JP3110475B2 - Surface acoustic wave resonator - Google Patents

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 resonator in which a plurality of electrode structures in which a plurality of IDTs (interdigital converters) are sandwiched between a pair of reflectors are cascaded on a piezoelectric substrate. .

[0002]

2. Description of the Related Art In recent years, it has been proposed to use a surface acoustic wave device as a front-end filter for wireless communication using a VHF band and a UHF band to reduce the size and weight of a wireless device. The electrical characteristics required as a front-end filter are (a) low insertion loss, (b) low in-band ripple, (c) low out-of-band spurious level, and (d) high out-of-band attenuation. (E) To have an appropriate bandwidth in order to secure the number of channels required for the communication system, and it is required to satisfy all of these conditions.

As a conventional surface acoustic wave resonator filter, there is a resonator type filter in which an interdigital electrode is sandwiched between a pair of reflectors. Although this surface acoustic wave resonator filter has a small insertion loss, it has a characteristic that the fractional bandwidth is as narrow as about 0.05%, and thus an improvement is required to satisfy the above-mentioned conditions. I was As a conventional surface acoustic wave resonator filter, lithium tantalate (L
iTaO3) substrate and quartz substrate, and input IDT
And an output IDT sandwiched between a pair of reflectors. A vertical dual-mode bandpass filter is formed by utilizing two modes of vibration of the zeroth-order vertical and the first-order longitudinal that occur in the resonator constituted by the input IDT and the output IDT, and the fractional bandwidth. A surface acoustic wave resonator filter which attempts to widen the resonance frequency is known (Japanese Patent Laid-Open No. 61-285814).
No.).

However, in this vertical dual-mode bandpass filter, when a quartz substrate is used as the piezoelectric substrate, even if the normalized film thickness of the electrode is increased to 4%, the specific bandwidth is only up to 0.3%. There was a problem that it could not be achieved and the ripple in the band was large. Also, when lithium tantalate is used as the piezoelectric substrate, when the normalized film thickness is increased to 4%, the specific bandwidth can be achieved up to 0.47%, but there is a problem that the in-band ripple is large.

As described above, the conventional surface acoustic wave resonator filter is required to have a fractional bandwidth of 0.3% or more, a small in-band ripple, a low out-of-band spurious level, and a large out-of-band attenuation. It is difficult to use it for applications such as wireless communication front-end filters. In order to reduce the out-of-band spurious level, on the piezoelectric substrate,
There is a surface acoustic wave resonator in which a plurality of electrode structure rows in which a plurality of IDTs are sandwiched between a pair of reflectors are cascaded. That is, as shown in FIG.
An electrode structure row 50 in which 1, 52 and 53 are sandwiched between a pair of reflectors 54 and 55, and an electrode structure row 60 in which IDTs 61, 62 and 63 are sandwiched between a pair of reflectors 64 and 65 are formed. Connection IDT 52 and connection ID of structure column 50
One of the electrodes of T53 is connected to the connection IDT of the electrode structure row 60.
The electrode structure row 50 and the electrode structure row 60 are connected in cascade by being connected to the electrode 62 and one of the electrodes of the connection IDT 63, respectively.

The input I located at the center of the electrode structure row 50
Outside the DT 51, an input bonding pad 56 to which one of the electrodes of the input IDT 51 is connected is provided.
Outside the output IDT 61 located at the center of the electrode structure row 60, an output bonding pad 66 to which one of the electrodes of the output IDT 61 is connected is provided. Also,
IDTs for connection on both sides of the input bonding pads 56
Ground bonding pads 57 and 58 are provided for grounding the other of the electrodes 51 and 52, and ground bonding pads for grounding the other of the connection IDTs 61 and 62 on both sides of the output bonding pad 66. 6
7, 68 are provided.

