JP4998032B2 - Boundary acoustic wave device - Google Patents

Description

  The present invention relates to a boundary acoustic wave device used for, for example, a bandpass filter and a resonator, and a manufacturing method thereof, and more specifically, an elastic boundary in which an elastic discontinuity is formed in a medium in which the boundary acoustic wave propagates. The present invention relates to a wave device and a manufacturing method thereof.

Conventionally, surface acoustic wave devices have been widely used as bandpass filters and resonators. In order to reduce the size, a boundary acoustic wave device has been attracting attention in place of the surface acoustic wave device. For example, Patent Document 1 below discloses a boundary acoustic wave device 1001 shown in FIG. The boundary acoustic wave device 1001 has a structure in which a piezoelectric body 1002 and a dielectric body 1003 are stacked. An IDT electrode 1004 and reflectors 1005 and 1006 are formed at the interface between the piezoelectric body 1002 and the dielectric body 1003. Here, by using a metal having a high density such as Au as the IDT electrode 1004, the boundary acoustic wave is excited by concentrating vibration energy on the portion where the IDT electrode 1004 is provided.
WO2004 / 070946

In the boundary acoustic wave device described in Patent Document 1, a structure using, for example, LiNbO ₃ as a piezoelectric body and SiO ₂ as a dielectric is disclosed. When a laminated structure is expressed in order from the top, SiO ₂ / A stacked structure of IDT electrode / LiNbO ₃ is shown. Although such a structure is relatively simple, in order to improve the group delay time temperature coefficient TCD in the boundary acoustic wave device 1001, various materials of the piezoelectric body 1002, the dielectric body 1003, and the IDT electrode 1004 are changed, It is necessary to adjust the thickness of the IDT electrode 1004 and the width of the electrode finger.

  However, when such a material change or adjustment of the thickness or electrode finger width of the IDT electrode 1004 is performed, the propagation characteristics of the boundary acoustic wave tend to be greatly affected. Therefore, characteristics other than the TCD of the boundary acoustic wave device may be deteriorated, and it is difficult to improve the group delay time temperature coefficient TCD without impairing other performances.

  The object of the present invention is to provide an absolute value of the group delay time temperature coefficient TCD without significantly affecting the propagation characteristics of the boundary acoustic wave, that is, without significantly deteriorating other characteristics, in view of the current state of the prior art described above. It is an object of the present invention to provide a boundary acoustic wave device and a method for manufacturing the same.

According to the first invention of the present application, an IDT having a piezoelectric body, a dielectric layer laminated on the piezoelectric body, and a plurality of electrode fingers, and disposed at an interface between the piezoelectric body and the dielectric body. A first elastic discontinuity is formed along the side wall of each electrode finger of the IDT electrode, and the height dimension of the first elastic discontinuity is the IDT When the wavelength of the boundary acoustic wave excited by the IDT electrode is λ, the dimension in the boundary acoustic wave propagation direction of the first elastic discontinuity is 0.07λ or less. A boundary acoustic wave device is provided.

In the boundary acoustic wave device according to the first aspect of the present invention, preferably, the first elastic discontinuity is formed along side walls on both sides of each electrode finger. While further suppressing the deterioration of the electro-mechanical coupling coefficient K ^2, it is possible to adjust the absolute value of the absolute value and temperature coefficient of frequency TCF of the group delay time temperature coefficient TCD.

  In a specific aspect of the boundary acoustic wave device according to the first aspect of the invention, the IDT electrode is formed on a surface of the piezoelectric body laminated on the dielectric of the piezoelectric body, and the first elastic discontinuity portion is formed. Is formed in the dielectric.

  In another specific aspect of the boundary acoustic wave device according to the first invention, the IDT electrode is formed on a dielectric surface laminated on the piezoelectric body of the dielectric, and the first elastic A discontinuous portion is formed in the piezoelectric body.

According to the second invention of the present application, the piezoelectric body, the dielectric layer laminated on the piezoelectric body, and the IDT electrode disposed at the interface between the piezoelectric body and the dielectric body and having a plurality of electrode fingers A second elastic discontinuity disposed in the dielectric body or the piezoelectric body with a gap in a direction perpendicular to the interface from a space between adjacent electrode fingers in the plurality of electrode fingers. And the second elastic discontinuity is formed across the space and the gap in all the spaces between the adjacent electrode fingers, and the wavelength of the boundary acoustic wave excited by the IDT , The dimension of the boundary elastic wave propagation direction of the second elastic discontinuity is 0.10 λ or less, and further, the plurality of the second elastic discontinuities along the boundary acoustic wave propagation direction. Elastic discontinuities are provided with a period of λ / 2 Characterized Rukoto, boundary acoustic wave device is provided.

In the second invention, preferably, the dimension of the gap along a direction perpendicular to the previous SL interface than 0.05 [lambda], are the following 1 [lambda. In this case, even if the lower end of the second elastic discontinuity portion fluctuates up and down, the group delay time temperature coefficient TCD hardly varies. Therefore, it is possible to provide a boundary acoustic wave device with little variation in the group delay time temperature coefficient TCD.

