CN116094487A

CN116094487A - Acoustic surface wave resonator

Info

Publication number: CN116094487A
Application number: CN202310160797.0A
Authority: CN
Inventors: 周鸿燕; 高安明; 姜伟
Original assignee: Zhejiang Xingyao Semiconductor Co ltd
Current assignee: Zhejiang Xingyao Semiconductor Co ltd
Priority date: 2023-02-20
Filing date: 2023-02-20
Publication date: 2023-05-09

Abstract

The invention provides an acoustic surface wave resonator, which comprises a piezoelectric substrate and an interdigital transduction structure; the interdigital transduction structure is positioned on one side of the piezoelectric substrate and comprises two bus bars which are oppositely arranged, and a plurality of electrode fingers which are arranged between the two bus bars side by side, wherein each electrode finger is alternately and electrically connected to one of the two bus bars; and sound velocity buffer parts are arranged between the adjacent electrode fingers on the same bus bar, and the free ends of the electrode fingers are opposite to the sound velocity buffer parts and keep a preset gap. The invention realizes sound velocity slow change by utilizing the structure characteristic of the width slow change of the sound velocity slow change part, thereby effectively inhibiting various stray modes and high-order transverse clutters generated by the resonator, having good clutter inhibition effect and enabling the filter to have a flat passband.

Description

Acoustic surface wave resonator

Technical Field

The invention relates to the technical field of surface acoustic wave devices, in particular to a surface acoustic wave resonator.

Background

In modern communication systems, filters are often used to filter unwanted signals outside the target communication frequency band, and saw resonators have been widely used in rf filter design due to the advantages of high Q, small size, high reliability, and easy mass production. In general, conventional saw resonators produce some spurious modes as well as higher order transverse modes at the same time when exciting the dominant acoustic wave mode. These spurious and transverse modes can affect the energy constraint of the main acoustic mode, so that the problems of reduced Q value of the resonator, increased insertion loss of the SAW filter, etc. are caused; spurious and lateral modes within the filter design passband can lead to spurious responses, which in turn affect the passband flatness of the acoustic surface filter. In summary, the creation of spurious and lateral modes can degrade the electrical performance of the SAW resonator and/or filter and even lead to device failure.

In the prior art, the interdigital structure of the electrode is mainly subjected to some treatment to inhibit the transverse mode. Such as providing a sufficiently small acoustic aperture between the electrode fingers and the bus bar, but this can result in undesirable source impedance; apodization weighting the electrode fingers, but this can lead to undesirably large impedances, reduced electromechanical coupling coefficients, and even reduced Q values of the resonator; or a mass loading layer is arranged at the tail end of the interdigital electrode, but the size of the mass loading layer needs to be precisely controlled, and the process is relatively complex and the realization difficulty is extremely high.

For example, publication No. CN114866062a discloses a surface acoustic wave resonator, in which sound velocity abrupt structures are provided at the ends of electrode fingers and dummy fingers, that is, a mass-loaded layer suppressing transverse mode is provided, so that the accuracy of the size requirement of the mass-loaded layer is high as in the aforementioned technique, and especially when the designed filter operates at a higher frequency, the size of the required mass-loaded layer is extremely small, and the conventional process technique is difficult to realize, so that the purpose or requirement of suppressing the transverse mode cannot be satisfied.

For another example, publication No. CN114629461a discloses a surface acoustic wave resonator in which a sound velocity abrupt structure is provided at an electrode finger tip and/or a dummy finger near a bus bar tip. In practice, the implementation is too complex and unstable, and in particular the patterning and filling of the piezoelectric layer requires a CMP process to be completed, but this process can affect the surface structure of the piezoelectric layer and deteriorate the resonator performance. In particular, the sound velocity abrupt structure is formed prior to the interdigital electrode, and the position of the sound velocity abrupt structure is difficult to control at a required position at the lower part of the interdigital electrode, so that alignment deviation is easy to occur, and the transverse wave suppression effect is affected.

Disclosure of Invention

In view of the drawbacks of the prior art, an object of the present invention is to provide a surface acoustic wave resonator.

The invention provides an acoustic surface wave resonator, which comprises a piezoelectric substrate and an interdigital transduction structure;

the interdigital transduction structure is positioned on one side of the piezoelectric substrate and comprises two bus bars which are oppositely arranged, each bus bar is connected with a plurality of electrode fingers to form a comb-shaped structure, and the electrode fingers on the two bus bars are mutually crossed;

and sound velocity buffer parts are arranged between the adjacent electrode fingers on the same bus bar, and the free ends of the electrode fingers are opposite to the sound velocity buffer parts and keep a preset gap.

In some embodiments, the sound velocity gradually changing portion is a structure having a continuously changing width or a structure having a stepwise changing width.

In some embodiments, the sound velocity ramp is a saw tooth structure.

In some embodiments, at least one sound velocity buffer is disposed between adjacent electrode fingers on the same bus bar.

In some embodiments, a plurality of the sound velocity gradually changing parts are arranged between the adjacent electrode fingers on the same bus bar, and the sound velocity gradually changing parts between the adjacent electrode fingers on the same bus bar are connected and/or arranged at intervals.

In some embodiments, the sound speed reducing portions of the same bus bar between adjacent electrode fingers have the same or different structures.

In some embodiments, the sonic ramp structures on both of the bus bars are the same or different.

In some embodiments, the sound speed buffer part is an i-shaped structure, the sound speed buffer part is electrically connected between adjacent electrode fingers on the same side, one end of the sound speed buffer part keeps a predetermined gap with the end of the electrode finger, and the other end of the sound speed buffer part keeps a predetermined gap with the bus bar.

In some embodiments, the overall height H4 of the sound speed buffer is set to 0.003-0.75λ, the middle portion height H3 is 0.3-0.8H4, and the upper and lower heights H1 and H2 are the same or different, where λ is the wavelength of the surface acoustic wave.

In some embodiments, the distance between the free end of the electrode finger and the opposing bus bar is 0.01 to 2.5λ, where λ is the surface acoustic wave wavelength.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the acoustic surface wave resonator provided by the embodiment, the bus bar with the sound velocity slowly-varying part is formed, sound velocity slowly-varying is realized by utilizing the structural characteristic of width slowly-varying of the sound velocity slowly-varying part, so that various stray modes and high-order transverse clutters generated by the resonator are effectively restrained, particularly, the resonator has a good clutter restraining effect, the filter has a flat passband, and meanwhile, the energy constraint of a target acoustic mode is enhanced by the sound velocity slowly-varying part structure, so that the resonator has a good Q value, and the resonator and the filter formed by the electric connection of the resonator have good electric properties, so that the filter has small insertion loss.

2. The I-shaped sound velocity buffer part is directly arranged between the electrode fingers of the resonator, so that the effect of inhibiting various stray modes and high-order transverse clutters generated by the resonator can be achieved to a certain extent, the electromechanical coupling coefficient is directly regulated and controlled on the resonator unit, the structure is simple, the miniaturization of the size of the device is facilitated, and the cost is reduced.

3. According to the invention, the sound velocity slowly-changing parts are arranged on the same bus bar, so that the bus bar has a larger size compared with a rectangular area with abrupt sound velocity; and the bus bar is connected, the number of independent side lengths in the structure is reduced, the adverse effect on overexposure or underexposure of the edge in the process can be effectively reduced, and the bus bar is suitable for the current large-scale mass production process.

Drawings

Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of a first embodiment of the invention in which the width of a sound velocity modulation section is varied stepwise;

FIG. 2 is a schematic view of a second embodiment of the invention in which the width of the sonic velocity ramp varies stepwise;

FIG. 3 is a schematic view of a third embodiment of the invention in which the width of the sonic velocity ramp varies stepwise;

FIG. 4 is a schematic view of a fourth embodiment of the invention in which the width of the sonic velocity ramp varies stepwise;

FIG. 5 is a schematic cross-sectional view of a SAW resonator of the present invention;

FIG. 6 is a schematic view showing the structure of the sound velocity buffer part of the present invention in an I shape;

FIG. 7 is a schematic view of structural parameters of an I-shaped sonic velocity ramp portion of the present invention;

fig. 8 is a schematic diagram of a surface acoustic wave resonator according to the present invention having a reflective grating.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.

Example 1

The present embodiment provides an acoustic surface wave resonator, as shown in fig. 1-8, including a piezoelectric substrate 100 and an interdigital transducer structure 200 disposed on one side of the piezoelectric substrate 100. The piezoelectric substrate 100 may be made of a piezoelectric material such as lithium tantalate, lithium niobate, aluminum nitride or quartz, or may be a composite substrate composed of a piezoelectric material such as lithium tantalate, lithium niobate, aluminum nitride or quartz and a single-layer or multi-layer support substrate, and the support substrate material may include materials such as lithium tantalate, lithium niobate, aluminum nitride, sapphire, spinel, silicon carbide, quartz, etc.

The interdigital transduction structure 200 mainly comprises two bus bars 201 which are oppositely arranged, a plurality of electrode fingers 203 are arranged on each bus bar 201 at intervals to form a comb-shaped structure, the electrode fingers 203 on the two comb-shaped structures are sequentially arranged in a gap between two adjacent electrode fingers 203 on the opposite side at intervals, and the adjacent electrode fingers 203 are not contacted. A sound velocity buffer 202 is provided between two adjacent electrode fingers 203 on the same bus bar 201, and the free ends of the electrode fingers 203 on the other bus bar 201 are opposite to the sound velocity buffer 202 and keep a gap. The sound velocity modulation section 202 is a structure whose width varies continuously or a structure whose width varies stepwise. The continuous change of the width of the sound velocity buffer 202 means that the width gradually increases or gradually decreases from one end to the other end, and the stepwise change of the width of the sound velocity buffer 202 means that the width gradually increases from one end to the other end, then gradually decreases, or first gradually decreases and then gradually increases, and at the same time, the width is stepwise changed, so that a small region with a constant width is allowed in the middle region. The interdigital transduction structure 200 is an integrally formed structure, and can be formed in one step by sequentially performing coating, photoetching and etching processes, and can be formed in one step by sequentially performing photoetching, coating and stripping processes.

According to the invention, the sound velocity slowly-changing parts are arranged on the same bus bar, so that the bus bar has a larger size compared with a rectangular area with abrupt sound velocity; and the bus bar is connected, the number of independent side lengths in the structure is reduced, the adverse effect on overexposure or underexposure of the edge in the process can be effectively reduced, and the bus bar is suitable for the current large-scale mass production process.

According to the acoustic surface wave resonator provided by the embodiment, the bus bar with the sound velocity slowly-varying part is formed, sound velocity slowly-varying is realized by utilizing the structural characteristic of width slowly-varying of the sound velocity slowly-varying part, so that various stray modes and high-order transverse clutters generated by the resonator are effectively restrained, particularly, the resonator has a good clutter restraining effect, the filter has a flat passband, and meanwhile, the energy constraint of a target acoustic mode is enhanced by the sound velocity slowly-varying part structure, so that the resonator has a good Q value, and the resonator and the filter formed by the electric connection of the resonator have good electric properties, so that the filter has small insertion loss.

In some embodiments, as shown in fig. 8, a reflection grating 300 is provided at both ends of the resonator, and a sound velocity reducing portion 202 is provided on the reflection grating 300.

Example 2

In example 2, an example was provided in which the width of the sound velocity gradient portion was changed stepwise on the basis of example 1, as shown in fig. 1. The sound velocity modulation section 202 is a zigzag structure. Two adjacent electrode fingers 203 on the same bus bar 201 are provided with 2 sonic speed buffer parts 202, the root parts of the two saw-tooth sonic speed buffer parts 202 are abutted at the position close to the bus bar 201, and at the moment, the sum of the transverse dimensions of the two sonic speed buffer parts 202 is basically the same as the gap between the two electrode fingers. One end of the electrode finger 203 is connected to the protruding part of the adjacent two sonic ramp parts 202, and the other end, i.e. the free end, is close to the groove formed by the two sonic ramp parts 202 in abutting contact but not in contact. The saw-tooth type sound velocity buffer portion 202 is connected with the bus bar 201 and the electrode finger 203, the distance L1 between the sound velocity buffer portion 202 and the bus bar 201 is 0.1-1λ, and the distance L2 between the sound velocity buffer portion 202 and the electrode finger 203 is 0.01-2.5λ.

In some embodiments, the two saw-tooth-shaped sonic ramp portions 202 between two adjacent electrode fingers 203 on the same bus bar 201 have the same structure. The saw-tooth-like sound speed reducing portions 202 on the two opposing bus bars 201 are identical or different in structure. In some embodiments, the two saw-tooth-like sonic ramp portions 202 between two adjacent motor fingers 203 on the same bus bar 201 are different in structure. The saw-tooth sound speed ramp portions on the two opposing bus bars 201 are identical or different in structure. The structure of the sonic-velocity-reducing portion 202 herein mainly refers to the length and width of the zigzag structure, and as shown in fig. 1, the length is the connection length between the sonic-velocity-reducing portion 202 and the bus bar 201, and the width is the height in the connection direction between the sonic-velocity-reducing portion 202 and the electrode finger 203.

Example 3

As shown in fig. 2, this embodiment 3 is a modification of embodiment 2, in which the sound velocity gradient portion 202 is of a zigzag structure, and the modification is mainly that the root portions of two zigzag sound velocity gradient portions 202 between two adjacent electrode fingers 203 on the same bus bar 201 are not directly connected, and the other is the same as that described in embodiment 2.

The form provided in this embodiment 3 in which the roots of the adjacent two saw tooth type sound velocity transition portions 202 are not directly connected belongs to the category that the width of the sound velocity transition portion is stepwise changed.

Example 4

This embodiment 4 is a variation formed on the basis of both embodiments 2 and 3, and provides an embodiment in which the width of the sound velocity gradient portion is changed stepwise. The main variation of this embodiment 4 with respect to embodiments 2 and 3 is the arrangement of the sound speed varying portion on the bus bar, including:

some embodiments are: the root parts of the two zigzag sonic ramp parts 202 between two adjacent electrode fingers 203 on the same bus bar 201 are in contact with each other and are not directly connected with each other, for example, 4 sonic ramp areas are formed between the 5 electrode fingers 203,5 connected with the

same bus bar

201, 2 areas including the root parts of the sonic ramp parts 202 in contact with each other in the 4 sonic ramp areas, and 2 areas not directly connected with each other are formed. This is just an example, and the number and configuration of regions where the roots of the sound speed buffer portions 202 abut and are not directly connected among the 4 sound speed buffer regions are determined according to the design.

Some embodiments are: in the two opposite bus bars 201, the roots of the two zigzag sonic speed-reducing portions 202 between the adjacent two electrode fingers 203 on one bus bar 201 are abutted, and the roots of the two zigzag sonic speed-reducing portions 202 between the adjacent two electrode fingers 203 on the other bus bar 201 are not directly connected.

Example 5

Embodiment 5 is a variation of embodiment 2, and as shown in fig. 3, the main variation of embodiment 2 is that the sound velocity buffer portion 202 with a single saw-tooth structure is provided between adjacent electrode fingers 203 on the same bus bar 201, and an embodiment in which the width of the sound velocity buffer portion is continuously changed is provided.

In some embodiments, the saw tooth type sonic ramp 202 between adjacent electrode fingers 203 on the same bus bar 201 is identical in structure. The saw-tooth type sound velocity buffer portions 202 on the two bus bars 201 disposed opposite to each other are identical or different in structure. In some embodiments, the saw tooth type sonic ramp 202 between adjacent electrode fingers 203 on the same bus bar 201 is structurally different. The saw-tooth-shaped sound velocity buffer portions 202 on the two bus bars 201 disposed opposite to each other are identical in structure or do not pass through.

Example 6

In embodiment 6, as shown in fig. 4, a main change from embodiment 2 is that the number of saw-tooth-shaped sound velocity buffer parts 202 between adjacent electrode fingers 203 on the same bus bar 201 exceeds 2. The number of structural forms presented in this embodiment exceeds 2, and belongs to the category of stepwise changes in the width of the sound velocity buffer portion.

In some embodiments, the saw-tooth type acoustic velocity buffer portions 202 between adjacent electrode fingers 203 of the same bus bar 201 are different in structure, as shown in fig. 4, and are 4 saw-tooth type acoustic velocity buffer portions 202, including two acoustic velocity buffer portions 202 with larger sizes on both sides and 2 acoustic velocity buffer portions 202 with smaller sizes in the middle. Similarly, the saw-tooth-shaped sound velocity reducing portions 202 on the two bus bars 201 disposed opposite to each other are identical or different in structure. In some embodiments, the saw tooth type sonic ramp 202 between adjacent electrode fingers 203 of the same bus bar 201 is identical in structure. The saw-tooth type sound velocity buffer portions 202 on the two bus bars 201 disposed opposite to each other are identical or different in structure.

Example 7

In example 7, a modified example of the embodiment 1 is shown in fig. 6, in which the sound velocity gradient portion 202 is configured as an i-shaped structure. The i-shaped sonic velocity modulation portion 202 is sandwiched between two adjacent electrode fingers 203 of the same-side bus bar 201, the free ends of the electrode fingers 203 connected to the opposite-side bus bar 201 are disposed in a gap with one end of the sonic velocity modulation portion 202, and the sonic velocity modulation portion 202 is disposed in a gap with the bus bar 201. In this embodiment, the sound speed buffer 202 is designed into an i-shaped structure, and the i-shaped sound speed buffer 202 does not have the characteristic of gradual width change, but the i-shaped sound speed buffer 202 can adjust the regional sound speed of the electrode finger end gap region, especially the middle part of the i-shaped sound speed is weakened, so as to play a role in suppressing various spurious modes and high-order transverse clutter generated by the resonator to a certain extent. Meanwhile, the sound velocity buffer part 202 is designed into an I-shaped structure, so that the electromechanical coupling coefficient of the resonator unit can be adjusted, the structure is simple, the miniaturization of the size of the device is facilitated, and the cost is reduced. The specific reasons are as follows: the coupling coefficients of the resonator elements for the specific substrates and for the several frequency bands of different bandwidths are certain, which results in that the electromechanical coupling coefficients of the resonator elements may be larger or smaller for the different bandwidth frequency bands. Therefore, in the design process of the conventional filter, some electrical devices such as a capacitor and an inductor are often added to the topology structure of the filter to adjust the effective electromechanical coupling coefficient of the resonator unit, so as to obtain the required bandwidth of the filter. However, the Q values of the capacitor and inductor components manufactured at present are extremely low and far lower than those of the acoustic resonator parts, so that the problems of large insertion loss of the final filter product and the like are caused. The i-shaped sound velocity buffer part is directly arranged between the electrode fingers of the resonator, so that the effects of inhibiting various stray modes and high-order transverse clutters generated by the resonator can be achieved to a certain extent, and the electromechanical coupling coefficient is directly regulated and controlled on the resonator unit, so that the defects are overcome.

