JP2001053581A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the surface acoustic wave filter of a wide pass band pro vided with flatness and provided with steep attenuation characteristics near the pass band, even at the time of being miniaturized. SOLUTION: First and second filter tracks 12 and 13 are constituted in parallel on a piezoelectric substrate 11 and input IDT-(interdigital transducer) electrodes 14 and 16 and output IDT electrodes 15 and 17 are respectively provided. Also, the input IDT electrode 14 and the input IDT electrode 16 are connected electrically in parallel, and the output IDT electrode 15 and the output IDT electrode 17 are connected electrically in parallel. Then, for the phase difference of the first and second filter tracks 12 and 13, they are the almost same phase within the pass band and the almost opposite phase on the outside of the pass band. Furthermore, the frequencies of (maximum valu-3 dB) of the transmission function of the first and second filter tracks 12 and 13 are almost matched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter used for a high frequency circuit or the like in a wireless communication device.

[0002]

2. Description of the Related Art IFs for CDMA that have recently attracted attention
When it is important that the passband is wide and the flatness of the phase characteristics in the passband and the attenuation characteristics near the passband are important, as in a filter, a transversal that can independently design the amplitude and phase characteristics Surface acoustic wave filters of the type are suitable.

A conventional transversal type surface acoustic wave filter will be described below with reference to FIG. FIG.
In the figure, reference numeral 301 denotes a single-crystal piezoelectric substrate on which output interdigital transducer electrodes (hereinafter referred to as IDT electrodes) 302 and 303 are formed at predetermined intervals.

[0004] As shown in FIG.
By performing weighting by thinning out the electrode fingers 02 and 303, a wide and flat pass band and excellent attenuation characteristics near the pass band are realized.

[0005]

In recent years, portable terminals have been reduced in size and weight, and accordingly, the surface acoustic wave filters at the IF stage have also been required to be reduced in size.

However, when the surface acoustic wave filter is reduced in size, the input and output IDT electrodes cannot be sufficiently weighted, and a desired characteristic cannot be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface acoustic wave filter having a wide pass band, flatness, and a steep attenuation characteristic near the pass band even if the size is reduced.

[0008]

To achieve this object, a surface acoustic wave filter according to the present invention comprises a piezoelectric substrate and first and second filters having input and output IDT electrodes formed on the piezoelectric substrate. Tracks, the first and second filter tracks being substantially in phase within the passband,
Outside the pass band, the phases are almost opposite, and the input IDT electrode of the first filter track and the input IT of the second filter track
DT electrodes are connected in parallel, and an output IDT electrode of the first filter track and an output IDT electrode of the second filter track are connected in parallel.
(Maximum value −3 dB) of the transfer function of the filter track of FIG. 3 is almost the same, the passband is made in-phase, and the frequency of the (maximum value −3 dB) is almost the same, so that a flat passband is obtained. As a result, since the phases outside the pass band are reversed to cancel each other, each of the filter tracks has an attenuation characteristic that is equal to or greater than the attenuation characteristic of each filter track, so that the above object can be achieved.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The invention as set forth in claim 1 of the present invention comprises a piezoelectric substrate and first and second filter tracks having input and output IDT electrodes formed on the piezoelectric substrate. The first and second filter tracks have substantially the same phase within the pass band and substantially opposite phases outside the pass band, and the input IDT electrodes of the first and second filter tracks are connected in parallel. The output IDT electrode of the first filter track and the output IDT electrode of the second filter track are connected in parallel, and the frequency of the transfer function (maximum value −3 dB) of the first and second filter tracks is changed. The surface acoustic wave filters have almost the same characteristics, and have flatness of a pass band and steep attenuation characteristics near the pass band.

The invention according to claim 2 is an input / output IDT.
2. The surface acoustic wave filter according to claim 1, wherein at least one of the electrodes is a unidirectional electrode, and the insertion loss can be reduced.

According to a third aspect of the present invention, there is provided an electrode in which the direction is enhanced in at least one region of the unidirectional electrode, and the direction opposite to the direction is enhanced in at least one other region. The surface acoustic wave filter according to claim 2, wherein a finger is arranged, and the IDT electrode has desired characteristics even if the length of the IDT electrode is shortened, that is, even if the IDT electrode is reduced in size.

According to a fourth aspect of the present invention, there is provided the surface acoustic wave filter according to the second aspect, wherein the metallization ratio is 0.45 to 0.65. As a result, ripples in the pass band due to insufficient directionality or conversely excessive directionality are suppressed, and the flatness in the pass band is excellent.

The invention according to claim 5 is an input / output IDT.
At least one of the electrodes has four electrode fingers within one wavelength, and has electrode finger pairs of different line widths intersecting in at least a part of the area, and the thin electrode finger lines of this electrode finger pair are provided. The surface acoustic wave filter according to claim 2, wherein a line width ratio (L2 / L1) of the width (L1) and the line width (L2) of the thick electrode finger is larger than 1. Also, by optimizing the excitation efficiency, the insertion loss can be reduced.

According to a sixth aspect of the present invention, there is provided an input / output IDT.
The surface acoustic wave filter according to claim 5, wherein the line width ratios of the electrodes are different, and the directionality of the surface acoustic wave is controlled by optimizing the input and output IDT electrodes for each of the electrodes. Ripple in the pass band due to excessive directivity or the like is suppressed, and the flatness in the pass band is excellent.

According to a seventh aspect of the present invention, there is provided the surface acoustic wave filter according to the fifth aspect, wherein the electrode finger pairs composed of electrode fingers having different line widths satisfy Expression (5). Ripple in the pass band is suppressed and the flatness is excellent, and the symmetry near the pass band is improved, so that the attenuation characteristics are excellent.

[0016]

(Equation 5)

According to the invention described in claim 8, at least two pairs of electrode fingers having electrode fingers having different line widths are provided.
The surface acoustic wave filter according to claim 5, wherein at least one pair of the electrode finger pairs satisfies (Equation 6) and the other satisfies (Equation 6), and has a small ripple and excellent flatness in a pass band. It is a thing.

[0018]

(Equation 6)

According to a ninth aspect of the present invention, there is provided the surface acoustic wave filter according to the eighth aspect, wherein the electrode finger pairs satisfying (Equation 6) and (Equation 6) are substantially equal in number. , The ripples in the pass band due to insufficient or excessive directionality are suppressed, and the flatness in the pass band is excellent.

