Acoustic resonator

Abstract

The present invention relates to an acoustic resonator, wherein each resonant element is at least partially coated with vertical electrodes on the sidewalls of its top piezoelectric portion and has its bottom portion firmly mounted on an underlying support substrate. The bottom portion of each resonant element has a width less than λ / 2, where λ is the wavelength of the shear acoustic wave in the bottom portion at the resonant frequency determined by the top portion. In this case, the total width of the top portion and the electrodes is greater than the width of the bottom portion, and vibrations from the top portion cannot propagate through the bottom portion, thereby enhancing piezoelectric coupling and providing structural robustness. In addition, a heat removal path can be provided in each resonant element from its top portion through its bottom portion to the substrate, which can improve the power handling characteristics of the resonator.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to international patent application No. PCT / CN2022 / 118572, filed on September 14, 2022, entitled “ACOUSTIC RESONATOR WITH VERTICAL ELECTRODES”, which is incorporated herein by reference in its entirety. Technical Field

[0002] The present invention relates generally to the field of acoustic devices. In particular, the present invention relates to an acoustic resonator in which each resonant element is provided with vertical electrodes on the sidewalls of its top piezoelectric portion and has its bottom portion firmly mounted on an underlying support substrate, thereby providing high voltage electrical coupling and improving heat removal capabilities. Background Art

[0003] Acoustic resonators can be used to implement signal processing functions in various electronic applications. For example, acoustic resonators are used in existing wireless and wired communication devices, such as mobile phones, to implement frequency filters and / or multiplexers for sending and / or receiving wireless and / or wired signals. Some examples of acoustic resonators include bulk acoustic wave (BAW) resonators, film bulk acoustic resonators (FBAR), laterally excited bulk acoustic wave resonators (XBAR), transversally excited shear wave resonators (YBAR), stacked bulk acoustic resonators (SBAR), double bulk acoustic resonators (DBAR), and solidly mounted resonators (SMR).

[0004] XBARs are based on the use of suspended piezoelectric (e.g., lithium niobate or LN) membranes of sub-micron thickness and have been demonstrated to be a high-voltage electrically coupled acoustic resonator. In XBARs, a horizontal electric field is used to produce horizontal displacement and A1 mode resonance in the piezoelectric layer of the membrane. However, since the membrane in an XBAR is very thin and needs to be suspended above an air cavity for acoustic isolation, the membrane is a fragile structure. In addition, since the bottom side of the membrane must be open, this significantly increases the complexity of the entire XBAR manufacturing process. In addition, due to the low thermal conductivity of the suspended piezoelectric film of the XBAR (i.e., heat is mainly discharged along the electrodes attached to the film), the power handling characteristics are poor. Summary of the invention

[0005] The present invention summary briefly introduces a series of concepts, which will be further described in the detailed description. The present invention summary is not intended to identify the key features of the present invention, nor is it intended to limit the scope of the present invention.

[0006] It is an object of the present invention to provide an acoustic resonator that provides high voltage electrical coupling and exhibits improved (eg, compared to existing XBARs) power handling characteristics.

[0007] The above objects are achieved by the features of the independent claims in the attached claims. Further embodiments and examples are apparent from the dependent claims, the detailed description and the drawings.

[0008] According to one aspect, an acoustic resonator is provided. The acoustic resonator includes a supporting substrate and at least one resonant element disposed on the supporting substrate. Each of the at least one resonant element has a top portion and a bottom portion. The top portion is made of a piezoelectric material and has two opposing side walls, each of which is at least partially coated with an electrode. The bottom portion has a width less than λ / 2, wherein λ is the wavelength of a shear acoustic wave in the bottom portion at a resonant frequency determined by the top portion. In an acoustic resonator configured in this way, the shear acoustic wave generated in the top portion of each resonant element can be prevented from leaking into the supporting substrate in response to a radio frequency (RF) electrical signal applied to the electrode because the total width of the electrode and the top portion is always greater than the width of the bottom portion. This may provide high voltage electrical coupling (HV) in the acoustic resonator. ), thereby providing a large resonance-antiresonance (RaR) frequency gap, which is an important condition for using the resonator in a broadband filter. In addition, since there is a heat dissipation path from its top portion through its bottom portion to the supporting substrate in each resonant element, the acoustic resonator configured in this way can exhibit excellent power handling characteristics. The above advantages can enable the acoustic resonator to operate with a fairly high piezoelectric coupling in the 5 GHz frequency range.

