Bulk acoustic wave resonator

Abstract

The bulk acoustic wave resonator comprises a substrate, a reflective element and a resonance unit arranged on the reflective element, the resonance unit comprises a bottom electrode, a piezoelectric layer and a top electrode, the bottom electrode is arranged between the reflective element and the piezoelectric layer, and the piezoelectric layer is arranged between the bottom electrode and the top electrode; the top electrode comprises a connecting end and a non-connecting end, at least one connecting end is provided with a bridge structure, the middle part of the bridge structure protrudes towards one side far away from the piezoelectric layer, and a first gap is formed between the middle part of the bridge structure and the piezoelectric layer; at least one non-connecting end is provided with a cantilever structure, one end of the cantilever structure is connected with the non-connecting end, the other end of the cantilever structure is arranged above the piezoelectric layer, and a second gap is formed between the cantilever structure and the piezoelectric layer; the highest point of the upper surface of the cantilever structure is higher than that of the upper surface of the bridge structure; in the other scheme, the height of the second gap is larger than that of the first gap. According to the invention, the adverse effect of a transverse mode can be effectively reduced, and the quality factor Q of the resonator is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of communication devices, and particularly relates to a bulk acoustic wave resonator. BACKGROUND

[0002] The basic structure of the bulk acoustic wave resonator is a "sandwich" structure of a bottom electrode, a piezoelectric layer and a top electrode. When a high-frequency electrical signal is applied between the top and bottom electrodes, a bulk acoustic wave (BAW) propagating along the thickness direction of the piezoelectric layer is excited in the piezoelectric layer due to the inverse piezoelectric effect of the piezoelectric layer. The transmission path of the bulk acoustic wave is equal to the thickness of the top and bottom electrodes and the piezoelectric layer. When a certain relationship is satisfied between the wavelength of the bulk acoustic wave and the propagation path, a standing wave oscillation is generated, and at this time, the signal resonates inside the material, and the equivalent impedance of the device reaches a maximum value. To optimize the performance of the bulk acoustic wave in the high-frequency band (above 1 GHz), the optimal solution is to miniaturize the "sandwich" structure from a bulk structure to a thin film structure.

[0003] The resonator is divided into a film bulk acoustic resonator (FBAR) and a solidly mounted resonator (SMR) according to the different acoustic wave reflection structures. The acoustic wave reflection structure of the FBAR is a cavity, and the SMR is a Bragg reflection mirror. The cavity of the film bulk acoustic resonator includes an underground cavity embedded in the substrate and an overground cavity located on the surface of the substrate according to different positions.

[0004] As a radio frequency device, the FBAR needs a radio frequency voltage applied on the two electrodes to act as a power source. Under the action of the radio frequency voltage, the piezoelectric layer generates an alternating electric field, and due to the inverse piezoelectric effect, the piezoelectric layer produces deformation, which is microscopically manifested as the vibration of phonons and macroscopically forms an acoustic wave. This acoustic wave is a bulk acoustic wave inside the piezoelectric body, and through this process, the electrical energy is converted into mechanical energy.

[0005] Ideally, the acoustic wave is expected to be a longitudinal wave mode propagating along the thickness direction of the piezoelectric layer, but in fact, there are transverse modes propagating along other directions. The existence of the transverse mode belongs to energy loss, which adversely affects the quality factor Q.

[0006] Therefore, how to further reduce the transverse mode of the acoustic wave and improve the performance of the device has become a problem that needs to be considered in the design of the resonator. CONTENT OF THE INVENTION

[0007] In order to solve the above technical problems in the prior art, the present application provides a bulk acoustic wave resonator to solve the above problems.

[0008] According to the first aspect of the utility model, a kind of bulk acoustic wave resonator, including substrate, reflective element and the resonant unit being arranged on reflective element, reflective element is arranged between the substrate and resonant unit;Resonant unit includes bottom electrode, piezoelectric layer and top electrode, bottom electrode is set between reflective element and piezoelectric layer, piezoelectric layer is set between bottom electrode and top electrode;

[0009] Top electrode includes connecting end and non-connecting end, at least one connecting end is provided with bridge structure, both ends of bridge structure are supported on piezoelectric layer and middle part is raised to the side away from piezoelectric layer, and first gap is formed between bridge structure and piezoelectric layer;

[0010] At least one non-connecting end is provided with cantilever structure, one end of cantilever structure is connected with non-connecting end, the other end is arranged above piezoelectric layer, and second gap is formed between cantilever structure and piezoelectric layer;

[0011] The highest point of the upper surface of cantilever structure is higher than the highest point of the upper surface of bridge structure. By the setting, the adverse effect of transverse mode on the performance of resonator can be reduced, and the quality factor Q of resonator is helped to improve.

