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.The resonator comprises a substrate, a bottom electrode, a piezoelectric layer and a top electrode which are sequentially connected from bottom to top, and the substrate is provided with an acoustic reflector; the piezoelectric layer is provided with a first groove, the edge of the projection of the first groove in the overlook direction does not exceed the edge of the projection of the acoustic reflector in the overlook direction, the top electrode is provided with a second groove, and the edge of the projection of the second groove in the overlook direction does not exceed the edge of the projection of the first groove in the overlook direction; according to the resonator, the problem that the air gap cannot completely play a role in reducing energy leakage due to the appearance defect of the air gap can be effectively solved; the quality factor of the bulk acoustic wave resonator and the improvement effect of parallel resonance impedance are limited; and the mechanical stability of an external connection part of a top electrode is reduced due to the fact that the external connection part of the top electrode loses support.

Description

Technical Field

[0001] This application relates to the technical field of bulk acoustic wave resonators, and in particular, to a bulk acoustic wave resonator and a preparation method thereof. Background Art

[0002] In the technical field of bulk acoustic wave resonators, related technologies usually reduce energy leakage by forming an air gap between the top electrode and the piezoelectric layer to improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator. This air gap can be divided into an air gap located in the non-external connection area of the top electrode and an air gap located in the external connection area of the top electrode. The process for forming the air gap located in the non-external connection area of the top electrode in related technologies is as follows: First, a dielectric layer is formed on the piezoelectric layer within the projection area of the acoustic mirror, then a top electrode is formed on the dielectric layer, and finally the dielectric layer is removed. The process for forming the air gap located in the external connection area of the top electrode in related technologies is as follows: First, a sacrificial layer is formed on the piezoelectric layer outside the projection area of the acoustic mirror, then a top electrode is formed on the sacrificial layer, and finally the sacrificial layer is released.

[0003] Due to process bottlenecks, both the dielectric layer and the sacrificial layer formed on the piezoelectric layer have topography defects, and these topography defects will cause the finally formed air gap to also have topography defects. Therefore, related technologies have problems that due to the topography defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, and the improvement effects of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator are limited. Moreover, after the sacrificial layer is released, the external connection part of the top electrode will lose support. Therefore, related technologies also have problems that due to the loss of support of the external connection part of the top electrode, the mechanical stability of the external connection part of the top electrode decreases.

[0004] In view of the above problems, there is currently no effective technical solution. It should be noted that the above information disclosed in this part is only used to understand the background of the inventive concept of the present invention, and therefore may include information that does not constitute prior art. Summary of the Invention

[0005] The purpose of this application is to provide a bulk acoustic wave resonator and a preparation method thereof, which can effectively solve the problems that due to the topography defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, the improvement effects of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator are limited, and due to the loss of support of the external connection part of the top electrode, the mechanical stability of the external connection part of the top electrode decreases.

[0006] In a first aspect, this application provides a bulk acoustic wave resonator, which includes: A substrate, a bottom electrode, a piezoelectric layer, and a top electrode connected in sequence from bottom to top, and an acoustic mirror is provided on the substrate; A first groove is provided on the piezoelectric layer, and the edge of the projection of the first groove in the top view direction does not exceed the edge of the projection of the acoustic mirror in the top view direction. A second groove is provided on the top electrode, and the edge of the projection of the second groove in the top view direction does not exceed the edge of the projection of the first groove in the top view direction.

[0007] A bulk acoustic wave resonator provided by the present application can reduce the acoustic wave leakage amount and energy leakage by forming a first groove on the piezoelectric layer and a second groove on the top electrode. That is, the present application is equivalent to using the first groove and the second groove to replace the air gap in the prior art. That is, the present application can improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problems that due to the morphological defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external connection part of the top electrode decreases due to the loss of support of the external connection part of the top electrode.

[0008] Optionally, the piezoelectric layer has a step group located in the first groove. The step group includes at least one step portion, and the height of the step portion is less than the depth of the first groove. When the number of step portions is multiple, the multiple step portions are distributed inside and outside with the center of the piezoelectric layer as the center and are arranged at intervals.