[0009] In an exemplary embodiment, each of the at least one resonant element is ridge-shaped. In this embodiment, the ridge has a transverse (or aperture) dimension and a cross-sectional dimension, and two opposing side walls at least partially coated with electrodes in each of the at least one resonant element extend along the transverse dimension. The transverse dimension may be much larger (e.g., at least 10 times) than the cross-sectional dimension. For example, such a ridge-shaped resonant structure may be easier to implement and less fragile than a columnar structure. In addition, it is much easier to implement electrode connections in such a ridge-shaped resonant structure.

[0010] In an exemplary embodiment, each of the two opposing side walls of the top portion of each of the at least one resonant element is tilted at an angle of -40° to 40° relative to the normal of the support substrate. This wide range of side wall tilt angles can provide tolerance for the manufacturing process of the acoustic resonator (for example, by using photolithography). It should also be noted that at this side wall tilt angle, a high Q value and piezoelectric coupling factor ( ).

[0011] In an exemplary embodiment, the top portion in each of the at least one resonant element has a positive tapered or inverse tapered profile. This can also provide flexibility in the manufacturing process of the acoustic resonator and enable the acoustic resonator to have multiple uses (e.g., different top portion profiles of the resonant element can be used for different acoustic applications, research, etc.).

[0012] In an exemplary embodiment, the top portion and the bottom portion in each of the at least one resonant element are equal in height. This may also provide flexibility during the manufacturing process of the acoustic resonator (e.g., the equal height of the top portion and the bottom portion may simplify the actual manufacturing process of the acoustic resonator).

[0013] In another exemplary embodiment, each of the top portion and the bottom portion in each of the at least one resonant element has a different height. This may also provide flexibility during the manufacturing process of the acoustic resonator (e.g., from a manufacturing process point of view, it may be easier to make the top portion and the bottom portion different in height than to make them equal in height).

[0014] In an exemplary embodiment, the top portion of each of the at least one resonant element has an aspect ratio ranging from 0.4 to 2. The top portion having height and width values ​​within this range may provide an optimal piezoelectric coupling factor value and may be easily manufactured.

[0015] In an exemplary embodiment, the bottom portion of each of the at least one resonant element has an aspect ratio ranging from 0.4 to 2. The bottom portion having height and width values ​​within this range can provide good heat dissipation from the top portion to the supporting substrate, can serve as a strong support for the top portion, and can be easily manufactured. If the aspect ratio of the bottom portion is less than 0.4, redundant (parasitic) coupling may occur between the top portion and the supporting substrate. If the aspect ratio of the bottom portion is higher than 2, such a high bottom portion will be difficult to manufacture and more fragile.

[0016] In an exemplary embodiment, the support substrate is made of the piezoelectric material, and the bottom portion in each of the at least one resonant element is made of the piezoelectric material. In this embodiment, the acoustic resonator can be realized by using only the piezoelectric substrate, that is, each resonant element can be formed, for example, by etching a cavity on the surface of the piezoelectric substrate and forming an electrode on the side wall of each cavity close to the original surface of the piezoelectric substrate. For example, when it is necessary to reduce material consumption (that is, the same piezoelectric material is used for the substrate and each resonant element of the acoustic resonator) and reduce manufacturing costs (for example, a one-layer LN substrate is at least one order of magnitude cheaper than a multi-layer substrate (such as LN / SiO2 / submicron LN)).

[0017] In an exemplary embodiment, the support substrate is made of a first dielectric material, and the bottom portion in each of the at least one resonant element is made of a second dielectric material. In this embodiment, the first dielectric material and the second dielectric material can be the same or different. Again, this can provide flexibility in the manufacturing process of the acoustic resonator.

[0018] In an exemplary embodiment, the first dielectric material includes one of silicon (Si), diamond, silicon carbide (SiC) and silicon dioxide (SiO2), and the second dielectric material includes one of Si, SiO2, quartz and glass. These materials have good mechanical properties and thermal conductivity, so they can provide strong support for the top portion in each resonant element and improve heat removal capability with almost no piezoelectric coupling loss (i.e., avoiding redundant coupling between the top portion and the supporting substrate).

[0019] In an exemplary embodiment, the piezoelectric material includes one of lithium niobate (LN), lithium tantalate (LT), Al(Sc)N, lithium iodate (LiIO3), zinc oxide (ZnO), lead zirconate titanate (PZT), and quartz. These materials exhibit appropriate piezoelectric properties to enable the acoustic resonator to operate efficiently.

[0020] In an exemplary embodiment, the piezoelectric material includes one of LN cut at 30°+ / -30° rotation in the Y direction and LN cut at 120°+ / -30° rotation in the Y direction. By using these cuts of LN, strong piezoelectric coupling (e.g., up to ). 30° rotation of the Y-cut LN can be used to obtain the maximum The main resonant mode (such as SH1 mode) of the LN cut in the 120° rotation direction can be used to obtain the maximum The main resonant mode (such as A1 mode).

