JP3250252B2 - Surface wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge reflection type surface acoustic wave device utilizing an SH type surface acoustic wave, and more particularly to a surface acoustic wave device having an improved interdigital transducer structure.

[0002]

2. Description of the Related Art BGS waves, Love waves, and the like are known as SH type surface waves whose displacement mainly consists of displacement in a direction perpendicular to the surface wave propagation direction. 2. Description of the Related Art An end surface reflection type surface wave resonator using a BGS wave has been conventionally known. As shown in the plan view of FIG. 2, an end-face reflection type surface acoustic wave resonator 1 utilizing a BGS wave has a pair of comb-shaped electrodes having a plurality of electrode fingers 3a and 4a interposed on a piezoelectric substrate 2. 3,4
Has a structure in which an interdigital transducer made of In the surface acoustic wave resonator 1, the excited surface wave is completely reflected between the opposite end faces 2 a and 2 b of the piezoelectric substrate 2. In the surface acoustic wave resonator 1 using the BGS wave of the end face reflection type, it is possible to provide a resonator that can be used in a high frequency region that cannot be obtained by a surface acoustic wave resonator using a Rayleigh wave.

Incidentally, surface acoustic wave resonators utilizing SH waves such as the above BGS waves include LiNbO ₃ and LiTaO.
₃ and a substrate using a piezoelectric substrate made of a material such as Pb (Ti _1-x Zr _x ) O ₃ have been reported. In consideration of cost, electromechanical coupling coefficient, and the like, these piezoelectric substrate materials have higher Pb (Ti) than LiNbO ₃ and LiTaO _3.
It is preferable to use a piezoelectric ceramic such as _1-x Zr _x ) O ₃ or lead titanate.

[0004]

However, Pb
(Ti _1-x Zr _x ) O ₃ has a large relative dielectric constant ε,
When a surface acoustic wave device is formed by forming a regular interdigital transducer, there is a problem that the capacitance C of the surface acoustic wave device becomes so large that it cannot be actually used, and a reduction in the capacitance is required. In order to reduce the capacitance of the surface acoustic wave resonator 1, it is conceivable to reduce the cross width of the interdigital transducer or reduce the logarithm of the electrode fingers 2a and 3a. However, these methods reduce the capacitance. There was a limit to what we could do.

On the other hand, a method of reducing the capacitance by dividing one interdigital electrode constituting the interdigital transducer into a plurality of interdigital electrodes and electrically connecting the divided electrodes in series can be considered. . For example,
When one of the comb electrodes is divided into two, the capacity of the surface acoustic wave device is greatly reduced to 1/4. However, when one comb electrode is simply divided into a plurality of comb electrodes, as shown in FIG. 3, when the number of electrode fingers is N on the impedance-frequency characteristic, 2N ± n
There is a problem that spurious vibration (waveform disturbance indicated by arrow A in FIG. 3) due to the higher-order mode occurs at the position (n is an even number).

Accordingly, an object of the present invention is to provide a high-order mode in a surface acoustic wave device using an SH type surface acoustic wave having a structure in which one interdigital electrode of an interdigital transducer is divided into a plurality of parts to reduce the capacitance. An object of the present invention is to provide a surface acoustic wave device having a configuration capable of effectively suppressing spurious vibration caused by the spurious vibration.

[0007]

Each of the inventions according to claims 1 to 4 of the present application is an edge-reflection type surface acoustic wave device utilizing an SH type surface acoustic wave, comprising: a piezoelectric substrate; And an interdigital transducer composed of a pair of comb-shaped electrodes having a plurality of electrode fingers interposed between each other. According to the first aspect of the present invention, in the surface wave propagation direction, the
In order to arrange multiple epicenters with epicenter number a on each side,
One interdigital electrode of the interdigital transducer is divided into first and second interdigital electrodes that are not connected to each other, and the number N of electrode fingers of the interdigital transducer is 8.5 or more and 45 or less. The range is.

According to the second aspect of the present invention, in the surface wave propagation direction, a plurality of hypocenters having the number of hypocenters a are arranged on both sides around a hypocenter * to which a voltage twice as large as the remaining hypocenter is applied. As a result, one interdigital electrode of the interdigital transducer is divided into first and second interdigital electrodes that are not connected to each other, and the logarithm N of the electrode fingers of the interdigital transducer is 7.
It is in the range of 5 or more and 45 or less.

