WO2009125536A1

WO2009125536A1 - Boundary acoustic wave device and method of manufacturing the same

Info

Publication number: WO2009125536A1
Application number: PCT/JP2009/000891
Authority: WO
Inventors: 野竹直弘; 稲手謙二; 三村昌和
Original assignee: 株式会社村田製作所
Priority date: 2008-04-10
Filing date: 2009-02-27
Publication date: 2009-10-15

Abstract

The frequency is increased while maintaining high surge withstand pressure. A boundary acoustic wave device (1) is provided with a piezoelectric body (10), a dielectric body (20), and an electrode (30) disposed at the boundary between the piezoelectric body (10) and the dielectric body (20), and utilizes boundary acoustic waves propagating through the boundary. The electrode (30) comprises a first comb-tooth electrode (31) comprising a plurality of finger electrodes (31b), and a second comb-tooth electrode (32) comprising a plurality of finger electrodes (32b). The finger electrodes (32b) are arranged alternately with the finger electrodes (31b) in the propagation direction of the boundary acoustic waves. The second comb-tooth electrode (32) is connected to a potential different from that of the first comb-tooth electrode (31). In the surface (10a) of the piezoelectric body (10) on the side of the dielectric body (20), grooves (11) are formed extending in the direction in which the finger electrodes extend. The grooves (11) are positioned respectively between the finger electrodes (31b) and the finger electrodes (32b) respectively adjacent to each other.

Description

Boundary acoustic wave device and manufacturing method thereof

The present invention relates to a boundary acoustic wave device and a manufacturing method thereof.

Conventionally, surface acoustic wave devices and boundary acoustic wave devices are known as devices using elastic waves. A surface acoustic wave device normally requires a package in which the surface acoustic wave element is hermetically sealed and a space is formed on the propagation surface of the surface acoustic wave element.

In contrast, in the boundary acoustic wave device, the energy of the boundary acoustic wave is substantially confined in the boundary portion between the piezoelectric body and the dielectric body. Therefore, in the boundary acoustic wave device, it is not necessary to provide a package required in the surface acoustic wave device. Therefore, since the boundary acoustic wave device can be further reduced in size, it has been actively studied in recent years.

For example, Patent Document 1 below discloses a boundary acoustic wave device using an SH type boundary acoustic wave. Patent Document 1 describes that a high resonance frequency of 1370 MHz and a high anti-resonance frequency of 1460 MHz can be obtained by reducing the period of the IDT and the reflector to 2.2 μm.
WO2004 / 070946 A1 Publication

As shown in Patent Document 1, it is possible to realize a high resonance frequency and anti-resonance frequency by reducing the period of the IDT and the reflector. However, when the period of the IDT and the reflector is reduced in order to realize high frequency, there is a problem that the surge withstand voltage is lowered. Therefore, it has been difficult to increase the frequency while maintaining a high surge withstand voltage.

An object of the present invention is to increase the frequency while maintaining a high surge withstand voltage.

The boundary acoustic wave device according to the present invention includes a piezoelectric body, a dielectric layer laminated on one surface of the piezoelectric body, and an electrode disposed at a boundary between the piezoelectric body and the dielectric body, and an elastic property that propagates through the boundary. The present invention relates to a boundary acoustic wave device using boundary waves. In the boundary acoustic wave device according to the present invention, the electrode includes a first comb electrode and a second comb electrode. The first comb electrode has a plurality of electrode fingers. The second comb electrode has a plurality of electrode fingers. The plurality of electrode fingers of the second comb electrode are alternately arranged with the electrode fingers of the first comb electrode in the propagation direction of the boundary acoustic wave. The second comb electrode is connected to a potential different from that of the first comb electrode. A groove extending in the extending direction of the electrode finger is formed on the surface of the piezoelectric body on the dielectric side. The groove is located between the electrode fingers of the adjacent first comb electrode and the electrode fingers of the second comb electrode.

In the boundary acoustic wave device according to the present invention, a groove located between the electrode finger of the adjacent first comb electrode and the electrode finger of the second comb electrode is formed on the surface of the piezoelectric body on the dielectric side. Yes. Therefore, the distance between the electrode fingers of the adjacent first comb electrode and the electrode finger of the second comb electrode is relatively long, and the adjacent first comb electrode The dielectric constant of the region between the electrode finger and the electrode finger of the second comb electrode can be made relatively low. Therefore, even in the boundary acoustic wave device having a small pitch between the electrode fingers of the adjacent first comb electrodes and the electrode fingers of the second comb electrodes, the surge withstand voltage of the boundary acoustic wave device can be increased. That is, in the boundary acoustic wave device, high frequency can be achieved while maintaining a high surge withstand voltage.

In a specific aspect of the boundary acoustic wave device according to the present invention, the dielectric includes a first dielectric layer laminated on one surface of the piezoelectric body, and a first dielectric layer laminated on the first dielectric layer. A second dielectric layer having a speed of sound greater than the speed of sound of the layer. In this case, the resonance frequency and antiresonance frequency can be further increased. In other words, when the resonance frequency and the anti-resonance frequency are the same, the electrode fingers of the adjacent first comb electrodes and the second comb electrodes are formed by forming the groove and the second dielectric layer. The pitch with the electrode fingers can be made relatively long. Therefore, the surge withstand voltage of the boundary acoustic wave device can be further increased.