[0021] In an exemplary embodiment, the width of the top portion in each of the at least one resonant element and each of the electrodes is selected based on the resonant frequency of the acoustic resonator. Thus, by changing the width of the top portion and the electrodes, the resonant frequency of the acoustic resonator can be changed or tuned.

[0022] In an exemplary embodiment, the bottom portion in each of the at least one resonant element comprises a set of alternating low acoustic impedance layers and high acoustic impedance layers, each layer having a thickness of λ / 4, wherein λ is the wavelength of a sheared acoustic wave propagating across the set of alternating low acoustic impedance layers and high acoustic impedance layers. By using such a collection or stack of layers, the active (top) portion of the acoustic resonator can be isolated from the supporting substrate, thereby avoiding acoustic losses (i.e., providing strong piezoelectric coupling).

[0023] In one exemplary embodiment, the support substrate comprises a set of alternating low and high acoustic impedance layers, each layer having a thickness of λ / 4, where λ is the wavelength of a shear acoustic wave propagating across the set of alternating low and high acoustic impedance layers. By using such a collection or stack of layers, the active (top) portion of the acoustic resonator can also be isolated from the support substrate, thereby avoiding acoustic losses (i.e., providing strong piezoelectric coupling).

[0024] In an exemplary embodiment, the at least one resonant element comprises an array of identical resonant elements disposed on the supporting substrate. In this embodiment, the array of identical resonant elements has an inter-element spacing selected such that there is no mechanical contact between electrodes of each two adjacent resonant elements of the array of identical resonant elements. The use of multiple identical resonant elements in an acoustic resonator may be beneficial in some acoustic applications. For example, the desired parameters of the acoustic resonator (not only its resonant frequency, but also, for example, impedance and static capacitance at the resonant frequency, etc.) may be obtained by selecting the number of resonant elements and their geometry (i.e., their width, height, and length / aperture).

[0025] In an exemplary embodiment, the inter-element spacing is greater than the total width of the top portion and the electrode.Such an inter-element spacing can provide efficient operation of an acoustic resonator having a plurality of identical resonant elements.

[0026] In another exemplary embodiment, the inter-element spacing is defined as: ,in, is the inter-element spacing, is the minimum acoustic wave velocity in the supporting substrate, is the resonant frequency of the acoustic resonator. Such an inter-element spacing can provide efficient operation of an acoustic resonator having multiple identical resonant elements. In this resonator configuration, the inter-element spacing can be quite large (up to 5 μm), but energy will not leak from the top portion down to the substrate. Such a large inter-element spacing can also provide flexibility in the fabrication process of the acoustic resonator.

[0027] In an exemplary embodiment, the acoustic resonator comprises a first array of identical resonant elements and a second array of identical resonant elements, both of which are arranged on the substrate. The first array of identical resonant elements and the second array of identical resonant elements differ from each other in at least one of the following aspects: inter-element spacing; profile of the top portion; size of the top portion; size of the bottom portion; the piezoelectric material of the top portion; material of the bottom portion; number of resonant elements; aperture of each resonant element. By using two different arrays of identical resonant elements, two acoustic resonators with different resonant frequencies can be realized, which is necessary for using such a resonator, for example, in a "ladder" filter.

[0028] Other features and advantages of the present invention will become apparent upon reading the following detailed description and upon viewing the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention is explained below with reference to the accompanying drawings, in which:

[0030] Figure 1A and Figure 1B Different schematic diagrams of suspended piezoelectric films used in laterally excited bulk acoustic wave resonators (XBARs) provided in the prior art are shown, namely: Figure 1A shows a perspective view of the membrane, Figure 1B Shown in Figure 1A An enlarged side view of the membrane taken within the area defined by circle A in FIG.

[0031] Figure 2 shows a schematic side view of an acoustic resonator provided by a first exemplary embodiment;

[0032] Figure 3 shows a schematic side view of an acoustic resonator provided by a second exemplary embodiment;

[0033] Figure 4 shows a schematic side view of an acoustic resonator provided by a third exemplary embodiment;

[0034] Figure 5 shows a schematic side view of an acoustic resonator provided by a fourth exemplary embodiment;

[0035] Figure 6 shows the piezoelectric coupling factor Included in Figure 4 dependence of the side wall tilt angle in the top piezoelectric portion of each resonant element in the acoustic resonator, wherein the width of the top piezoelectric portion is equal to 300 nm;

[0036] Figure 7 Shows Figure 4 The admittance curve of the optimized parameters of the acoustic resonator confirms that Figure 4 The acoustic resonator has strong piezoelectric coupling ( ), parasitic mode-free, and high frequency (3 GHz to 4 GHz) configurations. DETAILED DESCRIPTION

[0037] Various embodiments of the present invention are further described in detail in conjunction with the accompanying drawings. However, the present invention can be embodied in many other forms and should not be construed as being limited to any specific structure or function disclosed in the following description. On the contrary, these embodiments are provided to describe the present invention in detail and completely.