According to a tenth aspect of the present invention, in the adjacent electrode finger pairs, one of the electrode finger pairs satisfies (Equation 6) and the other satisfies (Equation 6). This is a filter that controls the unidirectionality of the surface acoustic wave, suppresses ripples in the passband due to insufficient or excessive directivity, and has excellent flatness in the passband.

According to the eleventh aspect of the present invention, the electrode finger is formed of a metal containing aluminum as a main component, and the thickness ratio (h / λ) of the electrode finger thickness h to the wavelength λ of the surface acoustic wave is increased. The surface acoustic wave filter according to claim 2, wherein the surface acoustic wave filter has a value of 0.005 to 0.035, and controls one direction of the surface acoustic wave.
Ripple in the pass band due to insufficient directionality or excessive directionality is suppressed, and the flatness in the pass band is excellent.

According to a twelfth aspect of the present invention, the piezoelectric substrate has two piezoelectric substrates.
2. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is formed using a quartz substrate having a Y-cut of 8 ° to 42 ° rotation, and has a small frequency drift in a required operating temperature range.

According to a thirteenth aspect of the present invention, there is provided a piezoelectric substrate comprising:
First and second filter tracks having input and output IDT electrodes formed on the piezoelectric substrate, wherein the first and second filter tracks are substantially in phase within the pass band and substantially opposite phase outside the pass band. The input IDT electrode of the first filter track and the input IDT electrode of the second filter track are connected in parallel, and the output IDT electrode of the first filter track and the output IDT electrode of the second filter track are connected to each other. Are connected in parallel, and the center frequencies of the first and second filter tracks are substantially matched, and the pass bandwidth of the first filter track is larger than the pass bandwidth of the second filter track. Surface acoustic wave filter that has a wide pass band even if it is miniaturized, has flatness, and is close to the pass band. And it has a Shun attenuation characteristics.

The invention according to claim 14 is an input / output ID
14. The surface acoustic wave filter according to claim 13, wherein at least one of the T electrodes is a unidirectional electrode, wherein the insertion loss is small.

According to a fifteenth aspect of the present invention, there is provided an electrode in which the direction is enhanced in at least one region of the unidirectional electrode, and the direction opposite to the direction is enhanced in at least one other region. The surface acoustic wave filter according to claim 14, wherein a finger is arranged, and the IDT electrode has desired characteristics even if the length of the IDT electrode is shortened, that is, even if the IDT electrode is reduced in size.

According to a sixteenth aspect of the present invention, there is provided the surface acoustic wave filter according to the fourteenth aspect, wherein the metallization ratio is 0.45 to 0.65. Can suppress ripples in the passband due to insufficient directionality or conversely excessive directionality,
The flatness in the pass band is excellent.

The invention according to claim 17 is an input / output ID
At least one of the T electrodes has four electrode fingers within one wavelength, and has electrode finger pairs having different line widths in at least a part of the intersecting regions. 15. The surface acoustic wave filter according to claim 14, wherein the line width ratio (L2 / L1) of the line width (L1) and the line width (L2) of the thick electrode finger is larger than 1. In addition, by optimizing the excitation efficiency, the insertion loss can be reduced.

The invention according to claim 18 is an input / output ID
18. The surface acoustic wave filter according to claim 17, wherein the line width ratios of the T electrodes are different from each other, and the unidirectionality of the surface acoustic wave is controlled by optimizing the input and output IDT electrodes for each electrode. Ripple in the pass band due to excessive directivity or excessive directivity is suppressed, and the flatness in the pass band is excellent.

According to a nineteenth aspect of the present invention, there is provided the surface acoustic wave filter according to the seventeenth aspect, wherein the electrode finger pairs formed of the electrode fingers having different line widths satisfy Expression (5).
Further, ripples in the pass band are suppressed, and the flatness is excellent, and the symmetry in the vicinity of the pass band is improved, so that the attenuation characteristics are excellent.

According to a twentieth aspect of the present invention, at least two pairs of electrode fingers each having an electrode finger having a different line width are provided, and at least one pair of the electrode finger pairs satisfies (Equation 6), and the others satisfy (Equation 6). Claim 17 which satisfies 6).
Wherein the surface acoustic wave filter has a small ripple and excellent flatness in a pass band.

According to a twenty-first aspect of the present invention, there is provided the surface acoustic wave filter according to the twentieth aspect, wherein the electrode finger pairs satisfying (Equation 6) and (Equation 6) are substantially equal in number. , The ripples in the pass band due to insufficient or excessive directionality are suppressed, and the flatness in the pass band is excellent.

According to a twenty-second aspect of the present invention, the surface acoustic wave according to the twentieth aspect, wherein one of the adjacent electrode finger pairs satisfies the expression (6) and the other satisfies the expression (6). This is a filter that controls the unidirectionality of the surface acoustic wave, suppresses ripples in the passband due to insufficient or excessive directivity, and has excellent flatness in the passband.

According to a twenty-third aspect of the present invention, the electrode fingers are formed of a metal containing aluminum as a main component, and the thickness ratio (h / λ) of the electrode finger thickness h to the wavelength λ of the surface acoustic wave is increased. The surface acoustic wave filter according to claim 14, which is 0.005 to 0.035, controls one direction of the surface acoustic wave, and causes ripple in a pass band due to insufficient direction or excessive direction. And has excellent flatness in the pass band.

According to a twenty-fourth aspect of the present invention, the piezoelectric substrate has two piezoelectric substrates.
14. The surface acoustic wave filter according to claim 13, wherein the surface acoustic wave filter is formed using an 8 ° to 42 ° rotated Y-cut quartz substrate, and has a small frequency drift in a required operating temperature range.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that each filter track is surrounded by a dotted line so that the configuration of the filter track can be easily understood.

(Embodiment 1) FIG. 1 is a top view of a surface acoustic wave filter according to Embodiment 1 of the present invention. FIG.
As shown in FIG. 1, a first filter track 12 and a second filter track 13 are arranged in parallel on a piezoelectric substrate 11 formed using a quartz substrate having a Y-cut rotated by 28 ° to 42 °. 1 filter track 12 is an input ID
It has a T electrode 14 and an output IDT electrode 15. Similarly, the second filter track 13 has an input IDT electrode 16 and an output IDT electrode 17.

The input IDT electrode 14 of the first filter track 12 and the input I
The DT electrodes 16 are electrically connected in parallel, and the output IDT electrodes 15 of the first filter track 12 and the output IDT electrodes 17 of the second filter track 13 are electrically connected in parallel.

The operation of the surface acoustic wave filter configured as described above will be described below.

