JP2008306422A - Surface acoustic wave resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave resonator which is easily miniaturized and is excellent in frequency accuracy. <P>SOLUTION: The surface acoustic wave resonator is provided with: a interdigital transducer 11 where SH type surface acoustic waves are excited on a crystal substrate 10; and one reflector 13 disposed on one side of the interdigital transducer 11. When the width dimension of electrode fingers 11a and 11b is defined as LT and the dimension of an area where the electrode finger is not present is defined as ST, PT which is an IDT array cycle length is PT=LT+ST. The reflector 13 is composed of a metal conductor 13a, and when the width dimension of the metal conductor 13a is defined as LR and the dimension of an area where the metal conductor is not present is defined as SR, PR which is the reflector array cycle length is PR=LR+SR. The ratio PR/PT of the reflector array cycle length PR and the IDT array cycle length PT is in the range of 1.01 to 1.02, the area where the electrode is not present in a dimension PST less than the IDT array cycle length PT is provided on the other side of the interdigital transducer 11, and the crystal substrate 10 is provided with a vertically cut surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave resonator using SH waves.

Conventionally, surface acoustic wave resonators configured using a quartz ST cut substrate (an example of a piezoelectric flat plate) have been used in ASK transmitters and the like. This surface acoustic wave resonator is used in various types of wireless piezoelectric oscillators because its frequency temperature characteristic has a zero temperature coefficient, has high accuracy, and can directly oscillate a desired frequency. In recent years, surface acoustic wave resonators can be used for keyless entry devices that use weak radio waves to open and close a door of a passenger car because they can obtain a signal having no jitter and excellent phase noise.
More recently, sensor networks that transmit information from various sensors to a central processing unit for processing have attracted attention. This sensor network requires weak wireless communication over a relatively short distance used indoors, and there is an urgent need to reduce the size and cost of the transmitter / receiver.
As a surface acoustic wave resonator, a surface acoustic wave resonator using an SH wave as disclosed in Patent Document 1 is known. The surface acoustic wave resonator using the SH wave uses a quartz substrate and has a frequency temperature characteristic that is excellent in frequency accuracy with respect to the quartz ST cut. The crystal substrate cutting direction is Euler angle display (φ, θ, ψ) on the basic axis of the crystal crystal, and φ is in the range of 0 ° ± 1 ° counterclockwise around the Z axis (optical axis). Next, θ is in the range of 29.2 ° to 40.7 ° counterclockwise around the X axis (electric axis), and then in the piezoelectric plate around the newly generated Z ′ axis. The direction in which the surface rotates in the counterclockwise direction starting from the X axis and ψ is in the range of 90 ° ± 2 ° is the phase propagation direction of the surface acoustic wave. Also in the case of the piezoelectric plate having the above-mentioned orientation using the SH wave, the surface acoustic wave resonator can be formed with the same configuration as the surface acoustic wave resonator using the conventional quartz ST cut substrate. For example, an interdigital transducer (hereinafter referred to as IDT (Interdigital Transducer)) in which a large number of parallel conductor electrode fingers made of an aluminum film are periodically formed is formed, and a pair of reflectors are formed on both sides from a number of strip shapes. It is possible to form a 1-port surface acoustic wave resonator by arranging the metal conductors in parallel and periodically.
In addition, as a surface acoustic wave resonator using an SH wave, one that realizes miniaturization by cutting an end face of an element substrate without providing a reflector is known (see Patent Document 2).

