JPH11168350A - Lateral multiplex mode saw filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen the pass band width and miniaturize by arranging plural SAW resonators having a pair of reflectors in parallel to the transmission direction of a surface acoustic wave and providing an electrode finger group for exciting the plural SAW resonators for the reflectors. SOLUTION: In the reflectors 1, 2: 104 and 105, electrode patterns for selectively exciting different oscillation modes are formed. The reflector 2: 105 is for a basic wave lateral oblique symmetric mode AO and the reflector 1: 104 is for a primary/higher-order lateral symmetric mode S1. An electrode finger group excited for the plural SAW resonators of the reflectors can selectively excite the basic wave lateral oblique symmetric mode AO and the primary/high- order lateral symmetric mode S1. For preventing the AO mode from being deteriorated by the shorting of positive/negative loads generated at the AO mode, a third connection resonator 3:113 (SAW #3) is divided in the transmission direction X of a surface acoustic wave at the almost center of an interdigital electrode IDT 103.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator type SAW filter constructed using surface acoustic waves.
The present invention relates to a technique for reducing the size of a transverse multi-mode SAW filter that realizes a wider band by using a plurality of transverse modes obtained by arranging resonators in parallel.

[0002]

2. Description of the Related Art As a conventional resonator-type transverse multi-mode SAW filter, a so-called transverse dual-mode SAW filter in which two SAW resonators are arranged in parallel is famous (Japanese Patent Publication No. 2-16613). Gazette). When this filter is used to form a filter with a crystal ST cut X propagation substrate that is a rotation Y cut from about 30 degrees to 45 degrees and has excellent frequency-temperature characteristics, the plane size of the element is 2 mm × 6.5 mm.
Excellent characteristics are obtained in which the 3-dB bandwidth of the two-stage cascade connection filter is expressed as a fractional bandwidth of about 700 ppm and the insertion loss is 5 dB.

[0003]

However, using the above-described prior art of the transverse dual mode SAW filter, an intermediate frequency filter (IF) used in a GSM or PHS portable telephone, which has been remarkably developed in recent years, has been developed. A filter having a relative bandwidth of 900 to 1000 ppm and a plane size of 3.8 × 3.8 mm or less, which is required in the filter, could not be realized with satisfactory performance by the quartz ST cut.

Analyzing the cause that cannot be realized, when the element is accommodated in the above-described container plane size, the element size becomes about 2 × 3 mm, and the IDTs constituting one SAW resonator (hereinafter, omitted). IDT (Interdigital
It is necessary to make the sum M + N of the number M of electrode fingers and the number N of reflector conductors on one side approximately 200 or less. Therefore, horizontal 2
Depending on the excitation intensity of the resonance amplitude of the SAW resonator constituting the double mode and the transverse triple mode SAW filter and the mode used, the Q value decreases, and the transmission characteristics of the SAW filter deteriorate. FIG. 9 shows a horizontal triple mode SAW having an element size of 2 × 3 mm according to the prior art.
FIG. 10 shows the transmission characteristics of the filter, and FIG. 10 shows the S11 reflection characteristics as viewed from the input terminal side of the SAW filter. The transmission characteristic in FIG. 9 is the center frequency of the filter (the center of the pass bandwidth).
Is severely missing from above. As can be seen in FIG. 10, three resonance modes of the lateral triple mode, S0, A
It is concluded that the resonance amplitude is small and the resonance Q value is small because the reflection intensity of A0 and S1 modes is small among 0 and S1. This is the reason why the transmission characteristics (curve 900 in FIG. 9) of the SAW filter are significantly deteriorated.

Therefore, the present invention solves such a problem, and an object of the present invention is to use a substrate having an excellent frequency-temperature characteristic such as a quartz crystal ST-cut and having an excellent Q value of a material, which has not been achieved conventionally. It is an object of the present invention to provide an IF filter having an excellent frequency stability and a good S / N ratio to a market, with a view to widening and miniaturizing a passband.

[0006]

(1) A transverse multi-mode SAW filter according to the present invention has at least one
Two or three SAW resonators having a pair of reflectors for reflecting the surface acoustic waves generated by the IDTs and the SAW generated by the IDTs on both sides thereof, in the propagation direction X of the surface acoustic wave And the reflectors are arranged substantially parallel to each other, and the reflector has a group of electrode fingers for exciting across a plurality of SAW resonators.

(2) A transverse multi-mode SAW filter according to the present invention is provided on a piezoelectric plate with at least one interdigital electrode and a surface acoustic wave generated by the interdigital electrode on both sides thereof. Three SAW resonators each having a pair of reflectors are arranged adjacently and substantially parallel to the propagation direction X of the surface acoustic wave, and the SA located in the middle
The W-resonator is characterized in that substantially the center of the interdigital transducer is divided in the surface acoustic wave propagation direction X.

(3) The transverse multi-mode SAW filter according to the present invention is provided on a piezoelectric flat plate with at least one interdigital electrode and a surface acoustic wave generated by the interdigital electrode on both sides thereof. The first SAW resonator on the input terminal side and the second SAW resonator on the output terminal side are arranged side by side in parallel with each other with a pair of reflectors. The third coupling resonator is formed by arranging the third coupling resonator, wherein the reflector has a group of electrode fingers for exciting the plurality of SAW resonators, and the transmission characteristic of the transverse multi-mode SAW filter is improved. , The fundamental transverse symmetric mode S0, the fundamental transverse oblique symmetric mode A0, and the first-order higher-order transverse symmetric mode S1.
It is characterized by being synthesized from the double mode.

