Transverse excitation film bulk acoustic resonator and manufacturing method thereof

Abstract

The invention provides a transverse excitation film bulk acoustic resonator and a preparation method thereof, and belongs to the technical field of acoustic resonators. The transverse excitation film bulk acoustic resonator comprises a substrate, a piezoelectric layer located on the substrate and an interdigital transducer located on the piezoelectric layer. A cavity is formed between the substrate and the piezoelectric layer; the interdigital transducer comprises an interdigital electrode; the piezoelectric layer is provided with at least one groove or at least one first through hole, and at least one part of the groove or the first through hole is covered by the interdigital electrode; second through holes are formed in the positions, located on the two sides of the interdigital transducer, of the piezoelectric layer in the direction perpendicular to the extending direction of the interdigital electrode and parallel to the piezoelectric layer. And the second through hole is communicated with the cavity. A part of the contact area of the interdigital electrode and the piezoelectric layer is hollowed out, so that the contact area of the interdigital electrode and the piezoelectric layer is reduced, the stray mode is reduced, and the quality factor of the device is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of acoustic wave resonators, and in particular relates to a transversely excited thin film bulk acoustic wave resonator and a manufacturing method thereof. Background Art

[0002] Laterally excited film bulk acoustic resonator (XBAR) has a high electromechanical coupling coefficient (k t 2 >20%) and high figure of merit (FoM = Q*k t 2 )) and become an ideal solution for broadband filters above 6GHz to achieve low loss, high power handling capability and low cost. However, the A1 (first-order antisymmetric Lamb wave) devices shown in the prior art have a large number of transverse spurious modes, resulting in multiple spurious resonance peaks in the device response, corresponding to ripples in the passband of the filter device, leading to increased insertion loss, poor passband edge steepness and other problems, seriously affecting the accuracy and stability of signal reception and transmission. Therefore, the existence of transverse spurious modes is still the main bottleneck for further promoting XBAR devices into practical applications. In order to make XBAR devices suitable for practical applications, spurious mode suppression must be performed.

[0003] In order to reduce lateral stray modes, the U.S. patent application publication US20230111410A1 discloses a lateral excitation thin film bulk acoustic wave resonator with a curved finger-shaped end or a relative busbar, having a substrate with a surface and a single crystal piezoelectric plate, a portion of the piezoelectric plate forming a diaphragm across the cavity in the substrate. An interdigital transducer (IDT) is formed on the surface of the single crystal piezoelectric plate, so that the staggered fingers of the interdigital transducer are arranged on the diaphragm. The ends of the staggered fingers of the IDT or the inner surface of the relative busbar have a curved shape. In this scheme, the distance between the busbar and the end of the IDT is increased by setting the edge between the busbar and the IDT to an arc shape or a parabola shape, so as to reduce the influence of the propagation of lateral acoustic waves (vibrations excited by the electric field Ey in a direction parallel to the IDT fingers and perpendicular to the busbar), thereby reducing the lateral stray modes. However, the arc-shaped boundary between the IDT and the bus bar will focus and enhance the acoustic waves of other stray modes (except the stray modes caused by the electric field Ey) transmitted to the end of the IDT and reflect them to the IDT.

[0004] The Chinese patent application publication CN116529557A discloses a transversely excited thin film bulk acoustic resonator with spiral interdigital transducer fingers, including a substrate and a piezoelectric plate, a portion of which is a diaphragm spanning a cavity in the substrate. The conductor pattern on the front surface of the piezoelectric plate includes interlaced interdigital transducer (IDT) fingers alternately connected to a first busbar and a second busbar. The interlaced IDT fingers are on the diaphragm, and the interlaced IDT fingers include at least a first pair of interlaced spiral IDT fingers. In this scheme, since the electrode edges of the spirally structured IDT are not parallel, the shear wave has a different reflection path at each point on the electrode edge, and the propagation path becomes longer. When the shear wave propagation path becomes longer, the energy of the standing wave is attenuated very low, so the stray mode amplitude on the impedance curve is greatly reduced. However, in this solution, the spiral structure of the electrode leads to a longer electrode length, greater resistance and thermal resistance, which in turn increases the RF current in the IDT, increases the TCF (Temperature Coefficient of Frequency) of the device, reduces the quality factor (Q value), increases power consumption, and exacerbates the heat dissipation and temperature drift problems of the device.