International Publication No. WO2005 / 099089 Pamphlet US Pat. No. 5,953,433

Since the surface acoustic wave resonator of Patent Document 1 is a surface acoustic wave resonator that performs fundamental wave operation, the relationship between the array period length P that is a repetition of the electrode finger of the IDT and the metal conductor of the reflector and the operating frequency is , V is the velocity of the surface acoustic wave, and f is the operating frequency, f = V / (2P). Thus, the operating frequency f is limited by the speed V and the array period length P.
Taking the frequency 315 MHz often used in the market as an example, when the surface acoustic wave velocity V = 3200 m / s, the IDT array period length P = 5 × 10 ⁻⁶ m, and the reflection coefficient γ used normally. In the range of 0.05 to 0.06, the number of electrode finger pairs M of the IDT is 100 to 120 and the number of reflector metal conductors N is 60 to 40.
The element designed as described above has a longitudinal dimension XL of about 1.6 mm, and it is difficult to further reduce the size when maintaining good characteristics.
On the other hand, in the configuration of Patent Document 2, when the frequency is 315 MHz, the number of electrode finger pairs M of IDT is 30 and the number of metal conductors of the reflector is N = 0, and the element has a longitudinal dimension XL of about 0.3 mm. However, the change in element frequency (element frequency sensitivity) with respect to the change in the longitudinal dimension XL of the element is large. For this reason, the dimensional processing accuracy of the longitudinal dimension XL is severe, and it is difficult to realize ± 50 ppm as the frequency accuracy.

  The present invention has been made to solve at least a part of the above problems. The following forms or application examples can solve the above problems.

  Application Example 1 A surface acoustic wave resonator according to this application example includes at least one interdigital electrode in which an SH type surface acoustic wave having a phase propagation direction X ′ is excited on a piezoelectric plate, and the interdigital transducer. A reflector disposed on one side of the electrode, wherein the interdigital electrode comprises M pairs of electrode fingers disposed perpendicular to the phase propagation direction X ′ of the surface acoustic wave, The width dimension of the electrode finger along the phase propagation direction X ′ of the surface acoustic wave is LT, the dimension of the region where the electrode finger does not exist is ST, and the PT that is the IDT array period length is PT = LT + ST. The reflector includes N metal conductors arranged orthogonal to the phase propagation direction X ′ of the surface acoustic wave, and the width of the metal conductor along the phase propagation direction X ′ of the surface acoustic wave. The dimension is LR and the presence of the metal conductor The dimension PR of the reflector array period length is PR = LR + SR, where SR is the dimension of the long region, and the ratio PR / PT between the reflector array period length PR and the IDT array period length PT is 1.01 or more. A cut surface in which the piezoelectric flat plate is vertically cut with a region having a dimension PST less than the IDT arrangement period length PT on the other side of the interdigital electrode, which is a range of 02 or less It is characterized by having.

  According to this configuration, the SH wave excited by the interdigital electrode (IDT) propagates to one side of the IDT and is reflected by the reflector disposed there. Further, the SH wave propagating to the other side of the IDT is reflected by the end face of the piezoelectric flat plate. And vibration energy is confined in the central part of the part in which these reflected SH waves formed IDT. As described above, in Application Example 1, a surface acoustic wave resonator using a normal SH wave having reflectors on both sides of the IDT is cut at the center. As described above, since the resonance frequency of the surface acoustic wave resonator depends only on the electrode arrangement of the IDT, a small surface acoustic wave resonator with good frequency accuracy can be realized.

  Application Example 2 In the surface acoustic wave resonator according to the application example described above, it is preferable that the number M of electrode fingers included in the interdigital electrode is in a range of 20 to 80 pairs.

  According to this configuration, the equivalent series resonance resistance value R1 of the surface acoustic wave resonator can be set to 25Ω or less. When the surface acoustic wave resonator is incorporated into the oscillation circuit, the surface acoustic wave resonator can be oscillated with low power consumption. Also, with this configuration, the capacity ratio γ can be 1000 or less, and when the capacitor is added, the variable amount of the frequency can be increased, and when the surface acoustic wave resonator is mounted on a circuit board or the like, the variable capacitor Using this makes it easy to adjust the frequency.

  Application Example 3 In the surface acoustic wave resonator according to the application example described above, the piezoelectric plate is made of a single crystal of crystal, and is displayed around the Z axis, which is the optical axis, in Euler angle display (φ, θ, ψ). In the counterclockwise direction, φ is in the range of 0 ° ± 1 °, and next, in the counterclockwise direction around the X axis, which is the electric axis, θ is in the range of 29.2 ° to 40.7 °, In the piezoelectric plate around the newly generated Z 'axis, the surface is rotated in the counterclockwise direction starting from the X axis, and the direction in which ψ is in the range of 90 ° ± 2 ° is the phase propagation of the surface acoustic wave. It is desirable to have an orientation.

