Bulk acoustic resonator and manufacturing method therefor, and filter

Abstract

The present application relates to the technical field of resonators, and provides a bulk acoustic resonator and a manufacturing method therefor, and a filter. The bulk acoustic resonator comprises a substrate and a first electrode, a piezoelectric layer, a second electrode and an auxiliary layer which are sequentially arranged on the substrate; first gaps are formed between the piezoelectric layer and the second electrode; a second gap is formed between the second electrode and the auxiliary layer; the first gaps and the second gap are both located at the boundary of an effective resonance area of the bulk acoustic resonator. In this way, the bulk acoustic resonator can form an impedance mismatch at the boundary of the effective resonance area by means of the first gaps, and the bulk acoustic resonator can also form an impedance mismatch at the boundary of the effective resonance area by means of the second gap for reflecting acoustic waves. On the basis of the respective hierarchical positions of the first gaps and the second gap, acoustic waves can be better reflected through mutual cooperation of the first gaps and the second gap, thereby improving the mechanical quality factor of the bulk acoustic resonator, and reducing the energy loss of the bulk acoustic resonator.

Description

Bulk acoustic wave resonator, preparation method thereof and filter

[0001] Cross-reference to Related Applications

[0002] This application claims priority to the Chinese patent application No. 202410820054.6, filed on June 24, 2024, and entitled "Bulk acoustic wave resonator, preparation method thereof and filter", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of resonators, in particular to a bulk acoustic wave resonator, a preparation method thereof and a filter. BACKGROUND

[0004] A radio frequency filter is a core component applied to a radio frequency front end in a wireless communication field, and a resonator is a key and a basic unit for constituting the radio frequency filter. The resonators currently applied to the radio frequency market include a surface acoustic wave resonator and a bulk acoustic wave resonator. The bulk acoustic wave resonator gradually becomes a market mainstream due to the advantages of high resonant frequency, high quality factor, high electromechanical coupling coefficient, high power capacity, low loss and small size, and compatibility with a semiconductor process.

[0005] After an electrode of the bulk acoustic wave resonator is applied with alternating current, mainly longitudinal vibration is generated, and other transverse mode acoustic waves are also excited, causing energy leakage.

[0006] SUMMARY

[0007] The present application aims at the deficiencies in the prior art, and provides a bulk acoustic wave resonator, a preparation method thereof and a filter.

[0008] To achieve the above object, the technical solutions adopted by the embodiments of the present application are as follows.

[0009] In one aspect of the embodiments of the present application, a bulk acoustic wave resonator is provided, which includes a substrate and a first electrode, a piezoelectric layer, a second electrode and an auxiliary layer which are sequentially arranged on the substrate. A first gap is arranged between the piezoelectric layer and the second electrode, and a second gap is arranged between the second electrode and the auxiliary layer. The first gap and the second gap are both located at the boundary of an effective resonant region of the bulk acoustic wave resonator.

[0010] Optionally, the first gap and the second gap have an overlapping region in the orthogonal projection along the thickness direction of the substrate.

[0011] Optionally, the second gap is located outside the effective resonant region, and one end of the second gap extends to the boundary of the effective resonant region; and / or, the first gap has a first part located inside the effective resonant region and a second part located outside the effective resonant region.

[0012] Optionally, at least one first pillar is arranged in the first gap, and the first gap is divided into a plurality of first sub-gaps by the at least one first pillar; and / or at least one second pillar is arranged in the second gap, and the second gap is divided into a plurality of second sub-gaps by the at least one second pillar.

[0013] Optionally, a protection layer is further arranged between the second electrode and the auxiliary layer, and the second gap is located between the protection layer and the auxiliary layer.

[0014] Optionally, the number of the first gaps is a plurality, and the plurality of first gaps are sequentially arranged along the boundary of the effective resonance region.

[0015] In another aspect of the embodiments of the present application, a bulk acoustic wave resonator preparation method is provided, and the method comprises:

[0016] providing a substrate;

[0017] forming a first electrode and a piezoelectric layer on the substrate in sequence;

[0018] forming a first sacrificial layer and a second electrode covering the first sacrificial layer on the piezoelectric layer in sequence;

[0019] forming a second sacrificial layer and an auxiliary layer covering the second sacrificial layer on the second electrode in sequence;

[0020] releasing the first sacrificial layer to form a first gap between the piezoelectric layer and the second electrode, and releasing the second sacrificial layer to form a second gap between the second electrode and the auxiliary layer.

