JP2001189637A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device of which the transmission function characteristics in a signal passing band is more satisfactory and the insertion loss is reduced as well. SOLUTION: Electrode fingers of plural pairs comprise first split electrode groups 5a1, 5b1, 5a2, 5b2, 5a3, 5b3, etc. Besides, the electrode fingers of plural pairs comprise second split electrode groups 6a1, 6b1, 6a2, 6b2, 6a3, 6b3, etc. Concerning the electrode fingers of plural pairs in the mutual groups, the pairs are alternately interleaved. Then, the electrode fingers of a pair include an electrode finger narrower than width λ/8 (λis the wavelength of a surface acoustic wave being an operation center frequency) and an electrode finger wider than λ/8 and a distance between the centers of the adjacent electrode fingers is different from λ/4.

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 device having an interdigital transducer formed on a piezoelectric substrate.

[0002]

2. Description of the Related Art A surface acoustic wave device is mainly used as an intermediate frequency filter in electronic equipment. Electronic devices include television receivers, communication devices, and mobile phones (CDs).
MA system). The surface acoustic wave device has a feature of being small and lightweight, and can be used in a mobile phone to take advantage of the feature.

Meanwhile, an intermediate frequency filter used in a portable telephone is required to have low loss, a narrow band, and a frequency characteristic having a sharp cutoff. As a filter for realizing this kind of intermediate frequency filter, a surface acoustic wave device based on an interdigital transducer (IDT) has been developed.

[0004] In this surface acoustic wave device, a piezoelectric substrate using a material such as quartz which has little fluctuation in vibration characteristics due to temperature changes is used in order to satisfy the requirements of frequency characteristics having a narrow band and a steep cutoff.

In a surface acoustic wave device, a surface acoustic wave (SAW)
It is known that an internal reflected wave (acoustic reflected wave, electric reflected wave) is generated by utilizing such mechanical vibration. The internal reflected wave is
This has adverse effects such as amplitude attenuation and phase distortion.
Therefore, the technology to adjust or trim the width of the electrode finger in the IDT part of the surface acoustic wave device to reduce the influence of the reflected wave on the fundamental wave and to set the transmission direction of the fundamental wave to a predetermined direction has been developed. Have been. This technique is disclosed in, for example,
No. -17647.

[0006]

However, the above-mentioned device does not completely eliminate the adverse effect of the internally reflected wave on the fundamental wave. This adverse effect, when looking at the transfer function characteristic of the signal pass band of the surface acoustic wave device, appears as a characteristic curve that is asymmetric about the fundamental frequency or appears with distortion.

Here, in the surface acoustic wave device, the phase relationship between the excitation wave and the reflected wave, which the present inventors paid particular attention to, will be described.

FIGS. 1A and 1C are cross-sectional views of a main part of a surface acoustic wave device. The electrode finger of this surface acoustic wave device is a pair of a narrow electrode finger of λ / 16 and a wide electrode finger of 3λ / 16. A plurality of pairs of electrode fingers protruding from the first common electrode and a plurality of pairs of electrode fingers protruding from the second common electrode are arranged alternately. The distance between the electrode fingers is selected to be λ / 8.

FIG. 1B shows the phase relationship between the excitation wave and the internally reflected wave traveling leftward in the figure. FIG. 1D shows the excitation wave and the internally reflected wave traveling rightward in the figure. The relationship is shown. Now, in the figure, the phase of the excitation wave is based, and
The clockwise direction from the phase of the excitation wave vector is the phase delay amount of the reflected wave.

First, referring to FIGS. 1A and 1B,
The relationship between the reflected wave traveling to the left in the figure and the excitation wave will be described.

With reference to an arbitrary surface acoustic wave excitation point P1, a reflected wave reflected from one edge EA of an electrode finger having a width (λ / 16) closest to this excitation point is denoted by A, and this electrode is also denoted by A. Let B be the reflected wave reflected from the other edge EB of the finger. Further, the reflected wave passing through the electrode finger and reflected from one edge EC of the electrode finger having a width (3λ / 16) adjacent thereto with respect to the excitation point is denoted by C, and the other edge ED of the same electrode finger is denoted by C.
Let D be the reflected wave reflected from.

In the phase of the reflected wave A, a phase delay element corresponding to a path length of 0.125λ is generated with respect to the phase of the excitation wave at the excitation point, and a phase delay of 45 ° is generated with respect to the phase of the excitation wave. . That is, assuming that the delay amount = X, X (45 °) can be obtained from ((0.125 / 2) × 2) λ: X = λ: 360 °.

In this equation, (× 2) is a coefficient for obtaining a reciprocating path length.

The phase of the reflected wave B has a phase delay element corresponding to the path length of (0.125+ (1/8)) λ with respect to the phase of the excitation wave at the excitation point P1. Causes a phase delay of (270 °) with respect to the phase of the excitation wave. That is, assuming that the delay amount = X, ｛((0.125 / 2) × 2) + ((1/16) × 2)
+ (1/2)｝ λ: X = λ: 360 to X = 360 × (0.125+ (１ ／) + (（))
= 270 ° is obtained.

In the above equation, (× 2) is a coefficient for obtaining a reciprocating path length, and (1/2) is a phase inversion at the edge EB.