[0012] In some embodiments, the maximum thickness of bridge structure and cantilever structure is same. Specifically, the thickness of bridge structure, cantilever structure and top electrode in the active region of resonator is same, and the active region of resonator is the overlapping region of reflective element, bottom electrode, piezoelectric layer and top electrode

[0013] In some embodiments, the maximum thickness of cantilever structure is greater than the maximum thickness of bridge structure, and the maximum height of first gap and second gap is same. Specifically, in the case of keeping the maximum thickness of bridge structure and the maximum thickness of top electrode in the active region of resonator same, the maximum thickness of cantilever structure is greater than the maximum thickness of bridge structure and the maximum height of first gap and second gap is same.

[0014] In some embodiments, the maximum thickness of cantilever structure is greater than the maximum thickness of bridge structure, and the maximum height of first gap is greater than the maximum height of second gap. Specifically, in the case of keeping the maximum thickness of bridge structure and the maximum thickness of top electrode in the active region of resonator same, the maximum thickness of cantilever structure is greater than the maximum thickness of bridge structure and the maximum height of first gap is greater than the maximum height of second gap.

[0015] According to the second aspect of the utility model, a kind of bulk acoustic wave resonator, including substrate, reflective element and the resonant unit being arranged on reflective element, reflective element is arranged between the substrate and resonant unit;Resonant unit includes bottom electrode, piezoelectric layer and top electrode, bottom electrode is set between reflective element and piezoelectric layer, piezoelectric layer is set between bottom electrode and top electrode;

[0016] The top electrode comprises a connecting end and a non-connecting end, at least one connecting end is provided with a bridge structure, two ends of the bridge structure are supported on the piezoelectric layer and the middle part is raised to the side away from the piezlectric layer, and a first gap is formed between the bridge structure and the piezoelectric layer;

[0017] At least one non-connecting end is provided with a cantilever structure, one end of the cantilever structure is connected to the non-connecting end, the other end is arranged above the piezoelectric layer, and a second gap is formed between the cantilever structure and the piezoelectric layer;

[0018] The maximum height of the second gap is greater than the maximum height of the first gap. Through the setting, the adverse effects of the transverse mode can be reduced, and the quality factor Q of the resonator is improved.

[0019] In some embodiments, the highest point of the upper surface of the cantilever structure is the same as the highest point of the upper surface of the bridge structure.

[0020] In some embodiments, the highest point of the upper surface of the bridge structure is higher than the highest point of the upper surface of the cantilever structure.

[0021] In some embodiments, the first gap is filled with a cavity or a low acoustic impedance filling material, the second gap is filled with a cavity or a low acoustic impedance filling material, and the low acoustic impedance filling material comprises carbon-doped silicon dioxide, dielectric resin or benzocyclobutene.

[0022] In some embodiments, the reflective element comprises a cavity structure or a Bragg reflection layer, and the cavity structure comprises a subsurface cavity embedded in the substrate or a surface cavity located on the surface of the substrate.

[0023] The bulk acoustic wave resonator of the utility model through setting bridge structure, cantilever structure and corresponding gap, and further through the setting of different height setting, thickness relationship and gap filler, reduce the adverse effects of the transverse mode from multiple aspects, improve the quality factor Q of the resonator, and reduce the stray mode. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings are included to provide a further understanding of 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 utility model. Other embodiments and many of the intended advantages of the 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.

[0025] Figure 1 is the cross-sectional schematic view of the bulk acoustic wave resonator of the first embodiment of the utility model;

[0026] Figure 2 is the cross-sectional schematic view of the bulk acoustic wave resonator of the second embodiment of the utility model;

[0027] Figure 3 is a cross-sectional schematic view of a bulk acoustic wave resonator of a third embodiment of the utility model;

[0028] Figure 4 is a cross-sectional schematic view of a bulk acoustic wave resonator of a fourth embodiment of the utility model;

[0029] Figure 5 is a cross-sectional schematic view of a bulk acoustic wave resonator of a fifth embodiment of the utility model;

[0030] Figure 6 is a cross-sectional schematic view of a bulk acoustic wave resonator of a sixth embodiment of the utility model;

[0031] Figure 7 is a cross-sectional schematic view of a bulk acoustic wave resonator of a seventh embodiment of the utility model. DETAILED DESCRIPTION

[0032] The application will be further described below in detail with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related utility model, and not to limit the utility model. In addition, it should be noted that, for the convenience of description, only the parts related to the utility model are shown in the drawings.

[0033] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and embodiments.

[0034] Figure 1 shows a cross-sectional schematic view of a bulk acoustic wave resonator according to a first embodiment of the utility model, as Figure 1 shown, the resonator comprises a reflective element 1, a bottom electrode 2, a piezoelectric layer 3, a top electrode 4 and a substrate 5, wherein the reflective element 1 is arranged between the substrate 5 and the resonant unit, the resonant unit comprises the bottom electrode 2, the piezoelectric layer 3 and the top electrode 4 arranged in layers, the bottom electrode 2 is arranged between the reflective element 1 and the piezoelectric layer 3, and the piezoelectric layer 3 is arranged between the bottom electrode 2 and the top electrode 4.

