JP2005204042A - Surface acoustic wave resonator and surface acoustic wave filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave resonator and a resonator type SAW filter, where the resonator is by the transverse higher mode supriousness is suppressed and with the SAW filter being characterized in that an increase in out-band attenuation quantity due to the longitudinal higher mode supriousness is suppressed. <P>SOLUTION: The surface acoustic wave resonator, comprising one inter-digital electrode which excites surface acoustic waves in a propagation direction (x) on a piezoelectric body plane plate and a couple of reflectors arranged on both sides of it in the propagation direction, is provided with at least one control region in the region of the interdigital electrode; the array period length PT2 of the interdigital electrode sectioned in the control region and the array period length PT1 of the interdigital electrode which is not in the control area are so related that PT2>PT1; a plurality of displacement functions of energy confinement states are generated in the longitudinal direction (x) of elements; and a plurality of resonators are longitudinally connected to suppress the higher longitudinal mode spuriousness. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention uses a Rayleigh type or STW (Surface Transversal Wave) type surface acoustic wave on a piezoelectric plate such as quartz, and a surface acoustic wave resonator having no longitudinal higher-order mode spurious (hereinafter abbreviated, And a lateral multimode type SAW filter (hereinafter abbreviated as a SAW filter) in which a plurality of the surface acoustic wave resonators are arranged close to each other.

  Conventionally, SAW resonators constructed using a quartz ST-cut substrate with piezoelectricity (an example of a piezoelectric flat plate) have a zero temperature coefficient and high accuracy, so that data transmission of various high-speed network systems is possible. This is because a signal free from jitter and excellent in phase noise can be easily obtained with high reliability and low cost.

  The ST-cut quartz plate is already well known, and is orthogonal to the mechanical axis Y in an orthogonal coordinate system composed of an electric axis X, a mechanical axis Y, and an optical axis Z, which are basic axes of the quartz crystal. A Rayleigh surface acoustic wave propagating in the electric machine axial direction X is used on a substrate obtained by rotating the Y plate around the electrical axis X by θ degrees (particularly θ = 31 degrees to 42 degrees at which a zero temperature coefficient is obtained).

  For the SAW resonator using the ST substrate, for example, interdigital electrodes (hereinafter abbreviated as IDT: Interdegital Transducer) in which a large number of parallel conductor electrode fingers made of metal aluminum are periodically formed are formed. A pair of reflectors can be formed on both sides by arranging a number of strip-shaped electrode conductors in parallel and periodically to form a 1-port SAW resonator. More specifically, as a main point in configuring the IDT, when the positive electrode and the negative electrode are paired into M pairs, the total reflection coefficient Γ of the entire electrode fingers of the IDT is expressed by the following equation (1). If defined as 10> Г> 0.8, a so-called energy-confined SAW resonator in which vibration energy is concentrated at the center of the resonator (Non-patent Document 1: energy confined surface acoustic wave resonator, signal) It is known that the academic technique US87-36, pp9-16 (1987. 9)) can be realized.

[Equation 1]
Г = 4MbH / λ (1)
Here, M is the logarithm of the IDT, b is the reflection coefficient ratio of the surface acoustic wave per electrode, H is the thickness of the conductor, and λ is the wavelength of the surface acoustic wave to be used.

  For example, in the case of an IDT formed of an aluminum conductor with an ST cut quartz plate, if b = 0.255, H / λ = 0.03 (3%) and M = 80 pairs, Q and CI characteristics are A good conventional 1-port SAW resonator can be constructed. At this time, the above-mentioned Γ = 2.448. Note that the reflection coefficient γ per electrode generally referred to is, in the case of this ST cut quartz plate, γ = b (H / λ) = Γ / (4M) = 0. 00765 (0.76%) (Patent Document 1: Japanese Patent Laid-Open No. 57-73513).

