Bulk acoustic wave resonator and preparation method thereof

Abstract

The invention relates to the technical field of bulk acoustic wave resonators, and particularly provides a bulk acoustic wave resonator and a preparation method thereof, and the method comprises the following steps: S1, forming an acoustic stack and an acoustic reflector located below the acoustic stack on a substrate; s2, acquiring corresponding recess depth information and target metal layer thickness information according to a preset conversion relation based on the target series resonant frequency; s3, forming a patterned metal layer located above the acoustic stack on the passivation layer based on the target metal layer thickness information, and forming a first groove in the passivation layer based on the recess depth information; according to the method, the problem that the insertion loss of the bulk acoustic wave filter is affected due to the fact that the impedance change trend of the bulk acoustic wave resonator in the area nearby the series resonant frequency is smooth and the impedance value is high can be effectively solved, and therefore performance improvement of the bulk acoustic wave resonator is facilitated.

Description

Technical Field

[0001] The present application relates to the technical field of bulk acoustic wave resonators, and in particular to a bulk acoustic wave resonator and a method for preparing the same. Background Art

[0002] The BAW resonator of the related art includes a substrate, a bottom electrode, a piezoelectric layer, a top electrode, a passivation layer and a patterned metal layer connected in sequence from bottom to top. The BAW resonator of the related art has a gentle impedance change trend and a high impedance value in a region near the series resonant frequency. Therefore, the related art has a problem in that the insertion loss of the BAW filter is affected due to the gentle impedance change trend and high impedance value of the BAW resonator in a region near the series resonant frequency, which is not conducive to improving the performance of the BAW filter.

[0003] There is no effective technical solution to the above problems. It should be noted that the above information disclosed in this section is only used to understand the background of the present invention, and therefore may contain information that does not constitute prior art. Summary of the invention

[0004] The purpose of the present application is to provide a bulk acoustic wave resonator and a preparation method thereof, which can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected due to the gentle impedance change trend and high impedance value of the bulk acoustic wave resonator in the area near the series resonance frequency, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0005] In a first aspect, the present application provides a bulk acoustic wave resonator, comprising: A substrate, an acoustic stack and a patterned metal layer are connected in sequence from bottom to top, the acoustic stack includes a bottom electrode, a piezoelectric layer, a top electrode and a passivation layer connected in sequence from bottom to top, an acoustic reflector is arranged under the acoustic stack, the thickness of the patterned metal layer is equal to the target metal layer thickness information and has a first opening, the passivation layer has a first groove, the depth of the first groove is equal to the recess depth information, and the outer boundary of the projection of the first opening in the top-down direction coincides with the outer boundary of the projection of the first groove in the top-down direction.

[0006] A bulk acoustic wave resonator provided by the present application includes a substrate, an acoustic stack and a patterned metal layer connected in sequence from bottom to top. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by making the thickness of the patterned metal layer equal to the target metal layer thickness information and forming a first groove with a depth equal to the recess depth information on the passivation layer, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the gentle impedance change trend and high impedance value of the bulk acoustic wave resonator in the area near the series resonance frequency, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0007] Optionally, when the top electrode is not externally connected, the outer boundaries of the projections of the top electrode, the passivation layer and the patterned metal layer in the top-view direction do not exceed the outer boundaries of the projections of the acoustic reflector in the top-view direction; when the top electrode is externally connected, one side of the top electrode extends outside the acoustic reflector, and one side of the passivation layer and the patterned metal layer both extend outside the acoustic reflector along with the top electrode.

[0008] When the top electrode is not externally connected, the outer boundaries of the projections of the top electrode, the passivation layer and the patterned metal layer in the top-view direction do not exceed the outer boundaries of the projections of the acoustic reflector in the top-view direction, so as to avoid the generation of noise caused by the outer boundaries of the projections of the top electrode, the passivation layer and the patterned metal layer in the top-view direction exceeding the outer boundaries of the projections of the acoustic reflector in the top-view direction. When the top electrode is externally connected, one side of the top electrode extends to the outside of the acoustic reflector, and one side of the passivation layer and the patterned metal layer extend to the outside of the acoustic reflector along with the top electrode. The passivation layer and the patterned metal layer extending outward can reduce the series resonant impedance of the bulk acoustic wave resonator, thereby further improving the electrical performance of the bulk acoustic wave resonator.

[0009] Optionally, the edge of the passivation layer that does not exceed the outer boundary of the projection of the acoustic reflector in the top-view direction has a second groove, the depth of the second groove is the same as the depth of the first groove, and the outer boundary of the projection of the patterned metal layer in the top-view direction coincides with the inner boundary of the projection of the second groove in the top-view direction.

