JPH10303698A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the electric power resistance by composing a 1st and a 2nd one-terminal-couple surface acoustic wave resonator of inter-digital electrodes having electrode digits, and setting cycle of the electrode digits of at least one one-terminal-couple surface acoustic wave resonator of the 2nd one-terminal couple surface acoustic wave resonator within a specific range. SOLUTION: The cycle λ of the electrode digits of the oneterminal-couple surface acoustic wave resonator is presented as 0.99λav2 <λ<1.01λav2 (where λav2 is the mean value of cycles of the electrode digits of the 2nd one-terminal- couple surface acoustic wave resonator). Currents flowing to respective series resonators S1 , S2 , and S3 are so related that is1 >is2 >is3 and currents flowing to parallel resonators P1 , P2 , and P3 are so related that iP1 >iP2 >iP3 , so the series and parallel resonators S1 and P1 of the initial stages have the largest electric power resistance. The electric power resistance is the weakest almost at the cutoff frequency where the temperature of the element is the highest. The low cutoff frequency of the surface acoustic wave element is close to the resonance frequency of the parallel resonators and the high cutoff frequency is close to the resonance frequency of the series resonators.

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, and more particularly to a surface acoustic wave device used for an RF unit (high-frequency unit) of a mobile communication terminal or the like.

[0002]

2. Description of the Related Art In recent years, the development of small and lightweight mobile communication terminals such as car phones and mobile phones has been rapidly progressing. Along with this, there is a demand for smaller and higher-performance components used, and a surface acoustic wave (SAW) element (resonator, interstage filter, antenna, etc.) contributing to miniaturization of the RF section (high-frequency section). Demand for duplexers is also growing rapidly.

[0003] Among them, the antenna duplexer is located at the front end of the RF unit and requires high power durability. Hitherto, since a surface acoustic wave element (hereinafter also referred to as a SAW filter) has insufficient power durability, a dielectric filter has been mainly used for an antenna duplexer.
However, since the size of the dielectric filter is large, it has been difficult to reduce the size of the mobile communication terminal.

[0004] On the other hand, when used in a high frequency band such as a SAW filter quasi-microwave band (1.8GH _z band), the electrode wiring becomes finer, the power durability of SAW filters becomes a problem. Therefore, there is a great need to further improve the power durability of the SAW filter as well as to reduce the size of the mobile communication terminal.

Conventionally, the following design improvement techniques have been reported to improve the power durability of surface acoustic wave devices. JP-A-6-29779 discloses a ladder type S.
In the AW filter, the number of pairs of electrode fingers of the first-stage series resonator on the input side is made larger than the number of pairs of electrode fingers of the other-stage series resonators, or the opening length of the first-stage series resonator on the input side is increased. A technique is described in which the opening length of the series resonator is made narrower to reduce the resistance of the first series resonator, suppress a temperature rise, and improve the power durability of the SAW filter. In addition, a technique for improving the power durability of the SAW filter by improving the electrode material of each resonator forming the SAW filter has been proposed.

[0006]

With the above-described measures, a life test (for example, an environment temperature of 85 ° C. and an applied frequency of 188) in which a signal of a constant frequency is continuously applied.
At 5 MHz and an applied power of 0.3 w), a life of several tens of hours is ensured. However, in the antenna duplexer, a power load of about 1 to 2 w may be applied, so that it cannot be said that the antenna duplexer has sufficient power durability when a high-frequency signal is applied. In particular, when viewed from the input side, even if no change is observed in the electrodes of the later-stage resonator forming the SAW filter, the electrodes of the first-stage series resonator often melt.

Accordingly, the present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances. By changing the electrode period of a resonator constituting a surface acoustic wave element, an elastic surface having improved power durability can be obtained. It is an object to provide a wave element.

[0008]

According to the present invention, a first one-port surface acoustic wave resonator having a predetermined resonance frequency is provided on a parallel arm, and an anti-resonance of the first one-port surface acoustic wave resonator is provided. A ladder-type surface acoustic wave element in which a plurality of second one-port surface acoustic wave resonators having a resonance frequency substantially equal to a frequency are arranged on a serial arm, respectively, wherein the first and second one-port pairs are arranged. The surface acoustic wave resonator is constituted by a comb-shaped electrode having a predetermined number of electrode fingers, and at least one of the second one-terminal-to-surface acoustic wave resonators has one electrode-to-electrode finger of the surface acoustic wave resonator. The period λ is given by the following equation: 0.99λ _av2 <λ <1.01
It is an object of the present invention to provide a surface acoustic wave device characterized by being represented by λ _av2 (where λ _{av2 is} an average value of the period of the electrode fingers of the second one- _port surface acoustic wave resonator).

