Bulk acoustic wave resonator, method of manufacturing the same, filter, and duplexer

Abstract

The application provides a bulk acoustic resonator, comprising a substrate, a bottom electrode, a piezoelectric layer and a top electrode, wherein the bottom electrode comprises a bottom electrode main body part and a bottom electrode reflection part; the bottom electrode main body part comprises a first metal layer, a first space release layer after heating or cooling, a first air gap and a second metal layer from bottom to top in sequence, the second metal layer is formed on the first metal layer and covers the first air gap and the first space release layer after heating or cooling, wherein the first air gap is formed by the space released by the volume contraction of the first space release layer after heating or cooling; the bottom electrode reflection part comprises a first recessed frame and / or a first protruding frame formed on the upper surface of the bottom electrode main body part at the edge of the effective area of the bulk acoustic resonator; and the horizontal direction projection overlapping area of the top electrode, the piezoelectric layer, the second metal layer and the first air gap constitutes the effective area of the bulk acoustic resonator. The application has the characteristics of simple process, low cost and excellent performance.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a bulk acoustic wave resonator, its manufacturing method, a filter, and a duplexer. Background Technology

[0002] Please refer to Figure 1 , Figure 1 This is a cross-sectional schematic diagram of a common bulk acoustic wave resonator in the prior art. As shown, the bulk acoustic wave resonator includes a substrate 10, a bottom electrode 11, a piezoelectric layer 12, a top electrode 13, and a cavity 14. A groove is formed on the substrate 10, the bottom electrode 11 is formed on the substrate 10 and above the groove, the piezoelectric layer 12 is formed on the bottom electrode 11, and the top electrode 13 is formed on the piezoelectric layer 12. The groove on the substrate 10 and the bottom electrode 11 form the cavity 14 for sound wave reflection. Furthermore, the overlapping area of ​​the horizontal projections of the top electrode 13, the piezoelectric layer 12, the bottom electrode 11, and the cavity 14 constitutes the effective region of the bulk acoustic wave resonator.

[0003] In existing technologies, the cavity is formed by first etching a substrate to create a groove, filling the groove with sacrificial material, and then removing the sacrificial material through a release channel using an etching solution after forming the top electrode. This method results in a complex and costly manufacturing process for bulk acoustic wave resonators. Furthermore, ideally, the sound waves generated by a bulk acoustic wave resonator should be completely confined within the effective region, but in reality, some sound waves still leak out from the effective region (i.e., lateral leakage of sound waves), leading to a decrease in the quality factor of the bulk acoustic wave resonator. Summary of the Invention

[0004] To overcome the aforementioned deficiencies in the prior art, the present invention provides a method for manufacturing a bulk acoustic resonator, the method comprising:

[0005] Provide substrate;

[0006] A bottom electrode is formed on the substrate. The bottom electrode includes a bottom electrode body and a bottom electrode reflective portion. The bottom electrode body includes, from bottom to top, a first metal layer, a first space release layer, and a second metal layer. The second metal layer is formed on the first metal layer and covers the first space release layer. The bottom electrode reflective portion includes a first recessed frame and / or a first protruding frame formed on the upper surface of the bottom electrode body at the edge of the effective region of the bulk acoustic wave resonator. The first space release layer shrinks in volume after heating or cooling.

[0007] A piezoelectric layer is formed on the bottom electrode, and a top electrode is formed on the piezoelectric layer;

[0008] The manufacturing method further includes: heating or cooling the first space release layer to shrink its volume and release the space to form a first air gap in the bottom electrode body;

[0009] The horizontal projection overlap of the top electrode, the piezoelectric layer, the second metal layer, and the first air gap constitutes the effective region of the bulk acoustic resonator.

[0010] According to one aspect of the present invention, in the manufacturing method, the step of forming a bottom electrode on the substrate includes: depositing a first metal layer on the substrate; depositing a space release material on the first metal layer and patterning it to form a first space release layer; forming a second metal layer covering the first space release layer on the first metal layer; etching the second metal layer and the first metal layer to form a bottom electrode body portion; etching the upper surface of the bottom electrode body portion to form a first recessed frame; and / or depositing a first protruding frame on the upper surface of the bottom electrode body portion.

[0011] According to another aspect of the invention, in this manufacturing method, the material of the first metal layer is the same as the material of the second metal layer; or the material of the first metal layer is different from the material of the second metal layer.

[0012] According to another aspect of the invention, after forming a piezoelectric layer on the bottom electrode, the manufacturing method further includes: etching the upper surface of the piezoelectric layer to form a groove located at the edge of the effective region; forming a second space release layer within the groove, the thickness of the second space release layer being greater than the depth of the groove, wherein the volume of the second space release layer shrinks upon heating or cooling; the step of forming a top electrode on the piezoelectric layer includes: depositing a third metal layer on the piezoelectric layer and patterning it to form a top electrode, the top electrode including a top electrode body portion and a top electrode connecting portion connected to the edge of the top electrode body portion and located above the second space release layer; the manufacturing method further includes: heating or cooling the second space release layer to release space through volume shrinkage, thereby forming a second air gap below the top electrode connecting portion.

[0013] According to another aspect of the invention, in this manufacturing method, the thickness of the heated or cooled second space release layer is greater than the depth of the groove, or the thickness of the heated or cooled second space release layer is equal to the depth of the groove, or the thickness of the heated or cooled second space release layer is less than the depth of the groove.

[0014] According to another aspect of the invention, in this manufacturing method, the upper surface of the portion of the top electrode connection located above the second air gap is stepped.

[0015] According to another aspect of the invention, in the manufacturing method, the top electrode further includes a top electrode reflective portion, which includes a second recessed frame and / or a second protruding frame formed on the upper surface of the top electrode body at the edge of the effective area.