The phase of the reflected wave C is (0.125+ (1/8) + (1/2) with respect to the phase of the excitation wave at the excitation point P1.
4) A phase delay element corresponding to the path length of λ is generated, and a phase delay of 180 ° with respect to the phase of the excitation wave is generated. That is, the delay amount = X
Then, ｛((0.125 / 2) × 2) + ((1/16) × 2)
+ ((1/8) × 2)｝ λ: X = λ: 360 to X = 360 × (0.125+ (1/8) + (1/4))
= 180 ° is obtained.

In the above equation, (× 2) is a coefficient for obtaining a reciprocating path length.

The phase of the reflected wave D is (0.125+ (１ ／) + (1/25) with respect to the phase of the excitation wave at the excitation point P1.
4) + (3/8)) A phase delay element corresponding to the path length of λ occurs, and a phase inversion at the edge ED occurs, so that a phase delay of 135 ° with respect to the phase of the excitation wave occurs. That is, assuming that the delay amount = X, ｛((0.125 / 2) × 2) + ((1/16) × 2)
+ ((1/8) × 2) + (3/16) × 2 + (1 /
2) From｝ λ: X = λ: 360 to X = 360 × ((１ ／) + (１ ／) + (１ ／) +
(3/8) + (1/2)) = 495 ° = 135 °.

In the above equation, (× 2) is a coefficient for obtaining a reciprocating path length, and (1/2) is a phase inversion at the edge ED.

The result of combining the vectors of the reflected waves A, B, C, and D is the phase delay of the internally reflected wave with respect to the excitation wave. As shown in FIG. 1B, the internally reflected waves A, B,
The phase of the composite vector of the C and D vectors is 157.5.
°. This value is the phase (1) in the direction to cancel the excitation wave.
80 °) and 22.5 °.

The combined vector is obtained as a result of combining the x component and the y component of the vector of the reflected waves A, B, C, and D in the orthogonal coordinate system.

Next, with reference to FIGS. 1C and 1D, the relationship between the reflected wave traveling to the right in the figure and the excitation wave will be described.

With reference to an arbitrary surface acoustic wave excitation point P2,
The reflected wave reflected from one edge EE of the electrode finger having the width (3λ / 16) closest to the excitation point is E, and the reflected wave reflected from the other edge EF of the electrode finger is F.
And One edge EG of an electrode finger having a width (λ / 16) adjacent to the electrode finger and passing through the electrode finger with respect to the excitation point.
G is a reflected wave reflected from the other, and H is a reflected wave reflected from the other edge EH of the same electrode finger.

In the phase of the reflected wave E, a phase delay element corresponding to a path length of 0.125λ is generated with respect to the phase of the excitation wave at the excitation point P2, and a phase delay of 45 ° with respect to the phase of the excitation wave is generated. Occurs.

The phase of the reflected wave F has a phase delay element corresponding to the path length of (0.125+ (3/8)) λ with respect to the phase of the excitation wave at the excitation point P2. Causes a phase delay of 0 ° with respect to the phase of the excitation wave.

The phase of the reflected wave G is (0.125+ (3/8) +0.2 with respect to the phase of the excitation wave at the excitation point P2.
5) A phase delay element corresponding to the path length of λ is generated, and a phase delay of 270 ° with respect to the phase of the excitation wave is generated.

The phase of the reflected wave H is (0.125+ (3/8) +0.2 with respect to the phase of the excitation wave at the excitation point P2.
5+ (1/8)) λ, a phase delay element corresponding to the path length is generated,
Further, since phase inversion occurs at the edge EH, a phase delay of 190 ° occurs with respect to the phase of the excitation wave.

The above-mentioned phase delays are shown in FIGS.
It can be derived by an expression having the same concept as the expression shown in the description of (B).

The result of combining the vectors of the reflected waves E, F, G, and H is the phase delay of the internally reflected wave with respect to the excitation wave. As shown in FIG. 1D, the internally reflected waves E, F,
The phase of the composite vector of the G and H vectors is 22.5 °
Becomes This phase is in the same direction as the excitation wave (0 °)
22.5 °.

From the above results, due to the influence of the reflected wave,
It can be seen that the efficiency with which the excitation wave (fundamental wave) propagates in the desired direction is not sufficiently obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface acoustic wave device exhibiting better transfer function characteristics in a signal pass band and having a small insertion loss.

[0032]

In order to achieve the above object, the present invention provides: (A) a first substrate formed parallel to a piezoelectric substrate;
A first split electrode group connected to the first and second common electrodes, the first common electrode, and extending in the direction of the second common electrode, and a first split electrode group connected to the second common electrode;
A second split electrode group extending in the direction of the common electrode, and a surface acoustic wave device including an interdigital transducer having: a plurality of pairs of electrode fingers constituting the first split electrode group;
And a plurality of pairs of electrode fingers constituting the split electrode group are interleaved with each other alternately at a λ / 2 cycle, and the electrode fingers of the pair are λ / 8 (where λ is the operating center frequency and And the electrode fingers are narrower than the width of the surface acoustic wave (wavelength of the surface acoustic wave) and the electrode fingers are wider than λ / 8. The phase of the combined vector of the reflected waves generated by the electrode fingers included within the distance within λ / 2 along the direction is nπ−5 ° ≦ φ ≦ nπ +
It has a configuration having a phase φ expressed by 5 ° (n is a natural number).