(4) The transverse multi-mode SAW filter according to the present invention is provided on a piezoelectric flat plate with at least one interdigital electrode and a surface acoustic wave generated by the interdigital electrode on both sides thereof. Two SAW resonators each having a pair of reflectors are arranged adjacent to and substantially parallel to the propagation direction X of the surface acoustic wave.
It has a group of electrodes for exciting across the AW resonators, and the transmission characteristics of the transverse multimode SAW filter are synthesized from the fundamental transverse symmetric mode S0 and the fundamental transverse oblique symmetric mode A0. And

In (3) or (4), the electrode finger group for exciting across the plurality of SAW resonators of the reflector is composed of the fundamental wave oblique symmetric mode A0 or the fundamental wave transverse symmetric mode S0 and the fundamental wave transverse symmetric mode S0. It is desirable that the wave oblique symmetric mode A0 can be selectively excited.

In (3), a group of electrode fingers for exciting across a plurality of SAW resonators of the reflector is a first-order high-order laterally symmetric mode S1 or a fundamental wave laterally oblique symmetric mode A.
It is desirable to be able to selectively excite the 0th and first-order higher-order transversely symmetric modes S1.

In (3), it is preferable that the center of the interdigital transducer of the third coupled resonator (SAWR # 3) be divided in the propagation direction X of the surface acoustic wave. In this case, it is desirable that the center division width of the IDT of the coupled resonator (SAWR # 3) is not more than 0.2 wavelength.
Further, the propagation direction X of the third coupling resonator (SAWR # 3)
It is desirable that the potential of the electrode fingers of the interdigital transducer divided along the direction has a phase difference of 180 degrees from the potential of the electrode fingers at the same X coordinate position of the SAW resonators on both sides.

Further, in (3), the coupling resonator is composed of a large number of conductor strips periodically arranged perpendicular to the phase propagation direction of the surface acoustic wave, and the interval between the conductor strips is the first and second. Is desirably substantially equal to the electrode spacing of the SAW resonator.

In (3), the frequency potential P3 of the coupled resonator is smaller than the frequency potentials P1 and P2 of the first and second SAW resonators (P1, P2 ≧
P3) Then, the frequency difference Δf ₁ between S0 and A0, A0 and S
It is desirable to make the frequency difference Δf ₂ between 1 approximately equal. In this case, the difference in frequency potential ε = P1−P3
= P2-P3 is preferably from 1000 to 3000 ppm.

In (3), it is desirable to set the frequency potential difference ε of the coupled resonator so that the line-to-space ratio (L ₃ / S ₃ ) of the conductor strip is 1 or more.

In (3), the first and second SAs
The IDT cross finger width (Wc1 = Wc2) of the W resonator is
9 ± 1 wavelength, conductor strip length W of third coupled resonator
c3 is 9 ± 1 wavelength, and gap Gc between resonators is 0.69.
It is desirable to be ± 0.2 wavelength.

In (3) or (4), it is preferable that the piezoelectric flat plate is made of quartz and has a Y-cut X propagation azimuth rotated from 29 to 33 degrees.

In (3) or (4), the piezoelectric flat plate is made of quartz, and the ratio H / λ of the electrode film thickness H made of aluminum constituting the interdigital transducer and the reflector to the wavelength λ of the surface acoustic wave is used. Is desirably 0.036 to 0.05.

In (3) or (4), the number of interdigital electrodes in one SAW resonator ranges from 140 to 40, and the number of conductors in one reflector is from 60 to 160. Is preferably within the range.

The above-described transverse multiplex mode SAW filter may be configured so as to be cascaded in two stages.

[0021]

(Embodiment 1) Embodiments of the present invention will be described below in order from FIG. FIG. 1 is a plan view showing an electrode pattern used in a horizontal triple mode SAW filter which is a kind of a horizontal multi-mode SAW filter of the present invention. The name of each part in FIG.
0 is a piezoelectric flat plate, 101 is an interdigital transducer of the SAW resonator 1, that is, IDT1 and 102 are IDs of the SAW resonator 2.
T2 and 103 are SAW resonators 3 serving as third coupling resonators.
IDT3. The coupling resonator is composed of a number of conductor strips that are periodically arranged orthogonally to the phase propagation direction of the surface acoustic wave, and the interval between the conductor strips is equal to the electrode interval between the first and second SAW resonators. Is almost equal to

Further, the third coupling resonator (SAW)
The feature of the IDT 3 of R # 3) is that the center of the IDT 3 is divided in the propagation direction X of the surface acoustic wave. The first reason for the division is to form a negative-phase excitation electrode for exciting the A0 mode shown in FIG. The main reason for the division is that the positive and negative charges generated in the A0 mode are short-circuited in the coupled resonator (SAWR # 3), and thus the A0
This is to prevent the mode from attenuating (see FIG. 1).
1). That is, if the electrodes are not divided, positive and negative charges generated in the A0 mode are short-circuited through non-divided electrodes having a resistance of several mΩ.