FIG. 2A shows the amplitude characteristic 21 of the first filter track 12 and the amplitude characteristic 22 of the second filter track 13 in FIG. 1, and FIG.
3 shows a phase characteristic 23 of the filter track 12 and a phase characteristic 24 of the second filter track 13.

As shown in FIG. 2B, in the pass band, the phase difference between the first filter track 12 and the second filter track 13 is almost 0 °, that is, almost the same phase. Substantially the same phase is a phase difference in the range of −50 ° to + 50 °, preferably −20 ° to + 20 °.

Outside the pass band, the phase difference between the first filter track 12 and the second filter track 13 is almost 180 °, that is, almost opposite in phase. Substantially opposite phase means 130 ° to 230 °, preferably 160 °
The phase difference is within the range of 200 °.

As shown in FIG. 2A, the amplitude characteristic 21 of the first filter track 12 has two peaks, has a wide pass band, but has a large insertion loss near the center frequency. On the other hand, the amplitude characteristic 22 of the second filter track 13 has a peak near the center frequency and low insertion loss, but has a narrow pass bandwidth.

Here, the first filter track 12 and the second
Since the filter track 13 has substantially the same phase in the pass band, a flat and wide pass bandwidth can be obtained by electrically connecting them in parallel.

In both the amplitude characteristic 21 of the first filter track 12 and the amplitude characteristic 22 of the second filter track 13, the spurious level outside the pass band is not so much suppressed. Furthermore, each spurious is almost the same without any difference in peak frequency.

However, the first filter track 1
Since the second filter track 13 and the second filter track 13 have substantially opposite phases outside the pass band, the first filter track 12
And the spur of the second filter track 13 cancel each other out. Therefore, a large amount of attenuation is obtained outside the pass band.

As described above, the first filter track 12
And the second filter track 13 have a relative phase relationship of substantially the same phase within the pass band and substantially opposite phase outside the pass band, thereby providing a flat and wide pass band width and attenuation outside the pass band. A surface acoustic wave filter having an excellent amount can be obtained.

In order to obtain a surface acoustic wave filter having a flat and wide pass band, the point where the amplitude characteristics 21 and 22 of the first and second filter tracks 12 and 13 intersect in the pass band (FIG. 2A ) Are approximately (maximum value-
3 dB).

(Embodiment 2) FIG. 3 is a top view of a surface acoustic wave filter according to Embodiment 2 of the present invention. As in Embodiment 1, input and output IDT electrodes 34 and 35 on piezoelectric substrate 31 are provided. , 36, and 37, and a first filter track 32 and a second filter track 33 are formed. Also, the first and second filter tracks 32, 3
3 have the same amplitude and phase characteristics as those of the first embodiment.

The difference from the first embodiment is that the input and output IDs are different.
EWC-SPUDT for T electrodes 34, 35, 36, 37
(Electrode Width Controlled Single Phase Unidirec
directional transducer). That is, the input and output IDT electrodes 34, 35, 36,
When 37 is divided by the surface acoustic wave wavelength λ, a region is provided in which a total of three electrode fingers are present, one electrode finger having a λ / 4 width and two electrode fingers having a λ / 8 width. In FIG. 3, the input IDT electrodes 34 and 36 have a rightward directivity, and the output IDT electrodes 35 and
Numeral 37 designates a left direction.
Also, the first and second filter tracks 32 and 33 are
The connection is made in the same manner as in the first embodiment, and the relative phase relationship is substantially the same within the pass band and substantially opposite phase outside the pass band.

With this configuration, not only the flat and wide pass band width and the excellent attenuation outside the pass band are obtained, but also the first and second filter tracks 32 and 3 are provided.
In No. 3, the excitation center and the reflection center of the surface acoustic wave have an asymmetrical relationship, and the bidirectional loss is reduced, so that the insertion loss can be reduced.

The input and output IDT electrodes 3
When 4, 35, 36, and 37 have unidirectionality, the metallization ratio [sum of electrode finger widths present in the range of λ / λ] is set to 0.45 to 0.65, preferably 0.5 to 0.65.
By setting the ratio to 0.6, the insertion loss can be effectively reduced and the ripple in the pass band can be suppressed. On the other hand, if the metallization ratio is smaller than 0.45, the line width of the electrode finger becomes small, and the resistance loss increases. Conversely, if it is larger than 0.65, the distance between the electrode fingers becomes narrow, and it becomes difficult to form the electrode fingers.

Further, when the input and output IDT electrodes are formed of a metal mainly composed of aluminum, the thickness ratio (h / λ) between the electrode finger thickness h and the wavelength λ of the surface acoustic wave is 0.00.
By setting the value to 5 to 0.035, the insertion loss can be reduced and the ripple in the pass band can be suppressed.

(Embodiment 3) FIG. 4 is a top view of a surface acoustic wave filter according to Embodiment 3 of the present invention.

In the third embodiment, the piezoelectric substrate 41
The input and output IDT electrodes 44 and 44 constituting the first filter track 42 and the second filter track 43 formed above.
45, 46 and 47 are R-SPUDT (Resonant SPUD)
It has an electrode configuration called T). This electrode configuration is the same as in the second embodiment, and the input and output IDT electrodes 44, 45, 4
6, 47 divided by the surface acoustic wave wavelength λ, λ / 4
It has a region in which a total of three electrode fingers are present, one electrode finger having a width and two electrode fingers having a width of λ / 8. The amplitude and phase characteristics of the first and second filter tracks 42 and 43 are the same as in the first embodiment.

In FIG. 5, arrows indicate the direction of each of the regions A, B, and C surrounded by a dotted line. Regions A and C are:
The unidirectionality is given in the right direction of the drawing, but in the area B, the unidirectionality is given in the opposite direction, that is, the left direction of the drawing, and the input IDT electrode 46 as a whole is unidirectional in the right direction of the drawing. That is, the property is given.

Other input / output IDT electrodes 44, 45, 47
Has the same configuration and is unidirectional, but the input and output IDs in the respective filter tracks 42 and 43 are
The directions of the T electrodes 44, 45, 46, 47 are made to face each other.

In the second embodiment, all regions of one IDT electrode have the same directionality. On the other hand, R-SP
In UDT, in one IDT electrode, ID is given by giving a direction to a part of a region in a direction opposite to that of another region.
A resonant cavity will be formed in the T electrode.

Therefore, compared with the second embodiment, the IDT
The length of the electrode can be further reduced, and the surface acoustic wave filter can be further reduced in size.