(B) In the present invention, (A)
In this device, the center distance (t1) between an arbitrary electrode finger and one of the electrode fingers disposed across the electrode finger is different from the center distance (t2) between the other electrode finger. ing.

(C) Still further, according to the present invention, in the device of the above (A), the electrode fingers of the pair are λ / 16
And a narrow electrode finger having a width of 0.1465λ ≦ w ≦ 0.
And a wide electrode finger having a width w of 1605λ.

(D) Still further, according to the present invention, in the surface acoustic wave device, a plurality of pairs of electrode fingers constituting the first split electrode group and a plurality of pairs constituting the second split electrode group are provided. The electrode fingers and the pairs are alternately interleaved with each other, and the electrode fingers of the pair are narrower than the width of λ / 8 (where λ is the wavelength of the surface acoustic wave that is the operating center frequency). , Λ / 8, and the sum of the widths of the narrow electrode finger and the wide electrode finger is smaller than λ / 4, the width of the narrow electrode finger and the wide electrode finger, and the width of the two electrode fingers. Is characterized in that the sum of the distances between adjacent edges is 3λ / 8.

[0036]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 2, reference numeral 11 denotes a piezoelectric substrate made of quartz, and an interdigital transducer section 12 is formed on one surface thereof.

Inter digital transducer section 12
In the first embodiment, the first common electrode 13 and the second common electrode 14 are arranged in parallel at an interval. The first common electrode 13 has a first split electrode group (electrode fingers 5 a 1, 5 b 1, 5 a 2, 5 b 2) extending in the direction of the second common electrode 14.
5a3, 5b3,...) Are connected. The second common electrode 14 has a second split electrode group (electrode fingers 6a1, 6b1, 6a) extending in the direction of the first common electrode 13.
2, 6b2, 6a3, 6b3,...) Are connected.

In the first split electrode group, a narrow electrode finger (an electrode finger having a suffix a) and a wide electrode finger (an electrode finger having a suffix b) are paired, and the pair is spaced apart from each other. Are repeatedly arranged. Also in the second split electrode group, a narrow electrode finger (electrode with suffix a) and a wide electrode finger (electrode with suffix b) form a pair, and this pair is repeated at intervals. Are arranged.

Then, a pair of electrode fingers (5a1, 5b1), (5a2,
5b2), (5a3, 5b3),... And a pair of electrode fingers (6a1,
6b1), (6a2, 6b2), (6a3, 6b3),
... are interleaved alternately. As a whole, wide electrode fingers and narrow electrode fingers are alternately arranged.

The common electrodes 13 and 14 and the split electrode group are formed of an electrode film mainly composed of aluminum (Al) or an aluminum (Al) alloy.

Further, in this embodiment, the pair of electrode fingers
The electrode fingers 5b1, 5b2, 5b having a width smaller than the width of λ / 8 (where λ is the wavelength of the surface acoustic wave serving as the operation center frequency)
, 6a1, 6a2, 6a3,..., And electrode fingers 5a1, 5a2, 5a3,.
1, 6b2, 6b3,... Furthermore,
In this embodiment, the width of the narrow electrode finger is λ / 16, and the width of the wide electrode finger is 3λ / 16.

The distance t1, between the centers of adjacent electrode fingers,
t2, t1, t2,... are distances different from λ / 4 (here, this value is used as a reference value). Distance t1 between centers
Has a positive deviation (greater than the reference value) with respect to the reference value, and the distance t2 between the centers has a negative deviation (smaller than the reference value) with respect to the reference value. And this distance t1,
t2 is repeatedly arranged.

That is, the distance between the centers of adjacent electrode fingers is alternately arranged with a positive / negative deviation from the reference value λ / 4. Due to this deviation, the reflected wave in the IDT becomes
The amount of phase delay for the excitation wave is adjusted. And this adjustment, as described later, the traveling direction of the internal reflected wave,
The direction can be set in the direction most suitable for the traveling direction of the fundamental wave of the surface acoustic wave.

In this embodiment, t1 = ((0.152+ (1/8)) λ t2 = ((0.098+ (1/8)) λ, and t1 + t2 = λ / 2. In the formula, 0.152λ and 0.098λ are the distances between the opposing edges of the electrode fingers, and λ / 8 is the sum of the (）) widths of the adjacent electrode fingers, thus any one electrode The distance between the centers of the electrode fingers on both sides of the finger is λ / 2.

Distances t1 and t2 between the centers of the above-mentioned electrode fingers
Has been found as a value that can be exhibited in a state where the unidirectionality of the fundamental wave of the surface acoustic wave is most excellent as a result of the studies by the inventors. The way of thinking when deciding the values of t1 and t2 is represented by a generalized equation as follows.

Of the pair of electrode fingers, the width of one electrode finger is w, and the width of the other electrode finger is ((λ / 4) −w).
Assuming that the distance between the centers of the two electrode fingers is x1, tan {k (x1- (λ / 8))} = 1 / cos {k
((3λ / 4) + 2w)｝ (where k is a wave number and indicates k = 2π / λ), x1 is selected. In this state, the unidirectionality of the fundamental wave of the surface acoustic wave is the most excellent.