[0038] Based on the detailed description, it will be apparent to those skilled in the art that the scope of the present invention includes any embodiment of the present invention disclosed herein, whether the embodiment is implemented independently or in combination with any other embodiment of the present invention. For example, the apparatus disclosed herein can be implemented in practice by using any number of embodiments provided herein. In addition, it should be understood that any embodiment of the present invention can be implemented using one or more features set forth in the appended claims.

[0039] The word “exemplary” is used herein to mean “serving as an illustration.” Any embodiment described herein as “exemplary” is not to be construed as preferred or advantageous over other embodiments unless otherwise stated.

[0040] For convenience, any positioning terms such as "left", "right", "top", "bottom", "above", "below", "up", "down", "horizontal", "vertical", etc. may be used herein to describe the relationship of an element or feature to one or more other elements or features according to the accompanying drawings. It is obvious that the positioning terms are intended to include different orientations of the devices disclosed herein, as well as one or more orientations depicted in the accompanying drawings. For example, if it is imagined that the device in the figure is rotated 90 degrees clockwise, the elements or features described as "left" and "right" relative to other elements or features will be oriented "above" and "below" the other elements or features, respectively. Therefore, the positioning terms used herein should not be interpreted as any limitation to the present invention.

[0041] In addition, although the numerical terms "first", "second", etc. may be used herein to describe various embodiments, elements, or features, it should be understood that these embodiments, elements, or features should not be limited by the numerical terms. The numerical terms used herein are only to distinguish one embodiment, element, or feature from another embodiment, element, or feature. For example, the first resonant element array discussed below may be referred to as the second resonant element array, and vice versa, without departing from the teachings of the present invention.

[0042] Figure 1A and Figure 1B 1 shows different schematic diagrams of a suspended piezoelectric film 100 used in a laterally excited bulk acoustic wave resonator (XBAR) provided in the prior art. More specifically, Figure 1A A perspective view of the film 100 is shown, Figure 1B Shown in Figure 1A , an enlarged side view of the membrane 100 taken within the area defined by circle A in FIG. The membrane 100 is assumed to be suspended above an air cavity (not shown) for acoustic isolation. The membrane 100 is a submicron layered structure that includes a supporting substrate 102 (e.g., a high acoustic velocity solid substrate such as a diamond or SiC substrate) and a piezoelectric (e.g., LN) layer 104 disposed on the substrate 102. The substrate 102 and the layer 104 may be made of the same piezoelectric material (e.g., LN). It is assumed that a vertical positive electrode 106 (schematically shown by using a zigzag pattern) and a vertical negative electrode 108 (schematically shown by using a dashed line pattern) are embedded in the piezoelectric layer 104 (and, if necessary, also in the substrate 102) to provide a more uniform horizontal electric field to enhance piezoelectric coupling. However, from a mechanical point of view, the membrane 100 is fragile, and the embedded vertical electrodes 106 and 108 make it even more fragile. Moreover, it is difficult to manufacture the membrane 100 in practice. In addition, as Figure 1B As shown, the membrane 100 suffers from inefficient electric field distribution and redundant (parasitic) coupling between the piezoelectric layer 104 and the substrate 102, which can significantly weaken the piezoelectric coupling in the XBAR. In addition, since the membrane 100 is suspended above the air cavity in the XBAR, heat can only be discharged from the membrane 100 through the piezoelectric layer 104 and the vertical electrodes 106 and 108, which have low thermal conductivity. For this reason, the XBAR using the membrane 100 shows poor power handling characteristics.

[0043] The exemplary embodiments disclosed herein provide a technical solution that can alleviate or even eliminate the above-mentioned disadvantages that are unique to the prior art. Specifically, the technical solution disclosed herein relates to an acoustic resonator, in which each resonant element is at least partially coated with a vertical electrode on the sidewall of its top piezoelectric portion, and its bottom portion is firmly mounted on an underlying supporting substrate. The bottom portion of each resonant element has a width less than λ / 2, where λ is the wavelength of the shear acoustic wave in the bottom portion at the resonant frequency determined by the top portion. In this case, the total width of the top portion and the electrode is always greater than the width of the bottom portion, and the vibration from the top portion cannot propagate through the bottom portion in each resonant element, thereby enhancing piezoelectric coupling and providing structural robustness at the same time. In addition, in the acoustic resonator configured in this way, a heat removal path can reach the substrate from its top portion through its bottom portion in each resonant element, which can significantly improve the power handling characteristics of the acoustic resonator.

