-film multilayer electrode 103 has a thin-film conductor layer 104a formed on the surface of a dielectric substrate 102, and then has a thin-film dielectric layer 1 on the thin-film conductor layer 104a.
05a are stacked. Thereafter, in order, the thin film conductor layer 104
b, 104c, 104d, and thin film dielectric layer 105
b, 105c are alternately stacked and arranged, and the thin-film multilayer electrode 10
3 are formed. By setting the length in the longitudinal direction of the thin-film multilayer electrode 103 to 波長 wavelength of the desired frequency,
It functions as a resonator.

At this time, the thin-film conductor layer 104a, the ground conductor 106, and the dielectric substrate 102 constitute a TEM mode microstrip line (hereinafter, referred to as a main transmission line) 107. On the main transmission line 107, a thin film dielectric layer 105a is formed by a pair of thin film conductor layers 104a.
A TEM-mode sub-transmission line is sandwiched between the thin-film dielectric layers 105b and 105b.
c also constitutes a sub transmission line. Here, the thin-film multilayer electrode 103 of the conventional example is manufactured by using the method disclosed in International Patent Application Publication No. WO95 / 06336, and (a) the TE transmission through the main transmission line 107 and each of the sub transmission lines.
The thickness of each of the thin film dielectric layers 105a, 105b, and 105c and the dielectric constant ε are set so that the phase velocities of the M waves substantially match each other, and (b) each of the thin film conductor layers 104a
A predetermined film thinner than the skin depth at the operating frequency so that the electromagnetic fields are coupled to each other between the main transmission line 107 and the sub-transmission line and between the sub-transmission lines adjacent to each other. Set to thick.

Thus, a part of the high-frequency energy flowing through the main transmission line 107 is transferred to the sub-transmission line, and a high-frequency current flows through each of the thin film conductor films 104a, 104b, 104c, and 104d. That is, the skin effect of the electrode in the region is largely suppressed.

Here, International Application Publication No. WO 95/063
The thin-film multilayer electrode disclosed in Japanese Patent Publication No. 36-136 is formed on a dielectric substrate 102 having a flat surface (an example is a sapphire substrate made of a single crystal of alumina which has been subjected to mirror polishing). As a premise, the respective film thicknesses of the thin film conductor layer and the thin film dielectric layer are set.

[0009]

However, for example, when a ceramic substrate is used as a dielectric substrate,
Usually, the substrate surface has irregularities due to the presence of pores and the like. These irregularities can be flattened to some extent by surface polishing or the like. However, since a large number of pores exist not only on the substrate surface but also inside the substrate, new pores become apparent on the surface by the polishing treatment, and the substrate surface cannot be sufficiently planarized. Here, FIG. 6 is a cross-sectional view showing a film structure when a thin-film multilayer electrode is formed on a dielectric substrate having irregularities. In this case, as can be seen from FIG. 6, each thin-film conductor layer and each thin-film dielectric layer constituting the thin-film multilayer electrode also have irregularities corresponding to the irregularities of the substrate. If each layer is formed with irregularities in this manner, it becomes impossible to match the phase speeds of the TEM waves propagating through the main transmission line and the sub transmission lines as originally designed. In addition, when a thin film is stacked on a substrate having irregularities, the risk of short-circuiting between adjacent thin film conductor layers becomes extremely high in the film formation process. All of these situations greatly deteriorate the effect of suppressing the skin effect of the thin-film multilayer electrode.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned technical problems, and is intended to be applied to a case where a thin film multilayer electrode is formed on a dielectric substrate having an uneven surface. It is another object of the present invention to provide a thin-film multilayer electrode in which the respective films constituting the thin-film multilayer electrode are formed flat without being affected by the unevenness of the substrate surface, and the thin-film conductor layers are not short-circuited.