FIG. 7 is a diagram showing characteristics of the surface acoustic wave filter shown in FIG. FIG. 8 shows the characteristics of a conventional surface acoustic wave filter for comparison. The surface acoustic wave filter according to the third embodiment has a wide and flat pass band and has an attenuation characteristic in the vicinity of the pass band, although it is reduced in area ratio by about 30% as compared with the conventional surface acoustic wave filter. It turns out that it is excellent. In addition, the insertion loss can be reduced.

(Embodiment 4) FIG. 6 is a top view of a surface acoustic wave filter according to Embodiment 4 of the present invention. FIG.
The difference from the third embodiment shown in FIG. 5 is that the third embodiment (FIG. 4) has three electrode fingers for one wavelength λ of the surface acoustic wave propagating on the piezoelectric substrate 41, Form 4
(FIG. 6) shows the insertion of the first and second filter tracks 62 and 63 imparting unidirectionality on the piezoelectric substrate 61.
The output IDT electrodes 64, 65, 66, and 67 have four electrode fingers during one wavelength λ of the surface acoustic wave,
That is, two electrode fingers having different widths form an electrode finger pair and cross each other (for example, 64a and 64b in FIG. 6).

When the width of the thinner finger is L1 and the width of the thicker finger is L2, the line width ratio (L2 / L1) is larger than 1, preferably in the range of 1.4 to 3.6. I do. With this configuration, the excitation efficiency of the surface acoustic wave is increased or the input and output IDT electrodes 64, 65, 66,
67 can be reduced compared to EWC-SPUDT. Therefore, the insertion loss is reduced, the unidirectionality of the surface acoustic wave is controlled, ripples in the pass band due to insufficient directivity or conversely excessive directivity, etc. are suppressed, and excellent flatness is obtained. Become.

FIG. 9 shows the characteristics of the surface acoustic wave filter according to the fourth embodiment. Compared with the characteristics of the surface acoustic wave filter according to the third embodiment shown in FIG. 7, the insertion loss (f _{0) at the} center frequency is obtained. ) Is reduced by 1.5 dB, and it can be seen that there is a great effect on reducing the insertion loss.

The input and output IDT electrodes 64, 65, 6
When the configurations such as the length of 6, 67 and the number of reflector electrodes are different, the insertion loss can be further reduced by increasing the value of the line width ratio to be more than 1 and changing each to the optimum value. .

(Fifth Embodiment) FIG. 13 is a top view of a filter track according to a fifth embodiment of the present invention, and corresponds to the filter track according to the first to fourth embodiments. FIG. 14 is an enlarged top view of a main part of FIG.

An input IDT electrode 136 containing aluminum as a main component and an output IDT electrode 137 on a piezoelectric substrate 131.
And the input and output IDT electrodes 136 and 137 are connected to the electrode finger pairs 132a, 132b and 1
33a, 133b and the lead electrode 13 connecting them
4a and 134b and 135a and 135b. The line width ratio between the input and output IDT electrodes 136 and 137 is larger than 1.0, and preferably 1.4 to 3.6.

The electrode finger pairs 132a, 132b, 13
Reference numerals 3a and 133b each include two electrode fingers having different line widths, each of which is formed so as to exist in a half area of one wavelength λ of the surface acoustic wave.

In FIG. 14, dotted lines are boundary lines 138 and 139 when the input IDT electrode 136 is divided by λ / 2. The area between the boundary lines 138 and 139 is defined as an area A.

In this region A, the value obtained by normalizing the distance between the thin electrode finger of the electrode finger pair 132b and the thick comb electrode by λ / 16 is γ, the thin electrode finger of the electrode finger pair 132b is
Α is the value obtained by standardizing the distance to λ / 16 with λ / 16, and electrode finger pair 1
The distance between the thick electrode finger of 32b and the boundary 139 is λ / 16
If the value normalized by is β, then γ> α + β.

Another electrode finger pair 13 of input IDT electrode 136
2a, electrode finger pair 133a, 13 of output IDT electrode 137
3b has the same configuration. However, the input and output IDT electrodes 136 and 137 are made to face each other.

FIG. 15 (a) shows the electro-mechanical conversion characteristic of the filter track having the stronger direction, and FIG. 15 (b) shows the electro-mechanical conversion characteristic of the filter track having the weaker direction. The input and output IDT electrodes 136 and 137 each have 100 pairs of electrode fingers having different line widths, and have a thickness ratio of 0.01.
5, line width ratio 3, α = β = 0.41, γ = 2.

Also, except that α = β = 1 and γ = 2, the electric power of the filter track having the same direction with the stronger
FIG. 16A shows the mechanical conversion characteristics, and FIG. 16B shows the electro-mechanical conversion characteristics of the weaker directionality.

As can be seen from a comparison between FIG. 15 and FIG. 16, since the fifth embodiment is superior in symmetry, it is possible to further reduce the ripple in the pass band and increase the attenuation outside the pass band. it can.

Therefore, the filter tracks having the structure shown in FIG. 13 are connected in parallel on the same piezoelectric substrate as shown in the first to fourth embodiments, and the relative phase relationship is substantially the same within the pass band and outside the pass band. By forming a surface acoustic wave filter having almost the opposite phase, the ripple in the pass band is reduced and the attenuation outside the pass band is increased.
In this case, the amplitude characteristics of the two filter tracks are set to be the same as in the first embodiment.

Also, FIG.
The film thickness ratio is 0.005, 0.010, 0.015, 0.020, when the center frequency is 110 MHz, and the number of electrode finger pairs is 100, using a quartz substrate having a Y-cut rotated by about 42 °.
The optimum value of α + β when 0.030 and γ = 2 is shown. As can be seen, when the line width ratio is greater than 1, α
The optimum value of + β is always smaller than γ.

(Sixth Embodiment) FIG. 18 is a top view of a filter track according to a sixth embodiment of the present invention, and FIG. 19 is an enlarged top view of the same part. Input IDT electrode 146, output IDT
Having electrode 147, input and output IDT electrodes 146, 147
Are electrode finger pairs 142a and 142b that cross each other
And 143a, 143b and lead electrodes 144a, 144b and 145a, 145b connecting them. These input and output IDT electrodes 146, 14
7 has a line width ratio of greater than 1.0, preferably 1.4 to
Set to 3.6.

The electrode finger pairs 142a, 142b, 14
As for 3a and 143b, a combination of two electrode fingers having different line widths and a combination of two electrode fingers having the same line width are mixed. Each of the electrode finger pairs 142a, 142b, 143a, and 143b exists in a region of 1/2 of one wavelength λ of the surface acoustic wave.

