JP2001024471A - Surface acoustic wave resonator and surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an SAW(surface acoustic wave) resonator having a high input and output terminal impedance for preventing the increase of an occupancy area and the degradation of characteristics. SOLUTION: In a 1 port SAW resonator, the cross width W of first and second IDT(interdigital electrodes) 43 and 44 electrically connected with an input electrode 46 and an output electrode 47 connected with an input terminal 48 and an output terminal 49 is divided, and the first and second IDT 43 and 44 are serially connected through a third electrode 43. Thus, an SAW filter can be constituted by ladder connection or lattice connection by using the 1 port SAW resonator whose impedance is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave resonator and a surface acoustic wave filter, and more particularly, to a surface acoustic wave resonator and a surface acoustic wave filter having improved matching with connected elements.

[0002]

2. Description of the Related Art With the recent development of mobile communication technology and integration technology, mobile communication terminals that have been reduced in size and weight have rapidly become widespread. As a high-frequency circuit in the mobile communication terminal, a surface acoustic wave (Surface Acoustic) is used.
Wave: hereinafter abbreviated as SAW. ) A filter is used. SAW filters are characterized by being suitable for integration and having excellent frequency selectivity due to steep filter characteristics. By employing the SAW filter, it is possible to achieve both miniaturization and high performance of the terminal. Such a SAW filter is generally formed by connecting a one-port SAW resonator, which is easily integrated, by ladder connection or lattice connection.

FIG. 4 shows a conventional one-port SAW resonator. FIG. 1A shows a conventional one-port SAW.
5 is a diagram schematically illustrating a planar structure of a resonator. FIG. 1B shows the one-port SAW resonator by symbols. As shown in FIG.
The resonator includes a first and a second interdigital electrode (InterDigital T) formed of an aluminum thin film or the like and electrically insulated from each other on the upper surface of a flat piezoelectric substrate 10 having piezoelectricity.
ransducer: hereinafter abbreviated as IDT. ) 11 and 12 are arranged. Each of the first and second IDTs 11 and 12 has a plurality of elongated strip-shaped electrode groups in a direction perpendicular to the SAW propagation direction, and these electrode groups are electrically connected at one end and electrically at the other end. Are arranged in an insulated screen. The first and second IDTs 11 and 12 are arranged to face each other, and the band-shaped electrodes having IDTs are alternately arranged.

[0004] On the upper surface of the piezoelectric substrate 10, an input electrode 13 and an output electrode 14 formed of an aluminum thin film or the like are arranged. The input electrode 13 is connected to the first IDT 11
Are electrically connected to electrode ends on the side to which the respective electrode groups are electrically connected. The output electrode 14 is connected to the second I
Each band-shaped electrode group of the DT 12 is electrically connected to the electrode end on the side to which it is electrically connected. The input electrode 13
The input terminal 1 is connected via a bonding wire made of gold wire.
5 is electrically connected. The output electrode 14 is electrically connected to the output terminal 16 via a bonding wire made of a gold wire.

Further, on the upper surface of the piezoelectric substrate 10, a plurality of strip-shaped parallel electrodes are provided on both sides of the first and second IDTs 11 and 12 which are opposed to each other in a direction perpendicular to the SAW propagation direction. First and second reflector electrodes 17 and 18 are disposed.

In the one-port SAW resonator having such a configuration, when an electric signal is applied to the input terminal 15, the output terminal 1
6, the piezoelectric substrate 10 is distorted in accordance with the voltage value. As a result of this distortion, the SAW excited by the first IDT 11 propagates on the piezoelectric substrate 10 and the second IDT
Reach twelve. The second IDT 12 converts the transmitted SAW into an electric signal. The SAW excited by the first IDT 11 moves on the piezoelectric substrate 10 to the second IDT 1.
2, the first and second reflector electrodes 17 and 18 are arranged on both sides of the first and second IDTs 11 and 12, which are opposed to each other, so that the propagating SAW is reflected. I try to make it. The strip-shaped electrodes of the first and second reflector electrodes 17 and 18 reflect the SAW excited from the first IDT 11 with a constant reflectance. Therefore, the first and second reflector electrodes 1
7 and 18 are each provided with a plurality of strip electrodes,
SAW almost 100% excited from the first IDT11
Is reflected.