JP-A-57-73513 Science technique US87-36, pp9-16 (1987.9)

  However, when the above-described conventional technology is used and the configuration of the same SAW resonator is used, spurious in the higher-order modes (A0, S1, A1,...) Are generated below the main resonance mode. These problems become a frequency jump phenomenon when an oscillator using a SAW resonator or a variable frequency voltage controlled oscillator is manufactured. Alternatively, when a SAW filter is configured using a conventional SAW resonator, spurious noise that cannot be ignored occurs in the attenuation region in the vicinity of the pass band in the pass characteristics of the filter, causing deterioration in communication quality. there were.

  Therefore, the present invention solves such problems by utilizing a “frequency potential design method”. The above-mentioned “frequency potential design method” is simply described. The relational expression of the frequency potential function FP (X), the surface acoustic wave velocity Vs, and the spatial wavelength 2P (X) of the element FP (X) = Vs / {2P (X )} Is used to control vibration displacement.

The purpose is to use a ST substrate or the like to form a SAW resonator using a quartz substrate having excellent frequency temperature characteristics and excellent material Q value, and further using this to make a small, high Q value and Realizing a spurious-free SAW resonator and providing a SAW oscillator and a voltage-controlled SAW oscillator, which are low-jitter and low-phase-noise clock signals using these, to the gigabit high-speed wired communication market,
Furthermore, when the SAW resonator is applied to a SAW filter or the like and various communication methods have recently been introduced, countermeasures for deterioration of communication quality due to radio wave interference are required. Therefore, the suppression characteristic of the attenuation region in the vicinity of the passband is improved.

(1) A surface acoustic wave resonator according to the present invention comprises one interdigital electrode for exciting a surface acoustic wave in a propagation direction x on a piezoelectric plate and a pair of reflectors disposed on both sides of the propagation direction. In the surface acoustic wave resonator, at least one control region is provided in the region of the interdigital electrode,
The relationship between the arrangement period length PTc of the interdigital electrodes divided into the control area, the arrangement period length PT of the interdigital electrodes other than the control area, and the dimension of the arrangement period length PR of the reflector is expressed as PTc> PT. PTc / PT ratio R is in the range of 1.0 <R <1.04, PR / PT is in the range of 1.0 to 1.02,
The ratio Mc / M, which is the ratio of the interdigital log pair Mc of the control region to the entire logarithm M, is in the range of 0.1 to 0.3.

  According to the configuration of (1) above, in the conventional surface acoustic wave resonator, the high-order longitudinal mode spurious generated in the lower several thousand ppm range of the main resonance vibration frequency fs can be suppressed or eliminated sufficiently small. As a result, when the voltage controlled oscillator is configured using the surface acoustic wave resonator of the present invention, it is possible to avoid an unnecessary spurious oscillation phenomenon when it is necessary to extend the frequency variable range using the extension coil. There is an effect.

(2) In the surface acoustic wave filter of the present invention, two surface acoustic wave resonators having interdigital electrodes divided into the control region are placed in parallel with the longitudinal axis X of the surface acoustic wave resonator being substantially parallel. A transverse dual-mode resonator that is arranged and operates in two fundamental wave modes of symmetry (ψ0, ψ0) and oblique symmetry (ψ0, -ψ0) standing in the width direction of the surface acoustic wave resonator. A filter is constructed.

  With the configuration of (2) above, since a transverse dual mode type resonator filter is configured using a surface acoustic wave resonator having no longitudinal higher-order mode spurious, the lower number of passbands % Spurious can be significantly suppressed, and as a result of the recent introduction of various communication methods, it is possible to improve the S / N ratio of narrowband communication devices that have been deteriorated in communication quality due to radio wave interference.

(3) In the surface acoustic wave filter of the present invention, two surface acoustic wave resonators having interdigital electrodes divided into the control region are placed in parallel with the longitudinal axis X of the surface acoustic wave resonator substantially parallel. A transverse dual-mode resonator that is arranged and operates in two primary modes of symmetry (ψ1, ψ1) and oblique symmetry (ψ1, -ψ1) standing in the width direction of the surface acoustic wave resonator. A filter is constructed.

