Bulk acoustic wave structure with conductive bridge structure and manufacturing method thereof

Abstract

A bulk acoustic wave (BAW) resonator structure is provided. The BAW resonator structure comprises a transducer, and the transducer comprises a first electrode; a second electrode; the piezoelectric layer is positioned between the first electrode and the second electrode; a dielectric layer in contact with the piezoelectric layer on a surface of the piezoelectric layer; and a conductive layer, the conductive layer being over the first electrode. The transducer further includes a conductive bridge portion in contact with the first electrode, the conductive layer, and over and in contact with the dielectric layer. The conductive bridge portion and the conductive layer form a conductive bridge structure between the ends of the first electrode.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 487,233, filed February 27, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to a bulk acoustic wave (BAW) structure. In particular, the present disclosure relates to a BAW structure having a conductive bridge structure between an electrode and a reflector layer. Background Art

[0004] Acoustic resonators (e.g., particularly bulk acoustic wave (BAW) resonators or BAW filters) are used in high-frequency communication applications, such as 3rd generation (3G), 4th generation (4G), and 5th generation (5G) wireless devices. Specifically, BAW resonators are typically used to provide a flat passband, a steep filter skirt, and square shoulders at the upper and lower ends of the passband, and provide excellent rejection outside the passband in the filter network. BAW resonators also have relatively low insertion loss, tend to decrease in size as the operating frequency increases, and are relatively stable over a wide temperature range. These wireless devices typically support various communication means, such as cellular, wireless fidelity (Wi-Fi), Bluetooth, and / or near-field communication, and therefore require the high performance of BAW resonators.

[0005] To meet the filtering requirements of certain applications, BAW resonators operating at higher frequencies typically have thinner electrodes and / or smaller resonator areas. As a result, BAW resonators can have higher electrical losses, which negatively impacts their performance. Therefore, there is a need to improve the performance of BAW resonators. Summary of the Invention

[0006] Aspects of the present invention include a BAW resonator structure. The BAW resonator structure includes a transducer, the transducer including a first electrode; a second electrode; a piezoelectric layer located between the first electrode and the second electrode; a dielectric layer in contact with the piezoelectric layer on a surface of the piezoelectric layer; and a conductive layer located above the first electrode. The transducer also includes a transducer, the transducer including a conductive bridge portion, the conductive bridge portion in contact with the first electrode and the conductive layer, and located above and in contact with the dielectric layer. The conductive bridge portion and the conductive layer form a conductive bridge structure between ends of the first electrode.

[0007] In some embodiments, the conductive bridge portion contacts the first electrode and includes the same conductive material as the first electrode.

[0008] In some embodiments, the transducer further includes a second dielectric layer, the second dielectric layer contacting the piezoelectric layer on the second surface of the piezoelectric layer. In some embodiments, a second conductive bridge structure is located above and in contact with the second dielectric layer, and is in contact with the second electrode. The second conductive bridge structure comprises the same conductive material as the second electrode.

[0009] In some embodiments, the length of the conductive bridge portion is smaller than the length of the second conductive bridge portion in the horizontal direction. In some embodiments, the projection of the conductive bridge structure partially overlaps with the projection of the second conductive bridge portion in the vertical direction. In some embodiments, the boundary between the conductive bridge portion and the first electrode is aligned with the boundary between the second conductive bridge portion and the second electrode.

[0010] In some embodiments, in a horizontal direction, the length of the conductive bridge portion is smaller than the length of the second conductive bridge portion. In some embodiments, in a vertical direction, a projection of the conductive bridge portion does not overlap with a projection of the second conductive bridge portion.

[0011] In some embodiments, in a vertical direction, a projection of the first electrode partially overlaps with a projection of the dielectric layer. In some embodiments, a projection of the second electrode does not overlap with a projection of the second dielectric layer.

[0012] In some embodiments, the first electrode has a first thickness in the active area and a frame area surrounding the active area, and has a second thickness outside the active area and the frame area, the second thickness being greater than the first thickness. In some embodiments, the second electrode has the same thickness in the active area, the frame area, and outside the frame area.

[0013] In some embodiments, the transducer further includes a first insulating layer located above and in contact with the first electrode in the active region and the frame region, wherein the first insulating layer has a first thickness in the active region and a second thickness in the frame region, the first thickness being greater than the second thickness.

[0014] In some embodiments, the transducer further includes a second insulating layer located above and in contact with the second electrode in the active region and the frame region. The second insulating layer may have the same thickness in the active region and the frame region.

[0015] In some embodiments, the angle between the side surface of the first dielectric layer and the vertical direction is between about 30 degrees and about 60 degrees. In some embodiments, the angle between the side surface of the second dielectric layer and the vertical direction is between about 5 degrees and about 15 degrees.

[0016] In some embodiments, an angle between a side surface of the first insulating layer and a vertical direction is between about 30 degrees and about 50 degrees.

[0017] In some embodiments, an angle between a side surface of the second insulating layer and a vertical direction is between about 5 degrees and about 15 degrees.

[0018] In some embodiments, in the vertical direction, the thickness of the first dielectric layer is between about 20 nm and about 200 nm.

[0019] In some embodiments, the transducer further comprises one or more insulating layers, each of the one or more insulating layers being in contact with a corresponding electrode of the first electrode and the second electrode. The one or more insulating layers may each comprise an air gap.

[0020] In some embodiments, the transducer further includes a conductive layer in contact with the second insulating layer. In a vertical direction, a surface of the second conductive bridge portion may be located between the first surface and the second surface of the conductive layer.

[0021] In some embodiments, the transducer further includes an aluminum nitride-tungsten-aluminum nitride structure located between the second dielectric layer and the second conductive bridge portion.

[0022] In some embodiments, an angle between a side surface of the conductive bridge portion and a vertical direction is approximately zero, and an angle between a side surface of the second conductive bridge portion and the vertical direction is approximately zero.

[0023] In some embodiments, in a vertical direction, a projection of the conductive bridge portion is aligned with a projection of the second conductive bridge portion.

[0024] In some embodiments, the transducer further includes an insulating layer located above and in contact with at least one of the first electrode layer and the second electrode layer, wherein the insulating layer is in contact with the corresponding conductive bridge portion. An interface between the insulating layer and the corresponding conductive bridge portion may be aligned with the vertical direction.

[0025] In some embodiments, the transducer further includes a pair of reflective layers located above each of the first electrode and the second electrode and conductively connected to a corresponding conductive bridge in contact with the corresponding electrode. The pair of reflective layers may include a tungsten layer and an aluminum-copper layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1A and 1B Each shows a portion of an exemplary BAW structure according to an embodiment of the present disclosure.

[0027] Figure 1C The embodiment according to the present disclosure is shown Figure 1A and 1B Performance diagram of the BAW structure shown in .

[0028] Figures 2A-2D Each shows a portion of another exemplary BAW structure according to an embodiment of the present disclosure.