The characteristics of the piezoelectric substrate on which the electrodes are arranged, and the SAW of each strip-like electrode alternately arranged to face each other
By changing various parameters such as the cross width 19, which is the length of the electrode in the direction perpendicular to the propagation direction of the electrode, and the number of pairs of strip-like electrodes alternately arranged opposite to each other,
And the transfer characteristics between the second IDTs 11 and 12 can be adjusted.

[0008] The SAW filter is the one-port SA described above.
When the W resonator is represented by the symbol shown in FIG. 4B, it is configured as follows.

FIG. 5 schematically shows the configuration of a SAW filter in which the one-port SAW resonator shown in FIG. 4 is ladder-connected. That is, the ladder-connected SAW
In the filter, the first SAW resonator 20 is inserted between the first input terminal 21 and the first output terminal 22, and the second SAW resonator 23 is connected between the first output terminal 22 and the second input terminal. It is inserted between the terminal 24 and the second output terminal 25.

The ladder-connected SAW filter has a low-pass characteristic of the first SAW resonator 20 and
Utilizing the high-pass characteristic of the second SAW resonator 23,
It has steep narrow band pass characteristics.

FIG. 6 shows an outline of the configuration of a SAW filter in which the one-port SAW resonator shown in FIG. 4 is lattice-connected. That is, a lattice-connected SAW
In the filter, a first SAW resonator 26 is inserted between a first input terminal 27 and a first output terminal 28, and a second SAW resonator 29 is connected between a second input terminal 30 and a second output terminal. It is inserted between the terminal 31. Further, a third SAW resonator 32 is inserted between the first input terminal 27 and the second output terminal 31, and a fourth SAW resonator 33 is connected between the second input terminal 30 and the first output terminal. 28.

Such a lattice-connected SAW filter includes a ladder-connected SAW filter including a first SAW resonator 26 and a fourth SAW resonator 33, and a second SAW resonator 29 and a third SAW resonator 29. And a ladder-connected SAW filter composed of the SAW resonators 32. Since the lattice-connected SAW filter is a parallel type drive different from the ladder-connected SAW filter, the ground on the input side and the ground on the output side can be made non-common, and the propagation of noise that appears when the ground is common is eliminated. be able to.

By the way, RF (Radio Frequenc)
y) The input / output terminal impedance of the SAW filter in the band is usually designed so that the characteristic impedance is 50Ω. However, in recent mobile terminal communication devices,
Since a multifunctional and high-performance semiconductor integrated circuit is built in and the number of components is reduced, it is necessary to design with an input / output terminal impedance having a high characteristic impedance such as 200Ω or 450Ω in order to eliminate the impedance conversion element.

Generally, the admittance G of the one-port SAW resonator shown in FIG. 4 is expressed by the following equation in the case of a so-called normal type IDT in which a plurality of band-shaped electrodes provided in an interdigital shape are equal in length. it can.

G∝8 × k ² × ε ₀ × fc × W × M ² (1)

Here, k ² is the electromechanical coupling coefficient, ε ₀ is the dielectric constant, fc is the center frequency, W is the cross width, and M is the number of electrode finger pairs.

Therefore, when designing a SAW filter having a high input / output impedance, a plurality of one-port SAW resonators shown in FIG. 4 may be connected in series, or the number M of electrode fingers may be increased from the equation (1). In this case, a high input / output terminal impedance is realized by reducing the crossover width W or the like.

For example, Japanese Unexamined Patent Application Publication No. 63-13511 discloses a "surface acoustic wave filter" in which the first and second IDTs opposing each other on a piezoelectric substrate are meandered by passing between them. A technology for realizing high impedance by providing a meander electrode opposed to the first and second IDTs and additionally connecting an inductance element in parallel to each of the first and second IDTs and simultaneously connecting those having the same radiation conductance in series with each other. Is disclosed.

[0019]

However, a conventional SAW filter shown in FIG. 4 which is constructed by ladder-connecting or lattice-connecting a one-port SAW resonator is disclosed in, for example, Japanese Patent Application Laid-Open No. And Japanese Patent Application Laid-Open No. 08-65089, “Surface Acoustic Wave Filter”, when the impedance is increased by N times by connecting them in series, there is a problem that the occupied area is also increased by N times. . Further, when the number M of electrode finger pairs is increased, there is a characteristic problem that longitudinal mode spurious appearing as ripples in the pass band of the filter is likely to occur. Further, when the cross width W is reduced, there is a problem that, besides the occurrence of the longitudinal mode spurious, the beam becomes more susceptible to the diffraction effect and the characteristics are further deteriorated. Japanese Patent Laid-Open No. 63
In the technique disclosed in JP-A-135511, it is necessary to form a meander electrode between the first and second IDTs, so that it is more difficult to form the first and second IDTs and the meander electrode. Since the cross width W of the first and second IDTs is reduced, the influence of the above-described diffraction effect is unavoidable.