[0016] According to another aspect of the invention, after providing the substrate and before forming the bottom electrode on the substrate, the manufacturing method further includes forming a seed layer on the substrate.

[0017] The present invention also provides a bulk acoustic resonator, the bulk acoustic resonator comprising:

[0018] A substrate, a bottom electrode formed on the substrate, a piezoelectric layer formed on the bottom electrode, and a top electrode formed on the piezoelectric layer, wherein the bottom electrode includes a bottom electrode body portion and a bottom electrode reflective portion;

[0019] The bottom electrode body includes, from bottom to top, a first metal layer, a first space release layer after heating or cooling, a first air gap, and a second metal layer. The second metal layer is formed on the first metal layer and covers the first air gap and the first space release layer after heating or cooling. The first air gap is formed by the space released by the volume contraction of the first space release layer after heating or cooling.

[0020] The bottom electrode reflective portion includes a first recessed frame and / or a first protruding frame formed on the upper surface of the bottom electrode body portion at the edge of the effective region of the bulk acoustic resonator.

[0021] The top electrode, the piezoelectric layer, the second metal layer, and the horizontally overlapping region of the first air gap constitute the effective region of the bulk acoustic resonator.

[0022] According to one aspect of the invention, in the bulk acoustic resonator, the material of the first metal layer is the same as the material of the second metal layer; or the material of the first metal layer is different from the material of the second metal layer.

[0023] According to another aspect of the present invention, in the bulk acoustic resonator, the top electrode includes a top electrode body and a top electrode connecting portion connected to the edge of the top electrode body, the top electrode connecting portion including a suspended portion; a groove is formed on the upper surface of the piezoelectric layer at a position opposite to the suspended portion in the top electrode connecting portion, a second space release layer after heating or cooling is formed in the groove, a second air gap is formed between the second space release layer after heating or cooling and the top electrode connecting portion, the second air gap being formed by the space released by the volume contraction of the second space release layer after heating or cooling.

[0024] According to another aspect of the invention, in the bulk acoustic resonator, the thickness of the heated or cooled second space release layer is greater than the depth of the groove, or the thickness of the heated or cooled second space release layer is equal to the depth of the groove, or the thickness of the heated or cooled second space release layer is less than the depth of the groove.

[0025] According to another aspect of the invention, in the bulk acoustic resonator, the upper surface of the portion of the top electrode connection located above the second air gap is stepped.

[0026] According to another aspect of the invention, in the bulk acoustic resonator, the top electrode further includes a top electrode reflector, which includes a second recessed frame and / or a second protruding frame formed on the upper surface of the top electrode body at the edge of the effective region.

[0027] According to another aspect of the invention, the bulk acoustic resonator further includes a seed layer formed between the substrate and the bottom electrode.

[0028] The present invention also provides a filter comprising a bulk acoustic wave resonator, which is manufactured using the aforementioned manufacturing method or implemented using the aforementioned bulk acoustic wave resonator.

[0029] The present invention also provides a duplexer, which includes a transmit filter and a receive filter, wherein the transmit filter and / or the receive filter are implemented using the aforementioned filters.

[0030] The bulk acoustic wave resonator and its manufacturing method provided by this invention, on the one hand, form an air gap inside the bottom electrode, which can reflect sound waves entering the bottom electrode back to the effective region. This eliminates the need for a cavity between the substrate and the bottom electrode, as in existing technologies. Furthermore, the air gap inside the bottom electrode is formed by the space released when the volume of a space release layer filled inside the bottom electrode shrinks due to heating / cooling. Compared to existing technologies that form a cavity between the substrate and the bottom electrode by etching the substrate, filling with sacrificial material, and removing the sacrificial material through a release channel using an etchant, this air gap formation method is simpler and less costly. On the other hand, a raised and / or recessed bottom electrode reflector is formed on the upper surface of the bottom electrode at the edge of the effective region. This reflector provides a discontinuity in acoustic impedance, so that when sound waves propagate from inside the effective region to the reflector, they are reflected back into the effective region, effectively reducing lateral sound leakage and thus significantly improving the quality factor of the bulk acoustic wave resonator. Correspondingly, the filters and duplexers formed based on the bulk acoustic resonator provided by this invention also have the characteristics of simple process, low cost and good performance. Attached Figure Description

[0031] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0032] Figure 1 This is a cross-sectional schematic diagram of a common bulk acoustic resonator in the prior art;

[0033] Figure 2 This is a flowchart of a method for manufacturing a bulk acoustic resonator according to a specific embodiment of the present invention;

[0034] Figures 3(a) to 3(j) According to Figure 2 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic resonator.

[0035] Figures 4(a) to 4(f) This is a cross-sectional schematic diagram of each stage in which the top electrode body is formed and the top electrode connection part is formed simultaneously on the structure shown in Figure 3(h).

[0036] Figure 5 This is a cross-sectional schematic diagram of a bulk acoustic resonator according to a preferred embodiment of the present invention;

[0037] Figure 6 This is a cross-sectional schematic diagram of a bulk acoustic resonator according to another preferred embodiment of the present invention.

[0038] The same or similar reference numerals in the accompanying drawings represent the same or similar parts. Detailed Implementation

[0039] To better understand and explain the present invention, a further detailed description of the invention will be provided below in conjunction with the accompanying drawings.

[0040] This invention provides a method for manufacturing a bulk acoustic resonator. Please refer to [link / reference]. Figure 2 , Figure 2 This is a flowchart illustrating a method for manufacturing a bulk acoustic resonator according to a specific embodiment of the present invention. As shown, the manufacturing method includes:

[0041] In step S101, a substrate is provided;

[0042] In step S102, a bottom electrode is formed on the substrate. The bottom electrode includes a bottom electrode body and a bottom electrode reflective portion. The bottom electrode body includes a first metal layer, a first space release layer and a second metal layer from bottom to top. The second metal layer is formed on the first metal layer and covers the first space release layer. The bottom electrode reflective portion includes a first recessed frame and / or a first protruding frame formed on the upper surface of the bottom electrode body at the edge of the effective region of the bulk acoustic wave resonator. The first space release layer shrinks in volume after heating or cooling.

