JPH07212175A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To reduce the wiring width of a signal line and to contribute to the miniaturization of a chip size by forming surf ace acoustic wave resonators, etc., by the same material as the one forming a surface acoustic wave resonator and forming film thickness thicker than a conductive film. CONSTITUTION:Surface acoustic wave resonators 2 and 3 composed by forming plural surface acoustic wave resonators 2 and 3 on a piezoelectric body substrate 1 and performing a cascade connection of the resonators 2 and 3 are connected with an input/output electrode pad 4 or a ground electrode pad 5 by a signal line 6. At least the part of this line 6, the input/output electrode pad 4 or a ground electrode pad 5 is formed by the same material as that of the conductive film forming the resonators 2 and 3 and the film thickness is formed thicker than this conductive film. As a result, the wiring width of the signal line 6 can be reduced and the matter is capable of contributing to the miniaturization of a chip size. The number of step to be connected of the resonators 2 and 3 can be increased and a surface acoustic wave filter having the attenuation amount outside high band area is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter used for mobile communication equipment and the like.

[0002]

2. Description of the Related Art With the development of mobile communication, a surface acoustic wave filter used as an interstage filter for transmitting / receiving of various mobile communication devices, an antenna filter, etc. is required to have electrical characteristics, small size and light weight. It is becoming more and more severe. In particular, the demand for the out-of-band attenuation amount is strict, and the attenuation amount of 40 to 60 dB has been required for the reception filter in the transmission band and for the transmission filter in the reception band. In this way, by realizing the surface acoustic wave filter having the high out-of-band attenuation amount, the receiving unit or the transmitting unit circuit of the mobile communication device, which is conventionally configured by using two or more filters, can be integrated into one unit. It can be realized by a surface acoustic wave filter, and the downsizing and cost reduction of equipment can be realized.

A conventional surface acoustic wave filter will be described below. FIG. 3 is a top view schematically showing a conventional surface acoustic wave filter. In FIG. 3, 1 is a component
Is a piezoelectric substrate, 2 is a series arm surface acoustic wave resonator, 3 is a parallel arm surface acoustic wave resonator, 4 is an input / output electrode pad, 5 is a ground electrode pad, and 6 is a signal line.

In the conventional surface acoustic wave filter, a plurality of series arm surface acoustic wave resonators 2 and parallel arm surface acoustic wave resonators 3 are ladder type on a piezoelectric substrate 1 such as lithium tantalate or lithium niobate. A surface acoustic wave filter was constructed by connecting in series. Further, since the wiring patterns of the signal line 6, the input / output electrode pad 4, the ground electrode pad 5, etc. are formed at the same time as the surface acoustic wave resonators 2 and 3, they have the same conductivity as the surface acoustic wave resonators 2 and 3. Material and had the same film thickness. Further, in the structure of the surface acoustic wave filter, the resistance of the wiring such as the signal line 6 and the influence of the inductor are greatly affected. Therefore, the surface acoustic wave resonators 2 and 3 are formed by the signal line 6 having a wiring width of about 100 μm.
Was making a connection.

[0005]

In the case of realizing a surface acoustic wave filter having a high attenuation outside the band, the electrode capacitance of the series arm surface acoustic wave resonator 2 and the parallel arm surface acoustic wave resonance are mainly used. A method of controlling the ratio with the electrode capacitance of the child 3 and a method of increasing the number of cascade connection stages of the surface acoustic wave resonators 2 and 3 are used. However, there is a limit to the improvement of out-of-band attenuation only with the former method, and increasing the number of cascade connection stages of the latter surface acoustic wave resonators 2 and 3 is the most effective method. However, in the above-mentioned conventional configuration, there is a limit to the multi-stage connection of the surface acoustic wave resonators 2 and 3 due to the chip size restriction.

The present invention solves the above-mentioned conventional problems, and enables the wiring width of the signal line to be reduced without impairing the electrical characteristics of the surface acoustic wave filter, which is the same chip as the conventional one. It is an object of the present invention to realize a surface acoustic wave filter having a high out-of-band attenuation amount, which enables a multi-stage connection of surface acoustic wave resonators in size.

[0007]

To achieve the above object, a surface acoustic wave filter according to the present invention comprises a plurality of surface acoustic wave resonators formed on a piezoelectric substrate, and the surface acoustic wave resonators are In a surface acoustic wave filter configured by cascade connection, a signal line connecting between the surface acoustic wave resonators, or a signal line connecting the surface acoustic wave resonator and an input / output electrode pad or a ground electrode pad, or A configuration in which at least a part of the input / output electrode pad or the ground electrode pad is formed of the same material as the conductive film forming the surface acoustic wave resonator, and is formed thicker than the conductive film, or The surface acoustic wave resonator is formed of a material having a higher conductivity than the conductive film forming the surface acoustic wave resonator.