[0011]

In order to achieve the above object, a thin-film multilayer electrode according to the present invention comprises a plurality of thin-film electrodes arranged on the other main surface of a dielectric substrate having a ground conductor formed on one main surface. In a thin-film multilayer electrode formed by alternately stacking conductor layers and thin-film dielectric layers, the ground conductor, the dielectric substrate, and the first-layer thin-film conductor provided in contact with the dielectric substrate The main transmission line is constituted by the layers, the sub-transmission line is constituted by the thin-film dielectric layer, and a pair of thin-film conductor layers sandwiching the thin-film dielectric layer, and the main transmission line and the sub-transmission line are formed. The thickness and permittivity of each thin-film dielectric layer are set so that the phase velocities of the respective high-frequency waves to propagate substantially coincide with each other, and between the adjacent main transmission line and sub-transmission line and each sub-transmission line. Between,
The thickness of each thin film conductor layer is set to a predetermined thickness smaller than the skin depth at the operating frequency so that electromagnetic fields are coupled to each other, and the thickness of the thin film dielectric layer closest to the substrate surface of the dielectric substrate is set. The film thickness is formed larger than the film thickness of the other thin film dielectric layers. At this time, when forming the thin film dielectric layer closest to the substrate surface of the dielectric substrate to be thick,
A dielectric material having a relative dielectric constant derived from the following equation (1) is used.

[0012]

(Equation 2)

By adopting the above configuration,
A thin-film multilayer electrode can be formed after alleviating the influence of irregularities on the surface of the dielectric substrate, and the phase velocities of the high-frequency waves propagating through the main transmission line and each sub-transmission line can be matched as originally designed. . In addition, since the thin film dielectric layer can be formed by absorbing the unevenness of the substrate by forming the film thick, there is no possibility that the thin film conductor layers are short-circuited in the film forming process. It is not necessary to limit the thin film dielectric layer having a large thickness to the first thin film dielectric layer closest to the substrate surface. If necessary, the film thickness may be adjusted over a plurality of thin film dielectric layers located near the substrate.

Further, a high-frequency transmission line, a high-frequency resonator, and a high-frequency filter are formed using the above-described thin-film multilayer electrodes. A high-frequency transmission line having electrodes, a high-frequency resonator, and a high-frequency filter can be obtained.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First Embodiment, FIGS. 1-2] First Embodiment of the Present Invention
The thin film multilayer electrode of the embodiment will be described with reference to FIGS.

FIG. 1 shows a structure 1 using a thin film multilayer electrode 3.
FIG. 2 is a perspective view of a half-wavelength line resonator 1. A 波長 wavelength line resonator 1 is a band-shaped thin film multilayer electrode 3 having a longitudinal length of λg / 2 (λg is a guide wavelength) on a dielectric substrate 2 having a ground conductor 6 formed on the entire back surface. Are arranged and configured.

The dielectric substrate 2 is a dielectric ceramic substrate containing (Zn, Sn) TiO ₄ as a main component and having a relative dielectric constant of 38, and a large number of pores having a diameter of about 1.0 μm are present in the substrate. The surface of the dielectric substrate 2 has irregularities with a height and width of about 1 μm due to the presence of pores and the like.

On the dielectric substrate 2, a thin-film multilayer electrode 3 having a laminated structure shown in FIG. 2 is formed. The thin-film multilayer electrode 3 has thin-film conductor layers 4a and 4 made of a metal material such as Cu.
b, 4c, 4d and thin film dielectric layers 5a, 5b, 5c made of a dielectric material such as SiO ₂ are alternately laminated. The layers may be formed by a technique such as sputtering.

Table 1 shows the film configuration of the thin-film multilayer electrode 3 of the present embodiment when operated at a frequency of 3 GHz.

[0021]

[Table 1]

As a comparative example, the thickness of each thin-film multi-layer electrode in the case of operating at a frequency of 3 GHz and using only SiO ₂ having a relative dielectric constant of 4 as the thin-film dielectric layer is described in International Patent Application No. Table 2 below shows design values obtained by designing the film thickness using the method disclosed in the publication WO95 / 06336.

