JP3498729B2 - Surface acoustic wave resonator - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a piezoelectric flat plate,
The present invention relates to a surface acoustic wave resonator which suppresses longitudinal higher-order resonance modes generated in a SAW resonator constructed by using STW (Surface Transversal Wave) type surface acoustic waves.

[0002]

2. Description of the Related Art Conventionally, a SAW resonator constructed by using a quartz ST cut substrate (an example of a piezoelectric plate) having piezoelectricity is
Since its frequency-temperature characteristic has a zero temperature coefficient and good accuracy, it is used as an oscillating element for crystal oscillators for data transmission in various high-speed network systems, but it is excellent in phase noise and low in jitter-free signals. This is because it has the advantage that it can be easily obtained with. In recent years, the signal transmission speed of the network system has been increased to the GHz band, and a crystal oscillator with a higher frequency has been demanded. Therefore, what has recently been attracting attention is the ST cut of 3150 m / s.
It is to develop a SAW resonator using STW type surface acoustic wave having a high velocity of about 5000 m / s for the above velocity. It has become known that the STW type surface acoustic wave is a pure transverse wave, but the vibrational energy of the wave is concentrated on the surface and takes the form of a surface acoustic wave. First, the STW type surface acoustic wave (STW for short) is the basic axis (OX, Y, Z) of the quartz crystal.
Is known to exist in a specific phase propagation direction of a substrate in a specific direction. The direction is shown in FIG. In the figure, 1002 is the electric axis X, which is the basic axis of the quartz crystal, 1003 is the mechanical axis Y, 1004 is the optical axis Z, and the substrate on which STW exists is the Y plate shown by 1001 that is θ degrees around the electric axis X. Substrate 1 rotated (θ = 35 to 40 degrees in which a zero temperature coefficient is obtained in particular)
000, the substrate (1000 and 1007
Is the same), and the in-plane rotation angle Ψ = ± 90 degrees from the electric axis X-axis (= y-axis of element) is the phase propagation direction of STW (Z ′ = x-axis of element).

A SAW resonator 1006 using STW is formed along the x-axis. For example, an IDT is formed by periodically arranging electrode fingers of a large number of parallel conductors made of metal aluminum, and a pair of reflectors are arranged on both sides of the IDT in parallel and periodically to form an IDT. A port type SAW resonator can be formed.

For example, in more detail, in the well-known ST cut (θ = 31 to 42 degrees and the phase propagation direction is the X-axis azimuth), the SAW resonator has a positive electrode as a key point in constructing the IDT. When the negative electrode and the negative electrode are paired as M pairs, the total reflection coefficient Γ of the entire electrode fingers of the IDT
Is defined as the following equation (1), and if 10>Γ> 0.8, the so-called energy confinement type SAW resonator in which the vibration energy is concentrated in the center of the resonator (reference: energy trapping elasticity Surface acoustic wave resonator, US85-
36, pp9-16 (1987.)) is known to be realized. [Equation 1] Γ = 4 MbH / λ (1) where M is the logarithm of the IDT, b is the reflection coefficient of the surface acoustic wave per electrode, H is the thickness of the conductor, and λ is the surface acoustic wave. Is the wavelength of.

For example, in the case of an IDT made of the aluminum conductor with a ST cut quartz plate, b = 0.25
5 and H / λ = 0.03 and M = 80 pairs, FIG.
1-port SAW resonator can be constructed. At this time Γ =
It will be about 2.448.

[0006]

However, using the above-mentioned prior art, the SAW utilizing STW, which is the subject of the present application, is used.
Appropriate constituent conditions for the resonator cannot be obtained (first problem). The reason for this is that the Rayleigh wave used in ST-cut (combining longitudinal and transverse waves) and STW have considerably different basic physical properties. The vibration displacements of the waves are localized on the substrate surface in all the waves, but it is clear from the results of the authors' research that the STW has only the pure transverse wave component Uy, and the reflection coefficients differ greatly. For this reason, the problem that the SAW resonator configuration condition is not clear becomes clear.