[0043] In step S103, a piezoelectric layer is formed on the bottom electrode, and a top electrode is formed on the piezoelectric layer;

[0044] In step S104, the first space release layer is heated or cooled to shrink its volume and release the space to form a first air gap in the bottom electrode body, wherein the horizontal projection overlap of the top electrode, the piezoelectric layer, the second metal layer and the first air gap constitutes the effective area of ​​the bulk acoustic resonator.

[0045] Below, we will combine Figures 3(a) to 3(j) The steps S101 to S104 described above will be explained in detail with reference to a specific embodiment.

[0046] Specifically, in step S101, as shown in FIG3(a), a substrate 100 is provided. The present invention does not limit the specific implementation of the substrate 100, and it can be implemented using semiconductor materials such as silicon, germanium, or germanium-silicon. Preferably, the thickness of the substrate 100 ranges from 50 μm to 1000 μm. Those skilled in the art will understand that the thickness of the substrate 100 should not be limited to the above range, and can be customized according to actual design requirements.

[0047] Preferably, a seed layer (not shown) is deposited on the upper surface of the provided substrate 100. In this embodiment, the material of the seed layer can be aluminum nitride, scandium-doped aluminum nitride, etc. The formation of the seed layer is beneficial to ensuring the crystal orientation growth of the bottom electrode.

[0048] In step S102, a bottom electrode is formed on the substrate 100, wherein the bottom electrode includes a bottom electrode body portion and a bottom electrode reflective portion. In this embodiment, the formation process of the bottom electrode is as follows:

[0049] First, as shown in Figure 3(b), a first metal layer 101 is deposited on the substrate 100. The material of the first metal layer 101 can be made of existing conventional metal electrode materials such as molybdenum. For the sake of simplicity, all possible materials of the first metal layer 101 will not be listed here.

[0050] Next, as shown in Figure 3(c), a space release material (not shown, and referred to below as the first space release material) is deposited on the first metal layer 101, and then the first space release material is patterned to form a space release layer 102 (hereinafter referred to as the first space release layer 102). After the space release layer 102 is formed, a portion of the upper surface of the first metal layer 101 is exposed. In this embodiment, the first space release material has the characteristic of changing volume upon heating or cooling, specifically, shrinking in volume upon heating or cooling. The first space release material that shrinks in volume upon heating can be a porous and loose material such as porous silica or porous silicon, or it can be a material containing volatile substances, such as SiO2 containing water vapor. For the sake of simplicity, all possible materials that shrink in volume upon cooling will not be listed here. It should be noted that the present invention utilizes the characteristic of the first space release material to form an air gap by shrinking its volume after heating or cooling. In order to ensure the stability of the air gap, the first space release material also needs to have volume stability after heating or cooling. That is to say, the volume of the first space release material that has already shrunk after heating or cooling will not change much.

[0051] Next, as shown in Figure 3(d), a second metal layer 103 is deposited on the structure shown in Figure 3(c), which covers the first metal layer 101 and the first space release layer 102. The material of the second metal layer 103 can also be made of existing conventional metal electrode materials such as molybdenum. Preferably, the material of the second metal layer 103 is the same as the material of the first metal layer 101. Those skilled in the art will understand that the material of the second metal layer 103 can also be different from the material of the first metal layer 101.

[0052] Next, as shown in Figure 3(e), the second metal layer 103 and the first metal layer 101 are etched to form a metal layer structure with the first space release layer 102 inside. This metal layer structure is referred to as the bottom electrode body in the following text.

[0053] Next, as shown in FIG3(f), the upper surface of the bottom electrode body (i.e., the upper surface of the second metal layer 103) is etched to form a recessed frame 104a (hereinafter referred to as the first recessed frame 104a), and as shown in FIG3(g), a raised frame 104b (hereinafter referred to as the first raised frame 104b) is formed on the upper surface of the bottom electrode body by deposition. The first recessed frame 104a and the first raised frame 104b constitute the bottom electrode reflector. In this embodiment, the bottom electrode reflector is formed at the edge of the effective region of the bulk acoustic wave resonator. The effective region of the bulk acoustic wave resonator refers to the overlapping area of ​​the horizontal projections of the top electrode, piezoelectric layer, bottom electrode, and acoustic mirror. For the purposes of this invention, the acoustic mirror is an air gap subsequently formed within the bottom electrode body using the volume shrinkage characteristic of the first space release layer. It should be noted that since the position of the effective region is pre-designed before the actual manufacturing of the bulk acoustic wave resonator, the bottom electrode reflector can be formed at the edge of the effective region on the upper surface of the bottom electrode body according to the pre-design. It should be noted that the bottom electrode reflector being formed at the edge of the effective region of the bulk acoustic resonator means that the outer edge of the horizontal projection of the bottom electrode reflector is located outside the horizontal projection of the effective region, and its inner edge coincides with or falls within the edge region of the horizontal projection of the effective region. Furthermore, in this embodiment, as shown in FIG3(g), the first protruding frame 104b is located outside the first recessed frame 104a, and the two are adjacent to each other without any gap (i.e., the first protruding frame 104b and the first recessed frame 104a share the same sidewall).