A signal source 44 is inserted between the input terminal IN and the ground together with a termination impedance 42 of 50 Ω often used in the UHF band, and a termination impedance 46 of the same 50 Ω is connected between the output terminal OUT and the ground. Have been.
Grounding bonding pads 59 and 69 are provided between the electrode structure row 50 and the electrode structure row 60 to ground the other of the interdigital electrodes of the input IDT 52 and the other of the interdigital electrodes of the output IDT 62. Have been. This is because thin wires cannot be routed for grounding. It is also conceivable to adopt a two-layer wiring structure without providing the bonding pads 59 and 69 for grounding, but this is not realistic due to high cost.

[0008]

As described above, in the conventional surface acoustic wave resonator, the bonding pads 59 and 69 for grounding which require a large surface area are connected to the electrode structure rows 50 and 60.
Since it is necessary to provide them between them, there is a problem that the chip size becomes large and the surface acoustic wave resonator device becomes large.

An object of the present invention is to satisfy the conditions that the fractional bandwidth is 0.3% or more, the in-band ripple is small, the out-of-band spurious level is low, and the out-of-band attenuation is large, and the device size is increased. It is another object of the present invention to provide a surface acoustic wave resonator that does not cause the problem.

[0010]

SUMMARY OF THE INVENTION The present inventor has studied various conditions required when a surface acoustic wave resonator is used for applications such as a front end filter for wireless communication, and satisfies these conditions. In addition, a surface acoustic wave resonator that can be connected in cascade without providing a ground bonding pad between the electrode structure rows was realized.

In order to use a surface acoustic wave resonator for a front end filter, as described above, (a) the insertion loss is small, (b) the ripple in the band is small, and (c) the spurious level outside the band is low. Strict electrical characteristics must be satisfied: low, (d) large amount of out-of-band attenuation, and (e) having an appropriate bandwidth to secure the required number of channels.

In order to satisfy such many electric characteristics, it is desirable that the surface acoustic wave resonator has a large degree of freedom in designing. Therefore, first, a plurality of IDTs having interdigital electrodes are provided, and these IDTs are sandwiched between a pair of reflectors to form one electrode structure row. A resonator was configured.

The input IDT in the electrode structure row,
Instead of providing a bonding pad for grounding to connect one of the electrodes of the output IDT, a connection reflector having a plurality of electrode fingers connected to one electrode of these IDTs is provided between the IDTs. did. Consideration was given to reducing the in-band ripple. What is in-band ripple?
The difference between the maximum value and the minimum value of the insertion loss in the pass band. If there is a ripple in the band, the transmitted power in the band will be different, and when using a surface acoustic wave resonator filter, The magnitude of the in-band ripple is a very important characteristic.

Therefore, as described later, the inventor manufactured surface acoustic wave resonators having various electrode thicknesses, various electrode pairs, and various connection reflector electrodes, and measured the pass band characteristics. As a result, the total logarithm NT of the plurality of IDTs in each electrode structure row is α + β (h / λ) −γ + δNt ≦ NT ≦ α + β (h / λ) + γ + δNt where h / λ is the thickness h of the electrodes of the plurality of IDTs. Is normalized by the wavelength λ of the surface acoustic wave, Nt is the total electrode index of the connecting reflector, and is in the range of α = 125, β = −2000, γ = 30, δ = −0.65. It is concluded that it is desirable.

Further, of the plurality of IDTs, the sum N2 + N of the logarithm N1 of the central IDT formed at the center position and the logarithms of the IDTs on both sides formed at the position sandwiching the central IDT.
The ratio of NC (= (N2 + N3) / N1) is p + q (h / .lambda.)-R + sNt.ltoreq.NC.ltoreq.p + q (h / .lambda.) + R + sNt where p = 1.1, q = 20, r = 0.8 , S = −0.03.

When the surface acoustic wave resonator is used as a front-end filter, the terminal impedance is desirably 50Ω, but may be about 50 to 500Ω in some cases. At this time, the maximum aperture length is adjusted so as to best match the termination impedance, so that in-band ripple and insertion loss can be reduced.