[0008]

With the structure of the surface acoustic wave filter, the resistance component and the inductor component due to the wiring of the signal line can be reduced, and the wiring width of the signal line can be reduced without impairing the electrical characteristics of the surface acoustic wave filter. It is possible to realize a surface acoustic wave filter having a high out-of-band attenuation by connecting the surface acoustic wave resonators in multiple stages with the same chip size as the conventional one. further,
The realization of a high attenuation surface acoustic wave filter will reduce the number of parts for mobile communication devices and the like, and will also enable downsizing and cost reduction of the devices. Further, since the wiring width of the signal line can be reduced, in the case of the surface acoustic wave filter having the same structure as the conventional one, the chip size can be reduced.

[0009]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a top view showing a schematic configuration of a surface acoustic wave filter according to a first embodiment of the present invention. The same reference numerals are used for the same components as those shown as the conventional example. In FIG. 1, 1 is a piezoelectric substrate, 2 is a series arm surface acoustic wave resonator, 3 is a parallel arm surface acoustic wave resonator, 4 is an input / output electrode pad, 5 is a ground electrode pad, and 6 is a signal line. Is.

In the present embodiment, 36 ° Y-cut X-propagation lithium tantalate is used as the piezoelectric substrate 1, and two series arm surface acoustic wave resonators 2 and one parallel arm surface acoustic wave resonator 3 are used. The basic unit is a series of Ts connected in series.
A three-stage surface acoustic wave filter was formed. The chip size was 2.2 mm × 1.6 mm. In this example, an aluminum thin film was used as the electrode material. The film thickness of aluminum forming the surface acoustic wave resonators 2 and 3 is about 4300.
It was Å. On the other hand, the signal line 6, the input / output electrode pad 4, and the ground electrode pad 5 are connected to the surface acoustic wave resonator 2,
An aluminum film having a thickness of about 4000 Å was further formed on the aluminum film formed at the same time as 3, and the total thickness was about 8300 Å, which was about twice as large as that of the surface acoustic wave resonators 2 and 3. . In addition, the signal line 6
The wiring width was 50 μm, which was half that of the conventional surface acoustic wave filter. The surface acoustic wave filter according to this example is a reception filter for a mobile phone having a center frequency of 872.5 MHz, and has an insertion loss of 4.5 dB and an out-of-band attenuation amount (transmission band) of about 60 dB.

As described above, the wiring width of the signal line 6 and the like is halved as compared with the conventional one, so that the surface acoustic wave resonators 2 and 3 have the same structure as the conventional one, but in the region shown by the dotted line in FIG.
Etc. can be arranged. The effect of reducing the chip size was about 20% in this example. In the case of the surface acoustic wave filter having the conventional configuration, the wiring width of the signal line, particularly the wiring width from the series arm resonator to the parallel arm resonator is 100 μm.
In the case of reduction from 50 μm to 50 μm, deterioration of about 5 to 7 dB was observed in the out-of-band attenuation amount due to an increase in wiring resistance and inductor. However, in this embodiment, since the wiring film thickness is sufficiently thick, it is possible to suppress an increase in the resistance component and the inductor component, and it is possible to obtain the same electrical characteristics as in the case of the conventional wiring width.

In this embodiment, as the piezoelectric substrate 1,
Although 36 ° Y-cut X-propagation lithium tantalate was used, it is clear that the same effect can be obtained also in the case of another piezoelectric substrate or a substrate using a piezoelectric thin film. Further, although the present embodiment is applied to the surface acoustic wave filter of 800 MHz band, when applied to the surface acoustic wave filter operating in a higher frequency band, the film of the conductive film forming the surface acoustic wave resonator is used. Needless to say, it is particularly effective because the thickness is absolutely thin.