The above condition is satisfied when the width of one electrode finger is λ / 1.
6. When the above is applied to the case where the width of the other electrode finger is 3λ / 16, the distance x2 between the centers of the two electrode fingers almost satisfies tan {k (x2−λ / 8)} = √2. What is necessary is just to comprise.

The phase relationship between the internally reflected wave of the surface acoustic wave device of this embodiment and the excitation wave (fundamental wave) will be described with reference to FIGS. 3A to 3D.

FIGS. 3A and 3C are cross-sectional views of a main part of the surface acoustic wave device shown in FIG. 2, and FIG. 3B is a diagram showing an excitation wave and an inner part traveling leftward in the figure. Shows the phase relationship with the reflected wave,
FIG. 3D shows a relationship between the excitation wave and the internally reflected wave traveling rightward in the figure. In the drawing, it is assumed that the phase of the excitation wave is basically used, and the clockwise direction from the phase of the vector of the excitation wave is the phase delay amount of the reflected wave.

First, referring to FIGS. 3A and 3B,
The relationship between the reflected wave traveling to the left in the figure and the excitation wave will be described.

With reference to an arbitrary surface acoustic wave excitation point P1, a reflected wave reflected from one edge EA of an electrode finger having a width (λ / 16) closest to this excitation point is denoted by A, and this electrode is also denoted by A. Let B be the reflected wave reflected from the other edge EB of the finger. Also, the reflected wave passing through the electrode finger and reflected from one edge EC of the electrode finger having a width (3λ / 16) adjacent to the electrode finger is referred to as C, and the other edge ED of the same electrode finger is referred to as the excitation point. Let D be the reflected wave reflected from.

The phase of the reflected wave A has a phase delay element corresponding to a path length of 0.098λ with respect to the phase of the excitation wave at the excitation point, and a phase delay of 35.28 ° with respect to the phase of the excitation wave. Occurs. That is, assuming that the delay amount = X, X (35.28 °) is obtained from ((0.098 / 2) × 2) λ: X = λ: 360 °.

In this equation, (× 2) is a coefficient for obtaining a reciprocating path length.

The phase of the reflected wave B has a phase delay element corresponding to the path length of (0.098+ (1/8)) λ with respect to the phase of the excitation wave at the excitation point P1, and the edge EB Causes a phase delay of 260.28 ° with respect to the phase of the excitation wave. That is, assuming that the delay amount = X, ｛((0.098 / 2) × 2) + ((1/16) × 2)
+ (1/2)｝ λ: X = λ: 360 to X = 360 × (0.098+ (１ ／) + (１ ／))
= 260.28 ° is obtained.

In the above equation, (× 2) is a coefficient for obtaining a reciprocating path length, and (1/2) is a phase inversion at the edge EB.

The phase of the reflected wave C is (0.098+ (1/8) +0.3 with respect to the phase of the excitation wave at the excitation point P1.
04) A phase delay element corresponding to the path length of λ is generated, and a phase delay of 189.72 ° with respect to the phase of the excitation wave is generated. That is, assuming that the delay amount = X, ｛((0.098 / 2) × 2) + ((1/16) × 2)
+ (0.152 × 2)｝ λ: X = λ: 360 to X = 360 × (0.098+ (1/8) +0.304)
= 189.72 °.

In the above equation, (× 2) is a coefficient for obtaining the reciprocating path length.

The phase of the reflected wave D is (0.098+ (１ ／) + 3/3) with respect to the phase of the excitation wave at the excitation point P1.
8) A phase delay element corresponding to the path length of λ occurs, and
The phase inversion at the ED causes a phase delay of 144.72 ° with respect to the phase of the excitation wave. That is, the delay amount =
Assuming that X, ｛((0.098 / 2) × 2) + ((1/16) × 2)
+ (0.152 × 2) + (3/16) × 2 + (1 /
2) From｝ λ: X = λ: 360 to X = 360 × (0.098+ (1/8) +0.304+
(3/8) + (1/2)) = 504.72 ° = 144.
72 ° is obtained.

In the above equation, (× 2) is a coefficient for obtaining a reciprocating path length, and (1/2) is a phase inversion at the edge ED.

The result of combining the vectors of the reflected waves A, B, C, and D is the phase delay of the internally reflected wave with respect to the excitation wave. As shown in FIG. 3B, the internally reflected waves A, B,
The phase of the composite vector of the C and D vectors is 179.9.
7 °, which is almost in opposite phase with respect to the phase of the excitation wave.

The combined vector is obtained by combining the x component and the y component of the vector of the reflected waves A, B, C, and D in the orthogonal coordinate system.

Next, with reference to FIGS. 3 (C) and 3 (D), the relationship between the reflected wave traveling to the right in the figure and the excitation wave will be described.

With reference to an arbitrary surface acoustic wave excitation point P2,
The reflected wave reflected from one edge EE of the electrode finger having the width (3λ / 16) closest to the excitation point is E, and the reflected wave reflected from the other edge EF of the electrode finger is F.
And One edge EG of an electrode finger having a width (λ / 16) adjacent to the electrode finger and passing through the electrode finger with respect to the excitation point.
G is a reflected wave reflected from the other, and H is a reflected wave reflected from the other edge EH of the same electrode finger.

