CN111669141A - Electrode structure of bulk acoustic wave resonator and manufacturing process - Google Patents
Electrode structure of bulk acoustic wave resonator and manufacturing process Download PDFInfo
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- H—ELECTRICITY
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- H—ELECTRICITY
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Abstract
The invention discloses an electrode structure of a bulk acoustic wave resonator and a manufacturing process thereof, and the electrode structure comprises a bottom electrode layer, a piezoelectric layer and a top electrode layer which are sequentially formed in a stacking manner, wherein an acoustic wave reflection blocking edge covering at least one side edge of the top electrode layer is formed on the piezoelectric layer, the acoustic wave reflection blocking edge extends from the side edge of the top electrode layer to the top edge of the top electrode layer to form a mass loading layer, and the projection area of the outer edge of the acoustic wave reflection blocking edge on the piezoelectric layer is completely positioned in the area range of the bottom electrode layer. The acoustic wave reflection barrier edge formed by the high and low acoustic impedance at the edge of the top electrode layer alternately reflects transverse waves, so that the transverse waves are prevented from leaking from the edge of the resonator and taking away energy, and the performance of the device is improved. Preferably, the sound wave reflection blocking edge is manufactured through a simple process, and meanwhile, the mass loading layer and the connecting portion of the top electrode which is electrically connected with other resonators can be formed.
Description
Technical Field
The application relates to the field of communication devices, in particular to an electrode structure of a bulk acoustic wave resonator and a manufacturing process thereof.
Background
With the increasing crowding of electromagnetic spectrum and the increase of frequency bands and functions of wireless communication equipment, the electromagnetic spectrum used for wireless communication increases at a high speed from 500MHz to more than 5GHz, and the demand for a radio frequency front-end module with high performance, low cost, low power consumption and small size also increases increasingly. The filter is one of radio frequency front end modules, can improve transmitting and receiving signals and is mainly formed by connecting a plurality of resonators through a topological network structure. Fbar (thin film bulk acoustic resonator) is a bulk acoustic wave resonator, and a filter formed by the bulk acoustic wave resonator has the advantages of small volume, strong integration capability, high quality factor Q guarantee during high-frequency operation, strong power bearing capability and the like and is used as a core device of a radio frequency front end.
Fbar is a basic structure consisting of upper and lower electrodes and a piezoelectric layer sandwiched between the electrodes. The piezoelectric layer mainly realizes the conversion of electric energy and mechanical energy. When the upper and lower electrodes of Fbar apply electric field, the piezoelectric layer converts the electric energy into mechanical energy, and the mechanical energy exists in the form of sound wave. The acoustic wave has two vibration modes of transverse wave and longitudinal wave, the longitudinal wave is the main mode in the Fbar working state, and the transverse wave is easy to leak from the edge of the resonator to take away energy. The Q value is an important measure of the performance of a resonator and is equal to the ratio of the energy stored in the resonator to the energy lost from the resonator. Therefore, the energy taken away by the transverse wave inevitably attenuates the Q value, so that the performance of the device is reduced.
In the prior art, the piezoelectric layer of the bulk acoustic wave resonator is not flat, and a special design structure of the top electrode layer is required to make up for the defects caused by the non-flat piezoelectric layer, so that the top electrode layer needs to be isolated from the piezoelectric layer at the edge and a cavity is formed to reflect transverse waves, but the film layer above the cavity is easy to collapse and the like.
Therefore, the invention aims to design an improved electrode structure of the bulk acoustic wave resonator, thereby avoiding energy loss caused by leakage of transverse waves from the edge of the resonator and improving the performance of the device.
Disclosure of Invention
The method aims at the problems that the conventional bulk acoustic wave resonator structure can take away energy of transverse waves and attenuate a Q value, so that the performance of a device is reduced and the like. The present application proposes an electrode structure of a bulk acoustic wave resonator and a manufacturing process to solve the above existing problems.
In a first aspect, an embodiment of the present application provides an electrode structure of a bulk acoustic wave resonator, including a bottom electrode layer, a piezoelectric layer, and a top electrode layer, which are sequentially stacked, where an acoustic wave reflection edge that covers at least one side edge of the top electrode layer is formed on the piezoelectric layer, the acoustic wave reflection edge extends from the side edge of the top electrode layer to a top edge of the top electrode layer to form a mass loading layer, and a projection area of an outer edge of the acoustic wave reflection edge on the piezoelectric layer is completely located within an area range of the bottom electrode layer. The acoustic wave reflection barrier edge formed by the high and low acoustic impedance at the edge of the top electrode layer alternately reflects transverse waves, so that the transverse waves are prevented from leaking from the edge of the resonator and taking away energy, and the performance of the device is improved. And the mass load layer can cause acoustic impedance mutation so as to reflect transverse waves, inhibit the transverse waves from taking away energy and improve the Q value.
In some embodiments, the acoustic reflection rims comprise a combination of at least one set of low acoustic impedance reflection rims and high acoustic impedance reflection rims stacked alternately. The transverse wave is reflected by the composite thin film layer with alternating high and low acoustic impedance close to or covered on the edge of the top electrode, one part of the reflected transverse wave is converted into longitudinal wave, and the other part of the reflected transverse wave is trapped in the resonator, so that the phenomenon that the energy leakage of the transverse wave at the edge of the resonator causes the Q value attenuation is avoided, and the device performance is improved.
In some embodiments, the reflective ledge closest to the edge of the top electrode layer is a low acoustic impedance reflective ledge. A low high impedance difference can be created along the edge of the top electrode layer, resulting in acoustic wave reflection.