[0017]

According to the present invention, one of the input IDT and output IDT electrodes of the cascade-connected electrode structure row is connected to the connection reflector having a plurality of electrode fingers. The size reduction of the surface acoustic wave resonator device can be realized without providing a bonding pad for grounding therebetween.

Further, according to the present invention, by setting the total logarithm of the IDT within a predetermined range with respect to the electrode thickness, the in-band ripple can be reduced with a wide specific bandwidth. Further, by keeping the log ratio of the IDT within a predetermined range,
In-band ripple can be further reduced.

[0019]

FIG. 1 shows a basic structure of a surface acoustic wave resonator according to the present invention. As shown in FIG. 1, on the surface of the piezoelectric substrate 10, three IDTs, two ground reflectors (grounded connection reflectors) inserted between the three IDTs, and three IDTs are provided.
Two electrode structure rows 20 and 30 each formed by a pair of reflectors sandwiching T and two ground reflectors are formed.

That is, as the electrode structure row 20, an input IDT having N1 pairs of interdigital electrodes at the center.
A ground reflector 24 having N4 grounded electrodes and a ground reflector 25 having N5 grounded electrodes are formed on both sides of the input IDT 21. Further, ground reflectors 24 and 25 are formed. A connection IDT 22 having N2 pairs of interdigital electrodes and a connection IDT 23 having N3 pairs of interdigital electrodes are formed on both sides. These input IDT 21, ground reflector 24,
5. Connecting IDTs 22 and 23 to a pair of reflectors 26 and 27
To form an electrode structure row 20.

As the electrode structure row 30, an output IDT 31 having N1 pairs of interdigital electrodes in the center is formed, and a ground reflector 34 having N4 grounded electrodes on both sides of the output IDT 31 and N5 electrodes. And a connection IDT 32 having N2 pairs of interdigital electrodes on both sides of the ground reflectors 34 and 35, and a connection IDT33 having N3 pairs of interdigital electrodes. Are formed. The output IDT 31, the ground reflectors 34 and 35, and the connection IDTs 32 and 33 are sandwiched between a pair of reflectors 36 and 37 to form an electrode structure row 30.

The input bonding pad 28 is formed outside the input IDT 21 of the electrode structure row 20 and is connected to an interdigital electrode outside the input IDT 21. The interdigital electrode inside the input IDT is commonly connected to the ground reflectors 24 and 25 on both sides.
Ground bonding pads 29a, 29b, 29c and 29d are formed on both sides of the input bonding pad 28. The bonding pad 29a for grounding is a connection ID.
The ground bonding pad 29c is connected to the electrode of the ground reflector 24, and is connected to the interdigital electrode outside T22. Ground bonding pad 29b
Is connected to the interdigital electrode outside the connection IDT 23, and the ground bonding pad 29d is connected to the electrode of the ground reflector 25.

The output bonding pad 38 is formed outside the output IDT 31 of the electrode structure row 30 and is connected to an interdigital electrode outside the output IDT 31. The interdigital electrode inside the output IDT is commonly connected to the ground reflectors 34 and 35 on both sides.
Ground bonding pads 39a, 39b, 39c, 39d are formed on both sides of the output bonding pad 38. The ground bonding pad 39a is a connection ID.
The ground bonding pad 39 is connected to the electrode of the ground reflector 34, and is connected to the interdigital electrode outside T32. The bonding pad 39b for grounding
The connection is made to the interdigital electrode outside the connection IDT 33, and the ground bonding pad 39 d is connected to the electrode of the ground reflector 35.

The interdigital electrode inside the connection IDT 22 of the electrode structure row 20 is connected to the connection IDT of the electrode structure row 30.
By connecting the interdigital electrode inside the connection IDT 23 of the electrode structure row 20 to the interdigital electrode inside the connection IDT 33 of the electrode structure row 30 by connecting to the interdigital electrode inside the DT 32. The structure row 20 and the electrode structure row 30 are connected in cascade.