With the configuration of (3) above, the passband width can be 30% (300 ppm) wider than that using the fundamental wave mode, LiTaO having a larger frequency coefficient of electromechanical coupling than the crystal ST cut, but a large electromechanical coupling coefficient k ^2. _In a SAW filter with low insertion loss using ₃ substrates, etc., a transverse dual mode type resonator filter is formed using a surface acoustic wave resonator that does not have longitudinal higher-order mode spurious. As a result of the recent introduction of various communication methods, it is possible to improve the S / N ratio of a narrowband communication device whose communication quality has been degraded due to radio wave interference.

(4) In the surface acoustic wave filter of the present invention, two surface acoustic wave resonators having interdigital electrodes divided into the control region are placed in parallel with the longitudinal axis X of the surface acoustic wave resonator substantially parallel. A transverse dual-mode resonator that is arranged and operates in two primary modes of symmetry (ψ1, ψ1) and oblique symmetry (ψ1, -ψ1) standing in the width direction of the surface acoustic wave resonator. The filter is configured to operate with a WAVE electrode.

  With the configuration of (4) above, the shape of the electrode pattern connecting the electrode fingers becomes simple, so the design cost is reduced, and a simple and well-balanced SAW filter is used to integrate multiple elements. Is easy, and it has the effect that the oxide insulating treatment of the electrode pattern is easy.

(5) In the surface acoustic wave resonator according to the present invention, the piezoelectric flat plate is an ST-cut crystal obtained by rotating a quartz rotation Y plate counterclockwise around an electric axis (X axis) from a rotation angle θ = 31 degrees to 42 degrees. 2. The surface acoustic wave resonator according to claim 1, wherein the total logarithm M of the drainage electrode is in the range of 100 to 140 pairs.

  With the configuration of (5) above, it can be used in the cutoff region of the longitudinal higher-order mode spurious that is higher than the first-order mode (S1), and these spurious will not exist. As a result, when the voltage controlled oscillator is configured using the surface acoustic wave resonator of the present invention, it is possible to avoid an unnecessary spurious oscillation phenomenon when it is necessary to extend the frequency variable range using the extension coil. There is an effect.

  The aforementioned ST cut is cut out from a piezoelectric material made of quartz, and its surface is mirror-polished, and then perpendicular to the phase propagation direction x of the Rayleigh type or STW type surface acoustic wave, for example, a large number of metal aluminum. An IDT in which electrode fingers of parallel conductors are periodically arranged is formed, and a pair of reflectors are arranged on both sides of the IDT in parallel and periodically to form one port. A SAW resonator of the type is formed.

  Hereinafter, in order to facilitate understanding of the embodiment of the 1-port SAW resonator of the present invention, the configuration of a specific example will be described with reference to FIG. 1, and then FIG. 6, FIG. 7, FIG. The characteristics of the SAW resonator of the present invention will be described in detail with reference to FIGS.

  Further, an example of the SAW filter using the SAW resonator of the present invention is described for the lateral dual mode type with the configuration of the specific embodiment shown in FIGS. 2 and 3, and FIG. 4 and FIG. The characteristics will be described in detail.

  FIG. 1 shows an electrode pattern formed on a piezoelectric plate for one embodiment of a SAW resonator (hereinafter simply referred to as the present element) according to the inventions of claims 1 and 5.