[0029] Figure 2E The embodiment according to the present disclosure is shown Figures 2A-2D Performance diagram of the BAW structure shown in .

[0030] Figure 3A and 3B A portion of another exemplary BAW structure according to an embodiment of the present disclosure is respectively shown.

[0031] Figure 4A and 4B Each shows a portion of another exemplary BAW structure according to an embodiment of the present disclosure.

[0032] Figure 5A and 5B Each shows a portion of another exemplary BAW structure according to an embodiment of the present disclosure.

[0033] Figure 6 A flow chart illustrating an exemplary fabrication process for forming a BAW structure according to an embodiment of the present disclosure is presented. DETAILED DESCRIPTION

[0034] The following specific embodiments are illustrative in nature and are not intended to limit the scope, applicability or configuration of the embodiments of the invention disclosed herein in any way. On the contrary, the following embodiments provide actual examples, and those skilled in the art will recognize that some of the examples may have suitable alternatives. The following embodiments will be described in conjunction with the accompanying drawings, which are not drawn to scale (unless otherwise indicated), in which the same numbers / letters represent the same elements. However, it should be understood that the use of numbers to refer to components in a given figure is not intended to limit the components marked with the same numbers in another figure. In addition, the use of different numbers to refer to components in different figures is not intended to indicate that different numbered components cannot be the same or similar to other numbered components. Examples of construction, materials, dimensions and manufacturing processes are provided for selected elements, and all other elements adopt construction, materials, dimensions and manufacturing processes known to those skilled in the art.

[0035] As used herein, the term "approximately" refers to a value of a given amount that may vary based on a particular technology node associated with a semiconductor device. Based on the particular technology node, the term "approximately" may refer to a value of a given amount that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±20%, or ±30% of the value).

[0036] Reference will now be made in detail to various embodiments of the presently disclosed subject matter, some of which are illustrated in the accompanying drawings.

[0037] Efforts have been made to improve the performance of BAW resonators. For example, to meet filtering requirements in certain applications, thinner electrodes and / or smaller resonator areas have been used in BAW resonators for BAW resonators operating at higher frequencies (e.g., greater than 5 GHz). However, reducing the electrode thickness may cause an increase in resistance and / or electrical losses. In addition, reducing the resonator area may result in multiple resonators being cascaded in series to handle high power levels, thereby adding more resistance and / or electrical losses. In some applications, materials with high conductivity (e.g., aluminum copper (AlCu)) are made thicker to reduce electrical losses, but doing so may cause an increase in acoustic losses because these materials are generally acoustically lossy and the greater thickness will generate a greater proportion of energy (stress / strain) in these layers.

[0038] In order to reduce the electrical losses in BAW resonators, embodiments of the present disclosure provide BAW structures, e.g., BAW resonators / filters, having reduced electrical losses compared to existing BAW resonators. The disclosed BAW structures may also have comparable / improved resonance performance (e.g., quality factor or Q factor) compared to existing BAW resonators. The BAW structure has a piezoelectric layer, a pair of electrodes sandwiching the piezoelectric layer, and one or more Bragg reflector stacks, each Bragg reflector stack being located above a corresponding electrode. The BAW structure also has at least one conductive bridge structure (e.g., a conductive ring) between the ends of the electrodes. The conductive bridge structure includes a metal portion of the Bragg reflector stack and a conductive bridge portion, the conductive bridge portion being conductively connected to the ends of the electrodes, thereby forming an electrical loop and reducing the electrical losses of the BAW structure. The metal portion of the Bragg reflector stack may include one or more conductive Bragg reflector layers. For example, the metal portion may include the entire Bragg reflector stack (e.g., formed by a conductive layer) or one or more Bragg reflector layers in the Bragg reflector layer. The size and / or location of components in the disclosed BAW structure are optimized to minimize electrical losses while maintaining / improving acoustic performance. For example, the conductive bridge structure can reduce the electrical resistance, thermal resistance, and / or ohmic losses of the BAW structure while having comparable or improved acoustic performance.

[0039] In the disclosed BAW structure, an electrode and a dielectric layer in contact with each other are disposed on the piezoelectric layer. The conductive bridge portion may be located outside the active / resonant region and may be an extension of the electrode. The conductive bridge portion may be disposed above the dielectric layer and may be in contact with a Bragg reflector layer (e.g., a metal portion of a Bragg reflector stack above the electrode) such that the electrode is conductively connected to the Bragg reflector stack. The conductive bridge portion may partially or completely cover the dielectric layer. In some embodiments, the BAW structure includes two conductive bridge portions, each of which is an extension of a corresponding electrode. For example, a first conductive bridge portion (e.g., an extension of a first / top electrode) may partially cover the first dielectric layer, and a second conductive bridge portion (e.g., an extension of a second / bottom electrode) may completely cover the second dielectric layer. In some embodiments, the first conductive bridge portion and the second conductive bridge portion may partially or completely overlap vertically. For example, the first conductive bridge portion and the second conductive bridge portion are aligned with each other in the vertical direction. In some embodiments, in an "aligned bridge" configuration (e.g., Figure 1A ), the boundary between the first conductive bridge portion and the first / top electrode (e.g., or the end of the first conductive bridge portion facing the active region) is vertically aligned with the boundary between the second conductive bridge portion and the second / bottom electrode (e.g., or the end of the second conductive bridge portion facing the active region). In some embodiments, in an "offset bridge" configuration (e.g., Figure 1BIn some embodiments, the first conductive bridge portion and the second conductive bridge portion do not overlap, and the second conductive bridge portion is positioned further away from the active area than the first conductive bridge portion. In some embodiments, an end of the first conductive bridge portion facing away from the active area is vertically aligned with an end of the second conductive bridge portion facing the active area. In some embodiments, a bottom surface of the second conductive bridge portion is located between a top surface and a bottom surface of a Bragg reflector layer in contact with the second electrode. In some embodiments, the BAW structure includes a protection structure positioned between the second conductive bridge portion and the second dielectric layer. The protection structure may include an aluminum nitride-tungsten-aluminum nitride structure.

[0040] An insulating layer is positioned between each electrode and the corresponding Bragg reflector stack. The end of the insulating layer facing away from the active region can serve as a boundary between the electrode and the corresponding conductive bridge portion. In some embodiments, the side surface of the insulating layer facing away from the active region can contact the Bragg reflector layer, which in turn contacts the corresponding conductive bridge portion. In some embodiments, the side surface of the insulating layer can contact the corresponding conductive bridge portion. For example, the angle between the side surface of the insulating layer and the vertical direction can be approximately zero degrees. The insulating layer can then contact the corresponding conductive bridge portion on the side surface. Because the insulating layer and the conductive bridge portion can include acoustically similar materials, scattering of acoustic energy (e.g., at the interface between the insulating layer and the conductive bridge portion) is reduced / minimized. For example, the insulating layer can include silicon oxide, and the conductive bridge portion can include aluminum copper, which is acoustically similar to silicon oxide. The BAW resonator can have two insulating layers, e.g., a first insulating layer above the first electrode and a second insulating layer above the second electrode. In some embodiments, both insulating layers include silicon oxide. In some embodiments, one or both insulating layers can include an air gap / cavity. In addition to improving electrical losses, the air gap can also help confine the acoustic energy in the piezoelectric layer and thereby improve the acoustic coupling of the BAW structure.