[0023]

[Table 2]

As can be seen from Table 1, in the thin-film multilayer electrode 3 of this embodiment, the first thin-film dielectric layer 5a closest to the substrate surface of the dielectric substrate 2 has a different thickness from the other thin-film dielectric layers. It is formed much thicker than 5b and 5c. This is because the unevenness on the surface of the dielectric substrate 2 is flattened by forming a thick film.

It should be noted that in order to flatten the surface of the dielectric substrate with irregularities, it is necessary to form a film about 1.5 times the height and width of the irregularities from the substrate surface. I found it as a rule of thumb. Therefore, in the case of the present embodiment, a flattened film is obtained when the film is formed to a thickness of about 1.5 μm from the substrate surface. Therefore, the film thickness of the first thin-film conductor layer 4a must be 0.53 μm. Therefore, if the thin film dielectric layer 5a is formed to a thickness of about 1.0 μm or more, a flattened film can be obtained.

When the thickness of the thin-film dielectric layer 5a is increased as described above, the dielectric material to be used must be changed simultaneously with the change of the thickness. That is, when the thickness of the thin film dielectric layer is changed, the phase speed of the TEM wave propagating through the transmission line formed by the thin film dielectric layer changes. Thus, a TE that propagates through a certain transmission line
The phase velocity of the M wave changes and T propagates through another transmission line.
If there is a deviation from the phase velocity of the EM wave, the thin film multilayer electrode cannot achieve the desired low-loss operation. Therefore, when changing the thickness of the thin-film dielectric layer, it is necessary to adjust the relative permittivity of the dielectric material used so that the phase velocities of the TEM waves propagating through each transmission line are substantially equal (note that the velocities are the same). In the case of forming a thick film as in this embodiment, a dielectric material having a higher dielectric constant than the initially used material is used.) In order to determine the optimum relative dielectric constant according to the current film thickness, the following proportional expression (1) is used.
May be used.

[0027]

(Equation 3)

That is, now, International Application Publication No. WO 95/0
By forming the film thickness in accordance with the method disclosed in JP-A-6336, when forming a thin-film dielectric layer of SiO ₂ having a relative dielectric constant of 4 on a substrate having a relative dielectric constant of 38, the thickness is reduced to 0.4 μm. It can be deduced that the setting allows the phase velocities between the transmission lines to be matched (see Table 2). Therefore, by using the proportional expression represented by Expression (1), When a thin film dielectric layer having a thickness of about 1.0 μm is formed, it can be understood that the phase speed can be matched by using a dielectric material having a relative dielectric constant of about 10. Therefore, as a film design of the thin film dielectric layer 5a, a dielectric material having a relative dielectric constant of 10, for example, Al ₂ O
_3, it is found that may be formed to a thickness of a thickness of 1.22 .mu.m.

As described above, the thin film dielectric layer in the vicinity of the dielectric substrate is formed so thick that the unevenness on the substrate surface is flattened, and at this time, the film thickness is set to a value satisfying the above proportional expression (1). By setting the relative permittivity and the relative permittivity, it is possible to form the thin film multilayer electrode by absorbing the influence of the unevenness of the substrate, and to make the phase speeds of the TEM waves propagating through the respective transmission lines coincide. Further, since the unevenness is flattened by increasing the film thickness, the risk of short circuit between the thin film conductor layers in the film forming process is extremely reduced.

Second Embodiment, FIG. 3 A thin film multilayer electrode according to a second embodiment of the present invention will be described with reference to FIG.

In the present embodiment, the pore size of the dielectric substrate used is about 2.0 μm in diameter,
The surface of the dielectric substrate 12 has unevenness with a height of about 2.0 μm. Therefore, in order to flatten the unevenness on the surface of the substrate, it is necessary to form a film about 1.5 times as thick as that, that is, about 3.0 μm from the substrate surface.