In the boundary acoustic wave device according to the second aspect of the present invention, preferably, a first elastic discontinuity is formed along the sidewall of each electrode finger of the IDT electrode, and the elasticity excited by the IDT electrode. When the wavelength of the boundary wave is λ, the dimension of the first elastic discontinuity in the boundary acoustic wave propagation direction is 0.07λ or less . The first elastic discontinuity is likely to occur when the thickness of the IDT electrode is increased. Even in such a case, since the second elastic discontinuity is provided, the group delay time temperature coefficient It becomes possible to reduce the absolute value of TCD.

  In the boundary acoustic wave device according to the first invention, the first elastic discontinuity is formed along the side wall of each electrode finger of the IDT electrode, and the elastic boundary of the first elastic discontinuity is formed. Since the dimension in the wave propagation direction is 0.07λ or less, the temperature characteristics of the boundary acoustic wave device can be adjusted without causing a significant decrease in the electromechanical coupling coefficient.

  In addition, according to the second invention, since the second elastic discontinuity is provided at a period of λ / 2, other characteristics can be obtained as compared with the case where the elastic discontinuity is not provided. The boundary acoustic wave device can be provided in which the absolute value of the group delay time temperature coefficient TCD can be reduced without much lowering, and the characteristic change due to temperature change is small.

  According to the third invention, the sputtered particles are inclined with respect to the piezoelectric surface so that the first elastic discontinuity is formed between the sidewall of the electrode finger of the IDT and the lower dielectric film. Since the upper dielectric film is formed by being sputtered so as to be incident, the first elastic discontinuity can be easily and surely formed, whereby the elastic boundary according to the first invention can be formed. A wave device can be easily provided.

  According to the fourth invention, in the film forming step, the piezoelectric material or the second elastic discontinuity is formed with a gap in the direction perpendicular to the interface between the dielectric material and the piezoelectric material. Sputtering is performed so that the sputtered particles are incident on the surface of the dielectric obliquely, and the dielectric or piezoelectric film is formed. Therefore, the second elastic discontinuity can be easily and reliably formed. Can do. Therefore, the boundary acoustic wave device according to the second invention of the present application having the second elastic discontinuity can be provided easily and reliably.

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

  FIG. 1A is a schematic front cross-sectional view of a boundary acoustic wave device according to an embodiment of the present invention, and FIG. 1B is an enlarged view of a portion indicated by an alternate long and short dash line A in FIG. It is a partial front sectional view.

The boundary acoustic wave device 1 includes a piezoelectric body 2 and a dielectric body 3 stacked on the piezoelectric body 2. In the present embodiment, the piezoelectric body 2 is made of 15 ° Y cut X propagation LiNbO ₃ . The dielectric 3 is composed of SiO _2. LiNbO ₃ is a material having a negative frequency temperature coefficient TCF, and SiO ₂ is a material having a positive frequency temperature coefficient TCF.

  An IDT electrode 4 is formed on the upper surface of the piezoelectric body 2. The IDT electrode 4 is made of a laminated metal film in which an Al film having a thickness of 0.05λ is laminated on an Au film having a thickness of 0.05λ when the boundary acoustic wave has a wavelength λ. The duty ratio of the IDT electrode 4 is 0.6.

  In the boundary acoustic wave device 1, the boundary acoustic wave boundary wave resonator having the IDT electrode is configured.

  In the boundary acoustic wave device 1, by applying an AC electric field to the IDT electrode 4, an SH type boundary acoustic wave mainly composed of an SH component is excited, and resonance characteristics based on the SH type boundary acoustic wave are extracted.

  The feature of the present invention is that in the boundary acoustic wave device 1, first elastic discontinuous portions 5 a and 5 b and a second elastic discontinuous portion 6 are formed.

The first elastic discontinuities 5 a and 5 b are formed along the side walls 4 a ₁ and 4 a ₂ on both sides of the electrode finger 4 a of the IDT electrode 4. The elastic discontinuous portions 5a and 5b are disposed in the dielectric 3 and are formed by gaps in which the dielectric 3 does not exist. As apparent from FIG. 1, in the present embodiment, the height H1 of the elastic discontinuities 5a and 5b is set lower than the height of the IDT electrode 4, ie, the thickness T. The width of the first elastic discontinuities 5a and 5b, that is, the dimension along the boundary acoustic wave propagation direction is defined as a width W1.

  On the other hand, the second elastic discontinuity 6 is located above the upper surface of the piezoelectric body 2 on which the IDT electrode 4 is formed, that is, above the space between the electrode fingers 4a and 4b adjacent to the IDT electrode 4. The space and the gap are arranged. The second elastic discontinuity 6 is also formed by a gap where the dielectric 3 does not exist. The dimension in the height direction of the second elastic discontinuity 6, that is, the dimension along the thickness direction of the IDT electrode 4 is H 2 as shown in FIG. The width of the second elastic discontinuity 6 is W2. The width W2 of the second elastic discontinuity 6 is a dimension along the boundary acoustic wave propagation direction, like the width W1 of the first elastic discontinuities 5a and 5b.