As for the phase of the reflected wave E, a phase delay element corresponding to a path length of 0.098λ is generated with respect to the phase of the excitation wave at the excitation point P2, and the phase of the excitation wave is 35.28 °. There is a delay.

The phase of the reflected wave F has a phase delay element corresponding to the path length of (0.098+ (3/8)) λ with respect to the phase of the excitation wave at the excitation point P2. 350.2 with respect to the phase of the excitation wave
An 8 ° phase delay occurs.

The phase of the reflected wave G is (0.098+ (3/8) +0.3 with respect to the phase of the excitation wave at the excitation point P2.
04) A phase delay element corresponding to the path length of λ is generated, and a phase delay of 279.72 ° is generated with respect to the phase of the excitation wave.

The phase of the reflected wave H is (0.098+ (3/8) +0.3 with respect to the phase of the excitation wave at the excitation point P2.
A phase delay element corresponding to a path length of 04+ (1/8) λ occurs,
Further, since phase inversion occurs at the edge EH, a phase delay of 144.72 ° occurs with respect to the phase of the excitation wave.

The above-described phase delays are shown in FIGS.
It can be derived by an expression having the same concept as the expression shown in the description of (B).

The result of synthesizing the vectors of the reflected waves E, F, G, and H is the phase delay of the internally reflected wave with respect to the excitation wave. As shown in FIG. 3D, the internally reflected waves E, F,
The combined vector of the G and H vectors is + 0.03 °, and has a substantially in-phase relationship with the phase of the excitation wave.

According to the above invention, a plurality of pairs of electrode fingers each having a pair of an electrode finger narrower than λ / 8 and an electrode finger wider than λ / 8 are provided on each of the common electrodes 13 and 14. ing. Here, a plurality of groups of paired electrode fingers provided on the common electrode 13 are referred to as a first group, and a plurality of groups of paired electrode fingers provided on the common electrode 14 are referred to as a second group. Then, the plurality of pair electrodes of the first group and the second group are interleaved with each other.

As a result, as a whole, electrode fingers narrower than λ / 8 and electrode fingers wider than λ / 8 are alternately arranged. Here, in the above invention, an electrode finger having a width of λ / 16 and an electrode finger having a width of 3λ / 16 are paired. Then, by selecting the interval between the pair of electrode fingers, FIG.
(B) and vector characteristics shown in FIG. 3 (D) are obtained.

As can be seen from the vector characteristics shown in FIGS. 3B and 3D, in the above embodiment, the direction of the combined vector is nπ ± 0.
The range is 03 °. Here, n is a natural number, and n is an even number (including 0) when the excitation wave and the reflected wave are in phase, and n is an odd number when the excitation wave and the reflected wave are out of phase.

However, the present invention is not limited to the above numerical values.

In the above embodiment, the position of one of the electrode fingers having a width of λ / 16 and the electrode finger having a width of 3λ / 16 is selected (for example, the electrode finger having a width of 3λ / 16). This is an example in which the electrode spacings of 0.098λ and 0.152λ are finally selected. As a result, the direction of the combined vector of the reflected wave is ±± with respect to the ideal propagation direction of the surface acoustic wave.
The range was 0.03 °.

However, a sufficient effect can be obtained even if the direction of the synthetic vector of the reflected wave is within ± 5 ° with respect to the ideal propagation direction of the surface acoustic wave.

In this case, an electrode finger having a width of λ / 16
The position of one of the pair of electrode fingers having a width of λ / 16 is shifted, and the electrode interval is set to 0.152λ ± 0.0.
07λ and 0.098λ − / + 0.007λ.

Note that the above-mentioned sign-/ + means minus plus, and is shown in a compound same order with respect to the above ±.

FIG. 4A shows the results of measuring the transfer characteristics and the group delay characteristics by matching the surface acoustic wave device with an external circuit. As can be seen from this characteristic diagram, both the transfer characteristic and the group delay characteristic have characteristics that are substantially symmetric about the fundamental frequency f0.

FIG. 4B shows a state in which a surface acoustic wave device configured by applying the present invention is matched with an external circuit. The entire surface acoustic wave device FA is actually a transducer for generating a surface acoustic wave shown in FIG.
And a transducer which receives the propagated surface acoustic wave and converts the vibration into electricity.

The external matching circuit is composed of elements connected to the input side and the output side of the surface acoustic wave device. On the input side, there is an inductor L12 connected between the signal input terminal and the ground connection terminal, and a capacitor C11 one of which is connected to the signal input terminal. On the output side, there is an inductor L22 connected between the signal output terminal and the ground connection terminal, and a capacitor C21 one of which is connected to the signal output terminal. In this example, L
And a matching circuit composed of C and C. However, as another means, the impedance of the surface acoustic wave device may be adjusted to perform matching.

In the above embodiment, the best directionality of the transmission direction of the fundamental wave of the surface acoustic wave is obtained.
Strictly, the distances t1 and t2 between the centers of the electrode fingers were determined. However, the present invention is not limited to this concept.
That is, t1 and t2 are set according to the characteristics required for the surface acoustic wave device.
It goes without saying that the deviation value of t2 may be increased or decreased.