[0041] In some embodiments, the BAW structure includes one or more regions surrounding the active area to help improve the lateral confinement and quality factor of the acoustic energy. The length and / or thickness of these regions are optimized to improve the acoustic performance (quality factor). For example, the BAW structure may include a recessed frame area in contact with and surrounding the active area. The recessed frame area is defined by a portion of the top insulating layer, the thickness of which is reduced compared to the thickness in the active area. The BAW structure may also include an inner boundary ring area in contact with and surrounding the recessed frame area. The inner boundary ring area is defined by a portion of the first electrode, the thickness of which is increased compared to the thickness of the active area. The BAW structure may further include an outer boundary ring area in contact with and surrounding the inner boundary ring area. The outer boundary ring area is defined by a portion of the insulating layer above the dielectric layer.

[0042] In the present disclosure, the position and / or geometric parameters of the electrodes, conductive bridge portions, insulating layers, and dielectric layers are adjusted to optimize the performance of the BAW structure, for example, minimized electrical losses and comparable quality factors. For example, the length of the first dielectric layer can be about 0.5um to about 4um, and the length of the second dielectric layer can be about 1um to about 4um. In some embodiments, the angle between the side surface of the first dielectric layer and the vertical direction is about 30 degrees to about 60 degrees, and the angle between the side surface of the second dielectric layer and the vertical direction is about 5 degrees to about 15 degrees. In some embodiments, the angle between the side surface of the first insulating layer and the vertical direction is about 30 degrees to about 50 degrees, and the angle between the side surface of the second insulating layer and the vertical direction is about 5 degrees to about 15 degrees. In some embodiments, the length of the recessed frame area is between about 0.5um and about 4um, and the thickness of the first insulating layer in the recessed frame area is about 5nm to about 50nm less than the thickness of the first insulating layer in the active area. The details of the geometric parameters of each layer are described below in conjunction with the accompanying drawings.

[0043] Figure 1A 、 1B , 2A-2D, 3A, 3B, 4A, 4B, 5A and 5B illustrate exemplary BAW structures, each of which has at least one conductive bridge portion. Figure 1AAn exemplary BAW structure 100 is shown having two conductive bridge portions, each located above a corresponding dielectric layer, in accordance with some embodiments. The BAW structure 100 may be referred to as an "aligned bridge" configuration. The BAW structure 100 may include a transducer comprising a piezoelectric layer 102 and a first electrode 104 (e.g., a top electrode) and a second electrode 106 (e.g., a bottom electrode), each of which is in contact with the piezoelectric layer 102. The BAW structure 100 may include a substrate 150 on which the transducer is disposed. The substrate 150 may include a suitable material, such as a semiconductor material (e.g., silicon), glass, plastic, or a combination thereof. The piezoelectric layer 102 may include a suitable piezoelectric material, such as aluminum nitride (AlN), zinc oxide (ZnO), aluminum scandium nitride (AlScN), and / or other suitable materials. In some embodiments, the piezoelectric layer 102 includes AlN. The first electrode 104 and the second electrode 106 may each include one or more suitable conductive materials and may have a single-layer or multi-layer structure. For example, the first electrode 104 and the second electrode 106 may each include one or more of the following: copper (Cu), tungsten (W), aluminum copper (AlCu), molybdenum (Mo), and / or platinum (Pt). In some embodiments, the first electrode 104 includes a first metal layer 104-1 in contact with the piezoelectric layer 102, and a second metal layer 104-2 in contact with the first metal layer 104-1. In some embodiments, the second electrode 106 includes a first metal layer 101-1 in contact with the piezoelectric layer 102, and a second metal layer 106-2 in contact with the first metal layer 106-1. In some embodiments, the first metal layer 104-1 and the first metal layer 106-1 each include W, and the second metal layer 104-2 and the second metal layer 106-2 each include AlCu. The first insulating layer 110 and the second insulating layer 112 may be disposed in contact with the first electrode 104 (or the second metal layer 104-2) and the second electrode 106 (or the second metal layer 106-2), respectively. In the present disclosure, the portion of the electrode material covered by the corresponding insulating layer is referred to as the electrode, and the portion of the electrode material extending beyond the coverage of the corresponding insulating layer is referred to as the conductive bridge portion. Figure 1A As shown, the first electrode 104 may be covered by a first insulating layer 110, and the second electrode 106 may be covered by a second insulating layer 112. The first insulating layer 110 and the second insulating layer 112 may each include a suitable insulating material, such as silicon oxide, silicon nitride, silicon oxynitride, and / or epoxy resin.

[0044] The BAW structure 100 may also include one or more Bragg reflector stacks, each of which is positioned above an electrode. A first insulating layer 110 and a second insulating layer 112 may each separate an electrode from a corresponding Bragg reflector stack. In some embodiments, the BAW structure 100 includes a first Bragg reflector stack 108-1 positioned above (e.g., in contact with) the first insulating layer 110, and a second Bragg reflector stack 108-2 positioned above (e.g., in contact with) the second insulating layer 112. Each of the first Bragg reflector stack 108-1 and the second Bragg reflector stack 108-2 includes a plurality of alternating first and second reflective layers. The first and second reflective layers may include one or more conductive materials having sufficiently high reflectivity and a desired low resistance. In some embodiments, the first reflective layer includes W and the second reflective layer includes AlCu. Each of the first Bragg reflector stack 108-1 and the second Bragg reflector stack 108-2 may include one or more W-AlCu pairs. It should be noted that, depending on the design, the first Bragg reflector stack 108-1 and the second Bragg reflector stack 108-2 may include any suitable number of W-AlCu pairs. For example, the first Bragg reflector stack 108-1 and the second reflector stack 108-2 may each include at least five W-AlCu pairs, although the specific number is not limited by the embodiments / figures of the present disclosure. In some embodiments, the first reflective layer and the second reflective layer may also include other suitable conductive materials, such as Cu, Mo, and / or Pt. The BAW structure 100 may further include a passivation layer 114 that covers the exterior of the BAW structure 100. The passivation layer 114 may include one or more insulating materials, such as silicon oxide, silicon nitride, silicon oxynitride, or a combination thereof.