  The second elastic discontinuity 6 is provided with a period of λ / 2 along the boundary acoustic wave propagation direction. That is, as shown in FIG. 1 (a), one second elastic discontinuity 6 is disposed in the space between the adjacent electrode fingers 4a and 4a, and a plurality of second elasticity The discontinuous portions 6 are arranged at a pitch of λ / 2 in the boundary acoustic wave propagation direction.

  Further, a dimension along the thickness direction of the IDT electrode 4 between the upper surface of the IDT electrode 4 and the lower end of the second elastic discontinuous portion 6 is defined as P1. This dimension P1 is the height of the gap between the upper end between the electrode fingers 4a and 4b on both sides and the lower end of the second elastic discontinuity 6 in the part where the electrode fingers 4a and 4b of the IDT electrode 4 are adjacent to each other. It corresponds to the vertical dimension. Therefore, the dimension P1 is set to the height direction dimension of the gap.

  In the boundary acoustic wave device 1, the plurality of first elastic discontinuities 5a are periodically arranged. That is, the plurality of first elastic discontinuities 5a are arranged at an equal pitch in the boundary acoustic wave propagation direction. Similarly, the plurality of first elastic discontinuities 5b are also arranged at an equal pitch in the boundary acoustic wave propagation direction. Further, the plurality of second elastic discontinuities 6 are also arranged at an equal pitch in the boundary acoustic wave propagation direction.

In the present embodiment, since the first elastic discontinuous portions 5a and 5b are provided and the width W1 of the first elastic discontinuous portions 5a and 5b is 0.07λ or less, it is elastic. discontinuities 5a, a case where 5b does not exist and the electromechanical coupling coefficient K ² can be made equal.

  Further, since the second elastic discontinuous portion 6 is provided so that the height dimension P1 of the gap is 0.05λ or more, as compared with the case where the elastic discontinuous portion 6 is not provided. Thus, the absolute value of the group delay time temperature coefficient TCD can be reduced. The group delay time temperature coefficient TCD = −frequency temperature coefficient TCF.

  Therefore, in the boundary acoustic wave device 1, the first elastic discontinuous portions 5a and 5b and the second elastic discontinuous portions can be obtained without changing the materials of the piezoelectric body 2, the dielectric 3 and the IDT electrode 4. 6 makes it possible to reduce the absolute value of the group delay time temperature coefficient TCD without significantly affecting the propagation characteristics of the boundary acoustic wave. Therefore, the boundary acoustic wave device 1 having good temperature characteristics can be easily provided. This will be described more specifically.

The boundary acoustic wave device 1 has a structure in which SiO ₂ as a dielectric 3, an IDT electrode 4, and a 15 ° Y-cut X-propagation LiNbO ₃ as a piezoelectric body 2 are stacked in order from above. Such a laminated structure is represented as LiNbO _{3 of} SiO ₂ / IDT electrode / 15 ° Y-cut X propagation. In other words, each layer is described in order from the top of the laminate to indicate a laminate structure.

As shown in Table 1 below, in the boundary acoustic wave device 1, the piezoelectric body 2 made of LiNbO ₃ and the dielectric body 3 made of SiO ₂ are both 8λ, and the height direction dimension P1 of the gap is The width W2 = 0.005λ and the height H2 = 0.030λ of the second elastic discontinuity 6 were 0.020λ. With respect to the boundary acoustic wave device having such a structure, the group delay time temperature coefficient TCD and the propagation characteristic of the boundary acoustic wave of the boundary acoustic wave device 1 are set with the height H1 and the width W1 of the first elastic discontinuity 5 as variables. Asked.

The calculation is an extension of the finite element method proposed in "Fine Element Analysis of Periodically Structured Piezoelectric Waveguides" (The IEICE Transactions Vol.J68-C No1,1985 / 1, pp.21-27). Then, as shown in FIG. 1, one strip was arranged in the half-wavelength section, and the sound speeds at the upper and lower ends of the stop band of the electrically released strip and the short-circuited strip were obtained. The release strip lower end sound velocity is V _o1 , the upper end sound velocity is V _o2 , the short-circuit strip lower end sound velocity is V _s1 , and the upper end sound velocity is V _s2 . In some of the drawings, V _s1 is abbreviated as V. Since most of the energy is concentrated in the vicinity of 1λ above and below the IDT in the vibration of the boundary wave, the boundary condition between the front and back surfaces is fixed elastically, with 8λ being sufficiently large in the vertical direction. Next, based on the method proposed in "Excitation characteristics evaluation of surface acoustic wave interdigital electrode by mode coupling theory" (Technical Report of IEICE, NW90-62, 1990, pp.69-74) Κ ₁₂ / k ₀ and the electromechanical coupling coefficient K ² representing the amount of reflection of the boundary wave at λ were obtained. Incidentally, kappa ₁₂ shows the inter-mode coupling coefficient based on mode coupling theory, k ₀ denotes the wave number 2 [pi / lambda of the elastic wave propagating IDT electrode. Note that the κ ₁₂ / k ₀ was determined in consideration of the influence of frequency dispersion because the frequency dispersion of sound velocity is larger in the structure shown in Table 1 than the structure dealt with in the above document. The TCD was determined by the formula [1] from the phase velocities V _{15 ° C.} , V _{25 ° C.} , and V _{35 ° C. at the} lower end of the short-circuit strip stop zone at ₁₅ , ₂₅ , and _{35 ° C.}

Here, α _s is the linear expansion coefficient of the LiNbO ₃ substrate in the boundary wave propagation direction.