Further, a first one having a predetermined resonance frequency is provided.
A terminal-to-surface acoustic wave resonator is provided in a parallel arm, and a second one-terminal-to-surface acoustic wave resonator having a resonance frequency substantially equal to the anti-resonance frequency of the first terminal-to-surface acoustic wave resonator is provided in a serial arm. A plurality of ladder-type surface acoustic wave devices, each of which is arranged on the ladder-type surface acoustic wave resonator,
The first electrode comprises a comb-shaped electrode having a predetermined number of electrode fingers.
The period λ of the electrode fingers of at least one of the one-port surface acoustic wave resonators is expressed by the following equation:
0.99λ _av1 <λ <1.01λ _av1 (where, λ _{av1 is} the average value of the period of the electrode fingers of the first one- _port surface acoustic wave resonator) Is provided.

Further, a first one-port surface acoustic wave resonator having a predetermined resonance frequency is connected to a parallel arm, and a resonance frequency substantially matching the anti-resonance frequency of the first one-port surface acoustic wave resonator is set. A ladder-type surface acoustic wave element in which a plurality of second one-port pair surface acoustic wave resonators are arranged in series arms, respectively, wherein the first one-terminal second pair of surface acoustic wave resonators is viewed from the signal input side. A surface acoustic wave device comprising a plurality of divided surface acoustic wave resonators connected in series. Here, when viewed from the signal input side, the first one-terminal pair surface acoustic wave resonator in the first stage is composed of a plurality of one-terminals having a capacitance larger than the capacitance when one resonator is formed. What is necessary is just to comprise by dividing into a surface acoustic wave resonator. By employing such a configuration, a surface acoustic wave element having excellent power durability can be provided.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a surface acoustic wave device having the above-described configuration, the first stage of a second surface acoustic wave device viewed from a signal input side.
The period of the electrode fingers of the terminal-to-surface acoustic wave resonator may be smaller than the period of the electrode fingers of the other second one-terminal-to-surface acoustic wave resonators. The period of the electrode fingers of the surface acoustic wave resonator may be equal or larger in order from the signal input side.

Also, the first stage of the first stage viewed from the signal input side.
The period of the electrode fingers of the terminal-to-surface acoustic wave resonator may be greater than the period of the electrode fingers of the other first one-terminal to surface-parallel surface acoustic wave resonators. The period of the electrode fingers of the surface acoustic wave resonator may be equal or smaller in order from the signal input side.

Further, in the case of a surface acoustic wave element used for reception, the period of the electrode fingers of the first one-terminal / surface acoustic wave resonator at the first stage when viewed from the signal input side is different from that of the other first. The period of the electrode fingers of the one-port surface acoustic wave resonator may be smaller than that of the first one-terminal-surface acoustic wave resonator. Or larger.

Further, the second stage of the first stage viewed from the signal input side.
In the case where the terminal-to-surface acoustic wave resonator is a surface acoustic wave device composed of a plurality of divided surface acoustic wave resonators connected in series, when viewed from the signal input side, the second first SAW element other than the first stage. The terminal-to-surface acoustic wave resonator may also be constituted by a plurality of divided surface acoustic wave resonators connected in series.

Hereinafter, the first one-port pair surface acoustic wave resonator configured as a parallel arm is referred to as a “parallel resonator”, and the second one-port pair surface acoustic wave resonator configured as a serial arm. Is called a “series resonator”.

First, the configuration and operation principle of a ladder type surface acoustic wave resonator composed of a series resonator and a parallel resonator will be described. FIG. 1 shows an example of a circuit diagram of a ladder type surface acoustic wave device. The terminals on the signal input side are a ₁ and a ₂ , and the terminals on the signal output side are b ₁ and b ₂ . In general, a ladder-type surface acoustic wave element has a series resonator (S ₁ , S ₂ , S ₃ ,...) Connected in series between an input terminal and an output terminal, and outputs a signal between two input terminals and an output terminal. And parallel resonators (P ₁ , P ₂ , P ₃ ,...) Connected in parallel as viewed from the terminals.