[0021] Optionally, forming the first sacrificial layer and the second electrode covering the first sacrificial layer on the piezoelectric layer in sequence comprises:

[0022] forming a first sacrificial layer with a plurality of sacrificial blocks on the piezoelectric layer, wherein the plurality of sacrificial blocks are distributed at intervals;

[0023] forming a first pillar filled between two adjacent sacrificial blocks on the piezoelectric layer, and forming a second electrode covering the plurality of sacrificial blocks.

[0024] Optionally, forming the second sacrificial layer and the auxiliary layer covering the second sacrificial layer on the second electrode in sequence comprises:

[0025] forming a plurality of second pillars at intervals on the second electrode;

[0026] forming a second sacrificial layer filled between two adjacent second pillars on the second electrode;

[0027] forming an auxiliary layer covering the second sacrificial layer on the second electrode.

[0028] In yet another aspect of the embodiments of the present application, a filter is provided, comprising a plurality of resonators, the plurality of resonators comprising series resonators connected in series and / or parallel resonators connected in parallel with the series resonators, at least one of the plurality of resonators being the bulk acoustic wave resonator of any of the above. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0030] Fig. 1 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0031] Fig. 2 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0032] Fig. 3 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0033] Fig. 4 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0034] Fig. 5 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0035] Fig. 6 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0036] Fig. 7 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0037] Fig. 8 is a structural diagram of a bulk acoustic wave resonator according to an embodiment of the present application;

[0038] Fig. 9 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0039] Fig. 10 is a state diagram of a bulk acoustic wave resonator preparation method according to an embodiment of the present application;

[0040] Fig. 11 is a structural diagram of another bulk acoustic wave resonator according to an embodiment of the present application;

[0041] Fig. 12 is a simulation curve diagram of a bulk acoustic wave resonator and a conventional resonator according to the present application.

[0042] Icon: 201-substrate; 202-air cavity; 203-temporary sacrificial layer; 204-seed layer; 205-first electrode; 206-piezoelectric layer; 207-first sacrificial layer; 2071-sacrificial block; 208-electrode lead hole; 209-thickening layer; 2091-first pillar; 210-electrode layer; 211-second electrode; 212-protective layer; 213-second sacrificial layer; 214-assistant layer; 215-first gap; 2151-first sub-gap; 216-second gap; 2161-second sub-gap; 217-release hole; 218-second pillar. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. It should be noted that, in the case of no conflict, each feature in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the protection scope of the present application.

[0044] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms “center”, “upper”, “lower”, “left”, “right”, “vertical”, “horizontal”, “inner”, “outer” and the like is the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as a limitation on the present application. In addition, the terms “first”, “second”, “third” and the like are only used for differentiation in description, and cannot be understood as indicating or implying relative importance.

[0045] In the description of the present application, it should also be noted that, unless otherwise explicitly specified and limited, the terms “setting”, “mounting”, “connecting”, “connecting” should be understood in a broad sense, for example, can be directly connected, can be indirectly connected through an intermediate medium, and can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0046] In one aspect of the embodiments of the present application, a bulk acoustic wave resonator is provided, as shown in FIG. 8, which includes a substrate 201 and a first electrode 205, a piezoelectric layer 206, a second electrode 211 and an assistant layer 214 arranged in sequence on the substrate 201, wherein the first electrode 205, the piezoelectric layer 206 and the second electrode 211 are laminated to form a sandwich structure with the piezoelectric layer 206 in the middle. After alternating current is applied to the first electrode 205 and the second electrode 211, the piezoelectric layer 206 can realize mutual conversion between electrical energy and mechanical energy.

[0047] On this basis, the first electrode 205, the piezoelectric layer 206 and the second electrode 211 have an overlapping region in the thickness direction of the substrate 201 (or the direction in which the three are stacked), and the aforementioned conversion of electrical energy and mechanical energy is mainly concentrated in this region. Of course, the overlapping region formed by the first electrode 205, the piezoelectric layer 206 and the second electrode 211 is also referred to as an effective resonance region in the art. In addition, when the air cavity 202 is provided between the substrate 201 and the first electrode 205, the overlapping region of the air cavity 202, the first electrode 205, the piezoelectric layer 206 and the second electrode 211 in the thickness direction of the substrate 201 is also often referred to as an effective resonance region. The present application does not make specific limitations thereto.