Furthermore, in the SAW resonator using STW, spurious resonance, which is regarded as a longitudinal high-order resonance mode, largely occurs, and the main frequency of the voltage controlled SAW oscillator (VCSO) is lower than the lower frequency band in the range of 1000 ppm. When manufacturing a crystal oscillator that uses a crystal oscillator, abnormal oscillation may occur, and it was necessary to suppress these.
(Second task). This spurious is shown in FIGS. 4 and 5. In FIG. 4, 401 is the amplitude characteristic of the 1-port type STW-SAW resonator, 403 is the main resonance mode, and
02 is regarded as a longitudinal higher-order resonance mode spurious. FIG. 5 shows the phase characteristic 501 of the resonator characteristic. The longitudinal higher-order resonance mode 402 represented by three peaks shows a phase change over several degrees (5
02). Regarding the suppression of the longitudinal and higher modes, the suppression methods for ST cut are already known (see Japanese Patent Application Laid-Open No. 10-13185 of the present application). However, regarding the suppression condition of the SAW resonator using STW, the appropriate suppression condition has not been clarified due to the difference in the fundamental physical properties of the wave.

Therefore, the present invention solves such a problem, and an object of the present invention is to utilize a crystal STW and use a crystal substrate having excellent frequency-temperature characteristics and a material Q value for SAW. A resonator is formed, and by using this, a clock signal source S having low jitter and low phase noise is generated.
The purpose is to provide an AW oscillator and a voltage control type SAW oscillator to the gigabit high-speed wired communication market.

[0009]

(1) A surface acoustic wave resonator according to the present invention comprises one interdigital electrode that excites a STW surface acoustic wave in a propagation direction x on a piezoelectric flat plate, and both sides in the propagation direction. In the surface acoustic wave resonator composed of a pair of reflectors arranged in the above, the piezoelectric flat plate is a quartz rotary Y plate, and an electric axis (X
Axis) is a crystal flat plate obtained by rotating in the counterclockwise direction by θ degrees, and the propagation direction is a Z direction (in the piezoelectric flat plate of the piezoelectric flat plate) rotated on the piezoelectric flat plate by 90 degrees in the plane from the electric axis X. x-axis direction), the interdigital electrode has a sufficient number of pairs of electrode fingers, one pair of positive and negative electrode fingers, and a stress function generated by resonance at an end portion of the reflector on the interdigital electrode side. τ (x) is a frequency-raising type energy confinement type node, and the crossing width W (x) of the electrode fingers forming the interdigital transducer is the longitudinal mode fundamental wave along the propagation direction x. Function W proportional to displacement function U (x)
Width weighting (W (x) = BU (x)) by (x)
Do the electrode finger at the end of the interdigital electrode and the reflector end
The space length G of the interdigital electrode is the conductor of the reflector.
Cycle length PR of strip and frequency drop characteristic RR of reflector
To use ST + PR / RR or ST + 2PR / R
R Is characterized in that. (2) In (1) above, the intersection width of the interdigital transducers.
Is a displacement function of the main resonance mode.
U (x) = COS (k ₀ x) and the displacement function
Shows that the vertical dispersion constant Ax is Ax = −4.4 to −4.4 / 5.
Is a solution of the second- order differential equation, Axω ₀ ² U ( x ), xx + (ω ² −ω ₀ ² ) U ( x ) = 0 . (3) In the above (1), the interdigital transducer is positive or negative.
The electrode fingers below 200 pairs 20 or more pairs as a pair of electrodes
The wavelength ratio H / λ of the film thickness to the surface acoustic wave is 0.01 to 0.
The range is 05. (4) In (1) above, the piezoelectric plate is a quartz crystal.
Rotate the rolling Y plate counterclockwise around the electric axis (X axis) by θ = 35 degrees
It is characterized by being a crystal flat plate rotated by 37 degrees.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be explained theoretically before explaining specific embodiments to help understanding of the present invention.

A flat plate is cut out from a piezoelectric material made of quartz (FIG. 10), its surface is mirror-polished, and then a large number of, for example, metal aluminum is formed orthogonal to the phase propagation direction of the STW type surface acoustic wave. An IDT in which electrode fingers of parallel conductors are periodically arranged is formed, and further, a pair of reflectors are arranged on both sides of the IDT in parallel and periodically to constitute a 1-port type SAW resonance. Form a child.