According to the third aspect of the present invention, in the surface wave propagation direction, the plurality of hypocenters are located at the center of the plurality of hypocenters, and the hypocenters of the epicenter number b are arranged on both sides of the hypocenters. One interdigital electrode of the interdigital transducer is divided into first to third interdigital electrodes that are not connected to each other, and the number N of electrode fingers of the interdigital transducer is not less than 7.0 and not more than 60. Range.

Further, in the invention according to the fourth aspect, in the direction of propagation of the surface wave, a plurality of epicenters having a number of epicenters b is centered, and a voltage twice as large as each epicenter of the number of epicenters b is applied to both sides thereof. One interdigital transducer of the interdigital transducer is divided into three so as to have first to third interdigital electrodes that are not connected to each other so that epicenters having the epicenter number b are arranged with the * interposed therebetween. In addition, the logarithm N of the electrode fingers of the interdigital transducer is not less than 7.0 and not more than 60.

[0011]

The present inventors provide a surface acoustic wave device utilizing the above-mentioned SH type surface acoustic wave, wherein one of a plurality of interdigital electrodes constituting an interdigital transducer is provided. In the structure divided into individual comb electrodes, as a result of studying to suppress spurious vibrations caused by higher-order modes, the method of dividing the comb electrodes was devised, and the logarithm of the electrode fingers was determined according to the division method. It has been found that the above-mentioned problem can be achieved by selecting a specific range. That is, as will be apparent from the embodiment described later, the invention according to claim 1 has a structure in which one comb electrode is divided into two, and an equal number of hypocenters are arranged on both sides of the zero hypocenter. In this case, the logarithm N of the electrode fingers of the interdigital transducer is 8.5 or more,
By setting it to 45 or less, it is possible to suppress spurious vibration caused by the higher-order mode by 24 dB or more.

Further, as in the second aspect of the present invention, one of the interdigital electrodes is divided into two parts, and the number of hypocenters a is located on both sides around a hypocenter * to which a voltage twice as large as the remaining hypocenter is applied. In the structure in which the epicenter is arranged, by setting the logarithm N of the electrode fingers of the interdigital transducer to be not less than 7.5 and not more than 45, the spurious vibration caused by the higher mode is reduced by 24d.
B or more can be suppressed.

Further, as in the invention according to claim 3,
In a structure in which one of the interdigital electrodes is divided into three, the arrangement of the epicenters is arranged along the direction of surface wave propagation, with a source having a source number b, a zero source, a source having a source number b, a zero source, and a plurality of sources having a source number b. In this case, by setting the number of pairs of electrode fingers of the interdigital transducer to be 7.0 or more and 60 or less, it becomes possible to suppress spurious vibration caused by the higher-order mode by 24 dB or more.

According to the fourth aspect of the present invention, in the structure in which one of the comb electrodes is divided into three, the arrangement of the epicenters is determined along the propagation direction of the surface wave by a plurality of epicenters-b In the case where there are hypocenters to which a voltage twice as large as each epicenter b is applied * -a plurality of epicenters of epicenter number b- epicenters * -a plurality of epicenters of epicenter number b, the logarithm of the electrode finger of the interdigital transducer is 7 If it is set to be equal to or more than 0.0 and equal to or less than 60, spurious vibration caused by the higher-order mode can be suppressed by 24 dB or more.

That is, according to the first to fourth aspects of the present invention, in a configuration in which one of the interdigital transducers constituting the interdigital transducer is divided into two or three, the number of pairs of electrode fingers depends on the arrangement of the epicenter. If N is selected in the above specific range, spurious vibrations caused by higher-order modes can be suppressed by 24 dB or more, and one interdigital electrode of the interdigital transducer is divided into a plurality of interdigital electrodes as described above. Therefore, the capacity of the surface acoustic wave device is also effectively reduced. Therefore, it is possible to provide a surface acoustic wave device that can be used in a high frequency band by using a piezoelectric ceramic such as a lead zirconate titanate-based ceramic which is advantageous in terms of an electromechanical coupling coefficient and cost.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 (a) and 1 (b) are a plan view and a sectional view showing an embodiment of the surface acoustic wave device according to the first aspect of the present invention. The surface acoustic wave device 11 has a structure in which comb electrodes 13 to 15 are formed on a rectangular piezoelectric substrate 12. Comb electrode 13 has a plurality of electrode fingers 13a,
The piezoelectric substrate 12 is formed in a region from the end faces 12a to 12b. On the other hand, the comb electrodes 14 and 15 correspond to the first and second comb electrodes of the present invention, and the plurality of electrode fingers 14 interposed with the electrode fingers 13a of the comb electrode 13 respectively.
a and 15a. Each of the electrode fingers 13a to 15a of the comb electrodes 13 to 15 has a width of λ / 8 at both ends of the comb electrode 13 when the wavelength of the surface wave is λ. The width of the remaining electrode fingers is all λ / 4, and the width of the gap between the plurality of electrode fingers is also λ / 4.
It has been.