[0005] US patent application US17133498 discloses a transversely excited thin film bulk acoustic resonator with two layers of electrodes having a narrower top layer, comprising a substrate having a surface and a single crystal piezoelectric plate having a front surface and a rear surface, wherein the rear surface is attached to the surface of the substrate in the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning the cavity. The device also includes an interdigital transducer formed on the front surface of the piezoelectric plate, wherein the staggered fingers of the IDT arranged on the diaphragm are configured so that the radio frequency signal applied to the IDT excites the main shear acoustic mode in the diaphragm. The staggered fingers include a first metal layer adjacent to the diaphragm and a second metal layer located above the first layer, the second metal layer having a narrower width than the first metal layer. The second metal layer uses a metal with high transverse acoustic impedance, and the first metal layer uses a metal with low acoustic impedance. Through this structural setting, the transition from low transverse acoustic impedance to high transverse acoustic impedance can limit some parasitic modes to the first metal layer, reducing acoustic losses. However, this solution requires the deposition of two layers of IDT finger electrodes and the control of the sidewall angle of the IDT, thus increasing the difficulty and complexity of the process. Summary of the invention

[0006] Based on the above technical problems, the present invention provides a transversely excited thin film bulk acoustic wave resonator and a preparation method thereof. Since the acoustic impedance mismatch between the interdigital electrode material and the piezoelectric layer material causes a stray mode between the resonant frequency and the anti-resonant frequency, the transversely excited thin film bulk acoustic wave resonator of the present invention hollows out a part of the contact area between the interdigital electrode and the piezoelectric layer, thereby reducing the contact area between the interdigital electrode and the piezoelectric layer, thereby reducing the stray mode and increasing the quality factor of the device.

[0007] Specifically, the present invention adopts the following technical solutions to achieve the above objectives:

[0008] A laterally excited thin film bulk acoustic wave resonator comprises a substrate, a piezoelectric layer located on the substrate and an interdigital transducer located on the piezoelectric layer; a cavity is formed between the substrate and the piezoelectric layer; the interdigital transducer comprises interdigital electrodes; the piezoelectric layer is provided with at least one groove or at least one first through hole, and at least a portion of the groove or the first through hole is covered by the interdigital electrode; second through holes are opened on the piezoelectric layer at positions on both sides of the interdigital transducer in a direction perpendicular to the extension direction of the interdigital electrodes and parallel to the piezoelectric layer; the second through holes are connected to the cavity.

[0009] In a preferred solution, along a direction perpendicular to the extension direction of the interdigital electrodes and parallel to the piezoelectric layer, a size of the groove or the first through hole is larger than a size of the interdigital electrodes.

[0010] In a preferred solution, along a direction parallel to the extending direction of the interdigital electrodes, the size of the groove or the first through hole is larger than the size of the interdigital electrodes.

[0011] In a preferred solution, the substrate includes a base and an intermediate layer.

[0012] In a further preferred embodiment, the material of the substrate is at least one of high-resistance silicon, silicon carbide, diamond, and sapphire.

[0013] In a further preferred embodiment, the material of the intermediate layer is at least one of silicon dioxide, silicon nitride and polysilicon.

[0014] In a further preferred embodiment, a size of the intermediate layer along a direction from the substrate to the piezoelectric layer is 10 nm to 50 μm.

[0015] In a preferred embodiment, the material of the piezoelectric layer is a single crystal material of at least one of lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, and aluminum nitride.