Further, in solving the first and second problems to be solved by the invention in the surface acoustic wave device of the present invention, a vibration displacement of a so-called longitudinal mode is used by using the theory described below. The resonance frequency was calculated and the resonator was designed. The contents will be described in order. The longitudinal mode is the longitudinal direction of the SAW resonator (STW
Is a natural vibration mode existing depending on the length (logarithm M) of the IDT in the phase propagation direction x of the surface acoustic wave.
The length in the width direction generally refers to the electrode finger crossing width W of the IDT. The electrode finger crossing width W is a dimension in the width direction in which the positive and negative electrode fingers overlap each other.

Next, the longitudinal direction (x
As a method for easily calculating the vibration displacement of the SAW resonator, the following differential equation governing the longitudinal mode is used. When this equation is described, the equation (2) is obtained. [Formula 2] Axω ₀ ² (X) U (X), _XX + {ω ² −ω ₀ ² (X)} U (X) = 0 (2) where ω is the angular frequency and ω ₀ (x) Is the element angular frequency of the corresponding region, Ax is the longitudinal dispersion constant in the longitudinal x direction, U (x) is the amplitude of the surface acoustic wave displacement in the x direction, and X is the x coordinate standardized by the wavelength λ of the surface acoustic wave. (X = x / λ). Also, ω ₀
(X) uses the half cycle length P of the electrode at the coordinate X,
It is a quantity defined by angular frequency ω ₀ (X) = 2πVs / (2P (X)) and will be called a frequency potential function. The above-mentioned formula (2) is a basic formula for calculating the cross width dimension W (x) of the orthogonal width weighting electrodes for suppressing the longitudinal high-order mode spurious. Using these, a SAW resonator using STW, which is a specific example to be described later, was designed, and a prototype was manufactured and measured. These will be described in order.

(Embodiment) An embodiment of the present invention will be described below in order from FIG. FIG. 1 shows a piezoelectric surface acoustic wave resonator (hereinafter abbreviated as “element” hereinafter) using the STW type surface acoustic wave (hereinafter abbreviated as STW) of the present invention, which is obtained by using the orientation substrate shown in FIG. It is one example which illustrated the electrode pattern formed on the body flat plate.

In the names of the parts in FIG. 1, 116 is the x-axis which is the propagation direction of the STW used in this element, and 107 is the y-axis orthogonal to the x-axis. 100 surrounded by broken lines
Reference numerals 112 and 112 are the reflector 1 and the reflector 2 of this element. 101
And 102, 111 and the like are a group of conductor strips made of aluminum metal and serve to reflect STW by the perturbation effect. Reference numeral 103 surrounded by a broken line is a comb-shaped electrode or IDT composed of positive and negative electrode finger pairs (104, 105) and the like (hereinafter abbreviated as IDT). The ID
T (103) electrode finger group 104, 115 or 10
Reference numerals 113 and 109 for vertically connecting 5, 114, 110 and the like are input / output terminals called feeding conductors (bus bars).

Symbols LR and SR in FIG. 1 are the width LR of the conductor strips of the reflector 1 and the reflector 2 and the clearance length SR between the conductor strips, and PR = LR + SR is the arrangement period length of the conductor strips. . LT and ST are the line width LT of the electrode finger in the IDT and the gap length (space) ST between them. The function specified by 106 is
Stress function τ generated in this device under vibration
It shows a state of (x), and U (x) of 108 is an amplitude envelope function of the stress wave function τ (x). The symbol G is the distance between the endmost conductor 102 (and 111) of the reflector 1 (and 2) and the electrode finger 104 (and 110) of the IDT. W (x) is a function indicating the cross width at which the positive electrode finger 115 and the negative electrode finger 114 face each other.
The symbols SR, LR, PR, LT, S in this element
The proper setting of the values of T, PT, G and W (x) will be described later.