  According to this configuration, a quartz substrate (SH cut substrate) of Euler angle display excellent in frequency temperature characteristics (0 ° ± 1 °, 29.2 ° ≦ θ ≦ 40.7 °, 90 ° ± 2 °) can be obtained. By using this, a small and highly accurate surface acoustic wave resonator can be realized.

  Application Example 4 In the surface acoustic wave resonator according to the application example, the electrode fingers of the interdigital electrode and the metal conductor of the reflector are made of an aluminum film, and the film thickness H of the interdigital electrode and the SH The ratio H / λ of the surface acoustic wave to the wavelength λ is preferably 0.05 or more and 0.06 or less.

  According to this configuration, while maintaining the Q value of the surface acoustic wave resonator at the maximum, the reflection coefficient γ of one electrode can be increased to the maximum of about 0.06. As a result, the electrode finger of the interdigital electrode Therefore, a small surface acoustic wave resonator can be realized.

  Application Example 5 In the surface acoustic wave resonator according to the application example described above, the dimension PST provided on the other side of the interdigital electrode, which is less than the IDT array period length PT, and the IDT array period length PT The ratio PST / PT is desirably in the range of 0.4 to 0.9.

  According to this configuration, the fundamental wave of the excited SH wave and the edge mode (EDM) of the reflected wave reflected at the end portion are not coupled, so that the frequency jump phenomenon or the distortion of the frequency temperature characteristic does not occur, which is good. A surface acoustic wave resonator that outputs a simple signal source can be realized.

  Application Example 6 In the surface acoustic wave resonator according to the application example described above, it is preferable that the surface of the piezoelectric plate is bonded and fixed to the substrate on the back surface of the portion where the reflector is formed.

  According to this configuration, a cantilever support structure can be adopted as the support structure of the surface acoustic wave resonator, and the frequency is changed because the back surface of the portion where the reflector apart from the IDT is formed is adhered and fixed to the substrate. A surface acoustic wave resonator having excellent variation and small variation in frequency temperature characteristics can be obtained.

Hereinafter, specific embodiments will be described with reference to the drawings.
(Embodiment)

1A and 1B show a configuration of a surface acoustic wave resonator according to the present embodiment, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along the line AA in FIG.
A surface acoustic wave resonator (hereinafter sometimes referred to as the present element) 1 includes an interdigital electrode 11 (hereinafter referred to as “IDT11”) on the surface of a quartz substrate 10 as a piezoelectric plate, and one side of the IDT11. And a single reflector 13 disposed in the.
The IDT 11 is configured by alternately interposing positive electrode fingers 11a and negative electrode fingers 11b. And the polarity of this electrode finger 11a and the electrode finger 11b is comprised so that it may become an alternating reverse phase with time. One adjacent electrode finger 11a and one electrode finger 11b are referred to as a pair of electrode fingers. This number of electrode fingers is called a logarithm, and 20 to 80 electrode fingers are formed. The positive electrode finger 11a is connected to the power supply conductor 12a, and the negative electrode finger 11b is connected to the power supply conductor 12b. The reflector 13 includes a large number of metal conductors 13a that are continuously arranged at an equal pitch. The number of metal conductors 13a is set to 40 to 60.
As described above, the surface acoustic wave resonator 1 has a configuration in which the IDT 11 is arranged on the right side in the drawing and the reflector 13 is arranged on the left side in the drawing.

The electrode fingers 11a and 11b of the IDT 11 and the metal conductor 13a of the reflector 13 are formed substantially orthogonal to the phase propagation direction X ′ of the SH type surface acoustic wave.
Further, connection pads 15a and 15b are formed at the corners of the present element on the side where the reflector 13 is formed, and are connected to the power supply conductors 12a and 12b, respectively.
The IDT 11, the reflector 13, the power supply conductors 12a and 12b, and the connection pads 15a and 15b provided on the surface of the quartz substrate 10 of the surface acoustic wave resonator 1 are metal patterns formed by photolithography of an aluminum film.