FIG. 2 shows a basic pattern configuration diagram of a series resonator and a parallel resonator. Both resonators are so-called one-port surface acoustic wave resonators. An interdigital transducer portion is composed of two excitation electrodes 1 and 2 in which comb-shaped electrode fingers 10 are intertwined with each other, and are disposed on both sides thereof. Reflectors 3 and 4. As shown in the figure, the length of the repetition cycle of the electrode finger 10 of the excitation electrode is called the period λ of the electrode finger, and the length of the portion where the electrode fingers intersecting each other from the vertical direction cross each other when viewed from the lateral direction. The length is called an opening length Y. The relationship with the circuit diagram symbols of the resonator of FIG. 1 is as shown on the right side of FIG. 2, in which one terminal A of the excitation electrode is a signal input side and the other terminal B is a signal output side.

FIG. 3 is a graph showing the relationship between the frequency and the attenuation of such a ladder type surface acoustic wave device, and the relationship between the frequency and the temperature of the device. Here, the period of the electrode fingers of the series resonator of the surface acoustic wave element is 2.065 μm, which is the same, and the period of the electrode fingers of the parallel resonator is 2.140 μm, which are all the same. When an electric signal is input from the antenna, the surface acoustic wave element functions as a band-pass filter that passes only a signal having a certain frequency bandwidth.

Referring to FIG.
Near the cutoff frequency ₁, Fh_Two)smell
Thus, it can be seen that the temperature of the element is highest. one
In general, higher temperatures mean lower power durability.
Near the cut-off frequency where the temperature of the element is highest.
In this case, the surface acoustic wave element has the weakest power durability. Meanwhile, elastic
Cutoff frequency Fh on the low frequency side of the surface acoustic wave element₁Is average
Close to the resonance frequency of the column resonator and the cutoff frequency on the high frequency side
Wave number Fh_TwoAre close to the resonance frequency of the series resonator,
In the vicinity of the resonance frequency of the vibrator, the weakest power
You.

FIG. 4A shows the impedance (Z _S = r + jx, r: resistance, x: reactance) of the series resonator (S ₁ and the like) and the admittance (Y) of the parallel resonator (P _{1 and the} like). _P = g + jb, g: conductance component, b: susceptance component). The vertical axis of the figure indicates impedance or admittance, and the positions where the reactance x and the susceptance b become zero are the resonance frequencies of the series resonator and the parallel resonator, respectively.

FIG. 4B shows the filter characteristics of the surface acoustic wave element drawn according to the frequency characteristics of FIG. 4A. In the specification band for passing a signal, the resonance frequency of the series resonator is included, and the impedance Z _S is almost zero, so that current flows almost directly to the resonator. In addition, in the vicinity of the resonance frequency of the series resonator, the admittance of the parallel resonator is not always zero, so that a small amount of current flows through the parallel resonator.

In FIG. 1, the serial connection of the first stage on the signal input side is
Shaker S₁The current flowing through_S12nd and 3rd stages in series
Shaker S_Two, S_ThreeThe current flowing through_S2, I_S3And signal input
Side first stage parallel resonator P₁The current flowing through_P1, Two steps
Eye, third stage parallel resonator P_Two, P _ThreeThe current flowing through_P2,
i_P3And At this time, consider the current loss of each resonator.
Then, the current flowing through each series resonator is i_S1> I_S2> I_S3
Is established. That is, the first stage on the signal input side
Series resonator S₁Has the largest current and the highest temperature
The first series resonator S₁Has the weakest power durability
Will be.

As shown in FIG. 4A, near the resonance frequency of the parallel resonator, the signal attenuation increases and almost all current flows through the parallel resonator. However, near the resonance frequency of the parallel resonator, the impedance of the series resonator is not infinite, so that a small amount of current flows through the series resonator. Therefore, when a signal having a frequency near the resonance frequency of the parallel resonator is input, the current flowing through each parallel resonator has a relationship of i _P1 > i _P2 > i _P3 . That is, the parallel resonators P ₁ of the first-stage signal input side, since the greatest current flows, will be the most that power resistance is low. From the above description, it can be seen that in order to improve the power durability of the surface acoustic wave element, it is necessary to improve the power durability of the first-stage series resonator or parallel resonator viewed from the signal input side.

