JP2002111438A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device in which, between a plurality of SAW filter elements, the parasitic capacity influence due to the connected ground structure can be effectively eliminated and its stable characteristic can be exploited. SOLUTION: This surface acoustic wave device is made up of SAW filter elements 1 and 2 that are contained in a cavity 30 of a container 3, conductive films 51 and 52 which bring ground pads, 35 to 40, and ground external terminals, 41 to 49, into conduction with the region where the SAW filter elements are contained, and a metal lid 7 to seal the cavity 30. Each one of the ground pads, 35 to 40 is connected with only one SAW filter element 1 or 2. In addition, the ground conductive film 51 conducting to be ground pads 35, 38, and 39 is electrically separated from the ground conductive film 52 conducting to the other SAW filter element 2 featuring this device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device in which a plurality of SAW filter elements used for a duplexer and a filter for extracting a weak signal are housed in a single container.

[0002]

2. Description of the Related Art In recent years, a surface acoustic wave filter (hereinafter, referred to as a SAW filter) composed of a surface acoustic wave element has been used in many communication fields and has characteristics such as high performance, small size, and mass productivity. From the spread of mobile phones.

For example, in a duplexer, a SAW filter element constituting a receiving filter and a SAW filter element constituting a transmitting filter are arranged in one container. Further, the weak signal extraction filter includes a front-stage SAW filter element, an amplifier circuit, and a rear-stage SAW filter element, and the above-described front-stage SAW filter element and rear-stage SAW filter element are arranged in the cavity of the same container.

In any case, it is important to suppress stray capacitance between a plurality of SAW filter elements to prevent mutual interference (crosstalk). In particular, in the weak signal extraction filter, the center frequencies of the bands of the front-stage SAW filter element and the rear-stage SAW filter element are substantially the same, and it is necessary to drive two SAW filter elements at the same time. It is important to reduce.

[0005] That is, if mutual interference is large, when a preceding SAW filter element and a succeeding SAW filter element are cascaded by external wiring, the expected total attenuation cannot be obtained as it is from the respective attenuations of the two SAW filter elements. Often. This is because the two SAs
This is because the total attenuation of the W filter element is restricted by the isolation level between the preceding SAW filter element and the subsequent SAW filter element. In actual equipment, an amplifier circuit is often used between two SAW filter elements, but the same problem also occurs in that case.

Conventionally, as a method for reducing the mutual interference of the SAW filter elements as described above, for example, Japanese Patent Laid-Open No.
It is disclosed in, for example, No. 1-205077.

In the technique disclosed in the above publication, two SAW filter elements are accommodated in a cavity of a container, and input, output, and ground electrodes of the SAW filter element are connected to input, output, and ground pads of the container. Are electrically connected to form a surface acoustic wave device. In particular, it discloses that a plurality of ground pads are provided in the cavity of the container, and the ground electrode of one SAW filter element and the ground electrode of the other SAW filter element are connected to another ground pad.

[0008]

However, in the above-mentioned prior art, only the connection relationship between the SAW filter element and the ground pad formed in the cavity is specified. The present inventor has conducted various experiments. As a result, mutual interference occurs due to the connection means between the ground electrode of the SAW filter element and the ground pad of the container. That is, the SAW filter element is mounted in addition to the bonding wire. It has been found that mutual interference occurs due to the ground conductor film formed on the mounting surface of the cavity portion and the ground external terminal.

A conventional surface acoustic wave device SW is shown in FIGS.
FIG. FIG. 16 is an external view of the conventional surface acoustic wave device SW in a state where the metal lid is omitted.
FIG. 17 is an external view of a state in which the SAW filter element is omitted in FIG. In the drawing, reference numeral 100 denotes a front SAW filter element, 200 denotes a rear SAW filter element, 300 denotes a concave container, and 136 denotes a front SA formed on a step portion of the container 300.
A ground pad 13 connected to the ground electrode 101 of the W filter element 100 via a bonding wire;
Reference numeral 9 denotes a ground pad formed on the step portion of the container 300 and connected to the ground electrode 102 of the subsequent-stage SAW filter element 200 via a bonding wire.
The ground conductor films 145, 146, and 148 formed on substantially the entire mounting surface of the cavity portion 317 of the container
0 is an external ground terminal connected to a metal cover (not shown).

[0010] As shown in FIG.
0 is connected to the ground pad 136 and is electrically connected to the ground external terminal 145 formed on the outer surface of the container 300. Similarly, the ground conductor film 500 is connected to the ground pad 139 and the ground external terminal 146, and the ground conductor film 500 is connected to the ground pad 138 and the ground external terminal 147.
00 is connected to the ground pad 137 and is electrically connected to the ground external terminal 148. The ground external terminals 145, 146, 147, and 148 are provided from a plurality of locations to strengthen the ground of the ground conductor film 500.

With the above configuration, for example, the ground pad 136 connected from the SAW filter element 100 and the SA
Ground pad 1 connected from W filter element 200
39 and the ground conductor film 500 in the container 300 as a result.
Therefore, the two SAW filter elements 100 and 200 are connected in common.