The piezoelectric flat plate is obtained from quartz according to FIG. 10, which has already been described. In particular, the rotation angle θ = 35 to 37 so that the temperature coefficient of the frequency of this element has a zero temperature coefficient near room temperature. The propagation direction x of in-plane rotation Ψ = 90 degrees in the degree-rotated Y plate is set. The IDT, the reflector, and the like that form the present element formed on the above 100 are formed by forming a thin film of a metal film of aluminum by means such as vapor deposition and sputtering, and then forming a pattern by the photolithography technique. A large number of electrode fingers of the IDT and the reflector are arranged in parallel and periodically, orthogonal to the phase traveling direction (longitudinal direction x) of the STW to be used.

Next, a detailed description will be given of the setting of the symbols of the present element which answers the above-mentioned first problem. First, Fig. 1
Reflector 1 (100) and reflector 2 (112) conductor strip dimensions PR, LR, SR and IDT (103) electrode finger dimension P
The setting of T, LT and ST will be described with reference to FIG. Figure 6
Is the film thickness H of the electrode finger and the wavelength λ of STW (λ = 2P
The center frequency fR0 (point P) of the reflection characteristic Γ (Ω) (603) of the IDT with respect to the film thickness ratio H / λ which is the R) ratio.
And the frequency drop characteristic which is a state of change of the maximum value frequency fT0 (Q point) of the radiation conductance YG (Ω) (604). The horizontal axis is H / λ, and the vertical axis is the frequency f0 = VF / (2PT) when the film thickness H of the electrode finger is H = 0, and the frequency of fR0 and fT0 is normalized by Ω = f /.
It is represented by f0. In this case, H / of fR0 and fT0
As for the λ dependency, fR0 has an RR characteristic (solid line 602) and fT
0 is the RT characteristic (broken line 601). When STW is used in the piezoelectric plate that constitutes this element,
The above-mentioned arrangement relationship between RR and RT is in a system between RR> RT, and for example, RT-RR = 10 at H / λ = 0.03.
It has been experimentally obtained to be 000 ppm. Usually, in order to set fR0 = fT0, 2PR = (VF
Since / f00) RR and 2PT = (VF / f00) RT are set, PR> PT. When setting in such a relationship, it is usually called a frequency rising type. PR and P
Once T is determined, for example, if the ratio of the line width of the electrode finger to the conductor strip and the space (space) is determined to be LT / ST = LR / SR = 1, each dimension is determined. Here, f00 is the nominal frequency of this element, and VF is the speed of STW on the free surface.

Next, regarding the symbol G in FIG. 1, G
Is a dimension commonly called a gap length, and particularly in the design method called an energy confinement type which is a type of this element, the above G = ST or ST + PR / RR,
It is necessary to set ST + 2 (PR / RR).
In particular, in the case of G = ST + PR / RR and ST + 2 (PR / RR), it became clear as a result of the longitudinal higher-order mode suppression experiment described later that it is necessary to make the size of PR divided by RR. To infer the reason for this, in the case of the above-mentioned energy trapping type, the stress wave function τ (x) (the above-mentioned stress wave function τ (x) (at the IDT side end of the electrode fingers 102 and 111 in FIG. 1) of the reflector is formed. Since it is an indispensable boundary condition that 106) in FIG. 1 becomes a node, the stress wave function τ (x) = U (x) COS (ω which comes from the fact that the gap G is a completely free surface.
The adjustment of the phase angle Φ (x) of t + Φ (x) is performed by dividing by RR. By setting the G, PR, and PT dimensions as described above and using an appropriate range of H / λ,
An energy trap SAW resonator that provides the stress wave function τ (x) of 106 in FIG. 1 can also be obtained using STW.
Only in this energy trap SAW resonator,
It is possible that the amplitude function U (x) of the vibration obtained by the differential equation of the equation (2) already described matches U (x) of 108 in FIG. 1 and the resonance frequency of the longitudinal higher mode also matches the actual measurement. It has been confirmed.

