JP2008228144A - Coupling type saw resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly accurate and small-sized coupling type SAW resonator of a wide using temperature range and excellent frequency temperature characteristics. <P>SOLUTION: For the coupling type SAW resonator 10, on the main surface of the crystal substrate 100 of SH cut indicated by Euler angle display (ϕ, θ, ψ), a 2-port type first resonator 120 for which a main IDT electrode 121, a sub IDT electrode 122 and reflectors 123 and 124 are disposed in a specified direction and a 2-port type second resonator 130 for which a main IDT electrode 131, a sub IDT electrode 132 and reflectors 133 and 134 are disposed are provided closely and also arranged side by side in parallel with the propagation direction of SH waves. The first resonator 120 is operated in an LS0 mode in a longitudinal direction, the second resonator 130 is operated in an LA0 mode in the longitudinal direction, the line widths L1 and L2 of the IDT electrodes are made different from each other, fundamental frequencies of the LS0 mode and the LA0 mode are roughly matched, and then the LS0 mode and the LA0 mode are operated in an elastically coupled state. Thus, a temperature characteristic curve is flattened. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a coupled SAW resonator, and more particularly to a coupled SAW resonator that operates in an elastically coupled state with two mode SAW resonators arranged close to each other.

  Conventionally, SAW resonators are configured by forming an electrode pattern on the surface of a quartz substrate using a metal such as aluminum, copper, titanium, or tungsten as an electrode by a film forming means such as vapor deposition. Also, the piezoelectric substrate orientation of the quartz substrate is a range of 0 ° ± 1 ° in the counterclockwise direction around the optical axis Z in the Euler angle display (φ, θ, ψ) on the fundamental axis of the quartz crystal. Next, θ is in the range of 29.2 ° to 40.7 ° counterclockwise around the X axis, which is the electric axis, and then in the piezoelectric plate around the newly generated Z ′ axis, There is an SH cut that rotates in the counterclockwise direction starting from the electric axis, and the direction in which ψ is in the range of 90 ° ± 2 ° is the phase propagation azimuth of the surface acoustic wave.

  In the above-described SH cut substrate, the surface acoustic wave used as the SAW resonator is an SH wave. The SH wave is the same as the bulk vibration mode conventionally used in AT-cut quartz resonators, and the surface wave velocity is reduced by the mass of the electrode, and the vibration energy is concentrated near the surface of the quartz substrate, and the depth of the substrate is reduced. It is confined in the vertical direction and used (for example, see Patent Document 1).

  In addition, two SAW resonators are configured on a quartz substrate having a frequency zero temperature coefficient, and the two SAW resonators are coupled and driven using an external lumped element to realize a flat frequency temperature characteristic. A SAW resonator is known (for example, see Patent Document 2).

  Further, it is also known that two SAW resonators are formed on a quartz substrate, and the propagation directions of the surface waves are arranged differently to couple the two SAW resonators to improve the frequency temperature characteristics. (See, for example, Non-Patent Document 1).

International Publication Number WO2005 / 099089 A1 U.S. Pat. No. 4,193,045 G. Martin, B. Wall: “Temperature Stable One-port SAW Resonators,” IEEE Ultrasonics 2006

Such an SH-cut quartz substrate used in Patent Document 1 has a frequency accuracy twice as high as the frequency temperature characteristic of a SAW resonator manufactured using a conventional ST-cut quartz substrate. However, it is insufficient for the accuracy requirement in recent electronic devices. In particular, when the operating temperature range required for outdoor use is in the range of −35 ° C. to + 85 ° C., it is difficult to achieve an accuracy of ± 25 ppm. Specifically, the secondary temperature coefficient of the frequency temperature characteristic of the SAW resonator according to Patent Document 1 is −1.6 × 10 ⁻⁸ / ° C. ² and its apex temperature is arranged at the center of the operating temperature range. Then, the frequency fluctuation amount due to temperature change is about 58 ppm, and there is a problem that an accuracy of ± 25 ppm cannot be realized when other frequency fluctuation amounts are taken into account.