A surface acoustic wave device SW having such a ground conductor film 500 is mounted on a mounting board (not shown, the same applies hereinafter).
In this case, a parasitic component caused by the ground external terminals 145, 146, 147, and 148 and a parasitic component caused by the ground conductor film 500 are provided between the ground potential of the ground conductor film 500 and the ground potential of the mounting substrate. Will occur. These parasitic components are generated in each SAW filter element 10
Ground conductor film 5 commonly conducted from both 0 and 200
00, the SAW filter element 100 is generated between the SAW filter element 100 and the ground electrode of the mounting board.
Parasitic components on the side also affect each other on the other SAW filter element 200.

As described above, depending on the connection state between the ground external terminal formed outside the container and the ground conductor film,
The ground level becomes common between the two SAW filter elements. For example, as shown in Japanese Patent Application Laid-Open No. 11-205077, even if the two SAW filter elements are connected to a unique ground pad, Could not be sufficiently suppressed, and stable characteristics could not be obtained.

The reason why the stable characteristics cannot be obtained is that a common ground conductor film is formed widely on the mounting surface of the cavity portion over the two SAW filter elements. It is considered that it is difficult to uniformly ground the entire ground conductor film to the ground potential because the area of the film is fundamentally large, and that the degree of occurrence of parasitic components is increased due to the large area. .

On the other hand, in the surface acoustic wave device, a configuration for electrically separating a ground conductor film formed on a mounting surface of a cavity portion of a container is disclosed in JP-A-10-224175 and JP-A-10-209800.

However, for any surface acoustic wave device, the ground conductor film connected on the input side or the output side of one SAW filter element may be separated (Japanese Patent Laid-Open No. HEI 1-1990).
0-224175), in which a ground conductor film connected to the receiving side or the transmitting side of the comb-shaped electrode in one SAW filter element is separated (Japanese Patent Laid-Open No. 10-20980).
0) In each case, the attenuation characteristics of out-of-band signals in one SAW filter element are improved.
Therefore, when a plurality of SAW filter elements such as a duplexer and a weak signal extraction filter are used, there is no disclosure of a technique capable of preventing mutual interference between SAW filters with respect to a technique for separating a ground conductor film.

The present invention has been devised in view of the above-mentioned problems, and for that purpose, in the container-side ground structure, formed from the ground electrode of each SAW filter element on the outer peripheral surface of the container. In the container, the ground connection structure between the ground external terminal electrodes is made independent for each SAW filter element, thereby effectively suppressing the influence of the parasitic component due to the ground connection structure of the other SAW filter elements.
Thus, a surface acoustic wave device from which stable filter characteristics can be derived is provided.

[0018]

According to the present invention, a plurality of input external terminals, output external terminals, and ground external terminals are provided on an outer peripheral surface.
A container having a plurality of input pads, output pads, and ground pads electrically connected to the input external terminal, the output external terminal, and the ground external terminal in a cavity portion, and at least two SAW filters accommodated in the cavity portion of the container An element, a ground conductor film for conducting the ground pad and a ground external terminal in a region where the SAW filter element in the cavity is accommodated, and a metal lid for sealing the cavity of the container. , Said S
In a surface acoustic wave device, an input electrode of an AW filter element is connected to the input pad, an output electrode is connected to the output pad, and a ground electrode is connected to the ground pad.
Only one SAW filter element is connected to the ground pad of the container, and the ground conductor film that conducts with the SAW filter element is electrically connected to the ground conductor film that conducts other SAW filter elements within the container. The surface acoustic wave device is characterized in that the surface acoustic wave device is electrically separated.

Further, the surface acoustic wave device is characterized in that the ground external terminal is connected to the metal cover.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave device according to the present invention will be described below with reference to the drawings. The embodiment will be described using a small signal extraction filter. The small signal is, for example,
A signal transmitted from a satellite to the ground is exemplified.

This small signal extraction filter is, for example,
As shown in FIG. 1, it is connected to the antenna circuit A and used together with the amplifying means P. Specifically, a front-stage (front-end) SAW filter element (hereinafter, simply referred to as a front-stage SAW filter element) 1 that allows the antenna circuit A to pass a specific frequency band, an amplification that amplifies a signal obtained by extracting a signal component of the specific frequency. Means P, a second-stage (interstage) SAW filter element (hereinafter simply referred to as a second-stage SAW filter element) 2 for extracting the amplified signal again is sequentially connected.
As a result, a signal obtained by amplifying the weak signal becomes a level signal that can be processed by a normal switch circuit or a receiving circuit, and furthermore, a signal with suppressed noise components can be obtained.

In such a configuration of the small signal extracting filter, at least the amplifying means P is handled as a separate component by an IC chip or the like. Then, the first-stage SAW filter element and the second-stage SAW filter element are housed in the same container and handled as one component.

The surface acoustic wave device SW according to the present invention is a component in which the first-stage SAW filter element 1 and the second-stage SAW filter element 2 are integrated. The SAW filter element is
The filter itself has a filter function, and does not include a filter having a function of a resonator and connecting these components to form a filter.

