Bulk acoustic wave resonator, filter, multiplexer and radio frequency front-end module

Abstract

The invention provides a bulk acoustic wave resonator which comprises a substrate, a lower electrode, a piezoelectric layer, an upper electrode, a first dielectric layer, a protection electrode and a second dielectric layer, the upper surface of the upper electrode is provided with a sunken structure, the area where the sunken structure is located is a sunken area in the overlook direction, the first dielectric layer is arranged on the surface, away from the lower electrode, of the piezoelectric layer, and the protection electrode is arranged on the surface of the piezoelectric layer. The protection electrode is arranged between the piezoelectric layer and the upper electrode, in the overlook direction, one part of the protection electrode is located between the area where the first dielectric layer is located and the concave area, a first distance is formed between the protection electrode and the concave area, the other part of the protection electrode at least covers at least one part of the first dielectric layer, and the first distance is kept between the protection electrode and the concave area. Under the condition that process errors exist, unnecessary fluctuation of the bulk acoustic wave resonator can be weakened, and the performance of the resonator is guaranteed. The invention also provides a filter, a multiplexer and a radio frequency front-end module.

Description

Technical Field

[0001] The present application relates to the field of radio frequency filtering technology, and in particular to a bulk acoustic wave resonator, a filter, a multiplexer and a radio frequency front-end module. Background Art

[0002] Resonators are widely used in the fields of radio, optoelectronics, etc., and with the technological iteration, they have developed from mechanical resonators and electrical resonators to bulk acoustic wave resonators. Bulk acoustic wave resonators input radio frequency signals between two electrodes, and FBAR uses the inverse piezoelectric effect to convert the input electrical signal into mechanical resonance, and then uses the piezoelectric effect to convert the mechanical resonance into an electrical signal output. Bulk acoustic wave resonators can have a wider operating frequency range, higher precision, etc.

[0003] In a BAW resonator, since the excitation of the actual acoustic field of the BAW resonator is not entirely a longitudinal wave mode in the thickness direction, there is often an excitation mode of the lateral acoustic field. This part of the lateral excited acoustic mode will cause the quality factor (Q) value of the resonator to decrease. BAW resonators with low quality factors (Q) will deteriorate the filter insertion loss and rectangularity, thereby reducing the sensitivity of the RF front-end module.

[0004] Therefore, improving the performance of BAW resonators has become an urgent issue to be solved. Summary of the invention

[0005] The present application provides a bulk acoustic wave resonator, a filter, a multiplexer and a radio frequency front-end module to improve the above-mentioned technical problems, to at least partially improve the above-mentioned technical problems.

[0006] In a first aspect, the present application provides a bulk acoustic wave resonator, comprising: a substrate, a lower electrode, a piezoelectric layer, an upper electrode, a first dielectric layer, a protective electrode and a second dielectric layer, wherein the substrate has a first surface, the lower electrode is arranged on the first surface, and an acoustic mirror is arranged between the substrate and the lower electrode, the piezoelectric layer is arranged on a surface of the lower electrode away from the substrate and covers the lower electrode, the upper electrode is arranged on a surface of the piezoelectric layer away from the lower electrode, the upper surface of the upper electrode has a concave structure, in a top view direction, the area where the concave structure is located is a concave area, and the first dielectric layer is arranged on a surface of the piezoelectric layer away from the lower electrode The first dielectric layer extends from the area between the upper electrode and the piezoelectric layer to the outside of the area between the upper electrode and the piezoelectric layer in the top-view direction, the protective electrode is arranged between the piezoelectric layer and the upper electrode, and in the top-view direction, a portion of the protective electrode is located between the area where the first dielectric layer is located and the recessed area, and has a first distance from the recessed area, and another portion at least covers at least a portion of the first dielectric layer, and the second dielectric layer is attached to the surface of the upper electrode away from the piezoelectric layer, and extends from the surface of the upper electrode away from the piezoelectric layer to the surface of the piezoelectric layer away from the lower electrode.

[0007] In one embodiment, the width of the recessed structure and the first distance satisfy the following relationship:

[0008] 0.05≤d1 / d2≤0.7

[0009] Wherein, d1 is the first distance, and d2 is the width of the recessed area.

[0010] In one embodiment, at least one of the upper electrode, the lower electrode and the piezoelectric layer has an opening on its upper surface, and the opening faces away from the substrate, so as to form a concave structure corresponding to the shape of the opening on the upper surface of the upper electrode.

[0011] In one embodiment, in a structure with an opening, the thickness of the structure is h2, the thickness of the structure at the opening is h1, and the structure is one of an upper electrode, a lower electrode, and a piezoelectric layer, wherein the following relationship is satisfied between h1 and h2: 0.8≤h1 / h2≤0.99.

[0012] In one embodiment, another portion of the protective electrode is attached to at least a portion of the side surface of the first dielectric layer, or another portion of the protective electrode is attached to at least a portion of the side surface of the first dielectric layer and extends to the surface of the first dielectric layer facing away from the piezoelectric layer to cover at least a portion of the surface of the first dielectric layer away from the piezoelectric layer.

[0013] In one embodiment, the region where the first dielectric layer and the protective electrode are located is a high acoustic impedance region, and the acoustic impedance value of the high acoustic impedance region is greater than the acoustic impedance value of the region outside the high acoustic impedance region; and

[0014] Along the direction from the recessed area to the first dielectric layer, the high acoustic impedance area has three sub-areas with different acoustic impedance values ​​in sequence, and the acoustic impedance values ​​of the sub-areas away from the recessed area gradually decrease along the direction from the recessed area to the first dielectric layer.

[0015] In one embodiment, the first distance is in the range of 50 nm to 800 nm; alternatively, the first distance is in the range of 50 nm to 600 nm.

[0016] In a second aspect, the present application provides a filter, comprising the BAW resonator according to the first aspect.

[0017] In a third aspect, the present application provides a multiplexer, comprising the filter according to the second aspect.

[0018] In a fourth aspect, the present application provides a radio frequency front-end module, comprising a filter as described in the second aspect above.

[0019] The BAW resonator, filter, multiplexer and RF front-end module provided by the present application, the BAW resonator can suppress the lateral mode by providing a recessed structure to ensure the quality factor of the BAW resonator. The BAW resonator is also provided with a first dielectric layer and a protective electrode, the first dielectric layer is used to reduce the longitudinal leakage of energy, and the protective electrode is used to protect the first dielectric layer from corrosion. In addition, the protective electrode and the recessed structure maintain a first distance, and in the case of process errors, the fluctuation of the BAW resonator near the right side of the resonant frequency point can be weakened to ensure the performance of the resonator, and the influence of the recessed area on the protective electrode structure, such as deformation, can be avoided, thereby ensuring the structural stability of the BAW resonator and reducing the influence on the Q value of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the implementation modes of the present application, the drawings required for use in the description of the implementation modes will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present application, and for those skilled in the art, they can be easily understood without creative work.

[0021] Figure 1 A schematic diagram of the structure of a bulk acoustic wave resonator provided in this application;

[0022] Figure 2 A schematic diagram of the structure of a recessed area provided in this application;

[0023] Figure 3 A schematic diagram of the structure of another recessed area provided in this application;

[0024] Figure 4 A schematic diagram of the structure of a protective electrode and a first dielectric layer provided in the present application;

[0025] Figure 5 A schematic diagram of the structure of another protective electrode and a first dielectric layer provided in the present application;

[0026] Figure 6 A schematic diagram of the structure of another protective electrode and a first dielectric layer provided in the present application;

[0027] Figure 7 A schematic diagram showing a comparison of admittance curves of a bulk acoustic wave resonator provided in the present application;

[0028] Figure 8 A schematic diagram showing a comparison of real part curves of admittance of a bulk acoustic wave resonator provided in the present application;

[0029] Fig. 9 A schematic diagram showing comparison of real part of admittance curves of another BAW resonator provided in the present application;

[0030] Fig.10A schematic diagram of passband comparison of a filter provided in this application. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the implementation mode of the present application will be clearly and completely described below in conjunction with the drawings in the implementation mode of the present application. Obviously, the described implementation mode is only a part of the implementation mode of the present application, not all the implementation modes. Based on the implementation mode in the present application, all other implementation modes obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0032] In this application, unless otherwise clearly specified or limited, the terms "installation", "connection", "fixation" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements, or it can be only surface contact, or surface contact connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0033] In addition, the terms "first", "second", etc. are only used to distinguish descriptions and cannot be understood as specific or special structures. The descriptions of the terms "some embodiments", "other embodiments", etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application. In the present application, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0034] In the related art, a dielectric layer is set between the upper electrode and the piezoelectric layer of the BAW resonator to reduce the longitudinal leakage of energy, thereby improving the Q value, but the dielectric layer is easily corroded during the process, thereby affecting the effect of suppressing the longitudinal leakage of energy. Normally, the BAW resonator is set with a recessed structure to suppress the lateral mode, but the setting of the recessed structure will produce fluctuations near the right side of the resonant frequency point of the resonator. If the relevant parameters of the recessed structure are within a suitable range, for example, matching other structures of the BAW resonator, the fluctuations there will not affect the performance of the resonator. Once the size of the recessed structure deviates, especially if the size is too large, it will cause the fluctuations near the right side of the resonant frequency point of the BAW resonator to increase, thereby affecting the performance of the resonator.

[0035] First embodiment

[0036] The present application embodiment provides a bulk acoustic wave resonator 10, see Figure 1 The BAW resonator 10 includes a substrate 11, a lower electrode 12, a piezoelectric layer 13, an upper electrode 14, a first dielectric layer 16, a protective electrode 17, and a second dielectric layer 18. In one embodiment, the substrate 11, the lower electrode 12, the piezoelectric layer 13, the first dielectric layer 16, the protective electrode 17, the upper electrode 14, and the second dielectric layer 18 can be stacked in sequence to form the BAW resonator 10.

[0037] Specifically, the substrate 11 has a first surface 111, and the lower electrode 12 is disposed on the first surface 111, and the lower electrode 12 may at least cover a portion of the first surface 111. An acoustic mirror 112 is provided between the substrate 11 and the lower electrode 12, wherein the acoustic mirror 112 may be a cavity or a Bragg reflection layer, which is not limited in this embodiment.

[0038] In one embodiment, the acoustic mirror 112 may be a cavity, which may be formed by the first surface 111 of the substrate 11 or a part of the first surface 111 being concavely arranged in a direction away from the lower electrode 12, and the concave is arranged corresponding to the lower electrode 12. Alternatively, the cavity may be formed by the surface of the lower electrode 12 close to the substrate 11 or a part of the surface being convexly arranged in a direction away from the substrate 11, and the cavity is arranged corresponding to the substrate 11, and the cavity may be used to confine the bulk acoustic wave in the piezoelectric layer 13.

[0039] In a more specific implementation, please continue to refer to Figure 1 , the piezoelectric layer 13 is attached to the surface of the lower electrode 12 away from the substrate 11, and covers the lower electrode 12. The upper electrode 14 is arranged on the surface of the piezoelectric layer 13 away from the lower electrode 12, and the upper electrode 14 can partially cover the piezoelectric layer 13, which is not limited in this application. The upper electrode 14, the piezoelectric layer 13 and the lower electrode 12 are arranged correspondingly, and the projections of the upper electrode 14, the piezoelectric layer 13 and the lower electrode 12 toward the substrate 11 cover the acoustic mirror 112. The close combination of the lower electrode 12, the piezoelectric layer 13 and the upper electrode 14 can produce a stable resonant frequency, and convert the input signal into an acoustic wave signal, and can also convert the acoustic wave signal into an electrical signal, and can effectively convert the electrical signal into the acoustic wave. And the area where the upper electrode 14, the piezoelectric layer 13, the lower electrode 12 and the acoustic mirror 112 overlap with each other is the effective area 20.

[0040] In the embodiment of the present application, the upper electrode 14 is disposed on the surface of the piezoelectric layer 13 away from the lower electrode 12, and the upper surface of the upper electrode 14 has a concave structure. The upper surface of the upper electrode 14 can be the surface of the upper electrode 14 away from the lower electrode 12, and in the top view direction, the area where the concave structure is located is the concave area 22, and the top view direction can be the line of sight from the side of the upper electrode 14 away from the piezoelectric layer 13 to the substrate 11.

[0041] The first dielectric layer 16 is disposed on the surface of the piezoelectric layer 13 away from the lower electrode 12. In the top view direction, the first dielectric layer 16 extends from the region between the upper electrode 14 and the piezoelectric layer 13 to the region outside the region between the upper electrode 14 and the piezoelectric layer 13. The top view direction is the line of sight from the side of the upper electrode 14 away from the piezoelectric layer 13 to the substrate 11.

[0042] In a more specific embodiment, the first dielectric layer 16 is disposed on the surface of the piezoelectric layer 13 away from the lower electrode 12, and a portion of the first dielectric layer 16 is located in the active area 20, and another portion is located outside the active area 20. In the top view direction, the first dielectric layer 16 is located outside the area surrounded by the recessed area 22.

[0043] In the embodiment of the present application, the first dielectric layer 16 is generally made of a low dielectric constant material such as silicon dioxide, and its dielectric constant is smaller than that of the piezoelectric layer 13 . The provision of the first dielectric layer 16 can reduce the longitudinal leakage of the acoustic wave energy.

[0044] In the process, when making the cavity of the resonator, it is necessary to prepare it through etching and other processes, that is, first fill the cavity with sacrificial material, then prepare the lower electrode 12, the piezoelectric layer 13, the first dielectric layer 16, the upper electrode 14 and other structures, and finally remove the sacrificial material through the release hole to form a cavity. During the release process, the corrosive liquid may also corrode the low dielectric constant material. Therefore, the setting of the first dielectric layer 16 may be affected by the corrosive liquid, resulting in a reduction in its effect, thereby causing the acoustic wave energy in the bulk acoustic wave resonator 10 to leak longitudinally.

[0045] In the embodiment of the present application, the protection electrode 17 may be disposed between the piezoelectric layer 13 and the upper electrode 14. In the top view direction, a portion of the protection electrode 17 is located between the region where the first dielectric layer 16 is located and the recessed region 22, and has a first distance from the recessed region 22. Another portion of the protection electrode 17 at least covers at least a portion of the first dielectric layer 16.

[0046] Figure 1 The area where the first distance is located is shown as 23. Exemplarily, the first distance may be 50 nm, 60 nm, 70 nm, etc., which is not limited in this embodiment.

[0047] The release hole generally corresponds to the cavity, and the protection electrode 17 can be disposed at a position of the first dielectric layer 16 close to the cavity side to protect the first dielectric layer 16 during the process of forming the cavity.

[0048] Specifically, the protective electrode 17 at least covers at least a portion of at least part of the side surface of the first dielectric layer 16 , so that the first dielectric layer 16 can be covered and shielded by the protective electrode 17 , effectively preventing the corrosive liquid from corroding the first dielectric layer 16 , and having a certain protective effect on the first dielectric layer 16 .

[0049] It can be understood that in the embodiment of the present application, only a schematic diagram of the area 23 where the first distance is located is shown, that is, the upper surface of the upper electrode 14 in the area 23 where the first distance is located is higher than the upper surface of the upper electrode 14 in the recessed area 22. Specifically, it can be parallel to or on the same horizontal plane as the upper surface of the upper electrode 14 in the area surrounded by the recessed area 22, and can also have a certain inclination angle. The inclination angle of the upper electrode 14 in the area 23 can be smaller than the inclination angle of the recessed structure of the upper electrode 14 in the recessed area 22. The specific structure is not limited in the embodiment of the present application.

[0050] In the embodiment of the present application, the second dielectric layer 18 is attached to the surface of the upper electrode 14 away from the piezoelectric layer 13, and extends from the surface of the upper electrode 14 away from the piezoelectric layer 13 to the surface of the piezoelectric layer 13 away from the lower electrode 12, so as to cover the upper electrode 14, the first dielectric layer 16 and the protective electrode 17. The upper electrode 14, the first dielectric layer 16 and the protective electrode 17 can be shielded and protected by the second dielectric layer 18. Exemplarily, the second dielectric layer 18 can be a frequency modulation layer, or a passivation layer, or can have the functions of a frequency modulation layer and a passivation layer at the same time, so that the second dielectric layer 18 can also be used to adjust the resonant frequency of the BAW resonator 10.

[0051] In actual applications, if the protective electrode 17 is arranged adjacent to the area where the recessed structure is located (recessed area 22) (that is, there is no distance between the two), the size deviation of the recessed structure will also affect the protective electrode 17. For example, if the recessed structure expands toward the protective electrode 17, the protective electrode 17 may collapse toward the substrate 11 and deform, which will not only affect the structural stability of the resonator, but also reduce the Q value.

[0052] The present application sets a first distance between the protective electrode 17 and the recessed area 22. In the case of process errors, the fluctuation of the BAW resonator 10 near the right side of the resonant frequency point can be weakened, and the influence of the size deviation of the recessed area 22 on the performance of the BAW resonator 10 can be effectively reduced. The influence of the recessed area 22 on the structure of the protective electrode 17, such as deformation, can also be avoided, thereby ensuring the structural stability of the BAW resonator 10 and reducing the influence on the Q value.

[0053] In the embodiment of the present application, the substrate 11 can be made of any one of materials such as single crystal silicon, gallium arsenide, gallium nitride, sapphire and quartz, and the present application does not make any specific restrictions here.

[0054] In the embodiment of the present application, the material of the piezoelectric layer 13 can be aluminum nitride, zinc oxide, lead zirconate titanate, or a rare earth element doped material with a certain atomic ratio of the above materials. In one implementation, the piezoelectric layer 13 can also be made of a single crystal piezoelectric material, such as single crystal aluminum nitride, lithium niobate, lithium tantalate, quartz, and other materials, and the present application does not make any specific restrictions here.

[0055] In the embodiment of the present application, the material of the upper electrode 14 and the lower electrode 12 can be a single metal material or a composite or alloy material of different metals. Optionally, the material of the lower electrode 12 can be one of molybdenum, tungsten, ruthenium, gold, magnesium, aluminum, copper, chromium, titanium, osmium, iridium or a composite of the above metals or an alloy thereof. Among them, the materials of the lower electrode 12 and the upper electrode 14 can be the same or different, and the present application does not make specific restrictions here.

[0056] In an embodiment of the present application, the material of the protective electrode 17 may be one of molybdenum, tungsten, ruthenium, gold, magnesium, aluminum, copper, chromium, titanium, osmium, iridium or a composite of the above metals or an alloy thereof. The material of the protective electrode 17 may be the same as at least one of the upper electrode 14 and the lower electrode 12, or may be different from the material of both the upper electrode 14 and the lower electrode 12. The present application does not make any specific restrictions here.

[0057] In the embodiment of the present application, the material of the second dielectric layer 18 can be silicon dioxide, silicon nitride, aluminum nitride, aluminum oxide, etc., and the present application does not make any specific limitation here.

[0058] In a feasible implementation manner, the width of the recessed structure and the first distance satisfy the following relationship:

[0059] 0.05≤d1 / d2≤0.7

[0060] Wherein, d1 is the first distance, and d2 is the width of the recessed structure.

[0061] It can be understood that the width of the recessed structure (which can also be understood as the width of the recessed area 22) can be the distance between the two ends along the direction from the inside of the effective area 20 to the outside of the effective area 20. The width can be the minimum width, the maximum width, or the average width. The present application does not make specific restrictions here. The first distance can be the minimum distance between the protective electrode 17 and the recessed structure, or it can be the average distance, etc. The present application does not make specific restrictions here. Exemplarily, the width of the recessed structure can be 1000nm, the first distance can be 50nm, and the first distance is 0.05 times the width of the recessed area 22. Alternatively, the width of the first distance can be 70nm, the width of the recessed area 22 can be 100nm, and the width of the first distance can be 0.7 times the width of the recessed area 22. Alternatively, the width of the first distance can be 400nm, the recessed area 22 can be 1000nm, and the width of the recessed area 22 can be 0.4 times the width of the first distance.

[0062] Specifically, the ratio of d1 / d2 can be 0.05, 0.2, 0.35, 0.5, 0.65, 0.7, etc., which is not limited in the embodiments of the present application.

[0063] In the embodiment of the present application, by limiting the relationship between the width of the recessed structure and the first distance, the influence of the dimensional deviation on the performance of the resonator can be further reduced in the presence of process errors, the fluctuation near the right side of the resonant frequency point of the resonator can be weakened, and the suppression effect of the lateral mode can be improved. If the ratio d1 / d2 between the first distance and the width of the recessed structure is too small, in the presence of process errors, obvious fluctuations will appear near the right side of the resonant frequency point of the resonator, and the resonator Q value will be reduced. If the ratio d1 / d2 between the first distance and the width of the recessed structure is too large, the suppression effect of the lateral mode will be affected.

[0064] In one embodiment, the first distance may be in the range of 40 nm to 800 nm. Specifically, the first distance may be 40 nm, 60 nm, 100 nm, 200 nm, 300 nm, 500 nm, 550 nm, 600 nm, 700 nm, 800 nm, etc., which is not limited in the embodiment of the present application. When the first distance is within this range, the fluctuation near the right side of the resonant frequency point can be weakened, thereby reducing the impact on the protective electrode 17.

[0065] It is understandable that, under the influence of process accuracy, the first distance fluctuating near the upper and lower limits of the range should also be within the protection scope of the present application, such as 35nm, 810nm, 820nm, etc.

[0066] In one embodiment, the first distance may be in the range of 50 nm to 800 nm. Specifically, the first distance may be 50 nm, 60 nm, 100 nm, 200 nm, 300 nm, 500 nm, 550 nm, 600 nm, 700 nm, 800 nm, etc., which is not limited in the embodiment of the present application. When the first distance is within this range, the fluctuation near the right side of the resonant frequency point can be further weakened, and the influence on the protective electrode 17 can be further reduced.

[0067] It is understandable that, under the influence of process accuracy, the first distance fluctuating near the upper and lower limits of the range should also be within the protection scope of the present application, such as 45nm, 810nm, etc.

[0068] In one embodiment, the first distance may be in the range of 50 nm to 600 nm. Within this range, the first distance may effectively reduce the impact of process errors on resonator performance, effectively weaken fluctuations near the right side of the resonance frequency point, and reduce the impact on the protection electrode 17.

[0069] In the present application, in the presence of process errors, if the first distance is too small, obvious fluctuations will appear near the right side of the resonant frequency point of the resonator, and the Q value of the resonator will be reduced. If the first distance is too large, it will affect the suppression effect of the lateral mode.

[0070] In a feasible embodiment, at least one of the upper electrode 14 , the lower electrode 12 and the piezoelectric layer 13 has an opening on its upper surface, and the opening faces away from the substrate 11 , so as to form a recessed structure corresponding to the shape of the opening on the upper surface of the upper electrode 14 .

[0071] In an exemplary embodiment, for example, Figure 1 As shown, the upper electrode 14 forms an opening on the surface away from the piezoelectric layer 13 , and the recessed structure is arranged in a direction away from the substrate 11 , so as to form a recessed structure corresponding to the shape of the opening on the upper surface of the upper electrode 14 .

[0072] In an exemplary embodiment, for example, Figure 2 As shown, an opening is formed on the surface of the piezoelectric layer 13 away from the lower electrode 12, and the recessed structure is arranged in a direction away from the substrate 11, and the surface of the upper electrode 14 close to the lower electrode 12 is filled in the opening, so that a recessed structure is formed correspondingly on the surface of the upper electrode 14 away from the piezoelectric layer 13.

[0073] In an exemplary embodiment, for example, Figure 3As shown, an opening is formed on the surface of the lower electrode 12 away from the substrate 11, and the opening is set in a direction away from the substrate 11. The surface of the piezoelectric layer 13 close to the lower electrode 12 and the surface of the upper electrode 14 close to the lower electrode 12 are filled in the opening in sequence, and the surface of the upper electrode 14 away from the piezoelectric layer 13 can also form a corresponding recessed structure.

[0074] In the implementation manner of the present application, the present application does not make any specific limitation on whether the recessed structure is formed on the upper electrode 14 , the lower electrode 12 , or the piezoelectric layer 13 .

[0075] In one possible implementation, please continue to refer to Figure 1 In the structure with an opening, the thickness of the structure is h2, the thickness of the structure at the opening is h1, and the structure with an opening is one of the lower electrode 12, the piezoelectric layer 13 and the upper electrode 14 having a concave structure, and the following relationship is satisfied between h1 and h2:

[0076] 0.8≤h1 / h2<1

[0077] The thickness of the structure at the opening is h1, which is the thickness of one of the lower electrode 12, the piezoelectric layer 13 and the upper electrode 14 at the opening, and the thickness of the structure is h2, which is the thickness of one of the lower electrode 12, the piezoelectric layer 13 and the upper electrode 14 excluding the opening. For example, the opening structure is formed by the upper electrode 14, h1 can be the thickness of the upper electrode 14 at the opening, and h2 can be the thickness of the upper electrode 14 excluding the opening.

[0078] In an exemplary embodiment, in a structure having an opening, the thickness h2 of the structure may be 200 nm, the thickness h1 at the opening of the structure may be 160 nm, and the thickness h1 at the opening of the structure may be 0.8 times the thickness h2 of the structure. Alternatively, in a structure having an opening, the thickness h2 of the structure may be 500 nm, the thickness h1 at the opening of the structure may be 495 nm, and the thickness h1 at the opening of the structure may be 0.99 times the thickness h2 of the structure. Alternatively, in a structure having an opening, the thickness h2 of the structure may be 350 nm, the thickness h1 at the opening of the structure may be 315 nm, and the thickness h1 at the opening of the structure may be 0.9 times the thickness h2 of the structure.

[0079] Specifically, the ratio of h1 / H2 can be 0.8, 0.85, 0.9, 0.95, 0.97, 0.99, etc., which is not limited in the embodiments of the present application. By limiting the thickness ratio of the structure and the thickness at the opening of the structure, the suppression effect of the recessed structure formed corresponding to the opening on the lateral mode can be improved. By setting a first distance between the recessed structure and the protective electrode 17, the influence of the process error on the resonator performance and the structural stability can be reduced.

[0080] In a feasible implementation, the angle between the side surface of the first dielectric layer 16 and the lower surface of the first dielectric layer 16 may be an acute angle, which is more conducive to the protection electrode 17 covering the side surface of the first dielectric layer 16, wherein the side surface of the first dielectric layer 16 may be at least one of the two end surfaces along the inside of the active area 20 toward the outside of the active area 20. The side surface of the first dielectric layer 16 intersects with the surface of the first dielectric layer 16 away from the piezoelectric layer 13 and the surface of the first dielectric layer 16 close to the piezoelectric layer 13, respectively.

[0081] In a feasible implementation, the thickness of the protection electrode 17 may be 50nm-500nm to improve the protection effect on the first dielectric layer 164. Specifically, the thickness of the protection electrode 17 may be 50nm, 100nm, 200nm, 300nm, 500nm, etc., which is not limited in this embodiment. The thickness of the protection electrode 17 refers to its size along the direction from the substrate 11 to the upper electrode 14, that is, the distance between the surface of the protection electrode 17 away from the piezoelectric layer 13 and the surface of the protection electrode 17 close to the piezoelectric layer 13.

[0082] In a feasible embodiment, the protective electrode 17 can be arranged between the piezoelectric layer 13 and the upper electrode 14. Specifically, a portion of the protective electrode 17 can be attached to the surface of the piezoelectric layer 13 away from the lower electrode 12, and another portion of the protective electrode 17 can be attached to at least part of the side surface of the first dielectric layer 16.

[0083] Please also read Figure 1 , Figure 4 as well as Figure 5 , the protective electrode 17 may include a first portion 171 and a second portion 172 adjacent to each other. In one embodiment, Figure 4 In the illustrated embodiment, the first portion 171 is attached to the surface of the piezoelectric layer 13 away from the lower electrode 12, the second portion 172 is attached to at least a portion of the side surface of the first dielectric layer 16, and the end of the second portion 172 away from the first portion 171 is lower than the surface of the first dielectric layer 16 away from the piezoelectric layer 13.

[0084] In another embodiment, see Figure 5 The first part 171 of the protective electrode 17 is attached to the surface of the piezoelectric layer 13 away from the lower electrode 12, and the second part 172 is attached to at least a part of the side of the first dielectric layer 16 and the end of the second part 172 (the end of the second part 172 away from the first part 171) is flush with the surface of the first dielectric layer 16 away from the piezoelectric layer 13.

[0085] In another embodiment, the first portion 171 of the protective electrode 17 is attached to the surface of the piezoelectric layer 13 away from the lower electrode 12, and the second portion 172 is away from the end of the first portion 171. A portion may be lower than the surface of the first dielectric layer 16 away from the piezoelectric layer 13, and another portion may be flush with the surface of the first dielectric layer 16 away from the piezoelectric layer 13. This embodiment of the present application is not limited here.

[0086] In another feasible implementation, the first portion 171 of the protective electrode 17 is attached to the surface of the piezoelectric layer 13 away from the lower electrode 12, and the second portion 172 is attached to at least a portion of the side surface of the first dielectric layer 16, and extends to the surface of the first dielectric layer 16 away from the piezoelectric layer 13, so as to cover at least a portion of the surface of the first dielectric layer 16 away from the piezoelectric layer 13. Among them, the portion of the second portion 172 covering the first dielectric layer 16 can be attached to the upper surface of the first dielectric layer 16. In addition, the first object and the second object are "attached" to each other, which means that the two are in direct contact, and the word "attached" has the same meaning in each embodiment, and will not be repeated in subsequent embodiments.

[0087] In the embodiment of the present application, by setting the protection electrode 17, the shielding and protection effect of the first dielectric layer 16 can be improved, and the corrosion of the first dielectric layer 16 by the corrosive liquid can be effectively avoided, thereby further reducing the longitudinal leakage of the resonator sound wave energy.

[0088] Please also read Figure 1 and Figure 6 , the area where the first dielectric layer 16 and the protective electrode 17 are located is the high acoustic impedance area 28, and the acoustic impedance value of the high acoustic impedance area 28 is greater than the acoustic impedance value of the area outside the high acoustic impedance area 28. Along the direction from the recessed area 22 to the first dielectric layer 16, the high acoustic impedance area 28 has three sub-areas with different acoustic impedance values ​​in sequence, and the acoustic impedance value of the sub-area away from the recessed area 22 gradually decreases along the direction from the recessed area 22 to the first dielectric layer 16. For example, Figure 6 As shown, along the direction from the recessed area 22 to the first dielectric layer 16, there are the first sub-area 281, the second sub-area 282 and the third sub-area 283 in sequence; wherein, the acoustic impedance value of the first sub-area 281 is less than the acoustic impedance value of the second sub-area 282, and the acoustic impedance value of the second sub-area 282 is greater than the maximum acoustic impedance value of the third sub-area 283, and along the direction from the recessed area 22 to the first dielectric layer 16, the acoustic impedance value of the third sub-area 283 gradually decreases, and such a setting can improve the effect of confining acoustic energy. In addition, along the direction from the recessed area 22 to the first dielectric layer 16, the acoustic impedance value of the first sub-area 281 remains unchanged, and the acoustic impedance value of the second sub-area 282 remains unchanged.

[0089] In the embodiment of the present application, the provision of the first dielectric layer 16 and the protection electrode 17 changes the distribution of the acoustic impedance value of the resonator in this area, which can further improve the Q value of the resonator.

[0090] In one embodiment, in the top-view direction of the BAW resonator 10, the top-view direction is the line of sight from the upper electrode 14 to the substrate 11, from the side of the upper electrode 14 away from the piezoelectric layer 13. The first sub-region 281 is a region where the protection electrode 17 overlaps with the upper electrode 14 and does not overlap with the first dielectric layer 16. In other words, the first sub-region 281 is also the region where the first portion 171 is located; the second sub-region 282 is a region where the upper surface of the upper electrode 14 overlaps with the protection electrode 17 and the first dielectric layer 16 and the thickness of the upper electrode 14 is not reduced; the third sub-region 283 is a region of the high acoustic impedance region 28 excluding the first sub-region 281 and the second sub-region 282.

[0091] In a feasible implementation, the BAW resonator 10 may further include a seed layer 15 . The seed layer 15 is located between the lower electrode 12 and the substrate 11 . The seed layer 15 at least covers the acoustic mirror 112 . The seed layer 15 is used to improve the acoustic performance of the piezoelectric layer 13 .

[0092] This embodiment does not limit the formation position and formation method of the recessed structure, but for the convenience of subsequent description, the recessed structures of the recessed area 22 are all formed on the surface of the upper electrode 14 away from the piezoelectric layer 13, that is, the above-mentioned structure with an opening is the upper electrode 14.

[0093] It can be understood that in other embodiments of the present application, the above-mentioned embodiments can be combined with each other to reduce the longitudinal leakage of acoustic wave energy and prevent the dielectric layer from being corroded, while further reducing the impact of process errors on the stability of the resonator structure and the performance of the resonator.

[0094] In this embodiment, please refer to Figure 7 and Figure 8 , Figure 7 is the admittance curve, Figure 8 is the real part curve of admittance. Figure 7 and Figure 8 The vertical axis is the Y parameter, the unit is dB, and the horizontal axis is the frequency of the sound wave, the unit is Hz.

[0095] Figure 7 and Figure 8 The solid lines in FIG. 1 show comparative examples, that is, a BAW resonator without a recessed structure, a first dielectric layer and a protection electrode. Figure 7 and Figure 8The dashed lines in the figure all show an embodiment, that is, there is a recessed structure, a first dielectric layer and a protection electrode, and the recessed structure and the protection electrode have a first distance from the bulk acoustic wave resonator, and the first distance is 400nm as an example. Figure 8 It can be seen from the solid line and the dotted line in that in the area to the left of the resonant frequency point, the dotted line is smoother than the solid line, that is, the embodiment can better suppress the lateral mode, and the embodiment improves the electromechanical coupling coefficient compared with the comparative example.

[0096] Fig. 9 is the real part of admittance curve, Fig. 9 The vertical axis is the Y parameter, the unit is dB, and the horizontal axis is the frequency of the sound wave, the unit is GHz. Fig. 9 To compare the effect of the size deviation of the concave structure on the resonator performance of two BAW resonators, Fig. 9 The solid line is the control group, which is the performance of the BAW resonator with a recessed structure, a first dielectric layer and a protective electrode, and the size of the recessed structure does not change (the real part of the admittance curve of the BAW resonator with no deviation in the size of the recessed structure in an ideal state). Fig. 9 The long dashed line is a comparative example, which is a real part curve of the admittance of a bulk acoustic wave resonator having a recessed structure, a first dielectric layer and a protective electrode, the recessed structure and the protective electrode being arranged adjacent to each other, and a process error of 10% in the recessed structure. Fig. 9 The short dashed line is an embodiment, which is a real part curve of the admittance of a bulk acoustic wave resonator having a recessed structure, a first dielectric layer and a protection electrode, a first distance between the recessed structure (recessed area 22) and the protection electrode, and a 10% process error in the recessed structure. That is, compared with the control group, the size of the recessed structure of both the comparative example and the embodiment increases by 10% deviation. Fig. 9 As shown in the middle a area, it can be seen that when the size of the recessed structure does not deviate (i.e., the control group), the fluctuation of the real part of the admittance curve near the right side of the resonance frequency point, near the resonance frequency point, is not obvious, and both the embodiment and the comparative example have fluctuations here, but the fluctuations generated by the embodiment near the right side of the resonance frequency point are significantly smaller than those of the comparative example, that is, the fluctuations generated by the embodiment at the position near the resonance frequency point on the right side of the resonance frequency point are significantly smaller than those of the comparative example. Therefore, the present application can reduce the fluctuations near the right side of the resonance frequency point by setting a first distance between the recessed structure (recessed area 22) and the protective electrode, and the bulk acoustic wave resonator can well avoid performance changes caused by photolithography and etching processes, and has a higher fault tolerance rate.

[0097] The BAW resonator provided by the present application sets a first distance between the recessed structure (recessed area 22) and the protective electrode 17, which can effectively reduce the influence of process errors on the recessed structure while suppressing the lateral mode, and reduce the influence of the recessed structure size deviation on the structural stability and various performances of the BAW resonator, such as being able to weaken the fluctuation near the right side of the resonant frequency point of the resonator, and improve the Q value, etc. In addition, through the present application, it is also possible to reduce the dependence on process accuracy, reduce process difficulty, improve process yield, and reduce costs to a certain extent.

[0098] Second embodiment

[0099] An embodiment of the present application further provides a filter, which includes the BAW resonator 10 of any of the above embodiments.

[0100] In this embodiment, the filter can be a ladder-type structure filter, that is, the series branch between the input end and the output end includes multiple series arm resonators connected in series, and multiple parallel branches connected between the series branch and the ground end, and the parallel branch includes multiple parallel arm resonators.

[0101] In a feasible implementation, the filter may be a filter formed by mixing a surface acoustic wave resonator and a bulk acoustic wave resonator.

[0102] In a feasible implementation, the filter may include a capacitor and an inductor.

[0103] See also Fig.10 , Fig.10 Figure 2 is a comparison diagram of the filter passband. Fig.10 The vertical axis is the S parameter, the unit is dB, and the horizontal axis is the frequency of the sound wave, the unit is GHz. Fig.10 To compare the effect of the size deviation of the concave structure of two BAW resonators on the filter passband, Fig.10 The solid line in the figure is the control group, which is the influence of the BAW resonator with a recessed structure, a first dielectric layer and a protection electrode, and the size of the recessed structure has not changed on the passband of the filter. Fig.10 The long dashed line in the figure is a comparative example, which is an influence of a bulk acoustic wave resonator on the passband of a filter having a recessed structure, a first dielectric layer and a protective electrode, wherein the recessed structure is arranged adjacent to the protective electrode and a process error of 10% exists in the recessed structure. Fig.10The short dashed line in the figure is an embodiment, which is an embodiment having a recessed structure, a first dielectric layer and a protective electrode, a first distance between the recessed structure (recessed area) and the protective electrode, and the influence of a bulk acoustic wave resonator on the passband of the filter when there is a 10% process error in the recessed structure. That is to say, compared with the control group, the size of the recessed structure of the bulk acoustic wave resonator included in the filter shown in the comparative example and the embodiment has a 10% deviation. Compared with the control group, both the embodiment and the comparative example have ripples in the passband, but the ripples in the passband of the embodiment are significantly smaller than those of the comparative example.

[0104] Therefore, in the filter of the present application, the BAW resonator has the features described in the above embodiments, which can reduce the filter passband ripple, thereby improving the filter performance.

[0105] Third embodiment

[0106] The embodiment of the present application further provides a multiplexer, which includes the filter described in the second embodiment, and the filter includes any one of the bulk acoustic wave resonators described in the first embodiment.

[0107] The multiplexer may be a duplexer, a triplexer, etc., which is not limited in this embodiment.

[0108] In the multiplexer of the present application, the BAW resonator has the features described in the above embodiments, which can reduce the passband ripple of the filter and improve the filter performance, thereby improving the working performance of the multiplexer.

[0109] Fourth embodiment

[0110] The embodiment of the present application also provides a radio frequency front-end module, which includes the filter described in the second embodiment. The filter includes any one of the bulk acoustic wave resonators described in the first embodiment. This embodiment uses the bulk acoustic wave resonator provided by the present application to improve the sensitivity of the radio frequency front-end module.

[0111] The BAW resonator, filter, multiplexer and RF front-end module provided by the present application, the BAW resonator can suppress the lateral mode by providing a recessed structure to ensure the quality factor of the BAW resonator. The BAW resonator is also provided with a first dielectric layer and a protective electrode, the first dielectric layer is used to reduce the longitudinal leakage of energy, and the protective electrode is used to protect the first dielectric layer from corrosion. In addition, the protective electrode and the recessed structure maintain a first distance, and in the case of process errors, the fluctuation of the BAW resonator near the right side of the resonant frequency point can be weakened to ensure the performance of the resonator, and the influence of the recessed area on the protective electrode structure, such as deformation, can be avoided, thereby ensuring the structural stability of the BAW resonator and reducing the influence on the Q value of the resonator.

[0112] The above implementation modes are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned implementation modes, a person skilled in the art should understand that the technical solutions described in the aforementioned implementation modes can still be modified, or some of the technical features can be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various implementation modes of the present application, and should all be included in the protection scope of the present application.

Claims

1. A bulk acoustic wave resonator, characterized in that: include: a substrate having a first surface; A lower electrode, the lower electrode is disposed on the first surface, and an acoustic mirror is provided between the substrate and the lower electrode; A piezoelectric layer, the piezoelectric layer is disposed on a surface of the lower electrode away from the substrate and covers the lower electrode; An upper electrode, the upper electrode being arranged on a surface of the piezoelectric layer away from the lower electrode, the upper surface of the upper electrode having a concave structure, and in a plan view, an area where the concave structure is located is a concave area; A first dielectric layer is disposed on a surface of the piezoelectric layer away from the lower electrode, and in the top view direction, the first dielectric layer extends from the region between the upper electrode and the piezoelectric layer to the outside of the region between the upper electrode and the piezoelectric layer; A protection electrode is disposed between the piezoelectric layer and the upper electrode, wherein in the top view direction, a portion of the protection electrode is located between the region where the first dielectric layer is located and the recessed region and has a first distance from the recessed region, and another portion of the protection electrode at least covers at least a portion of the first dielectric layer; as well as The second dielectric layer is attached to the surface of the upper electrode away from the piezoelectric layer and extends from the surface of the upper electrode away from the piezoelectric layer to the surface of the piezoelectric layer away from the lower electrode.

2. The bulk acoustic wave resonator according to claim 1, characterized in that The width of the recessed structure and the first distance satisfy the following relationship: 0.05≤d1 / d2≤0.7 Wherein, d1 is the first distance, and d2 is the width of the recessed area.

3. The bulk acoustic wave resonator according to claim 1, characterized in that: An upper surface of at least one of the upper electrode, the lower electrode and the piezoelectric layer has an opening, and the opening faces away from the substrate, so as to form a concave structure corresponding to the shape of the opening on the upper surface of the upper electrode.

4. The bulk acoustic wave resonator according to claim 3, characterized in that In a structure with an opening, the thickness of the structure is h2, the thickness of the structure at the opening is h1, and the structure is one of the upper electrode, the lower electrode, and the piezoelectric layer, wherein the following relationship is satisfied between h1 and h2: 0.8≤h1 / h2<1.

5. The bulk acoustic wave resonator according to claim 1, characterized in that: Another portion of the protective electrode is attached to at least a portion of the side surface of the first dielectric layer, or another portion of the protective electrode is attached to at least a portion of the side surface of the first dielectric layer and extends to the surface of the first dielectric layer facing away from the piezoelectric layer to cover at least a portion of the surface of the first dielectric layer away from the piezoelectric layer.

6. The bulk acoustic wave resonator according to claim 1, characterized in that The area where the first dielectric layer and the protective electrode are located is a high acoustic impedance area, and the acoustic impedance value of the high acoustic impedance area is greater than the acoustic impedance value of the area outside the high acoustic impedance area; as well as Along the direction from the recessed area to the first dielectric layer, the high acoustic impedance area has three sub-areas with different acoustic impedance values ​​in sequence, and the acoustic impedance values ​​of the sub-areas away from the recessed area gradually decrease along the direction from the recessed area to the first dielectric layer.

7. The BAW resonator according to claim 1, characterized in that: The first distance is in the range of 50nm to 800nm; or, the first distance is in the range of 50nm to 600nm.

8. A filter, characterized in that: The device comprises a bulk acoustic wave resonator as claimed in any one of claims 1 to 7.

9. A multiplexer, characterized in that: Comprising the filter as claimed in claim 8.

10. A radio frequency front-end module, characterized in that: Comprising the filter as claimed in claim 8.

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