In FIG. 1, the names of the respective parts are as follows: 100 is a piezoelectric plate made of quartz, LiTaO ₃ or the like, and 1091 on the piezoelectric plate is an x-axis (1091) which is a propagation direction of the surface acoustic wave used for this element. . The respective parts made up of the entire electrode pattern formed in the section divided by the broken line are the left side 101 and the right side 103 are the reflector 1 and the reflector 2 of this element, and 102 is the interdigital electrode (hereinafter abbreviated). IDT: Interdegital Transducer). The IDT is divided into three areas, and 1021 is referred to as end IDT1, 1023 as end IDT2, 1022 as control IDT. In the reflector 1, the reflector 2, and the IDT, 1040, 1041, 104, 105, etc. are electrode conductor strip groups made of aluminum metal, and serve to reflect surface acoustic waves by a perturbation effect. In the IDT, 104, 105, etc. are positive and negative electrode fingers. The positive electrode and the negative electrode are a pair of M as a whole, the control IDT is the Mc pair, and the end IDT1 and the end IDT2 are each (M-Mc) / Two pairs are formed. 106, which vertically connects and connects the electrode finger groups 104, 105, etc. of the three IDTs 1021, 1022, 1023, is called a power supply conductor (bus bar).

  Further, the symbol PR in FIG. 1 is the arrangement period length of the conductor strips of the reflectors 1 and 2, and is the sum of the conductor strip width LR and the gap length SR between the conductor strips, and PR = LR + SR. The dimension symbols LT and ST are the line width LT of the electrode finger and the gap length (space) ST in the IDT, respectively. Furthermore, the arrangement period length designated by PT and PTc is that PT is the end portions IDT1 and IDT2, PTc is the arrangement period length of the control IDT, and they are the line width LT of the electrode finger and the gap length ( Space) Sum of ST. Next, the proper setting of the dimension values represented by the symbols PR, PT, and PTc in this element will be described. The diagram consisting of the horizontal axis X and the vertical axis P (X) shown at the bottom of the element in FIG. 1 shows the functional relationship of the array period length P (X) corresponding to the x coordinate position of the element. Specifically, dimensional comparison characteristic lines 1080, 1090, 110 or 111, 1091, 1081 corresponding to PR, PT, PTc, PT, PR, respectively, are shown. The dimension lengths PR, PT, and PTc are constant in each section. Therefore, P (X) is expressed by a step-like function. As for the line width L of the interdigital electrode, when the dimension LT / ST ratio is also a constant value in all three sections of the IDT, the line width L of the interdigital electrode excludes processing variations within each section. The corresponding constant value is taken. More specifically, since the line width ratio PTc / PT is close to 1, the line width L can be made constant for all three sections of IDT. The line width L of the IDT is often set to a value that maximizes the reflection coefficient ratio b per electrode. Furthermore, for in-plane rotated ST-cut quartz plates, the LT / ST ratio for all IDTs and reflectors may be in the range of 0.42 to 0.67. Similarly, 1/4 of the wavelength λ of the surface acoustic wave and the film thickness H are also set to a constant value except for processing variations.

  Specifically, the arrangement period lengths PT and PTc of the interdigital electrodes (IDT) and the dimension of the arrangement period length PR of the reflectors are set in a relationship of PTc> PT, and a ratio R of PTc / PT is set as a specific configuration condition. 1.0 <R <1.04, PR / PT is 1.0 to 1.02, the logarithm of the interdigital electrode arranged in the center is Mc, and the total logarithm M The ratio Mc / M is in the range of 0.1 to 0.3. The basis of this configuration condition will be shown in the characteristic diagram described later.

  Here, mention will be made as to whether or not processing is possible in the range of “the range of the line width ratio R = PTc / PT is 1.0 <R <1.04”, which is a factor for determining the feasibility of the present invention. Between the element frequency f (MHz) and the dimensions PT and PTc (μm), for example, if the surface acoustic wave velocity Vs to be used is 5000 m / s (quartz STW cut), PTc and PT = Vs / (2f) There is a relationship. It is clear that the present invention is particularly disadvantageous for processing at high frequencies. As an example, when f = 1 GHz, PT is 2.5 μm and PTc is 2.52 μm as PT 1.02. The difference between the two is 0.05 μm. This processing accuracy resolution is 0.25 μm when converted to the mask accuracy used for a projector capable of 5 times reduction exposure, which is sufficiently large with respect to the current resolution of 0.01 μm of an electron beam exposure machine. It is feasible. If the logarithmic Mc of the control IDT area of the dimension PTc is 20 pairs, the mask dimension difference that is 5 times the corresponding area is 0.05 × 20 × 2 × 5 = 10 μm, which is sufficient with the current measuring instrument. Be identifiable.