In some embodiments, the low acoustic impedance reflection ledge and the high acoustic impedance reflection ledge are both formed of a metallic material. The sound wave reflection edge made of the low-high sound impedance metal material can have a good sound wave reflection effect on the one hand, and can also directly realize the electric connection between the two resonators, so that the insertion loss of the filter is prevented from being influenced by the connection effect.
In some embodiments, the acoustic wave reflecting rim extends outward on the piezoelectric layer of the front bulk acoustic wave resonator to form an electrode connection. The acoustic wave reflecting barrier edges are all made of metal materials and have good conductivity, so that the acoustic wave reflecting barrier edges can be extended to serve as electrode connecting parts to be directly electrically connected with the electrode layers of the two resonators.
In some embodiments, the low acoustic impedance reflective ledge is formed from a dielectric material and the high acoustic impedance reflective ledge is formed from a metallic material. The acoustic impedance of the dielectric material is low, and the acoustic impedance of the metal material is high, so that the acoustic wave reflection edge combined by the dielectric material and the metal material has a better acoustic wave reflection effect, and can reflect transverse waves. In some embodiments, a portion of the high acoustic impedance reflection rib at one end of the acoustic wave reflection rib extends to the top of the top electrode layer of the bulk acoustic wave resonator and is electrically connected with the top electrode layer to form a first electrode connection portion, and the other end of the acoustic wave reflection rib extends outward on the piezoelectric layer of the bulk acoustic wave resonator to form a second electrode connection portion. When the low acoustic impedance reflection rib is formed of a dielectric material, it is necessary to electrically connect the high acoustic impedance reflection rib formed of a metal material to the top electrode layer extending to the top of the top electrode layer to achieve electrical connection with another bulk acoustic wave resonator, and also to simultaneously form a mass loading layer on the top of the top electrode layer, because the electrical conductivity of the dielectric material is low.
In a second aspect, an embodiment of the present application further provides a bulk acoustic wave resonator, which includes the electrode structure according to the first aspect, and the bulk acoustic wave resonator further includes a substrate having a cavity, the electrode structure is formed on the substrate, and an adjacent barrier layer and a dielectric layer are formed around the bottom electrode layer, and surfaces of the barrier layer and the dielectric layer are flat with a surface of the bottom electrode layer.
In some embodiments, the piezoelectric layer is formed on the surfaces of the barrier layer, the dielectric layer, and the bottom electrode layer such that the piezoelectric layer does not contact the substrate. The piezoelectric layer is formed above the barrier layer and the dielectric layer with flat surfaces, so that the stress consistency of the piezoelectric layer can be improved, the stress influence of the piezoelectric layer is reduced, the electromechanical coupling system number of the device is controlled in an optimal range, and the quality factor of the resonator, the yield of the device and the consistency and reliability of a finished product of the device are improved.
In some embodiments, the bulk acoustic wave resonator further comprises a release hole extending into the cavity without passing through the bottom and top electrode layers. The release holes are used to remove the sacrificial material within the cavity.
In some embodiments, a protective layer is formed in the release holes covering sidewalls of the release holes. The protective layer can effectively protect the dielectric layer from being corroded by an etchant HF used when the cavity is released.
In some embodiments, a support layer is formed between the bottom electrode layer and the substrate. The PVD process forms a support layer overlying the substrate and sacrificial material to protect the bottom electrode layer.
In some embodiments, the projected area of the bottom electrode layer on the substrate is entirely within the cavity. Due to the existence of the supporting layer, the bottom electrode layer can be manufactured in the cavity and cannot collapse in the cavity.
In a third aspect, an embodiment of the present application further provides a process for manufacturing an electrode structure of a bulk acoustic wave resonator, including the following steps:
s1, etching the top electrode layer in the resonance function layer formed by sequentially laminating the bottom electrode layer, the piezoelectric layer and the top electrode layer to expose part of the piezoelectric layer;
s2, manufacturing an acoustic wave reflection edge wrapping at least one side edge of the top electrode layer on the piezoelectric layer, and manufacturing a mass loading layer on the top electrode layer at the same time, wherein the mass loading layer is formed by extending the acoustic wave reflection edge from the side edge of the top electrode layer to the top edge of the top electrode layer, and the projection area of the outer edge of the acoustic wave reflection edge on the piezoelectric layer is completely located in the area range of the bottom electrode layer.
The acoustic wave reflection barrier edge formed by alternately high and low acoustic impedance is manufactured at the edge of the top electrode layer to reflect transverse waves, so that the transverse waves are prevented from leaking from the edge of the resonator and taking away energy, and the performance of the device is improved. And the mass load layer can cause acoustic impedance mutation so as to reflect transverse waves, inhibit the transverse waves from taking away energy and improve the Q value.
In some embodiments, the acoustic reflection rims comprise a combination of at least one set of low acoustic impedance reflection rims and high acoustic impedance reflection rims stacked alternately. The transverse wave is reflected by the composite thin film layer with alternating high and low acoustic impedance close to or covered on the edge of the top electrode, one part of the reflected transverse wave is converted into longitudinal wave, and the other part of the reflected transverse wave is trapped in the resonator, so that the phenomenon that the energy leakage of the transverse wave at the edge of the resonator causes the Q value attenuation is avoided, and the device performance is improved.
In some embodiments, the reflective ledge closest to the edge of the top electrode layer is a low acoustic impedance reflective ledge. Therefore, the influence of the acoustic wave reflection barrier edge on the use of the top electrode layer can be avoided.