Reference numeral 104 denotes a reflector 1, reference numeral 105 denotes a reflector 2, reference numerals 106 and 108 and 116, reference numerals 110 and 110 denote pads for giving a negative potential, and reference numerals 107 and 109 denote input or output positive terminals. Rectangular portions partitioned by thin lines such as 111, 112, and 113 are SAW resonators 1 (SAW
R # 1), a SAW resonator 2 (SAWR # 2), and a SAW resonator 3 (SAWR # 3) that is a coupling resonator. The downward direction in the figure is + X axis direction, and the right direction in the figure is + X
Indicates a + Y direction orthogonal to.

The piezoelectric flat plate 100 comprises a substrate on which a piezoelectric single crystal such as quartz or lithium tantalate and a piezoelectric thin film such as ZnO are formed. The three SAW resonators 111, 112 formed on the 100;
The IDT, the reflector, and the like constituting the 113 are formed by forming a thin film of a conductive metal film such as aluminum and gold to a specific thickness by means of vapor deposition, sputtering, or the like, and then forming a pattern by photolithography. The IDT and a group of electrode fingers of the reflector are arranged in parallel and periodically at right angles to the phase traveling direction (longitudinal direction + X) of the surface acoustic wave (Rayleigh wave, leaky wave, etc.) to be used.

The reflectors 104 and 105 shown as one embodiment each have an electrode pattern for selectively exciting different vibration modes. Are for the first-order higher-order transversely symmetric mode S1. In the present embodiment, a plurality of S
An electrode finger group for exciting across the AW resonator is
Fundamental transverse oblique symmetric mode A0 and first-order high-order transverse symmetric mode S1
Can be selectively excited. These will be described in more detail with reference to FIG. 4, FIG. 5, and FIG. FIG. 11 shows a detailed description of the configuration of the IDTs 101, 102, and 103. Further, in the present embodiment, the transmission characteristics of the transverse multiplex mode SAW filter are such that the fundamental wave transverse symmetric mode S0 and the fundamental wave oblique symmetric mode A0
It is characterized by being synthesized from the triple mode of the first-order higher-order transversely symmetric mode S1.

(Embodiment 2) Next, FIG. 2 shows a horizontal dual mode SAW which is another embodiment of the horizontal multiple mode SAW filter.
3 illustrates a case of a filter. The names of the respective parts in FIG. 2 are as follows: 200 is a piezoelectric flat plate, 201 is an interdigital electrode of the SAW resonator 1, ie, IDTs 1 and 202 are SAW
This is the IDT2 of the resonator 2. 203 is a reflector 1, 204
Is a reflector 2. Reference numerals 205, 207, 208, and 210 denote pads for applying a negative potential, and reference numerals 206 and 209 denote input or output positive terminals. Rectangular portions separated by thin lines such as 211 and 212 are SAW resonators 1 respectively.
(SAWR # 1) and SAW resonator 2 (SAWR # 2). The downward direction in the drawing indicates the + X axis direction, and the right direction in the drawing indicates the + Y direction orthogonal to + X.

The piezoelectric flat plate 200 is constituted by the same means as 100 in FIG. The reflectors 203 and 204 are formed with electrode patterns for selectively exciting different vibration modes. 203 is for the fundamental transverse symmetric mode S0, and 204 is for the fundamental transverse oblique symmetric mode A0. is there. In the present embodiment, an electrode finger group for exciting across a plurality of SAW resonators of the reflector can selectively excite the fundamental transverse symmetric mode S0 and the fundamental transverse oblique symmetric mode A0. Things. These will be described in more detail with reference to FIGS. In this embodiment, the transmission characteristics of the transverse multiplex mode SAW filter are such that the fundamental wave transverse symmetric mode S0 and the fundamental wave oblique symmetric mode A
0 is synthesized from the dual mode.

(Embodiment 3) FIG. 3 shows an embodiment in which the horizontal multiplex mode SAW filter of FIG. In the figure, 300 is a piezoelectric flat plate, 310 is a first horizontal multi-mode SAW filter, and 311 is a second horizontal multi-mode SAW filter, surrounded by fine broken lines. 301, 303, 307, 309 etc.
A pad 302 for providing a negative potential on the input or output end side;
And 308 are pads for applying a positive potential on the input or output terminal side. Reference numerals 306 and 304 denote conductor patterns for connecting the negative electrodes between the first and second transverse multiplex mode SAW filters 310 and 311. Furthermore, 305 is the first
And a conductor pattern for connecting the positive electrode between the second horizontal multi-mode SAW filters 310 and 311.

Next, the reflector and the IDT used in FIGS. 1, 2 and 3 of the present invention will be described in detail.
First, FIG. 4 is a schematic diagram illustrating the function of a reflector that can selectively excite the fundamental symmetric mode S0 shown in the transverse dual mode SAW filter of FIG. In the configuration of the reflector, the positive electrode finger 402 and the negative electrode finger 401 are connected to the power supply conductor patterns 405 and 404, respectively.
The surface acoustic wave excited by the IDT in the left half area of the symmetry axis 403 located at the center between the electrode fingers 401 and 402 is
As a result of arriving at the above-mentioned reflector of FIG. 4 and reflecting, a standing wave is generated with the electrode finger 401 having a negative potential and the electrode 402 having a positive potential, and the same electrode finger potential is applied to the right half of the symmetry axis 403. Occurs in the area of. That is, the electric potential generated in the electrode fingers 401 and 402 is applied as it is to the electric field in the right half area of the reflector to be excited. Therefore, the fundamental wave transverse symmetric mode S0 indicated by 406 in FIG. 4 is excited. 406
Denotes a displacement V (Y) in the S0 mode, and 407 denotes a + Y axis.
409 in the figure is one wavelength λ of the surface acoustic wave.