[0048] Please continue to refer to FIG. 8, a first gap 215 is provided between the piezoelectric layer 206 and the second electrode 211, and a second gap 216 is provided between the second electrode 211 and the auxiliary layer 214, and the first gap 215 and the second gap 216 are both located at the boundary of the effective resonance region. In this way, the bulk acoustic wave resonator can form an impedance mismatch at the boundary of the effective resonance region by means of the first gap 215, and can be configured to reflect the acoustic wave, and at the same time, the bulk acoustic wave resonator can form an impedance mismatch at the boundary of the effective resonance region by means of the second gap 216, and can also be configured to reflect the acoustic wave. Based on the respective positions of the first gap 215 and the second gap 216, the two gaps can cooperate with each other to better reflect the acoustic wave, so that the vibration energy of the bulk acoustic wave resonator is confined within the effective resonance region, thereby improving the mechanical quality factor of the bulk acoustic wave resonator and reducing the energy loss of the bulk acoustic wave resonator.

[0049] Please refer to FIG. 12, the simulation curves of the conventional resonator and the bulk acoustic wave resonators shown in FIGS. 8 and 11 provided by the present application are shown respectively. The curve corresponding to the bulk acoustic wave resonator shown in FIG. 8 is a dotted line with low density, and the curve corresponding to the bulk acoustic wave resonator shown in FIG. 11 is a solid line. It can be seen that the simulation curve of the bulk acoustic wave resonator shown in FIGS. 8 and 11 provided by the present application is sharper, and thus the mechanical quality factor of the bulk acoustic wave resonator can be better improved, and the energy loss of the bulk acoustic wave resonator can be reduced.

[0050] Optionally, the number of the first voids 215 can be at least one, and when the number of the first voids 215 is at least two, the first voids 215 are arranged in sequence along the boundary of the effective resonance region. For example, in the cross section of the bulk acoustic wave resonator shown in FIG. 8 or FIG. 11, there are two first voids 215 between the piezoelectric layer 206 and the second electrode 211, in which the left first void 215 is closer to the left boundary of the effective resonance region, and the right first void 215 is closer to the right boundary of the effective resonance region. In different embodiments, the plurality of first voids 215 can be disconnected or connected with each other, for example, as shown in FIG. 8 or FIG. 11: the left first void 215 can be connected or disconnected with the right first void 215.

[0051] It should be noted that the first void 215 can be an air bridge or an air wing, for example, as shown in the bulk acoustic wave resonator in FIG. 8 or FIG. 11, the left first void 215 is an air wing, more specifically, it can be a closed air wing; the right first void 215 is an air bridge.

[0052] Optionally, as shown in FIG. 8 or FIG. 11, the second void 216 can be located outside the effective resonance region, and one end of the second void 216 extends to the boundary of the effective resonance region, so as to better reflect the acoustic wave through the second void 216.

[0053] Optionally, as shown in FIG. 8 or FIG. 11, the first void 215 can span across the boundary of the effective resonance region, so that the acoustic wave can be better reflected based on the hierarchical position of the first void 215. At the same time, the part of the first void 215 located in the effective resonance region can lift the piezoelectric layer 206, which is beneficial to heat dissipation, and the part of the first void 215 located outside the effective resonance region can realize electrical isolation of the non-resonance region, and reduce the influence of the pseudo mode on the target mode.

[0054] Optionally, as shown in FIG. 8 or FIG. 11, the first void 215 and the second void 216 have an overlapping region in the orthogonal projection along the thickness direction of the substrate 201, so that the second void 216 can reflect the acoustic wave above the first void 215, and the acoustic wave is better reflected through the superposition of the first void 215 and the second void 216. The overlapping manner of the first void 215 and the second void 216 can include the following forms:

[0055] Form one: the first gap 215 and the second gap 216 are partially overlapped along the normal projection of the substrate 201 in the thickness direction, such as shown in FIG. 8 or FIG. 11, the first gap 215 is across the boundary of the effective resonance region, while the second gap 216 is located outside the effective resonance region, and one end of the second gap 216 extends to the boundary of the effective resonance region. In this way, the left half of the second gap 216 and the right half of the first gap 215 are overlapped in the thickness direction of the substrate 201, and the stepped configuration of the first gap 215 and the second gap 216 can better reflect the sound wave.