FIG. 2 is an external view of a surface acoustic wave device SW of the present invention. FIG. 3 is a plan view in which the metal lid is omitted, FIGS. 7 and 9 show cross-sectional structures of the container, and FIGS. 6 and 8 are plan views of main parts of the container. .
FIGS. 5A and 5B show equivalent circuits of the SAW filter element of the present invention.

In FIG. 2, the surface acoustic wave device S of the present invention
W denotes a container 3 and a metal lid 6 adhered and sealed on the upper surface of the container.
It is composed of On the four end surfaces on the outside of the container 3, for example, eight grooves each having a semicircular shape as viewed from a plane for forming external terminals (three on each of a pair of sides and one on each of the other pair of sides) are provided. One) is formed.

The semicircular groove forming the external terminal is formed in the thickness direction of the container 3, and the external terminals 41 to 48 are formed in the groove. For example, on one surface of a pair of opposed end surfaces, a front-stage input external terminal 41 conducting to a front-stage SAW filter element input pad, a front-stage SAW
A ground external terminal 45 which is electrically connected to the filter element ground pad, and a second-stage input external terminal 43 which is electrically connected to the second-stage SAW filter element input pad are formed.

The other one of the pair of opposing end surfaces is connected to a front-stage output external terminal 42 that is connected to a front-stage SAW filter element output pad (described later), and is connected to the other SAW filter element ground pad (described later). A ground external terminal 46 and a post-stage output external terminal 44 electrically connected to a post-stage SAW filter element output pad (described later) are formed.

Further, a ground external terminal 47 which is electrically connected to the ground pad for the preceding SAW filter element is disposed on one of the pair of end surfaces. On the other of the pair of end surfaces, a ground external terminal 48 that is electrically connected to the ground pad for the subsequent-stage SAW filter element is arranged.

As shown in FIG. 3, on the upper surface of such a container 3, for example, a mounting surface 3C on which two SAW filter elements 1 and 2 are mounted, and a cavity portion having step portions 3a and 3b on both side surfaces. 30 are formed. The SAW filter elements 1 and 2 are disposed on the mounting surface 3C. In addition, the step portion 3a of the cavity portion 30 includes
3, an input pad 31 connected to an input electrode (described later) of the preceding SAW filter element 1, a ground pad 35 connected to a ground electrode (described later) of the preceding SAW filter element 1, and a ground electrode of the succeeding SAW filter element 2. A ground pad 36 connected to the input electrode of the subsequent-stage SAW filter element 2, and a ground pad 37 connected to the ground electrode of the subsequent-stage SAW filter element 2.

The other step 3b has a ground pad 38 connected to the ground electrode of the preceding SAW filter element 1, an output pad 32 connected to the output electrode of the preceding SAW filter element 1, Ground pad 3 connected to ground electrode of SAW filter element 1
9, a ground pad 40 connected to the ground electrode of the subsequent-stage SAW filter element 2 and an output pad 34 connected to the output electrode of the subsequent-stage SAW filter element 2 are arranged.

In the cavity 30, a ground conductor film is provided on the mounting surface 3 C of the cavity surrounded by the steps 3 a and 3 b in a region where the two SAW filter elements 1 and 2 are joined. 51 and 52 are formed (see FIG. 11).

That is, the mounting surface 3 of the cavity 3 in FIG.
c on the ground conductor film 51 on the upper side
The filter element 1 is arranged. On the lower ground conductor film 52, the subsequent-stage SAW filter element 2 is disposed.

As shown in FIG. 4, the SAW filter elements 1 and 2 are composed of a pair of comb-shaped electrode fingers that mesh with each other on the surfaces of piezoelectric substrates 53 and 54 such as lithium tantalate, lithium niobate, and a quartz substrate. Interdigital electrode P
S, connection conductor PPS, input electrodes 11, 21, output electrode 1
2, 22, ground electrodes 13, 14, 23 to 25 and, if necessary, a reflector electrode (indicated by a symbol x in the figure).

The interdigital electrode PS constitutes one resonance section. The resonance units are classified into a series resonance unit and a parallel resonance unit, and the series resonance unit and the parallel resonance unit are connected to each other via a connection conductor.

For example, the first-stage SAW filter element 1 shown in the upper part of FIG.
1 to S13 and the four parallel resonance portions P11 to P14 are connected in a ladder shape by connection conductors PPS. FIG. 5A shows this equivalent circuit diagram.

The SAW filter element 1 includes:
One input electrode 11, one output electrode 12, and two ground electrodes 13 and 14 are formed.

The second-stage SAW filter element 2 shown in the lower part of FIG.
Two and three parallel resonance portions P21 to P23 are connected in a ladder shape by connection conductors (omitted by reference numerals). This equivalent circuit diagram is shown in FIG.

The SAW filter element 2 includes:
One input electrode 21, one output electrode 22, and three ground electrodes 23 to 25 are adhered and formed.