In another specific aspect of the boundary acoustic wave device according to the present invention, the cross-sectional shape of the groove along the propagation direction of the boundary acoustic wave is rectangular. In this case, the distance between the electrode finger of the adjacent first comb electrode and the electrode finger of the second comb electrode is further increased on the surface of the piezoelectric body, and the electrode of the adjacent first comb electrode The dielectric constant of the region between the finger and the electrode finger of the second comb electrode can be further increased. Therefore, the surge withstand voltage of the boundary acoustic wave device can be further increased.

In another specific aspect of the boundary acoustic wave device according to the present invention, the cross-sectional shape of the groove along the propagation direction of the boundary acoustic wave is a trapezoid that becomes narrower in the depth direction. In this case, since the dielectric can be easily formed by the deposition method, the boundary acoustic wave device can be easily manufactured.

The method for manufacturing a boundary acoustic wave device according to the present invention relates to a method for manufacturing the boundary acoustic wave device according to the present invention. The method for manufacturing a boundary acoustic wave device according to the present invention includes an electrode forming step of forming an electrode on a piezoelectric body, a groove forming step of forming a groove on the piezoelectric body, and a step of laminating a dielectric on one surface of the piezoelectric body. Is provided.

According to the method for manufacturing the boundary acoustic wave device of the present invention, the groove located between the electrode finger of the adjacent first comb electrode and the electrode finger of the second comb electrode is formed on the dielectric side of the piezoelectric body. Formed on the surface. Therefore, the distance between the electrode fingers of the adjacent first comb electrode and the electrode finger of the second comb electrode is relatively long, and the adjacent first comb electrode The dielectric constant of the region between the electrode finger and the electrode finger of the second comb electrode can be made relatively low. Therefore, it is possible to manufacture a boundary acoustic wave device with a small surge between the electrode fingers of the adjacent first comb electrodes and the electrode fingers of the second comb electrodes and a high surge withstand voltage.

Note that the order of performing the electrode forming step and the groove forming step is not particularly limited. For example, the groove forming process may be performed after performing the electrode forming process, or the electrode forming process may be performed after performing the groove forming process.

In a specific aspect of the method for manufacturing the boundary acoustic wave device according to the present invention, the method for manufacturing the boundary acoustic wave device includes a frequency of the piezoelectric body on which the first and second comb electrodes are formed after the electrode forming step. A step of measuring the characteristics, and the groove forming step includes a frequency characteristic of the boundary acoustic wave device corresponding to the measured frequency characteristics and a predetermined target frequency of the boundary acoustic wave device. In this step, the groove is formed so as to have a depth that reduces the difference from the characteristics. In this case, the frequency characteristic is adjusted by adjusting the depth of the groove formed in accordance with the frequency characteristic of the piezoelectric body on which the first and second comb electrodes are measured before the groove is formed. Adjustments are made. For this reason, the dispersion | variation in the frequency characteristic of the boundary acoustic wave apparatus manufactured can be reduced.

In the groove forming step, the groove depth is substantially the same as the frequency characteristic of the boundary acoustic wave device corresponding to the measured frequency characteristic and the target frequency characteristic of the predetermined boundary acoustic wave device. It is preferable to be a step of forming a groove so as to have a depth. According to this, the dispersion | variation in the frequency characteristic of the elastic boundary wave apparatus manufactured can be reduced more.

Here, “frequency characteristics” refers to the overall characteristics related to frequency. The frequency characteristics include, for example, a resonance frequency and an antiresonance frequency when the boundary acoustic wave device is a resonator, and a center frequency when the boundary acoustic wave device is a filter.

In another specific aspect of the method for manufacturing the boundary acoustic wave device according to the present invention, the method for manufacturing the boundary acoustic wave device includes: a piezoelectric body on which the first and second comb electrodes are formed after the groove forming step; The step of measuring the frequency characteristic and the depth of the groove reduce the difference between the frequency characteristic of the boundary acoustic wave device corresponding to the measured frequency characteristic and the target frequency characteristic of the predetermined boundary acoustic wave device. And a step of deepening the groove formed in the groove forming step so as to obtain a depth to be formed. In this case, the frequency characteristic is adjusted by adjusting the depth of the groove in accordance with the frequency characteristic of the piezoelectric body on which the first and second comb electrodes are formed measured after the groove forming step. Is called. For this reason, the dispersion | variation in the frequency characteristic of the boundary acoustic wave apparatus manufactured can be reduced.

In the step of deepening the groove, the groove depth is substantially equal to the frequency characteristic of the boundary acoustic wave device corresponding to the measured frequency characteristic and the target frequency characteristic of the predetermined boundary acoustic wave device. It is preferable to deepen the grooves formed in the groove forming step so as to have the same depth. According to this, the dispersion | variation in the frequency characteristic of the elastic boundary wave apparatus manufactured can be reduced more.

In another specific aspect of the method for manufacturing a boundary acoustic wave device according to the present invention, the method for manufacturing the boundary acoustic wave device includes a first dielectric layer on one surface of the piezoelectric body after the electrode forming step and the groove forming step. A step of measuring, a step of measuring frequency characteristics of the piezoelectric body on which the first dielectric layer is formed, and an electrode finger of the first comb electrode and an electrode finger of the second comb electrode in the propagation direction. The thicknesses of the first dielectric layers in the alternately arranged regions are determined based on the frequency characteristics of the boundary acoustic wave device according to the measured frequency characteristics and the target frequency characteristics of the predetermined boundary acoustic wave device. Increasing or decreasing to a thickness that reduces the difference between and a second dielectric layer having a speed of sound higher than the speed of sound of the first dielectric layer, and laminating the first dielectric layer, Forming a dielectric having a first dielectric layer and a second dielectric layer; Further comprising the step. In this case, the frequency characteristic is adjusted by adjusting the thickness of the first dielectric layer according to the frequency characteristic of the piezoelectric body on which the first dielectric layer is formed. For this reason, the dispersion | variation in the frequency characteristic of the boundary acoustic wave apparatus manufactured can be reduced.