In the above embodiment, the distance between the electrode finger having a width of λ / 16 in the figure and the electrode finger on the left side of the electrode finger is reduced.
The distance between the electrode finger having a width of / 16 and the electrode finger on the right side is widened. However, the present invention is not limited to this, and when a piezoelectric substrate having a different propagation characteristic from the above-described piezoelectric substrate is used, the arrangement relationship of the narrow interval and the wide interval is opposite to that of the above-described embodiment. May be.

The present invention is not limited to the above embodiment.

FIG. 5 shows another embodiment of the present invention.

Reference numeral 11 denotes a piezoelectric substrate made of quartz, and an interdigital transducer section 12 is formed on one surface thereof.

Inter digital transducer section 12
In the example, the first common electrode 23 and the second common electrode 24 are arranged in parallel at an interval. The first common electrode 23 has a first split electrode group (electrode fingers 3a1, 3b1, 3a2, 3b2) extending in the direction of the second common electrode 24.
3a3, 3b3,...) Are connected. 3a3, 3b
3, ... are not shown. Also, the second common electrode 14 has a second split electrode group (electrode fingers 4a1, 4b1, 4a2, 4b2, 4a3, extending in the direction of the first common electrode 13).
4b3,...) Are connected. 4a2, 4b2, 4a
3, 4b3, ... are not shown.

In the first split electrode group, a narrow electrode finger (an electrode finger having a suffix a) and a wide electrode finger (an electrode finger having a suffix b) form a pair. Are repeatedly arranged. This repetition period is λ. Also in the second split electrode group, a narrow electrode finger (electrode with suffix a) and a wide electrode finger (electrode with suffix b) form a pair, and this pair is repeated at intervals. Are arranged. This repetition period is λ.

Then, a pair of electrode fingers (3a1, 3b1), (3a2,
5b2), (3a3, 3b3),..., And a pair of electrode fingers (4a1,
4b1), (4a2, 4b2), (4a3, 4b3),
... are interleaved alternately. As a whole, wide electrode fingers and narrow electrode fingers are alternately arranged.

The common electrodes 13 and 14 and the split electrode group are formed of an electrode film mainly composed of aluminum (Al) or an aluminum (Al) alloy.

Further, in this embodiment, the pair of electrode fingers
The electrode fingers 3b1, 3b2, 3b having a width smaller than the width of λ / 8 (where λ is the wavelength of the surface acoustic wave that is the operating center frequency)
, 4a1, 4a2, 4a3,..., And electrode fingers 3a1, 3a2, 3a3,.
2, 4b3,...

Further, in this embodiment, the width W1 of the narrow electrode finger is λ / 16, and the width W of the narrow electrode finger is W.
2 is 0.1535λ.

In this embodiment, the width of the electrode finger is smaller than the reference value (λ / 8) by W1.
When the width of the electrode finger wider than the reference value (λ / 8) is W2, cos (k · 2W2) + sin (k · 2W2) = 2-c
os (k · 2W1) −sin (k · 2W1) (where k represents a wave number k = 2π / λ). As a result of the study, the inventors have found that when this expression is satisfied, the fundamental wave of the surface acoustic wave exhibits the best unidirectionality.

In the above embodiment, the width of the pair of electrode fingers is λ
/ 16 and 3λ / 16, the IDT was designed.

However, in this embodiment, the sum of the width of the pair of electrode fingers is different from λ / 4, and the width of the wider electrode finger is determined based on the above relational expression.

With reference to FIGS. 6A to 6D, the phase relationship between the internally reflected wave of the surface acoustic wave device of this embodiment and the excitation wave (fundamental wave) will be described.

FIGS. 6 (A) and 6 (C) are cross-sectional views of a main part of the surface acoustic wave device of FIG. 5, and FIG. 6 (B) shows an excitation wave and an inner part traveling leftward in the figure. Shows the phase relationship with the reflected wave,
FIG. 6D shows the relationship between the excitation wave and the internally reflected wave traveling rightward in the figure. In the figure, the phase delay of the reflected wave is shown clockwise from the excitation wave vector based on the phase of the excitation wave.

First, referring to FIGS. 6A and 6B,
The relationship between the reflected wave traveling to the left in the figure and the excitation wave will be described.

With reference to an arbitrary surface acoustic wave excitation point P1, a reflected wave reflected from one edge EA of an electrode finger having a width (λ / 16) closest to the excitation point is denoted by A, and this electrode is also denoted by A. Let B be the reflected wave reflected from the other edge EB of the finger. One edge of the electrode finger having a width (0.1535λ) adjacent to the electrode finger and passing through the electrode finger with respect to the excitation point
The reflected wave reflected from EC is denoted by C, and the reflected wave reflected from the other edge ED of the electrode finger is denoted by D.

The phase of the reflected wave A has a phase delay element corresponding to the path length of (λ / 16) × 2 with respect to the phase of the excitation wave at the excitation point, and is 45 ° with respect to the phase of the excitation wave. A phase delay occurs.

The phase of the reflected wave B is (λ / 16) × 2 + (λ / 16) × the phase of the excitation wave at the excitation point P1.
2, a phase delay element corresponding to the path length of 2 occurs, and a phase inversion occurs at the edge EB.
0 °, that is, a phase delay of (−90 °) occurs.