[0010] This technical solution can improve the parallel resonant impedance of the BAW resonator by setting a second groove at the edge of the passivation layer and making the outer boundary of the projection of the patterned metal layer in the top view direction coincide with the inner boundary of the projection of the second groove in the top view direction, thereby further improving the electrical performance of the BAW resonator.

[0011] Optionally, the target metal layer thickness information is smaller than the recess depth information.

[0012] This technical solution is equivalent to increasing the steepness of the left side of the BAW filter passband by making the target metal layer thickness information smaller than the recess depth information, thereby effectively improving the insertion loss on the left side of the BAW filter passband, and further effectively improving the performance of the BAW filter.

[0013] In a second aspect, the present application provides a method for preparing a bulk acoustic wave resonator, which comprises the following steps: S1, forming an acoustic stack and an acoustic reflector located below the acoustic stack on a substrate, wherein the acoustic stack includes a bottom electrode, a piezoelectric layer, a top electrode and a passivation layer connected in sequence from bottom to top; S2. Acquire corresponding recess depth information and target metal layer thickness information according to a preset conversion relationship based on the target series resonant frequency; S3. Based on the target metal layer thickness information, a patterned metal layer is formed on the passivation layer above the acoustic stack, and based on the recess depth information, a first groove is formed on the passivation layer. The thickness of the patterned metal layer is equal to the target metal layer thickness information and has a first opening. The depth of the first groove is equal to the recess depth information. The outer boundary of the projection of the first opening in the top-down direction coincides with the outer boundary of the projection of the first groove in the top-down direction.

[0014] The present application provides a method for preparing a bulk acoustic wave resonator, which first forms an acoustic stack and an acoustic reflector located below the acoustic stack on a substrate, then obtains corresponding recess depth information and target metal layer thickness information based on a preset conversion relationship based on a target series resonant frequency, and finally forms a patterned metal layer located above the acoustic stack on a passivation layer based on the target metal layer thickness information, and forms a first groove on the passivation layer based on the recess depth information. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by forming a patterned metal layer located above the acoustic stack on the passivation layer based on the target metal layer thickness information and forming a first groove on the passivation layer based on the recess depth information, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the fact that the impedance change trend of the bulk acoustic wave resonator in the area near the series resonant frequency is gentle and the impedance value is high, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0015] Optionally, step S3 includes: S31, forming a patterned metal layer on the passivation layer, which is located above the acoustic stack and has a thickness greater than the target metal layer thickness information and has a first opening; S32, plasma bombarding the patterned metal layer and the passivation layer based on the target metal layer thickness information and the recess depth information, so that the thickness of the patterned metal layer is equal to the target metal layer thickness information and a first recess is formed on the passivation layer.

[0016] Optionally, step S31 includes: S311, forming a metal layer located above the acoustic stack and having a thickness greater than the target metal layer thickness information on the passivation layer 24 based on a magnetron sputtering process; S312, forming a first patterned photoresist layer having a second opening in the middle on the metal layer; S313, etching the metal layer based on the first patterned photoresist layer to form a patterned metal layer having a first opening.

[0017] Optionally, the acoustic reflector is an air cavity or several layers of Bragg reflection layers.

[0018] Optionally, the acoustic reflector is an air cavity, and step S1 includes: S11, etching the top of the substrate to form a third groove on the substrate, and depositing a sacrificial layer in the third groove; S12, sequentially growing a bottom electrode, a piezoelectric layer, a top electrode and a passivation layer on the substrate to form an acoustic stack on the substrate; S13, removing the sacrificial layer to form an acoustic reflector located below the acoustic stack on the substrate.

[0019] Optionally, step S12 includes: S121, sequentially growing a bottom electrode and a piezoelectric layer on a substrate; S122, forming a second patterned photoresist layer on the piezoelectric layer; S123 , growing a top electrode and a passivation layer on the piezoelectric layer based on the second patterned photoresist layer to form an acoustic stack on the substrate. As can be seen from the above, the present application provides a bulk acoustic wave resonator and a preparation method thereof, comprising a substrate, an acoustic stack and a patterned metal layer connected in sequence from bottom to top. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by making the thickness of the patterned metal layer equal to the target metal layer thickness information and forming a first groove with a depth equal to the recess depth information on the passivation layer, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the fact that the impedance change trend of the bulk acoustic wave resonator in the area near the series resonance frequency is gentle and the impedance value is high, thereby facilitating the performance improvement of the bulk acoustic wave resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic structural diagram of a bulk acoustic wave resonator provided in the first embodiment of the present application.

[0021] Figure 2 A schematic structural diagram of a bulk acoustic wave resonator provided in the second embodiment of the present application.

[0022] Figure 3 An impedance diagram of a bulk acoustic wave resonator provided in an embodiment of the present application.