Change in group delay time temperature coefficient TCD and electromechanical coupling coefficient K ² (%) when the width W1 of the first elastic discontinuities 5a and 5b is changed to 0.01λ, 0.05λ, and 0.09λ. 2, FIG. 2 to FIG. 5, respectively, show changes in electrode finger reflection coefficient κ ₁₂ / k ₀ and changes in acoustic velocity V (m / sec) of boundary acoustic waves.

As is clear from FIG. 2, in the boundary acoustic wave device 1, the height W1 of each of the first elastic discontinuities 5a and 5b is 0.01, 0.05, and 0.09. It can be seen that the group delay time temperature coefficient TCD shifts to the + side as H1 increases. This is because the first elastic discontinuities 5a and 5b are provided so as to be close to the piezoelectric body 2 made of LiNbO ₃ having a positive TCD value, and therefore the group delay time temperature coefficient in the boundary acoustic wave device. This is probably because TCD has shifted to the + side.

  That is, when the vibration energy of the boundary acoustic wave is distributed to the first elastic discontinuous portions that are periodically arranged, the inventor of the present application indicates that the vibration distribution of the boundary acoustic wave is the first elastic discontinuous portion. It has been found that the vibration energy easily changes to the elastic discontinuities 5a and 5b side due to the presence of 5a and 5b. Therefore, the group delay time temperature coefficient TCD of the boundary acoustic wave is close to the group delay time temperature coefficient TCD of the medium close to the elastic discontinuities 5a and 5b. That is, when the first elastic discontinuity is formed by making the group delay time temperature coefficient TCD a positive value or the medium itself close to the medium, the group delay time temperature coefficient TCD of the entire boundary acoustic wave device 1 becomes positive. Will shift.

  Conversely, when the first elastic discontinuities 5a and 5b are formed close to the medium itself or the medium having a negative group delay time temperature coefficient TCD, the group delay time temperature coefficient TCD of the entire boundary acoustic wave device is formed. Shifts to the-side.

Next, the specifications of the boundary acoustic wave device 1 were changed as shown in Table 2 below, and the characteristics of the boundary acoustic wave propagating through the boundary acoustic wave device 1 were obtained in the same manner. The results are shown in FIGS. 6 to 9 show the width W1 of the first elastic discontinuities 5a and 5b and the group delay time when the height H1 of the first elastic discontinuities 5a and 5b is 0.045. temperature coefficient TCD, the electromechanical coupling coefficient ^K 2 (%), is a graph showing respective relationships between the reflection coefficient κ ₁₂ / _{k 0} and the acoustic velocity V (m / sec).

As is apparent from FIG. 6, the group delay time temperature coefficient TCD does not change much even if the width W1 is changed. However, as is apparent from FIG. 7, it can be seen that when W1> 0.07, the electromechanical coupling coefficient K ² (%) tends to decrease. Therefore, W1 is required to be 0.07 or less, in that case, it can be seen that can suppress a decrease in the electromechanical coupling coefficient K ^2.

  Next, the specifications of the boundary acoustic wave device 1 were changed as shown in Table 3 below, and the characteristics of the boundary acoustic wave propagating through the boundary acoustic wave device 1 having the specifications shown in Table 3 were similarly determined. Here, the height H2 and the width W2 of the second elastic discontinuity 6 are used as variables.

10 to 13 show the characteristics of the boundary acoustic wave device that propagates through the boundary acoustic wave device having the structure shown in Table 3. FIG. That is, FIGS. 10 to 13 show that the width W2 of the second elastic discontinuity 6 is 0.0, 0.01, 0.05, or 0.10, and the height of the second elastic discontinuity 6 is high. The change of the group delay time temperature coefficient TCD, the change of the electromechanical coupling coefficient K ² (%), the change of the reflection coefficient κ ₁₂ / k _{0 and} the change of the sound velocity V (m / second) when the height H 2 is changed are shown. FIG.

The second elastic discontinuity 6 is disposed in SiO ₂ having a negative group delay time temperature coefficient TCD, and is separated from LiNbO ₃ having a positive group delay time temperature coefficient TCD. . Therefore, it can be seen that the group delay time temperature coefficient TCD of the boundary acoustic wave is shifted to the minus side by providing the second elastic discontinuous portion 6 and is improved. In other words, it can be seen that the absolute value of the group delay time temperature coefficient TCD of the boundary acoustic wave device 1 is reduced and improved.