The phase of the reflected wave C is (1/16) × 2 + (1/16) × the phase of the excitation wave at the excitation point P1.
2 + 0.159 × 2) A phase delay element corresponding to the path length of λ is generated, and a phase delay of 204.48 ° with respect to the phase of the excitation wave is generated.

The phase of the reflected wave D is (１ ／) + (１ ／) + 0.31 with respect to the phase of the excitation wave at the excitation point P1.
8 + 0.307) A phase delay element corresponding to a path length of λ occurs,
Further, since the phase inversion occurs at the edge ED, a phase delay of 135 ° occurs with respect to the phase of the excitation wave.

The result of combining the vectors of the reflected waves A, B, C, and D is the phase delay of the internally reflected wave with respect to the excitation wave. As shown in FIG. 6B, the internally reflected waves A, B,
The combined vector of the C and D vectors is 179.99 °, which is almost in opposite phase with respect to the phase of the excitation wave. That is, the vibration propagates rightward in the drawing.

Next, with reference to FIGS. 6C and 6D, the relationship between the reflected wave traveling to the right in the figure and the excitation wave will be described.

With reference to an arbitrary surface acoustic wave excitation point P2,
The reflected wave reflected from one edge EE of the electrode finger having the width (3λ / 16) closest to the excitation point P2 is denoted by E, and the reflected wave reflected from the other edge EF of the electrode finger is also denoted by E.
F. G is a reflected wave that passes through the electrode finger and is reflected from one edge EG of the electrode finger having a width (λ / 16) adjacent thereto with respect to the excitation point P2, and G is the other edge of the same electrode finger. Let H be the reflected wave reflected from EH.

As for the phase of the reflected wave E, a phase delay element corresponding to a path length of (λ / 16) × 2 is generated with respect to the phase of the excitation wave at the excitation point P2, and is 45 ° with respect to the phase of the excitation wave. Is caused.

The phase of the reflected wave F is ((1/16) × 2 + (0.153) with respect to the phase of the excitation wave at the excitation point P2.
5 × 2)) A phase delay element corresponding to a path length of λ occurs, and
The phase inversion at the edge EF causes a phase delay of 335.52 ° with respect to the phase of the excitation wave.

The phase of the reflected wave G is ((1/16) × 2 + 0.1535) with respect to the phase of the excitation wave at the excitation point P2.
(× 2 + 0.159 × 2) A phase delay element corresponding to the path length of λ is generated, and a phase delay of 270 ° with respect to the phase of the excitation wave is generated.

The phase of the reflected wave H is ((1/16) × 2 + 0.1535) with respect to the phase of the excitation wave at the excitation point P2.
× 2 + 0.159 × 2 + (1/16) × 2) Since a phase delay element corresponding to a path length of λ is generated and a phase inversion occurs at the edge EH, a phase of 135 ° with respect to the phase of the excitation wave is generated. There is a delay.

The result of vector synthesis of the vectors of the reflected waves E, F, G, and H is the phase delay of the internally reflected wave with respect to the excitation wave. As shown in FIG. 6D, the composite vector of the vectors of the internally reflected waves E, F, G, and H is 0.001.
°, which is substantially in-phase with the phase of the excitation wave.

As can be seen from the vector characteristics shown in FIGS. 6B and 6D, in the above-described embodiment, the direction of the combined vector is different from the ideal propagation direction (the right direction in the figure) of the surface acoustic wave. The range is ± 0.001 °.

However, the present invention is not limited to the above numerical values.

In the above embodiment, λ of the pair of electrode fingers
The electrode fingers having a width of / 16 are fixed, the width of the wide electrode fingers is set to 0.1535λ, and the distance between the electrode fingers is set to 0.159.
λ was chosen. As a result, the direction of the resultant vector of the reflected wave is ± 0.001 ° with respect to the ideal propagation direction of the surface acoustic wave.
Was in the range.

However, a sufficient effect can be obtained even if the direction of the synthetic vector of the reflected wave is within ± 5 ° with respect to the ideal propagation direction of the surface acoustic wave.

In this case, the electrode finger having a width of λ / 16 is fixed, and the width of the electrode finger having a large width is set to (0.1535λ ± 0.
007λ). The positions of the edges of the outer electrode fingers of the pair of electrode fingers are fixed.

FIG. 7 shows the results of measuring the transfer characteristics and the group delay characteristics by matching the surface acoustic wave device with an external circuit in the same manner as in the previous embodiment. As can be seen from this characteristic diagram, both the transfer characteristic and the group delay characteristic have characteristics that are substantially symmetric about the fundamental frequency f0.

In each of the above embodiments, a configuration in which a wide electrode finger and a narrow electrode finger are alternately arranged is illustrated. Configuration adjacent to each other). As a result, the excitation wave and the reflected wave can be weighted according to the required characteristics.

[0119]

According to the surface acoustic wave device of the present invention described above, the transmission function characteristics in the signal pass band exhibit better characteristics and the insertion loss is small.

[Brief description of the drawings]

FIG. 1 is a view for explaining the operation and characteristics of a surface acoustic wave device to which the present inventor pays attention.

FIG. 2 is an explanatory view showing an embodiment of the surface acoustic wave device according to the present invention.