[0009] Due to the acoustic impedance difference between the region where the step portion is located and the region outside the step portion, and under the action of this acoustic impedance difference, the step portion can play a role in hindering and reflecting the lateral transmission of the acoustic wave. Therefore, this technical solution is equivalent to increasing the number of reflections and the amount of reflection of the acoustic wave by setting a step group in the first groove, thereby effectively improving the suppression effect of acoustic wave leakage and further reducing the acoustic wave leakage amount and energy leakage, and further improving the quality factor and parallel resonance impedance of the bulk acoustic wave resonator.

[0010] Optionally, the minimum distance between the step portion and the top of the piezoelectric layer is greater than the minimum distance between the top of the step portion and the bottom of the first groove.

[0011] This technical solution can improve the suppression effect of acoustic wave leakage of the step portion by making the minimum distance between the step portion and the top of the piezoelectric layer greater than the minimum distance between the top of the step portion and the bottom of the first groove. Therefore, this technical solution can further reduce the acoustic wave leakage amount and energy leakage.

[0012] Optionally, the step portion is an annular structure, and the outermost step portion fits with the side wall of the first groove.

[0013] Optionally, the top electrode has at least one external connection portion, and the step portion is arranged on one side of the first groove close to the external connection portion.

[0014] The stepped portion of this technical solution is only provided on one side of the first groove close to the external connection portion. Therefore, this technical solution can reduce the coverage area of the stepped portion while ensuring the sound wave leakage suppression effect, thereby effectively reducing the production difficulty and production cost of the stepped portion, and further effectively reducing the production difficulty and production cost of the bulk acoustic wave resonator.

[0015] Optionally, the bulk acoustic wave resonator further includes a passivation layer, and the passivation layer is disposed above the top electrode.

[0016] In a second aspect, the present application also provides a method for manufacturing a bulk acoustic wave resonator, which includes the following steps: S1. Form a cavity on the substrate and form a sound reflector in the cavity; S2. Form a bottom electrode, a piezoelectric layer, and a first patterned photoresist layer on the substrate in sequence. The inner boundary of the projection of the first patterned photoresist layer in the top view direction does not exceed the edge of the projection of the sound reflector in the top view direction; S3. Etch the piezoelectric layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, and the edge of the projection of the first groove in the top view direction does not exceed the edge of the projection of the sound reflector in the top view direction; S4. Remove the first patterned photoresist layer; S5. Form a top electrode and a second patterned photoresist layer on the piezoelectric layer in sequence. The inner boundary of the projection of the second patterned photoresist layer in the top view direction is located at the edge of the projection of the first groove in the top view direction; S6. Etch the top electrode based on the second patterned photoresist layer to form a second groove on the top electrode, and the edge of the projection of the second groove in the top view direction does not exceed the edge of the projection of the first groove in the top view direction.

[0017] The method for manufacturing a bulk acoustic resonator provided by the present application can reduce the sound wave leakage amount and energy leakage by forming a first groove on the piezoelectric layer and a second groove on the top electrode. That is, the present application is equivalent to using the first groove and the second groove to replace the air gap in the prior art. That is, the present application can improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problems that due to the morphological defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external connection portion of the top electrode is reduced due to the loss of support of the external connection portion of the top electrode.

[0018] Optionally, the method for manufacturing a bulk acoustic wave resonator further includes a step performed between step S2 and step S3: A1. Perform surface treatment on the first patterned photoresist layer and the piezoelectric layer using oxygen.

[0019] This technical solution can perform surface treatment on the first patterned photoresist layer and the piezoelectric layer by using oxygen, so that the side walls of the first patterned photoresist layer and the exposed surfaces of the piezoelectric layer have good morphologies. Therefore, this technical solution can make the first groove formed on the piezoelectric layer have a good morphology by performing surface treatment on the first patterned photoresist layer and the piezoelectric layer before etching the piezoelectric layer, thereby effectively avoiding the situation where the first groove cannot fully play the role of reducing energy leakage due to the morphological defects of the first groove.

[0020] Optionally, step S3 includes: S31. Etch the piezoelectric layer based on the first patterned photoresist layer by using the TRIM technology to form a first groove on the piezoelectric layer, the edge of the projection in the top view direction of which does not exceed the edge of the projection of the acoustic mirror in the top view direction; Step S6 includes: S61. Etch the top electrode based on the second patterned photoresist layer by using the TRIM technology to form a second groove on the top electrode, the edge of the projection in the top view direction of which does not exceed the edge of the projection of the first groove in the top view direction.