Next, an appropriate range of H / λ can be found by the following procedure. First, S using Rayleigh wave
An SAW resonator using STW is prototyped under the electrode pattern dimension conditions in the case of T-cut. The longitudinal dispersion constant Ax of the equation (2) is adjusted so that the interval ratios of the higher-order longitudinal mode resonance frequencies generated at this time match. The Ax thus obtained is about 1/3 of that in the ST cut, and Ax =-
It was 4.4 / 3. This fact means that the reflection coefficient per electrode is about 3 times the ST cut (b = 0.255 × 3 in the formula (1)). Since the SAW resonator total reflection coefficient Γ represented by the equation (1) is equal to obtain the same resonance amplitude, it is a construction principle of the energy confinement type SAW resonator that the design condition of this element is derived. You can Therefore, the conditions that are usually used for ST cutting are that the film thickness ratio H / λ is 0.01 to 0.03 and the IDT logarithmic range M is 80 to 300 pairs. , H / λ in the range of 0.01 to 0.05 inclusive of the same range, M = 80 /
It should be set in the range of 3 to 300/3 (M =
27 to 100). M =
A range of 20 to 200 is sufficient. Where H /
The reason why λ is in the same range of 0.01 to 0.05 is as follows.
This is because it is convenient to obtain an aluminum film thickness that can withstand the tensile strength of wire bonding, which is the mounting condition for this element.
Further, in the range of H / λ = 0.01 to 0.03, the above-mentioned rotation angle θ of the piezoelectric flat plate is set to 35 so that the apex temperature of the frequency-temperature characteristic of the present element falls within the range of room temperature 20 ± 10 ° C. To 37 degrees (see FIG. 11).

FIG. 11 is a characteristic diagram (actual measurement) that gives the ratio of the temperature θmax that gives the highest peak frequency to the electrode film thickness in the frequency temperature characteristic that is convex on this element. The cutting azimuth angle of the piezoelectric flat plate in FIG. 10 is given by a straight line 1101 when the azimuth angle θ = 37 degrees, a straight line 1102 when the angle θ = 36 degrees, and a straight line 1103 when the angle θ = 35 degrees. In order to set the apex temperature θmax within the range of room temperature 20 ± 10 ° C., H / λ =
It can be seen that the value may be in the range of 0.01 to 0.05.