[0044] Figure 2 A schematic side view of an acoustic resonator 200 provided by a first exemplary embodiment is shown. The acoustic resonator 200 includes a support substrate 202 and three resonant elements 204 disposed on one (top) side of the support substrate 202. The support substrate 202 may be made of silicon (Si) or silicon dioxide (SiO2). Preferably, the support substrate 202 is made of a high acoustic velocity material, such as diamond, silicon carbide (SiC), boron nitride (BN), or any other material having an acoustic velocity in the range of 4000 m / s to 10000 m / s for shear acoustic waves. Each of the resonant elements 204 has a top portion 206 and a bottom portion 208. The top portion 206 is made of a piezoelectric material and has two opposing (i.e., left and right) side walls that are completely coated with vertical electrodes 210, 212. Some examples of piezoelectric materials may include, but are not limited to, lithium niobate (LN), lithium tantalate (LT), aluminum scandium nitride (AlScN), lithium iodate (LiIO3), zinc oxide (ZnO), lead zirconate titanate (PZT), and quartz. Preferably, the piezoelectric material of the top portion 206 is represented by LN cut at 30°+ / –30° rotated Y direction or LN cut at 120°+ / –30° rotated Y direction. The vertical electrodes 210, 212 may be made of any metal, such as copper (Cu), molybdenum (Mo), gold (Au), aluminum (Al), etc. The vertical electrodes 210, 212 provide a uniform horizontal electric field near the electrode area, thereby promoting strong piezoelectric coupling and providing weaker acoustic parasitic modes. The bottom portion 208 may be made of the same material as the supporting substrate 202, or may be made of a different material, such as quartz and glass. As Figure 2As shown, the width w1 of the bottom portion 208 is less than the width w2 of the top portion 206. Another embodiment is possible, where w1 = w2. Whether w1 = w2 or w1 < w2, the total width w3 of the top portion 206 and the electrodes 210, 212 is always greater than w1, which together with the vertical arrangement of the electrodes 210, 212 is an important condition for the efficient operation of the acoustic resonator 200 (i.e., achieving strong piezoelectric coupling).

[0045] In a preferred embodiment, the resonant frequency is determined by the top portion 206 of each resonant element 204. In this embodiment, the width of the bottom portion 208 of each resonant element 204 is less than the half-wavelength of the shear acoustic wave in the material of the bottom portion 208 at the resonant frequency This can prevent the vibration from propagating downward to the substrate 202, thereby avoiding wasting the energy of the resonator 200 and reducing its Q factor.

[0046] Generally, each resonant element in the resonant element 204 can be manufactured by using existing lithography techniques (e.g., the critical dimensions of the electrodes 210, 212 should be greater than 0.3 μm lithography).

[0047] During operation, the electrodes 210, 212 of each resonant element in the resonant element 204 are alternately connected to two different bus bars (not shown), such that the opposite electrodes of every two adjacent resonant elements 204 are connected to the same bus bar. Thereafter, an RF voltage signal having a frequency equivalent to the resonant frequency of the acoustic resonator 200 is applied to the bus bar. As a result of the piezoelectric effect, the top portion 206 of each resonant element 204 begins to vibrate, and the width of the top portion 206 approximately corresponds to λ / 2 of the shear acoustic wave. If the piezoelectric material of the top portion 206 is denoted as LN, there may be two main vibration modes depending on the LN cut used.

[0048] If 30° rotated Y-cut LN is used, this LN can provide strong piezoelectric coupling for shear deformation with displacement perpendicular to the Figure 2 plane. This situation is preferred because the shear acoustic wave has a starting frequency and exists in the top portion 206 of each resonant element 204, but cannot exist in its bottom portion 208.

[0049] If 120° rotated Y-cut LN is used, this LN provides almost the same piezoelectric coupling strength, but for other shear deformations: the displacement is perpendicular, and it is asymmetric on the left and right sides of the top portion 206 of each resonant element 204. However, the problem is that such displacement may generate a "bending" wave A0, which can propagate to any bottom portion 208 with a small thickness. This may increase the energy loss in the acoustic resonator 200.

[0050] In other words, the main vibration mode is substantially in the top portion 206 of each resonant element 204, but the 30° rotated Y-cut LN is preferred.