The input IDT 21 of the electrode structure row 20
May be connected in common with the interdigital electrode inside the output IDT 31 of the electrode structure row 30, but it is preferable in terms of characteristics to separate them as in the present embodiment. UHF between input terminal IN and ground
A signal source 14 is inserted together with a termination impedance 12 of 50Ω, which is often used in the band, and a termination impedance 16 of 50Ω is connected between the output terminal OUT and the ground.

In this embodiment, the piezoelectric substrate 10 is 45 °
A rotating X-plate Z- propagating lithium tetraborate (Li ₂ B ₄ O ₇ ) substrate was used. The propagation speed of the surface acoustic wave is 3440 m / sec. As a surface acoustic wave in the Z-axis direction of the piezoelectric substrate 10 is propagated, 45 ° rotated X-cut Z propagation lithium tetraborate propagation <br/> direction of a surface acoustic wave is a piezoelectric substrate 10 in the electrode structure row 20 and 30 The direction was the Z-axis direction of the substrate.

The IDTs 21, 22, 2 in this embodiment
The interdigital electrodes 3, 31, 32, and 33 were formed of an aluminum layer or an aluminum alloy layer.
However, since the lithium tetraborate substrate, which is a piezoelectric substrate, was dissolved in an aluminum etchant, electrodes were formed by a lift-off method. IDT21,22,2
The maximum crossing width of the interdigital electrodes at 3, 31, 32, and 33 is finally determined so that the image impedance of the filter matches 50Ω. The normalized maximum intersection width W / λ normalized by λ was set to 170. Weighting for transverse mode suppression was made by general cosine apoptosis.

The reflectors of the ground reflectors 24, 25, 34 and 35 and the reflectors 26, 27, 36 and 37 formed gratings as metal layers (electrode fingers) made of an aluminum layer or an aluminum alloy. Reflector 26, 2
The number of metal strips 7, 36, and 37 was set to 100 in consideration of the surface acoustic wave reflectivity per metal strip.

In the surface acoustic wave resonator having the above-described configuration, the normalized thickness of the aluminum layer of the interdigital electrode (the thickness h is normalized by the wavelength λ of the surface acoustic wave) h / λ; IDT21 for input or IDT31 for output
Logarithm N1 and connection IDTs 22 and 23 or connection IDTs
The logarithmic ratio NC of the sum N2 + N3 of the logarithms of 32 and 33 NC (= (N
2 + N3) / N1) and IDTs 21 to 23 or 31 to 3
The characteristics of the surface acoustic wave resonator filter when the total logarithm NT of 3 (= N1 + N2 + N3) and the total number of electrodes Nt of the ground reflectors 24, 25 or 34, 35 were respectively changed were measured. The measurement results are shown in FIGS.

FIGS. 2 and 3 show the normalized film thickness h / λ and the logarithmic ratio N.
This shows the change in the in-band ripple when the total logarithm NT is changed while C is kept at a constant value. FIG. 2 shows a case where the normalized film thickness h / λ is 0.01, the logarithmic ratio NC of the IDT is 1.2, and the total number of electrodes Nt of the ground reflector is 20.
The change of the magnitude of the in-band ripple when the total logarithm NT is changed from about 70 pairs to about 140 pairs is shown. As is apparent from FIG. 2, the in-band ripple has a total logarithm NT of about 80 to
It becomes 1.5 dB or less in the range of 110 pairs.

FIG. 3 shows that when the normalized film thickness h / λ is 0.025, the logarithmic ratio NC of the IDT is 1.14, and the total number Nt of electrodes of the ground reflector is 20, the total logarithm NT About 40
The change of the magnitude of the in-band ripple when changing from a pair to about 100 pairs is shown. As is apparent from FIG. 3, the in-band ripple is 1.1 when the total logarithm NT is in the range of about 60 to 90 pairs.
5 dB or less.

FIG. 4 shows the change in the in-band ripple when the logarithmic ratio NC is changed while the normalized film thickness h / λ and the total logarithm NT are kept constant. That is, the normalized film thickness h /
FIG. 4 shows a change in the magnitude of the in-band ripple when the logarithmic ratio NC is changed from 0.2 to 2.8 when .lambda. is 0.025 and the total logarithm NT is 73.5 pairs. . FIG.
As is apparent from the above, the in-band ripple is 1.5 dB or less when the logarithmic ratio NC is in the range of about 0.6 to 1.8.

