Thin film bulk acoustic wave resonator and method for manufacturing the same

Abstract

The present application relates to a thin film bulk acoustic wave resonator and a method for manufacturing the same. The thin film bulk acoustic wave resonator comprises a substrate, a first electrode, a piezoelectric layer and a second electrode which are stacked in sequence. A plurality of holes are arranged in a resonance region of the piezoelectric layer. The cross-sectional shape of the holes in a direction parallel to the substrate is adapted to a crystal structure in the piezoelectric layer, thereby greatly reducing the transmission of transverse sound waves in the piezoelectric layer and effectively avoiding the transverse leakage of sound wave energy.

Description

[Technical field]

[0001] The invention relates to the field of resonators, and in particular to a thin film bulk acoustic wave resonator and a manufacturing method thereof. [Background technology]

[0002] With the rapid development of wireless communications, wireless signals are becoming more and more crowded, which puts forward new requirements for filters working in the radio frequency band, such as integration, miniaturization, low power consumption, high performance and low cost.

[0003] Film bulk acoustic resonator (FBAR) is widely used in filters due to its advantages such as CMOS process compatibility, high quality factor (Q value), low loss, low temperature coefficient, and high power carrying capacity. At present, there are two main energy losses in the existing FBAR during operation: energy loss of lateral waves and friction loss between crystal columns during longitudinal vibration. How to reduce the energy loss of FBAR is the focus of current filter research. [Summary of the invention]

[0004] The object of the present invention is to provide a thin film bulk acoustic wave resonator and a manufacturing method thereof, which can effectively reduce the energy loss of the thin film bulk acoustic wave resonator and improve the overall performance of the filter.

[0005] According to a first aspect of the present invention, there is provided a thin film bulk acoustic wave resonator, comprising a substrate, a first electrode, a piezoelectric layer and a second electrode stacked in sequence, wherein a plurality of holes are provided in a resonance region of the piezoelectric layer, and a cross-sectional shape of the holes in a direction parallel to the substrate is adapted to a crystal structure in the piezoelectric layer.

[0006] The crystal structure is a wurtzite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a hexagon.

[0007] The crystal structure is a perovskite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a quadrilateral.

[0008] The hole penetrates the piezoelectric layer in a direction perpendicular to the substrate, or the top of the hole contacts the lower surface of the second electrode and the bottom does not contact the upper surface of the first electrode, or the bottom of the hole contacts the upper surface of the first electrode and the top does not contact the lower surface of the second electrode.

[0009] Wherein, the holes are filled with silicon dioxide.

[0010] According to another aspect of the present invention, there is provided a method for manufacturing a thin film bulk acoustic wave resonator, comprising:

[0011] providing a substrate;

[0012] forming a first electrode on the substrate;

[0013] forming a piezoelectric layer on the first electrode;

[0014] A plurality of holes and a second electrode are formed in the resonance region of the piezoelectric layer, and the cross-sectional shape of the holes in a direction parallel to the substrate is adapted to the crystal structure in the piezoelectric layer.

[0015] Wherein, forming a plurality of holes and a second electrode in the resonance region of the piezoelectric layer comprises:

[0016] forming a plurality of holes in the resonance region of the piezoelectric layer, and filling the holes with a sacrificial layer;

[0017] forming a second electrode on the piezoelectric layer filled with the sacrificial layer;

[0018] forming at least one channel on the piezoelectric layer on which the second electrode is formed, wherein the channel penetrates the hole in a direction parallel to the substrate;

[0019] The sacrificial layer in the hole is removed by dry etching using the pipe.

[0020] Wherein, forming a plurality of holes and a second electrode in the resonance region of the piezoelectric layer comprises:

[0021] forming a plurality of holes in the resonance region of the piezoelectric layer, and filling the holes with silicon dioxide;

[0022] A second electrode is formed on the piezoelectric layer filled with the silicon dioxide.

[0023] The crystal structure is a wurtzite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a hexagon.

[0024] The crystal structure is a perovskite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a quadrilateral.

[0025] The beneficial effect of the present application is that, different from the prior art, the thin film bulk acoustic wave resonator and its manufacturing method in the present application, by providing a plurality of holes in the resonance region of the piezoelectric layer, and making the cross-sectional shape of the holes in the direction parallel to the substrate adapt to the crystal structure in the piezoelectric layer, can greatly reduce the transmission of transverse sound waves in the piezoelectric layer, effectively avoid the lateral leakage of sound wave energy, and improve the performance of the thin film bulk acoustic wave resonator.