  Further, in Patent Document 2, an external concentrating element is used as a method for coupling two SAW resonators, which increases the number of mounted parts and makes it difficult to reduce the size.

  Further, according to Non-Patent Document 1, since the two SAW resonators are arranged so that the propagation directions of the respective surface waves are different, there is a problem that the plane area of the resonator is increased. Furthermore, since the vibration modes (resonance frequencies) of the two SAW resonators are different, it is predicted that variations in the resonance frequency and frequency temperature characteristics are likely to occur.

  An object of the present invention is to provide a highly accurate and small coupled SAW resonator having a wide operating temperature range and excellent frequency temperature characteristics.

  The coupled SAW resonator of the present invention has two IDT electrodes in a specific orientation on the main surface of an SH-cut quartz substrate represented by Euler angles (φ, θ, ψ) on the fundamental axis of the quartz crystal. And a plurality of two-port SAW resonators provided with reflectors provided on both sides of the specific orientation of the IDT electrode, and arranged in parallel in the specific orientation direction, The SAW resonator is operated in a longitudinally symmetric fundamental wave mode, and the other SAW resonator is operated in a longitudinally symmetric fundamental wave mode, and the line widths of the IDT electrodes are varied to change the symmetric fundamental wave. The symmetric fundamental wave mode and the obliquely symmetric fundamental wave mode are operated in a coupled state after substantially matching the fundamental frequency of the mode and the obliquely symmetric fundamental wave mode.

  According to the present invention, since the coupled oscillator is configured using the SH cut quartz substrate having a small secondary temperature coefficient, the coupled SAW resonance that realizes flat frequency temperature characteristics over a wide operating temperature range. Can provide a child.

  Further, since a symmetric fundamental wave mode (hereinafter, sometimes referred to as LS0 mode or LS0) and an obliquely symmetric fundamental wave mode (hereinafter, sometimes referred to as LA0 mode or LA0) are used, In addition, low impedance can be realized, and the configuration of an oscillation circuit of several hundred MHz band can be easily made.

  Further, the fundamental frequencies of the LS0 mode and the LA0 mode are substantially matched by changing and adjusting the line width of the IDT electrode. Since the line width can be formed with high accuracy by a photolithography technique or the like, it is possible to set the frequency with high accuracy and small frequency variation, and the frequency temperature characteristic (temperature characteristic curve) can be easily created.

  Furthermore, since a plurality of 2-port SAW resonators are provided close to each other and are arranged in parallel in a specific azimuth direction, the propagation direction of the surface wave is made different as in Non-Patent Document 1 described above. The plane size can be reduced as compared with the above. The specific azimuth direction is the SH wave propagation direction.

  The coupled SAW resonator of the present invention is characterized in that the line temperature of the IDT electrode is adjusted to provide a vertex temperature difference between the symmetric fundamental wave mode and the oblique symmetric fundamental wave mode.

  In this way, the flatness of the frequency temperature characteristic in the coupled state can be adjusted by the magnitude of the apex temperature difference, and there is an effect that a desired temperature characteristic curve can be easily created.

  The gist of the present invention is that the coupling between the symmetric fundamental wave mode and the obliquely symmetric fundamental wave mode is elastic coupling.

  Therefore, since it is elastically coupled to a configuration using an external lumped element as a method of coupling two SAW resonators as in Patent Document 2, an external lumped element is not required and the number of mounted components is small. Miniaturization and cost reduction are possible.

  Further, it is desirable that the frequency difference between the symmetric fundamental wave mode and the obliquely symmetric fundamental wave mode of each of the plurality of SAW resonators is substantially the same.