In the surface acoustic wave device 11 of the first embodiment, as shown in FIG.
Since the electrode fingers 13a ₁ and 13a ₂ are arranged adjacent to each other, as shown in FIG. 4, the comb electrode 13 is virtually set to the ground potential and an AC voltage is applied between the comb electrodes 14 and 15. The arrangement of the epicenter of the excited surface wave is as follows. That is, when the total number of electrode fingers of the comb electrodes 14 and 15 is n ₁ (n ₁ is an even number because the electrodes 14 and 15 are symmetrical), along the surface wave propagation direction, (n ₁
/ 2-1 Number of epicenter) - it becomes (number of source of n ₁ / 2-1) that is disposed - (zero epicenter). That is, when the number of hypocenters (n ₁ / 2-1) in the portion where the comb electrodes 14 and 15 are formed is a, along the propagation direction of the surface wave, (the number of hypocenters) − (zero hypocenter) )-(The number of epicenters of a) will be arranged.

In the first embodiment, in the surface acoustic wave device 11 having a structure in which a plurality of hypocenters are arranged as described above, the logarithm N of the electrode fingers of the interdigital transducer is 8.5.
As described above, the range of 45 or less is selected, whereby the spurious vibration caused by the higher-order mode is suppressed as described above. This will be described with reference to FIGS. In the surface acoustic wave device 11 shown in FIG. 1, the attenuation curve when the logarithm N of the electrode fingers of the interdigital transducer is N = 4.5 is shown in FIG. 5, and the attenuation curve when N = 15.5 is shown in FIG. The frequency curve is shown in FIG.

As is clear from FIG. 5, the logarithm of the electrode finger =
In the case of 4.5, 2N ± determined by the length of the piezoelectric substrate 12
n (where n is an even number) higher-order mode frequency positions
Do not match. For example, the frequency position of 2N-2 in FIG.
Between the virtual straight line and the attenuation-frequency curve
The attenuation pole must be located on the high frequency region side
I understand. In other words, the 2N-2 higher mode
And the amount of attenuation is as small as 20 dB or less.
You can see that the mode resonance appears as spurious vibration
You. Similarly, in other higher order modes of 2 ± n,
B₁, B_Two, B_Three, B _Four, B_FiveIs shifted from the attenuation pole
Located at several positions, so the attenuation is less than 20 dB
It turns out that it is small.

On the other hand, as is apparent from FIG.
When the logarithm N of the electrode fingers is 15.5, the point C where the virtual straight line extending upward from the frequency position of 2N-2 and the attenuation-frequency curve intersects is located almost near the attenuation pole. . Therefore, the amount of attenuation at the frequency position 2N-2 is 2
It turns out that it is as large as 9 dB or more. Similarly, at other frequency positions of higher-order modes, the attenuation is as large as 29 dB or more, as is apparent from the points C _{1 to} C ₅ .
As described above, it is understood that spurious vibration caused by a higher-order mode of the surface wave can be suppressed by changing the logarithm N of the electrode fingers of the interdigital transducer. Therefore, the present inventors set the logarithm N of the electrode fingers to 4.5.
From 15.5, and the attenuation at the frequency position of the resonance point of the higher-order mode of 2N ± 2, 2N ± 4 and 2N ± 6 was measured. The results are shown in Table 1 and FIG.

[0021]

[Table 1]

As is clear from Table 1 and FIG. 7, in the surface acoustic wave device having the two-divided interdigital transducer having the arrangement of source number a-zero source-source number a,
It was found that when the logarithm N of the electrode fingers changed from 7.5 to 8.5, the attenuation at the frequency position of 2N ± 2 at which the largest spurious vibration was generated increased, and exceeded 25 dB. Therefore, according to the first aspect of the present invention, it is understood that the logarithm N of the electrode fingers needs to be 8.5 or more.