If the configuration conditions are defined in more detail, it can be said as follows. The interdigital electrodes and reflectors are made of aluminum metal, and the interdigital electrodes are M pairs with one pair of positive and negative electrode fingers, and M is in the range of 100 to 140 pairs,
When the reflection coefficient γ of the surface acoustic wave per electrode is in the range of 0.01 to 0.03, the total reflection coefficient Γ of the entire interdigital electrode is 10>Γ> 0.8,
The distance between the parallel conductors closest to each other between the reflector and the interdigital electrode is a space ST among the line LT and the space ST having one period length of the interdigital electrode,
The dimensions of the array period lengths PT and PTc of the interdigital electrodes and the array period length PR of the reflector are set in a relationship of PTc> PT, and the ratio R of PTc / PT is in the range of 1.0 <R <1.04. PR / PT is in the range of 1.0 to 1.02, the logarithm of the control interdigital electrode disposed at the center is Mc, and the ratio Mc / M of the total logarithm is 0.0. It is in the range of 1 to 0.3.

  Again, as a condition of the piezoelectric plate, the crystal Y plate is rotated counterclockwise around the electric axis (X axis) by a rotation angle θ = 31 degrees to 42 degrees, and the propagation direction of the surface acoustic wave is set to An ST-cut quartz plate that is 0 degrees from the axis (X-axis) or a rotated ST-cut quartz plate that is rotated in-plane within a range of 40 to 46 degrees is used.

  Next, the operation and characteristics of the SAW resonator shown in FIG. 1 of the present invention will be described in detail with reference to FIGS. 6, 7, 8, 9, and 10. FIG.

  First, FIG. 6 illustrates the relative shape of the envelope amplitude U (X) of the vibration displacement with respect to the longitudinal x coordinate of the element in the SAW resonator of the present invention. A curve 600 in the figure is U (X) when the ratio R of PTc / PT is 1.0, and corresponds to the relative displacement of the conventional product. Curve 601 is U (X) when R is 1.02, and curve 602 is U (X) when R is 1.04. Further, the figure arranged at the bottom of the figure shows the relative value of the electrode period length function P (X) and the X coordinate relationship, and 604 and 608 are P (X) in the area of the reflector 1 and the reflector 2. , 605 and 607 are PTs of the end portions IDT1 and IDT2, and 6060, 6061 and 6062 are PTc of the control IDT. 6062 corresponds to the U (X) curve 600, 6061 corresponds to the U (X) curve 601 (R = 1.02), and 6060 corresponds to the U (X) curve 602 (R = 1.04). It corresponds to. As can be seen, as the ratio R increases, U (X) exhibits both displacement distributions in which the left and right energy confinement states are separated. However, Mc / M was 0.2. Further, it was found that when there are a plurality of control IDTs, the displacement state has a plurality of peaks.

Next, FIG. 7 shows frequency characteristics (resonance characteristics) of admittance Y (f) of a conventional SAW resonator in which PTc = PT. In the upper row, the configuration condition of the conventional product is IDT logarithm M = 120 pairs and the number of reflectors N = 100. In the lower row, the configuration condition of the conventional product is IDT logarithm M = 60 pairs and the number of reflectors N = 100. is there. The horizontal axis of the figure is the frequency, but it is displayed as a frequency change rate df / f (ppm unit), and the vertical axis is a logarithmic display of the admittance Y (f) of the SAW resonator (20LOG ₁₀ Y (f)). It is. First, in the upper conventional product, 700 is the Y (f) characteristic, the resonance frequency of the maximum peak of Y (f) is the fundamental wave mode LS0, and the mode LS1 at the lower side of 9000 ppm is the first higher-order longitudinal mode. It is.