[0045] The BAW structure 100 may include an active region, a mass-loading frame region, and an external region, such as Figure 1AAs shown. The active area may refer to a preferred area in which most of the acoustic energy is stored. The mass loading area may refer to a thickened area surrounding the active area and which may help reduce the scattering of acoustic energy (e.g., improve the confinement of acoustic energy in the active area). In some embodiments, the loading area includes a mass loading frame, which includes an inner boundary ring ("2L") area defined by the increased thickness of the first metal layer 104-1 (or the first electrode 104), and an outer boundary ring ("3L") area defined by the length of the first insulating layer 110 extending outside the inner boundary ring area. The outer boundary ring area may surround the inner boundary ring area, which surrounds the active area. In some embodiments, the loading area further includes a recessed frame ("1L") area in contact with and surrounding the active area. The inner boundary ring area may surround the recessed frame area. The recessed frame area may refer to an area in which the thickness of the first insulating layer 110 is reduced compared to the thickness in the active area. The piezoelectric layer 102, the top electrode 104 and the second electrode 106, and the first insulating layer 110 and the second insulating layer 112 may extend in the active area, the recessed area, the inner boundary ring area, and the outer boundary ring area. The first dielectric layer 116 may be disposed in the outer boundary ring area, and the second dielectric layer 118 may be disposed outside the outer boundary ring area and partially disposed in the outer area. Figure 1A In the illustrated "aligned bridge" configuration, the ends of the first insulating layer 110 and the second insulating layer 112 facing away from the active region are vertically aligned. In some embodiments, the second insulating layer 112 and the second electrode 106 extend through the active region, the recessed frame region, and are located in the outer boundary ring region. In the "aligned bridge" configuration of the BAW structure 100, the first insulating layer 110 and the first dielectric layer 116 overlap in the outer boundary ring region.

[0046] In some embodiments, the length d1 of the recessed frame region (e.g., in the x-direction) can be between about 0.5 μm and about 4 μm. In some embodiments, the length d2 of the inner boundary ring can be between about 0.25 μm and about 2 μm. In some embodiments, the length d3 of the outer boundary ring can be between about 0.5 μm and about 3 μm. Figure 1A As shown, in the active area and the recessed frame area, the thickness of the first electrode 104 is t1 (e.g., constant). In the inner boundary ring, the thickness of the first electrode 104 is t2 and is greater than t1. In some embodiments, t2 is about 10% to about 30% greater than t1. Figure 1A As shown, the first insulating layer 110 has a thickness t3 in the active area and a thickness t4 in the recessed frame area, wherein t4 is about 3% to about 15% less than t3. In some embodiments, the thickness t5 of the second insulating layer 112 is constant in the active area and the load area.

[0047] The BAW structure 100 may include a first dielectric layer 116 located on the piezoelectric layer 102 and on the same side as the first electrode 104, and a second dielectric layer 118 located on the piezoelectric layer 102 and on the same side as the second electrode 106. Extensions of the corresponding electrodes (or the same material of the electrodes) may be placed over and cover the corresponding dielectric layers, thereby forming corresponding conductive bridge portions. In some embodiments, the vertical projections (e.g., in the z-direction) of the first dielectric layer 116 and the second dielectric layer 118 may partially overlap. Figure 1A As shown, the first electrode 104 can be disposed on (e.g., partially covering) the first dielectric layer 116 and in contact with the first conductive bridge portion 120. The first conductive bridge portion 120 can also partially cover the first dielectric layer 116. The second conductive bridge portion 122 can completely cover the second dielectric layer 118 and can contact the second electrode 106 at the edge of the second dielectric layer 118. In some embodiments, the bottom surface of the second conductive bridge portion 122 is coplanar with the bottom surface of the second insulating layer 112 (or the top surface of the Bragg reflector layer in contact with the second insulating layer 112). The first conductive bridge portion 120 and the second conductive bridge portion 122 can respectively have the same material as the first electrode 104 and the second electrode 106. For example, the first conductive bridge portion 120 and the second conductive bridge portion 122 can each have a W layer (e.g., a first portion) in contact with the corresponding dielectric layer (e.g., 116 or 118) and an AlCu layer (e.g., a second portion) on the W layer. The first conductive bridge portion 120 and the second conductive bridge portion 122 may each be in contact with a Bragg reflector layer (eg, W) in the Bragg reflector stacks 108 - 1 and 108 - 2 , respectively.

[0048] The lengths of the first conductive bridge portion 120 and the second conductive bridge portion 122 can each be determined based on the portion of the electrode material that is above the corresponding dielectric layer and not covered by the corresponding insulating layer. In some embodiments, the first conductive bridge portion 120 partially covers the top surface (e.g., flat surface) of the first dielectric layer 116. In some embodiments, the second conductive bridge portion 122 completely covers the top surface (e.g., flat surface) and side surfaces (e.g., inclined surface) of the second dielectric layer 118. For example, Figure 1AAs shown, the length d4 of the first dielectric layer 116 (e.g., in the x-direction) can be between about 0.5 μm and about 4 μm, and the length d5 ​​of the second dielectric layer 118 can be between about 1 μm and about 4 μm. The first conductive bridge portion 120 can include conductive material outside the outer boundary ring area, and the length d6 of the first conductive bridge portion 120 (e.g., not covered by the first insulating layer 110 (e.g., exposed)) can be about 0.5 μm to about 1 μm. In some embodiments, d5 is greater than d6. The second conductive bridge portion 122 is not covered by the second insulating layer 112 and includes conductive material outside the outer boundary ring area. The length of the second conductive bridge portion 122 is d5, which is the same as the length of the second dielectric layer 118. In some embodiments, the first insulating layer 110, the second insulating layer 112, the first dielectric layer 116, and the second dielectric layer 118 can each have an inclined side surface. In some embodiments, the angle θ1 between the side surface of the first insulating layer 110 and the vertical direction (e.g., the z-direction) is between about 30 degrees and about 50 degrees, and the angle θ2 between the side surface of the second insulating layer 112 and the vertical direction is between about 5 degrees and about 15 degrees. In some embodiments, the angle θ3 between the side surface of the first dielectric layer 116 and the vertical direction is between about 30 degrees and about 60 degrees, and the angle θ4 between the side surface of the second dielectric layer 118 and the vertical direction is between about 5 degrees and about 15 degrees. In some embodiments, the thickness t6 of the first dielectric layer 116 is between about 20 nm and about 200 nm. In some embodiments, the thickness t7 of the second dielectric layer 118 is between about 40 nm and about 400 nm.