The step of increasing or decreasing the thickness of the first dielectric layer is performed in a region where the electrode fingers of the first comb electrode and the electrode fingers of the second comb electrode are alternately arranged in the propagation direction. The thickness of the first dielectric layer is substantially the same as the frequency characteristic of the boundary acoustic wave device according to the measured frequency characteristic and the target frequency characteristic of the predetermined boundary acoustic wave device. A step of increasing or decreasing the thickness is preferable. According to this, the dispersion | variation in the frequency characteristic of the elastic boundary wave apparatus manufactured can be reduced more.
(The invention's effect)

In the boundary acoustic wave device according to the present invention, a groove located between the electrode finger of the adjacent first comb electrode and the electrode finger of the second comb electrode is formed on the surface of the piezoelectric body on the dielectric side. Yes. For this reason, according to the present invention, in the boundary acoustic wave device, high frequency can be achieved while maintaining a high surge breakdown voltage.

FIG. 1 is a cross-sectional view showing a part of the boundary acoustic wave device according to the first embodiment. FIG. 2 is a plan view of the boundary acoustic wave device. FIG. 3 is a flowchart showing a manufacturing process of the boundary acoustic wave device according to the first embodiment. FIG. 4 is a flowchart showing a manufacturing process of the boundary acoustic wave device according to the second embodiment. FIG. 5 is a flowchart showing a manufacturing process of the boundary acoustic wave device according to the third embodiment. FIG. 6 is a cross-sectional view illustrating a part of the boundary acoustic wave device according to the fourth embodiment. FIG. 7 is a cross-sectional view illustrating a part of the boundary acoustic wave device according to the fifth embodiment. FIG. 8 is a cross-sectional view showing a part of the boundary acoustic wave device according to the sixth embodiment. FIG. 9 is a flowchart illustrating an example of a manufacturing process of the boundary acoustic wave device according to the sixth embodiment. FIG. 10 is an evaluation circuit diagram of a surge breakdown voltage in the first embodiment. FIG. 11 is a graph showing the correlation between the surge breakdown voltage ratio and the depth of the groove 11 in Example 1. FIG. 12 is a cross-sectional view of a boundary acoustic wave device having an FEM calculation model in the second embodiment. FIG. 13 is a graph showing the results of TCF simulation in Example 2. FIG. 14 is a graph showing the result of simulation of the electromechanical coupling coefficient in Example 2. FIG. 15 is a graph showing the result of simulation of the sound velocity (V) in the second embodiment. FIG. 16 is a graph showing TCF measurement results in Example 3. FIG. 17 is a graph showing the measurement result of the resonance frequency in Example 3. FIG. 18 is a graph showing the measurement result of the bandwidth ratio in Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Elastic boundary wave apparatus 10 ... Piezoelectric body 10a ... Surface 11 ... Groove 20 ... Dielectric material 21 ... 1st dielectric material layer 22 ... 2nd dielectric material layer 30 ... Electrode 31 ... 1st comb-tooth electrode 31a ... 1st 1 bus bar 31b ... 1st electrode finger 32 ... 2nd comb-tooth electrode 32a ... 2nd bus bar 32b ...

2nd electrode finger

33, 34 ... Grating reflector 35 ... 1st terminal 36 ... 2nd terminal 37 ... IDT

Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

(First embodiment)
FIG. 1 is a sectional view showing a part of a boundary acoustic wave device 1 according to the first embodiment. FIG. 2 is a plan view of the boundary acoustic wave device 1. For convenience of explanation, the drawing of the dielectric 20 is omitted in FIG.

In this embodiment, an example in which the boundary acoustic wave device is a resonator will be described. However, in the present invention, the boundary acoustic wave device is not limited to a resonator. The boundary acoustic wave device may be, for example, a filter using a boundary acoustic wave. Specific examples of the filter include a longitudinally coupled resonator type filter and a ladder type filter.

In the present invention, the type of boundary acoustic wave is not particularly limited. The boundary acoustic wave may be, for example, an SH type boundary acoustic wave or a Stoneley wave.

As shown in FIG. 1, the boundary acoustic wave device 1 includes a piezoelectric body 10. A dielectric 20 is stacked on one surface of the piezoelectric body 10. An electrode 30 is disposed at the boundary between the piezoelectric body 10 and the dielectric body 20.

The piezoelectric body 10 and the dielectric body 20 are not particularly limited as long as the piezoelectric body 10 and the dielectric body 20 are a combination that generates a boundary acoustic wave at the boundary between the piezoelectric body 10 and the dielectric body 20. For example, the dielectric 20 _is, SiO 2, SiON, or may be formed of SiN or the like. The piezoelectric body 10 may be made of, for example, LiNbO ₃ or LiTaO ₃ . More specifically, the piezoelectric body 10 may be, for example, 15 ° Y-cut X-propagation LiNbO ₃ .