[0023] Figure 4 A flow chart of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application.

[0024] Figure 5 A schematic diagram of a method for preparing a bulk acoustic wave resonator provided in the third embodiment of the present application.

[0025] Figure 6 A schematic diagram of a method for preparing a bulk acoustic wave resonator provided in the first embodiment of the present application.

[0026] Figure numerals: 1. substrate; 2. acoustic stack; 21. bottom electrode; 22. piezoelectric layer; 23. top electrode; 24. passivation layer; 3. acoustic reflector; 4. first opening; 5. patterned metal layer; 6. first groove; 7. sacrificial layer; 8. second groove. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0028] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0029] In a first aspect, the present application provides a bulk acoustic wave resonator, comprising: A substrate 1, an acoustic stack 2 and a patterned metal layer 5 are connected in sequence from bottom to top. The acoustic stack 2 includes a bottom electrode 21, a piezoelectric layer 22, a top electrode 23 and a passivation layer 24 connected in sequence from bottom to top. An acoustic reflector 3 is provided below the acoustic stack 2. The patterned metal layer 5 has a thickness equal to the target metal layer thickness information and has a first opening 4. The passivation layer 24 has a first groove 6. The depth of the first groove 6 is equal to the recess depth information. The outer boundary of the projection of the first opening 4 in the top-view direction coincides with the outer boundary of the projection of the first groove 6 in the top-view direction.

[0030] The material of the substrate 1 of this embodiment is preferably silicon material, the material of the bottom electrode 21 and the top electrode 23 of this embodiment is preferably any one or more of metal materials with high electrical conductivity, large acoustic impedance and large Young's modulus (such as gold, silver, ruthenium, tungsten, molybdenum, aluminum, platinum, niobium or hafnium), the material of the bottom electrode 21 of this embodiment is preferably the same as the material of the top electrode 23, the material of the bottom electrode 21 of this embodiment is preferably aluminum nitride or aluminum nitride doped with scandium (Sc), and the material of the passivation layer 24 of this embodiment is preferably aluminum nitride, silicon dioxide or silicon nitride (Si 3 N 4), the material of the patterned metal layer 5 of this embodiment is a metal material, and the passivation layer 24 can protect the top electrode 23, the piezoelectric layer 22 and the bottom electrode 21. Therefore, this embodiment can effectively prevent the top electrode 23, the piezoelectric layer 22 and the bottom electrode 21 from being corroded by the external environment or subsequent processing technology, thereby effectively extending the service life of the bulk acoustic wave resonator. Specifically, when the top electrode 23 is connected to an external signal source (equivalent to applying a voltage signal or an electrical signal to the top electrode 23), an electric field is formed at both ends of the piezoelectric layer 22 to excite the bulk acoustic wave (equivalent to exciting the piezoelectric layer 22 to generate a longitudinal wave), thereby realizing the mutual conversion of electrical energy and mechanical energy and the frequency selection of the bulk acoustic wave resonator. By the attached Figure 3 It can be seen that Figure 3 An impedance diagram of a bulk acoustic wave resonator with a patterned passivation layer provided in an embodiment of the present application. The present application can increase the impedance change trend and optimize the impedance in the area near the series resonance frequency by forming a first groove 6 on the passivation layer 24. Therefore, the present application can improve the insertion loss on the left side of the bulk acoustic wave filter passband and improve the performance of the bulk acoustic wave filter by forming a patterned metal layer 5 located above the acoustic stack 2 on the passivation layer 24 based on the target metal layer thickness information and the recess depth information and forming a first groove 6 on the passivation layer 24.

[0031] A bulk acoustic wave resonator provided by the present application includes a substrate 1, an acoustic stack 2 and a patterned metal layer 5 connected in sequence from bottom to top. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by making the thickness of the patterned metal layer 5 equal to the target metal layer thickness information and forming a first groove 6 with a depth equal to the recess depth information on the passivation layer 24, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the gentle impedance change trend and high impedance value of the bulk acoustic wave resonator in the area near the series resonance frequency, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0032] In some preferred embodiments, when the top electrode 23 is not externally connected, the outer boundaries of the projections of the top electrode 23, the passivation layer 24 and the patterned metal layer 5 in the top-view direction do not exceed the outer boundaries of the projections of the acoustic reflector 3 in the top-view direction; when the top electrode 23 is externally connected, one side of the top electrode 23 extends to the outside of the acoustic reflector 3, and one side of the passivation layer 24 and the patterned metal layer 5 both extend to the outside of the acoustic reflector 3 along with the top electrode 23.