  In addition, the absolute value of the group delay time temperature coefficient TCD is reduced and improved even when the stress and displacement are analyzed as discontinuous on the basis of the case where the width of the second elastic discontinuous portion 6 is zero. I understand that. Thus, it can be seen that the second elastic discontinuity need not have a very large width.

  In the case where the second elastic discontinuity is not provided, it is one point where W2 = 0.00 and H2 = 0.00.

Further, changes in the electromechanical coupling coefficient K ₂ , which is the propagation characteristic of boundary acoustic waves other than the group delay time temperature coefficient TCD, the inter-mode coupling coefficient κ ₁₂ corresponding to the reflection coefficient of the electrode finger, and the sound velocity V may be sufficiently small. Recognize.

  Next, the propagation characteristics of the boundary acoustic wave when the boundary acoustic wave device was configured with the specifications shown in Table 4 below were obtained in the same manner as described above. Here, the height P1 of the gap between the second elastic discontinuous portion 6 and the space between the adjacent electrode fingers was used as a variable.

14 to 17 show the characteristics of the boundary acoustic wave propagating through the boundary acoustic wave device having the structure shown in Table 4. FIG. 14 to 17 show changes in the group delay time temperature coefficient TCD, changes in the electromechanical coupling coefficient K ² (%), changes in the reflection coefficient κ ₁₂ / k ₀ , and sound speed when the gap height P 1 is changed. It is a figure which shows the change of V (m / sec).

  In addition, the boundary acoustic wave device 1 is manufactured with the specifications shown in Table 5 below, and the gap between the lower end of the second elastic discontinuous portion 6 and the upper end of the space between the adjacent electrode fingers is the same as described above. The propagation characteristic of the boundary acoustic wave of the boundary acoustic wave device 1 was obtained using the height P1 as a variable.

18 to 21 show the characteristics of the boundary acoustic wave propagating through the boundary acoustic wave device having the structure shown in Table 5. FIG. That is, FIGS. 18 to 21 show changes in the group delay time temperature coefficient TCD, changes in the electromechanical coupling coefficient K ² (%), and changes in the reflection coefficient κ ₁₂ / k ₀ when the gap height P 1 is changed. It is a figure which shows the change of sound velocity V (m / sec).

  As apparent from FIGS. 14 to 21, when the gap height P <b> 1 increases, that is, when the lower end of the second elastic discontinuity 6 is separated above the upper surface of the IDT electrode 4, P1 ≧ 0 in particular. When .05λ, the group delay time temperature coefficient TCD can be stabilized.

  Therefore, preferably, by setting P1 ≧ 0.05λ, it is possible to provide the boundary acoustic wave device 1 having stable characteristics due to a temperature change.

  FIG. 22 is a diagram showing the relationship between the gap height P1 and the acoustic velocity V of the boundary acoustic wave in the structure shown in Table 5. As is apparent from FIG. 22, when the second elastic discontinuous portion 6 moves away from the upper surface of the IDT electrode 4, especially when the gap height P1 is greater than 1λ, the sound velocity of the boundary acoustic wave is increased. It turns out to be stable. Therefore, it can be seen that the vibration mode of the boundary acoustic wave is hardly distributed in the portion where the second elastic discontinuity 6 is provided. Therefore, it is desirable that the second elastic discontinuous portion 6 is disposed at a position within 1λ from the upper end of the space between the electrode fingers 4a of the IDT electrode 4, whereby the second elastic discontinuous portion 6 is arranged. It turns out that the effect by having provided is acquired. Therefore, the height P1 of the gap is desirably 0.05λ or more and 1λ or less.

  Next, an embodiment of a method for manufacturing the boundary acoustic wave device 1 will be described.

In manufacturing the boundary acoustic wave device 1, the IDT electrode 4 is formed on the piezoelectric body 2 made of LiNbO ₃ by photolithography. The IDT electrode 4 can be formed by a well-known photolithography method. Thereafter, a SiO ₂ film is sputtered on the entire surface by RF magnetron sputtering under conditions of a film forming temperature of 270 ° C. and a gas pressure of Ar, O _{2 of} 0.3 Pa. Normally, when forming the SiO ₂ film by sputtering, the gas pressure is about 0.1 Pa. However, by increasing the gas pressure as described above, the straightness of the sputtered particles deteriorates, and the sputtered particles travel in an oblique direction. Therefore, the side walls 4a ₁ and 4a _{2 of} the electrode finger 4 are reliably covered with SiO ₂ . On the other hand, since the sputtered particles proceed in the oblique direction, the SiO ₂ film formed on the side walls of the electrode fingers grows sufficiently in the lateral direction. Depending on the structure, the SiO ₂ film collides while being deposited in the center of the space between the electrode fingers. As a result, the elastic discontinuous portion 6 can be formed. In other words, the first elastic discontinuity 6 is formed as a result of the SiO ₂ film grown from both sides being deposited and colliding at the center between the adjacent electrode fingers 4a ₁ and 4a ₂ .