[0049] Figure 1B Another exemplary BAW structure 101 having a pair of conductive bridge portions according to some embodiments is shown. The BAW structure 101 may be referred to as an "offset bridge" configuration. Unlike the BAW structure 100, the BAW structure 101 may include a second dielectric layer 119 that is "offset" from the first dielectric layer 116 such that a vertical projection of the first dielectric layer 116 does not overlap with a vertical projection of the second dielectric layer 119. In some embodiments, a second conductive bridge portion 123 overlying the second dielectric layer 119 is offset from the first conductive bridge portion 120 such that a vertical projection of the first conductive bridge portion 120 does not overlap with a vertical projection of the second conductive bridge portion 123. Figure 1B As shown, the second dielectric layer 119 can be disposed in the outer region (e.g., outside the outer boundary ring region). In some embodiments, the end of the second dielectric layer 119 facing the active region is vertically aligned with the end of the first dielectric layer 116 facing away from the active region. In various embodiments, d5 can be less than, equal to, or greater than d6. In some embodiments, d5 is between about 1 μm and about 4 μm. In some embodiments, the thickness t7 of the second dielectric layer 119 is between about 40 nm and about 400 nm.

[0050] The BAW structure 100 and the BAW structure 101 may include a second electrode 107 in contact with the bottom surface of the piezoelectric layer 102 and a second insulating layer 113 in contact with the second electrode 107. Similar to the second electrode 106 in the BAW structure 100, the second electrode 107 may include a first metal layer 107-1 in contact with the piezoelectric layer 102 and a second metal layer 107-2 in contact with the first metal layer 107-1. The materials of the first metal layer 107-1 and the second metal layer 107-2 and the second insulating layer 113 may be similar or identical to the materials of the first material layer 106-1 and the second material layer 106-2 and the second insulating layer 112, and a detailed description is not repeated herein. Unlike the BAW structure 100, the second electrode 107 and the second insulating layer 113 may extend through the active area, the recessed frame area, and the mass load frame (for example, beyond the outer boundary ring area). The second insulating layer 113 may stop at the boundary between the mass frame area and the external area, and the second conductive bridge portion 123 starts from the boundary.

[0051] Figure 1C The simulated quality factor (as the y-axis) is shown as a function of the width of the inner mass-loading frame (as the x-axis) and the length d3 of the outer boundary ring (as the lattice) according to an embodiment of the present disclosure. The simulated quality factors of the "aligned bridge" (e.g., BAW structure 100) and the "offset bridge" (e.g., BAW structure 101) are comparable to existing BAW resonators without conductive bridges.

[0052] Figure 2A Another exemplary BAW structure 200 according to some embodiments of the present disclosure is shown. The BAW structure 200 can also have an "aligned bridge" configuration such that vertical projections of the first conductive bridge portion 120 and the second conductive bridge portion 122 overlap. The BAW 200 includes a first insulating layer 210 above the first electrode 104 and a second insulating layer 212 above the second electrode 106. Unlike the BAW 100, the first insulating layer 210 and the second insulating layer 212 can each include an air gap, for example, an air cavity. The air gap can acoustically decouple the Bragg reflector stack from the electrodes and can maximize the acoustic energy storage in the piezoelectric layer 102 and the electrodes 104 and 106, resulting in higher / improved acoustic coupling and quality factor. As Figure 2AAs shown, the air gap can be located in the active area and can extend into the mass-loaded frame (e.g., the inner boundary ring area and the outer boundary ring area). In some embodiments, the ends of the first insulating layer 210 and the second insulating layer 212 facing away from the active area can be vertically aligned with each other. In some embodiments, the thickness t8 of the first insulating layer 210 is similar to t3, and the thickness t9 of the second insulating layer 212 is similar to t5. In some embodiments, the thickness of the first insulating layer 210 and the second insulating layer 212 remains unchanged in the active area and the mass-loaded frame.

[0053] In some embodiments, unlike the BAW structure 100, the BAW structure 200 does not include a recessed frame region. For example, the inner boundary ring region may contact and surround the active region, such as Figure 2A As shown. In some embodiments, the length of the inner boundary ring area of ​​the BAW structure 200 can be equal to the sum of the recessed frame area and the inner boundary ring area of ​​the BAW structure 100 (for example, (d1+d2)). The first insulating layer 210 and the second insulating layer 212 can extend from the active area into the inner boundary ring area, and further extend into the outer boundary ring area. In some embodiments, the thickness of the first electrode 104 in the active area and the inner boundary ring area of ​​the BAW structure 200 can be similar to or the same as the thickness of the BAW structure 100. In some embodiments, the geometric parameters (for example, length, angle, etc.) of the first conductive bridge portion 120, the second conductive bridge portion 122, the first dielectric layer 116 and the second dielectric layer 118 can be similar to or the same as the geometric parameters of the BAW structure 100, and the detailed description is not repeated herein.

[0054] Figure 2B Another exemplary BAW structure 201 according to some embodiments of the present disclosure is shown. The BAW structure 201 can also have an "offset bridge" configuration, such that the vertical projection of the first conductive bridge portion 120 does not overlap the vertical projection of the second conductive bridge portion 123. The BAW 201 includes a first insulating layer 210 above the first electrode 104 and a second insulating layer 212 above the second electrode 106. Unlike the BAW 101, the first insulating layer 210 and the second insulating layer 213 can each include an air gap, e.g., an air cavity. Similar to the BAW structure 200, the air gap can maximize the storage of acoustic energy in the piezoelectric layer 102 and the electrodes, resulting in higher / improved acoustic coupling and quality factor. The position and size of the first insulating layer 210 of the BAW structure 201 can be similar or identical to the position and size of the first insulating layer of the BAW structure 200, and a detailed description is not repeated herein. The second insulating layer 213 can extend through the active region and the mass-loading frame. Similar to the BAW structure 200, the BAW structure 201 does not include a recessed frame region. For example, the inner boundary ring region may contact and surround the active region, e.g. Figure 2BAs shown. In some embodiments, the length of the inner boundary ring area of ​​the BAW structure 201 can be equal to the sum of the recessed frame area and the inner boundary ring area of ​​the BAW structure 101 (for example, (d1+d2)). In some embodiments, the thickness of the first electrode 104 in the active area and the inner boundary ring of the BAW structure 200 can be similar to or the same as the thickness of the BAW structure 101. In some embodiments, the geometric parameters (for example, thickness, angle, etc.) of the first conductive bridge portion 120, the second conductive bridge portion 123, the first dielectric layer 116, and the second dielectric layer 119 can be similar to or the same as the geometric parameters of the BAW structure 101, and the detailed description is not repeated herein. In some embodiments, the BAW structures 200 and 201 can each include a recessed frame area located between the active area and the mass load frame area. The size and shape of the recessed frame area can be similar to Figure 1A and 1B The BAW structures 100 and 101 depicted in FIG. 1 are similar in size and shape and may include an air gap.