It is an object of the present invention to provide a SAW resonator and a SAW resonator having a high input / output terminal impedance while avoiding an increase in occupied area and deterioration of characteristics.

[0021]

According to the first aspect of the present invention, (a) a flat-plate-shaped piezoelectric substrate and (b) interdigital transducers in which one end of each of a plurality of parallel electrodes is electrically short-circuited. A first and a second interdigitated electrode disposed on the piezoelectric substrate facing each other, and (c) a predetermined interval between the first and the second interdigitated electrode on the piezoelectric substrate. And at least one of a plurality of third electrodes which are arranged facing each other at a predetermined distance from at least the first and second interdigital electrodes. And a surface acoustic wave resonator.

That is, in the first aspect of the present invention, the first and second interdigital electrodes are arranged on the flat piezoelectric substrate so as to face each other. Each of the first and second interdigital electrodes has an interdigital electrode in which one end of each of the plurality of parallel electrodes is electrically short-circuited. Further, one or a plurality of third electrodes having IDTs arranged opposite to each other at predetermined intervals between the first and second interdigital electrodes are arranged on the piezoelectric substrate. I made it. At this time, at least the first and second interdigital electrodes were arranged so as to be opposed to the interdigital electrodes at a predetermined interval.

According to a second aspect of the present invention, in the surface acoustic wave resonator according to the first aspect, the third electrode is formed of a plurality of strips arranged at predetermined intervals with respect to the parallel electrodes of the IDT. Are electrically short-circuited at an intermediate portion between the electrodes.

That is, according to the second aspect of the present invention, a plurality of strip-shaped electrodes are arranged at a predetermined distance from the parallel electrodes of the interdigital transducers of the first and second interdigital electrodes, and these are arranged. Since the third electrode is formed by electrically short-circuiting the intermediate portion, an increase in the occupied area when realizing high impedance can be further suppressed.

According to the third aspect of the present invention, the flat plate-shaped piezoelectric substrate and the interdigital transducers in which one ends of the plurality of parallel electrodes are electrically short-circuited are disposed opposite to each other on the piezoelectric substrate. First and second interdigital electrodes, and interdigital transducers disposed opposite to each other with a predetermined interval between the first and second interdigital electrodes on the piezoelectric substrate, A plurality of surface acoustic wave resonators having at least interdigital electrodes of the first and second interdigital electrodes and one or a plurality of third electrodes arranged to face each other at a predetermined distance are provided by surface acoustic waves. A plurality of surface acoustic wave resonators are ladder-connected to the filter.

That is, according to the third aspect of the present invention, the surface acoustic wave filter is formed by connecting the surface acoustic wave resonator according to the first aspect of the present invention in a ladder manner. It is possible to realize a SAW filter having high input / output terminal impedance while suppressing characteristic deterioration.

According to a fourth aspect of the present invention, in the surface acoustic wave filter according to the third aspect, a plurality of surface acoustic wave resonators are lattice-connected.

That is, according to the fourth aspect of the present invention, the surface acoustic wave filter is constructed by lattice-connecting the surface acoustic wave resonator of the first aspect of the present invention. It is possible to realize a surface acoustic wave filter having a high input / output terminal impedance while suppressing characteristic deterioration.

According to a fifth aspect of the present invention, in the surface acoustic wave filter according to the third or fourth aspect, the third electrodes are arranged at predetermined intervals with respect to the parallel electrodes of the IDT. It is characterized in that a plurality of strip-shaped electrodes are electrically short-circuited at an intermediate portion thereof.