The first-stage SAW filter element 1 and second-stage S
The AW filter elements 2 are slightly different in the number of connection stages in consideration of the characteristics in the passband and the selectivity.

The above SAW filter elements 1 and 2
The mounting surface 3 of the cavity 30 is interposed via the insulating adhesive.
c are connected to the ground conductor films 51 and 52.

The input electrode 11 of the preceding SAW filter element 1 is connected via a bonding wire to an input pad 31 formed on the right step 3a in FIG. 3, and the output electrode 12 is connected to the left step 3b. Output pad 32 formed
Are connected via bonding wires. Also,
The ground electrode 13 is connected to the ground pad 35 of the step 3a.
The ground electrode 14 is connected to a ground pad 38 of the step 3b via a bonding wire.

The input electrode 21 of the subsequent-stage SAW filter element 2 is connected via a bonding wire to an input pad 33 formed on the step 3a on the right side of FIG. 3, and the output electrode 22 is formed on the step 3b. Output pad 34 via a bonding wire. The ground electrode 23 is connected to a ground pad 36 formed on the step 3a via a bonding wire, and the ground electrode 24 is connected to a ground pad 40 formed on the step 3b.
The ground electrode 25 is connected to a ground pad 37 formed on the step 3a via a bonding wire.

Such a container 3 is composed of at least three ceramic layers. As described above, the outer terminals 41 of the container 3 are provided on a pair of outer end surfaces of the container 3 as shown in FIG. 45 and 43 are formed in the thickness direction. In the external terminals 41, 45, and 43, a conductor is formed from a bottom surface to a predetermined position inside a groove having a semicircular cross section.
For example, as shown in FIGS. 6 to 9, an input external terminal 41 connected to the input electrode 11 of the first-stage SAW filter element 1 (see FIG. 4) and an input electrode 21 of the second-stage SAW filter element 2
The input external terminal 43 connected to the container 3 (see FIG. 4) extends from the bottom surface of the container 3 to the outer end surface to a part of the thickness of the container 3. Further, the ground external terminal 45 located at a substantially central portion in the width direction of the outer end surface of the container 3 is formed to extend from the bottom surface of the container 3 to the entire region in the thickness direction of the container 3 through the outer end surface. Are electrically connected to the conductive film 61 for joining the seal ring.

Although the side view of the other outer end face of the container 3 is omitted in FIG.
2, 44 extend from the bottom surface to the middle of the thickness of the container, and the ground external terminal 46 extends from the bottom surface of the container 3 to the upper surface of the container, and further formed on the upper surface of the container 3 is a conductor film for joining a seal ring. 61.

In FIG. 7, reference numeral 61 denotes a seal ring bonding conductor film (ground potential) as described above.
62 is a seal ring and 7 is a metal lid.

FIG. 8 is an outer end face orthogonal to FIG. Only the external ground terminal 47 is formed on the outer end face. On the opposite end face of the container 3, only the ground external terminal 48 is formed. The ground external terminals 47 and 48 extend from the bottom surface of the container 3 to the top surface.

In the container 3 shown in FIGS. 7 and 9, the uppermost ceramic layer 3x has a ring shape for forming an opening of the cavity portion 30 (see FIG. 3). A conductor film 61 for joining a seal ring 62 made of Kovar, 42 alloy or the like by brazing is formed.

Here, as shown in FIG. 7, for example, a conductor film serving as the input external terminal 41 is not attached to the groove 30x formed in the uppermost ceramic layer 3x. this is,
The other input / output external terminals 42, 43, and 44 have the same structure.

On the other hand, as shown in FIG. 9, for the ground external terminals 45 to 48, conductor films are formed across the thickness of the three ceramic layers 3x to 3z.
FIG. 8 shows a side surface on which the ground external terminal 47 is formed.

FIG. 10 is a top view of the ceramic layer 3y located in the middle. The ceramic layer 3y forms the steps 3a and 3b on the inner wall of the cavity 30 (FIG. 3).
), And has a ring shape having an opening slightly smaller than the size of the opening of the cavity 30. On the outer periphery of the ceramic layer y, there are formed eight semicircular concave portions (symbols are omitted) in which grooves are formed on the outer end surface of the container 3 for securing a region for forming external terminals. ing. In each of the concave portions, a conductor film serving as the input external terminal 41 on the first-stage SAW filter element side, a conductor film serving as the ground external terminal 45, a conductor film serving as the input external terminal 43 on the second-stage SAW filter element side, and a ground external terminal 48 Output terminal 34 on the side of the subsequent SAW filter element
, A conductive film serving as the ground external terminal 46, a conductive film serving as the output external terminal 42 on the subsequent-stage SAW filter element side, and a conductive film serving as the ground external terminal 47.

Around the opening of the ceramic layer 3y, a conductor film serving as input pads 31 and 33 connected to the input electrodes 11 and 21 of each SAW filter element, and an output electrode 1
Conductor films serving as output pads 32, 34 connected to the second and second 22, 22; and ground pads 35, 36, 37, 38, 39, 4, connected to the ground electrodes 13, 14, 23, 24, 25;
The conductor film which becomes 0 is formed.