  In the lower conventional product, 701 is the Y (f) characteristic, and the resonance frequency of the maximum peak of Y (f) is the fundamental wave mode LS0, and there is a significant vertical higher-order mode in the lower 40000 ppm range. I understand that I do not.

  FIG. 8 illustrates the confirmation as described above by examining the generation frequency arrangement of the fundamental wave LS0 and the symmetric high-order longitudinal modes LS1, LS2, and LS3 with respect to the logarithm M of the IDT. The vertical axis is shown in units of 10 4 ppm. In the figure, 800 is the LS0 mode, 801 is the LS1 mode, 802 is the LS2 mode, and 803 is the LS3 mode. A region 804 surrounded by a two-dot chain line is a range of M in which the LS1, LS2, and LS3 modes disappear. As shown in FIG. 8, if M is 70 or less, these longitudinal higher order modes disappear. Therefore, if this fact is used in the present invention, the present invention can be interpreted as a plurality of resonance amplitudes connected in the vertical direction X. Therefore, when there is one control IDT, an appropriate logarithm of IDT is used. If M is 140 or less, which is twice 70, spurious can be eliminated. In addition, the larger M is, the smaller the insertion loss is. Therefore, from an empirical viewpoint, M = 100 or more is desirable.

  In FIG. 8, the SAW resonator of FIG. 7 corresponds to M = 60 and 120. Incidentally, the number N of the reflectors 1 and 2 is 100.

Next, FIG. 9 and FIG. 10 show the configuration conditions in FIG. 1 of the present invention as IDT logarithm number M = 120 pairs, reflector number N = 75, ETA = Mc / M = 0.1, R = PTc / PT = The admittance characteristic Y (f) when 1.01 is set. The horizontal axis of the figure is the frequency, but the frequency change rate df / f (in ppm) is displayed, and the vertical axis is a logarithmic display of the admittance Y (f) of the SAW resonator (20LOG ₁₀ Y (f)). It is. In the figure, 900 is the main resonance state A, and 901 B existing 1500 ppm below A is a unique resonance phenomenon that is considered not to be a high-order longitudinal mode. Further, as the ETA, a sufficient displacement control effect can be obtained in the range of 0.1 to 0.3.

  Further, FIG. 10 shows a calculation result of the relative vibration displacement U (X) corresponding to the resonance A in FIG. 9 (curve 1000). It can be seen that the displacement U (X) has a minimal two-peak shape at the center position X = 200.

  The above is a description of the surface acoustic wave resonator according to the present invention. Hereinafter, a SAW filter as an application example will be described.

  First, in FIG. 2, two longitudinally parallel longitudinal axes X of the surface acoustic wave resonators of FIG. 1 according to the present invention are arranged in parallel, and are symmetrically arranged in the width direction of the surface acoustic wave resonators (ψ0 , Ψ0) and a diagonally symmetric (ψ0, −ψ0) two-wavelength mode resonator filter that operates in two fundamental wave modes. In the figure, reference numeral 200 denotes a piezoelectric band plate, and 201 and 202 are plan views showing the configuration of the electrode pattern of the surface acoustic wave resonator according to the present invention. Further, the function P (X) shown in the lower stage is a state 203 of the electrode period length P (X) of the reflector 1 and the IDT. The two SAW resonators are arranged in parallel with a gap interval of several wavelengths indicated by 204 (approximately one wavelength = 2PR).

  This SAW filter operates by synthesizing two fundamental wave modes of a symmetric 205 vibration displacement state (ψ0, ψ0) and a diagonally symmetrical vibration displacement state (ψ0, −ψ0).

  FIG. 3 shows another embodiment of the SAW filter according to the present invention. In the present invention, the electrode period length is defined by the above-described function P (X) in the IDT of the surface acoustic wave resonator operating in the obliquely symmetric fundamental wave mode TA0. The SAW filter is constructed by arranging two pieces of the surface acoustic wave resonators in parallel, with the longitudinal axes X of the surface acoustic wave resonators approximately parallel, and being symmetrically arranged in the width direction of the surface acoustic wave resonators (ψ1, ψ1). ) And obliquely symmetrical (ψ1, −ψ1) two obliquely symmetric fundamental wave modes, which are O / T driven transverse dual mode type resonator filters (O / T drive: meaning of inharmonic harmonic drive) ).