[0035] The top electrode 4 comprises a connection end and a non-connection end, at least one connection end is provided with a bridge structure 6, both ends of the bridge structure 6 are supported on the piezoelectric layer and the middle part is raised to the side away from the piezoelectric layer 3, so as to form a first gap 7 between the bridge structure 6 and the piezoelectric layer 3.

[0036] At least one non-connection end of the top electrode 4 is provided with a cantilever structure 8, the cantilever structure 8 comprises a cantilever part 81 and a connecting part 82, both of which are not in the plane where the top electrode 4 is located, one end of the connecting part 82 is connected to the non-connection end of the top electrode 4, the other end is connected to the cantilever part 81, and the connecting part 82 forms an angle with the plane where the top electrode 4 is located, and the cantilever part 81 extends to the side away from the effective resonance area, thereby forming a second gap 9 between the cantilever structure 8 and the piezoelectric layer 3.

[0037] In this embodiment, the active area of the resonator is the overlapping area of the reflective element 1, the bottom electrode 2, the piezoelectric layer 3 and the top electrode 4. The thickness of the bridge structure 6 is the same as that of the top electrode 4 in the active area, the thickness of the cantilever structure 8 is the same as that of the top electrode 4 in the active area, the highest point of the upper surface of the bridge structure 6 is higher than that of the top electrode 4 in the active area, the highest point of the upper surface of the cantilever structure 8 is higher than that of the bridge structure 6, and the height difference between the two is h1 shown in the figure. Through this structure, the adverse effects of transverse modes on the performance of the resonator can be effectively reduced, and the quality factor Q of the resonator can be improved.

[0038] In this embodiment, the first gap 7 and the second gap 9 are air gaps. A sacrificial layer (not shown) containing phosphosilicate glass (PSG) containing 8% phosphorus and 92% silicon dioxide is deposited on a portion of the piezoelectric layer 3 by known technology, and the sacrificial layer is etched away by hydrofluoric acid after the top electrode 4 is formed, thereby leaving the first gap 7 and the second gap 9.

[0039] Figure 2 A cross-sectional schematic view of a bulk acoustic wave resonator according to a second embodiment of the present application is shown in FIG. 2, which is similar to Figure 2 FIG. 1, and Figure 1 The difference between the two embodiments is that the maximum thickness of the bridge structure 6 in this embodiment is the same as the maximum thickness of the top electrode 4 in the active area, the maximum thickness of the cantilever structure 8 is greater than the maximum thickness of the bridge structure 6, and the maximum height of the first gap 7 is the same as the maximum height of the second gap 9.

[0040] Figure 3 A cross-sectional schematic view of a bulk acoustic wave resonator according to a third embodiment of the present application is shown in FIG. 3, which is similar to Figure 3 FIG. 2, and Figure 2 The difference between the two embodiments is that the maximum thickness of the bridge structure 6 in this embodiment is the same as the maximum thickness of the top electrode 4 in the active area, the maximum thickness of the cantilever structure 8 is greater than the maximum thickness of the bridge structure 6, and the maximum height of the first gap 7 is greater than the maximum height of the second gap 9, and the height difference between the two is h2 shown in the figure.

[0041] Continuing to refer to Figure 4 and Figure 5 , Figure 4A cross-sectional schematic view of a bulk acoustic wave resonator of a fourth embodiment of the utility model is shown in the figure, Figure 4 As shown in the figure, this embodiment is based on the embodiment of Figure 1 The first gap 7 is set to a low acoustic impedance material, such as carbon (C) doped SiO2, dielectric resin or benzocyclobutene (BCB), and the second gap 9 remains as a void.

[0042] Figure 5 A cross-sectional schematic view of a bulk acoustic wave resonator of a fifth embodiment of the utility model is shown in the figure, Figure 5 As shown in the figure, this embodiment is based on the embodiment of Figure 1 The second gap 9 is set to a low acoustic impedance material, such as carbon (C) doped SiO2, dielectric resin or benzocyclobutene (BCB), and the first gap 7 remains as a void.

[0043] Figure 6 A cross-sectional schematic view of a bulk acoustic wave resonator of a sixth embodiment of the utility model is shown in the figure, Figure 6 As shown in the figure, the maximum thickness of the cantilever structure 8 in this embodiment is the same as the maximum thickness of the top electrode 4 in the active region, the maximum thickness of the bridge structure 6 is greater than the maximum thickness of the cantilever structure 8, and the upper surface highest point of the cantilever structure 8 is flush with the upper surface highest point of the bridge structure 6; the highest point of the second gap 9 is higher than the highest point of the first gap 7, and the height difference between the two is h3 shown in the figure.