For example, in the step 3a generated by the difference between the opening of the uppermost ceramic layer 3x and the opening of the ceramic layer 3y located in the middle, for example, a portion corresponding to the step 3a on the right side in FIG. 10, a conductive film serving as an input pad 31 connected to the input electrode of the preceding SAW filter element 1, a conductive film serving as a ground pad 35 connected to the ground electrode of the preceding SAW filter element 1,
A conductor film serving as a ground pad 36 connected to the ground electrode of the subsequent SAW filter element 2, a conductor film serving as an input pad 33 connected to the input electrode of the subsequent SAW filter element 2, and a ground connected to the ground electrode of the subsequent SAW filter element 2 A conductor film to be the pad 37 is formed.
Among these five pads, the conductor film serving as the input pad 31 connected to the input electrode 11 of the previous-stage SAW filter element 1 extends to the outside of this side and serves as the input external terminal 41 in the groove. Conducted to the membrane. Also, the latter stage S
The conductor film serving as the ground pad 36 connected to the ground electrode 23 of the AW filter element 2 extends outward on this side, and is electrically connected to the conductor film serving as the ground external terminal 45 in the groove. Further, the conductor film serving as the input pad 33 connected to the input electrode 21 of the subsequent-stage SAW filter element 2 extends to the outside of this side, and is directly connected to the conductor film serving as the input external terminal 43 in the groove. . The conductive film serving as the ground pad 37 connected to the ground electrode 25 of the subsequent-stage SAW filter element 2 is electrically connected to the conductive film serving as the ground external terminal 48 in the groove formed on a different side.

The ground pad 35, which is the second pad from the top of the step portion 3a and is connected to the ground electrode 13 of the preceding SAW filter element, is led out inside the step portion 3a and formed on the wall surface thereof. It is led into the shape recess.

The ground pad 38 connected to the ground electrode 14 of the preceding SAW filter element 1 is provided at each pad corresponding to the step 3b on the left side of the drawing.
Are ground external terminals 4 in grooves formed on different sides.
7 is electrically connected to the conductive film. In addition, the conductor film serving as the output pad 32 connected to the output electrode 12 of the previous-stage SAW filter element 1 extends to the outside of this side and is directly used as the conductor film serving as the output external terminal 42 in the groove on the left side of the drawing. Conducted. Further, the conductor film serving as the output pad 34 connected to the output electrode 22 of the subsequent-stage SAW filter element 2 extends to the outside of this side, and is directly used as the conductor film serving as the output external terminal 44 in the groove on the left side of the drawing. Conducted.

The ground pad 39 is directly connected to the conductor film serving as the ground-side external terminal 46 in the groove on the left side of the drawing. In addition, the ground pad 40 is connected to the step 3b.
And into a semicircular groove formed in the wall surface.

FIG. 1 is a top view of the lowermost ceramic layer 3z.
It is shown in FIG. The ceramic layer 3z has a flat plate shape,
Eight concave portions are formed on the outer periphery similarly to the ceramic layers 3x and 3y. A conductor film to be an external terminal is formed on the inner surface of each recess.

On the upper surface of the ceramic layer 3z, ground conductor films 51 and 52 extending in two planes are formed in a region to be a mounting surface of the cavity portion 30. One ground conductor film 51 is substantially the same as the previous stage SAW.
The other ground conductor film 52 is formed in a region where the filter element 1 is mounted, and is substantially formed in a region where the subsequent-stage SAW filter element 2 is mounted, and is not connected to each other.

The ground conductor film 51 to which the previous-stage SAW filter element 1 is joined extends to the lower part of the concave portion of the right step 3a so as to be connected to the second ground pad 35 from the drawing. (See the extension portion 51a). The ground conductor film 51 extends to a concave portion formed on the upper side in the drawing, and is connected to the ground external terminal 4.
7 and the conductive film. Further, in the drawing, it extends to a concave portion formed at the center of the left side, and is electrically connected to the ground external terminal 46. That is, the ground conductor film 51
Are connected, for example, to ground external terminals 47 and 46 formed on different sides of the container 3. Therefore, the ground is grounded from different directions to strengthen the ground.

Further, the ground conductor film 52 to which the previous-stage SAW filter element 2 is bonded is 4
It extends to the lower part of the groove so as to be connected to the third ground pad 40 (see the extension 52a). The ground conductor film 52 extends to a groove formed on the lower side in the drawing, and is electrically connected to the conductor film serving as the ground external terminal 48.

Further, in the drawing, it extends to a groove formed in the center of the right side, and is electrically connected to the ground external terminal 45. That is, similarly to the conductor film 51, the ground conductor film 52 is connected to, for example, the ground external terminals 48 and 45 formed on different sides of the container 3. Therefore, the grounds are grounded from different directions to strengthen the ground.

FIG. 12 is a bottom view of the ceramic layer 3z.
Shown in Each terminal electrode 41 is provided on the bottom surface of the ceramic layer 3z.
Planar terminal electrodes 41a to 48a that are electrically connected to .about.48 are formed.