  In this way, the temperature characteristic curves of each of the plurality of SAW resonators are translated in the temperature axis direction, which is the horizontal axis, and the temperature characteristic curve in the coupled state can be easily flattened.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an azimuth angle diagram of a quartz crystal substrate according to an embodiment of the present invention, and FIGS. 2 to 8 are diagrams showing the configuration, driving, and characteristics of a coupled SAW resonator.
(Embodiment)

First, the quartz substrate 100 will be described with reference to FIG.
FIG. 1 is an explanatory view showing the azimuth angle of the quartz crystal substrate according to the embodiment of the present invention. As shown in FIG. 1, the quartz substrate 100 is an in-plane rotating SH-cut quartz substrate and operates with an SH-type surface wave (a surface-concentrated slip wave having a component parallel to the main surface of the substrate).

  The quartz substrate 100 has a Z-plate whose principal surface is a plane formed by two axes of an X axis that is an electric axis and a Y axis that is a mechanical axis in the fundamental axis of a quartz crystal. In particular, θ = 29.2 ° to 40.7 ° is preferable because a zero temperature coefficient is obtained). In this quartz substrate 100, the direction in which the in-plane rotation angle ψ is 90 ± 2 ° around the Z ′ axis, which is a perpendicular to the main surface, is defined as the phase propagation azimuth axis of the SH type surface acoustic wave. It is a thing. In the Euler angle display (φ, θ, ψ) often used in SAW resonators, φ is in the range of 0 ± 1 °, θ is in the range of 29.2 ° to 40.7 °, and ψ is 90 The range is ± 2 °. Such a quartz substrate 100 is referred to as an SH cut quartz substrate.

Next, the coupled SAW resonator according to this embodiment will be described with reference to the drawings.
FIG. 2 is a plan view showing an example of the coupled SAW resonator according to the present embodiment. In FIG. 2, the coupled SAW resonator 10 is a first resonator 120 arranged in parallel in the SH wave propagation direction on the main surface of the above-described SH-cut quartz substrate 100 (hereinafter simply referred to as the quartz substrate 100). The second resonator 130 and a control electrode (sometimes referred to as a gate electrode) 140 are configured.

The first resonator 120 includes a main IDT electrode 121 and a sub IDT electrode 122 made of a metal such as Al, a gate electrode 140 between the main IDT electrode 121 and the sub IDT electrode 122, and the main IDT electrode 121 and the sub IDT electrode 122. The reflectors 123 and 124 are provided on both sides in the respective SH wave propagation directions.
The main IDT electrode 121 and the sub IDT electrode 122 are composed of a plurality of interdigital electrodes, and the reflectors 123 and 124 are composed of grid electrodes.

The second resonator 130 includes a main IDT electrode 131 and a sub IDT electrode 132 made of metal such as Al, a gate electrode 140 between the main IDT electrode 131 and the sub IDT electrode 132, a main IDT electrode 131 and a sub IDT electrode. The reflectors 133 and 134 are provided on both sides of each 132.
Further, the main IDT electrode 131 and the sub IDT electrode 132 are composed of a plurality of interdigital electrodes, and the reflectors 133 and 134 are composed of a plurality of lattice electrodes (lattice electrodes). ing.

  The gate electrode 140 is provided in common in the first resonator 120 and the second resonator 130. As shown in FIG. 2, the first resonator 120 and the second resonator 130 are symmetrically arranged with respect to the central axis R parallel to the Y ′ axis, and the first resonator 120 and the second resonator 130 are respectively , Symmetrical with respect to the central axis P parallel to the X ′ axis. Note that the number of crossed finger electrodes and grid electrodes constituting each IDT electrode and each reflector described above is reduced for convenience of illustration. Similarly, the number of electrode configurations of the gate electrode 140 is not limited to the number illustrated.

Here, main dimensions according to the present invention of each electrode will be described. The electrode pitch of the main IDT electrodes 121 and 131 and the sub IDT electrodes 122 and 132 is PT, the electrode length is W, the electrode pitch of the gate electrode 140 is PG, and the grid electrodes of the reflectors 123, 124, 133, and 134, respectively. The electrode pitch of is assumed to be PR.
Further, the line width L1 of each cross finger electrode of the first resonator 120 and the line width L2 of each cross finger electrode of the second resonator 130 are set such that the respective line widths satisfy L1> L2.
In addition, the distance in the X′-axis direction (distance between the interdigitated electrodes) between the first resonator 120 and the second resonator 130 is represented by a gap G.