FIGS. 5 to 7 show the distribution of in-band ripples when the total logarithm NT and the logarithmic ratio NC are changed while the normalized film thickness h / λ is kept constant. Points where the in-band ripple is 1.5 dB or less are indicated by ◎, points where the in-band ripple is in the range of 1.5 to 3 dB are indicated by ○, and points where the in-band ripple is 3 dB or more are indicated by ×. . FIG. 5 shows that the normalized film thickness h / λ is 0.01 and the total number of electrodes Nt of the ground reflector is Nt.
Shows the distribution of the band ripple when the number is 20. In the region where the in-band ripple is 3 dB or less (◎ and ○), the total logarithm NT is in the range of about 95 to 140 pairs and the log ratio NC is about 0.3.
The area (◎) in which the in-band ripple is 1.5 dB or less is included in this area.

FIG. 6 shows the distribution of in-band ripples when the normalized film thickness h / λ is 0.02 and the total number of electrodes Nt of the ground reflector is 20. The region where the in-band ripple is 3 dB or less (◎ and）) is the region where the total logarithm NT is in the range of about 70 to 115 pairs and the log ratio NC is in the range of about 0.3 to 1.9.
This region includes a region (◎) in which the in-band ripple is 1.5 dB or less.

FIG. 7 shows the band ripple distribution when the normalized film thickness h / λ is 0.03 and the total number of electrodes Nt of the ground reflector is 20. The region where the in-band ripple is 3 dB or less (◎ and ○) is the region where the total logarithm NT is in the range of about 50 to 80 pairs and the log ratio NC is in the range of about 0.5 to 2.2. Includes an area (◎) where the in-band ripple is 1.5 dB or less.

FIGS. 8 and 9 are graphs summarizing the measurement results shown in FIGS. FIG. 8 shows the normalized film thickness h / λ.
Is the horizontal axis, and the total logarithm NT is the vertical axis, and shows the region where the in-band ripple is below a predetermined value. As is clear from FIG. 8, the region where the in-band ripple is equal to or less than the predetermined value is the total logarithm N
T falls within the range of the function of the normalized film thickness h / λ represented by the following equation.

Α + β (h / λ) −γ + δNt ≦ NT ≦ α + β (h / λ) + γ + δNt where α, β, γ, and δ are constants. As is clear from FIG. 8, the localization numbers of the function indicating the region where the in-band ripple is 3 dB are α = 125 and β = −200.
0, γ = 30, δ = −0.65. In order to realize a smaller in-band ripple, γ may be reduced. FIG. 8 shows a range of γ = 20 and a range of γ = 10. γ
= 20, the in-band ripple becomes 1.5 dB or less, and if γ = 10, the in-band ripple can be further reduced. When the total number of electrodes Nt of the ground reflector increases, the line of γ = 0 shifts downward in FIG. FIG. 8 shows the case of Nt = 0 (two-dot chain line), the case of Nt = 20 (three-dot chain line), the case of Nt = 0 (one-dot chain line).

FIG. 9 shows a region where the in-band ripple is equal to or less than a predetermined value with the normalized film thickness h / λ as the horizontal axis and the logarithmic ratio NC as the vertical axis. As is clear from the figure, the region where the in-band ripple is equal to or less than the predetermined value is the range of the function of the normalized film thickness h / λ in which the total logarithm NT is expressed by the following equation. p + q (h / λ) -r + sNt ≦ NC ≦ p + q (h / λ) + r + sNt where p, q, r, and s are constants.

As is clear from FIG. 9, the constant of the function indicating the region where the in-band ripple is 3 dB or less is p = 1.
1, q = 20, r = 0.8, and s = −0.03. It should be noted that r can be reduced to realize even smaller in-band ripple. FIG. 9 shows a range of r = 0.6 and a range of r = 0.2. If r = 0.6, the in-band ripple is 1.
When it becomes 5 dB or less, and r = 0.2, the in-band ripple can be further reduced.