By the way, in a transmission filter, power is applied within a specified band. Also, from FIGS. 3 and 4 (b), the closer the transmitted signal is to the high frequency side of the specification band, the closer to the resonance frequency of the series resonator, and thus the weakest power durability is seen from the signal input side. The first-stage series resonator is easily deteriorated. Generally, the resonance frequency f of the resonator,
The period λ of the electrode fingers of the resonator is inversely proportional (v = fλ,
v is known to have a propagation velocity). Therefore, if the period λ of the electrode fingers of the series resonator is reduced, the resonance frequency f of the direct resonator is increased, so that the resonance frequency at which the power durability becomes weakest can be shifted to outside the specification band. The power durability in the band can be improved.

That is, according to the present invention, the period λ _S1 of the electrode finger of the first-stage series resonator on the signal input side is changed to the other-stage series resonator within a range that does not affect the frequency characteristics of the signal within the specification band. Is smaller than the period of the electrode finger. In particular,
The period λ _S1 of the electrode fingers of the first-stage series resonator on the input side is made smaller than the average value λ _Sav of the period of the electrode fingers of the entire series resonator by 1% or less. That is, 0.99λ _Sav ≦ λ _S1 <λ
_Sav . As a result, the resonance frequency of the input-side first-stage series resonator shifts to a higher frequency side than the resonance frequency of the other-stage series resonator, so that the input-side first-stage series resonator is less likely to deteriorate, and as a result, the elastic surface The power durability of the wave element can be improved.

From FIGS. 3 and 4B, the closer the transmitted signal is to the lower frequency side of the specification band, the closer to the resonance frequency of the parallel resonator. The first-stage parallel resonator having the weakest property tends to deteriorate. Therefore, if the period λ of the electrode fingers of the parallel resonator is increased, the resonance frequency f of the parallel resonator is reduced, so that the resonance frequency at which the power durability becomes weakest can be shifted out of the specification band. The power durability in the band can be improved.

That is, according to the present invention, as a second method for improving the power durability of the surface acoustic wave element, within a range that does not affect the frequency characteristics of the signal within the specified band,
The period λ _P1 of the electrode fingers of the first-stage parallel resonator on the signal input side is made larger than the period of the electrode fingers of the other-stage parallel resonators. Specifically, the period λ of the electrode fingers of the first-stage parallel resonator on the input side
_P1 is made larger than the average value λ _Pav of the period of the electrode fingers of the entire parallel resonator by 1% or less. That is, λ _Pav <λ _P1 ≦
1.01λ _Pav . As a result, the resonance frequency of the first-stage parallel resonator on the input side shifts to a lower frequency side than the resonance frequency of the other-stage parallel resonator, so that the first-stage parallel resonator on the input side is less likely to deteriorate, and as a result, the elastic surface The power durability of the wave element can be improved. Further, the surface acoustic wave element may be configured by combining the above-described decrease in the cycle of the input-side first-stage series resonator and the increase in the cycle of the input-side first-stage parallel resonator.

Next, a description will be given of the power durability when a receiving filter whose pass band is on the higher frequency side than the pass band of the transmitting filter is formed. Here, a duplexer using a surface acoustic wave element generally has a configuration as shown in FIG.
The transmission filter T _X (F2) and the reception filter R _X (F1) are connected to the antenna unit via the common signal terminal T _O. Here, as shown in FIG. 6, the passband of the receive filter R _X (center frequency f ₁₎ is, considering the case in the high-frequency side of the passband of the transmission filter T _X (center frequency f ₂₎ , receive filter R _X leakage power is applied from the transmission filter T _X to suppression range of the low frequency side of the reception filter R _X may deteriorate.

That is, since the leakage power of the transmission filter T _X is applied to the vicinity of the low frequency side of the pass band of the reception filter R _X , the leakage power is applied to the weakest part of the reception filter R _{X on} the low frequency side. A first-stage parallel resonator on a certain signal input side deteriorates.