[0033] When the top electrode 23 is not externally connected, the outer boundaries of the projections of the top electrode 23, the passivation layer 24 and the patterned metal layer 5 in the top-view direction do not exceed the outer boundaries of the projections of the acoustic reflector 3 in the top-view direction, so as to avoid the generation of noise due to the outer boundaries of the projections of the top electrode 23, the passivation layer 24 and the patterned metal layer 5 in the top-view direction exceeding the outer boundaries of the projections of the acoustic reflector 3 in the top-view direction. When the top electrode 23 is externally connected, one side of the top electrode 23 extends to the outside of the acoustic reflector 3, and one side of the passivation layer 24 and the patterned metal layer 5 extend to the outside of the acoustic reflector 3 along with the top electrode 23. The outwardly extended passivation layer 24 and the patterned metal layer 5 can reduce the series resonant impedance of the bulk acoustic wave resonator, thereby further improving the electrical performance of the bulk acoustic wave resonator.

[0034] In some preferred embodiments, the edge of the passivation layer 24 that does not exceed the outer boundary of the projection of the acoustic reflector 3 in the top view direction has a second groove 8, the depth of the second groove 8 is the same as the depth of the first groove 6, and the outer boundary of the projection of the patterned metal layer 5 in the top view direction coincides with the inner boundary of the projection of the second groove 8 in the top view direction.

[0035] This embodiment can improve the parallel resonant impedance of the BAW resonator by providing a second groove 8 at the edge of the passivation layer 24 and making the outer boundary of the projection of the patterned metal layer 5 in the top view direction coincide with the inner boundary of the projection of the second groove 8 in the top view direction, thereby further improving the electrical performance of the BAW resonator.

[0036] In some preferred embodiments, the target metal layer thickness information is less than the recess depth information. The applicant has learned through a large number of experiments that when the target metal layer thickness information is less than the recess depth information, the series resonant impedance of the area near the target series resonant frequency first drops rapidly and then rises steadily, and when the target metal layer thickness information is greater than the recess depth information, the impedance change trend of the area near the target series resonant frequency (the steep change degree of the impedance of the area near the target series resonant frequency) is small, and when the target metal layer thickness information is greater than the recess depth information, the impedance change trend of the area near the target series resonant frequency is large, and the increase in the impedance change trend of the area near the target series resonant frequency is conducive to improving the steepness of the left side of the BAW filter passband, so this embodiment is equivalent to improving the steepness of the left side of the BAW filter passband by making the target metal layer thickness information less than the recess depth information, thereby effectively improving the insertion loss on the left side of the BAW filter passband, and then effectively improving the performance of the BAW filter.

[0037] As can be seen from the above, a bulk acoustic wave resonator provided by the present application includes a substrate 1, an acoustic stack 2 and a patterned metal layer 5 connected in sequence from bottom to top. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by making the thickness of the patterned metal layer 5 equal to the target metal layer thickness information and forming a first groove 6 with a depth equal to the recess depth information on the passivation layer 24, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the fact that the impedance change trend of the bulk acoustic wave resonator in the area near the series resonance frequency is gentle and the impedance value is high, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0038] Second, as Figure 1-Figure 3 As shown, the present application provides a method for preparing a bulk acoustic wave resonator, which comprises the following steps: S1, forming an acoustic stack 2 and an acoustic reflector 3 located below the acoustic stack 2 on a substrate 1, wherein the acoustic stack 2 includes a bottom electrode 21, a piezoelectric layer 22, a top electrode 23 and a passivation layer 24 connected in sequence from bottom to top; S2. Acquire corresponding recess depth information and target metal layer thickness information according to a preset conversion relationship based on the target series resonant frequency; S3. Based on the target metal layer thickness information, a patterned metal layer 5 is formed on the passivation layer 24 and located above the acoustic stack 2. Based on the recess depth information, a first groove 6 is formed on the passivation layer 24. The thickness of the patterned metal layer 5 is equal to the target metal layer thickness information and has a first opening 4. The depth of the first groove 6 is equal to the recess depth information. The outer boundary of the projection of the first opening 4 in the top view direction coincides with the outer boundary of the projection of the first groove 6 in the top view direction.

[0039] In step S1, an acoustic stack 2 and an acoustic reflector 3 located below the acoustic stack 2 can be formed on a substrate 1 using an existing acoustic stack forming method and an existing acoustic reflector forming method. The acoustic reflector 3 is preferably formed on the top of the substrate 1. The acoustic stack 2 of this embodiment includes a bottom electrode 21, a piezoelectric layer 22, a top electrode 23 and a passivation layer 24 connected in sequence from bottom to top.