When the total number of electrodes Nt of the ground reflector increases, the line of γ = 0 shifts downward in FIG. FIG. 9 shows the case where Nt = 0 (dotted line), the case of Nt = 10 (dotted line), and the case of Nt = 20 (dotted line). In order to realize a surface acoustic wave resonator filter having a small in-band ripple, as shown in FIGS. 8 and 9, the normalized film thickness h / λ is in the range of 0.005 to 0.04. It is desirable.

FIGS. 10 and 11 show the shape of the in-band ripple of a specific example of the surface acoustic wave resonator filter. The solid line indicates the insertion loss. The horizontal axis represents the frequency fo (= 386.56 MHz) corresponding to the electrode period of the IDT. The characteristic of the surface acoustic wave resonator filter according to the embodiment of the present invention is shown in FIG. Is shown.
As shown in FIG. 1, the surface acoustic wave resonator filter according to the present embodiment has two cascade-connected electrode structures having the same configuration, and various constants are as follows.

Piezoelectric substrate = 45 ° rotating X-plate Z- propagating lithium tetraborate substrate Film thickness of interdigital electrode of each IDT 21, 22, 23 (31, 32, 33) = 210 nm Normalized film thickness h / λ = 0. Opening length of each IDT 21, 22, 23 (31, 32, 33) = 1300 μm Weighting of each IDT 21, 22, 23 (31, 32, 33) = cosine apoptization Total logarithm NT = 73.5 logarithmic ratio NC = 1.14 Log N1 of IDT21 (31) N3 = 33.5 Log N2 of IDT22 (32) = 24.5 Log N3 of IDT23 (33) N3 = 25.5 Strip of each ground reflector 24,25 (34,35) The number of electrodes = 10 The number of strip electrodes of each reflector 26, 27 (36, 37) = 100 At this time, the magnitude of the in-band ripple is a very small value of 0.8 dB. I realized it.

FIG. 11 shows the characteristics of a surface acoustic wave resonator filter according to a comparative example of the present invention. The respective constants of the surface acoustic wave resonator filter of this comparative example are as follows. Piezoelectric substrate = 45 ° rotating X-plate Z- propagating lithium tetraborate substrate Film thickness of interdigital electrode of each IDT 21, 22, 23 (31, 33, 33) = 210 nm Normalized film thickness h / λ = 0.024 Each IDT 21 , 22, 23 (31, 32, 33) = 1300 µm Weight of each IDT 21, 22, 23 (31, 32, 33) = cosine apoptization Total logarithmic NT = 120.5 Logarithmic ratio NC = 1.43 Logarithm N1 of IDT21 (31) = 49.5 Logarithm N2 of IDT22 (32) = 25.5 Logarithm N3 of IDT23 (33) N3 = 35.5 Number of strip electrodes of each ground reflector 24, 25 (34, 35) = 10 number of strip electrodes of each reflector 26, 27 (36, 37) = 100 At this time, the magnitude of the in-band ripple was as large as 4.6 dB.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, the electrode structure row 20,
Although the ground reflectors 24, 25 or 34, 35 are provided on both sides of the input IDT 21 or the output IDT 31 of 30, if the total number of electrodes is within a predetermined range, as shown in FIG. 24 or 34 may be provided. In the above embodiment, the unbalanced input and output are connected to the input terminal IN and the output terminal OUT.
4, 25, 34, 35 may be balanced input / output without grounding.

In the above embodiment, the ground reflectors 24, 2
The electrodes 5 or 34 and 35 were connected to the ground bonding pads 29c and 29d or 39c and 39d, respectively, as shown in FIG.
9a and 29b, 29c and 29d, 39a and 39b, 39
It may be grounded by connecting c and 39d, respectively. It is better not to connect the ground bonding pads 29a, 29b and the ground bonding pads 29c, 29d. Similarly, it is better not to connect the ground bonding pads 39a, 39b and the ground bonding pads 39c, 39d.