That is, according to the fifth aspect of the present invention, a plurality of strip-shaped electrodes are arranged at a predetermined distance from the parallel electrodes of the interdigital transducers of the first and second interdigital electrodes, and these are arranged. Since the surface acoustic wave filter is formed using the surface acoustic wave resonator in which the third electrode is formed by electrically short-circuiting the intermediate portion, an occupied area when realizing high impedance is provided. Can be further suppressed.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 schematically shows a planar structure of a one-port SAW resonator according to this embodiment of the present invention. In the one-port SAW resonator according to this embodiment, first and second IDTs 41 and 42 formed of an aluminum thin film or the like and electrically insulated from each other are arranged on the upper surface of a flat piezoelectric substrate 40 having piezoelectricity. ing. Each of the first and second IDTs 41 and 42 has a plurality of elongated strip-shaped electrode groups parallel to each other in a direction perpendicular to the SAW propagation direction. Are arranged in an electrically insulated blind.
The first and second IDTs 41 and 42 are arranged to face each other.

The one-port SAW resonator according to the present embodiment has a cross width W of each strip-like electrode in a direction perpendicular to the SAW propagation direction of the first and second IDTs 41 and 42.
Unlike the conventional one-port SAW resonator shown in FIG. 4, the electrodes are arranged so that their electrodes do not cross each other. Further, the one-port SAW resonator according to the present embodiment is formed of an aluminum thin film or the like, and has a plurality of strip-shaped electrodes parallel to each other in a direction perpendicular to the SAW propagation direction and electrically connected to each other. 4 electrodes 4
3, 44. One end of each of the plurality of band-shaped electrodes of the third electrode 43 is electrically connected, and the other end is insulated. The plurality of band-shaped electrodes of the first IDT 41 are alternately arranged with the IDT-shaped band-shaped electrodes. One end of each of the plurality of band-shaped electrodes of the fourth electrode 44 is electrically connected and the other end is insulated, and is alternately arranged with each of the interdigital band-shaped electrodes of the second IDT 42. These third and fourth electrodes 43,
Reference numeral 44 denotes a side to which each strip-shaped electrode is electrically connected, and is electrically connected by a short-circuit electrode 45.

On the upper surface of the piezoelectric substrate 40, an input electrode 46 and an output electrode 47 formed of an aluminum thin film or the like are arranged. The input electrode 46 is the first IDT 41
Are electrically connected to electrode ends on the side to which the respective electrode groups are electrically connected. The output electrode 47 is connected to the second I
Each band-shaped electrode group of the DT 42 is electrically connected to an electrode end on the side to which it is electrically connected. The input electrode 46 is
The input terminal 4 is connected via a bonding wire made of gold wire.
8 are electrically connected. The output electrode 47 is electrically connected to an output terminal 49 via a bonding wire made of a gold wire.

Further, on the upper surface of the piezoelectric substrate 40, a plurality of strip-shaped parallel electrodes are provided on both sides of the first and second IDTs 41 and 42, which are opposed to each other, in a direction perpendicular to the SAW propagation direction. First and second reflector electrodes 50 and 51 are disposed.

In the one-port SAW resonator of this embodiment having such a configuration, when an electric signal is applied to the input terminal 48, the piezoelectric substrate 40 is distorted in accordance with the voltage between the input terminal 48 and the output terminal 49. As a result of this distortion, the first ID
The SAW excited by T <b> 41 propagates on the piezoelectric substrate 40, and reaches the third electrode 43 which is disposed to face the first IDT 41. The third electrode 43 converts the reached SAW into an electric signal. Then, the short-circuit electrode 45
The second I of the fourth electrode 44 electrically connected through
The SAW is excited from the portion facing the DT. This SAW reaches the second IDT 42. Second IDT
Reference numeral 42 converts the transmitted SAW into an electric signal.

SAW excited by first IDT 41
Correspond to the third and fourth electrodes 43 and 44 on the piezoelectric substrate 40.
And the first and second IDTs 41 and 42 which are opposed to each other.
By disposing the first and second reflector electrodes 50 and 51 on both sides of the SAW, the propagating SAW is reflected. The strip-shaped electrodes of the first and second reflector electrodes 50 and 51 reflect the SAW excited from the first IDT 41 with a constant reflectance. Therefore, the first and second reflector electrodes 50 and 51 each include a plurality of strip electrodes, so that the first IDT 41 is almost 100%.
The more excited SAW is reflected.

The one-port SAW resonator in this embodiment is a so-called regular IDT, and its admittance G
Can be expressed as in the above equation (1). Considering a one-port SAW resonator originally designed with a characteristic impedance of Z ₀ , as shown in FIG. 1, the cross width W is divided into two to double the impedance, and these are connected in series to further increase the impedance. Is doubled so that the characteristic impedance in this embodiment is “4 ×
Becomes Z ₀ ". That is, without increasing the area occupied as shown in FIG. 1, it is possible to realize a high impedance that 2 ^twice.