[0021] Since the TRIM technology has the advantage of high etching accuracy, this technical solution can make both the formed first groove and the second groove have precise depths and low surface roughnesses, thereby effectively improving the suppression effect of the first groove and the second groove on acoustic wave leakage, and further improving the quality factor and parallel resonance impedance of the bulk acoustic wave resonator.

[0022] Optionally, step S2 includes: S21. Sequentially form a bottom electrode, a piezoelectric layer, a protective layer, and a first patterned photoresist layer on the substrate, and the inner boundary of the projection of the first patterned photoresist layer in the top view direction is located at the edge of the projection of the acoustic mirror in the top view direction; Step S3 includes: S31'. Etch the piezoelectric layer and the protective layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of the projection in the top view direction of which does not exceed the edge of the projection of the acoustic mirror in the top view direction; Step S4 includes: S41. Remove the first patterned photoresist layer and the protective layer.

[0023] As can be seen from the above, a bulk acoustic wave resonator and a preparation method thereof provided by the present application can reduce the acoustic wave leakage and energy leakage by forming a first groove on the piezoelectric layer and a second groove on the top electrode. That is, the present application is equivalent to using the first groove and the second groove to replace the air gap in the prior art. That is, the present application can improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problems that due to the morphological defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external connection part of the top electrode is reduced due to the loss of support of the external connection part of the top electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is a schematic cross-sectional structure diagram of a bulk acoustic wave resonator provided by the first embodiment of the present application.

[0025] Figure 2 FIG. is a schematic cross-sectional structure diagram of a bulk acoustic wave resonator without a passivation layer provided by the second embodiment of the present application.

[0026] Figure 3 FIG. is a schematic cross-sectional structure diagram of a substrate, a bottom electrode, a piezoelectric layer and a step portion provided by the third embodiment of the present application.

[0027] Figure 4 FIG. is a schematic structure diagram of a substrate, a bottom electrode, a piezoelectric layer and a step portion provided by the third embodiment of the present application.

[0028] Figure 5 FIG. is a schematic cross-sectional structure diagram of a substrate, a bottom electrode, a piezoelectric layer and a step portion provided by the fourth embodiment of the present application.

[0029] Figure 6 FIG. is a schematic structure diagram of a substrate, a bottom electrode, a piezoelectric layer and a step portion provided by the fourth embodiment of the present application.

[0030] Figure 7 FIG. is a schematic structure diagram of a substrate, a bottom electrode, a piezoelectric layer and a step portion provided by the fifth embodiment of the present application.

[0031] Figure 8 FIG. is a flowchart of a method for preparing a bulk acoustic wave resonator provided by an embodiment of the present application.

[0032] Figure 9 FIG. is a schematic flow diagram of a method for preparing a bulk acoustic wave resonator provided by an embodiment of the present application.

[0033] Figure 10 FIG. is a scanning electron microscope image of a piezoelectric layer and a first groove after surface treatment with oxygen.

[0034] Figure 11 SEM images of the piezoelectric layer and the first groove without surface treatment using oxygen.

[0035] Reference numerals: 1, substrate; 2, bottom electrode; 3, piezoelectric layer; 4, top electrode; 5, acoustic mirror; 6, first groove; 7, second groove; 8, step portion; 9, passivation layer; 10, first patterned photoresist layer; 11, second patterned photoresist layer; 12, protective layer. Detailed implementation manners

[0036] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying 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 the embodiments. Usually, the components of the embodiments of the present application described and shown in the accompanying 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 accompanying drawings is not intended to limit the scope of the present application to be protected, but only 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 creative efforts belong to the scope of protection of the present application.

[0037] It should be noted that: similar reference numerals and letters represent similar items in the following drawings. Therefore, 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 the present application, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0038] In a first aspect, as Figures 1 - 7 shown, the present application provides a bulk acoustic wave resonator, which includes: A substrate 1, a bottom electrode 2, a piezoelectric layer 3, and a top electrode 4 connected in sequence from bottom to top, and an acoustic mirror 5 is provided on the substrate 1; A first groove 6 is provided on the piezoelectric layer 3, and the edge of the projection of the first groove 6 in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction. A second groove 7 is provided on the top electrode 4, and the edge of the projection of the second groove 7 in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction.