In FIG. 19, the dotted line indicates the input IDT electrode 14.
6, 148, 149, 15 when 6 is divided by λ / 2
0. Region A between boundary lines 148 and 149, boundary line 1
A region between 49 and 150 is defined as a region B. As can be seen from this, the electrode finger pairs 142a and 142b correspond to the regions A and B, respectively.
Is formed to exist.

In the area B, the value obtained by normalizing the distance between the thin electrode finger and the thick electrode finger of the electrode finger pair 142a by λ / 16 is γ, and the distance between the thin electrode finger of the electrode finger pair 142a and the boundary line 149 is defined as γ. The value normalized by λ / 16 is α, the electrode finger pair 142
Assuming that a value obtained by standardizing the distance between the electrode finger having a large thickness a and the boundary 150 with λ / 16 is β, γ> α + β and α <β.

Other electrode finger pairs 14 of input IDT electrode 146
2a has the same configuration, and the output IDT electrode 137 has the same configuration as the input IDT electrode 146 so that the input and output IDT electrodes 146 and 147 face each other.

FIG. 20 (a) shows the electro-mechanical conversion characteristic of the filter track having the stronger direction, and FIG. 20 (b) shows the electro-mechanical conversion characteristic of the filter track having the weaker direction. In addition,
The input and output IDT electrodes 146 and 147 are respectively composed of 50 pairs of electrode fingers having different line widths and 40 pairs of electrode fingers having the same line width, and have a film thickness ratio of 0.015, a line width ratio of 3, α = 0.15,
β = 0.67 and γ = 2.

FIG. 21A shows the electro-mechanical conversion characteristic of the filter track having the same direction except that α = β = 0.41 and γ = 2, and the direction is weak. FIG. 21 (b) shows the electro-mechanical conversion characteristics.

As can be seen from a comparison between FIGS. 20 and 21, when electrode finger pairs having different line widths and electrode finger pairs having the same line width coexist, γ> α + β and α <β are set to further improve symmetry. And the ripple in the pass band can be reduced and the attenuation outside the pass band can be increased.

Therefore, the filter tracks having the structure shown in FIG. 13 are connected in parallel on the same piezoelectric substrate as shown in the first to fourth embodiments, and the relative phase relationship is substantially the same in the pass band and out of the pass band. By forming a surface acoustic wave filter having almost the opposite phase, the ripple in the pass band is reduced and the attenuation outside the pass band is increased.
In this case, the amplitude characteristics of the two filter tracks are set to be the same as in the first embodiment.

In FIGS. 22 and 23, a quartz substrate of a Y-cut rotated by 28 ° to 42 ° is used as the piezoelectric substrate 141, the center frequency is 110 MHz, and the electrode finger pairs 50 having different line widths are used.
Pair, input / output IDT consisting of 40 pairs of electrode fingers with the same line width
In a surface acoustic wave filter formed by connecting filter tracks having electrodes on the same piezoelectric substrate, a film thickness ratio of 0.005, 0.010, 0.015, 0.020,
The optimum values of α and β when 0.030 and γ = 2 are shown. As you can see, if the line width ratio is greater than 1,
γ> α + β and α <β.

(Embodiment 7) FIG. 24 is a top view of a filter track according to Embodiment 7 of the present invention, and FIG. 25 is an enlarged top view of a main part of FIG.

As shown in FIG. 24, an input IDT electrode 24 mainly composed of aluminum is formed on a piezoelectric substrate 241.
6. The output IDT electrodes 247 are formed at predetermined intervals in the propagation direction of the surface acoustic wave. This input / output IDT electrode 2
46 and 247 are electrode finger pairs 242a, 242b and 24
3a, 243b and lead electrode 244 connecting them
a, 244b and 245a, 245b. Also, electrode finger pairs 242a, 242b and 243
a and 243b are composed of two comb electrodes having different line widths. Further, the input and output IDT electrodes 246 and 247 are made to face each other.

Further, as shown in FIG. 25, when the input IDT electrode 246 is divided into 単 位 units of the wavelength λ of the surface acoustic wave, the electrode finger pairs 242a, 242
42b is present. Also, the electrode finger pairs 242a, 242b
Assuming that the line width of the narrow comb electrode is L1 and the line width of the thick comb electrode is L2, the line width ratio (L2 / L1) is larger than 1, preferably 1.4 to 3.6. I am trying to become.

In the input IDT electrode 246, the region A and the region B are formed so as to alternately exist. The boundaries between the areas A and B are designated as 251, 252 and 253,
The values of the electrode fingers 242a and 242b, in which the line width between the thin comb electrodes and the boundary lines 251 and 252 are normalized by λ / 16, are α1 and α2, respectively, and the distance between the thin and thick comb electrodes is λ. / 16 and the distances between the thick comb electrodes and the boundaries 252 and 253 are λ /
The values normalized at 16 are β1 and β2, respectively.

Further, the film thickness ratio (input IDT electrode 246)
H / λ) where h is the thickness of the film and the wavelength λ of the surface acoustic wave.
015, line width ratio 2, α1 = β1 = 0, γ1 = 4, α2
= Β2 = 1.5 and γ2 = 1, that is, γ1
> Α1 + β1, γ2 ≦ α2 + β2. The output IDT electrode 247 has the same configuration as the input IDT electrode 246.

FIG. 26 shows the electromechanical conversion characteristics of this filter track. For comparison, α1 = β1 = α2
= Β2 = 0.75, γ1 = γ2 = 2.5, that is, γ1
> Α1 + β1, γ2> shows electromechanical conversion characteristics of a filter track (corresponding to the fifth embodiment) having the same configuration except that it is formed so as to satisfy α2 + β2.

The seventh embodiment (FIG. 26) is similar to the fifth embodiment.
Compared with FIG. 27, the difference between the stronger and weaker directionality of the electro-mechanical conversion characteristics (hereinafter referred to as “directionality”) in the passband is averaged in the passband. , The fluctuation of the group delay time within the pass band is small. That is, the ripple can be reduced.

That is, the electrode finger pairs 242a, 242 having different line widths
When the input and output IDT electrodes are configured by 42b, 243a, and 243b, the flatness in the pass band can be further improved by satisfying γ1> α1 + β1, and γ2 ≦ α2 + β2.