  Next, connection wiring of the first resonator 120 and the second resonator 130 will be described. A wiring as shown in FIG. 2 is used, and an excitation signal is applied to the GND terminal and the IN / OUT terminal, whereby a simultaneous operation state of the first resonator 120 and the second resonator 130 is created. The gate electrode 140 is an electrically floating electrode.

  The coupled SAW resonator 10 configured as described above is a two-port SAW resonator, and has a vertical double mode (LS0 mode and LA0 mode exist) and a horizontal double mode (TS0 mode and TA0 mode exist). To be connected). Accordingly, the fundamental resonance frequencies in the vertical double mode and the horizontal double mode are the same. Further, the line width is changed and the line width ratio L2 / L1 of the crossing finger electrodes is set so that the resonance frequencies of the LS0 mode and the LA0 mode are matched.

  In order to create a good coupling state between the resonators of the first resonator 120 and the second resonator 130, the gap G is set to 1 to 5 wavelengths of the surface wave, and the electrode length W of the cross finger electrode is Set in the range of 10 to 20 wavelengths.

Next, the vibration mode used in the present invention will be described with reference to the drawings.
FIG. 3 is an explanatory diagram schematically showing an example of a vibration mode used in the present invention. The lower graph display shows a state viewed from the direction of the arrow U (X), the horizontal axis indicates the vibration region of the coupled SAW resonator 10, and the vertical axis indicates the displacement amplitude. Further, the graph display in the right direction represents a state viewed from the direction of the arrow V (Y), and the horizontal axis represents the displacement amplitude and the vertical axis represents the vibration region.

  LS0 (vertical symmetrical fundamental mode) in the figure illustrates the envelope displacement state of the resonance mode amplitude in the first resonator 120. On the other hand, LA0 (longitudinal obliquely symmetric fundamental wave mode) illustrates the envelope displacement state of the resonance mode amplitude in the second resonator 130. Note that LS0 and LA0 exist in the first resonator 120 and the second resonator 130, respectively. However, when the first resonator 120 is LS0, the second resonator 130 is LA0, and when the first resonator 120 is LA0. The second resonator 130 repeats alternately corresponding to the polarity of the excitation signal so as to be LS0. The region B is an SH wave basic excitation region, and the region A is a reflected wave region.

  It can also be seen that any of the illustrated displacement amplitude states can be excited by an electrical drive voltage. Therefore, even when both the LS0 and LA0 modes are coupled and operated, the impedance of the entire resonator can be realized low. The ratio between the electrode pitch PT of the IDT electrode and the electrode pitch PR of the reflector was set to PT / PR = 0.993. The frequency adjustment in both modes can be performed by setting the electrode pitch PG of the gate electrode 140 and the number of conductor pairs.

Next, the coupling between the first resonator 120 and the second resonator 130 will be described with reference to the drawings.
FIG. 4 is an explanatory diagram illustrating the relationship between the coupling mode and the frequency temperature characteristic in the present embodiment. In FIG. 4, in the resonance state of the first resonator 120 and the second resonator 130 by the input of the excitation signal, two resonances LS0 and LA0 exist simultaneously. Each resonance has a different frequency temperature characteristic. Specifically, the apex temperatures appear differently.
In this state, if weak coupling exists between the first resonator 120 and the second resonator 130, the frequency-temperature characteristic of the coupled state as shown in FIG. 4 is obtained, and the temperature characteristic curve becomes nearly flat, and the frequency-temperature characteristic. Is significantly improved.