It should be noted that as the logarithm N of the electrode fingers increases, the spurious vibration caused by the higher-order mode can be suppressed. However, when N exceeds 45, the capacity increases and a two-part comb-shaped electrode is provided. The capacity reduction effect when the interdigital transducer is configured is lost. Therefore,
According to the first aspect of the present invention, the logarithm N of the electrode fingers is set to 8.5 to 8.5.
It is necessary to select within the range of 45, whereby spurious vibration caused by the higher-order mode can be effectively suppressed while reducing the capacity.

Second Embodiment FIG. 8 is a plan view showing a surface acoustic wave device according to a second embodiment of the present invention. The surface acoustic wave device 21 has a structure in which comb electrodes 23, 24, and 25 are formed on a rectangular piezoelectric substrate 22. A plurality of electrode fingers 23a of the comb electrode 23
The plurality of electrode fingers 24a and 25a of the first and second comb electrodes 24 and 25 obtained by dividing the comb electrode interposed with the comb electrode 23 into two parts are arranged so as to be interleaved alternately. ing. Then, in the second embodiment, the electrode fingers 24a ₁ located at the end of the comb electrode 25 side of the electrode fingers 24a of the comb-shaped electrodes 24, comb-shaped electrodes of the comb electrode 25 24
And the electrode fingers 25a ₁ which is located at the end of the side is at a clearance of 4 / lambda are adjacently disposed.

Accordingly, in the surface acoustic wave device 21 of the second embodiment,
Are comb electrodes 23, first and second comb electrodes 24,
Assuming that the number of epicenters composed of 25 and a is each a,
A number of source-electrode fingers 24a along the surface wave propagation direction
₁And electrode finger 25a₁Earthquakes of epicenter number * -a composed of
The source will be located. The epicenter * is the electrode finger 24a ₁
And electrode finger 25a₁And is composed of
Voltages of different polarities were applied between the comb electrodes 24 and 25
In the case, the source is applied twice the voltage compared to the rest
Becomes In the surface acoustic wave device 21 of the second embodiment,
The logarithm N of all electrode fingers of the
As in the case of the first embodiment, the range is 4.5 to 15.5.
And the frequency position at which spurs occur is 2
Attenuation at resonance point of higher order mode of N ± n (n is an even number)
The amount was measured. The results are shown in Table 2 and FIG.

[0026]

[Table 2]

As is clear from Table 2 and FIG. 9, in the surface acoustic wave device 21 of the second embodiment, the logarithm N of the electrode fingers is N = 7.5.
From the above, it can be seen that the attenuation amount sharply increases and exceeds 25 dB at 2N ± 2, 2N ± 4. Therefore, in the surface acoustic wave device 21 in which the epicenter of the epicenter number a is located along the epicenter of the epicenter number a along the propagation direction of the surface wave, the logarithm N of the electrode fingers needs to be 7.5 or more. . On the other hand, as in the case of the first embodiment, when the number of pairs of electrode fingers exceeds 45, the capacity of the surface acoustic wave device 21 increases, and the capacity reduction effect of forming the split type comb electrode is impaired. Therefore, claim 2
In the invention described in (1), the logarithm N of the electrode fingers needs to be in the range of 7.5 to 45.

Third Embodiment FIG. 10 is a schematic plan view for explaining the structure of an interdigital transducer in a surface acoustic wave device 31 according to a third embodiment of the present invention. In the surface acoustic wave device 31 of this embodiment, interdigital transducers are formed by forming comb electrodes 33 to 36 on a rectangular piezoelectric substrate (not shown). Comb electrode 33
Of the plurality of electrode fingers 33a are the first to third comb-shaped electrodes 3
The electrode fingers 34a, 35a, and 36a are disposed so as to be interposed with each other. In addition, the comb electrode 33
Each of the electrode fingers 33a ₁ and 33a ₂ at both ends has a width of 8 / λ when the wavelength of the surface wave is λ, and the remaining electrode fingers have a width of 4 / λ. The width of the gap between all the electrode fingers is set to 4 / λ. Further, since the surface wave device is of the end-face reflection type, the electrode fingers 33a at both ends are used.
_1, 33a ₂ is formed along the edge of the piezoelectric substrate.