[0016] In a preferred solution, a dimension of the piezoelectric layer along a direction from the substrate to the piezoelectric layer is 100 nm to 1 μm.

[0017] In a preferred embodiment, the IDT includes a bus bar, and a material of the bus bar is at least one of aluminum, aluminum alloy, copper, copper alloy, chromium, titanium, platinum, beryllium, gold, molybdenum, and tungsten.

[0018] In a preferred embodiment, the material of the interdigital electrodes is at least one of aluminum, aluminum alloy, copper, copper alloy, chromium, titanium, platinum, beryllium, gold, molybdenum and tungsten.

[0019] In a further preferred embodiment, along the direction from the substrate to the piezoelectric layer, the bus bar and the interdigital electrodes have the same thickness.

[0020] The present invention also provides a method for preparing the transversely excited thin film bulk acoustic resonator described in any of the above solutions, comprising the following steps:

[0021] S1. providing a substrate, and forming a piezoelectric layer on the substrate;

[0022] S2, forming a groove or a first through hole on the piezoelectric layer, and forming a second through hole at the same time;

[0023] S3, using a filling material to fill the groove and the second through hole until they are flush with the upper surface of the piezoelectric layer; or using a filling material to fill the first through hole and the second through hole until they are flush with the upper surface of the piezoelectric layer;

[0024] S4, forming an interdigital transducer on the piezoelectric layer;

[0025] S5, removing the filling material filled in the groove and the second through hole; or removing the filling material filled in the first through hole and the second through hole;

[0026] S6. Etching the middle portion of the substrate through the second through hole to form a cavity between the piezoelectric layer and the substrate.

[0027] In a preferred embodiment, the filling material is at least one of silicon dioxide, silicon nitride, polysilicon, and aluminum oxide.

[0028] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0029] (1) The transversely excited thin film bulk acoustic wave resonator provided by the present invention is configured to open a groove or a first through hole in the piezoelectric layer so that a portion of the interdigitated electrode contacts the surface of the piezoelectric layer and the other portion is suspended above the opening of the groove or the first through hole, thereby reducing the contact area between the interdigitated electrode and the piezoelectric layer, thereby reducing the influence of stray modes caused by the mismatch in acoustic impedance between the material of the interdigitated electrode and the material of the piezoelectric layer, and facilitating increasing the quality factor of the device.

[0030] (2) Since the transversely excited thin film bulk acoustic wave resonator provided by the present invention reduces stray modes and increases the quality factor of the device, when the acoustic wave resonator is cascaded into a filter, the in-band ripple and insertion loss of the filter can be effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A top view of a transversely excited thin film bulk acoustic resonator having a groove on the piezoelectric layer provided by the present invention;

[0032] Figure 2 for Figure 1 A cross-sectional view of a transversely excited thin film bulk acoustic resonator along section AA;

[0033] Figure 3 A top view of a transversely excited thin film bulk acoustic resonator having a first through hole on a piezoelectric layer provided by the present invention;

[0034] Figure 4 for Figure 3 A cross-sectional view of the transversely excited film bulk acoustic resonator along section AA;

[0035] Figure 5 A top view of another transversely excited thin film bulk acoustic resonator having grooves on the piezoelectric layer provided by the present invention;

[0036] Figure 6 for Figure 5 A cross-sectional view of the transversely excited film bulk acoustic resonator along section AA;

[0037] Figure 7 A top view of another transversely excited thin film bulk acoustic resonator provided by the present invention having a first through hole on the piezoelectric layer;

[0038] Figure 8 for Figure 7 A cross-sectional view of a transversely excited thin film bulk acoustic resonator along section AA;

[0039] Fig. 9 A cross section of another transversely excited thin film bulk acoustic resonator having a first through hole on the piezoelectric layer provided by the present invention (refer to Figure 7 Section AA) diagram on;