Although the impedance can be doubled by simply dividing the cross width W into two, the deterioration of characteristics cannot be avoided due to the effect of the diffraction effect as described above. However, when trying to obtain the same double impedance with the one-port SAW resonator in this embodiment,
It is possible to change the impedance at 2 ^twice,
Since the number of divisions of the cross width W can be reduced, the characteristic deterioration due to the effect of the diffraction effect can be reduced as compared with the related art.

As described above, the one-port SA in this embodiment is
The W resonator has a first terminal connected to the input terminal and the output terminal.
And the cross width W of the second IDT is divided into two,
By connecting in series between the second IDT and the second IDT via an electrode, it is possible to avoid deterioration of characteristics and increase the impedance without increasing the occupied area.

Further, as shown in FIG. 5, for example, by performing ladder connection using the one-port SAW resonator according to the present embodiment, the steepness is obtained by utilizing the respective low-pass characteristics and high-pass characteristics. It is possible to realize a SAW filter that has a narrow band pass characteristic and can be terminated with high impedance.

Further, as shown in FIG. 6, for example, by performing lattice connection using the one-port SAW resonator in this embodiment, it is possible to make the ground on the input side and the ground on the output side non-common by parallel driving. As a result, it is possible to eliminate the propagation of noise that appears when the ground is common.

In any case, the one-port SAW resonator having the increased impedance as shown in FIG.
By performing ladder connection or lattice connection as shown in, termination with high impedance becomes possible,
It is possible to provide a SAW filter having a high input / output terminal impedance.

First Modified Example

In the one-port SAW resonator according to this embodiment, the third and fourth interleaved widths of the first and second IDTs connected to the input terminal and the output terminal are divided and inserted.
Although the electrodes 43 and 44 are electrically connected by the short-circuit electrode 45, the present invention is not limited to this.

FIG. 2 schematically shows a planar structure of a one-port SAW resonator according to a first modification of the present invention. However, one port S in the present embodiment shown in FIG.
The same parts as those of the AW resonator are denoted by the same reference numerals, and description thereof will be omitted. The one-port SAW resonator according to the first modification is
The cross width W of each strip-shaped electrode in the direction perpendicular to the SAW propagation direction of the first and second IDTs 41 and 42 is divided into two, and unlike the conventional one-port SAW resonator shown in FIG. The electrodes are arranged so as not to cross each other. Further, the one-port SAW resonator according to the first modification is formed of an aluminum thin film or the like, and includes a third electrode 52 having a plurality of strip-shaped electrodes electrically connected to each other in a direction perpendicular to the SAW propagation direction. have. The third electrode 52 is electrically connected to a plurality of band-shaped electrodes at intermediate portions thereof via band-shaped electrodes arranged in parallel to the SAW propagation direction. Each strip-shaped electrode of the third electrode 52 has a first ID and a second ID.
Each of the strip-shaped electrodes T41 and T42 is alternately arranged.

In the first modified example of such a configuration, 1
In the port SAW resonator, when an electric signal is applied to the input terminal 48, the piezoelectric substrate 40 is distorted according to the voltage between the input terminal 48 and the output terminal 49. As a result of this distortion, the SAW excited by the first IDT 41 propagates on the piezoelectric substrate 40, and reaches the third electrode 52 that is disposed to face the first IDT 41 once. The third electrode 52 converts the reached SAW into an electric signal. And again, the third
From the portion of the electrode 52 facing the second IDT 42
Excite the AW. This SAW reaches the second IDT 42. The second IDT 42 uses the transmitted SAW
Is converted into an electric signal.

As described above, the one-port SAW resonator according to the first modification includes the first and second IDTs 41 and 42 in addition to the effects of the one-port SAW resonator according to the present embodiment.
Since the area occupied by the third electrode 52 for connecting the 42 in series can be further reduced, it is possible to contribute to, for example, miniaturization of the mobile communication terminal.

Second Modified Example

Although the one-port SAW resonator in the present embodiment and the first modification has been described as dividing the cross width W into two, the number of divisions is not limited to this. For example, when the cross width W is divided into N (N is a natural number of 2 or more), the impedance can be increased by N ² times. That is, as shown in FIG. 1 or FIG. 2, it is possible to realize a high impedance of N ² times without increasing the occupied area.