[0051] In one embodiment, each of the resonant elements 204 may be shaped to have a substantially uniform distribution of light along the axis z (ie, perpendicular to the z axis). Figure 2 The ridge structure is a ridge structure extending in a plane (i.e., in a plane of the resonant element 204). Therefore, this ridge structure has a transverse dimension along the axis z and a cross-sectional dimension along the axis x. In this embodiment, the two opposing side walls coated with the electrodes 210, 212 in each of the resonant elements 204 extend along the transverse dimension (i.e., along the axis z). The transverse dimension may be at least 40 of the cross-sectional dimension. times, among which, is the pitch of the resonator structure (i.e., its geometric period, expressed as follows: w3+ ,in, is the inter-element spacing). In another embodiment, each of the resonant elements 204 may be shaped as a columnar structure or a tower structure, wherein the lateral dimension and the cross-sectional dimension are comparable to each other.

[0052] The top portion 206 and the bottom portion 208 in each of the resonant elements 204 may be equal in height or different in height. Figure 2 , the height is measured along the axis y. Preferably, each of the top portion 206 and the bottom portion 208 in each of the resonant elements 204 has an aspect ratio between 0.4 and 2.

[0053] The resonant frequency of the acoustic resonator 200 may be The width of the top portion 206 in each of the resonant elements 204 (ie, w2) and the width of each of the electrodes 210, 212 are selected based on the resonant frequency. λ may correspond to the width w2 of the top portion 206 (equal to λ / 2), i.e., half the wavelength of the shear acoustic wave generated in the top portion 206 due to the piezoelectric effect. In general, the selection of w2 is a design issue. For example, the necessary resonant frequency may be selected based on some filter specifications, and this frequency may be achieved in the acoustic resonator 200 by appropriately varying the width w2 of the top portion 206 and the width / thickness of the vertical electrodes 210 and 212. This may be optimized using appropriate finite element method (FEM) software while taking into account many other trade-offs (e.g., other parameters of the acoustic resonator 200, such as impedance and static capacitance at the resonant frequency, etc.).

[0054] It should be noted that the spacing between components or Spacing does not affect the resonant frequency. Larger values ​​of the spacing between components (e.g. >5 μm) can be used to achieve better metal deposition and lift-off during the fabrication of the sidewall vertical electrodes 210, 212. In one embodiment, the inter-element spacing may be greater than the total width w3 of the top portion 206 and the electrodes 210, 212 to avoid any mechanical contact between the electrodes of each two adjacent resonant elements 204. It can be defined as: ,in, is the minimum acoustic wave velocity in the supporting substrate 202 .

[0055] To additionally reduce acoustic losses (due to acoustic parasitic modes), the bottom portion 208 in each of the resonant elements 204 may include a set of alternating low and high acoustic impedance layers (not shown), each layer having a thickness of λ / 4, where λ is the wavelength of a sheared acoustic wave propagating across the set of alternating low and high acoustic impedance layers. Alternatively or additionally, a similar set of alternating low and high acoustic impedance layers (not shown) may be present in the support substrate 202.

[0056] Figure 3 A schematic side view of an acoustic resonator 300 provided by a second exemplary embodiment is shown. The acoustic resonator 300 comprises a piezoelectric (e.g., LN) substrate 302 and resonant elements 304 arranged on the substrate 302 by forming a cavity on its surface (e.g., by etching, stamping, or MEMS technology). If the cavity is shaped as an elongated (along the axis z) groove, each of the resonant elements 304 will have a ridge-like shape. Each of the resonant elements 304 can be conveniently divided into a top portion and a bottom portion by vertical (e.g., Cu, Au, Mo, or Al) electrodes 310, 312 formed close to the original surface of the substrate 302 (see Figure 3 The sidewalls of each cavity (the dotted lines in FIG. 1 ) are formed on the sidewalls of each cavity of the acoustic resonator 300. Therefore, each of the structural elements of the acoustic resonator 300 (except the electrodes 310 and 312) can be made of the same piezoelectric material (eg, LN). The working principle of the acoustic resonator 300 is the same as that of the acoustic resonator 200.

[0057] Figure 4A schematic side view of an acoustic resonator 400 provided by a third exemplary embodiment is shown. The acoustic resonator 400 includes a support substrate 402 and three resonant elements 404 disposed on one (top) side of the support substrate 402. Each of the resonant elements 404 has a top portion 406 and a bottom portion 408. The top portion 406 is made of a piezoelectric material and has two opposing (i.e., left and right) side walls that are completely coated with vertical electrodes 410, 412. In general, the acoustic resonator 400 can be implemented similarly to the acoustic resonator 200, i.e., by manufacturing the substrate 402 and the resonant elements 404 using the same manufacturing materials as the substrate 202 and the resonant elements 204, respectively. In addition, the size of the resonant elements 404 can be similar to the size of the resonant elements 204. The only difference between the acoustic resonator 200 and the acoustic resonator 400 is that the sidewalls of the top portion 406 in each of the resonant elements 404 are inclined at an angle α relative to the normal to the supporting substrate 402, thereby providing a positive tapered profile to the top portion 406. The operating principle of the acoustic resonator 400 is the same as that of the acoustic resonator 200.