  In the figure, reference numeral 300 denotes a piezoelectric strip, and 301 and 302 are plan views showing the electrode pattern configuration of the SAW resonator according to the present invention. Furthermore, the function P (X) shown in the lower stage is the state 303 of the electrode period length P (X) of the reflector 1 and the reflector 2 and the IDT. The two resonators are arranged in parallel with a gap interval of several wavelengths indicated by 304 (approximately one wavelength = 2PR).

  This SAW filter operates in two obliquely symmetric fundamental wave modes: a symmetrically 305 vibration displacement state (ψ1, ψ1) and a diagonally symmetrical 306 vibration displacement state (ψ1, −ψ1).

  By the way, as shown in FIG. 3, the electrode pattern of IDT looks like a wave, so it is called “WAVE electrode”. The WAVE electrode provides a convenient electrode pattern configuration method for reversing the positive / negative polarity of the IDT electrode between adjacent tracks in one SAW resonator.

  Next, FIGS. 4 and 5 are 50 (Ω) -terminated transmission characteristics of the 300 MHz SAW filter of Example 3 of the present invention (experimental values). First, the characteristics of FIG. 4 are for the case of PTc = PT according to the prior art, where the horizontal axis is a frequency axis and is displayed as an offset frequency from the center frequency f0, and the vertical axis is a logarithmic display of the attenuation Sb (dB). ). The light curve 300 in the figure is the transmission characteristic calculation result, and the dark solid line 301 is the actual measurement value. The lower 302 (actually measured) and 303 (calculated) constituting the passband of the SAW filter are spurious generated by the first-order high-order longitudinal mode LS1 in question, and are so large that they approach -40 dB and cannot be ignored. .

  FIG. 5 shows the transmission characteristics of the SAW filter according to the third embodiment of the present invention. The structural condition is that the piezoelectric flat plate uses a ST cut quartz plate obtained by rotating a quartz rotation Y plate around the electric axis (X axis) counterclockwise by a rotation angle θ = 31 degrees to 42 degrees. The total logarithm M of the electrodes was 140. In addition, the horizontal axis in the figure is the frequency axis and is displayed as an offset frequency from the center frequency f0, and the vertical axis is the attenuation Sb (dB). The light curve 500 in the figure is the calculation result of the characteristic, and the dark solid line 501 is the actual measurement value. 503 (actual measurement) and 502 (calculation) arranged in the lower frequency region of 504 constituting the pass band of the SAW filter are present at f0-1 MHz (−3000 ppm), and are not a high-order longitudinal mode. 9 is assumed to correspond to the unique spurious B shown in FIG. 9 (when converted as a surface acoustic wave resonator, it corresponds to M = 70 pairs, so the spurious generation frequency moves away from the pass band). By the way, the 3 dB pass bandwidth in this case is 1000 to 1200 ppm because this filter is an O / T drive system and a wide bandwidth can be secured for fundamental wave use.

As described above, the present invention has been described with respect to the configuration and characteristics of the surface acoustic wave resonator using the Rayleigh type and STW type surface acoustic waves for the substrate made only of quartz, but the substrate is made of a material other than quartz. However, it is added that even if a thin film such as SiO ₂ or ZnO is formed on the substrate surface to such an extent that the characteristics of the device are not impaired, it is effective as long as the constitutional conditions of the present invention are satisfied.

  The surface acoustic wave resonator and the surface acoustic wave filter of the present invention use an ST substrate or the like to form a SAW resonator using a quartz substrate having excellent frequency temperature characteristics and excellent material Q value, and further comprising A small, high-Q and spurious SAW resonator is realized, and a low-jitter and low-phase noise clock signal source using these SAW oscillators and voltage-controlled SAW oscillators are gigabit high-speed wired. Can be used in the telecommunications market.