Further, in the above embodiment, a surface acoustic wave resonator is formed by cascading two electrode structure rows, but a surface acoustic wave resonator is formed by cascading three or more electrode structure rows. Is also good. By cascading a plurality of electrode structure rows, a surface acoustic wave resonator filter having a low out-of-band spurious level and a large out-of-band attenuation can be realized. Furthermore, in the above embodiment, the IDT is weighted by cosine or linear apodization in order to suppress the transverse mode, but other weighting methods such as cosine squared apodization and modified cosine apodization may be used. When the weighting method is changed, by increasing or decreasing the number of interdigital electrodes of each IDT, a surface acoustic wave resonator filter having similar characteristics can be realized.

[0047]

As described above, the present invention provides a plurality of IDTs.
In a surface acoustic wave resonator in which a plurality of electrode structure rows sandwiched between a pair of reflectors are cascaded on a piezoelectric substrate, one of the IDT electrodes is connected between a plurality of IDTs in each electrode structure row. Since a connection reflector having a plurality of electrode fingers is inserted, the specific bandwidth is 0.3% or more, the in-band ripple is small, the out-of-band spurious level is low, and the A surface acoustic wave resonator that satisfies the condition that the external attenuation is large and does not increase the device size can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a basic structure of a surface acoustic wave resonator according to one embodiment of the present invention.

FIG. 2 is a graph showing a change in in-band ripple when the total logarithm NT is changed while the normalized thickness h / λ of the surface acoustic wave resonator and the logarithmic ratio NC are kept constant.

FIG. 3 is a graph showing a change in the in-band ripple when the total logarithm NT is changed while the normalized thickness h / λ of the surface acoustic wave resonator and the logarithmic ratio NC are kept constant.

FIG. 4 is a graph showing the change in the in-band ripple when the normalized film thickness h / λ of the surface acoustic wave resonator and the total logarithm NT are kept constant and the logarithmic ratio NC is changed.

FIG. 5 is a graph showing the distribution of in-band ripples when the normalized logarithmic thickness h / λ of the surface acoustic wave resonator is fixed and the total logarithm NT and the logarithmic ratio NC are changed.

FIG. 6 is a graph showing the distribution of in-band ripples when the normalized logarithmic value h / λ of the surface acoustic wave resonator is fixed and the total logarithm NT and the logarithmic ratio NC are changed.

FIG. 7 is a graph showing the distribution of in-band ripples when the normalized logarithmic value h / λ of the surface acoustic wave resonator is kept constant and the total logarithm NT and the logarithmic ratio NC are changed.

8 is a graph summarizing the measurement results shown in FIGS. 2 to 7 and showing a region of the total logarithm NT where the in-band ripple of the surface acoustic wave resonator is equal to or less than a predetermined value.

FIG. 9 is a graph summarizing the measurement results shown in FIGS. 2 to 7 and showing a region of a logarithmic ratio NC where the in-band ripple of the surface acoustic wave resonator is equal to or less than a predetermined value.

FIG. 10 is a graph showing an insertion loss characteristic of an example of the surface acoustic wave resonator according to the present invention.

FIG. 11 is a graph showing insertion loss characteristics of a comparative example of the surface acoustic wave resonator.

FIG. 12 is a perspective view showing a basic structure of a surface acoustic wave resonator according to one embodiment of the present invention.