[0039] Among them, the material of the substrate 1 in this embodiment is preferably a silicon material. The materials of the bottom electrode 2 and the top electrode 4 in this embodiment are preferably metal materials with high conductivity, large acoustic impedance, and large Young's modulus (such as any one or more of gold, molybdenum, ruthenium, and platinum). The material of the bottom electrode 2 in this embodiment is preferably the same as the material of the top electrode 4 in this embodiment. The material of the piezoelectric layer 3 in this embodiment is preferably aluminum nitride. Specifically, when a signal source is externally connected to the top electrode 4 and the bottom electrode 2 (equivalent to applying a voltage signal or an electrical signal to the top electrode 4 and the bottom electrode 2), an electric field is formed at both ends of the piezoelectric layer 3 to excite a bulk acoustic wave (equivalent to exciting a longitudinal wave in the piezoelectric layer 3), thereby realizing the mutual conversion of electrical energy and mechanical energy and the frequency selection of the bulk acoustic wave resonator. It should be understood that if it is necessary to increase the effective electromechanical coupling coefficient of the bulk acoustic wave resonator, scandium-doped aluminum nitride can be selected as the material of the piezoelectric layer 3 in this embodiment, and those skilled in the art can determine the specific scandium doping amount based on the actual requirements of the effective electromechanical coupling coefficient. A acoustic mirror 5 is provided on the substrate 1 in this embodiment. The acoustic mirror 5 can be an air cavity or several layers of Bragg reflection layers. Each layer of Bragg reflection layer is composed of a low acoustic impedance layer and a high acoustic impedance layer. In this embodiment, the substrate 1 can be etched first to form a groove on the substrate 1, and then several layers of Bragg reflection layers can be formed in the groove based on the existing Bragg reflection layer formation process. It should be understood that if the acoustic mirror 5 is an air cavity, the bulk acoustic wave resonator in this embodiment essentially belongs to a Film Bulk Acoustic Resonator (FBAR). If the acoustic mirror 5 is a Bragg reflection layer, the bulk acoustic wave resonator in this embodiment essentially belongs to a Solid Mounted Resonator (SMR). A first groove 6 is provided on the piezoelectric layer 3 in this embodiment. Since the difference in acoustic impedance between the region where the first groove 6 is located and the region outside the first groove 6 is large, and under the action of this acoustic impedance difference, the acoustic wave will encounter obstacles and be reflected when entering the region outside the first groove 6 from the region where the first groove 6 is located. Therefore, in this embodiment, the acoustic wave leakage amount can be reduced by forming the first groove 6 on the piezoelectric layer 3 to reduce energy leakage. It should be understood that if the edge of the projection of the first groove 6 in the top view direction exceeds the edge of the projection of the acoustic mirror 5 in the top view direction, the acoustic wave will leak from the region where the first groove 6 exceeds the edge of the projection of the acoustic mirror 5 in the top view direction. At this time, the quality factor and parallel resonance impedance of the bulk acoustic wave resonator cannot be improved by reducing the acoustic wave leakage amount. Therefore, in this embodiment, it is necessary to make the edge of the projection of the first groove 6 in the top view direction not exceed the edge of the projection of the acoustic mirror 5 in the top view direction.Based on the same principle as the first groove 6, the second groove 7 in this embodiment serves to reduce acoustic wave leakage. Therefore, this embodiment can further reduce the acoustic wave leakage amount and energy leakage by providing the second groove 7 on the top electrode 4, that is, this embodiment is equivalent to performing secondary constraint on the acoustic wave by providing the first groove 6 and the second groove 7.

[0040] A bulk acoustic wave resonator provided in this application can reduce the acoustic wave leakage amount and energy leakage by forming the first groove 6 on the piezoelectric layer 3 and forming the second groove 7 on the top electrode 4. That is, this application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art. That is, this application can improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, this application can effectively solve the problems that due to the morphological defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external connection part of the top electrode 4 decreases due to the loss of support of the external connection part of the top electrode 4.