Table 3 shows the film configuration of the thin-film multilayer electrode 13 when operated at a frequency of 3 GHz.

[0033]

[Table 3]

As can be seen from Table 3, in the thin-film multilayer electrode 13 of the present embodiment, two
The unevenness on the surface of the dielectric substrate 12 is absorbed by forming the thin film dielectric layers 15a and 15b of each layer thicker than the other thin film dielectric layers.

In this embodiment, as in the case of the first embodiment, only the thin film dielectric layer 15a closest to the dielectric substrate can be formed to have a large thickness to flatten the unevenness of the substrate surface. is there. In that case, the first thin film dielectric layer 15
It is necessary to form the film thickness of about a to a thickness of about 2.5 μm. However, in order to make the phase velocity equal to that of another transmission line at the film thickness of 2.5 μm, the ratio is calculated from the above-mentioned proportional expression (1). It can be derived that it is necessary to use a dielectric material having a dielectric constant of 16. However, a dielectric material having a relative dielectric constant of 16 and having low loss and suitable for sputtering film formation does not exist at present.
Therefore, in such a case, by adjusting the film thicknesses of the plurality of thin film dielectric layers near the substrate surface, the irregularities on the substrate surface may be absorbed using a suitable sputtering material. In this case, the thin film dielectric layer closest to the substrate surface does not completely flatten the unevenness on the substrate surface as in the first embodiment (some unevenness remains), but the substrate itself has Unevenness can be absorbed to a considerable extent,
There is no practical problem.

[Other Embodiments] The present invention is not limited to the above-described embodiments, but can be variously modified within the scope of the invention. For example, in each of the above-described embodiments, the high-frequency resonator (１ ／ wavelength line type resonator) using the thin film multilayer electrode of the present invention has been described as an example.
By providing an input / output electrode as shown by reference numeral 8 in FIG. 1 to the resonator, it is possible to function as a high-frequency filter. In that case, it is also possible to arrange a plurality of resonators on a dielectric substrate to form a multi-stage filter.
Further, the thin film multilayer electrode of the present invention can be used not only as a resonator or a filter but also as a transmission line such as a microstrip line. Further, in each of the embodiments described above, the case where the propagated high frequency is a TEM wave has been described. However, the present invention can be similarly applied to propagation of a high frequency of another mode, for example, a high frequency of a TM mode.

[0037]

As is clear from the above description, the following excellent effects can be obtained with the thin film multilayer electrode of the present invention.

That is, the relative dielectric constant of the dielectric material to be used is selected in accordance with the above-mentioned proportional expression (1), and the thickness of the thin film dielectric layer near the dielectric substrate is increased, thereby causing the influence of the unevenness of the substrate. The thin-film multilayer electrode can be formed in the form of absorbing the above, and the phase velocities of the high-frequency waves propagating through the respective transmission lines can be matched with each other as originally designed. Further, since the unevenness of the substrate is absorbed and flattened, there is no possibility that the thin film conductor layers are short-circuited in the process of forming each layer. Further, the thin film dielectric layer whose film thickness is adjusted in accordance with the above-mentioned proportional expression (1) is not limited to the thin film dielectric layer closest to the substrate surface, and the film thickness of a plurality of thin film dielectric layers is adjusted as necessary. You can also. Thereby, the range of choice of the dielectric material that can be used for flattening the unevenness of the substrate can be expanded.

When the above-described thin film multilayer electrode is used, a high-frequency transmission line, a high-frequency resonator and a high-frequency filter realizing the inherent low-loss operation of the thin-film multilayer electrode can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a resonator constituted by using thin-film multilayer electrodes according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a state in which the thin-film multilayer electrode of the first embodiment is formed on a dielectric substrate having irregularities.

FIG. 3 is a cross-sectional view showing a state in which a thin-film multilayer electrode according to a second embodiment is formed on a dielectric substrate having irregularities.

FIG. 4 is a perspective view showing a conventional resonator constituted by using thin-film multilayer electrodes.