[0058] It should be noted that if each of the resonant elements 404 is shaped as a columnar structure (i.e., its dimensions along the axis z and the axis x are comparable), then all (i.e., left, right, front, and rear) sidewalls of the resonant element 404 may be similarly inclined relative to the normal to the substrate 402, thereby providing a mushroom-shaped profile with the top portion 406.

[0059] Figure 5 A schematic side view of an acoustic resonator 500 provided by a fourth exemplary embodiment is shown. The acoustic resonator 500 includes a support substrate 502 and three resonant elements 504 disposed on one (top) side of the support substrate 502. Each of the resonant elements 504 has a top portion 506 and a bottom portion 508. The top portion 506 is made of a piezoelectric material and has two opposing (i.e., left and right) side walls that are completely coated with vertical electrodes 510, 512. In general, the acoustic resonator 500 can be implemented similarly to the acoustic resonator 200, i.e., by manufacturing the substrate 502 and the resonant elements 504 using the same manufacturing materials as the substrate 202 and the resonant elements 204, respectively. In addition, the size of the resonant elements 504 can be similar to that of the resonant elements 204. The only difference between the acoustic resonator 200 and the acoustic resonator 500 is that the side walls of the top portion 506 in each of the resonant elements 504 are inclined at an angle α relative to the normal of the support substrate 502, so that the top portion 506 has an inverted tapered profile. The working principle of the acoustic resonator 500 is the same as the working principle of the acoustic resonator 200 .

[0060] Preferably, in each of the acoustic resonators 400 and 500 , the sidewall inclination angle α is −40° to 40°. Such a wide range of the sidewall inclination angles can provide tolerance for the actual manufacturing process of the acoustic resonators 400 and 500 .

[0061] It should be noted that Figures 2 to 5 The number, arrangement and profile of the resonant elements shown are not intended to be any limitation of the present invention, but are merely intended to provide a general idea of ​​how the resonant elements may be implemented within the acoustic resonators 200 to 500. For example, the acoustic resonators 200 to 500 may include more resonant elements, which are respectively arranged on one or different (e.g., top and bottom) sides of the supporting substrate 202 to 502 (e.g., the number of resonant elements may vary from 20 to 200 along the axis x). Furthermore, the sidewalls of the top portions in the resonant elements of the acoustic resonators 200 to 500 may be only partially (i.e., not completely) coated with the vertical electrodes. Other embodiments are possible, in which the vertical electrodes in the resonant elements of the acoustic resonators 200 to 500 respectively at least partially cover the surface of the substrate 202 to 502 between adjacent bottom portions of the resonant elements.

[0062] It must also be remembered that the desired parameters of the acoustic resonator 200 to 500 (not only its resonant frequency, but also, for example, a certain impedance and a certain static capacitance at the resonant frequency) can be obtained by choosing the number of resonant elements and their geometry (i.e. their width, height and length / aperture).

[0063] Figure 6 shows the piezoelectric coupling factor Dependence on the sidewall inclination angle α in the top portion 406 of each resonant element 404 included in the acoustic resonator 400. Assume that the width w2 of the top portion 406 is equal to 300 nm. It can be seen that the optimal value of the piezoelectric coupling factor is observed in the angle range of 0° to 40° ( >30%).

[0064] Figure 7 The admittance curves of the optimized parameters of the acoustic resonator 400 (ie, the admittance Y11 and its real part Re(Y11), in dB) are shown, which confirms that the acoustic resonator 400 has a strong piezoelectric coupling ( 43%), parasitic mode-free, and high-frequency (3 GHz to 4 GHz) configurations. Figure 7 In the figure, the solid line corresponds to admittance Y11 and the dashed line corresponds to Re(Y11).

[0065] Although exemplary embodiments of the present invention are described herein, it should be noted that any various changes and modifications may be made in the embodiments of the present invention without departing from the scope of legal protection defined by the appended claims. In the appended claims, the word "comprising" does not exclude other elements or operations, and the term "a" or "an" does not exclude a plurality. The listing of certain measures in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. An acoustic resonator, characterized in that include: a supporting substrate; At least one resonant element is disposed on the supporting substrate, each of the at least one resonant element having a top portion and a bottom portion, the top portion being made of a piezoelectric material, the top portion having two opposing side walls, each side wall being at least partially coated with an electrode, and the bottom portion having a width less than λ / 2, wherein λ is the wavelength of a shear acoustic wave in the bottom portion at a resonant frequency of the acoustic resonator, the resonant frequency being determined by the top portion of each of the at least one resonant element.