Such a container 3 is formed by sequentially laminating a plurality of types, for example, three types of ceramic green sheets from which a plurality of containers 3 can be extracted. That is, the ceramic layer 3x located on the uppermost layer and the ceramic layer 3 serving as the intermediate layer
y, a sheet serving as the lowermost ceramic layer 3z is formed with a through hole serving as a groove at a predetermined position, and a conductive paste is applied on this sheet or on the inner surface of the through hole. The sheet serving as the ceramic layer 3x located at the uppermost layer and the ceramic layer 3y serving as the intermediate layer has an opening for forming a cavity.

The ceramic sheet is obtained by laminating and integrating such ceramic sheets, firing, and further dividing or cutting into the shape of the container 3. The division or cutting may be performed before the firing treatment. Here, various conductive films are made of tungsten (W), molybdenum (Mo),
g, Cu, etc. can be illustrated. These metals are determined by the ceramic material (different firing temperature and firing atmosphere). If the ceramic material is alumina,
Examples of the conductor material include W (tung testen) and Mo (molybdenum). If the ceramic material is a glass-ceramic material, examples thereof include Ag and Cu.

When Cu is used, the firing is performed in a reducing atmosphere.

The pads 31 to 4 exposed from the container 3
0, the external terminals 41 to 48 are plated with Ni,
u plating or the like is applied. Thereby, the pad 3
In the case of 1 to 40, bonding with a bonding wire can be easily performed, and in the external terminals 41 to 48, the bonding with solder or the like becomes easy. Also, the conductor film 6 located on the uppermost surface
In No. 1, brazing with the seal ring can be easily and firmly performed.

These three ceramic layers 3x to 3z
Conductive film 61 located on the surface of the surface of the container 3 made of a conductive material (connected to the ground external terminal located on the side surface of the container 4)
At the top, the seal ring 62 is joined by brazing to form the entire container 3.

As described above, the first-stage SAW filter element 1 and the second-stage SAW filter element 2 are placed in the cavity 30 of the container 3 via the adhesive, via the ground conductor film 51 and the adhesive.
52, and are connected via wire bonding such as Au.

The front-stage SAW filter element 1 and the rear-stage SAW filter element 2 thus housed in the cavity 30 of the container 3 are placed on the seal ring 62 disposed around the opening outside the cavity 30. Then, a predetermined current is applied to the joint between the metal lid 7 and the seal ring 62 to perform seam welding.

The thus formed metal cover 7 has an Ag layer formed on the mounting surface side according to the surface of a metal flat plate such as Kovar or 42 alloy. Practically, it is grounded to the ground potential via ground external terminals 45 to 48 arranged on the side surface of the container 3.

In the surface acoustic wave device configured as described above, the ground conductor films 51 and 52 on which the respective SAW filter elements 1 and 2 are mounted are connected to the cavity 30 of the container 3.
Without connecting to each other within the
48.

Here, an equivalent circuit considering the parasitic capacitance between the SAW filter elements 1 and 2 and the ground potential of the mounting board is considered.

FIG. 13 is an equivalent circuit showing a parasitic component centered on the ground conductor films 51 and 52 in the surface acoustic wave device SW of the present invention. FIG. 14 shows a conventional, that is,
As shown in FIG. 17, the ground conductor film 500 on the mounting surface of the cavity 317 is connected to two SAW filter elements 10.
5 shows an equivalent circuit showing a parasitic component of the surface acoustic wave device SW that is shared across the regions 0 and 200.

3 and 4, the ground electrodes 13 and 14 of the preceding SAW filter element 1 are connected to the ground pad 3.
5, 38, which are connected to the ground conductor film 51 occupied exclusively by the pre-stage SAW filter element, and are connected to the ground potential of the wiring board via a plurality of ground external terminals 46, 47 occupied exclusively by the pre-stage SAW filter element.

On the second-stage SAW filter element 2 side, the ground conductor film 5 exclusive to the second-stage SAW filter element 2 is provided.
2. Connected to ground potential via ground external terminals 45 and 48.

In FIG. 13, the parasitic components C1 and C2 are independent between the IN-OUT lines of the SAW filter elements 1 and 2 and the ground potentials G51 and G52 of the ground conductor films 51 and 52, respectively. Occur.

Further, between the ground potentials G51 and G52 of the ground conductor films 51 and 52 and the ground potential G0 of the wiring board, parasitic components C3 and C4 caused by the ground conductor films 51 and 52 respectively become independent. Occur.

Therefore, the influence of the parasitic component C3 caused by the preceding SAW filter element and the exclusive ground conductor film 51 is as follows.
It affects only the first-stage SAW filter element 1 and does not affect the other second-stage SAW filter element 2. Similarly, the influence of the parasitic capacitance C4 caused by the ground conductor film 52 occupied by the rear-stage SAW filter element 2 depends on
Does not affect

On the other hand, conventionally, as shown in FIG. 17, a ground conductor film 500 extending over the entire surface is formed on the upper surface of the lowermost ceramic layer.
The ground potential of 00, 200 is
00 was connected.