As described above, a surface acoustic wave filter constructed by forming a plurality of surface acoustic wave resonators 2 and 3 on the piezoelectric substrate 1 and connecting the surface acoustic wave resonators 2 and 3 in cascade. , A signal line 6 connecting the surface acoustic wave resonators 2 and 3 or a signal line 6 connecting the surface acoustic wave resonators 2 and 3 to the input / output electrode pad 4 or the ground electrode pad 5, or Output electrode pad 4
Alternatively, at least a part of the ground electrode pad 5 is formed of the same material as the conductive film forming the surface acoustic wave resonators 2 and 3, and is formed thicker than the conductive film. The wiring width of the signal line 6 can be reduced, which contributes to downsizing of the chip size. On the other hand, in the case of the same chip size as the conventional one, since the distance between the signal lines 6 can be kept large, the influence of the direct wave between the signal lines 6 can be reduced. Alternatively, the surface acoustic wave resonators 2, 3
It is possible to increase the number of connection stages of, and to obtain a surface acoustic wave filter having high out-of-band attenuation. (Embodiment 2) Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a top view showing the outline of the configuration of the surface acoustic wave filter according to the second embodiment of the present invention. In FIG. 2, 1 is a piezoelectric substrate, 2 is a series arm surface acoustic wave resonator, 3 is a parallel arm surface acoustic wave resonator, 4 is an input / output electrode pad, 5 is a ground electrode pad, and 6 is a signal line. , 7 are second conductive films.

In this embodiment, as in the first embodiment, 36 ° Y-cut X-propagation lithium tantalate is used as the piezoelectric substrate 1, and two series arm surface acoustic wave resonators 2 and one parallel arm acoustic wave resonator 2 are arranged in parallel. A T-type three-stage surface acoustic wave filter was formed by using, as a basic unit, the T-type cascade connection with the arm surface acoustic wave resonator 3. In FIG. 2, the dotted line shows the effect of reducing the chip size when compared with the case of the conventional configuration. In this embodiment, an aluminum thin film is used as an electrode material of the surface acoustic wave resonators 2 and 3, and gold is used as a part of the electrode material of the signal line 6, the input / output electrode pad 4, and the ground electrode pad 5, and the second electrode is used. It is shown as a conductive film 7.
The film thickness of the electrode material was about 4300Å and about 4000Å, respectively. Further, the wiring width of the signal line 6 was 50 μm, which was about half that of the conventional surface acoustic wave filter. In the case of the first embodiment, since the input / output electrode pad 4 and the ground electrode pad 5 are aluminum films, the connection with the terminals of the package is made by the aluminum wire, but in the present embodiment, the package is made by the gold wire. The connection with the terminal was made. The surface acoustic wave filter according to this example has a center frequency of 872.5 MHz.
Is a receiving filter for mobile phones with an insertion loss of 4.5.
The out-of-band attenuation (transmission band) was about 60 dB. Also in the case of the present embodiment, by using the electrode material having high conductivity, it is possible to suppress an increase in wiring resistance and inductor even if the wiring width is reduced to 1/2.
It was possible to obtain electrical characteristics equivalent to those of the conventional wiring width. Furthermore, since the transmission loss in the signal line 6 or the bonding wire can be minimized, the in-band characteristic can be slightly improved.

In this embodiment, the signal line 6 and the like are made of gold. However, it is needless to say that the same effect can be obtained even if the signal line 6 and the like are made of other material having high conductivity. Needless to say, this embodiment is also particularly effective when applied to a surface acoustic wave filter that operates in a higher frequency band.

As described above, a surface acoustic wave filter formed by forming a plurality of surface acoustic wave resonators 2 and 3 on the piezoelectric substrate 1 and connecting the surface acoustic wave resonators 2 and 3 in cascade. In, the signal line 6 connecting the surface acoustic wave resonators 2 and 3 or the signal line 6 connecting the surface acoustic wave resonators 2 and 3 to the input / output electrode pad or the ground electrode pad, or the input / output electrode At least a part of the pad 4 or the ground electrode pad 5 is made of a material having a conductivity higher than that of the conductive film forming the surface acoustic wave resonators 2 and 3, whereby the wiring width of the signal line 6 can be reduced. Contributes to downsizing of the chip size. On the other hand, even when the chip size is the same as the conventional one, the number of connection stages of the surface acoustic wave resonators 2 and 3 can be increased, and a surface acoustic wave filter having a high out-of-band attenuation amount can be obtained. (Embodiment 3) The third embodiment of the present invention will be described below.