  FIG. 23 is an electron micrograph showing a cross section of the boundary acoustic wave device for showing the second elastic discontinuity 6 in an example of the boundary acoustic wave device manufactured as described above. Here, as the IDT electrode, a laminated metal film formed by laminating these in the order of NiCr / Ti / Al / Ti / Ni / Au / Ni / Ti was used. The thickness of each layer was NiCr / Ti / Al / Ti / Ni / Au / Ni / Ti = 10/10/150/10/10/160/10/10 (unit: nm). The period of the electrode fingers in the IDT electrode 4 was 3.6 μm, and the duty was 0.6. The conditions shown in Table 1 were the same except for the IDT electrode.

  Further, the IDT electrode is made of a laminated metal film of NiCr / Ti / Al / Ti / Ni / Au / Ni / Ti = 10/10/50/10/10/70/10/10 (unit: nm), and the electrode A boundary acoustic wave device of another example was manufactured in the same manner as described above except that the period of the finger was 1.6 μm and the duty was 0.5. In other examples of the boundary acoustic wave device, other points are the same as those in the above example. FIG. 24 is an electron micrograph showing a cross section of a portion where an IDT electrode is formed in another example of the boundary acoustic wave device obtained as described above. In the structure of the electron micrograph shown in FIG. 23, the group delay time temperature coefficient TCD is improved by 3 ppm / ° C. compared to the case where the second discontinuous portion is not formed, and in the structure shown in FIG. 24, 6 ppm / ° C. It was confirmed that it was improving.

  FIG. 25 shows a state in which the second elastic discontinuities shown in FIG. 23 are periodically arranged with an electron micrograph at a different magnification.

Next, an example of another embodiment of the method for manufacturing the boundary acoustic wave device of the present invention will be described with reference to FIGS. Here, a multilayer SiO ₂ film was first formed on LiNbO ₃ as a piezoelectric body by sputtering so as to have a thickness of 25 nm. Thereafter, a photoresist pattern is formed on the lower SiO ₂ film, the multilayer SiO ₂ film is etched using the photoresist pattern as a mask, and then a laminated metal film for forming IDT is formed by vapor deposition. . Then, the photoresist pattern and the laminated metal film formed on the photoresist pattern were removed by a lift-off method. In this way, a structure was obtained in which an SiO ₂ film having a thickness of 25 nm was formed on the upper surface of LiNbO ₃ and an IDT electrode 4 having a thickness of 280 nm was formed in a portion where the SiO ₂ film was not provided. Up to this point, the manufacturing process of the conventionally known boundary acoustic wave device is almost the same. In addition, as said laminated metal film, the laminated metal film which laminated | stacked these by the thickness of AlCu / Ti / Ni / Au / Ni = 100/10/10/150/10 (nm) was used, and the electrode finger of an IDT electrode was used. The period was 3.6 μm and the duty was 0.6.

Thereafter, the RF magnetron sputtering, SiO ₂ is deposited at a deposition temperature 270 ° C. and the gas pressure of 0.2 Pa, thereby forming an upper SiO ₂ film. Here, the IDT electrode and the lower SiO ₂ film are formed so that a slight gap is formed between the lower SiO ₂ film and the side walls 4a ₁ and 4a ₂ of the electrode fingers 4a of the IDT electrode. Accordingly, the sputtered particles when the upper SiO ₂ film is formed enter the gap from an oblique direction at a constant ratio. For this reason, a cavity or a region where SiO ₂ is sparse is formed between the IDT electrode 4 and the lower SiO ₂ film, and elastic discontinuities 5a and 5b are formed. When the thickness of the lower SiO ₂ film is increased, the elastic discontinuities 5a and 5b are increased.

FIG. 27 is a diagram showing changes in the frequency temperature coefficient TCF of the boundary acoustic wave device 1 when the thickness of the lower SiO ₂ film is changed. It can be seen that the absolute value of the frequency temperature coefficient TCF increases when the thickness of the lower SiO ₂ film is increased.

In the boundary acoustic wave device 1 shown in FIG. 1A, the IDT electrode 4 is formed on the upper surface of the piezoelectric body 2 and the dielectric 3 made of SiO ₂ is formed. The IDT electrode may first be formed on the side where the piezoelectric bodies are laminated, and then the piezoelectric body may be formed. In that case, the dielectric 2 and the piezoelectric body 3 shown in FIG. 1A are reversed, and the elastic discontinuities 5a, 5b, and 6 are arranged in the piezoelectric body.

  In each of the embodiments of the method for manufacturing the boundary acoustic wave device described with reference to FIGS. 23 to 27, the dielectric is first prepared, and the IDT electrode is formed on the upper surface of the dielectric, and then the piezoelectric is formed. A film may be formed.

  In the present invention, the IDT electrode is not necessarily formed from a laminated metal film in which a plurality of metal films are laminated, and may be formed from a single metal. In addition to the Al / Au laminated metal film, a laminated metal film may be formed by combining various metals such as Au, Pt, Ag, Cu, Ni, Ti, Fe, W, and Ta as described above. . Further, in order to improve adhesion and power durability, a thin metal layer made of Ti, Cr, NiCr, Ni, Pt, Pd or the like is formed between the dielectric layer, the piezoelectric body, or an electrode. You may arrange | position between multilayer metal films.