In the equivalent circuit related to the parasitic component in the conventional structure shown in FIG. 14, the parasitic component C5 caused by the common ground conductor film 500 is the difference between the ground conductor film 500 and the ground potential G0 of the mounting board (not shown). Occurs in common between. In addition, the parasitic component C5 affects both the preceding SAW filter element and the succeeding SAW filter element.

Moreover, the parasitic component C5 is formed in a region corresponding to two SAW filter elements, and the size of the ground conductor film 500 is twice as large as that of the structure of the present invention. And one SAW filter element 10
The parasitic component C5 seen from 0 and 200 is doubled. As a result, the isolation characteristics between both SAW filter elements deteriorate.

The inventor of the present invention has proposed a first-stage SAW filter element 1,
The isolation characteristics of the rear-stage SAW filter element 2 were actually measured based on a small signal extraction filter device having a center frequency in the 1.57 GHz band.

As a result, the ground conductor film 51 of the present invention,
In the surface acoustic wave device SW having the structure of FIG. 52, as shown in FIG. 15, the low frequency side of the pass band (for example, 1.48 GHz)
In z), an attenuation of −50 dB can be ensured, whereas as shown in FIG.
In the surface acoustic wave device SW having the structure of No. 00, -40 on the low frequency side (for example, 1.48 GHz) of the pass band.
Only an attenuation of about dB can be secured.

Further, while an attenuation of -52 dB can be secured on the high frequency side (for example, 1.68 GHz) of the pass band as shown in FIG. 15, as shown in FIG.
Conventionally, only an amount of attenuation of about −40 dB can be secured.

It is considered that such a result is achieved by the following operation. (1) Since the ground conductor films 51 and 52 in the cavity 30 of the container 3 are dedicated to each of the SAW filter elements 1 and 2 and are physically divided, the mutual connection of the SAW filter elements 1 and 2 Interference is less likely to occur. (2) As a result of the division of the ground conductor films 51 and 52 themselves, the conductor area is reduced. Therefore, a parasitic component caused by one ground conductor film, for example, 51 is reduced. (3) One ground conductor film, for example, 52 is connected to a plurality of ground external terminals (two ground external terminals 4 in the embodiment).
6, 47), and these ground external terminals 46, 47 are connected in different directions, so that the ground potential of the ground conductor film 51 is relatively uniform. This is the same for the other ground conductor film 52.

Note that the ground conductor films 51 and 52 are
Even if the filter elements are occupied and divided, the ground electrodes 13 to 14 of the two SAW filter elements 1 and 2,
In connecting the ground electrodes 35 to 40 to the ground pads 35 to 40 by bonding wires, the ground electrodes of the two SAW filter elements 1 and 2 are connected to one ground pad, for example, the ground electrode 13 of the SAW filter element 1.
When the ground electrode 23 of the SAW filter element 2 is connected to one of the ground pads 35, the effect of dividing the ground conductor films 51 and 52 is reduced.

For this reason, the ground electrodes 13 to 14 and 23 to 25 of the SAW filter elements 1 and 2 and the ground pads 35 to 4 on the steps 3 a and 3 b of the cavity 30 are formed.
0, the ground pads 35, 38, and 39 that are electrically connected to one ground conductor film 51 have
The ground pads 36, 37, and 40 that are connected only to the AW filter element 1 and are electrically connected to the other ground conductor film 52.
In this case, it is important that only the subsequent-stage SAW filter element 2 is connected and that the ground electrodes of the respective SAW filter elements 1 and 2 are not connected to a common ground electrode pad.

As a comparative example, the inventor measured the isolation characteristics when the ground electrodes 13 and 23 of the two SAW filter elements 1 and 2 were connected to one ground pad 35. In this case, an experiment was performed with a structure using the ground conductor films 51 and 52 according to the embodiment of the present invention.

As shown in FIG. 19, the result is −44d on the low frequency side (for example, 1.48 GHz) of the pass band.
Only an attenuation of about B could be secured, and only an attenuation of -45 dB could be secured on the high frequency side (for example, 1.68 GHz).

As can be understood from the above results, the previous stage S
Each of the ground electrodes 13 to 14 of the AW filter element 1 is connected to the ground conductor film 5 on which the preceding SAW filter element 1 is mounted.
1 is connected to the ground pads 35, 38, and 39 that are electrically connected to the first and second ground electrodes 23 to 2 of the subsequent-stage SAW filter element 2.
5 are ground pads 36, 37, 4 which are electrically connected to the ground conductor film 52 on which the subsequent-stage SAW filter element 2 is mounted.
0 is important for isolation characteristics.

In the present invention, the mounting substrate and the ground external terminals 45 to 48, the mounting substrate and the ground conductor film 51,
Attention is paid to the parasitic component due to the relationship 52. But 4
The four ground external terminals 45 to 48 are formed near the approximate center of each of the four side surfaces of the container.
It is grounded to the ground potential via the two ground external terminals 45 to 48 and the seal ring 62. For this reason, although this metal lid 7 also has a relatively large area, its ground potential can be made relatively uniform, so that the influence from external noise can be effectively suppressed.