Although the drawings are not used in this embodiment, the pattern is the same as that in the above-mentioned embodiments. And the first and second
In the same manner as in the above example, 36 ° Y-cut X-propagation lithium tantalate is used as the piezoelectric substrate, and two series arm surface acoustic wave resonators and one parallel arm surface acoustic wave resonator are cascaded in a T-shape. A T-type three-stage surface acoustic wave filter was formed using the connected units as a basic unit. In this embodiment, an aluminum thin film (having a thickness of about 4300) is used as an electrode material of the surface acoustic wave resonator.
Å) was used. Further, about 4300 parts of the signal line, the input / output electrode pad, and a part of the ground electrode pad, which are formed at the same time as the surface acoustic wave resonator in the first layer as an electrode material.
Å aluminum, 300Å as a buffer layer on the second layer
Of nickel, and 3000 Å of gold was deposited on the uppermost third layer. The wiring width of the signal line was 50 μm, which was about half that of the conventional surface acoustic wave filter, as in the second embodiment. Also in this example, the connection with the terminal of the package was made by the gold wire. Also in the case of the present embodiment, it was possible to obtain the same electrical characteristics as in the case of the conventional wiring width. Further, since the transmission loss in the signal line or the bonding wire can be minimized, the in-band characteristic can be slightly improved.

In this embodiment, aluminum, nickel,
Although the signal line and the like are formed of a conductive film composed of three layers of gold, a conductive film of two or more layers using another conductive material may be used.

As described above, the wiring width of the signal line can be reduced by forming at least a part of the signal line, the input / output electrode pad, or the ground electrode pad with the conductive film made of two or more layers of different materials. Contributes to downsizing of the chip size. On the other hand, even if the chip size is the same as the conventional one, the number of connection stages of the surface acoustic wave resonator can be increased, and a surface acoustic wave filter having high out-of-band attenuation can be obtained.

[0020]

As is apparent from the above description of the embodiments, the present invention is constructed by forming a plurality of surface acoustic wave resonators on a piezoelectric substrate and connecting the surface acoustic wave resonators in cascade. In the surface acoustic wave filter described above, a signal line connecting between the surface acoustic wave resonators or a signal line connecting the surface acoustic wave resonator with an input / output electrode pad or a ground electrode pad, or an input / output electrode pad or ground. At least a part of the electrode pad is formed of the same material as the conductive film forming the surface acoustic wave resonator, and is formed thicker than the conductive film, or the surface acoustic wave resonance By using a material that has a higher conductivity than the conductive film that forms the child, the wiring width of the signal line can be reduced, which contributes to the miniaturization of the chip size. That. On the other hand, in the case of the same chip size as the conventional one, since the distance between the signal lines can be kept large, the influence of the direct wave between the signal lines can be reduced. Alternatively, the number of connection stages of the surface acoustic wave resonator can be increased, and a surface acoustic wave filter having high out-of-band attenuation can be obtained.

[Brief description of drawings]

FIG. 1 is a top view showing a configuration of a surface acoustic wave filter according to a first embodiment of the present invention.

FIG. 2 is a top view showing a configuration of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 3 is a top view showing a configuration of a conventional surface acoustic wave filter.

[Explanation of reference numerals] 1 piezoelectric substrate 2 series arm surface acoustic wave resonator 3 parallel arm surface acoustic wave resonator 4 input / output electrode pad 5 ground electrode pad 6 signal line 7 second conductive film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Eda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A surface acoustic wave filter configured by forming a plurality of surface acoustic wave resonators on a piezoelectric substrate and connecting the surface acoustic wave resonators in cascade. A signal line for connection, or a signal line for connecting the surface acoustic wave resonator and the input / output electrode pad or the ground electrode pad, or at least a part of the input / output electrode pad or the ground electrode pad, connects the surface acoustic wave resonator. A surface acoustic wave filter formed of the same material as a conductive film to be formed and having a thickness larger than that of the conductive film. 2. A surface acoustic wave filter comprising a plurality of surface acoustic wave resonators formed on a piezoelectric substrate, and the surface acoustic wave resonators are cascade-connected to each other. At least a part of the signal line for connection or the signal line for connecting the surface acoustic wave resonator and the input / output electrode pad or the ground electrode pad, or at least a part of the surface acoustic wave resonator A surface acoustic wave filter formed of a material having a conductivity higher than that of a conductive film to be formed. 3. A conductive film forming a surface acoustic wave resonator is an alloy film containing aluminum as a main component, and at least a part of the conductive film forming a signal line, an input / output electrode pad or a ground electrode pad is formed. 3. The surface acoustic wave filter according to claim 2, wherein the alloy film is composed mainly of gold. 4. A conductive film forming a signal line, an input / output electrode pad, and a ground electrode pad,
The surface acoustic wave filter according to claim 2, wherein the surface acoustic wave filter is formed of two or more layers of conductive films made of different materials. 5. The first layer is an aluminum alloy film formed simultaneously with a surface acoustic wave resonator, the second layer is an alloy film containing chromium or nickel as a main component, and the third layer is an alloy containing gold as a main component. The surface acoustic wave filter according to claim 4, wherein the surface acoustic wave filter is a film.