[0044] Figure 7 A cross-sectional schematic view of a bulk acoustic wave resonator of a seventh embodiment of the utility model is shown in the figure, Figure 7 As shown in the figure, this embodiment is different from the embodiment of Figure 6 The difference between this embodiment and the embodiment of

[0045] In all the above embodiments, the reflective element 1 can be a cavity structure or a Bragg reflection layer structure. When the reflective element 1 is a cavity structure, it can be a surface cavity structure on the surface of the substrate 5 in addition to the underground cavity structure embedded in the substrate 5 in the above embodiments.

[0046] With reference to the embodiments of Figure 4 and Figure 5 In the above other embodiments, the first gap 7 and the second gap 9 can be set to a void, a low acoustic impedance material or a combination of the two as needed to reduce the spurious mode of the resonator and improve the performance of the resonator.

[0047] The specific implementation of the present application is described above, but the protection scope of the present application is not limited thereto, any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0048] In the description of the present application, it should be understood that the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. The word 'comprising' does not exclude the existence of elements or steps not listed in the claims. The word 'one' or 'an' in front of an element does not exclude the existence of multiple such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that the combination of these measures cannot be used to improve. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. A bulk acoustic wave resonator, characterized in that: The invention comprises a substrate, a reflective element and a resonant unit arranged on the reflective element, wherein the reflective element is arranged between the substrate and the resonant unit; the resonant unit comprises a bottom electrode, a piezoelectric layer and a top electrode, wherein the bottom electrode is arranged between the reflective element and the piezoelectric layer, and the piezoelectric layer is arranged between the bottom electrode and the top electrode; The top electrode includes a connecting end and a non-connecting end, at least one of the connecting ends is provided with a bridge structure, both ends of the bridge structure are supported on the piezoelectric layer and the middle portion bulges away from the piezoelectric layer, and a first gap is formed between the bridge structure and the piezoelectric layer; A cantilever structure is provided on at least one of the non-connected ends, one end of the cantilever structure is connected to the non-connected end, and the other end is provided above the piezoelectric layer, and a second gap is formed between the cantilever structure and the piezoelectric layer; The highest point of the upper surface of the cantilever structure is higher than the highest point of the upper surface of the bridge structure.

2. The bulk acoustic wave resonator according to claim 1, wherein The bridge structure and the cantilever structure have the same maximum thickness.

3. The bulk acoustic wave resonator according to claim 1, wherein The maximum thickness of the cantilever structure is greater than the maximum thickness of the bridge structure, and the maximum heights of the first gap and the second gap are the same.

4. The bulk acoustic wave resonator according to claim 1, wherein The maximum thickness of the cantilever structure is greater than the maximum thickness of the bridge structure, and the maximum height of the first gap is greater than the maximum height of the second gap.

5. A bulk acoustic wave resonator, characterized in that: The invention comprises a substrate, a reflective element and a resonant unit arranged on the reflective element, wherein the reflective element is arranged between the substrate and the resonant unit; the resonant unit comprises a bottom electrode, a piezoelectric layer and a top electrode, wherein the bottom electrode is arranged between the reflective element and the piezoelectric layer, and the piezoelectric layer is arranged between the bottom electrode and the top electrode; The top electrode includes a connecting end and a non-connecting end, at least one of the connecting ends is provided with a bridge structure, both ends of the bridge structure are supported on the piezoelectric layer and the middle portion bulges away from the piezoelectric layer, and a first gap is formed between the bridge structure and the piezoelectric layer; A cantilever structure is provided on at least one of the non-connected ends, one end of the cantilever structure is connected to the non-connected end, and the other end is provided above the piezoelectric layer, and a second gap is formed between the cantilever structure and the piezoelectric layer; The maximum height of the second gap is greater than the maximum height of the first gap.

6. The bulk acoustic wave resonator according to claim 5, characterized in that The highest point on the upper surface of the cantilever structure is at the same height as the highest point on the upper surface of the bridge structure.

7. The bulk acoustic wave resonator according to claim 5, characterized in that The highest point of the upper surface of the bridge structure is higher than the highest point of the upper surface of the cantilever structure.

8. The bulk acoustic wave resonator according to any one of claims 5 to 7, characterized in that: The first gap is filled with a cavity or a low acoustic impedance filling material, and the second gap is filled with a cavity or a low acoustic impedance filling material.

9. The bulk acoustic wave resonator according to any one of claims 5 to 7, characterized in that: The reflective element includes a cavity structure or a Bragg reflection layer. The cavity structure includes a subsurface cavity embedded in the substrate or an above-ground cavity located on the surface of the substrate.

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