In the third embodiment, the numbers of hypocenters constituted by the first to third comb-shaped electrodes 34 to 36 and the comb-shaped electrode 33 are made equal, and the number of hypocenters is assumed to be b. . Moreover, 33a ₃ and the electrode fingers between the epicenter constituted by the comb electrodes 33 and Source constituted by a first comb electrode 34, the comb electrode 33 and the second comb-shaped electrodes 35 zero epicenter is arranged constituted by the 33a _4. Similarly, electrode fingers 33a between comb electrodes 35 and 36 _5, 33
zero Source constituted by a ₆ is arranged. Therefore, along the direction of propagation of the surface wave, the hypocenter-zero hypocenter-b
The epicenters of the number of epicenters-zero epicenter-b epicenters will be arranged. Also in the surface acoustic wave device 31, since the other comb-shaped electrode interposed between the comb-shaped electrodes 33 as described above is divided into the first to third comb-shaped electrodes 34 to 36, the capacitance of the surface acoustic wave device is increased. Is effectively reduced. And
In the surface acoustic wave device 31, the attenuation N at the frequency position of the resonance point of the higher-order mode of 2N ± n (n is an even number) was measured while changing the logarithm N of the electrode fingers in the range of 4 to 11.5. The results are shown in Table 3 and FIG.

[0030]

[Table 3]

As is clear from Table 3 and FIG. 11, by setting the logarithm N of the electrode fingers to 7.0 or more, the largest spurious vibration, that is, the spurious vibration appearing at the frequency position of 2N ± 2, is suppressed by 24 dB or more. It turns out that it gets. Therefore, in the third embodiment, the logarithm N of the electrode fingers is set to 7.0.
It is necessary to do the above. On the other hand, when the number N of electrode fingers exceeds 60 in the surface acoustic wave device 31, the capacitance increases, and the capacitance reduction effect using the three-part comb-shaped electrode is impaired. Therefore, in the invention described in claim 3, it is necessary to set the logarithm N of the electrode fingers in the range of 7.0 to 60.

Fourth Embodiment FIG. 12 is a schematic plan view showing the structure of an interdigital transducer of a surface acoustic wave device 41 according to a fourth embodiment of the present invention. A comb-shaped electrode 43 and first to third comb-shaped electrodes 44 are formed on a rectangular piezoelectric substrate (not shown).
To 46 are formed. The plurality of electrode fingers 43a of the comb electrode 43 are arranged so as to be interposed with the plurality of electrode fingers 44a to 46a of the comb electrodes 44 to 46, respectively. In the surface acoustic wave device 41 of the fourth embodiment, the electrode fingers 44a ₁ of the inner end of the first comb electrode 44, the second
It is adjacently disposed first electrode finger 45a _one end of the comb electrode 44 side of the comb electrode 45 at a gap of 4 / lambda. Similarly, the third comb electrodes 46 side electrode fingers 45a ₂ located at the end of the second comb electrode 45, and the electrode fingers 46a ₁ of the inner end of the third comb electrodes 46 4 They are arranged with a gap having a width of / λ.

Therefore, a double voltage is applied to the epicenter between the electrode fingers 44a ₁ and 45a ₁ and between the epicenters between the electrode fingers 45a ₂ and 46a ₁ as compared with the epicenter formed by the remaining electrode fingers. Between the electrode fingers 44a ₁ and 45a ₁ and 45a
The epicenter composed of between _2, 46a ₁ and epicenter *, first to
Each of the third comb electrodes 44 to 46 is a comb electrode 4
Assuming that the epicenter has a hypocenter number of 3 and a hypocenter number b, the surface acoustic wave device 41 of this embodiment has a hypocenter number of epicenter number b and an epicenter number of epicenter number b along the surface wave propagation direction. * -B epicenters with the number of epicenters are located. In the surface acoustic wave device 41 of the fourth embodiment, the attenuation N at the frequency position of the resonance point of 2N ± n (n is an even number) was measured while changing the logarithm N of the electrode fingers in the range of 4 to 11.5. . The results are shown in Table 4 and FIG.

[0034]

[Table 4]

As is apparent from Table 4 and FIG. 13, when the logarithm N of the electrode fingers is equal to or greater than 7.0, the attenuation at the frequency position of 2N ± 2 at which the largest spurious vibration occurs exceeds 24 dB. On the other hand, also in the fourth embodiment, when the logarithm N of the electrode fingers exceeds 60, the capacity increases, and one of the comb electrodes is replaced with the first to third comb electrodes 34.
The capacity reduction effect due to the division into 36 is impaired. Therefore, it is understood that the logarithm N of the electrode fingers needs to be in the range of 7.0 to 60.