Brief Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 It is a schematic diagram of the propagation direction of acoustic wave energy in an existing thin film bulk acoustic resonator;

[0028] Figure 2 is a schematic top view of a thin film bulk acoustic resonator provided in an embodiment of the present application;

[0029] Figure 3 is a schematic top view of another thin film bulk acoustic resonator provided in an embodiment of the present application;

[0030] Figure 4 yes Figure 2 or Figure 3 Schematic cross-sectional view of the thin film bulk acoustic resonator along line nn;

[0031] Figure 5 yes Figure 2 or Figure 3 A schematic cross-sectional view of another thin film bulk acoustic resonator along line nn;

[0032] Figure 6 is a cross-sectional schematic diagram of another thin film bulk acoustic resonator provided in an embodiment of the present application;

[0033] Figure 7 is a cross-sectional schematic diagram of another thin film bulk acoustic resonator provided in an embodiment of the present application;

[0034] Figure 8 is a top view schematic diagram of another thin film bulk acoustic resonator provided in an embodiment of the present application;

[0035] Fig. 9 is a schematic top view of another thin film bulk acoustic resonator provided in an embodiment of the present application;

[0036] Fig.10 is a cross-sectional schematic diagram of another thin film bulk acoustic resonator provided in an embodiment of the present application;

[0037] Fig.11 is a flow chart of a method for manufacturing a thin film bulk acoustic resonator provided in an embodiment of the present application;

[0038] Fig.12 is a cross-sectional schematic diagram of another thin film bulk acoustic resonator provided in an embodiment of the present application;

[0039] Fig.13 is a schematic diagram of the structure of a ladder filter provided in an embodiment of the present application;

[0040] Fig.14 It is a schematic diagram of the structure of the grid filter provided in the embodiment of the present application. [Specific implementation method]

[0041] The present application is further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present application, but are not intended to limit the scope of the present application. Similarly, the following examples are only some embodiments of the present application rather than all embodiments, and all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present application.

[0042] It should be understood that, in the description of the present application, the terms "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, in the description of the present application, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0043] See also Figure 1 , Figure 1 The schematic diagram of the propagation direction of acoustic wave energy in an existing thin film acoustic wave resonator is shown in FIG. The thin film acoustic wave resonator 10 includes an upper electrode 11, a piezoelectric layer 12, and a lower electrode 13 stacked in sequence. When an RF signal is added to the upper electrode 11 and the lower electrode 13, each single crystal column in the piezoelectric layer 12 begins to resonate. The two adjacent crystal columns may generate friction losses along the direction of ① due to the asynchronous resonance. At the same time, the lateral expansion may cause losses along the direction of ② when the acoustic wave energy propagates, which greatly affects the performance of the thin film acoustic wave resonator 10.

[0044] See also Figure 2 , Figure 3 , Figure 4 and Figure 5 , Figure 2 A schematic top view of a thin film bulk acoustic resonator provided in an embodiment of the present application, Figure 3 A schematic top view of another thin film bulk acoustic resonator provided in an embodiment of the present application, Figure 4 and Figure 5 for Figure 2 or Figure 3 A thin film bulk acoustic wave resonator 20 comprises a substrate 21, a first electrode 22, a piezoelectric layer 23 and a second electrode 24 which are stacked in sequence, a plurality of holes (such as 231a and 231b) are provided in the resonance region of the piezoelectric layer 23, and the cross-sectional shape of the holes in the direction parallel to the substrate 21 is adapted to the crystal structure in the piezoelectric layer 23.

[0045] Specifically, a cavity M is formed between the substrate 21, the piezoelectric layer 23 and the first electrode 22. The cavity M can be formed by releasing the sacrificial layer made of the transition material during manufacturing. The substrate 21 can be a silicon substrate, and the first electrode 22 and the second electrode 24 can be made of a conductive material, such as gold (Au), titanium (Ti), tantalum (Ta), molybdenum (Mu), tungsten (Wu), aluminum (Al), etc., or any combination thereof, wherein the first electrode 22 serves as a bottom electrode and the second electrode 24 serves as a top electrode. The piezoelectric layer 23 can be made of materials having piezoelectric properties such as aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate PZT, or materials having piezoelectric properties after doping, and is usually transparent. In actual operation, when electrical energy such as an RF signal is applied to the first electrode 22 and the second electrode 24, the piezoelectric layer 23 will vibrate due to the piezoelectric effect, and the vibration will resonate through the reflection of the cavity M, thereby realizing the filtering function of the thin film bulk acoustic wave resonator 20 for the radio frequency signal.