[0056] Form two: the first gap 215 and the second gap 216 are overlapped along the normal projection of the substrate 201 in the thickness direction.

[0057] Optionally, as shown in FIG. 8 or FIG. 11, at least one first pillar 2091 is arranged in the first gap 215, one end of the first pillar 2091 is in contact with the piezoelectric layer 206, and the other end is in contact with the second electrode 211. In this way, the first gap 215 is divided into two or more first sub-gaps 2151 by the first pillar 2091, such as shown in FIG. 8 or FIG. 11, the first gap 215 has three first pillars 2091, and therefore, the first gap 215 is divided into four first sub-gaps 2151. It should be understood that the first pillar 2091 can be fabricated synchronously with the second electrode 211, that is, the first pillar 2091 and the second electrode 211 are patterned from the same metal layer.

[0058] Optionally, as shown in FIG. 8 or FIG. 11, in order to protect the second electrode 211 from oxidation, a protective layer 212 can also be covered on the upper surface of the second electrode 211, that is, the protective layer 212 is arranged between the second electrode 211 and the auxiliary layer 214, and at this time, the second gap 216 between the second electrode 211 and the auxiliary layer 214 is located between the protective layer 212 and the auxiliary layer 214.

[0059] Optionally, at least one second pillar 218 is arranged in the second gap 216. When the protective layer 212 is not arranged between the second electrode 211 and the auxiliary layer 214, one end of the second pillar 218 is in contact with the second electrode 211, and the other end is in contact with the auxiliary layer 214; as shown in FIG. 11, when the protective layer 212 is arranged between the second electrode 211 and the auxiliary layer 214, one end of the second pillar 218 is in contact with the protective layer 212, and the other end is in contact with the auxiliary layer 214. In this way, the second gap 216 is divided into two or more second sub-gaps 2161 by the second pillar 218, such as shown in FIG. 11, the second gap 216 has two second pillars 218, and therefore, the second gap 216 is divided into three second sub-gaps 2161. It should be understood that the second pillar 218 can be made of the same material as the auxiliary layer 214.

[0060] Optionally, in combination with FIG. 10 and FIG. 11, the second electrode 211 can include a thickening layer 209 and an electrode layer 210, wherein the thickening layer 209 can be first fabricated on the piezoelectric layer 206, and the effective electromechanical coupling coefficient of the bulk acoustic wave resonator finally prepared can be adjusted by adjusting the thickness, width, position, etc. of the thickening layer 209. Then the electrode layer 210 is fabricated on the thickening layer 209 to form the second electrode 211. In other embodiments, when the effective electromechanical coupling coefficient does not need to be adjusted by the thickening layer 209, the step of fabricating the thickening layer 209 can also be omitted.

[0061] Optionally, as shown in FIG. 8 or FIG. 11, when adjusting the effective electromechanical coupling coefficient of the bulk acoustic wave resonator, the position, number, shape, width, length, node, etc. of the first gap 215 and the first sub-gap 2151 can also be changed to achieve the adjustment.

[0062] Optionally, as shown in FIG. 11, when adjusting the effective electromechanical coupling coefficient of the bulk acoustic wave resonator, the position, number, shape, width, length, node, etc. of the second gap 216 and the second sub-gap 2161 can also be changed to achieve the adjustment. In this way, the means for adjusting the effective electromechanical coupling coefficient of the bulk acoustic wave resonator is further enriched, and the adjustment range of the effective electromechanical coupling coefficient is widened. Of course, since the first gap 215, the second gap 216, the first sub-gap 2151 and the second sub-gap 2161 are all formed by releasing the sacrificial layer, when adjusting the above-mentioned parameters of the first gap 215, the second gap 216, the first sub-gap 2151 and the second sub-gap 2161, it is actually achieved by adjusting the parameters of the sacrificial layer.