The piezoelectric body is not limited to LiNbO ₃ , and various piezoelectric materials such as LiTaO ₃ , KN, Ta ₂ O ₅ , ZnO, or various piezoelectric ceramics such as PZT can be used. The dielectric 3 is not limited to SiO ₂ but can be formed of various dielectric materials such as glass, Si, SiC, AlN, and Al ₂ O ₃ .

  Furthermore, a protective layer may be formed to increase the strength of the boundary acoustic wave device or prevent the invasion of corrosive gas. In some cases, a boundary acoustic wave device having a structure enclosed in a package is formed. Also good. The protective layer can be formed of an appropriate synthetic resin such as polyimide resin or epoxy resin, or an inorganic insulating material such as titanium oxide, aluminum nitride, or aluminum oxide. The protective layer may be formed of a metal film such as Al or W.

  Furthermore, the boundary acoustic wave device according to the present invention is not limited to the resonator, and may have various electrode structures such as a bandpass filter.

(A), (b) expands and shows the part enclosed with the dashed-dotted line A in typical front sectional drawing for demonstrating the boundary acoustic wave apparatus which concerns on one Embodiment of this invention, and (a). FIG. The height of the first elastic discontinuity when the width W1 of the first elastic discontinuity of the boundary acoustic wave device having the specifications shown in Table 1 is 0.01, 0.05, or 0.09. The figure which shows the relationship between thickness H1 and group delay time temperature coefficient TCD. The height of the first elastic discontinuity when the width W1 of the first elastic discontinuity of the boundary acoustic wave device having the specifications shown in Table 1 is 0.01, 0.05, or 0.09. diagram illustrating the relationship between the H1 and the electromechanical coupling coefficient ^K 2 (%). The height of the first elastic discontinuity when the width W1 of the first elastic discontinuity of the boundary acoustic wave device having the specifications shown in Table 1 is 0.01, 0.05, or 0.09. The figure which shows the relationship between the height H1 and the change of the ratio of the coupling coefficient (kappa) ₁₂ between modes. The height of the first elastic discontinuity when the width W1 of the first elastic discontinuity of the boundary acoustic wave device having the specifications shown in Table 1 is 0.01, 0.05, or 0.09. The figure which shows the relationship between the height H1 and the sound velocity V of an elastic boundary wave. In the boundary acoustic wave device having the specifications shown in Table 2, the group delay when the height H1 of the first elastic discontinuity is 0.045 and the width W1 of the first elastic discontinuity is changed. The figure which shows the change of time temperature coefficient TCD. In the boundary acoustic wave device having the specifications shown in Table 2, when the height H1 of the first elastic discontinuity is 0.045 and the width W1 of the first elastic discontinuity is changed, the electric machine It shows a variation of the coupling coefficient ^K 2 (%). In the boundary acoustic wave device having the specifications shown in Table 2, between the modes when the height H1 of the first elastic discontinuity is 0.045 and the width W1 of the first elastic discontinuity is changed. The figure which shows the change of the ratio of coupling coefficient (kappa) ₁₂ . In the boundary acoustic wave device having the specifications shown in Table 2, the elastic boundary when the height H1 of the first elastic discontinuity is 0.045 and the width W1 of the first elastic discontinuity is changed. The figure which shows the change of the sound velocity V of a wave. In the boundary acoustic wave device having the specifications shown in Table 3, the second elastic discontinuity when the width W2 of the second elastic discontinuity is 0.00, 0.01, 0.05, or 0.10. The figure which shows the relationship between height H2 and the group delay time temperature coefficient TCD. In the boundary acoustic wave device having the specifications shown in Table 3, the second elastic discontinuity when the width W2 of the second elastic discontinuity is 0.00, 0.01, 0.05, or 0.10. It shows the height H2 of the relationship between the electromechanical coupling coefficient K ^{2 (%).} In the boundary acoustic wave device having the specifications shown in Table 3, the second elastic discontinuity when the width W2 of the second elastic discontinuity is 0.00, 0.01, 0.05, or 0.10. The figure which shows the relationship between height H2 and the ratio of coupling coefficient (kappa) ₁₂ between modes. In the boundary acoustic wave device having the specifications shown in Table 3, the second elastic discontinuity when the width W2 of the second elastic discontinuity is 0.00, 0.01, 0.05, or 0.10. The figure which shows the relationship between height H2 and the sound velocity V of a boundary acoustic wave. FIG. 5 is a diagram showing the relationship between the height P1 of the gap between the second elastic discontinuity and the upper surface of the IDT electrode and the group delay time temperature coefficient TCD in the boundary acoustic wave device having the specifications shown in Table 4. In the boundary acoustic wave device having the specifications shown in Table 4, the relationship between the height P1 of the gap between the second elastic discontinuity and the upper surface of the IDT electrode and the electromechanical coupling coefficient K ² (%) FIG. In the boundary acoustic wave device having the specifications shown in Table 4, the relationship between the height P1 of the gap between the second elastic discontinuity and the upper surface of the IDT electrode and the ratio of the inter-mode coupling coefficient κ ₁₂ is shown. Figure. In the boundary acoustic wave apparatus of the specification shown in Table 4, the figure which shows the relationship between the height P1 of the gap between the 2nd elastic discontinuity part and the upper surface of an IDT electrode, and the sound velocity V of a boundary acoustic wave. In the boundary acoustic wave apparatus of the specification shown in Table 5, the figure which shows the relationship between the height P1 of the gap between the 2nd elastic discontinuity part and the upper surface of an IDT electrode, and group delay time temperature coefficient TCD. In the boundary acoustic wave device having the specifications shown in Table 5, the relationship between the height P1 of the gap between the second elastic discontinuity and the upper surface of the IDT electrode and the electromechanical coupling coefficient K ² (%) FIG. In the boundary acoustic wave device having the specifications shown in Table 5, the relationship between the height P1 of the gap between the second elastic discontinuity and the upper surface of the IDT electrode and the ratio of the inter-mode coupling coefficient κ ₁₂ is shown. Figure. In the boundary acoustic wave apparatus of the specification shown in Table 5, the figure which shows the relationship between the height P1 of the gap between the 2nd elastic discontinuity part and the upper surface of an IDT electrode, and the sound velocity V of a boundary acoustic wave. The figure which shows the relationship between the magnitude | size of the gap P1 between the lower end of a 2nd elastic discontinuity part, and the upper end of an IDT electrode, and the sound velocity V of an elastic boundary wave. The electron micrograph which shows an example of the elastic boundary wave apparatus in which the 2nd elastic discontinuity part is formed. The electron micrograph which shows the other example of the elastic boundary wave apparatus in which the 2nd elastic discontinuity part is formed. The electron micrograph of the boundary acoustic wave apparatus which shows the structure where the 2nd elastic discontinuity part is arrange | positioned periodically. The electron microscope for demonstrating the part in which the 1st elastic discontinuity part is formed in the elastic boundary wave apparatus of one Embodiment of this invention. Diagram showing the relationship between the temperature coefficient of frequency TCF of the underlying SiO ₂ film thickness and the boundary acoustic wave device. The typical front sectional view for explaining the conventional boundary acoustic wave device.