The coupling between the first resonator 120 and the second resonator 130 is elastic coupling due to strain energy generated in the gap G (see FIG. 2) region between the two resonators.
FIG. 5 is an equivalent circuit diagram schematically showing the elastic coupling. In FIG. 5, the equivalent circuit is configured by connecting a first resonator 120, a second resonator 130, and a capacitor 150 in parallel, and the capacitor 150 indicates a coupling portion.

  The apex temperature of the first resonator 120 shown in FIG. 4 appears on the low temperature side because the line width L1 and the line width L2 of the interdigitated electrode are set to L1> L2, and the second resonator 130 The apex temperature of appears on the high temperature side. At this time, the frequency-temperature characteristic in the coupled state is affected by the apex temperature difference between the first resonator 120 and the second resonator 130. That is, when the apex temperature difference is large, the drop of the joint portion becomes large and the flatness is deteriorated. When the apex temperature difference is small, the operating temperature range is narrowed.

Next, a method for setting the apex temperature difference will be described with reference to the drawings.
FIG. 6 is an explanatory diagram showing the frequency arrangement of the first resonator and the second resonator in the present embodiment. In the illustration in FIG. 6, the mass of the cross finger electrode of the first resonator 120 is set to be relatively larger than the mass of the cross finger electrode of the second resonator 130. That is, the relationship between the line width L1 of the first resonator 120 and the line width L2 of the second resonator 130 is set so that L1> L2. Therefore, the first resonator 120 appears with a lower resonance frequency, the fundamental mode is LS0, the resonance frequency is f10, and the resonance frequency of the LA0 mode is f11.

  On the other hand, the resonance frequency of the second resonator 130 appears higher, and the resonance frequency of the LA0 mode is f21 and the resonance frequency of the LS0 mode is f20.

  It is possible to adjust the electrode film thickness to adjust the mass of the interdigitated electrode. However, when the electrode pattern is formed by a photolithography technique or the like, the line width adjustment tends to suppress variation.

When the first resonator 120 and the second resonator 130 are symmetrical with respect to the central axis R parallel to the Y ′ axis in FIG. 2 (the shape including the arrangement and the line width L1 is symmetrical), f11 = f21 and f10 = f20, and no apex temperature difference appears.
Therefore, the ratio L2 / L1 of the line width L2 and the line width L1 is adjusted so that the LA0 mode resonance frequency f21 of the second resonator matches the resonance frequency f10 of the LS0 mode of the first resonator. In FIG. 6, it is expressed as f10 = f21 = F00 (reference frequency). The frequency difference D between LS0 and LA0 of the first resonator 120 is set so that the frequency difference D between LS0 and LA0 of the second resonator 130 is substantially equal.

Next, the relationship among the line width, vertex temperature, and frequency change of the IDT electrode will be described.
FIG. 7 is an explanatory diagram showing the relationship between the line width, vertex temperature, and frequency change amount of the IDT electrode of the coupled SAW resonator according to this embodiment. In FIG. 7, the coupled SAW resonator 10 has a calculation result when an SH-cut quartz with a cut angle θ = 33 °, a surface wave velocity Vs = 3150 m / sec, a resonance frequency f = 152 MHz, and L00 = 5.1 μm. Represents. The horizontal axis represents the line width ratio L1 / L00 with normalized line width, the left vertical axis represents the resonance frequency change amount F (ppm), and the right vertical axis represents the vertex temperature change amount Θ. A change and a broken line represent apex temperature.

  Note that L00 is a line width that serves as a standard for standardization, and is given by L00 (μm) = Vs (surface wave velocity (m / sec) / (use frequency f (MHz) / 4)).

  In FIG. 7, when the line width ratio L1 / L00 = 1 is F00 (reference frequency), the resonance frequency is F00 + 2000 (ppm) when the line width ratio L1 / L00 = 0.85, and the line width ratio L1 / L00 = It becomes F00-2000 (ppm) at 1.15. That is, it shows a change of ± 2000 ppm in the range of the line width ratio | L1 / L00 | ≦ 0.15.