Therefore, in such a receiving filter, the period λ _P1 of the electrode finger of the first-stage parallel resonator on the input side is calculated as follows:
The period is set smaller than the period of the electrode fingers of the parallel resonators in the other stages. Specifically, the period λ _P1 of the electrode fingers of the first-stage parallel resonator on the input side
_Is smaller than the average value λ _Pav of the period of the electrode fingers of the entire parallel resonator by 1% or less. That is, 0.99λ
Let _Pav ≦ λ _P1 <λ _Pav . As a result, the resonance frequency of the first-stage parallel resonator on the input side shifts to a higher frequency side than the resonance frequency of the other-stage parallel resonator, so that the first-stage parallel resonator on the input side is less likely to deteriorate. The power durability of the surface acoustic wave device can be improved.

It is known that the larger the capacitance C of a surface acoustic wave resonator, the better the power durability. Therefore, if the series resonator of the surface acoustic wave element is divided into resonators having a larger capacitance, a resonator excellent in power durability can be obtained. For example, a series arm surface acoustic wave resonator having a capacitance C divides the resonator into two rather than being constituted by a single resonator having a capacitance C, and has a capacitance 2C. When two resonators are connected in series, the power durability becomes higher. Alternatively, the capacitance is divided into three or more resonators whose capacitance is larger than the capacitance of one resonator, and these three or more resonators are connected in series.
One series arm surface acoustic wave resonator may be configured.

While the present invention has been described mainly with reference to four embodiments, examples of each embodiment will be described below. It should be noted that the present invention is not limited by these embodiments.

【Example】

Example 1 Change in Period of Electrode Fingers of Series Resonator In this example, a 1.8 GHz band transmission filter (transmission band; 1850 to 1885 MHz) was targeted. As shown in FIG. 7, four regular one-port surface acoustic wave resonators are provided in the serial arm (series resonators: S ₁ , S ₂ , S ₃ , S ₄ ), and two are provided in the parallel arm (parallel resonance). vessels: P _1, P ₂₎ to produce a transmission filter of the connected ladder (SAW device). A single crystal piezoelectric substrate using a substrate of LiTaO ₃ 36 ° Ycut-X propagation was used, and the excitation electrode and the electrode film of the reflector were formed by DC sputtering and A1 (700 °) / Cu (150 °) /
An A1 (700 °) three-layer film was formed. Here, S ₁ is a first-stage series resonator viewed from the input side, and P ₁ is a first-stage parallel resonator viewed from the input side.

Three kinds of samples A, B, and C having different periods of the series resonators were prepared and tested for power durability. The design details of the resonator of each sample are shown below. The aperture length and the logarithm of the electrode finger are common to each sample. For the series resonator, the aperture length is 30 μn, the logarithm is 155 pairs, and the reflector is:
80 pairs, the parallel resonator has an aperture length: 60 μm, and the number of logs:
90 pairs, reflector: 100 pairs.

Regarding the period of the electrode fingers, the parallel resonator was common to all the samples, and was 2.140 μm. Regarding the series resonators, sample A is 2.065 μm common to S _{1 to} S ₄ , and sample B has S ₁ of 2.0
60 μm, S _{2 to} S ₄ are 2.065 μm, sample C is
S ₁ is 2.055Myuemu, is S ₂ and S ₃ 2.060μm, S ₄
Is 2.065 μm. At this time, in sample B, S
The period of ₁ is -0.18% of the average value of the period of each series resonator.
In sample C, the period of S ₁ is −
0.24%, the period of S ₄ is changed by + 0.24%.

Each of the above samples was evaluated for power durability by a life test. The test conditions are: ambient temperature 85 ° C, applied frequency 1885MHz, the weakest frequency in the specification band
It is. FIG. 8 shows the evaluation results. Here, the life (time: hr) on the vertical axis is a time until the specified bandwidth of the transmission filter is reduced by 5% or more. The life when 0.3 W is applied is 80 hours and 165 hours in the order of samples A, B and C.
r, 270 hr.

As described above, by changing the period of the electrode fingers of each series resonator, the life, that is, the power durability is increased by about 2 times in the case of the sample B and by about 3.5 times in the case of the sample C. Has improved. In particular, it is effective to reduce the period of the input-side first-stage series resonator. Further, as in the case of the sample C, when viewed from the signal input side, the cycle of the electrode fingers of the series resonator may be sequentially increased, or the cycle of a part in the middle may be made equal.