Next, dimensions in the IDT 11 and the reflector 13 along the phase propagation direction X ′ of the SH type surface acoustic wave will be described.
In the IDT 11, the dimension LT is the width dimension of the electrode finger 11a or the electrode finger 11b, and the dimension ST is a dimension between the electrode finger 11a and the electrode finger 11b (a region where no electrode finger exists). The dimension PT is an IDT array period length composed of the sum of LT and ST (PT = LT + ST). Further, the dimension PST is a dimension from the other end of the IDT 11 to the end of the quartz substrate 10. The dimension of this PST is set to a dimension that is less than the IDT arrangement period length PT. In the present embodiment, the nominal resonance frequency f0 is f0 = V / (2PT), and V is the velocity of the SH type surface acoustic wave and V = 3200 m / s.

In the reflector 13, the dimension LR is a width dimension of the metal conductor 13a, and the dimension SR is a dimension between the metal conductor 13a and the metal conductor 13a (a region where no metal conductor exists). Further, the dimension PR is a reflector arrangement period length composed of the sum of LR and SR (PR = LR + SR).
The ratio PR / PT between the reflector arrangement period length PR and the IDT arrangement period length PT is set to 1.01 or more and 1.02 or less that exhibits the reflection effect.
Thus, no reflector is provided on the other side of the IDT 11, and the dimension from the end of the electrode finger to the end of the quartz substrate is cut by PST. The crystal substrate end is cut by a dicing device, a wire saw, or the like, and the cut surface is in a polished state.

Next, a cut surface of a quartz substrate as a piezoelectric plate used in the present embodiment will be described. FIG. 2 is a schematic diagram for explaining a cut surface of a quartz crystal substrate in the present embodiment.
A quartz crystal substrate 10 made of a quartz single crystal has an X axis (electrical axis), a Y axis (mechanical axis), and a Z axis (optical axis) as basic axes of the quartz crystal, and constitutes a right-handed orthogonal coordinate system. Yes.
The quartz substrate 10 is displayed with Euler angles (φ, θ, ψ). First, φ is in the range of 0 ° ± 1 ° counterclockwise around the Z axis, and then counterclockwise around the X axis. In the quartz substrate, θ is in the range of 29.2 ° to 40.7 °, and the surface formed by the X axis and the newly generated Y ′ axis is the main surface. Then, in the quartz substrate 10 around the newly generated Z ′ axis, the surface rotates in the counterclockwise direction (from the X axis to the Y ′ axis) starting from the X axis, and ψ is 90 ° ± 2 °. A direction X ′ as a range is a phase propagation azimuth of the surface acoustic wave. Such a quartz substrate 10 is referred to as SH cut. It is known that when an SH wave is excited using this SH-cut quartz substrate 10, a surface acoustic wave resonator having excellent frequency temperature characteristics can be formed.

Next, the characteristics of the surface acoustic wave resonator as described above will be described using characteristic diagrams. Here, the ratio of the dimension PST from the end of the IDT 11 to the end of the quartz substrate and the IDT arrangement period length PT is defined as ETAS (= PST / PT).
FIG. 3 is a characteristic diagram showing the relationship between the Q value of the surface acoustic wave resonator and the ETAS, and FIG. 4 is a characteristic diagram showing the relationship between the equivalent series resonance resistance R1 of the surface acoustic wave resonator and the ETAS. FIG. 5 is a characteristic diagram showing the relationship between the capacitance ratio γ of the surface acoustic wave resonator and ETAS.
According to FIG. 3, the surface acoustic wave resonator has a constant Q value regardless of ETAS.
In FIG. 4, it can be seen that the equivalent series resonance resistance R1 varies depending on the value of ETAS, and that the equivalent series resonance resistance R1 is 25Ω or less in the range where ETAS is 0.4 or more and 0.9 or less. If the equivalent series resonance resistance R1 is 25Ω or less, it is possible to oscillate with low power consumption when a surface acoustic wave resonator is incorporated in the oscillation circuit.
In FIG. 5, if ETAS is in the range of 0.4 to 0.9, the capacity ratio γ is about 950 or less. The small capacitance ratio γ allows a large amount of frequency variation when a capacitor is added. When a surface acoustic wave resonator is mounted on a circuit board or the like, the frequency can be adjusted using a variable capacitor. Becomes easy.