[0040] The target series resonant frequency of step S2 (reference Figure 3Fs) is the series resonant frequency of the target BAW resonator (the BAW resonator to be prepared by the BAW resonator preparation method), and the target series resonant frequency is a preset value. Specifically, the preset conversion relationship of this embodiment can be a pre-constructed resonant frequency metal layer thickness depression depth database or a resonant frequency-metal layer thickness-depression depth mapping relationship, and the database and the mapping relationship both store multiple series resonant frequency intervals, and each series resonant frequency interval corresponds to at least one metal layer thickness and at least one depression depth. Therefore, this embodiment can obtain the corresponding depression depth information and target metal layer thickness information from the resonant frequency metal layer thickness depression depth database or the resonant frequency-metal layer thickness-depression depth mapping relationship according to the target series resonant frequency by data extraction. It should be understood that if each series resonant frequency interval corresponds to multiple metal layer thicknesses and multiple depression depths, then this embodiment can use any metal layer thickness as the target metal layer thickness information (the thickness of the patterned metal layer 5 of the target BAW resonator) and the depression depth corresponding to the target metal layer thickness information as the depression depth information. The sum of the metal layer thickness and the recess depth of this embodiment is a preset value, so this embodiment can first determine the ratio of the metal layer thickness to the recess depth, and then calculate the corresponding target metal layer thickness information and recess depth information according to the ratio and the sum of the metal layer thickness and the recess depth. For example, the sum of the metal layer thickness and the recess depth is 10μm, and the ratio of the metal layer thickness to the recess depth is 3:2, then the target metal layer thickness information is 6μm, and the recess depth information is 4μm, that is, the preset conversion relationship of this embodiment can also be a pre-constructed resonant frequency ratio database or a resonant frequency-ratio mapping relationship, and the database and the mapping relationship both store multiple series resonant frequency intervals, each series resonant frequency interval corresponds to at least one ratio, so this embodiment can first obtain the corresponding ratio information from the resonant frequency ratio database or the resonant frequency-ratio mapping relationship according to the target series resonant frequency by data extraction, and then calculate the corresponding target metal layer thickness information and recess depth information according to the ratio information and the preset sum of the metal layer thickness and the recess depth. It should be understood that if each series resonant frequency interval corresponds to multiple ratios, then this embodiment can use any ratio as the ratio information. It should be understood that the target metal layer thickness information of this embodiment is preferably smaller than the recess depth information. Therefore, when the preset conversion relationship is a pre-constructed resonant frequency metal layer thickness recess depth database or a resonant frequency-metal layer thickness-recess depth mapping relationship, the metal layer thickness stored in the preset conversion relationship is preferably smaller than the recess depth. When the preset conversion relationship can also be a pre-constructed resonant frequency ratio database or a resonant frequency-ratio mapping relationship, the ratio of the metal layer thickness to the recess depth stored in the preset conversion relationship is preferably less than 1.

[0041] In step S3, a patterned metal layer 5 having a first opening 4 and located above the acoustic stack 2 and having a thickness equal to the target metal layer thickness information can be formed on the passivation layer 24 using an existing metal layer forming process based on the target metal layer thickness information, and then the passivation layer 24 can be etched based on the patterned metal layer 5 using an existing etching process to form a first groove 6 on the passivation layer 24. Preferably, the first opening 4 of this embodiment is located in the middle of the patterned metal layer 5, and the first groove 6 of this embodiment is located in the middle of the passivation layer 24. It should be understood that since this embodiment can change the impedance change trend in the area near the target series resonant frequency by changing the ratio of the target metal layer thickness information and the recess depth information while the sum of the target metal layer thickness information and the recess depth information remains unchanged, the present application can improve the electrical performance of the bulk acoustic wave filter in a targeted manner in combination with step S2 and step S3.

[0042] The present application provides a method for preparing a bulk acoustic wave resonator, which first forms an acoustic stack 2 and an acoustic reflector 3 located below the acoustic stack 2 on a substrate 1, then obtains corresponding recess depth information and target metal layer thickness information based on a preset conversion relationship based on a target series resonant frequency, and finally forms a patterned metal layer 5 located above the acoustic stack 2 on a passivation layer 24 based on the target metal layer thickness information, and forms a first groove 6 on the passivation layer 24 based on the recess depth information. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by forming a patterned metal layer 5 located above the acoustic stack 2 on the passivation layer 24 based on the target metal layer thickness information and forming a first groove 6 on the passivation layer 24 based on the recess depth information, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the gentle impedance change trend and high impedance value of the bulk acoustic wave resonator in the area near the series resonant frequency, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0043] In some preferred embodiments, step S3 comprises: S31, forming a patterned metal layer 5 on the passivation layer 24, which is located above the acoustic stack 2, has a thickness greater than the target metal layer thickness information, and has a first opening 4; S32 , plasma bombarding the patterned metal layer 5 and the passivation layer 24 based on the target metal layer thickness information and the recess depth information, so that the thickness of the patterned metal layer 5 is equal to the target metal layer thickness information and a first recess 6 is formed on the passivation layer 24 .