  Further, the vertex temperature is the line temperature ratio L1 / L00 = 0.85 when the line width ratio L1 / L00 = 1 and the vertex temperature Θ is the center vertex temperature (Θ = 0), and the vertex temperature Θ = + 25. The apex temperature Θ = −25 ° C. at a line temperature ratio L1 / L00 = 1.15. That is, it is shown that an apex temperature difference of 50 ° C. can be made in the range of the line width ratio L | 1 / L00 | ≦ 0.15.

Next, the frequency arrangement of the LS0 mode and the LA0 mode of the present embodiment will be described with reference to the drawings. PG / PT obtained by standardizing the electrode pitch PT of the IDT electrode and the electrode pitch PG of the gate electrode is referred to as PTG and will be described.
FIG. 8 is an explanatory diagram showing the relationship of the resonance frequency difference between the PGT, the LS0 mode, and the LA0 mode of the present embodiment. The horizontal axis represents PGT, and the vertical axis represents the frequency difference δ (df / f).
Here, in the SH cut quartz crystal, f = 152 MHz, 140 pairs of IDT electrodes, and the number of conductor pairs MG = 20 (pairs) are calculated.

If L1 / L00 corresponding to the frequency difference δ is selected, the resonance state of the first resonator 120 and the second resonator 130 can be matched to realize a coupled state.
For example, when the condition PTG = 1.05, which is the frequency change rate δ = df / f = 400 (ppm), is selected, the first resonator 120 and the second resonator 130 are half the frequency difference δ. For 200 ppm, the line width ratio is ± 1.5% of 1/10. If the line width ratio is set to L2 / L1 = (1−0.015) / (1 + 0.015) = 0.970, the resonance frequency of LS0 of the first resonator 120 and the resonance frequency of LA0 of the second resonator 130 coincide. Can be made. That is, by reducing the frequency of the LS0 mode of the first resonator 120 and increasing the frequency of the LA0 mode of the second resonator 130, the LA0 of the second resonator 130 is increased to LS0 (f10) of the first resonator 120. (F21) can be matched.
At this time, the apex temperature difference between both resonators is about 5 ° C. (see FIG. 7).

  Further, in order to widen the apex temperature difference, if the condition that the number of pairs of IDT electrodes of both resonators is reduced or the number of conductor pairs MG of the gate electrode (control region) is reduced is selected from 2 to 4 times (δ It is possible to ensure a vertex temperature difference of 1600 ppm.

Therefore, an apex temperature difference of about 20 ° C. can be secured, and 1.6 × 10 ⁻⁸ × {(85 + 35-20) / 2} ² = 40 ppm, that is, ± 20 ppm in the range of use temperature −35 ° C. to + 85 ° C. A degree of accuracy can be realized. If the apex temperature difference is 50 ° C. (frequency difference δ = 4000 ppm), an accuracy of about ± 10 ppm can be realized from the same calculation.

  As described above, the first important point of the present invention is that the frequency difference δ when the resonance frequency of the LS0 mode of the first resonator 120 and the resonance frequency of the LA0 mode of the second resonator 130 are matched. Variation becomes important. The second important point is to use the line width ratio L2 / L1 of the IDT electrode in order to set the resonance frequency difference f21−f10 = 0. In addition, since a coupling state is formed between the first resonator 120 and the second resonator 130, if the line widths coincide with each other under the condition of L1 = L2, the frequencies of both coincide. That is, the resonance frequency f10 = f20 (LS0) and f11 = f21 (LA0).

  When the line widths L1 and L2 are changed, the frequency arrangement of the first resonator 120 and the second resonator 130 shifts mutually. The factors that change the frequency difference df = f10−f11 or the frequency difference df = f20−f21 are the electrode film thickness H and the line width L. This frequency difference df is considered to depend on the mass m of one cross-finger electrode if the conditions other than the electrode width are the same for both resonators (the IDT electrode has the same logarithm). That is, the reflection coefficient r by the electrode is a function of the mass m, and the above-described frequency difference df is determined by the magnitude of the reflection coefficient r.