FIG. 6 is a characteristic diagram showing the relationship between the Q value and the normalized electrode thickness H / λ. Here, when the film thickness of the aluminum film in IDT 11 is H and the wavelength of the surface acoustic wave is λ, H / λ is the normalized electrode thickness.
From this characteristic diagram, the Q value varies depending on the value of the normalized electrode thickness H / λ, and when the normalized electrode thickness H / λ is 0.05 or more and 0.06 or less, the Q value is 15000 or more, and the surface acoustic wave It is in a good value to excite.

Next, the relationship between the number of pairs of electrodes in the IDT and each characteristic will be described.
FIG. 7 is a characteristic diagram showing the relationship between the equivalent series resonance resistance R1 of the surface acoustic wave resonator and the number M of electrode pairs of the IDT, and FIG. 8 is the relationship between the Q value of the surface acoustic wave resonator and the number of electrode pairs M of the IDT. FIG. FIG. 9 is a characteristic diagram showing the relationship between the capacitance ratio γ of the surface acoustic wave resonator and the number M of electrode pairs of IDT. 7, 8, and 9 show the characteristics of the surface acoustic wave resonator when ETAS = 0.8.

In FIG. 7, the equivalent series resonance resistance R1 tends to decrease as the number of electrode pairs M of the IDT increases. In FIG. 8, when the number of electrode pairs M of the IDT is 20, the Q value is about 19000, and when the number of electrode pairs M of the IDT is 40 pairs or more, the Q value is about 16000, which is a substantially constant value. Furthermore, it can be seen from FIG. 9 that the capacity ratio γ tends to increase as the number of electrode pairs M of the IDT increases.
As described above, if the equivalent series resonance resistance R1 is 25Ω or less, the Q value is 15000 or more, and the capacitance ratio γ is 1000 or less, the characteristics of the surface acoustic wave element are good, the IDT electrode pair number M is 20 pairs or more. Good surface acoustic wave element characteristics can be obtained within a range of 80 pairs or less.

Next, the vibration displacement amplitude state in the surface acoustic wave resonator having the above configuration will be described.
FIG. 10 is a schematic diagram showing a vibration displacement amplitude state of the surface acoustic wave resonator according to this embodiment. In this schematic diagram, the vertical axis represents the displacement of vibration, and the horizontal axis represents the length of the propagation direction of the elastic wave in the surface acoustic wave resonator, which corresponds to the position of the surface acoustic wave resonator. Further, this vibration displacement amplitude state shows an example when ETAS = 0.8.
It can be seen that the surface acoustic wave excited by the IDT is reflected by the reflector disposed on one side of the IDT, and the vibration displacement is sufficiently attenuated at the end of the reflector. On the other side of the IDT, the surface acoustic wave is reflected at the end of the quartz substrate, and the displacement of vibration is reduced. And it turns out that the displacement of vibration becomes the maximum in the substantially center part of IDT, and vibration energy is confined.
As described above, in the surface acoustic wave resonator according to this embodiment, the surface acoustic wave is reflected by the reflector on one side of the IDT, and the surface acoustic wave is reflected by the end face of the quartz substrate on the other side of the IDT.

As described above, in the surface acoustic wave resonator 1 of the present embodiment, since the resonance frequency depends only on the electrode arrangement, it is possible to realize a small surface acoustic wave resonator with good frequency accuracy.
In addition, the equivalent series resonance resistance value R1 of the surface acoustic wave resonator can be set to 25Ω or less by setting the number M of electrode fingers of the interdigital electrode to be in the range of 20 to 80 pairs. When the surface acoustic wave resonator is incorporated into the oscillation circuit, the surface acoustic wave resonator can be oscillated with low power consumption. Also, with this configuration, the capacity ratio γ can be 1000 or less, and when the capacitor is added, the variable amount of the frequency can be increased, and when the surface acoustic wave resonator is mounted on a circuit board or the like, the variable capacitor Using this makes it easy to adjust the frequency.
Further, by using an SH cut substrate as a quartz substrate having excellent frequency temperature characteristics, a small and highly accurate surface acoustic wave resonator can be realized.
Further, the electrode fingers of the interdigital electrode and the metal conductor of the reflector are made of an aluminum film, and the ratio H / λ between the thickness H of the interdigital electrode and the wavelength λ of the SH type surface acoustic wave is 0.05 or more and 0.06. By making the following, the reflection coefficient γ of one electrode can be increased to about 0.06 at the maximum while maintaining the Q value of the surface acoustic wave resonator at the maximum. As a result, since the sum of the number M of electrode fingers of the interdigital electrode and the number N of metal conductors of the reflector can be reduced, a small surface acoustic wave resonator can be realized.
Furthermore, when the ratio PST / PT between the dimension PST and the IDT arrangement period length PT is in the range of 0.4 to 0.9, the fundamental wave of the excited SH wave and the edge are reflected. Since the edge mode (EDM) of the reflected wave is not coupled, a frequency jump phenomenon or distortion of the frequency temperature characteristic does not occur, and a surface acoustic wave resonator that outputs a good signal source can be realized.