FIG. 3 schematically shows a planar structure of a one-port SAW resonator when the number of divisions is three in the second modification. However, the same portions as those of the one-port SAW resonator in the first modification shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. 1-port S in second modified example
In the AW resonator, first and second IDTs 53 and 54 formed of an aluminum thin film or the like and electrically insulated from each other are arranged on the upper surface of the piezoelectric substrate 40. Each of the first and second IDTs 53 and 54 has a plurality of strip-shaped electrode groups in a direction perpendicular to the SAW propagation direction,
These electrode groups are arranged in the form of a blind with one end electrically connected and the other end electrically insulated. First and second
IDTs 53 and 54 are arranged to face each other.

In the one-port SAW resonator according to the second modification, the cross width W of each strip-shaped electrode in the direction perpendicular to the SAW propagation direction of the first and second IDTs 53 and 54 is divided into three. Unlike the conventional one-port SAW resonator shown in FIG. 4, the electrodes are arranged so that the electrodes do not cross each other. The one-port SAW resonator according to the second modified example is formed of an aluminum thin film or the like, and has a plurality of strip-shaped electrodes electrically connected to each other in a direction perpendicular to the SAW propagation direction. It has electrodes 55 and 56.

The third electrode 55 is electrically connected to a plurality of strip-shaped electrodes at intermediate portions thereof through strip-shaped electrodes arranged in parallel to the SAW propagation direction. The fourth electrode 56 is electrically connected to a plurality of band-shaped electrodes at intermediate portions thereof via band-shaped electrodes arranged in parallel to the SAW propagation direction.
The strip-shaped electrodes of the third electrode 55 are alternately arranged with the strip-shaped electrodes of the first IDT 53 and the fourth electrode 56, each of which is shaped like an interdigital. Each strip-shaped electrode of the fourth electrode 56 is connected to the second IDT 54 and the third electrode 5.
5 are alternately arranged with the respective band-shaped electrodes provided in the respective interdigitated shapes.

In the one-port SAW resonator according to the second modification, the impedance is tripled by dividing the cross width W into three as shown in the equation (1), and these are connected in series to further reduce the impedance by three. By doubling, a one-port SAW resonator having a characteristic impedance of “9 × Z ₀ ” can be realized. That is, without increasing the area occupied as shown in FIG. 3, it is possible to realize a high impedance that 3 ^twice.

In the related art, the impedance can be increased by N times only by dividing the cross width W by N. However, as described above, the characteristic degradation cannot be avoided due to the effect of the diffraction effect. However, when trying to obtain the same N-fold impedance with the one-port SAW resonator in this embodiment,
It is possible to increase the impedance in the case N ² times the present embodiment, it is possible to reduce the number of divisions of overlap width W conventionally, in order to be able to reduce the characteristic deterioration due to the influence of conventionally diffraction effects Become.

In this embodiment and the first and second modifications, a so-called regular IDT in which the length of a plurality of band-shaped electrodes provided in an interdigital shape is equal has been described.
It is not limited to this. Even if the respective strip-shaped electrodes are not equal, it is expected that the same effect as described above can be obtained. That is, by dividing the crossing width of the opposing IDTs and connecting them in series by electrodes at predetermined intervals, it is possible to increase the occupied area and avoid deterioration in characteristics.
It is possible to realize a SAW resonator and a SAW filter compatible with realizing high impedance.

[0058]

As described above, according to the first aspect of the present invention, the widths of the first and second interdigital electrodes are divided, and they are opposed to each other at predetermined intervals. One or a plurality of third electrodes having interdigital electrodes arranged in such a manner as to be arranged, and arranged to face at least a predetermined interval with the interdigital electrodes of the first and second interdigital electrodes. Therefore, the impedance can be made twice as large as the number of divisions of the cross width in the same occupied area as in the related art. Therefore, even if the same impedance as that of the related art is realized, the number of divisions can be reduced, so that deterioration of characteristics due to the effect of the diffraction effect can be reduced as compared with the related art.

According to the second aspect of the present invention, a plurality of strip-shaped electrodes are arranged at a predetermined distance from the parallel electrodes of the interdigital transducers of the first and second interdigital electrodes. Since the third electrode is formed by electrically short-circuiting them at an intermediate portion thereof, an increase in occupied area when realizing high impedance can be further suppressed.