[0054] In this embodiment, the formation process of the first recessed frame 104a is as follows: First, a photoresist layer is formed on the upper surface of the bottom electrode body. Then, the photoresist layer is patterned to expose the area on the upper surface of the bottom electrode body used to form the first recessed frame. Then, the exposed area is etched to form the first recessed frame. Finally, the photoresist layer is removed. The formation process of the first raised frame 104b is as follows: First, a photoresist layer is formed on the upper surface of the bottom electrode body. Then, the photoresist layer is patterned to expose the area on the upper surface of the bottom electrode body used to form the first raised frame. Then, the first raised frame is formed in the exposed area by deposition. Finally, the photoresist layer is removed.

[0055] In this embodiment, both the first recessed frame 104a and the first protruding frame 104b are annular in shape. Since the first recessed frame 104a and the first protruding frame 104b are formed at the edge of the effective area, their shapes are generally related to the shape of the effective area. For example, if the effective area is a regular pentagon, then the first recessed frame and the first protruding frame will correspondingly be regular pentagonal annular shapes.

[0056] In this embodiment, the depth of the first recessed frame 104a (i.e., the vertical distance between the bottom surface of the first recessed frame 104a and the upper surface of the second metal layer 103, denoted by H1 in FIG3(f)) ranges as follows: to The width (i.e., the vertical distance between the sidewalls of the first recessed frame 104a, denoted as W1 in Figure 3(f)) ranges from 0.1 μm to 20 μm. The height of the first protruding frame 104b (i.e., the vertical distance between the top surface of the first protruding frame 104b and the upper surface of the second metal layer 103, denoted as H2 in Figure 3(g)) ranges from... to The width (i.e., the vertical distance between the sidewalls of the first protruding frame 104b, indicated by W2 in Figure 3(g)) ranges from 0.1 μm to 20 μm. Those skilled in the art will understand that the specific dimensions of the bottom electrode reflective portion are not limited to the above embodiments; in other embodiments, they can be tailored according to actual design requirements.

[0057] It should be noted that (1) the first protruding frame is made of existing conventional metal electrode material, which can be the same as or different from the material of the first metal layer and the second metal layer. (2) The first protruding frame can be formed first and then the first recessed frame can be formed, or vice versa. (3) Only the first recessed frame or only the first protruding frame can be formed, that is, the bottom electrode reflective part only includes the first recessed frame or only includes the first protruding frame.

[0058] In step S103, firstly, as shown in FIG3(h), a piezoelectric material (not shown) covering the bottom electrode is deposited on the substrate 100, and the piezoelectric material is planarized to form a piezoelectric layer 105 with a flat upper surface. It should be noted that in other embodiments, the piezoelectric material can be deposited directly to form the piezoelectric layer without performing a planarization operation. Next, as shown in FIG3(i), a top electrode 106 is formed on the piezoelectric layer 105. The material of the top electrode 106 can be made of existing conventional metal electrode materials such as molybdenum, and can be the same as or different from the metal material in the bottom electrode.

[0059] In step S104, as shown in Figure 3(j), the structure shown in Figure 3(i) is subjected to heat treatment or cooling treatment. Taking heat treatment as an example, it can be tubular annealing for no more than 10 hours in the temperature range of 300℃ to 1100℃, or peak annealing for no more than 20 seconds in the temperature range of 650℃ to 1300℃, or laser annealing or flash annealing for no more than 20 milliseconds in the temperature range of 700℃ to 1500℃. Of course, heat treatment is not limited to the above annealing operation, and the appropriate method can be selected according to the specific characteristics of the first space release layer material. For cooling treatment, the appropriate method can also be selected according to the specific characteristics of the first space release layer material. For the sake of simplicity, all possible cooling treatment methods will not be listed here. After heat treatment or cooling treatment, the volume of the first space release layer 102 shrinks, thereby releasing a certain space below the second metal layer 103. In this way, an air gap 107 (hereinafter referred to as the first air gap 107) can be formed in the bottom electrode. By rationally selecting the material and thickness of the first space release layer, it is preferable that the thickness of the first air gap 107 is greater than 10 μm to ensure the sound wave reflection effect. It should be noted here that the heating or cooling treatment of the first space release layer should not be limited to after the formation of the top electrode, but can be performed at any time after the deposition of the second metal layer 103 in Figure 3(d). For example, the heating or cooling treatment can be performed immediately after the formation of the structure shown in Figure 3(d), or after the formation of the entire bottom electrode, after the formation of the piezoelectric layer, or even after the formation of the passivation layer (usually formed on the top electrode). This article does not impose any limitations on this.

[0060] In this invention, the first air gap 107 serves as the acoustic mirror of the bulk acoustic wave resonator. It has a horizontally overlapping region (hereinafter referred to as the overlapping region) with the second metal layer 103, the piezoelectric layer 105, and the top electrode 106. This overlapping region constitutes the effective region of the bulk acoustic wave resonator. When sound waves within the effective region of the bulk acoustic wave resonator are transmitted to the interface between the second metal layer 103 and the first air gap 107, they are reflected back to the effective region by the first air gap 107. In other words, although this invention does not form a cavity between the substrate and the bottom electrode as in the prior art, it still achieves sound wave reflection, ensuring the normal operation of the bulk acoustic wave resonator. Furthermore, the first air gap inside the bottom electrode is formed by filling the bottom electrode with a first space release material and then heating or cooling it. Clearly, compared to the prior art, this invention eliminates the need for substrate etching, the formation of release channels, and the removal of sacrificial materials using an etching solution, thus effectively simplifying the manufacturing process and reducing manufacturing costs. Especially when using rapid heating or cooling methods (such as millisecond-level annealing), the manufacturing time of bulk acoustic wave resonators can be effectively shortened, thereby improving manufacturing efficiency. In addition, the bottom electrode reflector on the upper surface of the bottom electrode can provide impedance discontinuity. When sound waves are transmitted to the bottom electrode reflector, they will be reflected back into the effective region, thereby effectively reducing the lateral leakage of sound waves and thus effectively improving the quality factor of the bulk acoustic wave resonator.