Therefore, the filter tracks having the structure shown in FIG. 24 are connected in parallel on the same piezoelectric substrate as shown in the first to fourth embodiments, and the relative phase relationship is substantially the same within the pass band and outside the pass band. By forming a surface acoustic wave filter having substantially the opposite phase, the ripple in the pass band can be further reduced. Also in this case, the amplitude characteristics of the two filter tracks are set to be the same as in the first embodiment.

It is not necessary that the regions A and B alternately exist in one IDT electrode. However, by alternately presenting the IDT electrodes, the unidirectionality of the surface acoustic wave can be controlled, and the insufficient directivity or Ripple in the pass band due to excessive directionality or the like is suppressed, and the flatness in the pass band is further improved.

Further, by making the number of the regions A and the regions B substantially the same in one IDT electrode, the unidirectionality of the surface acoustic wave is controlled, and the unidirectionality of the surface acoustic wave is controlled by the insufficient or excessive directionality. Suppress ripple in the pass band,
The flatness in the pass band is excellent.

Further, in the seventh embodiment,
Since the input and output IDT electrodes 246 and 247 have the same configuration, they have the same line width ratio.
When the configurations of the T electrodes 246 and 247 are different, the unidirectionality of the surface acoustic wave is controlled by changing the line width ratio to each of the optimum values, and the passband within the passband due to insufficient directivity or excessive directivity is controlled. Is suppressed, and the flatness in the pass band is excellent. In any case, the insertion loss can be reduced by setting the line width ratio between the input and output IDT electrodes 246 and 247 to be larger than 1, preferably 1.4 to 3.6.

(Eighth Embodiment) FIG. 28 is a top view of a surface acoustic wave filter according to an eighth embodiment of the present invention. As shown in FIG. 28, a first filter track 282 and a second filter track 283 are placed on a piezoelectric substrate 281 formed using a quartz substrate of 28 ° to 42 ° rotation Y-cut.
Are arranged in parallel, and the first filter track 28
2 has an input IDT electrode 284 and an output IDT electrode 285. Similarly, the second filter track 283 has the input I
It has a DT electrode 286 and an output IDT electrode 287.

The input IDT electrode 284 of the first filter track 282 and the input IDT electrode 286 of the second filter track 283 are electrically connected in parallel.
Output IDT electrode 285 of first filter track 282
And the output IDT electrode 28 of the second filter track 283
7 are electrically connected in parallel.

The operation of the surface acoustic wave filter configured as described above will be described below.

FIG. 29A shows the amplitude characteristic 291 of the first filter track 282 and the amplitude characteristic 292 of the second filter track 282 in FIG. 1, and FIG.
8, the phase characteristic 2 of the first filter track 282
93 and the phase characteristic 294 of the second filter track 283
And

As shown in FIG. 29B, within the pass band, the phase difference between the first filter track 282 and the second filter track 283 is almost 0 °, that is, almost the same phase. Substantially the same phase is a phase difference in the range of −50 ° to + 50 °, preferably −20 ° to + 20 °.

Outside the pass band, the phase difference between the first filter track 282 and the second filter track 283 is almost 180 °, that is, almost the opposite phase.
Substantially opposite phase means 130 ° to 230 °, preferably 16 °
The phase difference is in the range of 0 ° to 200 °.

Further, as shown in FIG. 29A, the amplitude characteristic 291 of the first filter track 282 has a large pass band although the amount of attenuation is large. On the other hand, the amplitude characteristic 292 of the second filter track 283 has a small attenuation but a narrow pass band. Therefore, the first filter track 28
Since the second and second filter tracks 283 have substantially the same phase in the pass band, by connecting them electrically in parallel, a flat and wide pass band can be obtained.

The spurious level outside the pass band is not so much suppressed in both the amplitude characteristic 291 of the first filter track 282 and the amplitude characteristic 292 of the second filter track 283. Furthermore, each spurious is almost the same without any difference in peak frequency.
However, since the first filter track 282 and the second filter track 283 have substantially opposite phases outside the pass band, the spurious of the first filter track 282 and the spurious of the second filter track 283 cancel each other. Become. Therefore, a large amount of attenuation is obtained outside the pass band.

As described above, the relative phase relationship between the first filter track 282 and the second filter track 283 having the amplitude characteristics 291 and 292 as shown in FIG. In addition, by making the phases substantially opposite to each other outside the pass band, it is possible to obtain a surface acoustic wave filter having a flat and wide pass band width and excellent attenuation outside the pass band.

In the eighth embodiment, similar effects can be obtained by using the structures shown in the second to seventh embodiments for the input and output IDT electrodes 284, 285, 286 and 287.

Of course, the amplitude characteristic of the first filter track 282 has a large attenuation but has a wide pass band, and the amplitude characteristic of the second filter track 283 has a small attenuation and a narrow pass band. Further, both the first and second filter tracks 282 and 283 have excellent flatness in the pass band.

The points of the present invention will be described below.

(1) In order to obtain a surface acoustic wave filter having a flat, wide pass band width and excellent attenuation outside the pass band, the amplitude characteristics of the first and second filter tracks are as follows:
2A or FIG. 29A.

(2) The phase difference between the first and second filter tracks needs to be substantially opposite in the frequency region where the attenuation characteristic is required near the pass band, but the frequency region far away from the pass band is required. Then, even if the phases are not opposite, the first
A sufficient attenuation characteristic can be obtained by the amplitude characteristic of the second filter track.

(3) The surface acoustic wave filter according to the present embodiment has input and output IDT electrodes 14, 15, 1 when compared with a conventional surface acoustic wave filter having equivalent filter characteristics.
The length of 6, 17 is short, and the size can be greatly reduced. Therefore, it is possible to contribute to miniaturization of communication equipment such as a mobile phone.

(4) Similar effects can be obtained even if a sound absorbing material or the like is provided as required.

(5) In the above embodiment, the input and output terminals are of the balanced type, but the unbalanced type as shown in FIG. 10 or one of the balanced type as shown in FIG. In this case, the same effect can be obtained.

In FIG. 10, the input and output I of the first and second filter tracks 102 and 103 on the piezoelectric substrate 101 are shown.
DT electrodes 104, 105, 106, 107 and FIG.
The first filter track 1 on the piezoelectric substrate 111
Input and output ID of the 12th and 2nd filter tracks 113
Unidirectional electrodes such as T electrodes 114, 115, 116 and 117, or thinned and weighted input and output IDTs
In the case of using an electrode, it is preferable to ground the terminal on the electrode finger side to which the reflector electrode or the dummy electrode for adjusting the sound speed is provided from the viewpoint of suppressing the stray capacitance, reducing the loss, and increasing the attenuation.