[0041] In some preferred embodiments, as Figures 3 - 7 shown, the piezoelectric layer 3 has a step group. The step group is located in the first groove 6. The step group includes at least one step portion 8. The height of the step portion 8 is less than the depth of the first groove 6. When the number of step portions 8 is multiple, the multiple step portions 8 are distributed inside and outside with the center of the piezoelectric layer 3 as the center and are arranged at intervals (refer to Figure 7 ). Due to the acoustic impedance difference between the region where the step portion 8 is located and the region outside the step portion 8, under the action of this acoustic impedance difference, the step portion 8 can play a role in hindering and reflecting the lateral transmission of the acoustic wave. Therefore, this embodiment is equivalent to increasing the number of reflections and the amount of reflection of the acoustic wave by providing the step group in the first groove 6, thereby effectively improving the suppression effect of acoustic wave leakage and further reducing the acoustic wave leakage amount and energy leakage, and further improving the quality factor and parallel resonance impedance of the bulk acoustic wave resonator. It should be understood that the step group in this embodiment is a part of the piezoelectric layer 3. The more the number of step groups, the better the suppression effect of acoustic wave leakage, and the higher the production difficulty and production cost of the step group. Therefore, those skilled in the art can change the number of step portions 8 included in the step group according to the actual suppression effect, production difficulty and production cost requirements. Preferably, the number of step portions 8 in this embodiment is less than or equal to three to avoid the situation that the resonator frequency of the bulk acoustic wave resonator is affected due to too many step portions 8. It should also be understood that those skilled in the art can adjust the length, width and / or height of the step portion 8 according to the performance requirements of the bulk acoustic wave resonator.

[0042] In some preferred embodiments, the minimum distance between the stepped portion 8 and the top of the piezoelectric layer 3 is greater than the minimum distance between the top of the stepped portion 8 and the bottom of the first groove 6. This embodiment can improve the acoustic wave leakage suppression effect of the stepped portion 8 by making the minimum distance between the stepped portion 8 and the top of the piezoelectric layer 3 greater than the minimum distance between the top of the stepped portion 8 and the bottom of the first groove 6. Therefore, this embodiment can further reduce the acoustic wave leakage amount and energy leakage.

[0043] In some preferred embodiments, referring to Figure 3 and Figure 4 , the stepped portion 8 is an annular structure, and the outermost stepped portion 8 is in contact with the side wall of the first groove 6. The stepped portion 8 of this embodiment is preferably a polygonal ring structure, that is, the cross-sectional shape of the stepped portion 8 is polygonal. Since the stepped portion 8 of this embodiment is an annular structure, that is, the stepped portion 8 of this embodiment can suppress acoustic wave leakage in all directions, so this embodiment can make the acoustic wave leakage suppression effect of the stepped portion 8 reach the best.

[0044] In some preferred embodiments, the top electrode 4 has at least one external connection portion, and the stepped portion 8 is arranged on one side of the first groove 6 close to the external connection portion. The top electrode 4 of this embodiment has at least one external connection portion, and this external connection portion extends to the area outside the acoustic mirror 5. Since acoustic wave leakage usually occurs at the external connection portion of the top electrode 4, and the stepped portion 8 is arranged on one side of the first groove 6 close to the external connection portion (refer to Figure 5 and Figure 6 ), so this embodiment can reduce the coverage area of the stepped portion 8 while ensuring the acoustic wave leakage suppression effect, thereby effectively reducing the production difficulty and production cost of the stepped portion 8, and further effectively reducing the production difficulty and production cost of the bulk acoustic wave resonator.

[0045] In some preferred embodiments, the bulk acoustic wave resonator further includes a passivation layer 9, and the passivation layer 9 is arranged above the top electrode 4. The material of the passivation layer 9 of this embodiment can be aluminum nitride, silicon dioxide or nitrogen dioxide. Since the passivation layer 9 of this embodiment is arranged above the top electrode 4, the passivation layer 9 can protect the top electrode 4. Therefore, this embodiment can effectively avoid the situation that the top electrode 4 is oxidized, corroded or contaminated due to the contact between the top electrode 4 and the external environment, so that the top electrode 4 can maintain good electrical conductivity and structural integrity, thereby effectively improving the stability of the bulk acoustic wave resonator and extending the service life of the bulk acoustic wave resonator.

[0046] In some preferred embodiments, the ratio of the depth of the first groove 6 to the thickness of the piezoelectric layer 3 is 5% - 30%. This embodiment can effectively avoid the situation where the improvement effect of the quality factor of the bulk acoustic wave resonator is limited due to the first groove 6 being too shallow and the resonator frequency and effective electromechanical coupling coefficient of the bulk acoustic wave resonator being significantly affected due to the first groove 6 being too deep by setting the ratio of the depth of the first groove 6 to the thickness of the piezoelectric layer 3 to 5% - 30%.