In addition, the setting of the line width L1 of the cross finger electrode of the first resonator and the cross finger electrode L2 of the second resonator is important, and the concept of these setting conditions will be described using mathematical expressions. The amount of frequency change is df, and a is a frequency characteristic constant.
Therefore, in the first resonator, the frequency difference df ₁ between LS0 and LA0 is
df ₁ (m ₁ ) = a ₁ m ₁ + a ₂ m ₁ ² +... ≈a ₁ · m ₁ (1)
The frequency f10 in the LS0 mode is
f10 = b ₁ m ₁ (2)
However, b1 is the inclination of the frequency characteristic of FIG.
In the second resonator, the frequency difference df ₂ between LS0 and LA0 is
df ₂ (m ₂ ) = a ₁ m ₂ + a ₂ m ₂ ² +... ≈a ₁ · m ₂ (3)
If these frequency change amounts df ₁ and df ₂ are small, they can be approximated by a straight line as shown in FIG.
The frequency f21 of the LA0 mode of the second resonator is
f21 = f20 + df ₂
= B ₁ · m ₂ + df ₂ = b ₁ · m ₂ + a ₁ · m ₂ (4)
Here, if the frequencies of the first resonator and the second resonator are equal,
f10 = f21 (5)
Therefore, substituting equation (2) and equation (4) into equation (5),
b ₁ m ₁ = b ₁ · m ₂ + a ₁ · m ₂
m ₁ / m ₂ = 1 + a ₁ / b ₁ (6)
Can be expressed as
Here, the masses of the electrode fingers are m ₁ = ρHL1, m ₂ = ρHL2 (ρ is the electrode density, and H is the electrode film thickness), and the first resonator 120 and the second resonator 130 having the electrode film thickness H are Since they are close by the gap G, they can be considered the same. Substituting into equation (6),
m ₁ / m ₂ = ρHL1 / ρHL2 = L1 / L2
Therefore,
_{L1 / L2 = 1 + a 1} / b 1> 1 ( Note b1 <0, a1 <0) (7)
In this way, the line width ratio L2 / L1 can be determined, and L1> L2 may be set.

  Accordingly, only the line width ratio L2 / L1 can be regarded as a frequency change factor. If the frequencies are close to each other, the first resonator 120 and the second resonator 130 are coupled to each other and have only one resonance frequency as shown in FIG.

  Therefore, according to the above-described embodiment, the coupled oscillator is configured using the SH-cut quartz substrate having a small secondary temperature coefficient, so that a substantially flat frequency temperature characteristic is realized over a wide operating temperature range. A coupled SAW resonator can be provided.

  In addition, since the LS0 mode and the LA0 mode are used as the vibration mode, a low impedance can be realized even in the coupled state, and the configuration of the several hundred MHz band oscillation circuit can be facilitated.

  Further, the line width L1 of the IDT electrode of the first resonator 120 and the line width L2 of the IDT electrode of the second resonator 130 are changed and adjusted so that the fundamental frequencies of the LS0 mode and the LA0 mode are substantially matched. Since the line width can be formed with high accuracy by a photolithography technique or the like, it is possible to set a highly accurate frequency with little variation, and it is easy to create a temperature characteristic curve.

  Furthermore, since two 2-port SAW resonators are provided close to each other and are arranged in parallel to the propagation direction of the SH wave, the propagation direction of the surface wave as in Non-Patent Document 1 described above. The plane size can be reduced as compared with the case where the difference is made.

  In addition, the coupled SAW resonator 10 of the present invention adjusts the line widths L1 and L2 of the IDT electrodes of the first resonator 120 and the second resonator 130, respectively, so that the apex temperature difference between the LS0 mode and the LA0 mode is obtained. Provided. By adjusting the magnitude of the apex temperature difference, the flatness of the frequency temperature characteristic in the coupled state can be adjusted, and there is an effect that it is easy to create a desired temperature characteristic curve.