In the above-described embodiment, the description has been made of the small signal extraction filter in which the two SAW filter elements 1 and 2 are accommodated in the cavity 30 in the container 3. The above SAW filter elements may be arranged. Also, two SAW filter elements 1, 2
May be formed on the same substrate. For example, three S
When the AW filter element is accommodated, the three ground conductor films may be formed independently of each other, and may not be shared with other ground conductor films in connection with the external ground terminal. .

Further, in the above-described embodiment, a description has been given of a small signal extraction filter as an example. However, the present invention can be widely applied to all surface acoustic wave devices in which two or more SAW filter elements are accommodated in one container.

[0093]

According to the present invention, a surface acoustic wave device capable of significantly suppressing mutual interference (crosstalk) between two SAW filter elements can be realized.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram showing a mounting mode of a surface acoustic wave device according to the present invention.

FIG. 2 is an external perspective view of a surface acoustic wave device according to the present invention.

FIG. 3 is a schematic view showing a surface acoustic wave device of the present invention, in which a metal lid is omitted, and particularly showing a relationship between a SAW filter element and a conductive film.

FIG. 4 is a plan view showing an arrangement relationship of SAW filter elements used in the surface acoustic wave device according to the present invention.

FIG. 5A is an equivalent circuit diagram of a pre-stage SAW filter element of the present invention, and FIG. 5B is an equivalent circuit diagram of a pre-stage SAW filter element.

FIG. 6 is a side view of one side of a container in the surface acoustic wave device according to the present invention.

FIG. 7 is a sectional view of an input / output external terminal part in the surface acoustic wave device of the present invention.

FIG. 8 is a side view of the other end face side of the container in the surface acoustic wave device of the present invention.

FIG. 9 is a sectional view of a ground external terminal portion in the surface acoustic wave device according to the present invention.

FIG. 10 is a top view of an intermediate ceramic layer constituting a container of the surface acoustic wave device according to the present invention.

FIG. 11 is a top view of a lowermost ceramic layer constituting a container of the surface acoustic wave device of the present invention.

FIG. 12 is a bottom view of a lowermost ceramic layer constituting the container of the surface acoustic wave device according to the present invention.

FIG. 13 is an equivalent circuit diagram showing a parasitic component generated in the ground conductor film in the surface acoustic wave device according to the present invention.

FIG. 14 is an equivalent circuit diagram showing a parasitic component generated in a ground conductor film in a conventional surface acoustic wave device.

FIG. 15 is an isolation characteristic diagram of the surface acoustic wave device according to the present invention.

FIG. 16 is an external perspective view showing a conventional surface acoustic wave device in a state where a metal lid is omitted, and particularly showing a relationship between a SAW filter element and a conductive film.

FIG. 17 is an external perspective view for explaining a ground conductor film formed on a cavity mounting surface in FIG. 16;

FIG. 18 is an isolation characteristic diagram in a conventional surface acoustic wave device.

FIG. 19 is an isolation characteristic diagram when a wire bonding pad is shared by two SAW filter elements.

[Explanation of symbols]

1. Pre-SAW filter element 2. Post-SAW filter element 3. Container 30. Cavity part 41 .... Input external terminal for pre-stage SAW filter element 42 ... Output external terminal for pre-stage SAW filter element 46. 47 ··· Ground external terminal for pre-stage SAW filter element 43 ··· Input external terminal for post-stage SAW filter element 44 ··· Output external terminal for post-stage SAW filter element 45, 48 ··· Ground external terminal for post-stage SAW filter element 31 · Input pad for front SAW filter element 32 · · · Output pad for front SAW filter element 35, 38, 39 · · · Input ground pad for front SAW filter element 33 · · · Input pad for rear SAW filter element 34 · · · rear Output pad for SAW filter element 36, 37, 40 ··· Post-stage SAW filter Ground conductor film for the ground conductor film 52 ... rear stage SAW filter element for grounding pads 51 ... front SAW filter element for the child

Claims (2)

[Claims] 1. A plurality of input external terminals, output external terminals, and ground external terminals on an outer peripheral surface, and a plurality of input pads and output pads electrically connected to the input external terminals, output external terminals, and ground external terminals in a cavity portion. A container having a ground pad; at least two SAW filter elements housed in a cavity of the container; and electrically connecting the ground pad and a ground external terminal to a region in the cavity where the SAW filter element is housed. A ground conductor film to be sealed, and a metal lid for sealing a cavity of the container, wherein an input electrode of the SAW filter element is the input pad, an output electrode is the output pad, and a ground electrode is the ground. In the surface acoustic wave device connected to each of the pads, the ground pad of the container has one SA. A ground conductor film to which only the filter element is connected and which is conductive to the SAW filter element is electrically separated from the ground conductor film to which other SAW filter elements are conductive in the container. Surface acoustic wave device. 2. The surface acoustic wave device according to claim 1, wherein the ground external terminal is connected to the metal cover.