[0046] It should be explained that when the FBAR 20 is working, although the main energy is in the longitudinal direction (i.e. Figure 4 y direction) propagates, but at different wavelengths there will be a small amount of lateral (i.e. Figure 4 At the same time, considering that different materials have different acoustic impedances, when the transverse acoustic wave in the thin film bulk acoustic wave resonator 20 passes through a discontinuous interface and is transmitted from medium A to medium B, if the acoustic impedance of medium B is much greater than that of medium A, the transverse acoustic wave will be reflected and refracted, and finally the propagation direction will be changed to propagate in the longitudinal direction. In view of this mechanism, the piezoelectric layer 23 can be set as a discontinuous dielectric layer, for example, hollow holes are set in the piezoelectric layer 23, so that the piezoelectric layer 23 includes air and piezoelectric material, two media with completely different acoustic impedances. For details, see Figure 5 Alternatively, a solid hole may be provided in the piezoelectric layer 23, such as Figure 4 The holes 231a and 231b are filled with silicon dioxide SiO2, so that the piezoelectric layer 23 includes two media, SiO2 and piezoelectric material, which can greatly reduce the transmission of transverse waves and effectively avoid the transverse leakage of sound wave energy.

[0047] Among them, under normal solidification conditions, all metals, ceramic materials or certain polymer materials will form a crystal structure, that is, on the periodic table, atoms, ions or molecules are regularly arranged in space, and the structure of metal crystals is regular and infinitely extended, and all items are isotropic. Therefore, the crystal stacking structure can be regarded as a unit lattice, and the common lattice arrangements are face-centered cubic, body-centered cubic and hexagonal closest packing. In order to form holes in the piezoelectric layer 23 without destroying the rule of infinite extension of the material, the hole shape can be designed according to the shape of the crystal structure in the piezoelectric layer 23, so as to lose the least unit lattice. Preferably, in Figure 2 In the embodiment, when the crystal structure is a wurtzite structure, the cross-sectional shape of the hole 231a in the direction parallel to the substrate 21 is a hexagon. Figure 3 In the embodiment, when the crystal structure is a perovskite structure, the cross-sectional shape of the hole 231 b in a direction parallel to the substrate 21 is a quadrilateral.

[0048] It should be noted that the depth, arrangement and size of the holes in the piezoelectric layer 23 can be determined according to requirements. Specifically, the holes can penetrate the piezoelectric layer 23 in a direction perpendicular to the substrate 21. Figure 4 The holes 231a and 231b in the piezoelectric layer 23 may also penetrate a portion of the piezoelectric layer 23, for example, see Figure 6 and Figure 7 ,in, Figure 6 The top of the hole 231d in the hole 231d contacts the lower surface of the second electrode 24, but the bottom of the hole 231d does not contact the upper surface of the first electrode 22. Figure 7 The bottom end of the hole 213e in the piezoelectric layer 23 contacts the upper surface of the first electrode 22, but the top end thereof does not contact the upper surface of the second electrode 24. The holes in the piezoelectric layer 23 may be closely arranged at equal intervals, such as Figure 2 The holes 231b in the embodiment may also be arranged at equal intervals and far apart, for example Figure 8 Alternatively, the arrangement density may decrease gradually from the center to the edge, such as Fig. 9 The arrangement density of the holes 231g in the cavity may also be gradually increased from the center to the edge, for example Fig.10 Hole 231h in.

[0049] In addition, based on the above-mentioned film bulk acoustic wave resonator 20, the embodiment of the present application also provides a method for manufacturing the above-mentioned film bulk acoustic wave resonator 20, see Fig.11 and Figures 2 to 7 A method for manufacturing a thin film bulk acoustic wave resonator 20 includes the following steps S101 to S104, wherein:

[0050] Step S101, providing a substrate 21;

[0051] Step S102, forming a first electrode 22 on the substrate 21;

[0052] Step S103, forming a piezoelectric layer 23 on the first electrode 22;

[0053] Step S104 , forming a plurality of holes (such as 231 a and 231 b ) and a second electrode 24 in the resonance region of the piezoelectric layer 23 , wherein the cross-sectional shape of the holes in a direction parallel to the substrate 21 is adapted to the crystal structure of the piezoelectric layer 23 .

[0054] Preferably, Figure 2 In the embodiment, when the crystal structure is a wurtzite structure, the cross-sectional shape of the hole 231a in the direction parallel to the substrate 21 is a hexagon. Figure 3 In the embodiment, when the crystal structure is a perovskite structure, the cross-sectional shape of the hole 231 b in a direction parallel to the substrate 21 is a quadrilateral.

[0055] Specifically, the hole can be a hollow hole or a solid hole. When the hole is a solid hole (see Figure 4 ), the above step S104 may specifically include:

[0056] A plurality of holes 231a (231b) are formed on the piezoelectric layer 23, and silicon dioxide is filled in the holes 231a (231b);

[0057] A second electrode 24 is formed on the piezoelectric layer 23 filled with the silicon dioxide.

[0058] The holes 231 a ( 231 b ) formed by etching may be filled with SiO 2 , and then the second electrode 24 may be directly formed on the piezoelectric layer 23 .