Example 2 Change of Electrode Finger of Parallel Resonator A ladder-type transmission filter having the same configuration as that of Example 1 was prepared. However, here, all the periods of the series resonators are made constant, and only the period of each parallel resonator is changed. Samples were prepared two types, Sample A, using exactly the same as in example 1, sample D, the period of the parallel resonator P ₂ 2.140Myuemu, was 2.145μm a period of P _1.
At this time, the period of P ₁ sample D is changed by + 0.12% of the average value of the period of the parallel resonator. That is, when viewed from the input side to increase the period of the electrode fingers of the parallel resonator P ₁ of the first stage.

The power durability of the two samples was evaluated by a life test. The conditions for the test were an environmental temperature of 85 ° C. and an applied frequency of 1850 MHz, which is the leftmost frequency in the pass band. FIG. 9 shows the evaluation results. The life when 0.3 W was applied was 325 hr and 780 hr in the order of Samples A and D. As described above, by changing the period of each parallel resonator, the life, that is, the power durability was improved by about 2.4 times in the case of the sample A in the case of D. In the case of three or more parallel resonators, the cycle of the electrode fingers of the parallel resonator may be reduced in order or the cycle of a part thereof may be equal when viewed from the signal input side.

Embodiment 3 Change of Electrode Fingers of Parallel Resonator of Reception Filter In this embodiment, a 1.8 GHz band reception filter (reception band; 1930 to 1965 MHz) is targeted. As shown in FIG. 10, four normal type one-terminal surface acoustic wave resonators are provided in the series arm (series resonators: S ₁ , S ₂ , S ₃ , S ₄ ) and three are provided in the parallel arm (parallel resonators). : P ₁ , P ₂ , P ₃ ) A ladder-type reception filter connected to the ladder was manufactured. L on single crystal piezoelectric substrate
Using an iTaO ₃ 36 ° Ycut-X propagating substrate, the electrode film was formed by DC sputtering A1 (700 °)
/ Cu (150 °) / A1 (700 °) three-layer film.

E, F, and G were prepared from three types of samples in which the period of the parallel resonator was changed, and a power durability test was performed.
The design details of the resonator of each sample are shown below. The aperture length and the logarithm of the electrode fingers are common to each sample. For the series resonator, the aperture length is 30 μm, the logarithm is 150 pairs, and the reflector is 80 pairs. For the parallel resonator, the aperture length is 60 μm and the logarithm is: 90 pairs, reflector: 100 pairs.

Regarding the period of the electrode fingers, the series resonator is common to each sample, 2.040 μm, and for the parallel resonator, sample E is common to P _{1 to} P ₃ , 2.110 μm, sample F is, P ₁ is 2.105μ
m, P ₂ , and P ₃ are 2.110 μm. Sample G has a P ₁ of 2.105 μm, a P ₂ of 2.110 μm, and a P ₃ of 2.11.
5 μm. At this time, in sample F, which changed the period of P ₁ only -0.16% of the average value of the period of the parallel resonator, the sample G, the cycle of P ₁ is -0.24
%, Has been changed cycle of P ₃ is only + 0.24%.

The power durability of each sample was evaluated by a life test. By the way, in the antenna duplexer, in the case of the reception filter located on the higher frequency side than the transmission filter, the leakage power from the transmission filter is applied to the attenuation region on the low frequency side of the reception filter. The test conditions were as follows: the ambient temperature was 85 ° C., and the applied frequency was 188 of the frequency at which the power durability of the receiving filter was weakest in the band of the transmitting filter.
5 MHz.

FIG. 11 shows the evaluation results. The life at the time of applying 80 mW was 40 hr, 14 samples in the order of samples E, F, and G.
5 hours and 170 hours. As described above, by changing the period of each parallel resonator, the life, that is, the power durability was improved by about 3.6 times in the case of the sample F and by about 4.3 times in the case of the sample G as compared with the sample E. In particular, it is effective to reduce the period of the first-stage parallel resonator on the signal input side.

Embodiment 4: Divided Configuration of Series Resonator In this embodiment, a 1.8 GHz band transmission filter (transmission band: 1850 to 1885 MHz) is targeted. A single crystal piezoelectric substrate was a substrate of LiTaO ₃ 36 ° Ycut-X propagation, and the electrode film was formed by A1 (700 °) / Cu (150 °) / A1 (700) formed by DC sputtering.
Iii) It is a three-layer film. Four regular one-port surface acoustic wave resonators as shown in FIG. 4 (S ₁ , S ₂ , S ₃ ,
S ₄ ), a ladder-type transmission filter (sample A) connected to two parallel arms (P ₁ , P ₂ ), and an S-type filter as shown in FIG.
_The power durability of the transmission filter (sample H) obtained by dividing _one resonator into two was compared and evaluated.