Next, FIG. 5 shows the fundamental oblique symmetric mode A0 shown in the transverse multi-mode SAW filter shown in FIGS.
FIG. 3 is a schematic diagram for explaining the function of a reflector that can selectively excite. The configuration of the reflector includes a positive electrode finger 501.
And the negative electrode 502 are provided with power supply conductor patterns 505 and 5 respectively.
06. The electrode fingers of 510 are conductors 504 and 5
Since it is connected by 03, it becomes a positive electrode of the same potential as the electrode finger of 501. The surface acoustic wave excited by the IDT in the left half area of the negative electrode power supply conductor 506 arrives at the reflector shown in FIG. 5 and is reflected. As a result, the electrode finger 501 has a positive potential and 511 has a negative potential. Generates a standing wave. As is apparent from the configuration shown in FIG. 5, the potentials generated on the electrode fingers 501 and 511 are inverted and an electric field is applied to the right half area of the reflector to excite the same. Therefore, indicated by 507 in FIG.
The fundamental wave oblique symmetric mode A0 is excited. Reference numeral 509 denotes a displacement V (Y) axis in the A0 mode, and 508 denotes a + Y axis.

FIG. 6 shows the horizontal triple mode S of FIG.
FIG. 3 is a schematic diagram illustrating a function of a reflector that can selectively excite a first-order higher-order transversely symmetric mode S1 appearing in an AW filter.
As the configuration of the reflector, the positive electrode finger 605 and the negative electrode 613 are connected to the power supply conductor patterns 602 and 606, respectively. Since the electrode finger 614 is connected by the conductors 603 and 601, it becomes a positive electrode having the same potential as 605. On the other hand, the electrode finger 604 is connected to the conductors 606 and 615, and thus has a negative electrode of the same potential as 613. SAW
The electrode fingers 616 and 617 in the region of R # 3 are
It is floating without connecting to 06. The surface acoustic wave excited by the IDT in the area of the SAW resonator (SAWR # 1) 607 arrives at the above-described reflector in FIG.
A standing wave is generated with the electrode finger 605 at a positive potential and the electrode finger 613 at a negative potential.
The WR # 3 region generates an inverted potential, and the 609 SAWR # 2 region generates a potential in phase with the SAWR # 1 region. Therefore, a first-order higher-order transversely symmetric mode S1 indicated by 610 in FIG. 6 is excited. 612 is the displacement V (Y) of the A0 mode.
The axis, 611, represents the + Y axis.

FIG. 11 is a schematic diagram for explaining the details of the overall configuration of the IDTs 101 to 103 shown in the horizontal triple mode SAW filter of FIG. The IDT110
The configuration of 0 consists of a combination of three IDTs surrounded by fine dashed lines,
DT2 and IDT3 of 1103. The negative electrode finger 1108 of the IDT 1 is connected via a power supply conductor pattern 1105 to the electrode finger 1109 at a position 180 degrees out of phase. The electrode finger 1108 is a negative electrode having the same potential as 1110. On the other hand, the electrode finger of 1116 becomes a positive electrode having the same potential as that of 1111. 1101 SAW resonator SAWR # 1
The surface acoustic wave excited by the IDT 1 in the region of the above is excited by setting the aforementioned 1108 and 1109 to a negative potential,
The electrode fingers 1116 and 1109 at the same X coordinate position are 1
Excitation with a phase inversion of 80 ° is performed. Therefore, 1 in FIG.
It becomes easy to excite the fundamental wave oblique symmetric mode A0 indicated by 113. Reference numeral 1114 denotes a displacement V (Y) axis of A0 mode, 1
115 represents the + Y axis.

As described above, IDT3 of the third coupling resonator
In (1102), substantially the center of the IDT 3 is divided in the propagation direction X of the surface acoustic wave. The division width C
(Refer to FIG. 14 in detail).
In order to properly set the frequency interval of the 0 mode, the 0.
Preferably, the wavelength is equal to or less than two wavelengths (λ). FIG. 12 illustrates this point. The frequency of the S0 mode increases as the division width C increases. This is because the wave number k in the Y-axis direction of the S0 mode increases as the division width C increases. For example, a GSM-IF filter requires a 3 dB pass bandwidth of 1000 ppm or more, so the frequency difference between A0 and S0 is 500 ppm, which is half of that.
Therefore, the wavelength is preferably equal to or less than 0.2 wavelength (λ).

The above is a specific example of the configuration of the transverse multiplex mode SAW filter of the present invention in which the lack of transmission characteristics of the filter of FIG. 9 (conventional example), which is a technical problem to be solved by the present invention, has been improved. .