FIG. 13 is a perspective view showing a basic structure of a conventional surface acoustic wave resonator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Piezoelectric substrate 12, 16 ... Termination impedance 14 ... Signal source 20, 30 ... Electrode structure row 21 ... Input IDT 31 ... Output IDT 22, 23, 32, 33 ... Connection IDT 24, 25, 34, 35 ... Ground reflectors 26, 27, 36, 37 Reflector 28 Input bonding pad 38 Output bonding pad 29a, 29b, 29c, 29d, 39a, 39b, 3
9c, 39d: Grounding bonding pad 40: Piezoelectric substrate 42, 46 ... Termination impedance 44: Signal source 50, 60 ... Electrode structure row 51: Input IDT 61 ... Output IDT 52, 53, 62, 63 ... Connection IDT 54, 55, 64, 65 ... reflector 56 ... input bonding pad 66 ... output bonding pad 57, 58, 59, 67, 68, 69 ... grounding bonding pad

Continuation of front page (56) References JP-A-59-21116 (JP, A) JP-A-61-154021 (JP, U) Tokuyo Sho 57-501908 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H03H 9/145

Claims (4)

(57) [Claims] 1. A surface acoustic wave resonator in which a plurality of IDTs sandwiched between a plurality of IDTs by a pair of reflectors are connected in cascade on a piezoelectric substrate. A connection reflector having a plurality of electrode fingers connected to one electrode of the IDT is inserted , and two electrode structure rows are provided, and one of the electrodes of the IDT at the center of one electrode structure row is input. for
Connected to one end of the terminal and the other end of the IDT electrode is
Connected to the connecting reflector electrodes that, for outputting one of the central IDT electrodes of the other electrode structure column
Connected to one end of the terminal and the other end of the IDT electrode is
Connected to the electrode of the connection reflector, and on both sides of the central IDT of the one electrode structure row.
The other of the electrodes of the IDT and the center of the other electrode structure row
Common connection with the other of the IDT electrodes on both sides of the IDT
And one of the IDT electrodes on both sides of the one electrode structure row
And the IDT electrodes on both sides of the other electrode structure row
A surface acoustic wave resonator characterized in that one of the surfaces is grounded . 2. A plurality of IDTs are sandwiched by a pair of reflectors.
In a surface acoustic wave resonator in which a plurality of electrode structure rows are cascade-connected on a piezoelectric substrate, a plurality of electrode structure rows connected to one electrode of the IDT are provided between a plurality of IDTs of each electrode structure row. A connection reflector having two electrode fingers is inserted , the piezoelectric substrate is a lithium tetraborate single crystal, and the total logarithm NT of a plurality of IDTs in each electrode structure row is α + β (h / λ) -γ + δNt ≦ NT ≦ α + β (h /
λ) + γ + δNt where h / λ is a normalized film thickness obtained by normalizing the thickness h of the electrodes of the plurality of IDTs with the wavelength λ of the surface acoustic wave, Nt is the total number of electrodes of the connecting reflector, α = 125, β = −2000, γ = 30, δ = −0.6
5. A surface acoustic wave resonator characterized by being in the range of 5. 3. The surface acoustic wave resonator according to claim 2, wherein the plurality of IDTs are formed at a center I formed at a center position.
DT and the IDTs on both sides formed at positions sandwiching the central IDT. The ratio NC of the sum N2 + N3 of the logarithm N1 of the central IDT and the logarithm of the surrounding IDT is p + q (h / λ). −r + sNt ≦ NC ≦ p + q (h /
λ) + r + sNt where p = 1.1, q = 20, r = 0.8, s = −0.
03. A surface acoustic wave resonator characterized by being in the range of 03. 4. The surface acoustic wave resonator according to claim 2 , further comprising two rows of said electrode structure rows, wherein one of the center IDT electrodes of one of the electrode structure rows is connected to one end of an input terminal. The other of the electrodes of the IDT is connected to the electrode of the adjacent connection reflector, one of the electrodes of the center IDT of the other electrode structure row is connected to one end of the output terminal, and the other of the electrodes of the IDT is connected. Are connected to the electrodes of the adjacent connection reflectors, and the other IDT electrodes on both sides of the one electrode structure row sandwiching the central IDT and the IDTs on both sides sandwiching the center IDT of the other electrode structure row And one of the IDT electrodes on both sides of the one electrode structure row is grounded, and one of the IDT electrodes on both sides of the other electrode structure row is grounded. Surface acoustic wave resonator.