(6) In each of the above embodiments, the first filter track 12 and the second filter track 13 are connected in parallel by routing electrodes as shown in FIG. As described above, on the piezoelectric substrate 121,
Input IDT electrode 124 of first filter track 122
And the input IDT electrode 12 of the second filter track 123
6. Output IDT electrode 1 of first filter track 122
The same effect can be obtained even if the electrode fingers of the output IDT electrode 127 of the second filter track 123 are directly connected to the electrode fingers of the second filter track 123. With this configuration, the length in the cross width direction can be shortened, and further downsizing can be achieved.
The resistance loss due to the routing electrode can be reduced, and the insertion loss can be reduced.

(7) When quartz is used as the piezoelectric substrate,
The frequency drift is represented by a quadratic curve, and considering the practical film thickness and metallization ratio, the temperature at the top can be minimized when the temperature is at the center of the operating temperature range, that is, near room temperature. it can.

Therefore, by using a quartz substrate of 28 ° to 42 ° rotation Y-cut as the piezoelectric substrate, the peak temperature can be set near the center of the operating temperature range, and the frequency drift in the operating temperature range can be reduced. it can.

[0118]

As described above, according to the present invention, it is possible to provide a small surface acoustic wave filter having a wide, flat pass band and excellent attenuation characteristics near the pass band.

[Brief description of the drawings]

FIG. 1 is a top view of a surface acoustic wave filter according to Embodiment 1 of the present invention.

2A is an amplitude characteristic curve diagram of the surface acoustic wave filter shown in FIG. 1. FIG. 2B is a phase characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 3 is a top view of a surface acoustic wave filter according to Embodiment 2 of the present invention.

FIG. 4 is a top view of a surface acoustic wave filter according to Embodiment 3 of the present invention.

5 is a partially enlarged top view of an input IDT electrode of the surface acoustic wave filter of FIG. 4;

FIG. 6 is a top view of a surface acoustic wave filter according to Embodiment 4 of the present invention.

FIG. 7 is a characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 8 is a characteristic curve diagram of a conventional surface acoustic wave filter.

9 is a characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 10 is a top view of a surface acoustic wave filter according to another embodiment of the present invention.

FIG. 11 is a top view of a surface acoustic wave filter according to another embodiment of the present invention.

FIG. 12 is a top view of a surface acoustic wave filter according to another embodiment of the present invention.

FIG. 13 is a top view of a filter track according to the fifth embodiment of the present invention.

FIG. 14 is an enlarged top view of a main part of FIG. 13;

15A is an electro-mechanical conversion characteristic diagram of the filter track shown in FIG. 13 in which the directionality is strong. FIG. 15B is an electro-mechanical conversion characteristic diagram of the filter track having the weak directionality.

FIG. 16A is an electro-mechanical conversion characteristic diagram of a comparative example in which the directionality of a filter track is strong. FIG. 16B is an electro-mechanical conversion characteristic diagram of a filter track having a weak directionality.

FIG. 17 is a graph showing a relationship between a line width ratio and α in Embodiment 5 of the present invention.
Relation diagram of optimal value of + β

FIG. 18 is a top view of a filter track according to the sixth embodiment of the present invention.

19 is an enlarged top view of a main part of FIG. 18;

20A is an electro-mechanical conversion characteristic diagram of the direction of the filter track shown in FIG. 18 where the directionality is strong, and FIG. 20B is an electro-mechanical conversion characteristic diagram of the case where the directionality of the filter track is weak.

FIG. 21A is an electro-mechanical conversion characteristic diagram of the filter track of the comparative example in which the directionality is strong. FIG. 21B is an electro-mechanical conversion characteristic diagram of the filter track in which the directionality is weak.

FIG. 22 is a graph showing a relationship between a line width ratio and α in Embodiment 6 of the present invention;
Of the relationship with the optimal value of

FIG. 23 is a diagram illustrating a relationship between a line width ratio and β in Embodiment 6 of the present invention.
Of the relationship with the optimal value of

FIG. 24 is a top view of a filter track according to the seventh embodiment of the present invention.

FIG. 25 is an enlarged top view of a main part of FIG. 24;

FIG. 26 is a characteristic curve diagram of the filter track shown in FIG. 24;

FIG. 27 is a characteristic curve diagram of a filter track of a comparative example.

FIG. 28 is a top view of a surface acoustic wave filter according to Embodiment 8 of the present invention.

29A is an amplitude characteristic curve diagram of the surface acoustic wave filter shown in FIG. 1. FIG. 29B is a phase characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 30 is a top view of a conventional surface acoustic wave filter.

[Explanation of symbols]

 Reference Signs List 11 piezoelectric substrate 12 first filter track 13 second filter track 14 input IDT electrode 15 output IDT electrode 16 input IDT electrode 17 output IDT electrode 21 amplitude characteristic 22 amplitude characteristic 23 phase characteristic 24 phase characteristic 31 piezoelectric substrate 32 first Filter track 33 Second filter track 34 Input IDT electrode 35 Output IDT electrode 36 Input IDT electrode 37 Output IDT electrode 41 Piezoelectric substrate 42 First filter track 43 Second filter track 44 Input IDT electrode 45 Output IDT electrode 46 Input IDT Electrode 47 Output IDT electrode 61 Piezoelectric substrate 62 First filter track 63 Second filter track 64 Input IDT electrode 64a Electrode finger 64b Electrode finger 65 Output IDT electrode 66 Input IDT electrode 67 Output IDT electrode 10 Piezoelectric substrate 102 First filter track 103 Second filter track 104 Input IDT electrode 105 Output IDT electrode 106 Input IDT electrode 107 Output IDT electrode 111 Piezoelectric substrate 112 First filter track 113 Second filter track 114 Input IDT electrode 115 Output IDT electrode 116 Input IDT electrode 117 Output IDT electrode 121 Piezoelectric substrate 122 First filter track 123 Second filter track 124 Input IDT electrode 125 Output IDT electrode 126 Input IDT electrode 127 Output IDT electrode 131 Piezoelectric substrate 132a Electrode finger pair 132b Electrode finger pair 133a Electrode finger pair 133b Electrode finger pair 134a Extraction electrode 134b Extraction electrode 135a Extraction electrode 135b Extraction electrode 136 Input IDT electrode 1 7 output IDT electrode 141 piezoelectric substrate 142a electrode finger pair 142b electrode finger pair 143a electrode finger pair 143b electrode finger pair 144a extraction electrode 144b extraction electrode 145a extraction electrode 145b extraction electrode 146 input IDT electrode 147 output IDT electrode 241 piezoelectric substrate 242a electrode finger 242b electrode finger pair 243a electrode finger pair 243b electrode finger pair 244a extraction electrode 244b extraction electrode 245a extraction electrode 245b extraction electrode 246 input IDT electrode 247 output IDT electrode 251 boundary line 252 boundary line 253 boundary line 281 piezoelectric substrate 282 first filter track 283 second filter track 284 input IDT electrode 285 output IDT electrode 286 input IDT electrode 287 output IDT electrode 291 amplitude characteristic 292 Width characteristics 293 phase characteristic 294 phase characteristics