According to the third aspect of the present invention, a surface acoustic wave filter is formed by connecting the surface acoustic wave resonator according to the first aspect of the present invention to a ladder, so that the occupied area is the same as the conventional one. While maintaining the above, it is possible to realize a SAW filter having high input / output terminal impedance while suppressing characteristic deterioration.

According to the fourth aspect of the present invention,
In addition to the effect of the third aspect, the present invention can be applied as a parallel drive type filter that removes the influence of noise by separating the ground on the input / output side.

According to the fifth aspect of the present invention, the first
And a plurality of strip-shaped electrodes arranged at predetermined intervals with respect to the parallel electrodes of the interdigital transducers of the second interdigital electrode, and these are electrically short-circuited at an intermediate portion thereof to form the third electrode. Since the surface acoustic wave filter is configured by using the surface acoustic wave resonator in which the electrodes are formed, an increase in the occupied area when realizing a high impedance can be further suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a planar structure of a one-port SAW resonator according to an embodiment.

FIG. 2 is a schematic diagram showing a planar structure of a one-port SAW resonator according to a first modification.

FIG. 3 is a schematic diagram showing a planar structure of a one-port SAW resonator when a cross width is 3 in a second modified example.

FIG. 4A is a schematic view showing a planar structure of a conventional one-port SAW resonator. (B) is an explanatory view showing a symbol representing a one-port SAW resonator.

FIG. 5 shows a SA in which a one-port SAW resonator is ladder-connected.
FIG. 2 is a configuration diagram illustrating an outline of a configuration of a W filter.

FIG. 6 shows a SA in which a one-port SAW resonator is lattice-connected.
FIG. 2 is a configuration diagram illustrating an outline of a configuration of a W filter.

[Explanation of symbols]

 10, 40 Piezoelectric substrate 11, 41, 53 First IDT 12, 42, 54 Second IDT 13, 46 Input electrode 14, 47 Output electrode 15, 48 Input terminal 16, 49 Output terminal 17, 50 First reflection Device electrode 18, 51 second reflector electrode 19 crossover 20, 26 first SAW resonator 21, 27 first input terminal 22, 28 first output terminal 23, 29 second SAW resonator 24, REFERENCE SIGNS LIST 30 second input terminal 25, 31 second output terminal 32 third SAW resonator 33 fourth SAW resonator 43, 52, 55 third electrode 44, 56 fourth electrode 45 short-circuit electrode

Claims (5)

[Claims] 1. A flat-plate-shaped piezoelectric substrate, and first and second interdigitated electrodes each having one end of each of a plurality of parallel electrodes electrically short-circuited and disposed on the piezoelectric substrate. And interdigital transducers, and interdigital transducers arranged at predetermined intervals between the first and second interdigital transducers on the piezoelectric substrate, and each of the interdigital transducers has at least the first and second interdigital transducers. A surface acoustic wave resonator comprising: an interdigital transducer of a second interdigital electrode; and one or more third electrodes disposed to face each other at a predetermined interval. 2. The method according to claim 1, wherein the third electrode electrically short-circuits a plurality of strip-shaped electrodes arranged at a predetermined interval with respect to the parallel electrodes of the IDT. The surface acoustic wave resonator according to claim 1, wherein 3. A first piezoelectric substrate comprising: a plate-shaped piezoelectric substrate; and interdigital transducers each having one end of each of a plurality of parallel electrodes electrically short-circuited.
And a second interdigital electrode, and interdigital transducers arranged opposite to each other at a predetermined interval between the first and second interdigital electrodes on the piezoelectric substrate, respectively. A plurality of surface acoustic wave resonators having interdigital electrodes of the first and second interdigital electrodes and one or a plurality of third electrodes arranged to face each other at a predetermined interval; Wherein the surface acoustic wave resonators are connected in ladder. 4. The surface acoustic wave filter according to claim 3, wherein the plurality of surface acoustic wave resonators are connected in a lattice connection. 5. The method according to claim 1, wherein the third electrode electrically short-circuits a plurality of strip-shaped electrodes arranged at a predetermined interval with respect to the parallel electrodes of the interdigital transducer at an intermediate portion thereof. The surface acoustic wave filter according to claim 3 or 4, wherein