Next, the attributes and improved characteristics obtained by the configuration of the present invention will be described in more detail with reference to FIGS. 7, 8, 9, 10 and 12 to 20. There are three points for improvement. 1) Improvement of the Q value (resonance sharpness) of the input / output SAW resonator. 2) In the coupled resonator,
Reduction of transverse mode propagation loss. 3) Equalization of the frequency difference between modes by appropriate setting of the frequency potential value of the coupled resonator (Δf ₁ = Δf ₂ : Δf ₁ = f _a0 −f _s0 , Δf ₁ = f _s1
−f _a0 ).

First, a description will be given from the viewpoint of 1) improving the Q value (resonance sharpness) of the input / output side SAW resonator.

As shown in FIG. 18, in a crystal rotation Y-cut in which the rotation angle θ about the electric axis X, which is the basic crystal axis of the crystal, is 29 to 33 degrees, the element size is 2 × 3 mm.
A description will be given from the result of examining the conditions for miniaturization to the extent.

As an example of the frequency, the GSM system or P
Intermediate frequency filter (I
244 MHz which is a frequency close to the F filter.
At the frequency, the sum of the logarithm M of the IDT and the reflector N on one side needs to be 200 or less in order to be accommodated in the element size described above. Under these conditions, the Q value (resonance sharpness) of one SAW resonator (curves 700, 702, 70)
3) and the characteristic of the equivalent series resonance resistance R1 (curve 701)
FIG. 7 shows the ratio H / λ of the film thickness H of the electrode of the IDT and the reflector to the wavelength λ of the surface acoustic wave as a variable. Here, λ is the pattern period λ (409) of the reflector in FIG. The ratio H / λ of the thickness H of the electrode made of aluminum to the wavelength λ of the surface acoustic wave is 0.036.
If the logarithm M of the IDT is in the range of 40 to 140 (corresponding to N = 160 to 60 from the relation of M + N = 200 at this time), the Q of about 10,000 or more
The value of R1 is about 100Ω when M is in the range of 60 to 140 pairs. However, as clearly shown in FIG. 14, the I and I of the first and second SAW resonators are different.
DT cross finger width (Wc1 = Wc2) is 9 ± 1 wavelength, third
The conductor length Wc3 of the coupled resonator is 9 ± 1 wavelength, and the gap Gc between the resonators is 0.69 ± 0.2 wavelength. Within these ranges, it is possible to configure a transverse multiplex mode SAW filter having a 3 dB pass band width of about 1000 ppm.

By the way, the range of the electrode film thickness ratio H / λ for improving the resonator Q value is 0.036 to 0.05.
In this case, the conventional frequency-temperature characteristics cannot be realized. This is shown in FIGS. 19 and 20. First, FIG. 19 shows the relationship between H / λ and the apex temperature θmax (° C.) of the frequency temperature characteristic that forms an upwardly convex quadratic curve.
When H / λ = 0.03, θmax = 20 ° C. When H / λ = 0.36, about θmax = 0 ° C.
It has become. A peak temperature drop of about 20 ° C. has occurred. FIG. 20 shows the relationship between the cut angle .theta. (Degree) of the crystal shown in FIG. 18 and the angle .theta.max for the purpose of compensating for this. As is clear from FIG. 7, when θ = around 31 degrees, a normally used specification value θmax = 20 ° C. can be realized. Accordingly, when the temperature is in the range of 33 to 29 degrees, the θmax is approximately 0 to 40 ° C. at room temperature, which is preferable for use.

Next, regarding the above-mentioned 2) reduction of the transverse mode propagation loss in the coupled resonator, which is applied to the transverse triple mode SAW filter, this has already been described with reference to FIGS. As described above. That is, I of the third coupling resonator (SAWR # 3)
By dividing the approximate center of DT3 in the propagation direction X of the surface acoustic wave, the excitation intensity of the A0 mode is improved, and the A0 mode of the coupled resonator (SAWR # 3) is divided into (using non-divided electrodes). This is to prevent a short-circuit caused by Joule heat and loss. The above division does not affect the mode S1 at all if the division width C is small.

Finally, the last of the above-mentioned characteristic improvement is
3) Equalization of frequency difference between modes by appropriate setting of the frequency potential value of the coupled resonator (Δf ₁ = Δf ₂ : Δf
₁ = f _a0 −f _s0 , Δf ₁ = f _s1 −f _a0 )
This will be described with reference to FIGS.

FIG. 14 is a diagram showing the frequency potential P (Y) at the Y coordinate point in the horizontal width direction in the horizontal triple mode SAW filter of the present invention shown in FIG. Before describing the present invention, the frequency potential P (Y) will be briefly described.

In this regard, the S
In the AW resonator, with respect to a width direction (Y axis) orthogonal to a propagation direction of the surface acoustic wave (X axis),
As a method for easily calculating the vibration displacement of the SAW resonator, the inventors have already derived and published the differential equations governing these transverse modes (Takagi, Momozaki, et al .: “ K-cut quartz SAW resonator with static zero temperature coefficient ", The Institute of Electrical Engineers of Japan, Electronic Circuits Engineering Committee, 25th EM
Symposium, pp 79-80, (1996)). When this equation is described again, it becomes Equation (1).