[0063] Optionally, a seed layer 204 can also be arranged between the substrate 201 and the first electrode 205 to improve the quality of the first electrode 205.

[0064] Optionally, an inner recessed air cavity 202 can also be arranged on the substrate 201, and the air cavity 202 is located at least in the effective resonant area, so that the sound wave can be further reflected.

[0065] Optionally, as shown in FIG. 8 or FIG. 11, a release hole 217 is opened on the piezoelectric layer 206 to communicate with the air cavity 202, and the release hole 217 is located outside the effective resonant area. Of course, in other embodiments, the release hole 217 can also be located in the effective resonant area.

[0066] Another aspect of the embodiments of the present application provides a bulk acoustic wave resonator preparation method, the method comprising:

[0067] S10: providing a substrate 201;

[0068] The substrate 201 can be made of a material well known in the art, such as high-resistance silicon, etc., which is not limited in the present application.

[0069] As shown in FIG. 1, if the air cavity 202 is needed to be formed, the upper surface of the substrate 201 can be etched to form the concave air cavity 202. Meanwhile, as shown in FIG. 2, in order to avoid affecting the subsequent layers, a temporary sacrificial layer 203 can be filled in the air cavity 202, and the temporary sacrificial layer 203 and the upper surface of the substrate 201 can be made flush by chemical mechanical polishing.

[0070] Of course, if the quality of the first electrode 205 needs to be improved, a seed layer 204, such as aluminum nitride, etc., can be deposited on the upper surface of the substrate 201.

[0071] S20: sequentially forming the first electrode 205 and the piezoelectric layer 206 on the substrate 201.

[0072] As shown in FIG. 2, the metal layer is continuously deposited on the substrate 201, and is patterned to form the first electrode 205. Then the piezoelectric layer 206 is deposited on the first electrode 205.

[0073] S30: sequentially forming the first sacrificial layer 207 and the second electrode 211 covering the first sacrificial layer 207 on the piezoelectric layer 206.

[0074] As shown in FIG. 3, the whole layer of the sacrificial material is deposited on the piezoelectric layer 206, and then the first sacrificial layer 207 is formed by patterning. It should be understood that the first sacrificial layer 207 is configured to form the first gap 215 after being released, therefore, the position, pattern shape, size, etc. of the first sacrificial layer 207 can be reasonably set according to the required first gap 215. For example, as shown in FIG. 3, two first sacrificial layers 207 are formed on the piezoelectric layer 206, which are the left first sacrificial layer 207 and the right first sacrificial layer 207. The left first sacrificial layer 207 is configured to form the left first gap 215 in FIG. 8 or FIG. 11 after being released, and the right first sacrificial layer 207 is configured to form the right first gap 215 in FIG. 8 or FIG. 11 after being released. Of course, the two first sacrificial layers 207 can be connected, so that the two first gaps 215 formed subsequently can be communicated.

[0075] As shown in FIG. 4, after the first sacrificial layer 207 is formed, the electrode lead-out hole 208 is formed by etching the piezoelectric layer 206, which penetrates the piezoelectric layer 206 and exposes the first electrode 205. Then the metal layer is deposited on the piezoelectric layer 206, and is patterned to form the thickening layer 209 covering the first sacrificial layer 207. Meanwhile, the part of the metal layer in the electrode lead-out hole 208 is also reserved as the electrode lead-out part, so that the electrode lead-out part can lead out the first electrode 205 to the upper surface of the piezoelectric layer 206.

[0076] As shown in FIG. 5, the metal is continuously deposited on the thickened layer 209 and is patterned to form the aforementioned electrode layer 210, so that the second electrode 211 is formed by the electrode layer 210 in cooperation with the thickened layer 209.

[0077] S40: sequentially forming the second sacrificial layer 213 and the auxiliary layer 214 covering the second sacrificial layer 213 on the second electrode 211.

[0078] As shown in FIG. 6, if it is necessary to protect the second electrode 211, a protection layer 212 can also be formed on the surface of the second electrode 211. Of course, if it is not necessary to protect the second electrode 211, the protection layer 212 can also be omitted. For ease of understanding, the following will be described by taking the protection layer 212 as an example.