[0047] As can be seen from the above, a bulk acoustic wave resonator provided by the present application can reduce the acoustic wave leakage and energy leakage by forming the first groove 6 on the piezoelectric layer 3 and the second groove 7 on the top electrode 4. That is, the present application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art. That is, the present application can improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problems that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external connection part of the top electrode 4 decreases due to the loss of support of the external connection part of the top electrode 4.

[0048] Second, as Figures 8 - 11 shown, the present application also provides a method for manufacturing a bulk acoustic wave resonator, which includes the following steps: S1. Form a cavity on the substrate 1 and form an acoustic mirror 5 in the cavity; S2. Sequentially form a bottom electrode 2, a piezoelectric layer 3, and a first patterned photoresist layer 10 on the substrate 1. The inner boundary of the projection of the first patterned photoresist layer 10 in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction; S3. Etch the piezoelectric layer 3 based on the first patterned photoresist layer 10 to form a first groove 6 on the piezoelectric layer 3, the edge of the projection of which in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction; S4. Remove the first patterned photoresist layer 10; S5. Sequentially form a top electrode 4 and a second patterned photoresist layer 11 on the piezoelectric layer 3. The inner boundary of the projection of the second patterned photoresist layer 11 in the top view direction is located at the edge of the projection of the first groove 6 in the top view direction; S6. Etch the top electrode 4 based on the second patterned photoresist layer 11 to form a second groove 7 on the top electrode 4, the edge of the projection of which in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction.

[0049] Step S1 can etch the substrate 1 using an existing etching process to form a cavity on the substrate 1. Step S1 can form the acoustic mirror 5 in the cavity using an existing acoustic mirror 5 forming process. It should be understood that if the acoustic mirror 5 is an air cavity, then step S1 fills the cavity with a sacrificial layer and releases the sacrificial layer after performing step S5.

[0050] Step S2 can sequentially form the bottom electrode 2 and the piezoelectric layer 3 on the substrate 1 by sequentially depositing an electrode material and a piezoelectric material on the substrate 1. Step S2 can form a first patterned photoresist layer 10 on the piezoelectric layer 3 using an existing photoresist layer forming process. The first patterned photoresist layer 10 has an opening, and the inner boundary of the projection of the first patterned photoresist layer 10 in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction, that is, the edge of the projection of the opening of the first patterned photoresist layer 10 in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction, so as to ensure that the edge of the projection of the formed first groove 6 in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction. It should be understood that the shape of the opening in this embodiment is the same as the shape of the first groove 6.

[0051] Step S3 can etch the piezoelectric layer 3 based on the first patterned photoresist layer 10 using an existing RIE technology (Reactive Ion Etching technology) to form a first groove 6 whose projection edge in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction. Step S4 can remove the first patterned photoresist layer 10 using an existing photoresist removal process.

[0052] Step S5 can deposit an electrode material on the piezoelectric layer 3 using an existing physical deposition process or chemical deposition process to form a top electrode 4 on the piezoelectric layer 3. Step S5 can form a second patterned photoresist layer 11 on the top electrode 4 using an existing photoresist layer forming process. The second patterned photoresist layer 11 has an opening, and the inner boundary of the projection of the second patterned photoresist layer 11 in the top view direction is located at the edge of the projection of the first groove 6 in the top view direction, that is, the edge of the projection of the opening of the second patterned photoresist layer 11 in the top view direction is located inside the edge of the projection of the first groove 6 in the top view direction, so as to ensure that the edge of the projection of the formed second groove 7 in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction. Step S6 can etch the top electrode 4 based on the second patterned photoresist layer 11 using an existing RIE technology to form a second groove 7 whose projection edge in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction.

[0053] A method for manufacturing a bulk acoustic resonator provided in this embodiment is preferably used to manufacture the bulk acoustic wave resonator provided in the first aspect above. The principle of the method for manufacturing a bulk acoustic resonator provided in this embodiment is the same as that of the bulk acoustic wave resonator provided in the first aspect above, and will not be described in detail here.

[0054] In some preferred embodiments, the method for manufacturing a bulk acoustic wave resonator further includes a step performed between step S2 and step S3: A1. Surface-treat the first patterned photoresist layer 10 and the piezoelectric layer 3 with oxygen.