In some embodiments, the low acoustic impedance reflection ledge and the high acoustic impedance reflection ledge are both formed of a metallic material. The sound wave reflection blocking edge made of the metal material has good connection effect, and the insertion loss of the filter is prevented from being influenced by the connection effect.
In some embodiments, step S2 further includes: and meanwhile, an electrode connecting part formed by extending the acoustic wave reflecting barrier edge outwards is manufactured on the piezoelectric layer on one side of the front bulk acoustic wave resonator. The acoustic wave reflecting barrier edges are all made of metal materials and have good conductivity, so that the acoustic wave reflecting barrier edges can be extended to serve as electrode connecting parts to be directly electrically connected with the electrode layers of the two resonators.
In some embodiments, the low acoustic impedance reflective ledge is formed from a dielectric material and the high acoustic impedance reflective ledge is formed from a metallic material. The sound wave reflection barrier edge combined by the medium material and the metal material has better sound wave reflection effect.
In some embodiments, the sound wave reflecting barrier step S2 further includes: and simultaneously, a first electrode connecting part electrically connected with the top electrode layer is formed by extending part of the high acoustic impedance reflection edge at one end of the acoustic wave reflection edge on the top of the top electrode layer of the bulk acoustic wave resonator, and a second electrode connecting part formed by extending the other end of the acoustic wave reflection edge outwards is formed on the piezoelectric layer of the bulk acoustic wave resonator. When the low acoustic impedance reflection rib is formed of a dielectric material, it is necessary to electrically connect the high acoustic impedance reflection rib formed of a metal material to the top electrode layer extending to the top of the top electrode layer due to low electrical conductivity of the dielectric material, to finally achieve electrical connection to another bulk acoustic wave resonator, and also to simultaneously form a mass loading layer on top of the top electrode layer. The second electrode connection part may be connected as a lead wire to other resonators or a signal source lead-in, etc.
In a fourth aspect, an embodiment of the present application further provides a process for manufacturing a bulk acoustic wave resonator, including the process for manufacturing the electrode structure of the bulk acoustic wave resonator according to the third aspect, including the following steps:
s3, forming a cavity on the substrate;
s4, filling sacrificial materials in the cavity;
s5, manufacturing a bottom electrode layer on the filled cavity;
s6, sequentially applying a barrier layer and a dielectric layer around the bottom electrode layer to ensure that the surface of a composite layer formed by the barrier layer and the dielectric layer and the surface of the bottom electrode layer are kept flat; and
s7, fabricating a piezoelectric layer on the surface of the composite layer and the bottom electrode layer such that the piezoelectric layer does not contact the substrate.
In some embodiments, the method further comprises step S8: a top electrode layer is fabricated on the piezoelectric layer. The top electrode layer is manufactured through PVD, photoetching and etching processes, and forms an effective resonance area with the bottom electrode layer and the piezoelectric layer.
In some embodiments, the method further comprises step S9: release holes are made alongside the top and bottom electrode layers, the release holes penetrating from the top into the sacrificial material within the cavity. The release holes are used to remove the sacrificial material within the cavity.
In some embodiments, the method further comprises step S10: and manufacturing a protective layer, wherein the protective layer covers the side wall of the release hole. The protective layer can effectively protect the dielectric layer from being corroded by an etchant HF used when the cavity is released.
In some embodiments, the method further comprises, between steps S4 and S5: a support layer made of an aluminum nitride material is formed on a substrate. The support layer can realize that the bottom electrode layer and the piezoelectric layer have good C-axis orientation, and can play a supporting role to enable the projection area of the bottom electrode layer on the substrate to be completely positioned in the cavity.
In some embodiments, the projected area of the bottom electrode layer on the substrate is entirely within the cavity. Due to the existence of the support layer, the bottom electrode layer can be manufactured in the cavity and cannot collapse in the cavity.
The embodiment of the application provides an electrode structure of a bulk acoustic wave resonator and a manufacturing process, the electrode structure comprises a bottom electrode layer, a piezoelectric layer and a top electrode layer which are sequentially stacked, an acoustic wave reflection blocking edge covering at least one side edge of the top electrode layer is formed on the piezoelectric layer, the acoustic wave reflection blocking edge extends from the side edge of the top electrode layer to the top edge of the top electrode layer to form a mass load layer, and the projection area of the outer edge of the acoustic wave reflection blocking edge on the piezoelectric layer is completely located in the area range of the bottom electrode layer. The acoustic wave reflection barrier edge formed by high and low acoustic impedance close to or covering the edge of the top electrode layer alternately reflects transverse waves, one part of the reflected transverse waves are converted into longitudinal waves, and the other part of the reflected transverse waves are trapped in the resonator, so that the transverse waves are prevented from leaking from the edge of the resonator and taking away energy, and the performance of the device is improved. The mass loading layer can be manufactured and formed while the sound wave reflection blocking edge is manufactured, and the mass loading layer can be used as an electrical connection part between the top electrode layer and other resonators while the sound wave reflection blocking edge is manufactured, so that the process is simple.
Drawings
The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain the principles of the invention. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
Fig. 1 shows a flow chart of a process for fabricating an electrode structure of a bulk acoustic wave resonator according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an electrode structure and a bulk acoustic wave resonator manufactured by a process for manufacturing the electrode structure of the bulk acoustic wave resonator according to a first embodiment of the present invention;
fig. 3 is a flowchart illustrating a process of manufacturing a bulk acoustic wave resonator according to a first embodiment of the present invention;
4a-4o are schematic structural diagrams illustrating a manufacturing process of a bulk acoustic wave resonator according to a first embodiment of the invention;
fig. 5 is a schematic structural diagram of a bulk acoustic wave resonator according to a second embodiment of the present invention;
fig. 6 shows a schematic structural diagram of a bulk acoustic wave resonator according to a third embodiment of the present invention;
fig. 7 shows a schematic structural diagram of a bulk acoustic wave resonator according to a fourth embodiment of the present invention.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be noted that, for convenience of description, only the portions related to the related invention are shown in the drawings. It should be noted that the dimensions and sizes of the elements in the figures are not to scale and the sizes of some of the elements may be highlighted for clarity of illustration.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
The invention provides an electrode structure of a bulk acoustic wave resonator, which comprises a bottom electrode layer, a piezoelectric layer and a top electrode layer which are sequentially formed in a stacking mode, wherein an acoustic wave reflection blocking edge wrapping at least one side edge of the top electrode layer is formed on the piezoelectric layer, the acoustic wave reflection blocking edge extends from the side edge of the top electrode layer to the top edge of the top electrode layer to form a mass loading layer, and the projection area of the outer edge of the acoustic wave reflection blocking edge on the piezoelectric layer is completely located in the area range of the bottom electrode layer. The acoustic wave reflection barrier edge formed by the high and low acoustic impedance at the edge of the top electrode layer alternately reflects transverse waves, so that the transverse waves are prevented from leaking from the edge of the resonator and taking away energy, and the performance of the device is improved.
Correspondingly, the embodiment of the present application further provides a manufacturing process of an electrode structure of a bulk acoustic wave resonator, as shown in fig. 1, including the following steps:
s1, etching the top electrode layer in the resonance function layer formed by sequentially laminating the bottom electrode layer, the piezoelectric layer and the top electrode layer to expose part of the piezoelectric layer;
s2, manufacturing an acoustic wave reflection edge wrapping at least one side edge of the top electrode layer on the piezoelectric layer, and manufacturing a mass loading layer on the top electrode layer at the same time, wherein the mass loading layer is formed by extending the acoustic wave reflection edge from the side edge of the top electrode layer to the top edge of the top electrode layer, and the projection area of the outer edge of the acoustic wave reflection edge on the piezoelectric layer is completely located in the area range of the bottom electrode layer.
Example one
According to the electrode structure and the manufacturing process of the bulk acoustic wave resonator, the invention also correspondingly provides a bulk acoustic wave resonator and a manufacturing process, the structure of the bulk acoustic wave resonator is as shown in fig. 2, the bulk acoustic wave resonator comprises the electrode structure, the bulk acoustic wave resonator further comprises a substrate 101 with a cavity 201, the electrode structure is formed on the substrate 101, a barrier layer 501 and a dielectric layer 601 which are adjacent are formed around a bottom electrode layer 401, and the surfaces of the barrier layer 501 and the dielectric layer 601 are kept flat with the surface of the bottom electrode layer 401.
In a particular embodiment, the piezoelectric layer 801 is formed on the surfaces of the barrier layer 501, the dielectric layer 601, and the bottom electrode layer 401 such that the piezoelectric layer 801 does not contact the substrate 101. The piezoelectric layer 801 is formed above the barrier layer 501 and the dielectric layer 601 with flat surfaces, so that the stress consistency of the piezoelectric layer 801 can be improved, the stress influence of the piezoelectric layer 801 can be reduced, the electromechanical coupling coefficient of a device is controlled in an optimal range, and the quality factor of a resonator, the yield of the device and the consistency and reliability of a finished product of the device are improved. In a preferred embodiment, the barrier layer 501 is a silicon nitride material and the dielectric layer 601 is a silicon dioxide material. The selection of the materials of the barrier layer 501 and the dielectric layer 601 is beneficial to subsequent processing processes such as grinding and etching, and can effectively protect the bottom electrode layer 401.
In an embodiment of the present application, a process for manufacturing a bulk acoustic wave resonator is further provided, as shown in fig. 3, the process for manufacturing an electrode structure of a bulk acoustic wave resonator includes the following steps:
s3, forming a cavity on the substrate;
s4, filling sacrificial materials in the cavity;
s5, manufacturing a bottom electrode layer on the filled cavity;
s6, sequentially applying a barrier layer and a dielectric layer around the bottom electrode layer to ensure that the surface of a composite layer formed by the barrier layer and the dielectric layer and the surface of the bottom electrode layer are kept flat; and
s7, fabricating a piezoelectric layer on the surface of the composite layer and the bottom electrode layer such that the piezoelectric layer does not contact the substrate.
The schematic diagram of the manufacturing process of the bulk acoustic wave resonator is shown in fig. 4a-4 o. In a specific embodiment, the cavity 201 is etched in the substrate 101 in step S3, and the cross-sectional view of the cavity 201 is shown in fig. 4 a. In a preferred embodiment, the substrate 101 material is Si and the height of the cavity 201 is 3-4 μm. The height and the shape of the specific cavity 2 can be adjusted according to the requirements of the device.
In a specific embodiment, the sacrificial material 301 deposited in step S4 is PSG (P-doped SiO)2) Or SiO2. In a preferred embodiment, the process further comprises the following steps between steps S4 and S5: the surface of the substrate 101 filled with the sacrificial material 301 is subjected to Chemical Mechanical Polishing (CMP). As shown in fig. 4b, the sacrificial material 301 on the surface of the substrate 101 can be removed by chemical mechanical polishing, so as to planarize the surfaces of the substrate 101 and the sacrificial material 301, wherein the height of the cavity 201 after chemical mechanical polishing is 2 μm in the preferred embodiment.
In a specific embodiment, between steps S4 and S5, further comprising: a support layer 901 is fabricated on a substrate 101. In a preferred embodiment, the support layer 901 is made of an aluminum nitride material. A support layer 901 is formed on the surfaces of the substrate 101 and the sacrificial material 301 after the chemical mechanical polishing, and the support layer 901 is formed by a PVD process and has a thickness of 10 to 50 nm. The support layer 901 can not only promote the C-axis orientation of the subsequent piezoelectric layer, but also play a certain supporting role in the resonance function layer.
In a specific embodiment, as shown in fig. 4c, the support layer 901 covers the cavity 201 completely, and the bottom electrode layer 401 is formed in the support layer 901. The overlaying of the support layer 901PVD over the substrate 101 and sacrificial material 301 may also enable good C-axis alignment of the bottom electrode layer 401. In a preferred embodiment, the bottom electrode layer 401 is formed within the support layer 901 and is located entirely within the area of the cavity 201. The projected area of the bottom electrode layer 401 on the substrate 101 is now completely within the cavity 201. Even if the sacrificial material 301 is removed in the subsequent process, because the support layer 901 exists, the projection region of the bottom electrode layer 401 on the substrate 101 is completely located in the cavity 201, the bottom electrode layer 401 does not lose support and collapse into the cavity 201, but under the support of the support layer 901, on the premise that the mechanical stability of the resonator is maintained, the bottom electrode layer 401 can be manufactured inside the cavity 201.
In a specific embodiment, the bottom electrode layer 401 is fabricated over the cavity 201 by PVD, photolithography and etching processes, wherein the material of the bottom electrode layer 401 is Mo. As shown in fig. 4d, the cross-section of the bottom electrode layer 401 in the direction perpendicular to the substrate 101 is rectangular as a whole. Therefore, the point discharge effect can be effectively reduced, and the defects of the device caused by static electricity in the preparation process can be reduced.
In a specific embodiment, as shown in fig. 4e-4g, step S6 specifically includes the following steps: growing a barrier layer 501 on and around the bottom electrode layer 401 by a CVD process, growing a dielectric layer 601 on the barrier layer 501, and grinding the dielectric layer 601 by a CMP process until the barrier layer 501 on the bottom electrode layer 401 is exposed, wherein in a preferred embodiment, the top of the ground dielectric layer 601 and the top of the bottom electrode layer 401 are on the same plane. As shown in fig. 4h, the barrier layer 501 on the bottom electrode layer 401 is removed by photolithography and etching processes. In a preferred embodiment, the etching process is a wet etch and the etchant is BOE (HF and NH)3F) and the surface of the bottom electrode layer 401 are on the same plane, so that the appearance of the piezoelectric layer 801 is less affected by the change of the stress. The barrier layer 501 protects the bottom electrode layer 401 from being damaged by the CMP process of the dielectric layer 601, and the dielectric layer 601 keeps the surface of the composite layer and the surface of the bottom electrode layer 401 flat, thereby improving the stress consistency of the piezoelectric layer 801 and controlling the electromechanical coupling coefficient of the device in an optimal range. Excellence inIn an alternative embodiment, the material of the barrier layer 501 is silicon nitride, and the material of the dielectric layer 601 is silicon dioxide. The design of the barrier layer 501 and the selection of the material of the barrier layer 501 are beneficial to the subsequent processing processes such as grinding and etching, and can effectively protect the bottom electrode layer 401 from being damaged.
In a specific embodiment, as shown in fig. 4i, in step S7, a piezoelectric layer 801 is formed on the surface of the composite layer and the bottom electrode layer 401 by PVD, photolithography and etching processes, wherein the material of the piezoelectric layer 801 may be selected from AlN.
In a specific embodiment, the method further includes step S8: a top electrode layer 1001 is fabricated on the piezoelectric layer 801. As shown in fig. 4j, a top electrode layer 1001 is fabricated on the piezoelectric layer 801 by PVD, photolithography and etching processes, and the material of the top electrode layer 1001 may be Mo. The top electrode layer 1001 is etched to expose a portion of the piezoelectric layer 801. In a preferred embodiment, the bottom electrode layer 401 and the top electrode layer 1001 are shaped in a direction perpendicular to the substrate 101 as a closed irregular shape formed by straight lines and arcs, i.e. a closed figure enclosed by straight lines/arcs of any arc/straight lines in any combination. The bottom electrode layer 401 and the top electrode layer 1001 in this shape can effectively improve the Q value of the device. The top view shape of the cavity 201 is made in accordance with the shape of the electrode.
In a specific embodiment, as shown in fig. 4l, an acoustic wave reflecting edge 701 is formed on the piezoelectric layer 801 to cover at least one side edge of the top electrode layer 1001, and a projection area of an outer edge of the acoustic wave reflecting edge 701 on the piezoelectric layer 801 is completely located in an area of the bottom electrode layer 401.
In a particular embodiment, acoustic reflection rims 701 comprise a combination of at least one set of alternately stacked low acoustic impedance reflection rims 702 and high acoustic impedance reflection rims 703. In the preferred embodiment, acoustic reflection edge 701 is not limited to a low acoustic impedance reflection edge 702 and a high acoustic impedance reflection edge 703, and acoustic reflection edge 701 may be comprised of a plurality of alternating layers of composite film layers of high and low acoustic impedance. In view of the bragg reflection layer principle of the acoustic wave, the acoustic wave energy of more than 99.98% is reflected and the transverse wave is suppressed by the film layers with high and low impedance which are optimally matched. Transverse waves are reflected by the sound wave reflection barrier edges 701 which are close to or cover the edges of the top electrode layer 1001, so that the phenomenon that energy is leaked at the edges of the resonator to cause Q value attenuation is avoided, and the device performance is improved. In a preferred embodiment, as shown in fig. 4k-4l, the low acoustic impedance reflection edge 702 is first fabricated by photolithography and evaporation, the material of the low acoustic impedance reflection edge 702 may be Al, Ti, Mg, etc., and then the high acoustic impedance reflection edge 703 is fabricated by photolithography and evaporation, the material of the high acoustic impedance reflection edge 703 includes, but is not limited to, W, Au, Ru, Cu, Ag, Pt, etc. The projected area of the outermost position of the acoustic reflection edge 701 on the substrate 101 may not exceed the area range of the cavity and may be aligned with the edge of the cavity.
In a particular embodiment, the reflective ledge closest to the edge of the top electrode layer 1001 is the low acoustic impedance reflective ledge 702. Therefore, from the edge of the top electrode layer 1001, first, the low acoustic impedance reflection blocking edge 702, then the high acoustic impedance reflection blocking edge 703, and so on, a low high impedance difference may be generated from the edge of the top electrode layer, thereby generating acoustic wave reflection. The resulting acoustic reflector rim 701, which consists of a low acoustic impedance reflector rim 702 and a high acoustic impedance reflector rim 703, wraps around the top electrode layer 1001 and extends from the sides of the top electrode layer 1001 to the top edge of the top electrode layer 1001 to form a mass loading layer 704. The mass loading layer 704 is also a structure composed of a plurality of thin film layers, and the cross-sectional shape of the top electrode layer 1001 may have a certain inclination angle. The mass loading layer 704 is grown on the top of the top electrode layer 1001 while the sound wave reflection edge 701 is grown, so that the process is simple, the sound wave reflection edge 701 can prevent transverse waves from leaking from the edge of the resonator to take away energy, meanwhile, the mass loading layer 704 can be formed to cause acoustic impedance mutation to reflect the transverse waves, the transverse waves are restrained from taking away energy, and the Q value is improved. Both the low acoustic impedance reflection ledge 702 and the high acoustic impedance reflection ledge 703 are formed of a metallic material. The electric connection effect between the acoustic wave reflecting edge 701 made of the metal material and the top electrode layer 1001 is good, and the insertion loss of the filter is prevented from being influenced by the connection effect. In this case, the acoustic reflection ledge 701 may be used directly to connect twoA bulk acoustic wave resonator. In other preferred embodiments, low acoustic impedance reflection ledge 702 is formed of a dielectric material and high acoustic impedance reflection ledge 703 is formed of a metallic material. In the preferred embodiment, the dielectric material can be selected from PI and SiO2、Si3N4And the like. Because the acoustic impedance of the dielectric material is lower than that of the metal material, the acoustic wave reflection edge formed by combining the dielectric material and the metal material has a better acoustic wave reflection effect. The replacement or retention of the material of the low acoustic impedance reflection ledge 702 may be contingent on practical needs.
In a specific embodiment, the method further includes step S9: a release hole 1101 is made beside the top electrode layer 1001 and the bottom electrode layer 401, and as shown in fig. 4m, the release hole 1101 is made by a photolithography, dry etching process, and the release hole 1101 penetrates from the top to the sacrificial material 301 extending into the cavity 201. The release holes 1101 are used to remove the sacrificial material 301 within the cavity 201.
In a specific embodiment, the method further includes step S10: a protective layer 1201 is fabricated, the protective layer 1201 covering the sidewalls of the release hole 1101. As shown in fig. 4n, a protective layer 1201 is formed by a CVD process, and the protective layer 1201 covers both sides and the bottom of the release hole 1101. In a preferred embodiment, the material of the protection layer 1201 is aluminum nitride. As shown in fig. 4o, this process further includes: the protective layer 1201 at the bottom inside the release hole 1101 is removed by photolithography and etching. At this time, the sidewalls of the release holes 1101 are covered with the protective layer 1201, so that the protective layer 1201 can effectively protect the dielectric layer 601 (SiO) from the2) Not corroded by the etchant HF used when the cavity 201 is released. The protective layer 1201 at the bottom of the release hole 1101 is cleaned to facilitate subsequent removal of the sacrificial material 301 within the cavity 201. Finally, the sacrificial material 301 in the cavity 201 is removed by dry etching or wet etching, wherein the etchant may be HF, and the bulk acoustic wave resonator shown in fig. 2 is finally obtained.
Example two
The other steps of the second embodiment are the same as those of the first embodiment, and the difference between the second embodiment and the first embodiment is that: as shown in fig. 5, the acoustic wave reflection rib 711 surrounds only the outside of the top electrode layer 1011, and does not extend to the top edge of the top electrode layer 1011 to form a mass loading layer, the cross-sectional shape of the top electrode layer 1011 at this time may be rectangular, and after the top electrode layer 1011 at one end connected to the outside is etched, the acoustic wave reflection rib 711 formed by laminating the low acoustic impedance reflection rib 712 and the high acoustic impedance reflection rib 713 is connected to the outside, and the low acoustic impedance reflection rib 712 and the high acoustic impedance reflection rib 713 are made of a metal material and have a certain electrical conductivity.
EXAMPLE III
The other steps of the third embodiment are the same as those of the first embodiment, and the difference between the third embodiment and the first embodiment is that: the acoustic reflection rim 721 may also serve as a lead wire connected to the outside. In a specific embodiment, as shown in fig. 6, when the acoustic wave reflection rims 721 are each formed of a metal material, the step S2 further includes: meanwhile, an electrode connecting portion 725 formed by extending the acoustic wave reflecting rim 721 outward is formed on the piezoelectric layer 801 on one side of the front bulk acoustic wave resonator. At this time, the acoustic wave reflecting edge 721 made of a metal material has good electrical conductivity, so the acoustic wave reflecting edge 721 can be extended as the electrode connecting portion 725, and can also be connected as a lead wire to other resonators or signal source lead-in, etc. In other alternative embodiments, the mass loading layer 724 may be formed while the acoustic wave reflection barrier 721 is formed, and the electrode connection portion 725 may be formed as an electrical connection portion between the top electrode layer 1001 and another resonator, so as to achieve multiple functions of transverse acoustic wave reflection, mass loading, electrical connection, and the like through a simple process.
Example four
The other steps of the fourth embodiment are the same as those of the third embodiment, and the fourth embodiment is different from the third embodiment in that: as shown in fig. 7, a first electrode connection portion 736 electrically connected to the top electrode layer 1001 may be formed while growing the mass loading layer 734. In a particular embodiment, high acoustic impedance reflection ledge 733 is also formed of a metallic material when low acoustic impedance reflection ledge 732 is replaced with a dielectric material. At this time, step S2 further includes: meanwhile, a first electrode connection portion 736 electrically connected to the top electrode layer 1001 is formed by extending a part of the high acoustic impedance reflection stop edge 733 at one end of the acoustic wave reflection stop edge 731 on the top of the top electrode layer 1001 of the bulk acoustic wave resonator. The first electrode connecting portion 736 extends from a portion of the high acoustic impedance reflection rib 733 of the mass loading layer 734 to the top of the top electrode layer 1001 to connect with the top electrode layer 1001, and at least one high acoustic impedance reflection rib 733 is connected with the top electrode layer 1001 to ensure a smooth circuit connection. At this time, the first electrode connection portion 736 is formed in a step shape with the mass loading layer 734 on the top of the top electrode layer 1001. In addition, a second electrode connecting portion 735 formed by extending the other end of the acoustic wave reflection edge 731 outward is formed on the piezoelectric layer 801 of the front bulk acoustic wave resonator. When the low acoustic impedance reflection rib 732 is formed of a dielectric material, since the conductivity of the dielectric material is low, it is necessary to electrically connect the high acoustic impedance reflection rib 733 formed of a metal material to the top electrode layer 1001 along the top portion extending to the top electrode layer 1001, to finally achieve electrical connection to another bulk acoustic wave resonator, and also to simultaneously form the mass loading layer 734 on the top portion of the top electrode layer 1001. The acoustic reflection edge 731 made of a combination of a dielectric material and a metal material has a larger difference between high and low acoustic impedance, and therefore has a better acoustic reflection effect. The first electrode connection portion 736, the second electrode connection portion 735, and the mass loading layer 734 are fabricated at the same time as the acoustic wave reflection barrier edge 731 is fabricated, so that a plurality of functions such as transverse acoustic wave reflection, mass loading, and electrical connection can be finally achieved.
The embodiment of the application provides an electrode structure of a bulk acoustic wave resonator and a manufacturing process, the electrode structure comprises a bottom electrode layer, a piezoelectric layer and a top electrode layer which are sequentially stacked, an acoustic wave reflection blocking edge covering at least one side edge of the top electrode layer is formed on the piezoelectric layer, the acoustic wave reflection blocking edge extends from the side edge of the top electrode layer to the top edge of the top electrode layer to form a mass load layer, and the projection area of the outer edge of the acoustic wave reflection blocking edge on the piezoelectric layer is completely located in the area range of the bottom electrode layer. The acoustic wave reflection barrier edge formed by high and low acoustic impedance close to or covering the edge of the top electrode layer alternately reflects transverse waves, one part of the reflected transverse waves are converted into longitudinal waves, and the other part of the reflected transverse waves are trapped in the resonator, so that the transverse waves are prevented from leaking from the edge of the resonator and taking away energy, and the performance of the device is improved. The mass loading layer can be manufactured and formed while the sound wave reflection blocking edge is manufactured, and the mass loading layer can be used as an electrical connection part between the top electrode layer and other resonators while the sound wave reflection blocking edge is manufactured, so that the process is simple.
While the present invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
In the description of the present application, it is to be understood that the terms "upper", "lower", "inner", "outer", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present application and simplifying the description, and do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application. The word 'comprising' does not exclude the presence of elements or steps not listed in a claim. The word 'a' or 'an' preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.
Claims (25)
1. The electrode structure of the bulk acoustic wave resonator comprises a bottom electrode layer, a piezoelectric layer and a top electrode layer which are sequentially stacked, and is characterized in that an acoustic wave reflection edge is formed on the piezoelectric layer and wraps at least one side edge of the top electrode layer, the acoustic wave reflection edge extends from the side edge of the top electrode layer to the top edge of the top electrode layer to form a mass load layer, and the projection area of the outer edge of the acoustic wave reflection edge on the piezoelectric layer is completely located in the area range of the bottom electrode layer.
2. The electrode structure of claim 1, wherein the acoustic reflection rims comprise a combination of at least one set of low acoustic impedance reflection rims and high acoustic impedance reflection rims alternately stacked.
3. The electrode structure of claim 2, wherein the reflection ledge closest to the edge of the top electrode layer is a low acoustic impedance reflection ledge.
4. The electrode structure of claim 2, wherein the low acoustic impedance reflection ledge and the high acoustic impedance reflection ledge are both formed of a metallic material.