[0061] In a preferred embodiment, the top electrode includes a top electrode body and a top electrode connecting portion, wherein the top electrode body is located within the effective region of the bulk acoustic wave resonator, and the top electrode connecting portion is connected to the edge of the top electrode body. The top electrode connecting portion can be an air wing and / or an air bridge. An air wing is a structure with one end connected to the top electrode body and the other end suspended, while an air bridge is a structure with one end connected to the top electrode body, the other end formed on a piezoelectric layer, and the two ends partially suspended. The manufacturing method of the bulk acoustic wave resonator provided by the present invention will be described below using the example of forming a top electrode connecting portion including an air wing and an air bridge on the structure shown in FIG. 3(h).

[0062] Specifically, as shown in Figure 4(a), the upper surface of the piezoelectric layer 105 is etched to form grooves 108a and 108b. Groove 108a corresponds to the air wing to be formed, and groove 108b corresponds to the suspended portion in the air bridge to be formed. Since both the air wing and the air bridge are connected to the edge of the top electrode body located within the effective region, grooves 108a and 108b are formed on the upper surface of the piezoelectric layer 105 at the edge of the effective region.

[0063] Next, a space release material (not shown, and referred to below as the second space release material) is deposited on the upper surface of the piezoelectric layer 105, and the second space release material is planarized as shown in FIG. 4(b). The second space release material after planarization is indicated by reference numeral 109 in the figure. In this embodiment, the upper surface of the planarized second space release material is higher than the upper surface of the piezoelectric layer 105. The second space release material has the same characteristics as the first space release material, that is, its volume shrinks after heating or cooling and remains stable after shrinkage. The second space release material and the first space release material may be the same or different.

[0064] Next, considering that a portion of the top electrode body and the air bridge portion will be formed on the piezoelectric layer, the second space release material 109 is etched to expose the area on the upper surface of the piezoelectric layer used to form the top electrode body and the air bridge portion (hereinafter referred to as the first region). As shown in FIG4(c), after the etching of the second space release material is completed, a second space release layer 110a is formed in the groove 108a, a second space release layer 110b is formed in the groove 108b, and a second space release layer 110c is formed in other regions on the upper surface of the piezoelectric layer 105 outside the first region. In other embodiments, the second space release layer 110c may be removed, leaving only the second space release layer 110a located in the groove 108a and the second space release layer 110b located in the groove 108b.

[0065] Next, as shown in Figure 4(d), a third metal layer 111 is deposited on the piezoelectric layer 105, and as shown in Figure 4(e), the third metal layer 111 is patterned, and the portion of the third metal layer 111 located on the second space release layer 110c is removed to form the top electrode. The portion of the top electrode located above the bottom electrode (i.e., within the effective region) is the top electrode body 112a, the portion of the top electrode located on the second space release layer 110a is the air wing portion 112b, and the portion of the top electrode located on both the piezoelectric layer and the second space release layer 110b is the air bridge portion 112c.

[0066] Finally, as shown in Figure 4(e), the second space release layer 110a and the second space release layer 110b are subjected to heat treatment or cooling treatment. After heat treatment or cooling treatment, the volume of the second space release layer 110a shrinks, thereby releasing a certain space below the air wing 112b to form an air gap 113a (hereinafter referred to as the second air gap 113a). Similarly, the volume of the second space release layer 110b shrinks, thereby releasing a certain space below the air bridge wing 112c to form an air gap 113b (hereinafter referred to as the second air gap 113b). In this way, the air wing 112b is suspended in the air, and the part of the air bridge 112c located above the second space release layer 110b is also suspended in the air in an arch shape. It should be noted that in this embodiment, the first space release material and the second space release material are the same, so heat treatment or cooling treatment can be performed simultaneously to form the first air gap 107 and the second air gap 113a and the second air gap 113b in one step. In other embodiments, if the processing conditions for the material released in the first space and the material released in the second space are different, they can also be subjected to heating or cooling treatment respectively.

[0067] It should be noted that (1) in this embodiment, the materials of the second space release layer in grooves 108a and 108b are the same, while in other embodiments, the materials of the second space release layer in grooves 108a and 108b may be different. (2) If the materials of the second space release layer are different, their shrinkage volume will usually be different. In this embodiment, the thickness of the second space release layer after heating or cooling is greater than the depth of the groove (i.e., the upper surface of the second space release layer is higher than the upper surface of the piezoelectric layer). In other embodiments, the thickness of the second space release layer after heating or cooling may be exactly equal to the depth of the groove (i.e., the upper surface of the second space release layer is flush with the upper surface of the piezoelectric layer) or less than the depth of the groove (i.e., the upper surface of the second space release layer is lower than the upper surface of the piezoelectric layer). (3) Preferably, the materials of the first space release layer and the second space release layer have opposite temperature coefficients to the material of the piezoelectric layer, which can effectively play a role in temperature compensation.

[0068] The grooves forming the second space release layer on the top electrode connection and the piezoelectric layer can also provide acoustic impedance discontinuity, which is beneficial for reflecting sound waves back to the effective area of ​​the bulk acoustic resonator, thereby reducing lateral sound leakage and improving the quality factor of the bulk acoustic resonator. In the prior art, the space under the air bridge and air wing is also removed by an etching solution. This invention utilizes the material's volume shrinkage after heating or cooling to form the space, which is simple and inexpensive.