The material of the electrode 30 is not particularly limited. The electrode 30 can be formed of, for example, any one of Pt, Au, Cu, Ag, Al, and W, or an alloy obtained by adding other elements to Pt, Au, Cu, Ag, Al, and W. The electrode 30 may be composed of a plurality of conductive layers made of different materials. For example, the electrode 30 may be configured by a metal layer or alloy layer having strong adhesion to the piezoelectric body 10 and the dielectric 20 and the metal layer or alloy layer. Examples of the metal or alloy having strong adhesion to the piezoelectric body 10 and the dielectric body 20 include NiCr, Ti, and Cr.

As shown in FIG. 2, the electrode 30 includes an IDT 37 and

grating reflectors

33 and 34. The

grating reflectors

33 and 34 are disposed on both sides of the IDT 37 in the propagation direction d of the boundary acoustic wave. The IDT 37 includes a first comb electrode 31 and a second comb electrode 32.

The first comb electrode 31 is connected to the first terminal 35. The second comb electrode 32 is connected to the second terminal 36. The first terminal 35 and the second terminal 36 are connected to different potentials.

The first comb electrode 31 includes a first bus bar 31a and a plurality of first electrode fingers 31b connected to the first bus bar 31a. The plurality of first electrode fingers 31b are arranged substantially parallel to each other.

The second comb electrode 32 includes a second bus bar 32a and a plurality of second electrode fingers 32b connected to the second bus bar 32a. The plurality of second electrode fingers 32b are arranged in parallel to each other. The plurality of second electrode fingers 32b are alternately arranged with the first electrode fingers 31b in the propagation direction d of the boundary acoustic wave.

The pitch (electrode finger center interval) between the first electrode finger 31b and the second electrode finger 32b is not particularly limited. The pitch between the first electrode finger 31b and the second electrode finger 32b can be appropriately set according to the desired frequency characteristics. The pitch between the first electrode finger 31b and the second electrode finger 32b is generally set to about 0.5 μm to 3 μm.

The pitch (distance between electrode finger centers) between the first electrode finger 31b and the second electrode 32b is represented by λ / 2. Here, λ is the period of the IDT 37.

As shown in FIG. 1, a plurality of grooves 11 are formed on the surface 10a of the piezoelectric body 10 on the dielectric 20 side. The groove 11 extends in the extending direction of the

electrode fingers

31b and 32b between the adjacent first electrode finger 31b and the second electrode finger 32b. In addition, it is preferable that the groove | channel 11 is formed in all between the adjacent 1st electrode finger 31b and the 2nd electrode finger 32b. However, the groove 11 does not necessarily have to be formed at all between the adjacent first electrode finger 31b and the second electrode finger 32b.

Moreover, the groove | channel 11 may be formed in the whole between the adjacent 1st electrode finger 31b and the 2nd electrode finger 32b in planar view, and the adjacent 1st electrode finger 31b and 2nd You may form only in a part between electrode fingers 32b. However, it is preferable that the first electrode finger 31b and the second electrode finger 32b adjacent to each other are formed on the entire surface. This is because the surge withstand voltage of the boundary acoustic wave device 1 can be increased and the frequency temperature coefficient (TCF) can be reduced.

In the present embodiment, the cross-sectional shape of the groove 11 along the propagation direction D is a rectangle. The depth of the groove 11 is not particularly limited. The depth of the groove 11 can be appropriately set according to a desired surge withstand voltage, frequency temperature coefficient (TCF), or the like. The depth of the groove 11 can typically be set to about 0 to 500 nm.

Generally, the surge withstand voltage of the boundary acoustic wave device tends to decrease as the distance between the first electrode finger and the second electrode finger becomes shorter. For this reason, if the distance between the first electrode finger and the second electrode finger is shortened to increase the resonance frequency and anti-resonance frequency of the boundary acoustic wave device, the surge withstand voltage of the boundary acoustic wave device decreases. Become. That is, it is usually difficult to increase the resonance frequency and antiresonance frequency while maintaining the surge withstand voltage.

In contrast, in the present embodiment, the groove 11 is formed between the first electrode finger 31b and the second electrode finger 32b. For this reason, the distance on the surface 10a of the piezoelectric body 10 between the 1st electrode finger 31b and the 2nd electrode finger 32b can be made comparatively large. In addition, the substantial dielectric constant of the region between the adjacent first electrode finger 31b and the second electrode finger 32b can be made relatively small. Therefore, according to the present embodiment, the surge withstand voltage can be increased as compared with the case where the groove 11 is not formed between the first electrode finger 31b and the second electrode finger 32b. That is, according to the present embodiment, the surge withstand voltage can be increased even when the distance between the first electrode finger 31b and the second electrode finger 32b is short. Therefore, it is possible to increase the frequency of the boundary acoustic wave device 1 while maintaining the surge withstand voltage of the boundary acoustic wave device 1 high.

Also, the frequency temperature coefficient can be adjusted by changing the depth of the groove 11. Therefore, the absolute value of the frequency temperature coefficient can be further reduced by adjusting the depth of the groove 11. Specifically, for example, when the piezoelectric body 10 has a negative temperature characteristic and the dielectric body 20 has a positive temperature characteristic, the frequency temperature coefficient can be shifted to the positive side by deepening the groove 11. it can. Usually, in the boundary acoustic wave device in which the groove 11 is not formed, when the piezoelectric body 10 has a negative temperature characteristic and the dielectric body 20 has a positive temperature characteristic, the frequency temperature coefficient is negative. For this reason, the frequency temperature coefficient can be shifted to the positive side by forming the groove 11. Therefore, the absolute value of the frequency temperature coefficient of the boundary acoustic wave device can be reduced.