[0040] Fig.10 A cross section of another transversely excited thin film bulk acoustic resonator having a first through hole on the piezoelectric layer provided by the present invention (refer to Figure 7 Section AA) diagram on;

[0041] Fig.11 A top view of another transversely excited thin film bulk acoustic resonator having grooves on the piezoelectric layer provided by the present invention;

[0042] Fig.12 A top view of another transversely excited thin film bulk acoustic resonator provided by the present invention having a first through hole on the piezoelectric layer;

[0043] Fig.13 A top view of another transversely excited thin film bulk acoustic resonator having grooves on the piezoelectric layer provided by the present invention;

[0044] Fig.14 A top view of another transversely excited thin film bulk acoustic resonator provided by the present invention having a first through hole on the piezoelectric layer;

[0045] Fig.15 A comparison diagram of the admittance curve and conductance curve of a laterally excited thin film bulk acoustic wave resonator having a groove in the piezoelectric layer provided by the present invention (Figure (b)) and a thin film bulk acoustic wave resonator having no groove in the piezoelectric layer (Figure (a)).

[0046] In the figure: 1, substrate; 11, base; 12, intermediate layer; 2, piezoelectric layer; 21, groove; 22, first through hole; 23, second through hole; 3, interdigital transducer; 31, first bus bar; 32, second bus bar; 311, first electrode; 321, second electrode; 4, cavity; AA, cross section. DETAILED DESCRIPTION

[0047] The following content is combined with the embodiments to clearly and completely describe the technical solution of the present application so that those skilled in the art can fully understand the present application. Obviously, the described embodiments are only some preferred embodiments of the present application, rather than all embodiments. Any equivalent transformation or substitution made to the following implementation modes by those of ordinary skill in the art without creative work belongs to the protection scope of the present application.

[0048] Directional terms described in this application, such as "upper", "lower", "inner", "outer", "bottom", "upper surface", etc., indicate directions or positional relationships based on directions or positional relationships in the drawings of the specification, or directions or positional relationships in which the products of this application are usually placed when in use, and are only for the convenience of describing and understanding the product structure of this application. Therefore, directional terms cannot be understood as limiting this application. In this application, unless otherwise clearly defined, expressions such as "upper", "above", "above", and "upper surface" of a first feature on a second feature indicate that the first feature and the second feature may be in direct contact or indirect contact through an intermediate medium; the first feature may be directly above or obliquely above the second feature, or simply indicate that the first feature is higher in level than the second feature. Expressions such as "lower", "below", "below", and "lower surface" of a first feature on a second feature indicate that the first feature and the second feature may be in direct contact or indirect contact through an intermediate medium; the first feature may be directly below or obliquely below the second feature, or simply indicate that the first feature is lower in level than the second feature. Ordinal numbers used in this application, such as "first", "second", etc., are only used for descriptive purposes to distinguish similar objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. High-resistance silicon in this application refers to a silicon substrate with a resistivity greater than 10 kΩ·cm. The methods not described in detail in the following embodiments are all conventional methods well known to those skilled in the art.

[0049] Example 1

[0050] Reference Figure 1 to Figure 4 A thin film bulk acoustic wave resonator with suspended interdigital electrodes comprises a substrate 1, a piezoelectric layer 2 located on the substrate 1, and an interdigital transducer 3 located on the piezoelectric layer 2. A groove is provided on the substrate 1; the opening of the groove is on the surface of the substrate 1 close to the piezoelectric layer 2, and the bottom is located in the substrate 1. The groove and the piezoelectric layer 2 together form a cavity 4.