2. The acoustic resonator according to claim 1, characterized in that Each of the at least one resonant element has a ridge shape.

3. The acoustic resonator according to claim 1 or 2, characterized in that: Each of the two opposing side walls of the top portion in each of the at least one resonant element is inclined at an angle of −40° to 40° with respect to a normal line of the support substrate.

4. The acoustic resonator according to any one of claims 1 to 3, characterized in that The top portion in each of the at least one resonant element has a forward tapered or reverse tapered profile.

5. The acoustic resonator according to any one of claims 1 to 4, characterized in that The top portion and the bottom portion in each of the at least one resonant element are equal in height.

6. The acoustic resonator according to any one of claims 1 to 4, characterized in that Each of the top portion and the bottom portion in each of the at least one resonant element has a different height.

7. The acoustic resonator according to any one of claims 1 to 6, characterized in that The top portion of each of the at least one resonant element has an aspect ratio ranging from 0.4 to 2.

8. The acoustic resonator according to any one of claims 1 to 7, characterized in that The bottom portion of each of the at least one resonant element has an aspect ratio ranging from 0.4 to 2.

9. The acoustic resonator according to any one of claims 1 to 8, characterized in that The support substrate is made of the piezoelectric material, and the bottom portion in each of the at least one resonant element is made of the piezoelectric material.

10. The acoustic resonator according to any one of claims 1 to 8, characterized in that The support substrate is made of a first dielectric material, and the bottom portion in each of the at least one resonant element is made of a second dielectric material, the first dielectric material and the second dielectric material being the same as or different from each other.

11. The acoustic resonator according to claim 10, characterized in that The first dielectric material includes one of silicon (Si), diamond, silicon carbide (SiC) and silicon dioxide (SiO 2 ), and the second dielectric material includes one of Si, SiO 2 , quartz and glass.

12. The acoustic resonator according to any one of claims 1 to 11, characterized in that The piezoelectric material includes one of lithium niobate (LN), lithium tantalate (LT), aluminum scandium nitride (Al(Sc)N), lithium iodate (LiIO3), zinc oxide (ZnO), lead zirconate titanate (PZT) and quartz.

13. The acoustic resonator according to claim 12, characterized in that The piezoelectric material includes one of LN cut in the Y direction with a rotation of 30°+ / −30° and LN cut in the Y direction with a rotation of 120°+ / −30°.

14. The acoustic resonator according to any one of claims 1 to 13, characterized in that The top portion in each of the at least one resonant element and the width of each of the electrodes are selected based on a resonant frequency of the acoustic resonator.

15. The acoustic resonator according to any one of claims 1 to 14, characterized in that The bottom portion in each of the at least one resonant element comprises a set of alternating low acoustic impedance layers and high acoustic impedance layers, each layer having a thickness of λ / 4, wherein λ is the wavelength of a shear acoustic wave propagating across the set of alternating low acoustic impedance layers and high acoustic impedance layers.

16. The acoustic resonator according to any one of claims 1 to 15, characterized in that The support substrate includes a set of alternating low and high acoustic impedance layers, each layer having a thickness of λ / 4, wherein λ is the wavelength of a shear acoustic wave propagating across the set of alternating low and high acoustic impedance layers.

17. The acoustic resonator according to any one of claims 1 to 16, characterized in that The at least one resonant element comprises an array of identical resonant elements disposed on the support substrate, the array of identical resonant elements having an inter-element spacing selected such that there is no mechanical contact between electrodes of every two adjacent resonant elements of the array of identical resonant elements.

18. The acoustic resonator according to claim 17, characterized in that The inter-element spacing is greater than a combined width of the top portion and the electrode.

19. The acoustic resonator according to claim 17, characterized in that The inter-element spacing is defined as follows: ,in, is the inter-element spacing, is the minimum acoustic wave velocity in the supporting substrate, is the resonant frequency of the acoustic resonator.

20. The acoustic resonator according to any one of claims 1 to 16, characterized in that The at least one resonant element comprises a first array of identical resonant elements and a second array of identical resonant elements, both of which are disposed on the support substrate and differ from each other in at least one of the following aspects: Spacing between components; a profile of said top portion; the size of said top portion; the size of the bottom portion; said piezoelectric material of said top portion; the material of the bottom portion; The number of resonant elements; The aperture of each resonant element.

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