[0069] In another preferred embodiment, such as Figure 5As shown, the portion of the top electrode connection located above the second air gap (i.e., the suspended portion of the top electrode connection) has an upper surface that is stepped and undulating (circled by the dotted line in the figure). This stepped shape gradually increases in height as it moves away from the main body of the top electrode. The stepped shape of the upper surface of the top electrode connection further provides discontinuity in acoustic impedance, thereby further reducing lateral leakage of sound waves and further improving the quality factor of the bulk acoustic resonator.

[0070] In yet another preferred implementation, such as Figure 6 As shown, the top electrode may further include a top electrode reflector, which further includes a second recessed frame 114a and a second protruding frame 114b. The top electrode reflector is formed on the upper surface of the top electrode body at the edge of the effective region, corresponding to the bottom electrode reflector. The formation steps and dimensional parameters of the second recessed frame 114a and the second protruding frame 114b can be referenced accordingly to the first recessed frame 104a and the first protruding frame 104b. Those skilled in the art will understand that in other embodiments, the top electrode reflector may include only the second recessed frame 114a or only the second protruding frame 114b. Similar to the bottom electrode reflector, the top electrode reflector also provides acoustic impedance discontinuity, which can reflect sound waves back into the effective region to reduce lateral leakage of sound waves, thereby improving the quality factor of the bulk acoustic resonator.

[0071] Accordingly, the present invention also provides a bulk acoustic resonator, which includes:

[0072] A substrate, a bottom electrode formed on the substrate, a piezoelectric layer formed on the bottom electrode, and a top electrode formed on the piezoelectric layer, wherein the bottom electrode includes a bottom electrode body portion and a bottom electrode reflective portion;

[0073] The bottom electrode body includes, from bottom to top, a first metal layer, a first space release layer after heating or cooling, a first air gap, and a second metal layer. The second metal layer is formed on the first metal layer and covers the first air gap and the first space release layer after heating or cooling. The first air gap is formed by the space released by the volume contraction of the first space release layer after heating or cooling.

[0074] The bottom electrode reflective portion includes a first recessed frame and / or a first protruding frame formed on the upper surface of the bottom electrode body portion at the edge of the effective region of the bulk acoustic resonator.

[0075] The horizontal projection overlap of the top electrode, the piezoelectric layer, the second metal layer, and the first air gap constitutes the effective region of the bulk acoustic resonator.

[0076] The components of the above-mentioned bulk acoustic resonator will be explained below with reference to Figure 3(j).

[0077] Specifically, as shown in the figure, the bulk acoustic wave resonator provided by the present invention includes a substrate 100. The material, dimensions, etc. of the substrate 100 can be referred to the relevant part of the manufacturing method above, and will not be repeated here for the sake of simplicity.

[0078] As shown in the figure, the bulk acoustic wave resonator provided by the present invention further includes a bottom electrode formed on a substrate 100. The bottom electrode includes a bottom electrode body and a bottom electrode reflector. In this embodiment, the bottom electrode body includes, from bottom to top, a first metal layer 101, a first space release layer 102 after heating or cooling, a first air gap 107, and a second metal layer 103. The second metal layer 103 is formed on the first metal layer 101 and covers the first air gap 107 and the first space release layer 102 after heating or cooling.

[0079] The first metal layer 101 and the second metal layer 103 can be made of existing conventional metal electrode materials, such as molybdenum. The materials of the first metal layer 101 and the second metal layer 103 can be the same or different. If the materials of the first metal layer 101 and the second metal layer 103 are the same, then the first metal layer 101 and the second metal layer 103 present an integrated structure. In this case, the lower surface of the first space release layer 102 can be used as the boundary to define the portion of the bottom electrode located below the lower surface of the first space release layer 102 as the first metal layer and the portion located above the lower surface of the first space release layer 102 as the second metal layer.

[0080] The material of the first space release layer 102 has the characteristic of changing volume after heating or cooling, specifically shrinking in volume after heating or cooling. Taking the first space release layer 102, which shrinks in volume after heating, as an example, it can be a porous and loose material such as porous silica or porous silicon, or it can be a material containing volatile substances, such as SiO2 containing water vapor. For the sake of simplicity, all possible materials that shrink in volume after cooling will not be listed here. Before heating or cooling, the first space release layer 102 completely fills the space between the first metal layer 101 and the second metal layer 103. After heating or cooling, the first space release layer 102 shrinks in volume, releasing a certain space to form a first air gap 107. The thickness of the first air gap 107 is preferably greater than 10 μm to ensure sound wave reflection effect. It should be noted that the first air gap 107 is formed by heating or cooling the first space release layer 102 to shrink its volume and release a certain space. In order to ensure the stability of the first air gap, the first space release layer 102 also needs to have volume stability after heating or cooling. That is to say, the volume of the first space release layer 102 that has shrunk after heating or cooling will not change much.

[0081] This invention does not limit the heating or cooling treatments performed on the first space release layer 102. Taking heating treatment as an example, it can be tubular annealing for no more than 10 hours within a temperature range of 300℃ to 1100℃, or peak annealing for no more than 20 seconds within a temperature range of 650℃ to 1300℃, or laser annealing or flash annealing for no more than 20 milliseconds within a temperature range of 700℃ to 1500℃. Of course, heating treatment is not limited to the above-mentioned annealing operations; appropriate methods can be selected according to the specific characteristics of the first space release layer 102. Similarly, cooling treatment can also be selected according to the specific characteristics of the first space release layer 102. For the sake of simplicity, all possible cooling treatment methods will not be listed here.