FIG. 5 is a cross-sectional view showing a state in which a conventional thin-film multilayer electrode is formed on a dielectric substrate.

FIG. 6 is a cross-sectional view showing a state in which a conventional thin-film multilayer electrode is formed on a dielectric substrate having irregularities.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1/2 wavelength line type resonator 2 ... Dielectric substrate 3 ... Thin film multilayer electrode 4a, 4b, 4c, 4d ... Thin film conductor layer 5a, 5b, 5c ... Thin film dielectric Layer 6: ground conductor 7: main transmission line 8: input / output electrode

Claims (9)

[Claims] 1. A thin film multi-layer electrode which is arranged on the other main surface of a dielectric substrate having a ground conductor formed on one main surface, and is constituted by alternately laminating a plurality of thin film conductor layers and thin film dielectric layers. In the above, a main transmission line is constituted by the ground conductor, the dielectric substrate, and the first thin-film conductor layer provided in contact with the dielectric substrate, and the thin-film dielectric layer and the thin-film dielectric A sub-transmission line is constituted by a pair of thin-film conductor layers sandwiching the body layer, and each of the thin-film dielectrics is arranged such that the phase velocities of the respective high-frequency waves propagating through the main transmission line and the sub-transmission line substantially match. The thickness and dielectric constant of the layers are set, and the thickness of each thin-film conductor layer is set so that electromagnetic fields are mutually coupled between the adjacent main transmission line and sub-transmission line and between each sub-transmission line. Thinner than skin depth at operating frequency It is constant, thin-film multilayer electrode, wherein the thickness of the dielectric substrate closest thin-film dielectric layer on the substrate surface was formed thicker than the other thin film dielectric layer. 2. The thin film dielectric layer closest to the substrate surface of the dielectric substrate is made of a dielectric material having a higher dielectric constant than the dielectric material forming the other thin film dielectric layers. The thin-film multilayer electrode according to claim 1. 3. The sum of the thickness of a first thin-film conductor layer provided in contact with the dielectric substrate and the thickness of a thin-film dielectric layer closest to the substrate surface of the dielectric substrate is a dielectric material. At least 1.5 of the average diameter of the pores present on the surface of the substrate
3. The thin-film multilayer electrode according to claim 1, wherein the thin-film multilayer electrode has twice the thickness. 4. The thickness of the thin film dielectric layer closest to the substrate surface of the dielectric substrate and the thickness of the thin film dielectric layer second closest to the substrate surface of the dielectric substrate are respectively set to the other thin film dielectric layers. 2. A film according to claim 1, wherein said film is formed thicker than said film thickness.
A thin-film multilayer electrode according to claim 3. 5. A thin-film multilayer electrode which is disposed on a dielectric substrate and is formed by alternately laminating thin-film conductor layers and thin-film dielectric layers, wherein the thin-film dielectric layer located near the surface of the dielectric substrate With respect to the above, it is characterized in that the film thickness is formed thick enough to absorb the irregularities of the dielectric substrate, and the thin film dielectric layer is formed of a dielectric material having a relative permittivity derived from the formula (1). Thin film multilayer electrode. (Equation 1) 6. A thin film dielectric layer closest to the substrate surface of the dielectric substrate is formed to be thick enough to flatten the unevenness of the dielectric substrate, and the thin film dielectric layer is formed by the above formula. 2. The thin film multilayer electrode according to claim 1, wherein the electrode is formed of a dielectric material having a relative dielectric constant derived from (1). 7. A high-frequency transmission line characterized in that the thin-film multilayer electrode according to claim 1 is formed in a predetermined shape on at least one surface of a dielectric substrate. 8. A high-frequency resonator characterized in that the thin-film multilayer electrode according to claim 1 or 6 is formed in a predetermined shape on at least one surface of a dielectric substrate. 9. A high-frequency filter comprising the high-frequency resonator according to claim 8 and an input / output terminal.