[0079] Then the second sacrificial layer 213 is formed on the protection layer 212. It should be understood that the second sacrificial layer 213 is configured to the second gap 216 after subsequent release, and therefore the position, pattern shape and size of the second sacrificial layer 213 can be reasonably set according to the required second gap 216.

[0080] As shown in FIG. 7, then the auxiliary layer 214 covering the second sacrificial layer 213 is formed on the protection layer 212. The material of the auxiliary layer 214 can be consistent with that of the protection layer 212.

[0081] S50: releasing the first sacrificial layer 207 to form the first gap 215 between the piezoelectric layer 206 and the second electrode 211, and releasing the second sacrificial layer 213 to form the second gap 216 between the second electrode 211 and the auxiliary layer 214.

[0082] As shown in FIG. 8, the piezoelectric layer 206, the first electrode 205 and the seed layer 204 can be etched to form a release hole 217 penetrating to the temporary sacrificial layer 203, the temporary sacrificial layer 203 is released through the release hole 217, and then the air cavity 202 is formed. In addition, the first sacrificial layer 207 and the second sacrificial layer 213 are both released, so that the first gap 215 and the second gap 216 are formed.

[0083] Optionally, the sequentially forming the first sacrificial layer 207 and the second electrode 211 covering the first sacrificial layer 207 on the piezoelectric layer 206 through S30 comprises:

[0084] S31: forming the first sacrificial layer 207 with a plurality of sacrificial blocks 2071 on the piezoelectric layer 206, wherein the plurality of sacrificial blocks 2071 are distributed at intervals.

[0085] S32: forming the first pillar 2091 filled between two adjacent sacrificial blocks 2071 and the second electrode 211 covering the plurality of sacrificial blocks 2071 on the piezoelectric layer 206.

[0086] When a plurality of first pillars 2091 are needed to be formed in the first gap 215, at least one of the first sacrificial layers 207 is formed with a plurality of spaced-apart sacrificial blocks 2071 when the first sacrificial layers 207 are formed on the piezoelectric layer 206, such as the left first sacrificial layer 207 shown in FIG. 3, which includes four sacrificial blocks 2071 spaced apart by a distance. As shown in FIGS. 4 and 5, when the second electrode 211 is formed on the first sacrificial layer 207, a metal layer covering the first sacrificial layer 207 is first formed on the piezoelectric layer 206, and portions of the metal layer will correspondingly fill in between the adjacent sacrificial blocks 2071 and remain after subsequent patterning to form the first pillars 2091.

[0087] Optionally, when a plurality of second pillars 218 are needed to be formed in the second gap 216, on the basis of the structure shown in FIG. 5, the second sacrificial layer 213 and the auxiliary layer 214 covering the second sacrificial layer 213 are sequentially formed on the second electrode 211, including:

[0088] S41: forming a plurality of spaced-apart second pillars 218 on the second electrode 211.

[0089] A plurality of spaced-apart second pillars 218 are formed on the second electrode 211. When the protective layer 212 is also provided on the second electrode 211, as shown in FIG. 9, two spaced-apart second pillars 218 are formed on the protective layer 212. Of course, in other examples, the number of second pillars 218 can also be any other arbitrary number.

[0090] S42: forming a second sacrificial layer 213 on the second electrode 211 to fill in between the adjacent second pillars 218.

[0091] As shown in FIG. 10, the second sacrificial layer 213 is filled in between the adjacent second pillars 218 on the second electrode 211.

[0092] S43: forming an auxiliary layer 214 on the second electrode 211 to cover the second sacrificial layer 213.

[0093] As shown in FIG. 10, the auxiliary layer 214 is then formed. Subsequently, as shown in FIG. 11, the first gap 215 and the second gap 216 are formed by releasing the first sacrificial layer 207 and the second sacrificial layer 213.

[0094] In yet another aspect of the embodiments, a filter is provided, including a plurality of resonators, the plurality of resonators including series resonators in series and / or parallel resonators in parallel with the series resonators, at least one of the plurality of resonators being any of the above-described bulk acoustic wave resonators.

[0095] The filter is formed by the plurality of resonators, and thus, the resonators in series with each other among the plurality of resonators are series resonators, and the resonators in parallel with the series resonators are parallel resonators. By using the aforementioned bulk acoustic wave resonator, the performance of the resonator is optimized.