[0082] In this embodiment, the bottom electrode reflective portion includes a first recessed frame 104a and a first protruding recess 104b. In other embodiments, the bottom electrode reflective portion may include only the first recessed frame 104a or only the first protruding recess 104b. The bottom electrode reflective portion is formed at the edge of the effective region of the bulk acoustic wave resonator. The effective region of the bulk acoustic wave resonator refers to the overlapping area of ​​the horizontal projections of the top electrode, piezoelectric layer, bottom electrode, and acoustic mirror. For the purposes of this invention, the acoustic mirror is the first air gap 102, and correspondingly, the effective region of the bulk acoustic wave resonator is the overlapping area of ​​the horizontal projections of the top electrode, piezoelectric layer, second metal layer 103, and first air gap 102. It should be noted that the bottom electrode reflective portion being formed at the edge of the effective region of the bulk acoustic wave resonator means that the outer edge of the horizontal projection of the bottom electrode reflective portion is located outside the horizontal projection of the effective region, and its inner edge coincides with or falls within the edge region of the horizontal projection of the effective region. Furthermore, in this embodiment, as shown in the figure, the first protruding frame 104b is located outside the first recessed frame 104a, and the two are adjacent to each other without any gap (i.e., the first protruding frame 104b and the first recessed frame 104a share the same sidewall).

[0083] In this embodiment, both the first recessed frame 104a and the first protruding frame 104b are annular in shape. Since the first recessed frame 104a and the first protruding frame 104b are formed at the edge of the effective area, their shapes are generally related to the shape of the effective area. For example, if the effective area is a regular pentagon, then the first recessed frame and the first protruding frame will correspondingly be regular pentagonal annular shapes.

[0084] In this embodiment, the dimensions (including depth, height, width, material, etc.) of the first recessed frame 104a and the first protruding frame 104b can be referred to the relevant content in the aforementioned manufacturing method, and will not be repeated here for the sake of simplicity.

[0085] As shown in the figure, the bulk acoustic wave resonator provided by the present invention further includes a piezoelectric layer 105 formed above the bottom electrode and a top electrode 106 formed above the piezoelectric layer 105. The materials, dimensions, etc. of the piezoelectric layer 105 and the top electrode 106 can be referred to the relevant content in the aforementioned manufacturing method, and will not be repeated here for the sake of brevity.

[0086] Preferably, the bulk acoustic wave resonator provided by the present invention further includes a seed layer (not shown), which is formed between the substrate and the bottom electrode. In this embodiment, the material of the seed layer can be aluminum nitride, scandium-doped aluminum nitride, etc. The presence of the seed layer is beneficial to ensuring the crystal orientation growth of the bottom electrode.

[0087] The bulk acoustic wave resonator provided by this invention has two advantages. First, a first air gap is formed inside the bottom electrode, which reflects sound waves entering the bottom electrode back to the effective region. This eliminates the need for a cavity between the substrate and the bottom electrode, as in existing technologies. Furthermore, the first air gap inside the bottom electrode is formed by the space released when the volume of a first space release layer filled inside the bottom electrode shrinks due to heating / cooling. Compared to the cavity structure formed between the substrate and the bottom electrode in existing technologies by etching the substrate, filling with sacrificial material, and removing the sacrificial material through a release channel using an etchant solution, the bulk acoustic wave resonator provided by this invention has a simpler manufacturing process and lower cost. Second, a raised and / or recessed bottom electrode reflector is formed on the upper surface of the bottom electrode at the edge of the effective region. This reflector provides a discontinuity in acoustic impedance, so that when sound waves propagate from inside the effective region to the reflector, they are reflected back into the effective region, effectively reducing lateral leakage of sound waves and thus significantly improving the quality factor of the bulk acoustic wave resonator.

[0088] In a preferred embodiment, the top electrode includes a top electrode body and a top electrode connecting portion. The top electrode body is located within the effective region of the bulk acoustic wave resonator, and the top electrode connecting portion is connected to the edge of the top electrode body and includes a suspended portion. The top electrode connecting portion can be an air wing and / or an air bridge. An air wing is a structure where one end is connected to the top electrode body and the other end is suspended. An air bridge is a structure where one end is connected to the top electrode body, the other end is formed on a piezoelectric layer, and the two ends are partially suspended. The following description uses Figure 4(f) as an example.

[0089] Specifically, as shown in the figure, the top electrode includes a top electrode body 112a and air wing portions 112b and air bridge portions 112c connected to the edges of the top electrode body 112a. A groove is formed on the upper surface of the piezoelectric layer 105 at a position corresponding to the air wing portion 112b. A heated or cooled second space release layer 110a is formed within this groove, and a second air gap 113a is formed between the heated or cooled second space release layer 110a and the air wing portion 112b. The presence of the second air gap 113a causes the air wing portion 112b to suspend in the air. A groove is also formed on the upper surface of the piezoelectric layer 105 at a position corresponding to the air bridge portion 112c. A heated or cooled second space release layer 110b is formed within this groove, and a second air gap 113b is formed between the heated or cooled second space release layer 110b and the air bridge portion 112c. The presence of the second air gap 113b causes the portion between the two ends of the air bridge portion 112c to suspend in the air. It should be noted that since both the air wing and the air bridge are connected to the edge of the top electrode body located within the effective area, the groove on the upper surface of the piezoelectric layer and the second space release layer within the groove are located at the edge of the effective area.

[0090] The material of the second space release layer has the same properties as the material of the first space release layer 102, namely, its volume shrinks after heating or cooling and remains stable after shrinkage. The materials of the second space release layer and the first space release layer can be the same or different.

[0091] Before heating or cooling, the second space release layer 110a completely fills the space between the piezoelectric layer 105 and the air wing 112b. After heating or cooling, the second space release layer 110a shrinks in volume, releasing a certain space to form a second air gap 113a. Similarly, before heating or cooling, the second space release layer 110b completely fills the space between the piezoelectric layer 105 and the air bridge 112c. After heating or cooling, the second space release layer 110b shrinks in volume, releasing a certain space to form a second air gap 113b.