[0044] Since the thickness of the patterned metal layer 5 will decrease when the patterned metal layer 5 is plasma bombarded in step S32, and the target metal layer thickness information is the thickness of the patterned metal layer 5 of the target bulk acoustic wave resonator, step S31 needs to form a patterned metal layer 5 with a thickness greater than the target metal layer thickness information above the acoustic stack 2. Since the patterned metal layer 5 of this embodiment is located on the passivation layer 24, the passivation layer 24 covered by the patterned metal layer 5 will not be plasma bombarded, that is, the patterned metal layer 5 is equivalent to a mask for plasma bombarding the passivation layer 24, so this embodiment can form a first groove 6 on the passivation layer 24 by plasma bombarding the patterned metal layer 5 and the passivation layer 24. Specifically, step S32 can use the existing ion beam trimming process to plasma bombard the patterned metal layer 5 and the passivation layer 24 according to the target metal layer thickness information and the recess depth information, so that the thickness of the patterned metal layer 5 is equal to the target metal layer thickness information and the first groove 6 is formed in the passivation layer 24. It should be understood that, in this embodiment, the patterned metal layer 5 having a thickness greater than any value of the target metal layer thickness information can be formed on the passivation layer 24 by using step S31, and the specific process of step S32 can be: determining the metal layer thinning information (the thickness of the patterned metal layer 5 to be thinned) according to the actual thickness of the patterned metal layer 5 and the target metal layer thickness information; determining the bombardment parameters (including the composition ratio, partial pressure and power of the plasma, etc.) according to the metal layer thinning information and the recess depth information; and plasma bombarding the patterned metal layer 5 and the passivation layer 24 according to the bombardment parameters. It should also be understood that, in this embodiment, the bombardment parameters can be determined first, and then the metal layer thinning information can be determined according to the bombardment parameters, and the desired metal layer thickness information (the sum of the metal layer thinning information and the target metal layer thickness information) can be calculated according to the metal layer thinning information and the target metal layer thickness information, and finally, the patterned metal layer 5 having a thickness of the desired metal layer thickness information can be formed on the passivation layer 24 by using step S31. It should also be understood that if the BAW resonator to be formed in this embodiment has a second groove 8 at the edge of the passivation layer 24 that does not exceed the outer boundary of the projection of the acoustic reflector 3 in the top view direction, then the patterned metal layer 5 formed in step S31 has a second opening at the edge of the passivation layer 24 that does not exceed the outer boundary of the projection of the acoustic reflector 3 in the top view direction.

[0045] In some preferred embodiments, step S31 includes: S311, forming a metal layer located above the acoustic stack 2 and having a thickness greater than the target metal layer thickness information on the passivation layer 24 based on a magnetron sputtering process; S312, forming a first patterned photoresist layer having a second opening in the middle on the metal layer; S313 , etching the metal layer based on the first patterned photoresist layer to form a patterned metal layer 5 having a first opening 4 .

[0046] In step S312, a first patterned photoresist layer having a second opening in the middle can be formed on the metal layer using an existing photoresist layer forming process, and the shape and size of the second opening are the same as the shape and size of the first opening 4. In step S313, a patterned metal layer 5 having a first opening 4 can be formed by etching the metal layer based on the first patterned photoresist layer using an existing dry etching process, and this embodiment is equivalent to transferring the pattern on the first patterned photoresist layer to the metal layer.

[0047] In some preferred embodiments, the acoustic reflector 3 is an air cavity or several layers of Bragg reflective layers. The acoustic reflector 3 of this embodiment can be an air cavity or several layers of Bragg reflective layers, each of which is composed of a low acoustic impedance layer and a high acoustic impedance layer. Specifically, when the acoustic reflector 3 is a plurality of layers of Bragg reflective layers, the embodiment can first etch the substrate 1 to form a fourth groove on the substrate 1, and then form several layers of Bragg reflective layers in the fourth groove based on the existing Bragg reflective layer formation process. It should be understood that if the acoustic reflector 3 is an air cavity, the bulk acoustic wave resonator of this embodiment is substantially a film bulk acoustic wave resonator (FBAR), and if the acoustic reflector 3 is a Bragg reflective layer, the bulk acoustic wave resonator of this embodiment is substantially a solid mounted resonator (SMR).

[0048] In some preferred embodiments, the acoustic reflector 3 is an air cavity, and step S1 includes: S11, etching the top of the substrate 1 to form a third groove on the substrate 1, and depositing a sacrificial layer 7 in the third groove; S12, sequentially growing a bottom electrode 21, a piezoelectric layer 22, a top electrode 23 and a passivation layer 24 on the substrate 1 to form an acoustic stack 2 on the substrate 1; S13 , removing the sacrificial layer 7 to form an acoustic reflector 3 located below the acoustic stack 2 on the substrate 1 .