[0055] In this embodiment, by surface-treating the first patterned photoresist layer 10 and the piezoelectric layer 3 with oxygen, the sidewalls of the first patterned photoresist layer 10 and the exposed surface of the piezoelectric layer 3 can have good morphologies. Therefore, in this embodiment, by surface-treating the first patterned photoresist layer 10 and the piezoelectric layer 3 before etching the piezoelectric layer 3, the first groove 6 formed on the piezoelectric layer 3 can have a good morphology (refer to Figure 10 and Figure 11 , the morphology of the first groove 6 after surface-treatment with oxygen is better than that of the first groove 6 without surface-treatment with oxygen), thereby effectively avoiding the situation where the first groove 6 cannot fully play the role of reducing energy leakage due to the morphological defects of the first groove 6. Preferably, between step S5 and step S6, this embodiment also surface-treats the second patterned photoresist layer 11 and the top electrode 4 with oxygen.

[0056] In some preferred embodiments, step S3 includes: S31. Etch the piezoelectric layer 3 based on the first patterned photoresist layer 10 using the TRIM technique to form a first groove 6 whose edge of the projection in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction on the piezoelectric layer 3; Step S6 includes: S61. Etch the top electrode 4 based on the second patterned photoresist layer 11 using the TRIM technique to form a second groove 7 whose edge of the projection in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction on the top electrode 4.

[0057] In this embodiment, the piezoelectric layer 3 is etched based on the first patterned photoresist layer 10 using the TRIM technique (ion milling etching technique). Since the TRIM technique has the advantage of high etching accuracy, this embodiment can enable both the formed first groove 6 and second groove 7 to have precise depths and low surface roughness, thereby effectively improving the suppression effect of the first groove 6 and second groove 7 on acoustic wave leakage, and further improving the quality factor and parallel resonance impedance of the bulk acoustic wave resonator. Preferably, this embodiment selects a mixed gas of argon and sulfur hexafluoride as the etching gas. The ratio of the flow rate of argon to the flow rate of sulfur hexafluoride in this embodiment is preferably 1:5 - 1:3, and the pressure of the etching gas in this embodiment is preferably 5 - 10 mt.

[0058] In some preferred embodiments, step S2 includes: S21. A bottom electrode 2, a piezoelectric layer 3, a protective layer 12, and a first patterned photoresist layer 10 are sequentially formed on the substrate 1. The inner boundary of the projection of the first patterned photoresist layer 10 in the top view direction is located at the edge of the projection of the acoustic mirror 5 in the top view direction; Step S3 includes: S31’. Based on the first patterned photoresist layer 10, the piezoelectric layer 3 and the protective layer 12 are etched to form a first groove 6 on the piezoelectric layer 3, the edge of whose projection in the top view direction does not exceed the edge of the projection of the acoustic mirror 5 in the top view direction; Step S4 includes: S41. The first patterned photoresist layer 10 and the protective layer 12 are removed.

[0059] The material of the protective layer 12 in this embodiment is preferably silicon dioxide. The protective layer 12 in this embodiment can prevent the piezoelectric layer 3 from being corroded by the first patterned photoresist layer 10. Therefore, this embodiment can effectively avoid the situation where the piezoelectric layer 3 has morphological defects due to being corroded by the first patterned photoresist layer 10.

[0060] As can be seen from the above, a method for manufacturing a bulk acoustic wave resonator provided by the present application can reduce the acoustic wave leakage amount and energy leakage by forming a first groove 6 on the piezoelectric layer 3 and a second groove 7 on the top electrode 4. That is, the present application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art. That is, the present application can improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problems that due to the morphological defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external connection part of the top electrode 4 decreases due to the loss of support of the external connection part of the top electrode 4.

[0061] As can be seen from the above, a bulk acoustic wave resonator and a preparation method thereof provided by the present application can reduce the acoustic wave leakage and energy leakage by forming a first groove 6 on the piezoelectric layer 3 and a second groove 7 on the top electrode 4. That is, the present application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art. That is, the present application can improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problems that due to the morphological defects of the air gap, the air gap cannot fully play the role of reducing energy leakage, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external connection part of the top electrode 4 is reduced due to the loss of support of the external connection part of the top electrode 4.

[0062] In the embodiments provided by the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are only illustrative. For example, the above division of units is only a logical function division. In actual implementation, there may be other division methods. For another example, multiple units or components can be combined or integrated into another robot, or some features can be ignored or not executed. Another point is that the displayed or discussed mutual coupling or direct coupling or communication connection can be through some communication interfaces. The indirect coupling or communication connection of the device or unit can be in electrical, mechanical or other forms.