[0096] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application. Industrial applicability

[0097] The bulk acoustic wave resonator and the preparation method thereof and the filter provided by the present application can better reflect the acoustic wave, so that the vibration energy of the bulk acoustic wave resonator is confined in the effective resonance region, thereby improving the mechanical quality factor of the bulk acoustic wave resonator and reducing the energy loss of the bulk acoustic wave resonator.

Claims

1. A bulk acoustic wave resonator, characterized by, The bulk acoustic wave resonator comprises a substrate, a first electrode, a piezoelectric layer, a second electrode and an auxiliary layer which are sequentially arranged on the substrate, a first gap is arranged between the piezoelectric layer and the second electrode, and a second gap is arranged between the second electrode and the auxiliary layer, the first gap and the second gap are both located at the boundary of an effective resonant region of the bulk acoustic wave resonator.

2. The bulk acoustic resonator of claim 1, wherein, The first gap and the second gap have an overlapping region in the orthographic projection along the thickness direction of the substrate.

3. The bulk acoustic resonator of claim 1 or 2, wherein, The second gap is located outside the effective resonant region, and one end of the second gap extends to the boundary of the effective resonant region. The first gap has a first part located in the effective resonant region and a second part located outside the effective resonant region.

4. The bulk acoustic resonator of claim 1, wherein, At least one first pillar is arranged in the first gap, and the first gap is divided into a plurality of first sub-gaps by the first pillar; and / or at least one second pillar is arranged in the second gap, and the second gap is divided into a plurality of second sub-gaps by the second pillar.

5. The bulk acoustic resonator of claim 1, 2, or 4, wherein, A protection layer is further arranged between the second electrode and the auxiliary layer, and the second gap is located between the protection layer and the auxiliary layer.

6. The bulk acoustic resonator of claim 1, wherein, The number of the first gaps is plural, and the plural first gaps are sequentially arranged along the boundary of the effective resonant region.

7. A bulk acoustic resonator fabrication method, characterized by, The method comprises: providing a substrate; sequentially forming a first electrode and a piezoelectric layer on the substrate; sequentially forming a first sacrificial layer and a second electrode covering the first sacrificial layer on the piezoelectric layer; sequentially forming a second sacrificial layer and an auxiliary layer covering the second sacrificial layer on the second electrode; releasing the first sacrificial layer to form a first gap between the piezoelectric layer and the second electrode, and releasing the second sacrificial layer to form a second gap between the second electrode and the auxiliary layer.

8. The bulk acoustic resonator fabrication method of claim 7, wherein, The sequentially forming a first sacrificial layer and a second electrode covering the first sacrificial layer on the piezoelectric layer comprises: forming a first sacrificial layer with a plurality of sacrificial blocks on the piezoelectric layer, wherein the plurality of sacrificial blocks are distributed at intervals; forming a first pillar filled between two adjacent sacrificial blocks on the piezoelectric layer, and forming a second electrode covering the plurality of sacrificial blocks.

9. The bulk acoustic resonator fabrication method of claim 7, wherein, The sequentially forming a second sacrificial layer and an auxiliary layer covering the second sacrificial layer on the second electrode comprises: forming a plurality of second pillars at intervals on the second electrode; forming a second sacrificial layer filled between two adjacent second pillars on the second electrode; forming an auxiliary layer covering the second sacrificial layer on the second electrode.

10. A filter, characterized by, The bulk acoustic wave resonator comprises a substrate, a first electrode, a piezoelectric layer, a second electrode and an auxiliary layer which are sequentially arranged on the substrate, a first gap is arranged between the piezoelectric layer and the second electrode, and a second gap is arranged between the second electrode and the auxiliary layer, the first gap and the second gap are both located at the boundary of an effective resonant region of the bulk acoustic wave resonator. The bulk acoustic wave resonator comprises a substrate, a first electrode, a piezoelectric layer, a second electrode and an auxiliary layer which are sequentially arranged on the substrate, a first gap is arranged between the piezoelectric layer and the second electrode, and a second gap is arranged between the second electrode and the auxiliary layer, the first gap and the second gap are both located at the boundary of an effective resonant region of the bulk acoustic wave resonator.

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