For example, when the piezoelectric body 10 is formed of LiNbO ₃ and the dielectric body 20 is formed of SiO ₂ , a relatively large electromechanical coupling coefficient K ² can be obtained. Moreover, LiNbO ₃ has negative temperature characteristics, while SiO ₂ has positive temperature characteristics. For this reason, the frequency temperature coefficient can be made relatively small by forming the piezoelectric body 10 from LiNbO _{3 and} forming the dielectric body 20 from SiO ₂ . However, since the negative temperature characteristic of LiNbO ₃ is larger than the positive temperature characteristic of SiO ₂ , it is difficult to sufficiently reduce the absolute value of the frequency temperature coefficient.

However, in this embodiment, the frequency temperature coefficient is shifted to the positive side by forming the groove 11. Therefore, the piezoelectric body 10 is formed of SiO ₂ , the dielectric body 20 is formed of LiNbO ₃ , and the groove 11 is formed, whereby an elastic boundary where the electromechanical coupling coefficient K ² is large and the absolute value of the frequency temperature coefficient is small. A wave device can be realized.

Further, the depth and the electromechanical coupling coefficient K ² of the groove 11, as can be seen from the following examples, has a correlation. Therefore, by adjusting the depth of the groove 11, it is possible to adjust the electromechanical coefficient K ^2.

Furthermore, the depth of the groove 11 and the frequency characteristic of the boundary acoustic wave device 1 have a correlation as can be seen from the following examples. For this reason, the frequency characteristic of the boundary acoustic wave device 1 can be adjusted by adjusting the depth of the groove 11.

Thus, by adjusting the depth of the groove 11, can be adjusted frequency temperature coefficient, the frequency characteristics of the electro-mechanical coupling coefficient K ² and the boundary acoustic wave device 1. That is, by providing the groove 11, the temperature coefficient of frequency, the frequency characteristics of the electro-mechanical coupling coefficient K ² and the boundary acoustic wave device 1 can be adjusted.

Note that the cross-sectional shape of the groove 11 is preferably rectangular. By making the cross-sectional shape of the groove 11 rectangular, the distance on the surface 10a of the piezoelectric body 10 between the first electrode finger 31b and the second electrode finger 32b can be further increased. Therefore, the surge withstand voltage of the boundary acoustic wave device 1 can be further increased. In this case, the frequency temperature coefficient of the boundary acoustic wave device can be effectively shifted to the temperature characteristic side of the dielectric 20. Therefore, the frequency temperature coefficient of the boundary acoustic wave device can be effectively reduced.

Next, a method for manufacturing the boundary acoustic wave device 1 will be described. However, the manufacturing method of the boundary acoustic wave device 1 shown below is merely an example. The manufacturing method of the boundary acoustic wave device according to the present invention is not limited to the following method.

As shown in FIG. 3, first, in step S1, the piezoelectric body 10 is prepared.

Next, in step S2, an electrode forming process for forming the electrode 30 on the piezoelectric body 10 is performed. The electrode 30 can be formed, for example, by forming a metal film or an alloy film by a known thin film forming method and then patterning by a known patterning method. Examples of the thin film forming method include an electron beam evaporation method and a sputtering method. Examples of the patterning method include a photolithography method.

Next, in step S3, a groove forming step for forming the grooves 11 is performed. The groove 11 can be formed by, for example, a known etching method. Specific examples of the etching method include dry etching such as reactive ion etching, wet etching using an etchant, and the like. Examples of ions used in the reactive ion etching method include fluorine ions. An etchant used for wet etching includes, for example, hydrofluoric acid. Further, the groove 11 may be formed by milling using Ar ions, for example.

In formation of the groove 11, for example, the electrode 30 may be used as a mask for patterning, and a separately formed oxide film such as SiO ₂ or a nitride film such as Si ₃ N ₄ may be used as a mask for patterning. It may be used as

Next, the boundary acoustic wave device 1 is completed by forming the dielectric 20 in step S4. The method for forming the dielectric 20 is not particularly limited. The dielectric 20 can be formed by, for example, a known film forming method. Specifically, the dielectric 20 can be formed by, for example, a sputtering method such as RF magnetron sputtering.

(Second Embodiment)
In the first embodiment, the case where the groove 11 having a predetermined shape and dimension is formed and the dimension of the groove 11 is not adjusted has been described. However, in the manufacturing process of the boundary acoustic wave device, the dimension of the groove 11 may be adjusted for the purpose of adjusting the frequency characteristics and the like. Hereinafter, the manufacturing process of the boundary acoustic wave device according to the present embodiment will be described with reference to FIG. In the following description, FIGS. 1 and 2 are referred to in common with the first embodiment. In addition, members having substantially the same functions as those of the first embodiment are referred to by common reference numerals, and description thereof is omitted.

Also in this embodiment, step S1 and step S2 are performed as shown in FIG. In the second embodiment, step S5 is performed subsequent to step S2. In step S5, the frequency characteristic of the piezoelectric body 10 on which the electrode 30 is formed is measured. Specifically, when the boundary acoustic wave device to be manufactured as in this embodiment is a resonator, in step S5, for example, at least one of a resonance frequency and an anti-resonance frequency is measured. For example, when the boundary acoustic wave device to be manufactured is a filter, in step S5, for example, the center frequency is measured.

Next, in step S6, the depth of the groove 11 is determined. Specifically, the difference between the frequency characteristic of the boundary acoustic wave device 1 estimated according to the frequency characteristic measured in step S5 and the target frequency characteristic of the boundary acoustic wave device 1 determined in advance is reduced. As described above, the depth of the groove 11 is determined. Preferably, the frequency characteristic of the boundary acoustic wave device 1 estimated according to the frequency characteristic measured in step S5 is substantially the same as the target frequency characteristic of the predetermined boundary acoustic wave device 1. As described above, the depth of the groove 11 is determined.