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ken Matsunami 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazuki Nishimura 1006 Odaka Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor Hiroyuki Nakamura 1006 Kadoma Kadoma, Kadoma City, Osaka Pref. Matsushita Electric Industrial Co., Ltd. AA18 AA19 AA29 BB11 CC04 CC15 DD04 DD28 GG02 KK04 KK05

Claims (24)

[Claims] 1. A piezoelectric substrate having first and second filter tracks having input and output interdigital transducer electrodes formed on the piezoelectric substrate, wherein the first and second filter tracks are within a passband. The input inter-digital transducer electrode of the first filter track and the input inter-digital transducer electrode of the second filter track are connected in parallel with each other. An output interdigital transducer electrode and an output interdigital transducer electrode of the second filter track are connected in parallel, and the frequency of the transfer function (maximum value -3 dB) of the first and second filter tracks is substantially equal to the output interdigital transducer electrode. Matching surface acoustic wave Ruta. 2. The surface acoustic wave filter according to claim 1, wherein at least one of the input and output interdigital transducer electrodes is a unidirectional electrode. 3. The electrode finger is arranged so that the directionality is enhanced in at least one region of the unidirectional electrode, and the direction of the direction opposite to the directionality is enhanced in at least one other region. 3. The surface acoustic wave filter according to 1. 4. A metallization ratio of 0.45 to 0.45.
The surface acoustic wave filter according to claim 2, wherein the ratio is 0.65. 5. At least one of the input and output interdigital transducer electrodes has four electrode fingers within one wavelength and has electrode line pairs of different line widths in at least a part of the intersecting region. 3. The surface acoustic wave filter according to claim 2, wherein the line width ratio (L2 / L1) of the line width (L1) of the thin electrode finger and the line width (L2) of the thick electrode finger of the electrode finger pair is larger than 1. 6. The surface acoustic wave filter according to claim 5, wherein the input and output interdigital transducer electrodes have different line width ratios. 7. The surface acoustic wave filter according to claim 5, wherein the electrode finger pairs composed of electrode fingers having different line widths satisfy Expression (1). (Equation 1) 8. At least two pairs of electrode fingers having electrode widths different from each other are provided.
The surface acoustic wave filter according to claim 5, wherein at least one pair satisfies (Equation 2) and the other satisfies (Equation 2). (Equation 2) 9. The surface acoustic wave filter according to claim 8, wherein the electrode finger pairs satisfying (Equation 2) and (Equation 2) are substantially equal in number. 10. The surface acoustic wave filter according to claim 8, wherein one of the adjacent electrode finger pairs satisfies (Equation 2) and the other satisfies (Equation 2). 11. The electrode finger is formed of a metal containing aluminum as a main component, and the thickness ratio (h / λ) of the electrode finger thickness h to the wavelength λ of the surface acoustic wave is 0.005 to 0.035.
The surface acoustic wave filter according to claim 2, wherein 12. The surface acoustic wave filter according to claim 1, wherein the piezoelectric substrate is formed using a quartz substrate having a Y-cut of 28 ° to 42 ° rotation. 13. A piezoelectric substrate comprising: a piezoelectric substrate; first and second filter tracks having input and output interdigital transducer electrodes formed on the piezoelectric substrate;
The first and second filter tracks are substantially in phase within the passband and substantially out of phase outside the passband, and have an input interdigital transducer electrode of the first filter track and an input interdigital transducer electrode of the second filter track. And in parallel,
The output interdigital transducer electrode of the first filter track and the output interdigital transducer electrode of the second filter track are connected in parallel, and the center frequencies of the first and second filter tracks are substantially matched. And a surface acoustic wave filter having a pass band width of the first filter track larger than a pass band width of the second filter track. 14. The surface acoustic wave filter according to claim 13, wherein at least one of the input and output interdigital transducer electrodes is a unidirectional electrode. 15. The electrode finger according to claim 14, wherein the electrode fingers are arranged so as to enhance the direction in at least one region of the unidirectional electrode, and to enhance the direction opposite to the direction in at least one other region. 3. The surface acoustic wave filter according to 1. 16. The metallization ratio is 0.45.
The surface acoustic wave filter according to claim 14, wherein the value is from 0.65 to 0.65. 17. At least one of the input and output interdigital transducer electrodes has four electrode fingers within one wavelength, and has electrode line pairs having different line widths in at least a part of the intersecting region. 15. The line width ratio (L2 / L1) of the line width (L1) of the thin electrode finger and the line width (L2) of the thick electrode finger of the pair of electrode fingers is set to be larger than 1.
3. The surface acoustic wave filter according to 1. 18. The input / output interdigital transducer electrodes have different line width ratios.
3. The surface acoustic wave filter according to 1. 19. The surface acoustic wave filter according to claim 17, wherein the electrode finger pairs composed of electrode fingers having different line widths satisfy Expression (3). (Equation 3) 20. At least two pairs of electrode fingers each having an electrode finger having a different line width are provided, and at least one pair of the electrode finger pairs satisfies (Equation 4) and the other satisfies (Equation 4). Item 18. A surface acoustic wave filter according to item 17. (Equation 4) 21. The surface acoustic wave filter according to claim 20, wherein the electrode finger pairs satisfying (Equation 4) and (Equation 4) are substantially equal in number. 22. The surface acoustic wave filter according to claim 20, wherein one of the adjacent electrode finger pairs satisfies (Equation 4) and the other satisfies (Equation 4). 23. The electrode finger is formed of a metal containing aluminum as a main component, and the thickness ratio (h / λ) of the electrode finger thickness h to the wavelength λ of the surface acoustic wave is 0.005 to 0.035.
The surface acoustic wave filter according to claim 14, wherein: 24. The surface acoustic wave filter according to claim 13, wherein the piezoelectric substrate is formed using a quartz substrate that is Y-cut with a rotation of 28 ° to 42 °.