[0051] The IDT 3 includes a first bus bar 31, a second bus bar 32, a first electrode 311, and a second electrode 321. The first bus bar 31 and the second bus bar 32 are parallel to each other, and the two are collectively referred to as bus bars. The first electrode 311 and the second electrode 321 are parallel to each other. The first electrode 311 is vertically connected to the first bus bar 31 and extends to the second bus bar 32. The second electrode 321 is vertically connected to the second bus bar 32 and extends to the first bus bar 31. A direction perpendicular to the direction in which the first electrode 311 extends (or the direction in which the second electrode 321 extends) and parallel to the piezoelectric layer 2 is defined as a first direction (e.g., Figure 1 The direction from substrate 1 to piezoelectric layer 2 or the direction from piezoelectric layer 2 to substrate 1 is defined as the second direction (for example, Figure 1The direction parallel to the direction in which the first electrode 311 extends is defined as the third direction (eg Figure 1 The first direction, the second direction and the third direction are perpendicular to each other. A first electrode 311 and a second electrode 321 form a pair of interdigital electrodes. When the interdigital electrodes are a pair, the first electrode 311 and the second electrode 321 are arranged along the first direction. When the interdigital electrodes are multiple pairs, the first electrode 311 and the second electrode 321 are alternately arranged along the first direction.

[0052] The piezoelectric layer 2 is provided with at least one groove 21 or at least one first through hole 22 penetrating the piezoelectric layer 2. The opening of the groove 21 is located on the upper surface of the piezoelectric layer 2, and the bottom is located inside the piezoelectric layer 2. The dimension of the groove 21 along the second direction (i.e., the depth of the groove 21) is smaller than the dimension of the piezoelectric layer 2 along the second direction (i.e., the thickness of the piezoelectric layer 2). At least a portion of the groove 21 is covered by the interdigitated electrode, or at least a portion of the first through hole 22 is covered by the interdigitated electrode. Therefore, no matter whether the groove 21 or the first through hole 22 is provided on the piezoelectric layer 2, a portion of the interdigitated electrode is in contact with the upper surface of the piezoelectric layer 2, and the other portion is suspended above the groove 21 or the first through hole 22.

[0053] Along the first direction, two second through holes 23 are provided on the piezoelectric layer 2 on both sides of the IDT 3, and both second through holes 23 are connected to the cavity 4. The piezoelectric layer 2 and the IDT 3 are configured so that the radio frequency signal applied to the IDT 3 excites the main shear acoustic mode in the piezoelectric layer 2.

[0054] As an example, the substrate 1 includes a base 11 and an intermediate layer 12, wherein the intermediate layer 12 is located between the base 11 and the piezoelectric layer 2 and at both ends of the base 11. Therefore, a groove is formed between the intermediate layer 12 and the surface of the base 11 close to the piezoelectric layer 2, and the groove and the piezoelectric layer 2 together form a cavity 4 (such as Figure 2 , Figure 4 , Figure 6 , Figure 8 or, Fig. 9 As shown, a groove is provided on the substrate 11, the opening of the groove faces the piezoelectric layer 2, and the bottom is located inside the substrate 11; the groove, the intermediate layer 12, and the piezoelectric layer 2 together form a cavity 4. Alternatively, as Fig.10 As shown, the substrate only includes a base 11 , on which a groove is provided, the opening of the groove faces the piezoelectric layer 2 , and the bottom is located inside the base 11 ; the groove and the piezoelectric layer 2 together form a cavity 4 .

[0055] Furthermore, the material of the substrate 11 is any one of high-resistance silicon, silicon carbide, diamond, and sapphire, or a combination of several of them.

[0056] Further, the material of the middle layer 12 is any one of silicon dioxide, silicon nitride, and polysilicon, or a combination of several thereof. For example, the material of the middle layer 12 is silicon dioxide.

[0057] Furthermore, the size of the intermediate layer 12 along the second direction (i.e., the thickness of the intermediate layer 12) is 10nm~50μm, for example, 10nm, 12nm, 15nm, 20nm, 30nm, 50nm, 100nm...1000nm, 1001nm, 1005nm, 1100nm...2μm, 2.1μm, 2.2μm, 2.5μm...10μm, 10.1μm, 10.2μm...50μm.