Next, in step S7, the groove 11 is formed. In step S7, the groove 11 having the depth calculated in step S6 is formed. Thereafter, the boundary acoustic wave device 1 is completed by forming the dielectric 20 in step S4.

By the way, due to the formation variation of the electrode 30, the frequency characteristics of the produced boundary acoustic wave device may vary. On the other hand, as in this embodiment, the frequency characteristic of the piezoelectric body 10 on which the electrode 30 is formed is measured, and the groove 11 having a depth determined based on the measurement result is formed. The frequency characteristics of the boundary acoustic wave device can be finely adjusted. Therefore, variation in frequency characteristics of the produced boundary acoustic wave device 1 can be reduced. Specifically, for example, when the boundary acoustic wave device is a resonator, it is possible to suppress variation in at least one of the resonance frequency and the antiresonance frequency. For example, when the boundary acoustic wave device is a filter, it is possible to suppress variations in the center frequency.

(Third embodiment)
In the second embodiment, the example in which the frequency characteristic is measured before the formation of the groove 11 in step S7 has been described. However, the timing at which the frequency characteristic is measured is not limited to before the groove 11 is formed.

For example, as shown in FIG. 5, after the groove 11 having a predetermined depth is formed in step S3, the frequency characteristic may be measured in step S8. In step S8, the frequency characteristic of the piezoelectric body 10 in which the electrode 30 and the groove 11 are formed is measured.

Next, in step S9, the adjustment amount of the depth of the groove 11 is determined. Specifically, the difference between the frequency characteristic of the boundary acoustic wave device 1 estimated according to the frequency characteristic measured in step S8 and the target frequency characteristic of the boundary acoustic wave device 1 determined in advance is reduced. The depth of the groove 11 is calculated. Preferably, the frequency characteristic of the boundary acoustic wave device 1 estimated according to the frequency characteristic measured in step S8 is substantially the same as the target frequency characteristic of the predetermined boundary acoustic wave device 1. The depth of the groove 11 is calculated. An adjustment amount of the depth of the groove 11 is determined from the calculated preferable depth of the groove 11 and the current depth of the groove 11.

Next, in step S10, the depth of the groove 11 is adjusted. Specifically, the groove 11 is deepened so that the depth of the groove 11 becomes the depth calculated in step S9. As a method for deepening the groove 11, a known etching method, milling method, or the like can be used.

Then, in step S4, the boundary acoustic wave device 1 is completed by forming the dielectric 20.

Also in the present embodiment, since the depth of the groove 11 is adjusted based on the measurement result of the frequency characteristic, similarly to the second embodiment, variation in the frequency characteristic of the boundary acoustic wave device 1 to be manufactured is reduced. be able to.

(Fourth and fifth embodiments)
In the first embodiment, the case where the cross-sectional shape of the groove 11 is rectangular has been described. However, the cross-sectional shape of the groove 11 is not limited to a rectangle. For example, as shown in FIG. 6, the cross-sectional shape of the groove 11 may be, for example, a trapezoid that becomes narrower in the depth direction. Moreover, as shown in FIG. 7, the cross-sectional shape of the groove | channel 11 may be a triangle which becomes narrow toward a depth direction, for example. By forming the cross-sectional shape of the groove 11 into a trapezoid or triangle that becomes narrower in the depth direction, the dielectric 20 can be easily formed by a deposition method.

(Sixth embodiment)
In the first embodiment, the example in which the dielectric 20 is configured by one dielectric layer has been described. However, the dielectric 20 may be formed of a plurality of dielectric layers as shown in FIG.

In the boundary acoustic wave device according to this embodiment shown in FIG. 8, the dielectric 20 includes a first dielectric layer 21 and a second dielectric layer 22. The first dielectric layer 21 is formed so as to cover the piezoelectric body 10 and the electrode 30. The second dielectric layer 22 is formed on the first dielectric layer 21. In the present embodiment, the sound speed of the second dielectric layer 22 is faster than the sound speed of the first dielectric layer 21. For this reason, according to the present embodiment, the frequency characteristics of the boundary acoustic wave can be increased. Therefore, the distance between the first electrode finger 31b and the second electrode finger 32b adjacent to each other can be made relatively wide as compared with the case where the dielectric layer 20 is formed only by the first dielectric material 21. Therefore, the surge withstand voltage of the boundary acoustic wave device can be further increased.

Further, the frequency characteristic of the boundary acoustic wave device obtained by adjusting the thickness of the first dielectric layer 21 can be adjusted. Therefore, it is possible to reduce variation in frequency characteristics of the manufactured boundary acoustic wave device 1.

FIG. 9 is a flowchart showing an example of a manufacturing process of the boundary acoustic wave device according to the sixth embodiment. As shown in FIG. 9, in this embodiment as well, in the same manner as in the first embodiment, the preparation of the piezoelectric body 10 in step S1, the formation of the electrode 30 in step S2, and the formation of the groove 11 in step S3 are sequentially performed. .

In this embodiment, step S11 is performed following step S3. In step S11, the first dielectric layer 21 having a predetermined thickness is formed. Thereafter, in step S12, the frequency characteristics of the piezoelectric body 10 on which the first dielectric layer 21 is formed are measured.