Next, a state in which the surface acoustic wave resonator according to this embodiment is packaged will be described.
11A and 11B are schematic views showing a state in which the surface acoustic wave resonator is packaged. FIG. 11A is a plan view, and FIG. 11B is a cross-sectional view taken along the line BB in FIG. .
The surface acoustic wave resonator 1 is accommodated in a ceramic package 50 and the inside of the ceramic package 50 is hermetically sealed by a lid 58.
The surface acoustic wave resonator 1 is the element of the embodiment described with reference to FIG. 1, and is given the same reference numerals as those in FIG.
The ceramic package 50 includes a multilayer ceramic substrate 51 in which ceramic sheets are laminated to form a recess. A terminal 53 is formed in the concave portion of the multilayer ceramic substrate 51 and is connected to an external connection terminal 54 formed on the outer peripheral portion of the multilayer ceramic substrate 51. A seam ring 52 made of a metal such as kovar is fixed above the multilayer ceramic substrate 51.

The surface acoustic wave resonator 1 is fixed in a cantilevered state with an adhesive 55 on the bottom surface of the concave portion of the ceramic package 50. This adhesive portion is fixed by applying an adhesive 55 on the back surface of the portion of the quartz substrate 10 where the reflector 13 is formed. Further, the connection pads 15a and 15b of the surface acoustic wave resonator 1 and the terminal 53 of the ceramic package 50 are connected by a metal wire 56 such as an Au wire.
The seam ring 52 and a lid 58 made of a metal such as Kovar are seam welded to hermetically seal the inside of the ceramic package 50 in a dry nitrogen atmosphere.

  Thus, according to the surface acoustic wave resonator 1 of the present embodiment, since the cantilever support structure can be adopted as the support structure of the surface acoustic wave resonator 1, the crystal substrate 10 is not subjected to stress due to support, and the frequency is high. There is a stabilizing effect. Furthermore, since the back surface of the part where the reflector 13 apart from the IDT 11 is formed is bonded and fixed to the bottom surface of the concave portion of the ceramic package 50, the IDT 11 is affected by the change of the adhesive over time and the shrinkage due to the temperature change. Accordingly, the surface acoustic wave resonator 1 having excellent frequency change with time and less variation in frequency temperature characteristics can be obtained.

In addition to the above embodiment, the following implementation is also possible.
12A and 12B show the structure of a surface acoustic wave resonator according to another embodiment. FIG. 12A is a plan view, and FIG. 12B is a cross-sectional view taken along the line CC in FIG.
The surface acoustic wave resonator 3 includes an interdigital electrode 81 (hereinafter referred to as “IDT81”) on the surface of the quartz substrate 80 and two reflectors 83 disposed on both sides of the IDT81.
The quartz substrate 80 uses the SH cut substrate described in FIG. The IDT 81 is configured by alternately interposing positive electrode fingers 81a and negative electrode fingers 81b. And the polarity of this electrode finger 81a and the electrode finger 81b is comprised so that it may become a reverse phase alternately with time. One adjacent electrode finger 81a and one electrode finger 81b are referred to as a pair of electrode fingers. This number of electrode fingers is called a logarithm, and 40 to 80 electrode fingers are formed. The positive electrode finger 81a is connected to the power supply conductor 82a, and the negative electrode finger 81b is connected to the power supply conductor 82b. The reflector 83 includes a large number of metal conductors 83a that are continuously arranged at an equal pitch. The number of the metal conductors 83a is set to 1 to 8.
The IDT 81, the reflector 83, and the feed conductors 82a and 82b provided on the surface of the quartz substrate 80 of the surface acoustic wave resonator 3 are metal patterns formed by photolithography of an aluminum film.