[Brief description of the drawings]

FIGS. 1A and 1B are a plan view and a cross-sectional view taken along line BB for explaining a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is a plan view illustrating a conventional surface acoustic wave device.

FIG. 3 is a diagram showing impedance-frequency characteristics in a conventional surface acoustic wave device.

FIG. 4 is a schematic plan view for explaining an interdigital transducer in the surface acoustic wave device according to the first embodiment.

FIG. 5 is a diagram showing attenuation-frequency characteristics when the logarithm N of electrode fingers is 4.5.

FIG. 6 is a diagram showing attenuation-frequency characteristics when the logarithm N of electrode fingers is N = 15.5.

FIG. 7 is a diagram showing a change in attenuation when the number N of electrode fingers is changed in the first embodiment.

FIG. 8 is a plan view illustrating a surface acoustic wave device according to a second embodiment.

FIG. 9 is a diagram showing a change in attenuation when the logarithm N of electrode fingers is changed in the second embodiment.

FIG. 10 is a diagram showing a structure of an interdigital transducer of the surface acoustic wave device according to the third embodiment.

FIG. 11 is a diagram showing a change in the amount of attenuation when the number of electrode fingers is changed in the third embodiment.

FIG. 12 is a schematic plan view showing a structure of an interdigital transducer in a surface acoustic wave device according to a fourth embodiment.

FIG. 13 is a diagram showing a change in attenuation when the logarithm N of the electrode finger is changed in the fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Surface acoustic wave device 12 ... Piezoelectric substrate 12a, 12b ... End surface 13 ... Comb electrode 14 ... 1st comb electrode 15 ... 2nd comb electrode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03H 9/145 H03H 9/17

Claims (4)

(57) [Claims] An end reflection type surface acoustic wave device utilizing an SH type surface wave, comprising: a piezoelectric substrate; and a pair of electrode fingers formed on the piezoelectric substrate and having a plurality of electrode fingers interposed between each other. An interdigital transducer comprising a comb electrode, wherein one of the interdigital transducers of the interdigital transducer is arranged such that a plurality of epicenters having a number of epicenters are arranged on both sides of the zero epicenter in the surface wave propagation direction. But,
The surface is divided into first and second comb-shaped electrodes that are not connected to each other, and a logarithm N of electrode fingers of the interdigital transducer ranges from 8.5 to 45. Wave device. 2. An end surface reflection type surface acoustic wave device utilizing an SH type surface wave, comprising: a piezoelectric substrate; and a pair of electrode fingers formed on the piezoelectric substrate and having a plurality of electrode fingers interposed between each other. An interdigital transducer comprising a comb electrode is provided. In the surface wave propagation direction, a plurality of epicenters having the number of epicenters a are arranged on both sides of the epicenter, to which a voltage twice as large as the remaining epicenter is applied. As described above, one interdigital electrode of the interdigital transducer is divided into first and second interdigital electrodes that are not connected to each other, and the logarithm N of the electrode fingers of the interdigital transducer is 7.5. As described above, the surface acoustic wave device has a range of 45 or less. 3. An end surface reflection type surface acoustic wave device utilizing an SH type surface wave, comprising: a piezoelectric substrate; and a pair of electrode fingers formed on the piezoelectric substrate and having a plurality of electrode fingers interposed between each other. An interdigital transducer comprising a comb electrode is provided. In the surface wave propagation direction, a plurality of epicenters of the number b of the epicenters are arranged on both sides of the epicenter with the epicenter of the number of the epicenters b interposed therebetween. In addition, one of the interdigital transducers is divided into three so as to have first to third interdigital electrodes that are not connected to each other, and the number N of electrode fingers of the interdigital transducer is N. A surface acoustic wave device characterized by being at least 7.0 and at most 60. 4. An end surface reflection type surface acoustic wave device using an SH type surface wave, comprising: a piezoelectric substrate; and a pair of electrode fingers formed on the piezoelectric substrate and having a plurality of electrode fingers interposed between each other. An interdigital transducer comprising a comb electrode is provided. In the direction of surface wave propagation, a hypocenter * is applied to each of a plurality of epicenters having the number of epicenters b, and a voltage twice as large as each epicenter of the number of epicenters b is applied to both sides thereof. One interdigital electrode of the interdigital transducer is divided so as to have first to third interdigital electrodes that are not connected to each other so that a plurality of epicenters having the number of epicenters b are arranged therebetween. And the logarithm N of the electrode fingers of the interdigital transducer
Is in the range of 7.0 or more and 60 or less.