[0063] In addition, the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be raised to one place, or they can be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0064] Furthermore, in each embodiment of the present application, the functional modules can be integrated together to form an independent part, or each module can exist alone, or two or more modules can be integrated to form an independent part.

[0065] In this article, relational terms such as first and second are only 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.

[0066] The above description is only for the embodiments 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 can have various changes and modifications. 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 bulk acoustic wave resonator comprises: A substrate, a bottom electrode, a piezoelectric layer and a top electrode are connected in sequence from bottom to top, and an acoustic reflector is arranged on the substrate; A first groove is provided on the piezoelectric layer, and the edge of the projection of the first groove in the top-view direction does not exceed the edge of the projection of the acoustic reflector in the top-view direction. A second groove is provided on the top electrode, and the edge of the projection of the second groove in the top-view direction does not exceed the edge of the projection of the first groove in the top-view direction.

2. The bulk acoustic wave resonator according to claim 1, characterized in that The piezoelectric layer has a step group, which is located in the first groove. The step group includes at least one step portion, and the height of the step portion is less than the depth of the first groove. When there are multiple step portions, the multiple step portions are distributed inside and outside the center of the piezoelectric layer and are spaced apart.

3. The bulk acoustic wave resonator according to claim 2, characterized in that: The minimum distance between the step portion and the top of the piezoelectric layer is greater than the minimum distance between the top of the step portion and the bottom of the first groove.

4. The bulk acoustic wave resonator according to claim 2, characterized in that: The step portion is an annular structure, and the outermost step portion is in contact with the side wall of the first groove.

5. The bulk acoustic wave resonator according to claim 2, characterized in that: The top electrode has at least one external connection portion, and the step portion is arranged in the first groove on one side close to the external connection portion.

6. The bulk acoustic wave resonator according to claim 1, characterized in that The BAW resonator further includes a passivation layer disposed over the top electrode.

7. 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 a cavity on a substrate, and forming an acoustic reflection mirror in the cavity; S2, forming a bottom electrode, a piezoelectric layer and a first patterned photoresist layer in sequence on the substrate, wherein the inner boundary of the projection of the first patterned photoresist layer in the top-view direction does not exceed the edge of the projection of the acoustic reflector in the top-view direction; S3, etching the piezoelectric layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which projection in the top view direction does not exceed the edge of the projection of the acoustic reflector in the top view direction; S4, removing the first patterned photoresist layer; S5, sequentially forming a top electrode and a second patterned photoresist layer on the piezoelectric layer, wherein an inner boundary of a projection of the second patterned photoresist layer in a top-view direction is located at an edge of a projection of the first groove in a top-view direction; S6. Etching the top electrode based on the second patterned photoresist layer to form a second groove on the top electrode, the edge of which projection in the top-view direction does not exceed the edge of the projection of the first groove in the top-view direction.

8. The method for preparing a bulk acoustic wave resonator according to claim 7, characterized in that: The method for preparing a bulk acoustic wave resonator further includes a step performed between step S2 and step S3: A1. Surface treatment is performed on the first patterned photoresist layer and the piezoelectric layer using oxygen.

9. The method for preparing a bulk acoustic wave resonator according to claim 7, characterized in that: Step S3 includes: S31, etching the piezoelectric layer by using the TRIM technology based on the first patterned photoresist layer, so as to form a first groove on the piezoelectric layer, the edge of which projection in the top-view direction does not exceed the edge of the projection of the acoustic reflector in the top-view direction; Step S6 includes: S61. Etching the top electrode using the TRIM technology based on the second patterned photoresist layer to form a second groove on the top electrode, the edge of which projection in the top-view direction does not exceed the edge of the projection of the first groove in the top-view direction.

10. The method for preparing a bulk acoustic wave resonator according to claim 7, characterized in that: Step S2 includes: S21, forming a bottom electrode, a piezoelectric layer, a protective layer and a first patterned photoresist layer in sequence on the substrate, wherein an inner boundary of a projection of the first patterned photoresist layer in a top-view direction is located at an edge of a projection of the acoustic reflector in a top-view direction; Step S3 includes: S31', etching the piezoelectric layer and the protective layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which projection in the top view direction does not exceed the edge of the projection of the acoustic reflector in the top view direction; Step S4 includes: S41, removing the first patterned photoresist layer and the protective layer.

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