Next, in step S13, the adjustment amount of the thickness of the first dielectric layer 21 is determined. Specifically, the difference between the frequency characteristic of the boundary acoustic wave device 1 estimated according to the frequency characteristic measured in step S12 and the target frequency characteristic of the boundary acoustic wave device 1 determined in advance is reduced. The thickness of the first dielectric layer 21 is calculated. Preferably, the frequency characteristics of the boundary acoustic wave device 1 estimated according to the frequency characteristics measured in step S12 are substantially the same as the target frequency characteristics of the predetermined boundary acoustic wave device 1. The thickness of the first dielectric layer 21 is calculated.

Next, in step S14, the thickness of the first dielectric layer 21 is adjusted. Specifically, the thickness of the first dielectric layer 21 is adjusted so that the thickness of the first dielectric layer 21 becomes the thickness determined in step S13.

Next, in step S15, the second dielectric layer 22 is formed, and the boundary acoustic wave device is completed.

According to this manufacturing process, since the thickness of the first dielectric layer 21 is adjusted based on the measured frequency characteristics, variations in the frequency characteristics of the manufactured boundary acoustic wave device 1 can be reduced. .

In this embodiment, the depth of the groove 11 may be adjusted by measuring the frequency characteristics before or after the formation of the groove 11.

Hereinafter, the present invention will be clarified by giving specific embodiments and examples of the present invention.

Example 1
A one-port resonator 1 shown in FIGS. 1 and 2 was produced. Specifically, a 15 ° Y-cut LiNbO ₃ single crystal substrate was used as the piezoelectric body 10. An electrode 30 having a total film thickness of 315 nm was formed on the piezoelectric body 10 by forming a film by electron beam evaporation and then patterning by photolithography. The structure of the electrode 30 is NiCr film (film thickness: 30 nm) / AlCu film (film thickness: 150 nm) / Ti film (film thickness: 10 nm) / Pt film (film thickness: 105 nm) / NiCr film (film) from the piezoelectric body side. (Thickness: 10 nm). Note that λ is 1.6 μm, and the width of the electrode finger is 1 / 4λ. Next, the groove 11 was formed by etching the piezoelectric body 10 by reactive ion etching using a fluorine-based gas using the NiCr film located on the uppermost layer of the electrode 30 as a mask. Thereafter, a dielectric 20 was formed by forming a SiO ₂ film having a thickness of 5000 nm by RF magnetron sputtering, and the resonator 1 was obtained.

A machine model evaluation circuit shown in FIG. 10 was formed using the obtained resonator 1, and the surge breakdown voltage of the resonator 1 was measured based on the EIA / JESD22-A115-A standard. Specifically, first, the resonator 1 and the capacitor C having a capacitance of 200 pF were connected in parallel to the high voltage pulse power supply G. Then, a voltage was applied to the capacitor C by the high voltage pulse power source G with the switch SW connected to the high voltage pulse power source G side. Thereafter, the switch SW was switched to connect the capacitor C and the resonator 1, thereby applying a surge voltage to the resonator 1. Thereafter, whether or not the resonator 1 was broken was observed with a microscope, and impedance characteristics were measured. Repeat this inspection while increasing the voltage of the high-voltage pulse power supply in increments of 2 to 3 V. Surge breakdown voltage.

The measurement results of the surge breakdown voltage normalized with the surge breakdown voltage of the resonator in which the groove 11 is not formed are shown in Table 1 and FIG.

As shown in Table 1 and FIG. 11, it can be seen that the surge breakdown voltage is increased by forming the groove 11. That is, it can be seen that the surge withstand voltage of the resonator can be increased by forming the groove 11. It can also be seen that the surge breakdown voltage can be further increased by deepening the groove 11.

(Example 2)
Next, using the boundary acoustic wave device shown in FIG. 12 as a calculation model, the depth of the groove 11, the specific bandwidth, the electromechanical coupling coefficient K ² , the frequency temperature coefficient (TCF), and the speed of sound are each determined by a finite element method (FEM). The relationship was simulated. The simulation conditions are shown in Table 2 below. The simulation results are shown in Table 3 and FIGS.

The specific bandwidth is defined by the following formula (1).

(Fractional ^{bandwidth) = Δf / fr = K 2} /2 = (Vo1-Vs1) / Vs1 ····· (1)
However,
f: frequency,
fr: resonance frequency,
Vo1: boundary wave sound velocity at the open boundary,
Vs1: boundary wave sound velocity at the short-circuit boundary,
It is.

The frequency temperature coefficient (TCF) is defined by the following equation (2).

TCF = V ⁻¹ (25 ° C.) × {(V (30 ° C.) − V (20 ° C.)} / 10 (° C.) − ΑS (2)
However,
V (25 ° C.): speed of sound at 25 ° C.
V (30 ° C.): speed of sound at 30 ° C.
V (20 ° C.): speed of sound at 20 ° C.
αS: linear expansion coefficient,
It is.

As shown in Table 3 and FIG. 13, the value of the frequency temperature coefficient (TCF) can be increased by deepening the groove 11. It can be seen that the absolute value of the frequency temperature coefficient can be reduced by forming the groove 11 as compared to the case where the groove 11 is not formed. From the results shown in Table 3 and FIG. 13, the depth of the groove 11 is preferably 0.05λ or more, and more preferably 0.1λ or more and 0.15λ or less. This is because the absolute value of the frequency temperature coefficient can be particularly reduced by doing so.