A method of suppressing the higher-order longitudinal mode which is the second problem of the last element will be described. For the theoretical basis of this method, refer to the author's Japanese Unexamined Patent Publication No. 10-13185 for a detailed description. In the case of the STW of this element, it is necessary to find an appropriate cross width weighting function W (x) capable of suppressing the longitudinal high-order mode spurious. Therefore, a minimum description will be given to explain the process of obtaining W (x). First, the function W (x) is set in proportion to the above-mentioned U (x) of the main resonance mode (403 in FIG. 4) of this device. That is, W (x) = BU (x) (B is a constant). Therefore, it is necessary to first determine U (x). The differential equation of the equation (2) represents the energy conservation field in a state where the dispersion relation between the wave number K and the angular frequency ω is approximated by the following equation (3). [Equation 3] (ω / ω ₀ (x)) ² = 1 + AxK ² (3) As a condition, ω ₀ (x) is the reflector 1 and in the reflector 2 region, ω ₀ (x) = ω _R = 2πVF / (2PR), in the IDT area, ω ₀ (x) = ωm = 2πVF / (2PT)
Given the frequency potential function of
(X) will be calculated. This solution U (x) can be represented by the following set of equations (4), (5), (6). here,
X and X0 are standardized by the wavelength λ of STW.
= X / λ, X0 = M / 2. At this time, K _R, Km
Is the wavenumber determined by the formula (3) of the reflector and IDT region,
.omega.m, omega _R, the omega as the angular frequency, [Expression 4] region of the reflector _{2 U (X) = A 1} EXP {K R (X + X0)}, IDT region _{U (X) = A 2 COS} ( KMX) (case of symmetric mode), the reflector 1 of the area _{U (X) = a 3 EXP} {-K R (X-X0)} (4) _where, a _1, a 2, _{a 3} are arbitrary constants, [ number ^{5] Km 2 = {(ω} / ωm) 2 -1} / Ax, (Ax <0, ω / ωm <0), K R 2 = {1- (ωm / ω R) 2 (ω / ωm) ^{2} / Ax (5) (} πVF / PT = ωm>ω> ω R = πVF / PR) further, equation 6] tan (KmX0) = K relational expression _R / Km (6) holds. These are generally the frequency and amplitude Uj (x) of the longitudinal higher-order mode group having a plurality of natural resonances.
(J = 0 to n: n is an integer). Here, the W (x = λX) is the function U (X) = A of the IDT region.
_{In 2} COS (KmX), if K ₀ is the wave number of the main resonance mode (fundamental wave j = 0), then Km = K ₀ and [Equation 7] W (x = λX) = BU ₀ (X) = It is given by B · A2COS (K ₀ X) (7). The total electric charge q of the IDT that can be detected by the width-weighted electrode fingers given by the equation (7) is that U ₀ (x) and Uj (x) are orthogonal functions with respect to the longitudinal higher mode j> 1. Since it is known, [Equation 8] q (j) = ∫W (x) Uj (x) dx = BA ₂ ∫U ₀ (x) Uj (x) dx = 0 (j> 1) (8) q = It becomes 0, and the impedance of the vertical and higher modes becomes extremely high, making it impossible to excite. Therefore, it is possible to suppress higher-order modes. Next, by setting X = λN in Expression (7), the intersection width of the electrode fingers of the coordinate points corresponding to each N-th pair of IDTs can be set. The weighting function WT (M) (curve 201) normalized by the maximum intersection width Wmax in FIG. 2 is an example calculated in this way. The conditions in this case are nominal frequency f0 = 1276 MHz, M = 144, the number of reflector conductor strips NR = 523, and the maximum value Wm of the electrode finger crossing width.
ax = 40 wavelengths, LR / SR = LT / ST = 1, G = S
T or ST + PR / RR, ST + 2 (PR / R
R), the apex temperature θmax = 20 ° C., which is the temperature that gives the apex of the frequency temperature characteristic that is convex upward. At this time, the resonator equivalent constants of the main resonance mode of the STW-SAW resonator which is the present element are R ₁ = 21Ω, C ₁ = 0.91fF, L ₁ = 1.
Since 6.9 nH, C ₀ = 1.09 pF, Q = 6250, and capacity ratio γ = 1200, it can be said that the characteristics are sufficiently good. Here, it was found that the large value of the resonance sharpness Q is due to the slip displacement in which the STW does not work with respect to the atmosphere or N ₂ which is the surrounding environment of this element.

Further, under the above conditions, the longitudinal dispersion constant A
The experimental results of the suppression state of the vertical and higher modes with various x values are shown in FIGS. 7, 8 and 9. These characteristic diagrams are similar to the phase characteristic of FIG. 5, and FIG. 7 shows Ax = −
This is a case of 4.4 / 5, FIG. 8 shows a case of Ax = −4.4 / 2 to −4.4 / 4, and FIG. 9 shows Ax =
This is the case of -4.4 / 1 (same as ST cut) (same as ST cut). In the case of FIG. 8,
It can be seen that the vertical and higher modes are suppressed.

Further, these are summarized in FIG. 3 for easy understanding. In FIG. 3, the horizontal axis is Ax, and the state of occurrence of the vertical high-order mode is viewed. The inside of the broken line frame is the range where occurrence cannot be confirmed, and the inside of the solid line frame is the range where the phase change is within 0.1 degree. From this FIG. 3, the longitudinal dispersion constant Ax = −4.4 / 5−−
Suppression is possible in the range of 4.4 = −0.88 to −4.4, and is good in the range of Ax = −1.2 to −3.5.

As described above, the structure and characteristics of the surface acoustic wave resonator using the STW for the base plate made of only quartz crystal generated by STW of the present invention has been described. SiO ₂ and ZnO are formed on the surface of the base plate. It is added that the present invention is effective even if a thin film such as is formed to such an extent that the characteristics of the present device are not impaired.

[0026]

As described above, according to the present invention, ST
Using the STW type surface acoustic wave, which has a speed of about 5000 m / s, which is faster than the Rayleigh type surface wave with a speed of about 3150 m / s generated in the cut, set the appropriate electrode dimensions to create an energy trap SAW resonator. With this configuration, the resonance sharpness Q can obtain several thousand Q values superior to the conventional ST cut, and if a crystal oscillator is manufactured using this, a high-quality output signal with small phase noise can be easily obtained. It is possible to provide a clock signal source for the gigabit high-speed wired communication market, which is expected to expand significantly in the future, and great effects can be expected.