[0058] Furthermore, the material of the piezoelectric layer 2 is any single crystal material of lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, and aluminum nitride, or a combination of any several single crystal materials.

[0059] Furthermore, a dimension of the piezoelectric layer 2 along the second direction (ie, a thickness of the piezoelectric layer 2 ) is 100 nm to 1 μm, for example, 100 nm, 101 nm, 102 nm, 105 nm, 110 nm…500 nm, 501 nm, 502 nm, 503 nm…1 μm.

[0060] As an example, the number of grooves 21 corresponds to the number of interdigital electrodes (eg Figure 1 , Figure 2 , Figure 5 , Figure 6 ), or the number of the first through holes 22 corresponds to the number of the interdigital electrodes (as shown in Figure 3 , Figure 4 , Figures 7-10 shown).

[0061] As an example, a plurality of grooves 21 are arranged below the interdigitated electrodes at equal or unequal intervals along the third direction (eg Fig.11 As shown), or a plurality of first through holes 22 are arranged below the interdigitated electrodes at equal or unequal intervals along the third direction (as shown Fig.12 shown).

[0062] As an example, the projection of the groove 21 on the piezoelectric layer 2 along the first direction is a rectangle (eg Fig.13 ), or the projection of the first through hole 22 along the first direction on the piezoelectric layer 2 is a rectangle (as shown in Fig.14 shown).

[0063] As an example, the dimension of the groove 21 in the third direction is larger than the dimension of the interdigital electrode in the third direction (eg Figure 1 ), or the size of the first through hole 22 in the third direction is larger than the size of the interdigital electrode in the third direction (as shown in Figure 3shown).

[0064] As an example, the size of the groove 21 in the first direction is larger than the size of the interdigital electrode in the first direction (eg Figure 5 ), or the size of the first through hole 22 in the first direction is larger than the size of the interdigital electrode in the first direction (as shown in Figure 7 , Fig.12 , Fig.14 shown).

[0065] It is understandable that the size of the groove 21 in the first direction may also be smaller than the size of the interdigital electrode along the first direction, and the size of the groove 21 in the third direction is also smaller than the size of the interdigital electrode along the third direction. In this case, the groove 21 is completely covered by the interdigital electrode. Similarly, the first through hole 22 may also be completely covered by the interdigital electrode.

[0066] As an example, the structures of the first bus bar 31 , the second bus bar 32 , the first electrode 311 , and the second electrode 321 are all one or multiple conductive material layers.

[0067] As an example, a portion of the first bus bar 31, the second bus bar 32, the first electrode 311, and the second electrode 321 has a structure of a single conductive material layer, and another portion has a structure of multiple conductive material layers. For example, the first bus bar 31 and the second bus bar 32 are both multiple conductive material layers, and the first electrode 311 and the second electrode 321 are both single conductive material layers; or the first bus bar 31 and the first electrode 311 are both multiple conductive materials, and the second bus bar 32 and the second electrode 321 are both single conductive material layers.

[0068] As an example, the dimensions of the first bus bar 31, the second bus bar 32, the first electrode 311, and the second electrode 321 along the second direction (i.e., the thickness of the first bus bar 31, the second bus bar 32, the first electrode 311, and the second electrode 321) may be the same or different. For example, the thickness of the first bus bar 31 and the thickness of the second bus bar 32 are the same, and the thickness of the first electrode 311 and the second electrode 321 are the same; or, the thickness of the first bus bar 31 and the second bus bar 32 are the same, and the thickness of the first electrode 311 and the second electrode 321 are different; or, the thickness of the first bus bar 31 and the thickness of the second bus bar 32 are different, and the thickness of the first electrode 311 and the second electrode 321 are the same.

[0069] As an example, the materials of the first bus bar 31 , the second bus bar 32 , the first electrode 311 , and the second electrode 321 are any one or a combination of aluminum, aluminum alloy, copper, copper alloy, chromium, titanium, platinum, beryllium, gold, molybdenum, and tungsten.