[0044]

(Equation 1)

Here, ω is the angular frequency, ω ₀ (Y) is the element angular frequency in the corresponding area, a is the effective shear rigidity constant in the width direction, and V (Y) is the amplitude of the surface acoustic wave displacement in the width direction. , Y
Is the Y coordinate normalized by the wavelength of the surface acoustic wave. Also,
ω ₀ (Y) is an amount obtained by converting the velocity of the surface acoustic wave at the coordinate Y into an angular frequency, and is referred to as a frequency potential function. In the vicinity of the operating point of the SAW resonator, the frequency potential function has a surface acoustic wave propagation path (FIG. 1).
4 (range of W _C1 , W _C2 , and W _C3 ) depending on the function of the thickness H (Y) of the existing aluminum metal film. More generally, it has been found that it varies as a function of the mass m (Y) of the aluminum metal. Therefore, in the interdigital transducer constituting the main part of the SAW resonator, ω ₀ (Y) is determined by the mass m (Y) of the interdigital transducer. That is, ω ₀ (m (Y)). In the case of the crystal ST-cut, since the film thickness is thin, the ω ₀ (Y) falls almost linearly with respect to m. In the formula (1) in order to simplify the calculations here, divided by the frequency omega ₀₀ ² as a reference,

[0046]

(Equation 2)

Here, Ω = ω / ω ₀₀ is a normalized frequency,
P (m (Y)) is a normalized potential function.

The frequency potential P (Y) represented by the step function 1400 in FIG. 14 will be described. First, the horizontal axis Y is described in terms of the surface acoustic wave wavelength λ, and the vertical axis is the frequency of the conductor coating. frequency change rate relative to the frequency _f f ₌ Vs / λ at the free surface is a region without (omega ₀ =
It is represented by _{(f-f f) / f} f). ω ₀ = ₀ is said of _{f f.} Parts expressed in W _C1 and _{W C2} corresponds to the IDT area of the first and second SAW resonators described above (111 and 112 in FIG. 1), the same P (Y) = P1. Also, a region indicated by the coupling resonator (113 in FIG. 1)
Is set to have a frequency potential P3 and a relationship of P3 ≦ P1. Where the difference in frequency potential ε
If = P1-P3 is a 3000ppm from 1000, it can be made almost equal to the frequency difference △ _{f 2} between the frequency difference between the aforementioned S0 and A0 △ _{f 1} and A0 and S1. This will be described with reference to FIGS. Figure 15 is an illustration of IDT and in the case where the electrode conductor width L ₃ of the reflector is changed, the frequency change f of the coupling resonators (the 1500) of the coupling resonators (W _C3 region of FIG. 14) . Line width 3.197μm is, the ratio _L 3 / _{S 3} of a so-called conductor width L = _{L 3} and a space width _{S 3} corresponds to the case of one.
The larger the L _3, it is possible to reduce the frequency. That is, the frequency potential difference ε of the coupled resonator is set to the line-to-space ratio (L ₃
/ S ₃ ) is set to 1 or more.

Based on this fact, the frequency difference among the three resonance modes S0, A0, S1 used in FIG. 1 of the present invention can be adjusted equally. FIG. 17 shows this state. The horizontal axis in the figure is the frequency potentials P1 and P3.
Frequency deviation (ppm) in which the vertical axis represents the frequency of a SAW resonator having an infinite width as a reference 0.
It is. 1700 in the figure is a fundamental wave symmetric mode S0.
Of the frequency _{f S0,} the frequency _f a0 of the fundamental wave anti-symmetric mode 1701, 1702 primary higher-order transverse symmetric mode S1
F _S1 at the frequency of The frequency difference Δf ₁ = f _a0
In order to make −f _S0 equal to Δf ₂ = f _S1 −f _a0 , P3 is set lower than P1, that is, P3
It is understood that P3 / P1 is about 1.16. Further, this condition P3 / P1 = 1.16
(This value is 1 in the frequency potential difference ε described above.
(Equivalent to 500 ppm).
FIG. 16 shows a variation of the width dimension _{WC3 in the} direction.
At W _C3 = 9λ, the Δf ₁ = Δf ₂ (= BW /
2: 3 dB half of the pass band width), and the relationship of Δf ₁ ≠ Δf ₂ is established if W _C3 is away from 9. Δf ₁
= Δf ₂ , the impedance of the filter is also equal in both sections, and the ripple of Sb in the pass band is small and good.

The matters relating to the characteristic improvement points 1) to 3) have been described above. Finally, with the above improvement measures,
How the filter characteristics are realized as the ideal filter characteristics (FIG. 8) from FIGS. 9 and 10, which are the conventional characteristics, will be described with reference to FIG. The horizontal axis in the figure is the frequency f expressed in ppm.
The vertical axis indicates the reflection characteristic S11 (curve 1300) of the present invention viewed from the terminal 107 in FIG. S0 in the figure,
A0 and S1 are the above three vibration modes. First S0
In the mode, the strength increases due to the improvement of the Q value of the SAW resonator # 1, the strength B of the A0 mode increases due to the division of the coupling resonator, and the strength A makes the negative phase excitation and the L ₃ / S ₃ ratio larger than 1. Thereby, the reflection peaks of the S0 mode and the A0 mode can be made equal, and the improvement of the intensity of the S1 mode can be achieved by the aforementioned L ₃ / S
_This can be achieved by setting the ratio ₃ to be greater than ₁ and setting Δf ₁ = Δf ₂ .