[0049] In step S11, the top of the substrate 1 can be etched by using the existing dry etching process to form a third groove on the substrate 1, and then the sacrificial layer 7 is deposited in the third groove by using the existing chemical vapor deposition (CVD) process. The material of the sacrificial layer 7 is preferably P-doped silicon dioxide (PSG). It should be understood that the sacrificial layer 7 of this embodiment needs to be flush with the top surface of the substrate 1. Therefore, after the sacrificial layer 7 is deposited in the third groove, if the sacrificial layer 7 is not flush with the top surface of the substrate 1, step S11 can use the existing chemical mechanical polishing (CMP) process to grind and polish the top surface of the substrate 1 or the top surface of the sacrificial layer 7 until the sacrificial layer 7 is flush with the top surface of the substrate 1. Step S13 can remove the sacrificial layer 7 by removing the PSG material by using hydrofluoric acid (HF) to form an acoustic reflector 3 located below the acoustic stack 2 on the substrate 1. It should be understood that step S13 can be performed after step S3.

[0050] In some preferred embodiments, step S12 includes: S121, sequentially growing a bottom electrode 21 and a piezoelectric layer 22 on a substrate 1; S122, forming a second patterned photoresist layer on the piezoelectric layer 22; S123 , growing a top electrode 23 and a passivation layer 24 on the piezoelectric layer 22 based on the second patterned photoresist layer to form an acoustic stack 2 on the substrate 1 .

[0051] The specific process of step S121 can be: using the existing chemical vapor deposition process or physical vapor deposition process to deposit a layer of conductive material on the substrate 1 to form a first conductive material layer on the substrate 1; forming a third patterned photoresist layer on the first conductive material layer; etching the first conductive material layer based on the third patterned photoresist layer to form a bottom electrode 21 on the substrate 1, and removing the third patterned photoresist layer; depositing piezoelectric material on the bottom electrode 21 based on the existing physical vapor deposition process to form a piezoelectric layer 22 on the bottom electrode 21. The specific process of step S123 can be: using the existing chemical vapor deposition process or physical vapor deposition process to deposit a layer of conductive material on the second patterned photoresist layer to form a second conductive material layer on the second patterned photoresist layer and the piezoelectric layer 22; forming a fourth patterned photoresist layer on the second conductive material layer; etching the second conductive material layer based on the fourth patterned photoresist layer to form a top electrode 23 on the second patterned photoresist layer and the piezoelectric layer 22; removing the fourth patterned photoresist layer, and using the existing physical vapor deposition process to grow a passivation layer 24 on the top electrode 23.

[0052] In some preferred embodiments, the method for preparing a bulk acoustic wave resonator further includes the following steps performed after step S1: S4, removing the second patterned photoresist layer.

[0053] This embodiment is equivalent to using air to replace the second patterned photoresist layer. Since the noise suppression effect of air is better than that of the second patterned photoresist layer, this embodiment can effectively avoid the situation where the effect of improving the parallel resonant impedance of the BAW resonator is reduced and the electrical performance of the BAW resonator is reduced due to the appearance of noise in the BAW resonator.

[0054] As can be seen from the above, the present application provides a method for preparing a bulk acoustic wave resonator, first forming an acoustic stack 2 and an acoustic reflector 3 located below the acoustic stack 2 on a substrate 1, then obtaining corresponding recess depth information and target metal layer thickness information based on a preset conversion relationship based on a target series resonant frequency, and finally forming a patterned metal layer 5 located above the acoustic stack 2 on the passivation layer 24 based on the target metal layer thickness information, and forming a first groove 6 on the passivation layer 24 based on the recess depth information. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by forming a patterned metal layer 5 located above the acoustic stack 2 on the passivation layer 24 based on the target metal layer thickness information and forming a first groove 6 on the passivation layer 24 based on the recess depth information, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the gentle impedance change trend and high impedance value of the bulk acoustic wave resonator in the area near the series resonant frequency, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0055] As can be seen from the above, the present application provides a bulk acoustic wave resonator and a preparation method thereof, comprising a substrate, an acoustic stack and a patterned metal layer connected in sequence from bottom to top. Since the present application can improve the insertion loss on the left side of the passband of the bulk acoustic wave filter and improve the performance of the bulk acoustic wave filter by making the thickness of the patterned metal layer equal to the target metal layer thickness information and forming a first groove with a depth equal to the recess depth information on the passivation layer, the present application can effectively solve the problem that the insertion loss of the bulk acoustic wave filter is affected by the fact that the impedance change trend of the bulk acoustic wave resonator in the area near the series resonance frequency is gentle and the impedance value is high, thereby facilitating the performance improvement of the bulk acoustic wave resonator.