[0070] Example 2

[0071] A specific method for preparing the thin film bulk acoustic wave resonator with suspended interdigital electrodes of Example 1 comprises the following steps:

[0072] S1. Provide a substrate, and form a piezoelectric layer on the upper surface of the substrate by a smart-cut process or a thin film deposition process.

[0073] S2. Form a groove and a second through hole on the piezoelectric layer by photolithography and etching.

[0074] S3. Filling the groove and the second through hole with a filling material by PVD (physical vapor deposition) or CVD (chemical vapor deposition), and making the upper surface of the filled filling material flush with the upper surface of the piezoelectric layer by CMP (chemical mechanical polishing).

[0075] S4. Forming an interdigital transducer on the piezoelectric layer by lift-off process (or thin film deposition), photolithography, and etching.

[0076] S5. Remove the filling material filled in the groove and the second through hole by wet etching.

[0077] S6. Etch the middle part of the intermediate layer through the second through hole by wet etching or vapor phase hydrofluoric acid (VHF) etching to form a cavity between the piezoelectric layer and the substrate to form a resonator. It can be understood that when etching the intermediate layer, the etching can stop in the intermediate layer, and the bottom of the cavity is located in the intermediate layer; the etching can also stop on the upper surface of the substrate, that is, the middle part of the intermediate layer is penetrated, and the bottom of the cavity is the upper surface of the substrate; the etching can also continue after penetrating the intermediate layer, and then stop inside the substrate, and the bottom of the cavity is located in the substrate.

[0078] It is understandable that the first through hole and the second through hole may be formed on the piezoelectric layer at the same time in step S2. The first through hole and the second through hole are filled with a filling material in step S3. The filling material filled in the first through hole and the second through hole is removed in step S5.

[0079] As an example, the filling material is any one of silicon dioxide, silicon nitride, polysilicon, and aluminum oxide, or a combination of several of them.

[0080] As an example, the substrate in step S1 includes a base and an intermediate layer, and the intermediate layer is located on the base. The material of the base is high-resistance silicon, and the size of the base along the second direction (i.e., the thickness of the base) is 725μm. The material of the intermediate layer is silicon dioxide, and the size of the intermediate layer along the second direction (i.e., the thickness of the intermediate layer) is 1μm. The material of the piezoelectric layer is single-crystal lithium niobate, and the size of the piezoelectric layer along the second direction (i.e., the thickness of the piezoelectric layer) is 270nm. In step S2, the size of the groove along the second direction (i.e., the depth of the groove) is 200nm, and the size of the second through hole along the second direction is 270nm (the same as the thickness of the piezoelectric layer). The filling material in step S3 is silicon dioxide. The material of the interdigital transducer in step S4 is aluminum (Al).

[0081] Performance Test of Film Bulk Acoustic Wave Resonator

[0082] The following results are obtained by conducting simulation experiments on the transversely excited film bulk acoustic wave resonator with grooves on the piezoelectric layer and the film bulk acoustic wave resonator without grooves on the piezoelectric layer provided by the present invention. Fig.15 The comparison diagram of the admittance curve and the conductance curve is shown. The only difference in structure between the transversely excited thin film bulk acoustic wave resonator with grooves on the piezoelectric layer provided by the present invention and the thin film bulk acoustic wave resonator without grooves on the piezoelectric layer is whether the piezoelectric layer has grooves, and the structures, material types and sizes of other components are the same. Fig.15 It can be seen from the figure that by adding the groove structure, the frequency band between the resonant frequency and the anti-resonant frequency, the number or amplitude of the stray peaks in the admittance curve and the conductance curve of the resonator are reduced (or weakened). Therefore, the groove structure can effectively suppress the stray modes between the resonant frequency (fr) and the anti-resonant frequency (fa), which is beneficial to increase the quality factor of the resonator. At the same time, when the resonator is cascaded into a filter, it can effectively reduce the in-band ripple and insertion loss of the filter.