5. The electrode structure of claim 4, wherein the acoustic reflection rim extends outward from the piezoelectric layer of the bulk acoustic resonator to form an electrode connection.
6. The electrode structure of claim 2, wherein the low acoustic impedance reflection ledge is formed of a dielectric material and the high acoustic impedance reflection ledge is formed of a metallic material.
7. The electrode structure of claim 6, wherein a portion of the high acoustic impedance reflection rib at one end of the acoustic wave reflection rib extends to the top of the top electrode layer of the front bulk acoustic wave resonator and is electrically connected to the top electrode layer to form a first electrode connection portion, and the other end of the acoustic wave reflection rib extends outward on the piezoelectric layer of the front bulk acoustic wave resonator to form a second electrode connection portion.
8. The electrode structure of claim 7, wherein when the acoustic reflection ledge forms a mass loading layer at a top edge of the top electrode layer, the first electrode connection is stepped with the mass loading layer at a top of the top electrode layer.
9. A bulk acoustic resonator comprising an electrode structure according to any of claims 1-8, wherein the bulk acoustic resonator further comprises a substrate having a cavity, the electrode structure is formed on the substrate, an adjacent barrier layer and a dielectric layer are formed around the bottom electrode layer, and the surfaces of the barrier layer and the dielectric layer are kept flat with the surface of the bottom electrode layer.
10. The bulk acoustic wave resonator according to claim 11, further comprising a release hole extending into the cavity without passing through the bottom and top electrode layers, a protective layer being formed in the release hole covering sidewalls of the release hole.
11. The bulk acoustic wave resonator according to claim 9, wherein a support layer is formed between the bottom electrode layer and the substrate.
12. The bulk acoustic wave resonator according to claim 11, wherein a projected area of the bottom electrode layer on the substrate is entirely within the cavity.
13. A manufacturing process of an electrode structure of a bulk acoustic wave resonator is characterized by comprising the following steps:
s1, etching the top electrode layer in the resonance function layer formed by sequentially laminating the bottom electrode layer, the piezoelectric layer and the top electrode layer to expose part of the piezoelectric layer;
s2, manufacturing an acoustic wave reflection edge on the piezoelectric layer, the acoustic wave reflection edge covering at least one side of the top electrode layer, and manufacturing a mass loading layer on the top electrode layer, where the mass loading layer is formed by extending the acoustic wave reflection edge from the side of the top electrode layer to the top edge of the top electrode layer, and a projection area of an outer edge of the acoustic wave reflection edge on the piezoelectric layer is completely located in an area range of the bottom electrode layer.
14. The process of claim 13, wherein the acoustic reflection rims comprise a combination of at least one set of low acoustic impedance reflection rims and high acoustic impedance reflection rims alternately stacked.
15. The process of claim 14, wherein the reflection ledge closest to the edge of the top electrode layer is a low acoustic impedance reflection ledge.
16. The process of claim 15, wherein the low acoustic impedance reflection ledge and the high acoustic impedance reflection ledge are formed from a metallic material.
17. The process of manufacturing an electrode structure according to claim 16, wherein the step S2 further includes: and meanwhile, an electrode connecting part formed by outwards extending the acoustic wave reflection barrier edge is manufactured on the piezoelectric layer on one side of the front bulk acoustic wave resonator.
18. The process of claim 15, wherein the low acoustic impedance reflection ledge is formed of a dielectric material and the high acoustic impedance reflection ledge is formed of a metallic material.
19. The process of manufacturing an electrode structure according to claim 18, wherein the step S2 further includes: and simultaneously, a first electrode connecting part electrically connected with the top electrode layer is formed by extending a part of the high acoustic impedance reflection edge at one end of the acoustic wave reflection edge on the top of the top electrode layer of the bulk acoustic wave resonator, and a second electrode connecting part formed by extending the other end of the acoustic wave reflection edge outwards is formed on the piezoelectric layer of the bulk acoustic wave resonator.
20. A process for manufacturing a bulk acoustic wave resonator comprising a process for manufacturing an electrode structure of a bulk acoustic wave resonator according to any of claims 13 to 19, comprising the steps of:
s3, forming a cavity on the substrate;
s4, filling sacrificial materials in the cavity;
s5, manufacturing a bottom electrode layer on the filled cavity;
s6, sequentially applying a barrier layer and a dielectric layer around the bottom electrode layer to enable the surface of a composite layer formed by the barrier layer and the dielectric layer to be flat with the surface of the bottom electrode layer; and
s7, manufacturing a piezoelectric layer on the surface of the composite layer and the bottom electrode layer so that the piezoelectric layer does not contact the substrate.
21. The process for manufacturing a bulk acoustic wave resonator according to any one of claims 20, wherein the method further comprises step S8: and manufacturing a top electrode layer on the piezoelectric layer.
22. The process of fabricating a bulk acoustic wave resonator according to claim 21, wherein the method further comprises step S9: release holes are fabricated alongside the top and bottom electrode layers, the release holes penetrating from the top into sacrificial material within the cavities.
23. The process for fabricating a bulk acoustic wave resonator according to claim 22, wherein the method further comprises step S10: and manufacturing a protective layer which covers the side wall of the release hole.
24. The process of fabricating a bulk acoustic wave resonator according to claim 20, wherein the method further comprises, between steps S4 and S5: a support layer made of an aluminum nitride material is formed on the substrate.
25. The process for fabricating a bulk acoustic wave resonator according to claim 24, wherein a projected area of the bottom electrode layer on the substrate is entirely located in the cavity.
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