  Furthermore, when the SAW resonator is applied to a SAW filter or the like and various communication methods have recently been introduced, countermeasures for deterioration of communication quality due to radio wave interference are required. Therefore, the suppression characteristics of the attenuation region in the vicinity of the passband can be improved.

The top view which shows the electrode pattern which one Example of the surface acoustic wave resonator of this invention has. The top view of the electrode pattern which one Example of the SAW filter comprised using the surface acoustic wave resonator of this invention has. The top view of the electrode pattern which the other Example of the SAW filter comprised using the surface acoustic wave resonator of this invention has. The transmission characteristic figure which the conventional SAW filter has. The transmission characteristic figure which the SAW filter of this invention has. The displacement figure which shows the vibration displacement which the surface acoustic wave resonator of this invention has. The admittance characteristic figure which the conventional surface acoustic wave resonator has. The characteristic view which the conventional surface acoustic wave resonator has. The other characteristic view which the surface acoustic wave resonator of this invention has. The displacement figure which shows the vibration displacement which the surface acoustic wave resonator and SAW filter of this invention have.

Explanation of symbols

100 Piezoelectric plate 101 Reflector 1
103 reflector 2
1021 End IDT1
1022 Control IDT
1023 End IDT2
110 Frequency potential function

Claims (5)

In a surface acoustic wave resonator comprising one interdigital electrode for exciting a surface acoustic wave in a propagation direction x on a piezoelectric plate and a pair of reflectors arranged on both sides of the propagation direction, the region of the interdigital electrode In which at least one control region is provided,
The relationship between the arrangement period length PTc of the interdigital electrodes divided into the control area, the arrangement period length PT of the interdigital electrodes other than the control area, and the dimension of the arrangement period length PR of the reflector is expressed as PTc> PT. PTc / PT ratio R is in the range of 1.0 <R <1.04, PR / PT is in the range of 1.0 to 1.02,
A surface acoustic wave resonator characterized in that Mc / M, which is the ratio of the logarithm Mc of the interdigital electrodes in the control region to the overall logarithm M, is in the range of 0.1 to 0.3.   Two surface acoustic wave resonators having interdigital electrodes divided into the control region are disposed in parallel and close to each other so that the longitudinal axis X of the surface acoustic wave resonator is substantially parallel to the width of the surface acoustic wave resonator. A surface acoustic wave characterized by comprising a transverse dual mode resonator filter that operates in two fundamental wave modes of symmetry (ψ0, ψ0) and oblique symmetry (ψ0, -ψ0) standing in the direction. filter.   Two surface acoustic wave resonators having interdigital electrodes divided into the control region are disposed in parallel and close to each other so that the longitudinal axis X of the surface acoustic wave resonator is substantially parallel to the width of the surface acoustic wave resonator. A surface acoustic wave characterized in that it constitutes a transverse dual-mode resonator filter that operates in two first-order modes of symmetry (ψ1, ψ1) and oblique symmetry (ψ1, -ψ1). filter.   Two surface acoustic wave resonators having interdigital electrodes divided into the control region are disposed in parallel and close to each other so that the longitudinal axis X of the surface acoustic wave resonator is substantially parallel to the width of the surface acoustic wave resonator. A lateral dual mode resonator filter that operates in two primary modes of symmetry (ψ1, ψ1) and oblique symmetry (ψ1, -ψ1) standing in the direction is configured to be operated by a WAVE electrode. A characteristic surface acoustic wave filter. The piezoelectric plate is an ST cut quartz plate obtained by rotating the quartz rotation Y plate counterclockwise around the electric axis (X axis) at a rotation angle θ = 31 degrees to 42 degrees. 2. The surface acoustic wave resonator according to claim 1, wherein the surface acoustic wave resonator is in a range of 140 pairs.

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