A curve 800 in FIG. 8 is a transmission characteristic diagram of the horizontal triple mode filter in FIG. 1 in which the three resonators in FIG. 7 are arranged close to each other. It can be seen that there is no lack of insertion loss in the upper passband as compared with FIG. 9 according to the conventional configuration.

It is needless to say that the characteristics of the horizontal dual mode SAW filter shown in FIG. 2 are also improved in the same manner as described above.

The configuration and characteristics of the transverse multiplex mode SAW filter of the present invention have been described above. Although the configuration example is shown as a quartz ST cut, other cuts such as an LST cut and a K cut may be used, and it is easily understood that a piezoelectric material other than quartz may be used.

[0054]

As described above, according to the present invention, when miniaturizing a transverse multi-mode SAW filter using a piezoelectric substrate such as quartz, two or three SAW resonators constituting the SAW filter are used. By forming an electrode pattern that selectively excites a fundamental transverse symmetric mode S0, a fundamental transverse oblique symmetric mode A0, and a first-order high-order transverse symmetric mode S1, which are natural vibration modes that occur between children,
By increasing the resonance amplitude of each mode, good transmission characteristics can be realized, and an intermediate frequency filter for digital communication devices having a large frequency width between channels such as PHS and GSM can be provided to the market. Furthermore, by forming a split slit and an electrode finger having an inverted phase in a part of the IDT, the excitation of the fundamental wave oblique mode A0 can be enhanced, and similarly, a small size and good transmission characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view showing a conductor pattern of one embodiment of a horizontal triple mode filter of the present invention.

FIG. 2 is a plan view showing a conductor pattern of one embodiment of the horizontal dual mode filter of the present invention.

FIG. 3 is a diagram showing an embodiment of a horizontal multi-mode filter having a two-stage cascade connection according to the present invention.

FIG. 4 is a plan view showing one embodiment of the S0 mode excitation reflector of the present invention.

FIG. 5 is a plan view showing one embodiment of an A0 mode excitation reflector of the present invention.

FIG. 6 is a plan view showing an embodiment of an S1-mode excitation reflector according to the present invention.

FIG. 7 is a Q-value characteristic diagram of the transverse multiple mode filter of the present invention.

FIG. 8 is a transmission characteristic diagram of the embodiment of FIG. 1 of the present invention.

FIG. 9 is a transmission characteristic diagram of a conventional transverse multiple mode filter.

FIG. 10 is a reflection characteristic diagram of a conventional transverse multimode filter.

FIG. 11 is a plan view showing an embodiment of an IDT unit which is a component of the present invention.

FIG. 12 shows a division width C of the transverse multimode filter of the present invention.
FIG.

FIG. 13 is a reflection characteristic diagram of the transverse multiple mode filter of the present invention.

FIG. 14 is a frequency potential diagram of the Y-axis cross section of the embodiment of FIG. 1 of the present invention.

FIG. 15 is a frequency characteristic diagram of the electrode width of the coupled resonator of the present invention.

FIG. 16 is a frequency characteristic diagram of the electrode length of the coupled resonator of the present invention.

FIG. 17 is a frequency characteristic diagram of the coupled resonator of the present invention.

FIG. 18 is a view showing a cut direction of the piezoelectric substrate of the present invention.

FIG. 19 is a frequency temperature characteristic diagram of the transverse multiple mode filter of the present invention.

FIG. 20 is a frequency temperature characteristic diagram of the piezoelectric substrate of the present invention.

[Explanation of symbols]

100, 200, 300 Piezoelectric flat plates 101, 201, 1101 IDT1 102, 202, 1102 IDT2 103, 1103 IDT3 104, 203 Reflector 1 105, 204 Reflector 2 106, 108, 110, 116, 205, 207, 2
08, 210, 301, 303, 307, 309 Pads 107, 109, 206, 209, 302, 308
Positive terminal 111, 211 SAW resonator 1 112, 212 SAW resonator 2 113 SAW resonator 3 310 First transverse multi-mode SAW filter 311 Second transverse multi-mode SAW filter 400, 500, 600 Reflectors 401, 402, 501, 502, 510, 511, 6
04, 605, 613, 614, 616, 617, 11
08, 1109, 1110, 1111, 1116 Electrode fingers 404, 405, 503, 504, 505, 506, 6
01, 602, 603, 606, 615, 1104, 1
105, 1106, 1107 Feeding conductor pattern 403 Symmetry axis

Claims (20)