  In the IDT 81, the dimension LT is the width dimension of the electrode finger 81a or the electrode finger 81b, and the dimension ST is a dimension between the electrode finger 81a and the electrode finger 81b (a region where no electrode finger exists). The dimension PT is an IDT array period length composed of the sum of LT and ST (PT = LT + ST).

In the reflector 83, the dimension LR is a width dimension of the metal conductor 83a, and the dimension SR is a dimension between the metal conductor 83a and the metal conductor 83a (a region where no metal conductor exists). Further, the dimension PR is a reflector arrangement period length composed of the sum of LR and SR (PR = LR + SR). Further, the dimension PSR is a dimension from the end of the metal conductor 83 a in the reflector 83 to the end of the crystal substrate 80. The dimension of this PSR is set to a dimension less than the reflector arrangement period length PR. The crystal substrate end is cut by a dicing machine, a wire saw, etc., and further polished. As described above, the reflectors 83 on both sides are usually formed with 40 to 60 metal conductors 83a in order to reflect the surface acoustic waves with the reflector 83. In this embodiment, the reflectors are cut halfway. It is.
The ratio PR / PT between the reflector arrangement period length PR and the IDT arrangement period length PT is set to 1.01 or more and 1.02 or less.

Further, when the equivalent series resonance resistance R1, which is a value for obtaining a good surface acoustic wave resonator, is 25Ω or less, the Q value is 15000 or more, and the capacitance ratio γ is 1000 or less, the number M of electrode fingers of the IDT 81 is 40 pairs. The ratio H / λ between the film thickness H of the IDT 81 and the wavelength λ of the SH type surface acoustic wave is preferably set to a value of 0.05 or more and 0.06 or less.
Further, the ratio PSR / PR of the PSR and the PR of the reflector is set to 0 to 0 so that the fundamental wave of the excited SH wave and the edge mode (EDM) of the reflected wave reflected at the end are not coupled. .2 range, 0.3 to 0.6 range, and 0.7 to 1.0 range are preferred.

FIG. 13 is a schematic diagram showing a vibration displacement amplitude state of the surface acoustic wave resonator in the present embodiment. In this schematic diagram, the vertical axis represents the displacement of vibration, and the horizontal axis represents the length of the propagation direction of the elastic wave in the surface acoustic wave resonator, which corresponds to the position of the surface acoustic wave resonator.
In the reflectors arranged on both sides of the IDT, the surface acoustic wave excited by the IDT is reflected, and the displacement of the vibration becomes smaller toward the end of the quartz substrate. Then, it can be seen that the surface acoustic wave is reflected at the end of the quartz substrate, and the vibration displacement is maximized at almost the center of the IDT, so that the vibration energy is confined. Further, both ends of the quartz substrate are in a vibrating state, and the displacement of the central portion of the IDT is more than double the displacement of this end.
As described above, the actual surface acoustic wave resonator is configured such that the surface acoustic waves are reflected from both end faces of the quartz substrate.
As described above, in the surface acoustic wave resonator, the number of the metal conductors of the reflector is formed from 1 to 8, and the surface acoustic wave is reflected at both end faces of the quartz substrate, thereby reducing the size of the surface acoustic wave resonator. Is possible.