[0045] At this time, the S ₁ resonator one capacitor samples A, 2 pieces of the sum of the capacitance of the resonator S _{1 1,} S ₁₂ of sample H was set to the same. The two resonators S ₁₁ and S ₁₂ are
Connected in series, both of which are twice the capacitance of the S ₁ resonator of sample A. For example, when the capacitance of one S ₁ resonator is 100 μm in aperture length and about 4 × 10 ⁻² pF per pair, the capacitance of S ₁₁ and S ₁₂ is 100 μm in aperture length.
m, 8 × 10 ⁻² pF per pair.

The design contents of the resonator of each sample are shown below. Sample A is the same sample used in Example 1. Further, the two resonators S ₁₁ and S _{12 of} the sample H
Have the same configuration, opening length: 60 μm, logarithm: 155
Pairs, reflectors: 80 pairs. The cycle of the electrode fingers was 2.065 μm for all series resonators and 2.1 for all parallel resonators.
40 μm.

The power durability of each sample was evaluated by a life test. The conditions for the test were an environmental temperature of 85 ° C. and an applied frequency of 1885 MHz, the weakest frequency in the pass band. FIG. 13 shows the evaluation results. The life when 0.3 W was applied was 80 hr and 460 hr, respectively, for samples A and H. As described above, by dividing the series resonator without changing the overall capacitance of the series resonator, the life of H was improved by 5.8 times as compared with the sample A. In this embodiment, the series resonator is divided into two, but may be divided into three or more.

Further, the configuration of the surface acoustic wave resonator shown in the above four embodiments may be used in an appropriate combination as needed, when forming a duplexer or the like. Even in this case, the power durability can be improved without affecting the band characteristics of the transmission or reception filter.

[0049]

According to the present invention, the configuration is such that the period of the electrode fingers of each series resonator or parallel resonator is different, or a plurality of series resonators are provided so as to increase the capacity of one series resonator. In this case, the power durability of the surface acoustic wave element can be improved. Therefore,
The present invention not only contributes to the practical use of an antenna duplexer using a surface acoustic wave element, but also greatly improves the reliability of a quasi-microwave band surface acoustic wave element that requires a finer line width of an electrode finger. Can contribute.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a ladder type surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is a pattern configuration diagram of one embodiment of a one-terminal surface acoustic wave resonator according to the present invention.

FIG. 3 is a diagram showing the frequency characteristics of attenuation and temperature of the surface acoustic wave device of the present invention.

FIG. 4 is an explanatory diagram of a frequency characteristic of a resonator of the surface acoustic wave device according to the present invention.

FIG. 5 is a basic configuration diagram of a duplexer using the surface acoustic wave element of the present invention.

FIG. 6 is a frequency characteristic diagram of each filter in the duplexer of FIG.

FIG. 7 is a circuit diagram of the surface acoustic wave device according to the first embodiment of the present invention.

FIG. 8 is a graph of a life test result in Example 1 of the present invention.

FIG. 9 is a graph of a life test result in Embodiment 2 of the present invention.

FIG. 10 is a circuit diagram of a surface acoustic wave device according to a third embodiment of the present invention.

FIG. 11 is a graph of a life test result in Example 3 of the present invention.

FIG. 12 is a circuit diagram of a surface acoustic wave device according to a fourth embodiment of the present invention.

FIG. 13 is a graph of a life test result in Example 4 of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 excitation electrode 2 excitation electrode 3 reflector 4 reflector 10 electrode finger λ electrode finger period Y opening length S ₁ series resonator S ₂ series resonator S ₃ series resonator S ₄ series resonator P ₁ parallel resonator P ₂ Parallel resonator F1 Filter for reception (R _X ) F2 Filter for transmission (T _X )

Claims (12)