Also, as shown in Table 3, it can be seen that the specific bandwidth can be changed by changing the depth of the groove 11. Specifically, it can be seen that the specific bandwidth can be narrowed by deepening the groove 11.

Further, as shown in Table 3 and FIG. 14, it can be seen that the electromechanical coupling coefficient K ² can be changed by changing the depth of the groove 11. Specifically, it can be seen that the electromechanical coupling coefficient K ² can be reduced by deepening the groove 11.

Also, as shown in Table 3 and FIG. 15, it can be seen that the sound velocity (V) can be changed by changing the depth of the groove 11. Specifically, it can be seen that the sound velocity (V) can be increased by deepening the groove 11.

These results, by adjusting the depth of the groove 11, the relative bandwidth, it can be seen capable of adjusting the respective electromechanical coupling coefficient K ² and the sound velocity (V).

(Example 3)
A 1-port resonator similar to that in Example 1 was fabricated in the same procedure as in Example 1. For the obtained resonator, the frequency temperature coefficient, the resonance frequency, and the ratio band were measured. Specifically, the impedance temperature was measured, the frequency at each temperature was measured, and the frequency temperature coefficient (TCF), resonance frequency, and ratio band were obtained by applying the measurement results to the following formulas (3) and (4). .

fr: resonance frequency fa: anti-resonance frequency TCF = {(fr (60 ° C.) − fr (25 ° C.)) / fr (25 ° C.)} / (60 ° C.-25 ° C.) (3)
Ratio band = {(fa (25 ° C.) − Fr (25 ° C.)) / Fr (25 ° C.)} × 100 (4)

The results are shown in the following Table 4 and FIGS.

As shown in Table 4 and FIGS. 16 to 18, it can be seen that the frequency temperature coefficient is improved by deepening the groove 11 in the measurement results of this example as well as the simulation results. Moreover, it turns out that the depth of the groove | channel 11 and each of a resonant frequency and a specific band have a correlation. Specifically, as shown in FIG. 17, it can be seen that the resonance frequency is shifted to the lower frequency side by deepening the groove 11. In addition, as shown in FIG. 18, it can be seen that the ratio band is reduced by deepening the groove 11. From the above, it can be seen that each of the resonance frequency and the ratio band can be adjusted by adjusting the depth of the groove 11.

Claims

A piezoelectric body, a dielectric layer laminated on one surface of the piezoelectric body, and an electrode disposed at a boundary between the piezoelectric body and the dielectric body, and elastic using boundary acoustic waves propagating through the boundary A boundary wave device,
The electrode has a first comb electrode having a plurality of electrode fingers, and a plurality of electrode fingers alternately arranged with the electrode fingers of the first comb electrode in the propagation direction of the boundary acoustic wave, A second comb electrode connected to a potential different from that of the first comb electrode;
The surface of the piezoelectric body on the dielectric side is positioned between the electrode fingers of the adjacent first comb electrodes and the electrode fingers of the second comb electrodes, and extends in the extending direction of the electrode fingers. A boundary acoustic wave device in which grooves are formed.
The dielectric has a first dielectric layer laminated on one surface of the piezoelectric body, and a second dielectric layer laminated on the first dielectric layer and having a sound velocity faster than that of the first dielectric layer. The boundary acoustic wave device according to claim 1, comprising: a dielectric layer.
3. The boundary acoustic wave device according to claim 1, wherein a cross-sectional shape of the groove along a propagation direction of the boundary acoustic wave is a rectangle.
3. The boundary acoustic wave device according to claim 1, wherein a cross-sectional shape of the groove along a propagation direction of the boundary acoustic wave is a trapezoid that becomes narrower in a depth direction.
A method for manufacturing a boundary acoustic wave device according to claim 1,
Forming an electrode on the piezoelectric body; and
A groove forming step of forming the groove in the piezoelectric body;
And a step of laminating the dielectric on one surface of the piezoelectric body.
After the electrode forming step, further comprising a step of measuring frequency characteristics of the piezoelectric body on which the first and second comb electrodes are formed,
In the groove forming step, the depth of the groove is a difference between a frequency characteristic of the boundary acoustic wave device according to the measured frequency characteristic and a predetermined frequency characteristic of the boundary acoustic wave device. The method for manufacturing a boundary acoustic wave device according to claim 5, wherein the groove is formed so as to have a depth to reduce the depth.
Measuring the frequency characteristics of the piezoelectric body on which the first and second comb electrodes are formed after the groove forming step;
The depth of the groove is a depth that reduces a difference between the frequency characteristic of the boundary acoustic wave device according to the measured frequency characteristic and a predetermined frequency characteristic of the boundary acoustic wave device. The method for manufacturing the boundary acoustic wave device according to claim 5, further comprising a step of deepening the groove formed in the groove forming step.
Forming a first dielectric layer on one surface of the piezoelectric body after the electrode forming step and the groove forming step;
Measuring the frequency characteristics of the piezoelectric body on which the first dielectric layer is formed;
The thickness of the first dielectric layer in the region where the electrode fingers of the first comb electrode and the electrode fingers of the second comb electrode are alternately arranged in the propagation direction is measured. Increasing or decreasing to a thickness that reduces a difference between a frequency characteristic of the boundary acoustic wave device according to the frequency characteristic and a target frequency characteristic of the boundary acoustic wave device determined in advance;
The first dielectric layer and the second dielectric layer are formed by laminating a second dielectric layer having a speed of sound higher than that of the first dielectric layer on the first dielectric layer. The method for manufacturing the boundary acoustic wave device according to claim 5, further comprising: forming the dielectric body including: