High frequency acoustic wave resonator and communication device

Abstract

The application relates to the technical field of resonators, in particular to a high-frequency acoustic wave resonator and a communication device. The high-frequency acoustic wave resonator comprises, from bottom to top, a support substrate, a reflection structure, a piezoelectric layer and an interdigital electrode; the reflection structure comprises a first reflection layer and a second reflection layer which are stacked; the acoustic impedance of the first reflection layer and the second reflection layer is different; the target mode of the high-frequency acoustic wave resonator is a high acoustic speed mode; the product of the electrode finger spacing of the interdigital electrode and the anti-resonance frequency is greater than the slow shear wave speed of the support substrate, and the product of the electrode finger spacing of the interdigital electrode and the resonator frequency is less than the longitudinal wave speed of the support substrate; the electrode finger spacing of the interdigital electrode is the distance between the centers of adjacent electrode fingers on the same bus bar of the interdigital electrode; the upper limit of the acoustic speed of the target mode is increased from the slow shear wave speed of the support substrate to the longitudinal wave speed, and the high-frequency acoustic wave resonator can be applied to a high-frequency scene.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resonators, in particular to a high-frequency acoustic wave resonator and a communication device. BACKGROUND

[0002] Acoustic wave filters mainly include bulk acoustic wave (BAW) filters and surface acoustic wave (SAW) filters. In addition, in recent years, plate wave filters have also attracted much attention due to their high sound speed.

[0003] In order to improve the working frequency of the filter, the BAW device usually adopts a thinned piezoelectric thin film to achieve this, but for the BAW device with a suspended thin film, the piezoelectric thin film is too thin to have mechanical stability. For the BAW device of a solidly mounted resonator (SMR), it is achieved based on the Bragg reflection layer arranged therein, but as known, the Bragg reflection layer usually includes a layer structure of at least 6 layers or more, which greatly increases the difficulty of device processing, especially for the device using a single crystal piezoelectric thin film, it is difficult to prepare a qualified Bragg reflection layer. For the SAW device, the working frequency is improved by reducing the period of the electrode, but when the target mode is the common zero-order horizontal shear mode and Rayleigh mode, the sound speed is only 4000 m / s, and it is difficult to realize the application of more than 3.5 GHz frequency band under the existing photolithography condition. Therefore, how to provide a resonator with simple structure, easy to prepare and applicable to high frequency band has become a problem to be solved. SUMMARY

[0004] To solve the above technical problems, the present application discloses a high-frequency acoustic wave resonator in one aspect, comprising a support substrate, a reflection structure, a piezoelectric layer and an interdigital electrode arranged in sequence from bottom to top.

[0005] The reflection structure includes a first reflection layer and a second reflection layer stacked; the acoustic impedance of the first reflection layer and the second reflection layer is different;

[0006] The target mode of the high-frequency acoustic wave resonator is a high sound speed mode, the product of the electrode finger spacing of the interdigital electrode and the anti-resonance frequency is greater than the slow shear wave sound speed of the support substrate, and the product of the electrode finger spacing of the interdigital electrode and the resonator frequency is less than the longitudinal wave sound speed of the support substrate; the electrode finger spacing of the interdigital electrode is the distance between the centers of adjacent electrode fingers on the same bus bar of the interdigital electrode.

[0007] In a feasible embodiment, the first reflection layer is close to the piezoelectric layer; the acoustic impedance of the second reflection layer is greater than 2 times the acoustic impedance of the first reflection layer.

[0008] In an embodiment, the reflective structure comprises a plurality of first reflective layers and second reflective layers stacked alternately.

[0009] The total number of first reflective layers and second reflective layers comprised in the reflective structure is less than or equal to 5.

[0010] In an embodiment, the piezoelectric layer comprises at least two sub-piezoelectric layers stacked alternately.

[0011] The material type or the cut type of adjacent sub-piezoelectric layers in the at least two sub-piezoelectric layers is different.

[0012] In an embodiment, a functional layer is further provided between the reflective structure and the piezoelectric layer.

[0013] The functional layer comprises one or more of a temperature compensation layer, a heat dissipation layer, and a trap-rich layer.

[0014] In an embodiment, the support substrate comprises a support layer and a high acoustic velocity layer stacked alternately.

[0015] The high acoustic velocity layer is made of a material that is easy to process; the material of the high acoustic velocity layer is any one of silicon carbide, diamond, diamond-like carbon, aluminum oxide, aluminum nitride, boron nitride, boron carbide, and silicon nitride in different crystal forms and different cut types.

[0016] The material of the support layer comprises any one of quartz, silicon, sapphire, spinel, and yttrium aluminum garnet.

[0017] In an embodiment, a bonding layer is further comprised between the reflective layer and the support substrate.

[0018] In an embodiment, a bottom electrode is provided between the reflective structure and the piezoelectric layer.

[0019] The target mode is a high acoustic velocity mode excited by a longitudinal electric field.

[0020] In an embodiment, the bottom electrode is a combination of one or more of copper, aluminum, gold, silver, tungsten, platinum, nickel, chromium, molybdenum, titanium, graphene, copper-aluminum alloy, aluminum-silicon alloy, doped silicon, silicon carbide, and gallium nitride.

[0021] The width of the bottom electrode is not more than the width of an aperture region, which is a region where the electrode fingers of the interdigital electrode overlap.

[0022] In an embodiment, the material of the piezoelectric layer is any one or a combination of lithium tantalate, lithium niobate, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate, or lead magnesium niobate-lead titanate.

[0023] The support substrate is a combination of one or more of silicon carbide, diamond, diamond-like carbon, silicon, sapphire, aluminum nitride, boron nitride, boron carbide, and silicon nitride in different crystal forms and different cut types.

[0024] In one possible embodiment, the material of the first reflective layer is any one of silicon oxide, aluminum, germanium, titanium, silicon, magnesium alloy, and ion-implanted or doped silicon oxide;

[0025] The material of the second reflective layer is any one of tungsten, platinum, tungsten nitride, hafnium oxide, hafnium nitride, tungsten oxide, aluminum oxide, aluminum nitride, silicon carbide, titanium oxide, gold, nickel, molybdenum, tantalum, chromium, and copper.

[0026] In one possible embodiment, the product of the pitch of the electrode fingers of the interdigital electrode and the anti-resonant frequency exceeds 7000 m / s;

[0027] The longitudinal wave acoustic velocity of the support substrate exceeds 7000 m / s.

[0028] In one possible embodiment, the target mode of the high-frequency acoustic wave resonator is any one of a longitudinal leaky surface acoustic wave mode, a high-order horizontal shear mode, a high-order Lamb wave mode, and a high-order Rayleigh mode.

[0029] In another aspect, the application discloses a communication device comprising the high-frequency acoustic wave resonator.

[0030] The communication device comprises at least one of a filter, a diplexer, and a multiplexer.

[0031] With the technical scheme, the high-frequency acoustic wave resonator has the following beneficial effects:

[0032] The high-frequency acoustic wave resonator comprises, from bottom to top, a support substrate, a reflection structure, a piezoelectric layer and an interdigital electrode; the reflection structure comprises a first reflection layer and a second reflection layer stacked; the acoustic impedance of the first reflection layer and the second reflection layer is different; the target mode of the high-frequency acoustic wave resonator is a high acoustic speed mode, the product of the electrode finger spacing of the interdigital electrode and the anti-resonance frequency is greater than the slow shear wave speed of the support substrate, and the product of the electrode finger spacing of the interdigital electrode and the resonator frequency is less than the longitudinal wave speed of the support substrate; the electrode finger spacing of the interdigital electrode is the distance between the centers of adjacent electrode fingers on the same bus bar of the interdigital electrode, the overall structure is not only simple, but also convenient for forming and processing, and by arranging a pair of reflection layers with different acoustic impedance between the piezoelectric layer and the support substrate, the target mode can still be constrained on the surface of the support substrate when the target mode is at a higher frequency, so that the resonator can be applied to a high-frequency scene, and the upper limit of the high-order acoustic wave mode speed can be further improved, so that the acoustic speed difference between the target mode and the zero-order mode can be improved, and it is ensured that the parasitic mode appears outside the passband. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0034] Figure 1 is a structural schematic diagram of a first high-frequency acoustic wave resonator provided by the present application;

[0035] Figure 2 is Figure 1 is a kind of simulation admittance and conductance curve corresponding to the structure;

[0036] Figure 3 is Figure 1 is another simulation admittance and conductance curve corresponding to the structure;

[0037] Figure 4 is a structural schematic diagram of a second high-frequency acoustic wave resonator provided by the present application;

[0038] Figure 5 is Figure 4 is a partial top view of the structure shown;

[0039] Figure 6 is a structural schematic diagram of a comparative example 1 provided by the present application;

[0040] Figure 7 is a simulation admittance curve of a comparative example 1 and an example 1 provided by the present application;

[0041] Figure 8 is a simulation conductance curve of Comparative Example 1 and Example 1 provided by the present application;

[0042] Figure 9 is a simulation Bode-Q curve of Comparative Example 1 and Example 1 provided by the present application

[0043] Figure 10 is a mode shape diagram of Comparative Example 1 at the anti-resonance frequency f p ;

[0044] Figure 11 is a mode shape diagram of Example 1 at the anti-resonance frequency f p ;

[0045] Figure 12 is a simulation admittance curve and a simulation conductance curve of Comparative Example 2 provided by the present application;

[0046] Figure 13 is a simulation admittance curve and a simulation conductance curve of Example 2 provided by the present application;

[0047] Figure 14 is an S21 curve corresponding to a filter constructed based on the resonator of Comparative Example 2 provided by the present application;

[0048] Figure 15 is an S21 curve corresponding to a filter constructed based on the resonator of Example 2 provided by the present application;

[0049] Figure 16 is a structural schematic diagram of a third high-frequency acoustic wave resonator provided by the present application;

[0050] Figure 17 is a simulation admittance ratio corresponding to Comparative Example 3 provided by the present application;

[0051] Figure 18 is a simulation admittance curve corresponding to Comparative Example 3 provided by the present application;

[0052] Figure 19 is a simulation admittance ratio corresponding to Comparative Example 3 and Example 3 provided by the present application;

[0053] Figure 20 is a simulation admittance curve corresponding to Example 3 provided by the present application;

[0054] Figure 21 is a mode shape diagram corresponding to Example 3 provided by the present application;

[0055] Figure 22 is an admittance curve of Comparative Example 3 and Example 3 when the number of reflection layers N is equal to 2 provided by the present application;

[0056] Figure 23 is an example 4 simulation admittance curve and a simulation conductance curve provided by the present application;

[0057] Figure 24 is a structural schematic diagram of a fourth high-frequency acoustic wave resonator provided by the present application;

[0058] Figure 25 is a structural schematic diagram of a fifth high-frequency acoustic wave resonator provided by the present application;

[0059] Figure 26 is a structural schematic diagram of a sixth high-frequency acoustic wave resonator provided by the present application.

[0060] The following is a supplementary description of the drawings:

[0061] 1 - support substrate; 101 - support layer; 102 - high acoustic velocity layer; 2 - reflective structure; 201 - first reflective layer; 202 - second reflective layer; 3 - piezoelectric layer; 301 - sub-piezoelectric layer; 4 - interdigital electrode; 401 - first bus bar; 402 - second bus bar; 403 - electrode finger; 404 - aperture region; 5 - bottom electrode; 6 - bonding layer. DETAILED DESCRIPTION

[0062] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0063] The terms "one embodiment" or "an embodiment" as may appear in various places of the specification are not necessarily referring to the same embodiment nor are separate or alternative embodiments necessarily mutually exclusive of one another. The terms "first," "second," "third," etc. as may be used in the description and / or claims (such as, for example, used nomenclature "first," "second," "third," etc. to denote different timing or sequence intervals) should not be construed as indicating either an ordered sequence or importance, unless otherwise specifically stated. The use herein of terms such as "first" and / or "second," and the like, is generally meant to identify only a class of elements if more than one class is involved. Thus, a "first" element discussed below could be the same as or different from a "second" element. The use of the terms "first" and / or "second," etc. is also not limiting as those terms can be used to identify or describe different instances of the same element.

[0064] When a range of values is disclosed, unless otherwise indicated, the intended scope is a range between the minimum and maximum limits of that range. Further, the disclosure of a range of values includes each possible value within that range. Additionally, when a range of values is provided, it is intended to include every possible subset of values within that range. In other words, unless the context clearly indicates otherwise, within the present disclosure, the use of a numeric range should be interpreted as specifically disclosing and enabling the claim of every possible subset of values within that range. For example, a disclosure of "1 to 10" should be interpreted to mean that "1 to 10" as well as every possible subset of the same is specifically, individually, and explicitly disclosed and enabled. Exemplary sub-ranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0065] The following abbreviations and notations are used in the embodiments of the present application:

[0066] LL-SAW means Longitudinal Leaky Surface Acoustic Wave

[0067] SH0 means Fundamental shear horizontal mode

[0068] SH1 means First-order shear horizontal mode

[0069] S1 represents a first-order symmetric Lamb wave mode

[0070] f s represents a resonator frequency of the resonator, is a frequency corresponding to a maximum point of the admittance curve

[0071] f p represents an anti-resonance frequency of the resonator, is a frequency corresponding to a minimum point of the admittance curve

[0072] λ represents a pitch of the electrode fingers of the interdigital electrode of the resonator, the pitch of the electrode fingers of the interdigital electrode is a distance between centers of adjacent electrode fingers on the same bus bar of the interdigital electrode

[0073] ν p represents a product of the pitch of the electrode fingers of the interdigital electrode of the resonator and the anti-resonance frequency

[0074] ν s represents a product of the pitch of the electrode fingers of the interdigital electrode of the resonator and the resonator frequency

[0075] ν l represents a longitudinal wave speed of the support substrate of the resonator

[0076] ν ss represents a slow shear wave speed of the support substrate of the resonator

[0077] ν fs represents a fast shear wave speed of the support substrate of the resonator

[0078] In the prior art, there are mainly the following four kinds of acoustic resonators. The first kind is a zero-order horizontal shear mode as a target mode, and the structure includes a support substrate, a dielectric layer, a piezoelectric thin film and a top electrode which are stacked from bottom to top.ν p Only about 4000 m / s, which is less than the slow shear wave speed v ss Thus, the target mode can be constrained on the surface of the support substrate, and a high Q value is achieved. However, the acoustic speed is low, and it is difficult to realize the application of a frequency band above 3.5 GHz. The second kind is an S0 plate wave mode in lithium niobate as a target mode, and the structure includes a support substrate, a Bragg reflection layer, a piezoelectric thin film and a top electrode which are stacked from bottom to top,ν p Generally 6000 m / s to 7000 m / s, and the Bragg reflection layer is used to constrain the target mode. The third kind is an SH1 mode in X-cut lithium niobate as a target mode, and the structure is the same as the second kind,ν p About 10000 m / s, and the Bragg reflection layer is used to constrain the target mode. The fourth kind is a high-order acoustic wave mode as a target mode, and the structure includes a support substrate, a bottom electrode, a piezoelectric thin film and a top electrode which are stacked from bottom to top,νp The slow shear acoustic wave velocity v of the support substrate ss The high acoustic velocity support substrate is used to improve the upper limit of the target mode acoustic velocity.

[0079] However, the above four structural schemes have the following disadvantages respectively:

[0080] In the first structure, since its v p is about 4000m / s, which is less than the slow shear wave velocity v ss of most common support substrate materials. For example, the v ss of silicon is about 5800m / s, the v p of quartz is about 5000m / s, and the v ss of sapphire is about 6000m / s. This makes the SH0 mode well constrained on the substrate surface, achieving a high Q value. However, the working frequency is inversely proportional to λ, and in order to increase the frequency, the line width and pitch of the electrode must be reduced, which puts higher requirements on the photolithography technology. Under the existing photolithography conditions, it is difficult to develop beyond 3.5GHz.

[0081] In the second structure, although the effective constraint of the target mode is achieved, the multilayer Bragg reflection layer structure makes the device processing very complex.

[0082] In the third structure, although the effective constraint of the target mode is achieved, the multilayer Bragg reflection layer structure makes the device processing very complex. Moreover, the frequency of the target mode is very sensitive to the thickness of each layer of film, and the thickness of each reflection layer needs to be accurately controlled, which is very difficult for actual processing.

[0083] In the fourth structure, although the target mode can meet the demand of Sub-6GHz frequency band under relatively loose photolithography conditions, the working frequency cannot be further improved. Moreover, due to the upper limit of the acoustic velocity, the frequency difference between the parasitic mode and the target mode cannot be further adjusted, and the parasitic mode usually appears near the left edge of the target passband, resulting in a decrease in the out-of-band suppression level.

[0084] In view of the shortcomings of the above existing schemes, the present scheme proposes to use a high acoustic velocity support substrate, and insert two reflection layers between the support substrate and the piezoelectric film, and the acoustic impedance between the reflection layers is different. Unlike structures containing only one reflection layer or no reflection layer, when the v p of the target mode exceeds the v ss of the support substrate, the target mode can still be well constrained on the substrate surface. Unlike structures with multilayer Bragg reflection layers, this structure makes full use of the reflection of the high acoustic velocity support substrate itself to limit the v s of the target mode to the v l of the support substrate. By adding only two reflection layers, the high acoustic velocity target mode can be constrained on the substrate surface. The structure is greatly simplified, and common support substrates have a vl Generally close to 2 times of v ss , for example, v l of sapphire is up to 11113 m / s, v l of silicon carbide is up to 12493 m / s. This greatly improves the upper limit of the acoustic velocity of the target mode, and the frequency can be as high as 10 GHz or above, and the acoustic potential of the high acoustic velocity support substrate is brought to the limit.

[0085] In addition, when the target mode is a high-order mode, if its bandwidth is large. Generally, the zero-order mode will appear near the low-frequency cutoff frequency edge of the target passband, resulting in a decrease in the in-band ripple or out-of-band suppression level of the filter. The high-order mode has a strong dispersion effect, and its acoustic velocity can be changed by adjusting the thickness of the piezoelectric layer and the load, so that the frequency difference with the spurious mode can be changed. However, limited by the slow shear wave acoustic velocity v ss of the support substrate, the acoustic velocity regulation range of the high-order mode is limited. After adding two reflection layers, the upper limit of the acoustic velocity of the high-order mode is greatly improved, so that the relative frequency of the spurious mode and the target mode can be flexibly regulated to improve the out-of-band suppression level of a specific frequency band.

[0086] In general, the structure is relatively simple, avoids the use of multi-layer Bragg reflection layer, fully utilizes the advantages of high acoustic velocity support substrate, and is conducive to the mass production and yield improvement of high-performance high-frequency resonators and filters.

[0087] Specifically, refer to Figure 1 , which is a structural schematic diagram of a first high-frequency acoustic wave resonator provided by the present application. The high-frequency acoustic wave resonator comprises, from bottom to top, a support substrate 1, a reflection structure 2, a piezoelectric layer 3, and an interdigital electrode 4; the reflection structure 2 comprises a first reflection layer 201 and a second reflection layer 202 stacked one above the other; the acoustic impedance of the first reflection layer 201 and the second reflection layer 202 is different; the target mode of the high-frequency acoustic wave resonator is a high acoustic velocity mode, the product of the electrode finger 403 spacing of the interdigital electrode 4 and the anti-resonance frequency is greater than the slow shear wave acoustic velocity of the support substrate 1, and the product of the electrode finger 403 spacing of the interdigital electrode 4 and the resonator frequency is less than the longitudinal wave acoustic velocity of the support substrate 1; the electrode finger 403 spacing of the interdigital electrode 4 is the distance between the centers of adjacent electrode fingers 403 on the same bus bar of the interdigital electrode 4.

[0088] In a feasible embodiment, the first reflection layer 201 is close to the piezoelectric layer 3; the acoustic impedance of the second reflection layer 202 is greater than 2 times the acoustic impedance of the first reflection layer 201.

[0089] In one possible embodiment, the material of the piezoelectric layer 3 is one or a combination of lithium tantalate, lithium niobate, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate, or lead magnesium niobate-lead titanate.

[0090] In one possible embodiment, the material of the support substrate 1 is one or a combination of silicon carbide, diamond, diamond-like carbon, silicon, sapphire, aluminum nitride, boron nitride, boron carbide, and silicon nitride in different crystal forms and different cut types.

[0091] In one possible embodiment, the material of the first reflective layer 201 is one of silicon oxide, aluminum, germanium, titanium, silicon, magnesium alloy, and ion-implanted or doped silicon oxide.

[0092] In one possible embodiment, the material of the second reflective layer 202 is one of tungsten, platinum, tungsten nitride, hafnium oxide, hafnium nitride, tungsten oxide, aluminum oxide, aluminum nitride, silicon carbide, titanium oxide, gold, nickel, molybdenum, tantalum, chromium, and copper.

[0093] In one possible embodiment, the product of the pitch of the electrode fingers 403 of the interdigital electrode 4 and the anti-resonant frequency exceeds 7000 m / s; the longitudinal wave acoustic velocity of the support substrate 1 exceeds 7000 m / s.

[0094] In one possible embodiment, the target mode of the high-frequency acoustic wave resonator is one of a longitudinal leaky surface acoustic wave mode, a high-order horizontal shear mode, a high-order Lamb wave mode, and a high-order Rayleigh mode.

[0095] In one exemplary embodiment, as shown in the structure of Figure 1 , the material of the support substrate 1 is silicon, the material of the second reflective layer 202 is tungsten nitride with a thickness of 165 nm; the material of the first reflective layer 201 is silicon oxide with a thickness of 270 nm; the piezoelectric layer 3 is a 30% scandium-doped aluminum nitride with a thickness of 400 nm; the material of the interdigital electrode 4 is aluminum with a thickness of 50 nm, and λ is 1 μm. The target mode is an LL-SAW mode, the longitudinal wave acoustic velocity v s is 7181 m / s, and the longitudinal wave acoustic velocity v p is 7351 m / s. The longitudinal wave acoustic velocity v ss and the longitudinal wave acoustic velocity v fs of silicon are both 5846 m / s, and the longitudinal wave acoustic velocity v l of silicon nitride is about 8442 m / s. Subsequent correlation calculations can obtain the simulation admittance curve and the simulation conductance curve as shown in Figure 2 . It can be seen that the acoustic velocity of the LL-SAW mode is less than the longitudinal wave acoustic velocity v l of the support substrate 1, and thus can be constrained on the surface of the support substrate 1.

[0096] In another exemplary embodiment, as shown in the structure ofFigure 1 In the structure shown, the material of the support substrate 1 is silicon, the material of the second reflective layer 202 is tungsten nitride, and the thickness is 200 nm; the material of the first reflective layer 201 is silicon oxide, and the thickness is 370 nm; the piezoelectric layer 3 is a 30% scandium-doped aluminum nitride, and the thickness is 263 nm; the material of the interdigital electrode 4 is aluminum, and the thickness is 50 nm, and λ is 1 μm. The target mode is the S1 mode, and the longitudinal wave velocity v s is 7825 m / s, and the fast shear wave velocity v p is 7972 m / s. Subsequent correlation calculation can obtain the simulation admittance curve and the simulation conductance curve as shown in Figure 3 It can be seen that the velocities of the LL-SAW mode and the S1 mode are both less than the longitudinal wave velocity of the support substrate 1, so both are well constrained.

[0097] In another possible embodiment, please refer to Figure 4 , a bottom electrode 5 is arranged between the reflective structure 2 and the piezoelectric layer 3; and the target mode is a high-velocity mode excited by a longitudinal electric field.

[0098] In a possible embodiment, the bottom electrode 5 is a combination of one or more of copper, aluminum, gold, silver, tungsten, platinum, nickel, chromium, molybdenum, titanium, graphene, copper-aluminum alloy, aluminum-silicon alloy, doped silicon, silicon carbide, and gallium nitride; and the width of the bottom electrode 5 does not exceed the width of the aperture region 404, please refer to Figure 5 , the aperture region 404 is the region where the electrode fingers of the interdigital electrode 4 overlap, specifically, the interdigital electrode 4 includes a first bus bar 401, a second bus bar 402, and a plurality of electrode fingers 403, the first bus bar 401 is provided with a plurality of electrode fingers 403 arranged at intervals, the second bus bar 402 is also provided with a plurality of electrode fingers arranged at intervals, the electrode fingers 403 on different bus bars are arranged in an interlaced manner, and the distance between the centers of adjacent electrode fingers 403 on the same bus bar is the pitch λ of the electrode fingers 403 of the interdigital electrode 4.

[0099] For example, the present application provides a comparative example 1 and an example 1, wherein the comparative example 1 can be a structure as shown in Figure 6 , that is, including, from bottom to top, a support substrate 1, a first reflective layer 201, a bottom electrode 5, a piezoelectric layer 3, and an interdigital electrode 4. The structure of the example 1 can be as shown in Figure 4 , the main difference between the comparative example 1 and the example 1 is that the example 1 further includes a second reflective layer 202 having a different acoustic impedance from the first reflective layer 201, and the remaining parameters are the same, that is, the material of the support substrate 1 is 4H-SiC, the slow shear wave velocity v ss is about 7126 m / s, the fast shear wave velocity v fs is about 7794 m / s, and the longitudinal wave velocity v labout 12493m / s, the material of the first reflecting layer 201 is silicon oxide, and the material of the second reflecting layer 202 is tungsten; the bottom electrode 5 is platinum with a thickness of 20nm; the material of the piezoelectric layer 3 is Y171 cut lithium niobate with a thickness of 150nm; the interdigital electrode 4 is aluminum / tungsten with a thickness of 50nm / 12nm, λ is 1μm, and the number of interdigital electrode pairs (adjacent electrodes on different bus bars are usually referred to as an interdigital electrode pair) is 20 pairs. In the comparative example 1, the thickness of the first reflecting layer 201 is 100nm, and in the example 1, the thickness of the first reflecting layer 201 is 180nm, and the thickness of the second reflecting layer 202 is 100nm. The target mode of the comparative example 1 and the example 1 is SH1 mode. Simulation calculation is performed on both, and the simulation admittance results and the simulation conductance results shown in Figure 7 and 8 can be obtained. It can be seen that the anti-resonance frequencies f p of both are approximately equivalent, and both exceed the ratio of the slow shear wave speed v ss of the support substrate 1 to λ. The admittance ratio of the comparative example 1 is obviously lower than that of the example 1, especially in the frequency band exceeding v ss / λ, and the difference between the two is large. Figure 8 The conductance curves shown in Figure 8 can reflect the acoustic loss caused by the bulk wave radiation. It can be seen that the amplitude of the conductance curve of the example 1 is obviously lower than that of the comparative example 1, especially when the frequency is close to and greater than v ss / λ, and the difference between the two is large. The conductance curve of the example 1 still remains at a low level when the frequency is greater than v ss / λ, that is, the bulk wave radiation remains at a low level, which indicates that even if v p exceeds the slow shear wave speed of the support substrate 1, the example 1 can still maintain a high Q value, and the upper limit of the acoustic speed of the target mode is further improved. Further, by comparing the simulation Bode-Q curves of the comparative example 1 and the example 1, that is, Figure 9 it can be seen that the Q value of the comparative example 1 decreases greatly when the frequency is close to or exceeds v ss / λ, while the Q value of the example 1 still maintains a high level when the frequency exceeds v ss / λ. This indicates that the upper limit of the acoustic speed of the comparative example 1 is the slow shear wave speed v ss of the support substrate 1, while the example 1 breaks through this limit and still has no obvious acoustic energy leakage at least near the frequency of v fs / λ. Further, please refer to Figure 10 and 11 , which are the anti-resonance frequencies f pThe mode shape diagram of the resonator can be seen, and the acoustic wave energy of the comparative example 1 leaks into the support substrate 1, while the acoustic wave energy of the example 1 is well constrained on the surface of the substrate. Thus, it can be illustrated that the structure of the acoustic wave resonator provided in the present application, which comprises two reflection layers with different acoustic impedances, can still constrain the target mode on the surface of the support substrate 1 when the target mode is at a higher frequency, so that the resonator can be applied to a high-frequency scene, and the upper limit of the acoustic velocity of the high-order acoustic wave mode can be further improved, so that the acoustic velocity difference between the target mode and the zero-order mode can be improved, and it is ensured that the parasitic mode appears outside the passband.

[0100] The present application provides another comparative example 2 and example 2. The comparative example 1 can be a structure as shown in Figure 6 , and the structure of the example 2 can be a structure as shown in Figure 4 . The material of the support substrate 1 is 4H-SiC, the material of the first reflection layer 201 is silicon oxide, and the material of the second reflection layer 202 is tungsten; the bottom electrode 5 is tungsten with a thickness of 100 nm; the material of the piezoelectric layer 3 is X-cut lithium niobate with a thickness of 200 nm; and the interdigital electrode 4 is tungsten / aluminum with a thickness of 25 nm / 75 nm. In the comparative example 1, the thickness of the first reflection layer 201 is 200 nm, λ is 1.573 μm, and is slightly less than ν ss / f p . In the example 1, the thickness of the first reflection layer 201 is 200 nm, the thickness of the second reflection layer 202 is 255 nm, λ is 1.72 μm, and is slightly less than ν fs / f p . The target mode of the comparative example 1 and the example 1 is SH1 mode, simulation calculation is performed on the two, and the simulation results of the comparative example 2 and the example 2 are shown in Figure 12 and Figure 13 . It can be seen that in the comparative example 2, the LL-SAW appears as a parasitic mode on the left side of the resonant frequency of the target mode, and is limited by the ν ss of the support substrate 1, and the frequency difference Δf between the two modes has reached the limit, about 554 MHz. In the example 2, the LL-SAW also appears as a parasitic mode on the left side of the resonant frequency of the target mode, and since the target mode has a strong dispersion effect, the frequency is mainly determined by the thickness of the piezoelectric film and the load. When the upper limit of the acoustic velocity of the target mode is improved, λ increases, and the acoustic velocity difference between the LL-SAW and the SH1 mode increases, and at this time, Δf is about 740 MHz. Thus, it can be seen that the Δf in the comparative example 2 is less than the Δf in the example 2, that is, the spurious mode in the structure of the present application is farther away from the target mode, so that the position of the spurious mode can be flexibly adjusted subsequently.

[0101] When the resonator based on the comparative example 2 is used to construct a filter, the λ of each resonator in the filter satisfies λ < ν ss / f p , and the S21 curve corresponding to the filter is as shown inFigure 14 As shown, at this time, the LL-SAW appears as a parasitic mode on the left side of the target passband, resulting in a decrease in the out-of-band rejection level.

[0102] When a filter is constructed based on the resonator of Example 2, λ of each resonator in the composed filter satisfies λ > v ss / f p The S21 curve corresponding to the filter is as shown in Figure 15 As shown, at this time, the LL-SAW is moved to a lower frequency, and in this case, the parasitic mode is moved to the vicinity of the filter zero point, and the out-of-band rejection level on the left side of the passband is increased by about 20 dB. Due to the increase in the upper limit of the acoustic velocity, the parasitic mode can also be flexibly adjusted to a frequency band with lower requirements for the rejection level as needed.

[0103] In another possible embodiment, referring to Figure 16 , the reflective structure 2 comprises a plurality of first reflective layers 201 and second reflective layers 202 which are alternately stacked; the total number of the first reflective layers 201 and the second reflective layers 202 included in the reflective structure 2 is less than or equal to 5. For example, the reflective structure 2 can be a structure comprising only the first reflective layers 201 and the second reflective layers 202, i.e., a structure as shown in Figure 1 , or a structure comprising two first reflective layers 201 and one second reflective layer 202, specifically, the reflective structure 2 is a structure in which the first reflective layer 201, the second reflective layer 202 and the first reflective layer 201 are sequentially arranged from bottom to top, or a structure comprising two first reflective layers 201 and two second reflective layers 202, or a structure comprising three first reflective layers 201 and two second reflective layers 202.

[0104] For example, when the total number of the reflective layers included in the reflective structure 2 is set as N, the present application provides a comparative example 3, which has a structure as shown in Figure 16 , and the material of the support substrate 1 is sapphire; the material of the second reflective layer 202 is tungsten, and the thickness is 120 nm; the material of the first reflective layer 201 is silicon oxide, and the thickness is 145 nm; the material of the bottom electrode 5 is platinum, and the thickness is 50 nm; the material of the piezoelectric layer 3 is Y36-cut lithium niobate, and the thickness is 200 nm; the material of the interdigital electrode 4 is aluminum, and the thickness is 50 nm; λ is 1.25 μm. The target mode is the S1 mode, and v s and v p of the target mode both exceed 11300 m / s. The slow shear wave acoustic velocity v ss of sapphire is about 6045 m / s, the fast shear wave acoustic velocity v fs is about 6383 m / s, and the longitudinal wave acoustic velocity v l is about 11113 m / s. When the number of the reflective layers in the reflective structure 2 is changed, and the resonators comprising different reflective layers are simulated and calculated, the S21 curve of the filter can be obtained asFigure 17 As shown in the simulation admittance ratio, it can be seen that, since the target mode's v s and v p exceed the longitudinal wave speed of the supporting substrate 1, here 6 layers or more of the reflection layer are required to obtain a larger admittance ratio, and when the number of reflection layers N exceeds 8, the admittance ratio no longer increases. Further, please refer to Figure 18 , the simulation admittance curves of the reflection layer number of 1, 2 and 16 in the above comparative example 3 can be seen that, since the target mode's v s and v p exceed the longitudinal wave speed of the supporting substrate 1, the admittance ratio of the target mode is extremely low when N = 1, and is basically completely leaked, the admittance ratio of N = 2 is improved, but far cannot meet the actual needs of the filter element, and when N = 16, the target mode is completely constrained on the surface of the substrate.

[0105] The present application provides an example 3, which is a structure as shown in Figure 16 , the material of the supporting substrate 1 is Y45 cut 4H-SiC, and the remaining structure parameters are the same as those of the above comparative example 3, and the target mode is S1 mode. Except for the supporting substrate 1, it is the same as comparative example 3. The target mode's v s and v p are between 11300 m / s and 11900 m / s. The slow shear wave speed v ss of Y cut 4H-SiC is about 7467 m / s, the fast shear wave speed v fs is about 8602 m / s, and the longitudinal wave speed v l is about 12493 m / s. Please refer to Figure 19 , by comparing the admittance ratios of the above comparative example 3 and example 3 under different reflection layer numbers, it can be seen that, since the supporting substrate 1 of the comparative example 3 is sapphire, the target mode's v s and v p are slightly greater than the v l of the supporting substrate 1. The supporting substrate 1 of example 3 is Y45 cut 4H-SiC, and the target mode's v s and v p are less than the v l of the supporting substrate 1. When N ≥ 8, the admittance ratios corresponding to different supporting substrates 1 are basically the same, at this time the speed of the supporting substrate 1 has little effect on the target mode. When N is less than 8, a higher longitudinal wave speed of the supporting substrate 1 means a higher Q value. And when the longitudinal wave speed v l of the supporting substrate 1 is greater than the target mode's v s and v pWhen N=2, a larger admittance ratio can be obtained, and when N=6, the sound wave loss is minimized. Therefore, the total number of the first reflective layer 201 and the second reflective layer 202 included in the reflective structure 2 of this application can be set to less than or equal to 5, which can have the advantages of easy molding and processing and high-frequency application.

[0106] For further details, please refer to Figure 20 The figure shown is a simulation admittance curve of Example 3 provided in the embodiments of this application. It can be seen that the ν of the target mode in Example 3 s and ν p All values ​​are less than the longitudinal wave velocity of the supporting substrate 1. When N=1, the admittance ratio of the target mode is extremely low, and when N=2, the admittance ratio is only slightly less than when N=16. This indicates that as long as the ν of the target mode... s and ν p ν is smaller than that of the supporting substrate 1 l With only two reflective layers, the target mode is essentially confined to the substrate surface. (See also...) Figure 21 Figure (a) shows the mode shape when the number of reflective layers N=1 in Example 3, in which a large amount of acoustic waves leaks into the substrate. Please refer to [the original text]. Figure 21 Figure (b) shows the mode shape when the number of reflective layers N=2 in Example 3. In this case, the sound waves are basically confined to the substrate surface.

[0107] Furthermore, by comparing the admittance curves of Comparative Example 3 and Example 3 when the number of reflective layers N=2 (e.g., ... Figure 22 As shown in the figure, the resonant frequency is less than ν. l / λ is key to constraining the target mode using fewer reflective layers. Here, ν1 and ν2 are the longitudinal wave velocities of sapphire and silicon carbide, respectively. This further illustrates the reflective layers with two different acoustic impedances protected in this application, and the product ν of the spacing of the electrode fingers 403 of the interdigitated electrode 4 and the anti-resonant frequency. p The slow shear wave velocity ν greater than that of the supporting substrate 1 ss Furthermore, the product of the spacing of the electrode fingers 403 of the interdigitated electrode 4 and the resonator frequency ν s The longitudinal wave velocity ν is less than that of the supporting substrate 1 l The resonator under this condition can be used in the high-frequency domain. To further illustrate the above effect, this application provides another example 4, the structure of which can be as follows: Figure 4 As shown, the material of the supporting substrate 1 is Y45-cut 4H-SiC, the thickness of the first reflective layer 201 is 160 nm, the thickness of the second reflective layer 202 is 135 nm, the thickness of the piezoelectric layer 3 is 195 nm, the λ is 1.33 μm, and other structural parameters are the same as those in Comparative Example 3. At this time, the ν of the target mode... s Reaching 12090 m / s, close to the longitudinal wave velocity ν of the supporting substrate 1.l ν p ν l ν Figure 23 It can be seen that the body wave radiation is obviously enhanced near the anti-resonance frequency, but still has a high Q value near the resonance frequency. Therefore, as long as ν s ν l , the resonator can still constitute an effective filter element, which is sufficient for a series resonator in a filter.

[0108] In another possible embodiment, referring to Figure 24 , the piezoelectric layer 3 comprises at least two sub-piezoelectric layers 301 stacked; the material type or the cut type of adjacent sub-piezoelectric layers 301 in the at least two sub-piezoelectric layers 301 is different.

[0109] In another possible embodiment, a functional layer is further provided between the reflective structure 2 and the piezoelectric layer 3; the functional layer comprises one or more of a temperature compensation layer, a heat dissipation layer, and a trap-rich layer.

[0110] In another possible embodiment, referring to Figure 25 , a bonding layer 6 is further provided between the reflective layer and the support substrate 1.

[0111] In another possible embodiment, referring to Figure 26 , the support substrate 1 comprises a support layer 101 and a high-speed layer 102 stacked; the high-speed layer 102 is of a material easy to be formed and processed; the material of the high-speed layer 102 is any one of silicon carbide, diamond, diamond-like carbon, aluminum oxide, aluminum nitride, boron nitride, boron carbide, and silicon nitride in different crystal forms and different cuts; the material of the support layer 101 comprises any one of quartz, silicon, sapphire, spinel, and yttrium aluminum garnet.

[0112] It can be understood that the above several resonators (such as the structure shown in Figures 25-26 ) can further comprise a bottom electrode 5 provided below the piezoelectric layer 3, that is, the resonator protected by the present application can be all possible combination schemes of the above-mentioned several resonators, not limited to the illustrated schemes, for example, it can be Figure 24 + Figure 26 + bottom electrode scheme, that is, the resonator comprises, from bottom to top, a support layer 101, a high-speed layer 102, a second reflective layer 202, a first reflective layer 201, a bottom electrode 5, two sub-piezoelectric layers 301, and an interdigital electrode 4.

[0113] In another aspect, the present application discloses a communication device comprising the above high-frequency acoustic wave resonator; the communication device comprises at least one of a filter, a duplexer, and a multiplexer.

[0114] The above only is optional embodiment of the present application, and does not use to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application, should be included in the protection scope of the present application.

Claims

1. A high frequency acoustic wave resonator, characterized by, The high-frequency acoustic wave resonator comprises, from bottom to top, a support substrate, a reflection structure, a piezoelectric layer and an interdigital electrode; The reflection structure comprises a first reflection layer and a second reflection layer stacked in layers; the acoustic impedance of the first reflection layer and the second reflection layer are different; the first reflection layer is close to the piezoelectric layer, and the acoustic impedance of the second reflection layer is greater than 2 times the acoustic impedance of the first reflection layer; The target mode of the high-frequency acoustic wave resonator is a high acoustic velocity mode, the product of the electrode finger spacing of the interdigital electrode and the anti-resonance frequency is greater than the slow shear wave acoustic velocity of the support substrate, and the product of the electrode finger spacing of the interdigital electrode and the resonator frequency is less than the longitudinal wave acoustic velocity of the support substrate; the electrode finger spacing of the interdigital electrode is the distance between the centers of adjacent electrode fingers on the same busbar of the interdigital electrode; the product of the electrode finger spacing of the interdigital electrode and the anti-resonance frequency is more than 7000 m / s; the longitudinal wave acoustic velocity of the support substrate is more than 7000 m / s.

2. The high-frequency acoustic resonator of claim 1, wherein, The reflection structure comprises a plurality of first reflection layers and second reflection layers stacked in layers; The total number of the first reflection layers and the second reflection layers included in the reflection structure is less than or equal to 5.

3. The high-frequency acoustic resonator of claim 1, wherein, The piezoelectric layer comprises at least two sub-piezoelectric layers stacked in layers; The material type or cut type of adjacent sub-piezoelectric layers in the at least two sub-piezoelectric layers is different.

4. The high-frequency acoustic resonator of claim 1, wherein, A functional layer is further provided between the reflection structure and the piezoelectric layer; The functional layer comprises one or more of a temperature compensation layer, a heat dissipation layer, and a trap-rich layer.

5. The high-frequency acoustic resonator of claim 1, wherein, The support substrate comprises a support layer and a high acoustic velocity layer stacked in layers; The high acoustic velocity layer is made of a material that is easy to process; the material of the high acoustic velocity layer is any one of silicon carbide, diamond, diamond-like carbon, aluminum oxide, aluminum nitride, boron nitride, boron carbide, and silicon nitride in different crystal forms and different cut types; The material of the support layer comprises any one of quartz, silicon, sapphire, spinel, and yttrium aluminum garnet.

6. The high-frequency acoustic resonator of claim 1, wherein, A bonding layer is further included between the reflection layer and the support substrate.

7. The high-frequency acoustic resonator of claim 1, wherein, A bottom electrode is provided between the reflection structure and the piezoelectric layer; The target mode is a longitudinal electric field excited high acoustic velocity mode.

8. The high-frequency acoustic resonator of claim 7, wherein, The bottom electrode is a combination of one or more of copper, aluminum, gold, silver, tungsten, platinum, nickel, chromium, molybdenum, titanium, graphene, copper-aluminum alloy, aluminum-silicon alloy, doped silicon, silicon carbide, and gallium nitride; The width of the bottom electrode is not more than the width of the aperture region, and the aperture region is the overlapping region of the electrode fingers of the interdigital electrode.

9. The high-frequency acoustic resonator of claim 1, wherein, The material of the piezoelectric layer is a combination of one or more of lithium tantalate, lithium niobate, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate, or lead magnesium niobate-lead titanate. The support substrate is a combination of one or more of silicon carbide, diamond, diamond-like carbon, silicon, sapphire, aluminum nitride, boron nitride, boron carbide, and silicon nitride in different crystal forms and different cut types.

10. The high-frequency acoustic resonator of claim 1, wherein, The material of the first reflection layer is any one of silicon oxide, aluminum, germanium, titanium, silicon, magnesium alloy, and ion-implanted or doped silicon oxide; The material of the second reflection layer is any one of tungsten, platinum, tungsten nitride, hafnium oxide, hafnium nitride, tungsten oxide, aluminum oxide, aluminum nitride, silicon carbide, titanium oxide, gold, nickel, molybdenum, tantalum, chromium, and copper.

11. The high-frequency acoustic resonator of claim 1, wherein, The target mode of the high-frequency acoustic resonator is one of a longitudinal leaky surface acoustic wave mode, a high-order horizontal shear mode, a high-order Lamb wave mode, and a high-order Rayleigh mode.

12. A communication device, characterized by A high-frequency acoustic resonator as claimed in any of claims 1 to 11; The communication device includes at least one of a filter, a duplexer, and a multiplexer.

Images