  Further, in the present invention, since the coupling between the LS0 mode and the LA0 mode is an elastic coupling, an external lumped element is used as a coupling method of two SAW resonators as described in Patent Document 2 described above. No additional concentrating element is required, and the number of mounted parts is small, enabling downsizing and cost reduction.

  In addition, since the frequency difference between the LS0 mode and the LA0 mode is substantially the same, the temperature characteristic curves of the first resonator 120 and the second resonator 130 are substantially symmetric with respect to the reference frequency F00, and the coupled state This has the effect of facilitating flattening of the temperature characteristic curve.

It should be noted that the present invention is not limited to the above-described embodiment, but includes modifications and improvements as long as the object of the present invention can be achieved.
For example, in the above-described embodiment, the case where two resonators of the first resonator 120 and the second resonator 130 are used has been described as an example, but the number of resonators may be larger. If the conditions of the present invention are met using three resonators and the third resonator is provided between the first resonator 120 and the second resonator 130, the flatness of the temperature characteristic curve is further increased. Can be increased.

  Alternatively, if the third resonator is provided outside the first resonator 120 or the second resonator 130, the operating temperature range can be further expanded.

Explanatory drawing which shows the azimuth which the crystal substrate which concerns on embodiment of this invention has. FIG. 3 is a plan view showing an example of a coupled SAW resonator according to an embodiment of the present invention. Explanatory drawing which illustrated typically about one example of the vibration mode utilized for this invention. Explanatory drawing showing the relationship between the coupling mode and frequency temperature characteristic in embodiment of this invention. FIG. 3 is an equivalent circuit diagram schematically showing elastic coupling in the embodiment of the present invention. Explanatory drawing which shows the frequency arrangement | positioning of the 1st resonator and 2nd resonator in embodiment of this invention. Explanatory drawing showing the relationship between the line | wire width of the IDT electrode of the coupled SAW resonator in embodiment of this invention, vertex temperature, and the amount of frequency changes. Explanatory drawing which shows the relationship of the resonant frequency difference of PGT of embodiment of this invention, LS0 mode, and LA0 mode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Coupled SAW resonator, 100 ... Quartz substrate, 120 ... First resonator, 121, 131 ... Main IDT electrode, 122, 132 ... Sub IDT electrode, 123, 124, 133, 134 ... Reflector, 130 ... First 2 resonators.

Claims (4)

On the principal surface of the SH-cut quartz substrate represented by Euler angles (φ, θ, ψ) on the fundamental axis of the crystal, two IDT electrodes in a specific direction and the specific direction of the IDT electrode A plurality of two-port SAW resonators provided with reflectors provided on both sides are provided close to each other and arranged in parallel in the specific azimuth direction,
One SAW resonator is operated in a longitudinal symmetric fundamental mode;
Operating the other SAW resonator in a longitudinally symmetric fundamental wave mode;
After making the fundamental frequency of the symmetric fundamental wave mode and the obliquely symmetric fundamental wave mode substantially the same by changing the line width of the IDT electrode,
A coupled SAW resonator, wherein the symmetric fundamental wave mode and the obliquely symmetric fundamental wave mode are operated in a coupled state. The coupled SAW resonator according to claim 1,
The coupled SAW resonator is characterized in that a vertex temperature difference between the symmetric fundamental wave mode and the oblique symmetric fundamental wave mode is provided by adjusting a line width of the IDT electrode. In the coupled SAW resonator according to claim 1 or 2,
A coupled SAW resonator, wherein the coupling between the symmetric fundamental wave mode and the obliquely symmetric fundamental wave mode is an elastic coupling. In the coupled SAW resonator according to any one of claims 1 to 3,
A coupled SAW resonator in which the frequency difference between the symmetric fundamental wave mode and the obliquely symmetric fundamental wave mode of each of the plurality of SAW resonators is substantially the same.

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