Explanation of symbols

1 ... boundary acoustic wave device 2 ... piezoelectric element 3 ... dielectric 4 ... IDT electrode 4a ... electrode fingers 4a _1, 4a 2 _... sidewalls 5a, 5b ... first elastic discontinuity 6 ... second elastic discontinuous Part H1... Height of the first elastic discontinuity W1... Width of the first elastic discontinuity H2... Height of the second elastic discontinuity W2. Width P1 ... Gap height dimension

Claims (7)

A piezoelectric body, a dielectric laminated on the piezoelectric body, and an IDT electrode having a plurality of electrode fingers and disposed at an interface between the piezoelectric body and the dielectric;
A first elastic discontinuity is formed along the side wall of each electrode finger of the IDT electrode, and the height dimension of the first elastic discontinuity is made smaller than the thickness of the IDT. And the dimension of the boundary acoustic wave propagation direction of the first elastic discontinuity is 0.07λ or less when the wavelength of the boundary acoustic wave excited by the IDT electrode is λ. A boundary acoustic wave device.   The boundary acoustic wave device according to claim 1, wherein the first elastic discontinuity is formed along side walls on both sides of each electrode finger.   The IDT electrode is formed on a piezoelectric surface of the piezoelectric body laminated on the dielectric, and the first elastic discontinuity is formed in the dielectric. The boundary acoustic wave device as described.   The IDT electrode is formed on a dielectric surface of the dielectric layer laminated on the piezoelectric body, and the first elastic discontinuity is formed in the piezoelectric body. 2. The boundary acoustic wave device according to 2. A piezoelectric body, a dielectric layer laminated on the piezoelectric body, and an IDT electrode disposed at an interface between the piezoelectric body and the dielectric body and having a plurality of electrode fingers;
In the plurality of electrode fingers, a second elastic discontinuity disposed in the dielectric or the piezoelectric body is formed with a gap in a direction perpendicular to the interface from a space between adjacent electrode fingers. In each of the spaces between adjacent electrode fingers, a second elastic discontinuity is formed across the space and the gap, and the wavelength of the boundary acoustic wave excited by the IDT is λ. Sometimes, the dimension of the second elastic discontinuity in the boundary acoustic wave propagation direction is 0.10λ or less, and the plurality of second elastic discontinuities along the boundary acoustic wave propagation direction. The boundary acoustic wave device is characterized in that the portion is provided with a period of λ / 2. Before Symbol the size of the gap is more than 0.05λ along a direction perpendicular to the surface, is not more than 1 [lambda, the boundary acoustic wave device according to claim 5. A first elastic discontinuity is formed along the side wall of each electrode finger of the IDT electrode, and when the wavelength of the elastic boundary wave excited by the IDT electrode is λ, the first elasticity The boundary acoustic wave device according to claim 5 or 6, wherein the dimension of the elastic discontinuity in the boundary acoustic wave propagation direction is 0.07λ or less .