[0055] Figure 2C Another exemplary BAW structure 202 according to some embodiments of the present disclosure is shown. The BAW structure 202 may also have an "aligned bridge" configuration similar to the BAW structure 200. Unlike the BAW structure 200, the BAW structure 202 includes a first insulating layer 210 and a second insulating layer 214, wherein the first insulating layer includes an air gap and the second insulating layer includes a dielectric material (such as silicon oxide, silicon nitride and / or silicon oxynitride). In some embodiments, the second insulating layer 214 includes silicon oxide. In some embodiments, the geometric parameters (e.g., thickness, angle, etc.) of other portions of the BAW structure 202 (such as the first conductive bridge portion 120, the second conductive bridge portion 122, the first dielectric layer 116 and the second dielectric layer 118) may be similar or identical to the geometric parameters of the BAW structure 200. The geometric parameters of the second insulating layer 214 may be similar to those of the second insulating layer 112. The detailed description will not be repeated herein.

[0056] Figure 2DAnother exemplary BAW structure 203 according to some embodiments of the present disclosure is shown. The BAW structure 203 may also have an "offset bridge" configuration similar to the BAW structure 201. Unlike the BAW structure 201, the BAW structure 203 includes a first insulating layer 210 and a second insulating layer 215, wherein the first insulating layer includes an air gap and the second insulating layer includes a dielectric material (such as silicon oxide, silicon nitride and / or silicon oxynitride). In some embodiments, the second insulating layer 215 includes silicon oxide. In some embodiments, the geometric parameters (e.g., length, angle, etc.) of other portions of the BAW structure 202 (such as the first conductive bridge portion 120, the second conductive bridge portion 122, the first dielectric layer 116 and the second dielectric layer 119) may be similar or identical to the geometric parameters of the BAW structure 201. The geometric parameters of the second insulating layer 215 may be similar to those of the second insulating layer 113. The detailed description will not be repeated herein.

[0057] Figure 2E The simulated quality factor as a function of the width of the inner BO (as the x-axis) and the length d3 of the outer boundary ring (as the grid) according to an embodiment of the present disclosure is shown. "No air cavity" refers to a BAW structure with no air gap in the insulating layer (e.g., BAW structures 100 and 101); "TR5 air cavity" refers to a BAW structure with one air cavity below the top fifth Bragg reflector layer (e.g., BAW structures 202 and 203); "R5\TR5 air cavity" refers to a BAW structure with two air cavities below the top fifth Bragg reflector layer and above the bottom fifth Bragg reflector layer (e.g., BAW structures 200 and 201). The simulated quality factor of "R5 / TR5 air cavity" is generally higher than that of "TR5 air cavity", and the quality factor of "TR5 air cavity" is generally higher than that of "no air cavity" due to the improvement in acoustic energy confinement.

[0058] Figure 3A Another exemplary BAW structure 300 according to some embodiments of the present disclosure is shown. The BAW structure 300 has an "aligned bridge" configuration and can further reduce electrical losses. Unlike the BAW structure 100, the BAW structure 300 may include a second dielectric layer 318 that is thicker than the second dielectric layer 118. In some embodiments, the thickness t11 of the second dielectric layer 318 is approximately equal to the sum of the total thicknesses of the second electrode 106 and the second insulating layer 312. In some embodiments, the thickness t11 of the second dielectric layer 318 is between about 40 nm and about 1000 nm. The BAW structure 300 may also have a second conductive bridge portion 322 that extends above (e.g., covers) the second dielectric layer 318. As Figure 3AAs shown, the bottom surface of the second conductive bridge portion 322 can be located between the top surface and the bottom surface of the first Bragg reflector layer (e.g., W) in contact with the second insulating layer 312. The second insulating layer 312 can be similar to or different from the second insulating layer 112. In some embodiments, the second insulating layer 312 includes a portion extending between the top surface and the bottom surface of the first Bragg reflector layer. In some embodiments, the top surface of the second conductive bridge portion 322 is coplanar with the bottom surface of the second insulating layer 312. In some embodiments, the thickness t12 of the second conductive bridge portion 322 is similar to or the same as the thickness of the second electrode 106. In the BAW structure 300, the vertical projections of the first conductive bridge portion 120 and the second conductive bridge portion 322 overlap.

[0059] Figure 3B Another exemplary BAW structure 301 according to some embodiments of the present disclosure is shown. The BAW structure 301 has an "offset bridge" configuration and can further reduce electrical losses. Unlike the BAW structure 101, the BAW structure 301 can include a second dielectric layer 319 that is thicker than the second dielectric layer 119. In some embodiments, the thickness of the second dielectric layer 319 is approximately equal to the sum of the total thickness of the second electrode 106 and the second insulating layer 313. In some embodiments, the thickness of the second dielectric layer 319 is similar to the thickness of the second dielectric layer 318. The BAW structure 301 can also have a second conductive bridge portion 323 that extends above (e.g., covers) the second dielectric layer 319. As shown in FIG. Figure 3B As shown, the bottom surface of the second conductive bridge portion 323 can be located between the top and bottom surfaces of the first Bragg reflector layer (e.g., W) in contact with the second insulating layer 313. In some embodiments, the top surface of the second conductive bridge portion 323 is coplanar with the bottom surface of the second insulating layer 313. In some embodiments, the thickness of the second conductive bridge portion is similar to or the same as the thickness of the second conductive bridge portion 322. In the BAW structure 301, the vertical projection of the first conductive bridge portion 120 does not overlap with the vertical projection of the second conductive bridge portion 323.

[0060] Figure 4AAnother exemplary BAW structure 400 according to some embodiments of the present disclosure is shown. The BAW structure 400 can have an "aligned bridge" configuration, in which the second conductive bridge portion 422 completely covers the second dielectric layer 118 and overlaps the first conductive bridge portion 120 in the vertical direction. Unlike the BAW structure 100, the second conductive bridge portion 422 includes a first metal layer 422-1, a second metal layer 422-2 in contact with the first metal layer 422-1, and one or more protective layers 422-3 in contact with the first metal layer 422-1 and the second dielectric layer 118. The one or more protective layers 422-3 can include a single layer or multiple layers and can include suitable materials that can provide protection for the first metal layer 422-1 and the second metal layer 422-2. In some embodiments, the one or more protective layers 422-3 include a W layer sandwiched by two layers of AlN (e.g., an AlN-W-AlN structure). In some embodiments, the one or more protective layers 422-3 can also include other suitable materials, such as carbon, silicon nitride, etc. In some embodiments, the materials of the first metal layer 422 - 1 and the second metal layer 422 - 2 are similar to or the same as the first metal layer 106 - 1 and the second metal layer 106 - 2 , respectively.

[0061] Figure 4B Another exemplary BAW structure 401 according to some embodiments of the present disclosure is shown. The BAW structure 401 can have an "offset bridge" configuration, in which the second conductive bridge portion 423 covers the second dielectric layer 119 and does not overlap with the first conductive bridge portion 120 in the vertical direction. Unlike the BAW structure 101, the second conductive bridge portion 423 includes a first metal layer 421-1, a second metal layer 423-2 in contact with the first metal layer 423-1, and one or more protective layers 423-3 in contact with the first metal layer 423-1 and the second dielectric layer 119. The one or more protective layers 423-3 can include a single layer or multiple layers and can include suitable materials that can protect the first metal layer 423-1 and the second metal layer 423-2. In some embodiments, the one or more protective layers 423-3 include a W layer sandwiched by two layers of AlN (e.g., an AlN-W-AlN structure). In some embodiments, the one or more protective layers 423-3 can also include other suitable materials, such as carbon, silicon nitride, etc. In some embodiments, the materials of the first metal layer 423 - 1 and the second metal layer 423 - 2 are similar to or the same as the first metal layer 107 - 1 and the second metal layer 107 - 2 , respectively.