[Brief description of drawings]

FIG. 1 is a plan view showing a conductor pattern included in an example of a surface acoustic wave resonator of the present invention.

FIG. 2 is a diagram showing an example of a width weighting function of the IDT of the surface acoustic wave resonator of the present invention.

FIG. 3 is a diagram showing a generation state of a vertical high order mode with respect to a vertical dispersion constant Ax that determines a width weighting function of the IDT of the present invention.

FIG. 4 is a diagram of impedance characteristics (amplitude) of a conventional SAW resonator.

FIG. 5 is an impedance characteristic (phase) diagram of a conventional SAW resonator.

FIG. 6 is a frequency drop characteristic diagram showing the IDT of the present invention.

FIG. 7 is an amplitude characteristic diagram under conditions other than those shown in FIG. 1 of the present invention.

FIG. 8 is an amplitude characteristic diagram shown in FIG. 1 of the present invention.

FIG. 9 is an amplitude characteristic diagram under other conditions than that shown in FIG. 1 of the present invention.

FIG. 10 is a sectional view of the piezoelectric flat plate used in FIG. 1 of the present invention.

FIG. 11 shows θ max vs. H / λ shown in FIG. 1 of the present invention.
Characteristic diagram.

[Explanation of symbols]

100 reflector 1 103 IDT 112 reflector 2 106 stress wave function 108 Amplitude function U (x) 102,111 Conductor strip 114,115 electrode fingers

Claims (4)

(57) [Claims] 1. A surface acoustic wave resonator comprising one interdigital electrode for exciting a STW surface acoustic wave in a propagation direction x on a piezoelectric flat plate and a pair of reflectors arranged on both sides of the electrode in the propagation direction. The piezoelectric flat plate is a crystal flat plate obtained by rotating a quartz rotary Y plate around the electric axis (X axis) in the counterclockwise direction by θ degrees, and the propagation direction is the electric axis X on the piezoelectric flat plate. In the Z direction (x-axis direction of the piezoelectric plate) rotated in the plane from 90 degrees, and the interdigital electrode has a sufficient number of electrode fingers, one pair of positive and negative electrode fingers, Is an energy confinement type of frequency rising type in which the stress function τ (x) generated by resonance at the end of the interdigital transducer side of the container is a node, and the cross width W of the electrode fingers forming the interdigital transducer is
(X) performs width weighting (W (x) = BU (x)) by a function W (x) proportional to the displacement function U (x) of the longitudinal mode fundamental wave along the propagation direction x, and the blind Between the electrode finger at the extreme end of the electrode strip and the end of the reflector
The distance G is the period length PR of the conductor strip of the reflector and the reflector.
Using the frequency drop characteristic RR of ST + PR / RR
Or ST + 2PR / RR elastic table
Surface wave resonator. 2. A function for setting a crossing width of the interdigital electrodes.
The number W (x) is the displacement function of the main resonance mode U (x) =
COS (k ₀ x), and the displacement function is a vertical dispersion constant.
2 order differential in the number Ax is a -4.4 / 5 from Ax = -4.4
Min ^{_{equations, Axω 0 2 U (x)}} , xx + (ω 2 -ω 0 2) U (x) = 0 surface acoustic wave according to claim 1, characterized in that the solution of
Resonator. 3. The interdigital transducer has one positive electrode electrode and one negative electrode finger.
20 pairs or more and 200 pairs or less as a pair, and elasticity of the electrode film thickness
In the wavelength range ratio H / lambda of 0.0 5 0.01 of the surface wave
The surface acoustic wave resonance according to claim 1, wherein
Child. 4. The crystal flat Y plate is an electric plate that is a quartz rotary Y plate.
Rotate the axis (X axis) counterclockwise from θ = 35 degrees to 37 degrees
Bullet according to claim 1, wherein the the a quartz flat plate
Surface acoustic wave resonator.