FIG. 3 is a view shown for explaining the operation principle of the surface acoustic wave device of FIG. 2;

FIG. 4 is a diagram illustrating frequency characteristics of the surface acoustic wave device of FIG. 2;

FIG. 5 is a diagram showing another embodiment of the surface acoustic wave device according to the present invention.

FIG. 6 is a view shown for explaining the operation principle of the surface acoustic wave device of FIG. 5;

FIG. 7 is a view showing frequency characteristics of the surface acoustic wave device of FIG. 5;

[Explanation of symbols]

11: Piezoelectric substrate, 12: IDT part, 13, 14, 23, 24 ... Common electrode 5a1, 5b1, 5a2, 6a1, 6b1, 6a2, 6
b2: Electrode finger.

Claims (12)

[Claims] A first common electrode formed on the piezoelectric substrate so as to be parallel to the first common electrode; a first common electrode connected to the first common electrode and extending in a direction of the second common electrode; A surface acoustic wave device comprising an interdigital transducer having a split electrode group and a second split electrode group connected to the second common electrode and extending in the direction of the first common electrode. A plurality of pairs of electrode fingers constituting one split electrode group, and a plurality of pairs of electrode fingers constituting the second split electrode group, the pairs are alternately interleaved at λ / 2 cycle, The pair of electrode fingers has an electrode finger narrower than a width of λ / 8 (where λ is the wavelength of a surface acoustic wave that is an operation center frequency).
an electrode finger wider than λ / 8, and an electrode finger included within a distance of λ / 2 from an arbitrary excitation source along a surface wave propagation direction with respect to a phase of an excitation wave excited by the interdigital transducer. The phase of the resultant vector of the resulting reflected wave is nπ-5 ° ≦ φ ≦ n
A surface acoustic wave device having a phase φ represented by π + 5 ° (n is a natural number). 2. A center distance (t1) between an arbitrary electrode finger and one of the electrode fingers disposed across the electrode finger is different from a center distance (t2) between the other electrode finger and the other electrode finger. The surface acoustic wave device according to claim 1, wherein 3. The electrode finger of the pair includes a narrow electrode finger having a width of λ / 16 and 0.1465λ ≦ w ≦ 0.1605.
2. The surface acoustic wave device according to claim 1, comprising a wide electrode finger having a width w of [lambda]. 4. The arrangement of the electrode fingers is such that the narrow electrode fingers and the wide electrode fingers are alternately arranged, and the distances between the centers of the widths of the electrode fingers are different from each other.
The method of claim 1, wherein t2 alternates, wherein t1 has a positive deviation with respect to the reference value (λ / 4), and t2 has a negative deviation with respect to the reference value (λ / 4). 3. The surface acoustic wave device according to 2. 5. The sum of the width of the pair of electrode fingers is λ / 4.
3. The surface acoustic wave device according to claim 2, wherein 6. The surface acoustic wave device according to claim 5, wherein one of the pair of electrode fingers has a width of λ / 16 and the other electrode finger has a width of 3λ / 16. . 7. The width of one electrode finger constituting the pair of electrode fingers is w, and the width of the other electrode finger is (λ / 4) −w,
Assuming that the distance between the centers of these two electrode fingers is x1, tan {k (x1- (λ / 8))} = 1 / (cos ｛k
6. The elastic surface according to claim 5, wherein x1 is selected so as to substantially satisfy ((3λ / 4) + 2w)｝ (where k is a wave number and k = 2π / λ). Wave device. 8. A width of one electrode finger of the pair of electrode fingers is λ / 16, and a width of the other electrode finger is 3λ / 16, and a center distance x2 between these two electrode fingers is: The surface acoustic wave device according to claim 5, wherein the surface acoustic wave device is selected so as to substantially satisfy tan {k (x2-λ / 8)} = ／ 2. 9. A first and second common electrode formed in parallel on a piezoelectric substrate, and a first split electrode connected to the first common electrode and extending in the direction of the second common electrode. A group, a second common electrode connected to the second common electrode and extending in the direction of the first common electrode.
A plurality of pairs of electrode fingers forming the first split electrode group, and a plurality of pairs forming the second split electrode group. The electrode fingers of the pair are alternately interleaved with each other, and the electrode fingers of the pair have an electrode width narrower than the width of λ / 8 (where λ is the wavelength of the surface acoustic wave that is the operating center frequency). A finger and a wider electrode finger than λ / 8, wherein the sum of the width of the narrow electrode finger and the wide electrode finger is smaller than λ / 4; A surface acoustic wave device characterized in that the sum of the distances between adjacent edges of the electrode fingers is 3λ / 8. 10. The surface acoustic wave device according to claim 9, wherein the width of the narrow electrode finger is λ / 16. 11. When the width of one electrode finger constituting the pair of electrode fingers is w1 and the width of the other electrode finger is w2, cos (k · 2w2) + sin (k · 2w2) = 2-c
10. The w1 and w2 are selected to substantially satisfy os (k · 2w1) −sin (k · 2w1) (where k indicates a wave number k = 2π / λ). The surface acoustic wave device according to claim 1. 12. The width of one electrode finger constituting the pair of electrode fingers is λ / 16, and the width of the other electrode finger is 0.1535.
The surface acoustic wave device according to claim 10, wherein?