[0062] Figure 5AAnother exemplary BAW structure 500 according to some embodiments of the present disclosure is shown. The BAW structure 500 may include a substrate 150, a piezoelectric layer 102, a first electrode 504 and a second electrode 506 (each located above and in contact with the piezoelectric layer 102), a first insulating layer 510, a second insulating layer 512, an upper Bragg reflector stack 508-1, a lower Bragg reflector stack 508-2, and a passivation layer 514. The first electrode 504 may have a first metal layer 504-1 and a second metal layer 504-2; and the second electrode 506 may have a first metal layer 506-1 and a second metal layer 506-2. The materials of these components are similar or identical to their counterparts in the BAW structure 100, and a detailed description will not be repeated herein. Unlike the BAW structure 100, the BAW structure 500 includes a dielectric layer 516 (similar to the dielectric layer 216) in contact with the top surface of the piezoelectric layer 102, but does not have a dielectric layer in contact with the bottom surface of the piezoelectric layer 102. As Figure 5A As shown, the first insulating layer 510 may extend over the dielectric layer 516 and may partially cover the dielectric layer 516. Unlike the first insulating layer 110, the side surface of the first insulating layer 510 is aligned with the vertical direction (e.g., the z direction). The second insulating layer 512 may also have a side surface aligned with the vertical direction. In some embodiments, the side surfaces of the first insulating layer 510 and the second insulating layer 512 are aligned with each other in the vertical direction. In some embodiments, the BAW structure 500 includes an active region, a recessed frame region, a mass load frame region, and an external region. The length of the region and the thickness of the layer in the region can be similar to those in the BAW 100, and the detailed description will not be repeated herein.

[0063] The BAW structure 500 may include a first conductive bridge portion 520 and a second conductive bridge portion 522, each of which is conductively connected to a corresponding Bragg reflector stack. Figure 5AAs shown, the BAW structure 500 may include a first portion 520-1 as an extension of the first metal layer 504-1 and a second portion 520-2 as an extension of the second metal layer 504-2. Unlike the BAW structure 100, the second portion 520-2 may contact the side surface of the first insulating layer 510 and may include AlCu. In some embodiments, the second portion 520-2 does not include any material of the Bragg reflector layer (e.g., W) in contact with the first insulating layer 510 and may include only AlCu. In some embodiments, the top surface of the second portion 520-2 is coplanar with the top surface of the first insulating layer 510 in the outer boundary ring area. The second conductive bridge portion 522 may also include a first portion 521-1 as an extension of the first metal layer 506-1 and a second portion 522-2 as an extension of the second metal layer 506-2. Unlike the BAW structure 100, the second portion 522-2 may contact the side surface of the second insulating layer 512 and may include AlCu. In some embodiments, the second portion 522-2 does not include any material of the Bragg reflector layer (e.g., W) in contact with the second insulating layer 512 and may include only AlCu. In some embodiments, the bottom surface of the second portion 522-2 is coplanar with the bottom surface of the second insulating layer 512. Figure 5A As shown, in the first conductive bridge portion 520 and the second conductive bridge portion 522, the side surfaces facing the active region can be aligned with each other in the vertical direction, and the side surfaces facing away from the active region can be aligned with each other. In other words, the bridge portion has a constant (e.g., the same) width.

[0064] Figure 5BAnother exemplary BAW structure 501 according to some embodiments of the present disclosure is shown. The BAW structure 500 may include a substrate 150, a piezoelectric layer 102, a first electrode 505 and a second electrode 507 (each located above and in contact with the piezoelectric layer 102), a first insulating layer 511, a second insulating layer 513, an upper Bragg reflector stack 508-1, a lower Bragg reflector stack 508-2, and a passivation layer 514. The first electrode 505 may have a first metal layer 505-1 and a second metal layer 505-2; and the second electrode 507 may have a first metal layer 507-1 and a second metal layer 507-2. The materials of these components are similar or identical to their counterparts in the BAW structure 100, and a detailed description will not be repeated herein. Similar to the BAW structure 500, the BAW structure 501 includes a dielectric layer 516 in contact with the top surface of the piezoelectric layer 102, but does not have a dielectric layer in contact with the bottom surface of the piezoelectric layer 102. Unlike the first insulating layer 110, the first insulating layer 511 does not overlap with the dielectric layer 516, and the side surface of the first insulating layer 511 is aligned with the vertical direction (e.g., the z direction). The second insulating layer 512 may also have a side surface aligned with the vertical direction. In some embodiments, the side surfaces of the first insulating layer 511 and the second insulating layer 513 are aligned with each other in the vertical direction. Figure 5B As shown, side surfaces of the first insulating layer 511 and the second insulating layer 513 are aligned with each other on the boundary of the outer boundary ring region.

[0065] The BAW structure 501 may include a first conductive bridge portion 521 and a second conductive bridge portion 523, each of which is conductively connected to a corresponding Bragg reflector stack. Figure 5B As shown, the BAW structure 501 may include a first portion 521-1 that is an extension of the first metal layer 505-1 and a second portion 521-2 that is an extension of the second metal layer 505-2. Unlike the BAW structure 100, the second portion 521-2 may be in contact with the side surface of the first insulating layer 511 and may include AlCu. In some embodiments, the second portion 521-2 does not include any material of the Bragg reflector layer (e.g., W) that is in contact with the first insulating layer 511 and may include only AlCu. In some embodiments, the length of the second portion 521-2 (or the first conductive bridge portion 521) (e.g., in the x-direction) is the same as the length of the outer boundary ring area ("3"), for example, returning to reference Figure 1Ad3. The second conductive bridge portion 523 may also include a first portion 523-1 that is an extension of the first metal layer 507-1 and a second portion 523-2 that is an extension of the second metal layer 507-2. Unlike the BAW structure 100, the second portion 523-2 may be in contact with the side surface of the second insulating layer 513 and may include AlCu. In some embodiments, the second portion 523-2 does not include any material of the Bragg reflector layer (e.g., W) that is in contact with the second insulating layer 513 and may include only AlCu. In some embodiments, the bottom surface of the second portion 523-2 is coplanar with the bottom surface of the second insulating layer 513. In some embodiments, the length of the second portion 523-2 (or the second conductive bridge portion 523) is the same as the length of the outer boundary ring area ("3"), for example, returning to reference Figure 1A d3. Figure 5B As shown, in the first conductive bridge portion 521 and the second conductive bridge portion 523, the side surfaces facing the active region can be aligned with each other in the vertical direction, and the side surfaces facing away from the active region can be aligned with each other. In other words, each bridge portion has the same width as the outer boundary ring region.