In some embodiments, as shown in fig. 6, the distance between the free end of the electrode finger 203 and the corresponding bus bar 201 is denoted as gap, and the gap is also in the range of 0.01-2.5λ, where λ is the surface acoustic wave wavelength. As shown in fig. 7, the overall height H4 of the i-shaped sonic ramp portion 202 is set to 0.3-0.8 times gap, the height H3 of the middle portion of the i-shaped sonic ramp portion 202 is set to 0.3-0.8 times H4, and the upper and lower heights of the i-shaped sonic ramp portion 202 are the same or different. Through the design of the parameters, the effective electromechanical coupling coefficient of the resonator unit which can be achieved by the sound velocity buffer part 202 is 13.2%, and the coupling coefficient is better

In some embodiments, reflective gratings 300 are provided at both ends of the resonator, and an i-shaped sonic ramp 202 is provided on the reflective grating 300.

In the description of the present application, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientations or positional relationships illustrated in the drawings, merely to facilitate description of the present application and simplify the description, and do not indicate or imply that the devices or elements being referred to must have a specific orientation, be configured and operated in a specific orientation, and are not to be construed as limiting the present application.

The foregoing describes specific embodiments of the present invention. It is to be understood that the invention is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily without conflict.

Claims

1. A surface acoustic wave resonator comprising a piezoelectric substrate (100) and an interdigital transducing structure (200);

the interdigital transduction structure (200) is positioned on one side of the piezoelectric substrate (100), the interdigital transduction structure (200) comprises two bus bars (201) which are oppositely arranged, each bus bar (201) is connected with a plurality of electrode fingers (203) to form a comb-shaped structure, and the electrode fingers (203) on the two bus bars (201) are mutually crossed;

a sound speed buffer part (202) is arranged between adjacent electrode fingers (203) on the same bus bar (201), and the free end of each electrode finger (203) is opposite to the sound speed buffer part (202) and keeps a preset gap.

2. The surface acoustic wave resonator according to claim 1, characterized in that the sound velocity buffer (202) is a structure whose width is continuously changed or a structure whose width is stepwise changed.

3. The surface acoustic wave resonator according to claim 2, characterized in that the sound velocity buffer (202) is a saw-tooth structure.

4. A saw resonator according to claim 3, wherein at least one of said sound speed moderating portions (202) is provided between adjacent ones of said electrode fingers (203) on the same bus bar (201).

5. A surface acoustic wave resonator according to claim 3, characterized in that a plurality of said sound speed moderating portions (202) are provided between adjacent electrode fingers (203) on the same bus bar (201), and a plurality of said sound speed moderating portions (202) between adjacent electrode fingers (203) on the same bus bar (201) are connected to each other and/or provided at intervals.

6. The surface acoustic wave resonator according to claim 5, characterized in that the sound speed buffer parts (202) between adjacent electrode fingers (203) on the same bus bar (201) are identical or different in structure.

7. The surface acoustic wave resonator according to any of claims 3-6, characterized in that the sound speed modifying parts (202) on two of the bus bars (201) are identical or different in structure.

8. The surface acoustic wave resonator according to claim 1, characterized in that the sound speed buffer portion (202) is an i-shaped structure, the sound speed buffer portion (202) is electrically connected between the electrode fingers (203) adjacent on the same side, one end of the sound speed buffer portion (202) maintains a predetermined gap with an end of the electrode finger (203), and the other end of the sound speed buffer portion (202) maintains a predetermined gap with the bus bar (201).

9. The surface acoustic wave resonator according to claim 8, characterized in that the sound speed buffer (202) has an overall height H4 set to 0.003-0.75λ, a middle portion height H3 set to 0.3-0.8H4, and an upper height H1 and a lower height H2 set to be the same or different, wherein λ is a surface acoustic wave wavelength.

10. The surface acoustic wave resonator according to claim 8, characterized in that the distance between the free end of the electrode finger (203) and the opposing bus bar (201) is 0.01-2.5 λ, where λ is the surface acoustic wave wavelength.