[0059] When the hole is a hollow hole (see Fig.12 ), the above step S104 may specifically include:

[0060] A plurality of holes 231i are formed on the piezoelectric layer 23, and a sacrificial layer (not shown in the figure) is filled in the holes 231f;

[0061] forming a second electrode 24 on the piezoelectric layer 23 filled with the sacrificial layer;

[0062] At least one channel 232 is formed on the piezoelectric layer 23 having the second electrode 24 formed thereon, and the channel 232 penetrates the hole 231i in a direction parallel to the substrate 21;

[0063] The sacrificial layer in the hole 231 i is removed by dry etching using the channel 232 .

[0064] Among them, Fig.12In the figure, the thin film bulk acoustic wave resonator 20 also includes a pipe 232 that penetrates the hole 231i along a direction parallel to the substrate 21 (i.e., the x direction), and the pipe 232 is used to provide etching gas to the hole 231i, such as injecting a certain proportion of mixed gas into the pipe 232, thereby removing the sacrificial layer in the hole 231i to form a hollow hole.

[0065] In addition, based on the above-mentioned film bulk acoustic wave resonator 20 , an embodiment of the present application further provides a filter, comprising a plurality of any of the above-mentioned film bulk acoustic wave resonators 20 .

[0066] For details, see Fig.13 and Fig.14 , Fig.13 A ladder filter structure 30 is shown. Fig.14 A mesh filter structure 40 is shown, wherein both types of filters include a signal output terminal Vout and a signal input terminal Vin, the ladder filter 30 includes at least two thin film bulk acoustic wave resonators 20, and the mesh filter 40 includes at least four thin film bulk acoustic wave resonators 20.

[0067] Different from the prior art, the film bulk acoustic wave resonator 20 and its manufacturing method in the present application, by providing a plurality of holes on the piezoelectric layer 23 and making the cross-sectional shape of the holes in the direction parallel to the substrate 21 compatible with the crystal structure in the piezoelectric layer 23, can greatly reduce the transmission of lateral sound waves in the piezoelectric layer 23, effectively avoid lateral leakage of sound wave energy, and improve the performance of the film bulk acoustic wave resonator 20.

[0068] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A thin film bulk acoustic resonator, characterized in that: It comprises a substrate, a first electrode, a piezoelectric layer and a second electrode which are stacked in sequence, wherein a plurality of holes arranged at intervals are provided in a resonance region of the piezoelectric layer, and a cross-sectional shape of the holes in a direction parallel to the substrate is adapted to a crystal structure in the piezoelectric layer; The arrangement density of the holes gradually decreases or increases from the center to the edge.

2. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The crystal structure is a wurtzite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a hexagon.

3. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The crystal structure is a perovskite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a quadrilateral.

4. The thin film bulk acoustic resonator according to any one of claims 1 to 3, characterized in that: The hole penetrates the piezoelectric layer in a direction perpendicular to the substrate, or the top end of the hole contacts the lower surface of the second electrode and the bottom end does not contact the upper surface of the first electrode, or the bottom end of the hole contacts the upper surface of the first electrode and the top end does not contact the lower surface of the second electrode.

5. The thin film bulk acoustic resonator according to any one of claims 1 to 3, characterized in that: The holes are filled with silicon dioxide.

6. A method for manufacturing a thin film bulk acoustic resonator, characterized in that: include: providing a substrate; forming a first electrode on the substrate; forming a piezoelectric layer on the first electrode; A plurality of spaced holes and a second electrode are formed in the resonance region of the piezoelectric layer, the cross-sectional shape of the holes in a direction parallel to the substrate is adapted to the crystal structure in the piezoelectric layer, and the arrangement density of the holes gradually decreases or increases from the center to the edge.

7. The method for manufacturing a thin film bulk acoustic wave resonator according to claim 6, characterized in that: The forming of a plurality of holes and a second electrode in the resonance region of the piezoelectric layer comprises: forming a plurality of holes in the resonance region of the piezoelectric layer, and filling the holes with a sacrificial layer; forming a second electrode on the piezoelectric layer filled with the sacrificial layer; forming at least one channel on the piezoelectric layer on which the second electrode is formed, wherein the channel penetrates the hole in a direction parallel to the substrate; The sacrificial layer in the hole is removed by dry etching using the pipe.

8. The method for manufacturing a thin film bulk acoustic wave resonator according to claim 6, characterized in that: The forming of a plurality of holes and a second electrode in the resonance region of the piezoelectric layer comprises: forming a plurality of holes in the resonance region of the piezoelectric layer, and filling the holes with silicon dioxide; A second electrode is formed on the piezoelectric layer filled with the silicon dioxide.

9. The method for manufacturing a thin film bulk acoustic resonator according to any one of claims 6 to 8, characterized in that: The crystal structure is a wurtzite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a hexagon.

10. The method for manufacturing a thin film bulk acoustic resonator according to any one of claims 6 to 8, characterized in that: The crystal structure is a perovskite structure, and the cross-sectional shape of the hole in a direction parallel to the substrate is a quadrilateral.

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