[0083] The above-described embodiments are only preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. For any person skilled in the art, the present application may have various changes and modifications. Any simple equivalent changes and modifications made based on the scope of protection of the present application and the contents of the specification should be included in the scope of protection of the present application.

Claims

1. A transversely excited thin film bulk acoustic resonator, characterized in that: It comprises a substrate, a piezoelectric layer located on the substrate and an interdigital transducer located on the piezoelectric layer; a cavity is formed between the substrate and the piezoelectric layer; the interdigital transducer comprises interdigital electrodes; the piezoelectric layer is provided with at least one groove or at least one first through hole, and at least a part of the groove or the first through hole is covered by the interdigital electrode; second through holes are opened on the piezoelectric layer at positions on both sides of the interdigital transducer in a direction perpendicular to the extension direction of the interdigital electrodes and parallel to the piezoelectric layer; the second through holes are connected to the cavity.

2. The transversely excited thin film bulk acoustic resonator according to claim 1, characterized in that: Along a direction perpendicular to the extension direction of the interdigitated electrodes and parallel to the piezoelectric layer, the size of the groove or the first through hole is larger than the size of the interdigitated electrodes; or, along a direction parallel to the extension direction of the interdigitated electrodes, the size of the groove or the first through hole is larger than the size of the interdigitated electrodes.

3. The transversely excited thin film bulk acoustic resonator according to claim 1, characterized in that: The substrate includes a base and an intermediate layer.

4. The transversely excited thin film bulk acoustic resonator according to claim 3, characterized in that: The material of the substrate is at least one of high-resistance silicon, silicon carbide, diamond, and sapphire; or / and the material of the intermediate layer is at least one of silicon dioxide, silicon nitride, and polycrystalline silicon; or / and the size of the intermediate layer along the direction from the substrate to the piezoelectric layer is 10nm to 50μm.

5. The transversely excited thin film bulk acoustic resonator according to claim 1, characterized in that: The material of the piezoelectric layer is a single crystal material of at least one of lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride and aluminum nitride.

6. The transversely excited thin film bulk acoustic resonator according to claim 1, characterized in that: The dimension of the piezoelectric layer along the direction from the substrate to the piezoelectric layer is 100 nm to 1 μm.

7. The transversely excited thin film bulk acoustic resonator according to claim 1, characterized in that: The interdigital transducer includes a bus bar, the material of which is at least one of aluminum, aluminum alloy, copper, copper alloy, chromium, titanium, platinum, beryllium, gold, molybdenum, and tungsten; or / and the material of the interdigital electrodes is at least one of aluminum, aluminum alloy, copper, copper alloy, chromium, titanium, platinum, beryllium, gold, molybdenum, and tungsten.

8. The transversely excited thin film bulk acoustic resonator according to claim 7, characterized in that: The bus bar and the interdigital electrodes have the same thickness in a direction from the substrate to the piezoelectric layer.

9. The method for preparing a transversely excited thin film bulk acoustic resonator according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. providing a substrate, and forming a piezoelectric layer on the substrate; S2, forming a groove or a first through hole on the piezoelectric layer, and forming a second through hole at the same time; S3, using a filling material to fill the groove and the second through hole until they are flush with the upper surface of the piezoelectric layer; or using a filling material to fill the first through hole and the second through hole until they are flush with the upper surface of the piezoelectric layer; S4, forming an interdigital transducer on the piezoelectric layer; S5, removing the filling material filled in the groove and the second through hole; or removing the filling material filled in the first through hole and the second through hole; S6. Etching the middle portion of the substrate through the second through hole to form a cavity between the piezoelectric layer and the substrate.

10. The preparation method according to claim 9, characterized in that: The filling material is at least one of silicon dioxide, silicon nitride, polysilicon and aluminum oxide.

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