The structure of the surface acoustic wave resonator of this embodiment is shown, (a) is a top view, (b) is sectional drawing which follows the AA disconnection of the figure (a). The schematic diagram explaining the cut surface of the crystal substrate in this embodiment. The characteristic view which shows the Q value of a surface acoustic wave resonator, and the relationship of ETAS. The characteristic view which shows the relationship between the equivalent series resonance resistance R1 of a surface acoustic wave resonator, and ETAS. The characteristic view which shows the capacity ratio (gamma) of a surface acoustic wave resonator, and the relationship of ETAS. The characteristic view which shows the relationship between Q value and normalized electrode thickness H / λ. The characteristic view which shows the relationship between the equivalent series resonance resistance R1 of a surface acoustic wave resonator, and the electrode pair number M of IDT. The characteristic view which shows the relationship between the Q value of a surface acoustic wave resonator, and the electrode pair number M of IDT. The characteristic view which shows the relationship between the capacitance ratio (gamma) of a surface acoustic wave resonator, and the number M of electrode pairs of IDT. The schematic diagram which shows the vibration displacement amplitude state of the surface acoustic wave resonator in this embodiment. It is a schematic diagram which shows the state which packaged the surface acoustic wave resonator, (a) is a top view, (b) is sectional drawing which follows the BB disconnection of the figure (a). The structure of the surface acoustic wave resonator in the other implementation is shown, (a) is a plan view, (b) is a cross-sectional view taken along the line CC in FIG. The schematic diagram which shows the vibration displacement amplitude state of the surface acoustic wave resonator in other implementation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave resonator, 10 ... Quartz substrate, 11 ... Interdigital electrode (IDT), 11a, 11b ... Electrode finger, 12a, 12b ... Feeding conductor, 13 ... Reflector, 13a ... Metal conductor, 15a, 15b ... Connection pads, 50 ... ceramic package, 51 ... multilayer ceramic substrate, 52 ... seam ring, 53 ... terminal, 55 ... adhesive, 56 ... metal wire, 58 ... lid.

Claims (6)

At least one interdigital electrode on which an SH type surface acoustic wave having a phase propagation direction X ′ is excited on a piezoelectric plate;
One reflector disposed on one side of the interdigital electrode,
The interdigital electrode is composed of M pairs of electrode fingers arranged orthogonally to the phase propagation direction X ′ of the surface acoustic wave, and is formed along the phase propagation direction X ′ of the surface acoustic wave. The width dimension is LT, the dimension of the region where the electrode fingers are not present is ST, and the PT that is the IDT array period length is PT = LT + ST,
The reflector is composed of N metal conductors arranged orthogonal to the phase propagation direction X ′ of the surface acoustic wave, and the width dimension of the metal conductor along the phase propagation direction X ′ of the surface acoustic wave. LR, and the dimension of the region where the metal conductor does not exist is SR, and the reflector array period length PR is PR = LR + SR, and the ratio PR between the reflector array period length PR and the IDT array period length PT / PT is in the range of 1.01 to 1.02,
Elasticity characterized by having a cut surface in which the piezoelectric flat plate is cut perpendicularly with a region having no electrode having a dimension PST less than the IDT arrangement period length PT on the other side of the interdigital electrode. Surface wave resonator. The surface acoustic wave resonator according to claim 1,
2. The surface acoustic wave resonator according to claim 1, wherein the number M of pairs of the electrode fingers of the interdigital electrode is in a range of 20 to 80 pairs. The surface acoustic wave resonator according to claim 1,
The piezoelectric plate is made of a single crystal of crystal, and in Euler angle display (φ, θ, ψ), first, φ is in the range of 0 ° ± 1 ° counterclockwise around the Z axis that is the optical axis. In the counterclockwise direction around the X axis, which is the electrical axis, in the range of 29.2 ° to 40.7 °, and then in the piezoelectric plate around the newly generated Z ′ axis, A surface acoustic wave resonator characterized in that a phase propagation direction of the surface acoustic wave is a direction in which ψ is in a range of 90 ° ± 2 ° by rotating in a counterclockwise direction starting from an axis. The surface acoustic wave resonator according to claim 1,
The electrode finger of the interdigital electrode and the metal conductor of the reflector are made of an aluminum film, and the ratio H / λ between the thickness H of the interdigital electrode and the wavelength λ of the SH type surface acoustic wave is 0.05. The surface acoustic wave resonator is characterized by being 0.06 or less. The surface acoustic wave resonator according to claim 1,
The ratio PST / PT between the dimension PST provided on the other side of the interdigital electrode and less than the IDT arrangement period length PT and the IDT arrangement period length PT is in the range of 0.4 to 0.9. A surface acoustic wave resonator characterized by being. The surface acoustic wave resonator according to claim 1,
A surface acoustic wave resonator characterized in that the surface acoustic wave resonator is bonded and fixed to a substrate on a back surface of a portion where the reflector is formed on the piezoelectric flat plate.

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