[Claims] 1. A SAW resonator having at least one interdigital transducer on a piezoelectric flat plate and a pair of reflectors for reflecting surface acoustic waves generated by the interdigital transducer on both sides thereof. In a transverse multimode SAW filter in which two or three SAW filters are arranged adjacent to and substantially parallel to the propagation direction X of the surface acoustic wave, wherein the reflector excites over a plurality of SAW resonators. Multi-mode SAW filter characterized by having a group of electrode fingers for the same. 2. A SAW resonator having, on a piezoelectric plate, at least one interdigital electrode and a pair of reflectors for reflecting surface acoustic waves generated by the interdigital electrode on both sides thereof. In a transverse multi-mode SAW filter arranged adjacently and substantially parallel to the propagation direction X of the surface acoustic wave, wherein substantially the center of the interdigital transducer of the SAW resonator located in the middle is located at the center of the surface acoustic wave. A horizontal multiplex mode SAW filter characterized by being divided in the propagation direction X. 3. An input device comprising: a piezoelectric flat plate having at least one interdigital electrode and a pair of reflectors for reflecting surface acoustic waves generated by the interdigital electrode on both sides thereof; A first SAW resonator on the terminal side and a second SAW resonator on the output terminal side are arranged substantially parallel to each other, and are arranged substantially parallel between the two resonators to form a third coupling. In the transverse multi-mode filter having a resonator, the reflector has a group of electrode fingers for exciting across a plurality of SAW resonators. A transverse multi-mode SAW filter characterized by being synthesized from a triple mode of a symmetric mode S0, a fundamental oblique symmetric mode A0, and a first-order high-order transverse symmetric mode S1. 4. A SAW resonator having at least one interdigital electrode on a piezoelectric flat plate and a pair of reflectors for reflecting surface acoustic waves generated by the interdigital electrode on both sides thereof. , Two laterally arranged multi-modes SA which are arranged adjacent to and substantially parallel to the propagation direction X of the surface acoustic wave.
In the W filter, the reflector has an electrode finger group for exciting over a plurality of SAW resonators, and a transmission characteristic of the transverse multi-mode SAW filter has a fundamental transverse symmetric mode S0 and a fundamental transverse mode. A transverse multiple mode SAW filter characterized by being synthesized from the oblique symmetric mode A0. 5. A group of electrode fingers for exciting across a plurality of SAW resonators of the reflector can selectively excite a fundamental transverse symmetric mode S0 and a fundamental transverse oblique symmetric mode A0. 5. The transverse multi-mode SAW filter according to claim 3, wherein: 6. An electrode finger group for exciting across a plurality of SAW resonators of the reflector is capable of selectively exciting a fundamental oblique symmetric mode A0. 5. The horizontal multi-mode SAW filter according to 3 or 4. 7. An electrode finger group for exciting across a plurality of SAW resonators of the reflector is capable of selectively exciting a first-order higher-order transversely symmetric mode S1. Item 3. A transverse multiple mode SAW filter according to item 3. 8. An electrode finger group for exciting across a plurality of SAW resonators of the reflector can selectively excite a fundamental transverse oblique symmetric mode A0 and a primary transverse symmetric mode S1. 4. The transverse multiple mode SAW filter according to claim 3, wherein: 9. The third coupling resonator (SAWR # 3)
4. The transverse multi-mode SAW filter according to claim 3, wherein substantially the center of the interdigital transducer is divided in the propagation direction X of the surface acoustic wave. 10. The transverse multi-mode SAW filter according to claim 9, wherein the IDL of the coupled resonator (SAWR # 3) has a substantially center division width of 0.2 wavelength or less. 11. The third coupling resonator (SAWR #
3) wherein the potential of the electrode finger of the interdigital transducer divided along the propagation direction X has a phase difference of 180 degrees with the potential of the electrode finger at the same X coordinate position of the SAW resonators on both sides. The transverse multiple mode SAW filter according to claim 9. 12. The coupling resonator includes a plurality of conductor strips periodically arranged orthogonally to a phase propagation direction of a surface acoustic wave, and an interval between the conductor strips is defined by the first and second SAWs. 4. The transverse multi-mode SAW filter according to claim 3, wherein the distance between the electrodes of the resonator is substantially equal. 13. The frequency potential P3 of the coupled resonator is smaller than the frequency potentials P1 and P2 of the first and second SAW resonators (P1, P2 ≧ P3), and a frequency difference between S0 and A0. △ transverse multi-mode SAW filter according to claim 3, wherein the frequency difference △ f ₂ between f ₁ and A0 and S1 were substantially equal. 14. The difference ε = P1 between the frequency potentials.
14. The transverse multi-mode SAW filter according to claim 13, wherein -P3 = P2-P3 is 1000 to 3000 ppm. 15. The difference in frequency potential ε between the coupled resonators and the line-to-space ratio (L ₃
4. The transverse multiplex mode SAW filter according to claim _{3, wherein} / S ₃ ) is set to 1 or more. 16. The IDT cross finger width (Wc1 = Wc2) of the first and second SAW resonators is 9 ± 1 wavelength, and the conductor strip length Wc3 of the third coupling resonator is 9 ± 1.
4. The transverse multi-mode SAW filter according to claim 3, wherein one wavelength and the gap Gc between the resonators are 0.69 ± 0.2 wavelengths. 17. The transverse multi-mode SAW filter according to claim 3, wherein said piezoelectric flat plate is made of quartz and has a Y-cut X propagation azimuth rotated from 29 to 33 degrees. 18. The piezoelectric flat plate is made of quartz, and a ratio H / λ of an electrode film thickness H made of aluminum constituting the interdigital transducer and the reflector to a wavelength λ of the surface acoustic wave is 0.0.
5. The transverse multi-mode SAW filter according to claim 3, wherein the value is 36 to 0.05. 19. The SAW resonator according to claim 1, wherein the number of interdigital electrodes included in the SAW resonator is in a range from 140 to 40 pairs, and the number of conductors in one reflector is in a range from 60 to 160. 5. The transverse multi-mode SAW filter according to claim 3, wherein 20. The horizontal multiple mode SAW filter is
20. The transverse multiplex mode SAW filter according to claim 1, wherein the filters are connected in stages.