[Claims] 1. A first one-port surface acoustic wave resonator having a predetermined resonance frequency is connected to a parallel arm, and a resonance frequency substantially matching the anti-resonance frequency of the first one-port surface acoustic wave resonator is set. A ladder-type surface acoustic wave element in which a plurality of second one-port pair surface acoustic wave resonators are arranged on a serial arm, respectively.
The first and second one-port pair surface acoustic wave resonators are each composed of a comb-shaped electrode having a predetermined number of electrode fingers.
The period λ of the electrode fingers of at least one terminal-to-surface acoustic wave resonator among the terminal-to-surface acoustic wave resonators is expressed by the following equation:
A surface acoustic wave element characterized by being represented by 99λ _av2 <λ <1.01λ _av2 (where, λ _{av2 is} an average value of the period of the electrode finger of the second one- _port surface acoustic wave resonator). 2. The method of claim 1, wherein the period λ of the electrode finger of at least one of the first one-port surface acoustic wave resonator is 0.99λ _av1 <λ <1. .0
_{2. The} surface acoustic wave element according to claim 1, wherein the surface acoustic wave element is represented by 1 [lambda _{] av1} (where [lambda] _{av1 is} an average value of the period of the electrode fingers of the first one- _port surface acoustic wave resonator). 3. The period of the electrode finger of the second one-port pair surface acoustic wave resonator in the first stage as viewed from the signal input side is longer than the period of the electrode finger of the other second one-port pair surface acoustic wave resonator. 3. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave element is also small. 4. The surface acoustic wave device according to claim 1, wherein the periods of the electrode fingers of the plurality of second one-terminal surface acoustic wave resonators are equal or larger in order from the signal input side. . 5. A first one-port surface acoustic wave resonator having a predetermined resonance frequency is provided in a parallel arm with a resonance frequency substantially matching the anti-resonance frequency of the first one-port surface acoustic wave resonator. A ladder-type surface acoustic wave element in which a plurality of second one-port pair surface acoustic wave resonators are arranged on a serial arm, respectively.
The first and second one-terminal pair surface acoustic wave resonators are each formed of a comb-shaped electrode having a predetermined number of electrode fingers.
The period λ of the electrode fingers of at least one terminal-to-surface acoustic wave resonator among the terminal-to-surface acoustic wave resonators is expressed by the following equation:
A surface acoustic wave device characterized by being represented by 99λ _av1 <λ <1.01λ _av1 (where, λ _{av1 is} an average value of the period of the electrode finger of the first one- _port surface acoustic wave resonator). 6. The period of the electrode fingers of the first one-port pair surface acoustic wave resonator in the first stage as viewed from the signal input side is the same as the period of the electrode fingers of the other first one-port pair surface acoustic wave parallel resonators. The surface acoustic wave device according to claim 2, wherein the surface acoustic wave device is larger than the surface acoustic wave device. 7. The surface acoustic wave element according to claim 2, wherein the periods of the electrode fingers of the plurality of first one-port surface acoustic wave resonators are equal or smaller in order from the signal input side. . 8. A surface acoustic wave element for reception, wherein a period of an electrode finger of a first stage of a first stage pair and an electrode finger of a surface acoustic wave resonator as viewed from a signal input side is equal to that of another first series of one terminal pairs. 6. The surface acoustic wave device according to claim 2, wherein the period is smaller than a period of an electrode finger of the surface acoustic wave resonator. 9. A surface acoustic wave element for reception, wherein the periods of the electrode fingers of the plurality of first one-port surface acoustic wave resonators are equal or larger in order from the signal input side. A surface acoustic wave device according to claim 2. 10. A first one-port surface acoustic wave resonator having a predetermined resonance frequency is connected to a parallel arm, and a resonance frequency substantially matching the anti-resonance frequency of the first one-port surface acoustic wave resonator is set. A ladder-type surface acoustic wave element in which a plurality of second one-port pair surface acoustic wave resonators are arranged in series arms, respectively, wherein the first one-terminal second pair of surface acoustic wave resonators is viewed from the signal input side. A surface acoustic wave element comprising a plurality of divided surface acoustic wave resonators connected in series. 11. The second one-port surface acoustic wave resonator other than the first stage viewed from the signal input side is also constituted by a plurality of divided surface acoustic wave resonators connected in series. The surface acoustic wave device according to claim 10. 12. The second one-port surface acoustic wave resonator comprises:
6. The surface acoustic wave device according to claim 1, comprising a plurality of divided surface acoustic wave resonators connected in series.