[0066] Figure 6 A is a flow chart of a method 600 for fabricating a BAW structure according to some embodiments of the present disclosure. Method 600 is merely an example and is not intended to limit the present disclosure beyond what is explicitly recited in the claims. Additional operations may be provided before, during, and after method 600, and some of the operations described may be replaced, removed, or moved around for use in alternative embodiments of method 600. Method 600 will be described in more detail below.

[0067] At step 602, one or more layers of material may be deposited on a substrate. In some embodiments, one or more different materials may be deposited on a suitable substrate to form multiple layers for various functions. For example, a piezoelectric layer, a pair of electrodes, one or more insulating layers, one or more dielectric layers, and one or more Bragg reflector layers may be deposited on a substrate. The materials may be deposited using one or more suitable deposition processes (e.g., atomic layer deposition, chemical vapor deposition, physical vapor deposition, electroplating, electroless plating, or a combination thereof).

[0068] At step 604, one or more layers may be planarized and / or patterned. Step 604 may be performed between the deposition of two layers of material. The planarization process may include chemical mechanical polishing, etching, or a combination thereof.

[0069] At step 606, one or more layers are passivated. After the deposition and planarization of the layers is complete

[0070] Afterwards, a passivation layer is deposited on the outside of the layer. The passivation layer can be deposited by chemical vapor deposition, physical

[0071] The deposition can be performed by vapor phase deposition, atomic layer deposition or a combination thereof.

Claims

1. A bulk acoustic wave (BAW) resonator structure comprising a transducer, wherein the transducer comprises: a first electrode; a second electrode; a piezoelectric layer, the piezoelectric layer being located between the first electrode and the second electrode; a dielectric layer, the dielectric layer being in contact with the piezoelectric layer on a surface of the piezoelectric layer; a conductive layer, the conductive layer being located above the first electrode; as well as a conductive bridge portion, the conductive bridge portion being in contact with the first electrode and the conductive layer, and being located above and in contact with the dielectric layer, The conductive bridge portion and the conductive layer form a conductive bridge structure between end portions of the first electrode.

2. The BAW resonator structure according to claim 1 , wherein: The conductive bridge portion contacts the first electrode and includes the same conductive material as the first electrode.

3. The BAW resonator structure of claim 1 , wherein the transducer further comprises: a second dielectric layer in contact with the piezoelectric layer on a second surface of the piezoelectric layer; and a second conductive bridge structure, the second conductive bridge structure being located above and in contact with the second dielectric layer and in contact with the second electrode, The second conductive bridge structure includes the same conductive material as that of the second electrode.

4. The BAW resonator structure according to claim 3, wherein: In the horizontal direction, the length of the conductive bridge portion is smaller than the length of the second conductive bridge portion; In the vertical direction, the projection of the conductive bridge structure partially overlaps with the projection of the second conductive bridge portion; and A boundary between the conductive bridge portion and the first electrode is aligned with a boundary between the second conductive bridge portion and the second electrode.

5. The BAW resonator structure according to claim 3, wherein: In the horizontal direction, the length of the conductive bridge portion is smaller than the length of the second conductive bridge portion; and In a vertical direction, a projection of the conductive bridge portion does not overlap with a projection of the second conductive bridge portion.

6. The BAW resonator structure according to claim 3, wherein in the vertical direction, The projection of the first electrode partially overlaps with the projection of the dielectric layer; and A projection of the second electrode does not overlap with a projection of the second dielectric layer.

7. The BAW resonator structure according to claim 3, wherein: The first electrode has a first thickness in the active area and a recessed frame area surrounding the active area, and has a second thickness outside the active area and the recessed frame area, the second thickness being greater than the first thickness; and The second electrode has the same thickness in the active area, the recessed frame area, and outside the frame area.

8. The BAW resonator structure of claim 7 , wherein the transducer further comprises a first insulating layer located above and in contact with the first electrode in the active region and the recessed frame region, and The first insulating layer has a first thickness in the active area and a second thickness in the recessed frame area, and the first thickness is greater than the second thickness.

9. The BAW resonator structure of claim 7 , wherein the transducer further comprises a second insulating layer located above and in contact with the second electrode in the active region and the recessed frame region, and The second insulating layer has the same thickness in the active area and the recessed frame area.

10. The BAW resonator structure according to claim 3, wherein: The angle between the side surface of the dielectric layer and the vertical direction is between about 30 degrees and about 60 degrees; and An angle between a side surface of the second dielectric layer and the vertical direction is between about 5 degrees and about 15 degrees. 11 . The BAW resonator structure according to claim 8 , wherein an angle between a side surface of the first insulating layer and a vertical direction is between about 30 degrees and about 50 degrees. 12 . The BAW resonator structure according to claim 9 , wherein an angle between a side surface of the second insulating layer and a vertical direction is between about 5 degrees and about 15 degrees. 13 . The BAW resonator structure of claim 1 , wherein in a vertical direction, the dielectric layer has a thickness between about 20 nm and about 200 nm.

14. The BAW resonator structure of claim 3 , wherein the transducer further comprises one or more insulating layers, each of the one or more insulating layers being in contact with a corresponding electrode of the first electrode and the second electrode, and wherein the one or more insulating layers each contain an air gap.

15. The BAW resonator structure of claim 9, wherein the transducer further comprises a conductive layer in contact with the second insulating layer, and In the vertical direction, the surface of the second conductive bridge portion is located between the first surface and the second surface of the conductive layer.

16. The BAW resonator structure of claim 3, wherein the transducer further comprises an aluminum nitride-tungsten-aluminum nitride structure located between the second dielectric layer and the second conductive bridge portion. 17 . The BAW resonator structure of claim 3 , wherein an angle between a side surface of the conductive bridge portion and a vertical direction is approximately zero, and an angle between a side surface of the second conductive bridge portion and the vertical direction is approximately zero. 18 . The BAW resonator structure of claim 17 , wherein in a vertical direction, a projection of the conductive bridge portion is aligned with a projection of the second conductive bridge portion.

19. The BAW resonator structure of claim 17 , wherein the transducer further comprises an insulating layer located above and in contact with at least one of the first electrode layer and the second electrode layer, the insulating layer being in contact with the corresponding conductive bridge portion. An interface between the insulating layer and the corresponding conductive bridge portion is aligned with the vertical direction.

20. The BAW resonator structure of claim 1 , wherein the transducer further comprises a pair of reflective layers located above each of the first electrode and the second electrode and conductively connected to a respective conductive bridge in contact with the respective electrode, and The pair of reflective layers includes a tungsten layer and an aluminum-copper layer.

Images