[0056] In the embodiments provided in the present application, it should be understood that, herein, relational terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0057] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. 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.

Claims

1. A bulk acoustic wave resonator, characterized in that: The BAW resonator includes a substrate, an acoustic stack and a patterned metal layer connected in sequence from bottom to top, the acoustic stack includes a bottom electrode, a piezoelectric layer, a top electrode and a passivation layer connected in sequence from bottom to top, an acoustic reflector is provided under the acoustic stack, the thickness of the patterned metal layer is equal to the target metal layer thickness information and has a first opening, the passivation layer has a first groove, the depth of the first groove is equal to the recess depth information, and the outer boundary of the projection of the first opening in the top-down direction coincides with the outer boundary of the projection of the first groove in the top-down direction.

2. The bulk acoustic wave resonator according to claim 1, characterized in that When the top electrode is not externally connected, the outer boundaries of the projections of the top electrode, the passivation layer and the patterned metal layer in the top-view direction do not exceed the outer boundaries of the projections of the acoustic reflector in the top-view direction. When the top electrode is externally connected, one side of the top electrode extends to the outside of the acoustic reflector, and one side of the passivation layer and the patterned metal layer extend to the outside of the acoustic reflector along with the top electrode.

3. The bulk acoustic wave resonator according to claim 1, characterized in that: The edge of the passivation layer that does not exceed the outer boundary of the projection of the acoustic reflector in the top-view direction has a second groove, the depth of the second groove is the same as the depth of the first groove, and the outer boundary of the projection of the patterned metal layer in the top-view direction coincides with the inner boundary of the projection of the second groove in the top-view direction.

4. The bulk acoustic wave resonator according to claim 1, characterized in that The target metal layer thickness information is smaller than the recess depth information.

5. A method for preparing a bulk acoustic wave resonator, characterized in that: The bulk acoustic wave resonator preparation method comprises the following steps: S1, forming an acoustic stack and an acoustic reflector located below the acoustic stack on a substrate, wherein the acoustic stack includes a bottom electrode, a piezoelectric layer, a top electrode and a passivation layer connected in sequence from bottom to top; S2. Acquire corresponding recess depth information and target metal layer thickness information according to a preset conversion relationship based on the target series resonant frequency; S3. Based on the target metal layer thickness information, a patterned metal layer is formed on the passivation layer above the acoustic stack, and based on the recess depth information, a first groove is formed on the passivation layer, wherein the thickness of the patterned metal layer is equal to the target metal layer thickness information and has a first opening, the depth of the first groove is equal to the recess depth information, and the outer boundary of the projection of the first opening in the top-view direction coincides with the outer boundary of the projection of the first groove in the top-view direction.

6. The method for preparing a bulk acoustic wave resonator according to claim 5, characterized in that: Step S3 includes: S31, forming a patterned metal layer on the passivation layer, which is located above the acoustic stack, has a thickness greater than the target metal layer thickness information and has a first opening; S32. Plasma bombard the patterned metal layer and the passivation layer based on the target metal layer thickness information and the recess depth information, so that the thickness of the patterned metal layer is equal to the target metal layer thickness information and a first recess is formed on the passivation layer.

7. The method for preparing a bulk acoustic wave resonator according to claim 6, characterized in that: Step S31 includes: S311, forming a metal layer located above the acoustic stack and having a thickness greater than the target metal layer thickness information on the passivation layer based on a magnetron sputtering process; S312, forming a first patterned photoresist layer having a second opening in the middle on the metal layer; S313, etching the metal layer based on the first patterned photoresist layer to form a patterned metal layer having a first opening.

8. The method for preparing a bulk acoustic wave resonator according to claim 5, characterized in that: The acoustic reflector is an air cavity or a plurality of Bragg reflection layers.

9. The method for preparing a bulk acoustic wave resonator according to claim 8, characterized in that: The acoustic reflector is an air cavity, and step S1 comprises: S11, etching the top of the substrate to form a third groove on the substrate, and depositing a sacrificial layer in the third groove; S12, sequentially growing a bottom electrode, a piezoelectric layer, a top electrode and a passivation layer on the substrate to form an acoustic stack on the substrate; S13, removing the sacrificial layer to form an acoustic reflector located below the acoustic stack on the substrate.

10. The method for preparing a bulk acoustic wave resonator according to claim 9, characterized in that: Step S12 includes: S121, sequentially growing a bottom electrode and a piezoelectric layer on the substrate; S122, forming a second patterned photoresist layer on the piezoelectric layer; S123, growing a top electrode and a passivation layer on the piezoelectric layer based on the second patterned photoresist layer to form an acoustic stack on the substrate.

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