[0092] It should be noted that (1) in this embodiment, the materials of the second space release layer below the air wing and the air bridge are the same, but they can be different in other embodiments. (2) If the materials of the second space release layer are different, their volume after shrinkage is usually different. In this embodiment, the thickness of the second space release layer after heating or cooling is greater than the depth of the groove (i.e., the upper surface of the second space release layer is higher than the upper surface of the piezoelectric layer). In other embodiments, the thickness of the second space release layer after heating or cooling can be exactly equal to the depth of the groove (i.e., the upper surface of the second space release layer is flush with the upper surface of the piezoelectric layer) or less than the depth of the groove (i.e., the upper surface of the second space release layer is lower than the upper surface of the piezoelectric layer). (3) Preferably, the materials of the first space release layer and the second space release layer have opposite temperature coefficients to the material of the piezoelectric layer, which can effectively play a role in temperature compensation.

[0093] The grooves forming the second space release layer on the top electrode connection and the piezoelectric layer can also provide acoustic impedance discontinuity, which is beneficial for reflecting sound waves back to the effective area of ​​the bulk acoustic resonator, thereby reducing lateral sound leakage and improving the quality factor of the bulk acoustic resonator. In the prior art, the space under the air bridge and air wing is also removed by an etching solution. This invention utilizes the material's volume shrinkage after heating or cooling to form the space, which is simple and inexpensive.

[0094] In another preferred embodiment, such as Figure 5 As shown, the portion of the top electrode connection located above the second air gap (i.e., the suspended portion of the top electrode connection) has an upper surface that is stepped and undulating (circled by the dotted line in the figure). This stepped shape gradually increases in height as it moves away from the main body of the top electrode. The stepped shape of the upper surface of the top electrode connection further provides discontinuity in acoustic impedance, thereby further reducing lateral leakage of sound waves and further improving the quality factor of the bulk acoustic resonator.

[0095] In yet another preferred implementation, such as Figure 6 As shown, the top electrode may further include a top electrode reflector, which further includes a second recessed frame 114a and a second protruding frame 114b. The top electrode reflector is formed on the upper surface of the top electrode body at the edge of the effective region, corresponding to the bottom electrode reflector. The formation steps and dimensional parameters of the second recessed frame 114a and the second protruding frame 114b can be referenced accordingly to the first recessed frame 104a and the first protruding frame 104b. Those skilled in the art will understand that in other embodiments, the top electrode reflector may include only the second recessed frame 114a or only the second protruding frame 114b. Similar to the bottom electrode reflector, the top electrode reflector also provides acoustic impedance discontinuity, which can reflect sound waves back into the effective region to reduce lateral leakage of sound waves, thereby improving the quality factor of the bulk acoustic resonator.

[0096] This invention also provides a filter comprising the aforementioned bulk acoustic wave resonator provided by this invention. For the sake of simplicity, the bulk acoustic wave resonator provided by this invention will not be described again here; its structure can be referred to the relevant sections above. The bulk acoustic wave resonator can be placed in the series and / or parallel branches of the filter, and this invention does not limit this in any way. Since there are many possible structures for the filter, for the sake of simplicity, not all possible structures of the filter will be listed here. The filter formed based on the bulk acoustic wave resonator provided by this invention has the characteristics of simple manufacturing process, low cost, and excellent performance.

[0097] This invention also provides a duplexer, which includes a transmit filter and a receive filter, wherein the transmit filter and / or the receive filter is implemented using the aforementioned filter provided by this invention. For the sake of brevity, the filter provided by this invention will not be described again here; its structure can be referred to the relevant sections above. The duplexer formed based on the filter provided by this invention has the characteristics of simple manufacturing process, low cost, and excellent performance.

[0098] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other components, units, or steps, and the singular does not exclude the plural. Multiple components, units, or devices recited in the system claims may also be implemented by a single component, unit, or device in software or hardware.

[0099] The above-disclosed embodiments are merely some preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for manufacturing a bulk acoustic resonator, the method comprising: Provide substrate; A bottom electrode is formed on the substrate. The bottom electrode includes a bottom electrode body and a bottom electrode reflective portion. The bottom electrode body includes, from bottom to top, a first metal layer, a first space release layer, and a second metal layer. The second metal layer is formed on the first metal layer and covers the first space release layer. The bottom electrode reflective portion includes a first recessed frame and a first protruding frame formed on the upper surface of the bottom electrode body at the edge of the effective region of the bulk acoustic wave resonator. The first protruding frame is located outside the first recessed frame and is adjacent to the first recessed frame without any gap. Wherein, the volume of the first space release layer shrinks after heating or cooling, and the space release material of the first space release layer is a porous and loose material or a material containing volatile substances, and has volume stability after heating or cooling. After forming a piezoelectric layer on the bottom electrode, the upper surface of the piezoelectric layer is etched to form a groove located at the edge of the effective region; a second space release layer is formed in the groove, the thickness of the second space release layer being greater than the depth of the groove, the second space release layer being made of the same material as the first space release layer, and both the first and second space release layers having opposite temperature coefficients to the piezoelectric layer material, wherein the second space release layer shrinks in volume after heating or cooling; The step of forming a top electrode on the piezoelectric layer includes: depositing a third metal layer on the piezoelectric layer and patterning it to form a top electrode, the top electrode including a top electrode body portion and a top electrode connection portion connected to the edge of the top electrode body portion and located above the second space release layer; The manufacturing method further includes: shrinking the volume of the first space release layer and the second space release layer through the same heating or cooling step to form a first air gap in the bottom electrode body and a second air gap below the top electrode connection, and by selecting the material and thickness of the first space release layer to make the thickness of the first air gap greater than 10 μm; The horizontal projection overlap of the top electrode, the piezoelectric layer, the second metal layer, and the first air gap constitutes the effective region of the bulk acoustic resonator.

2. The manufacturing method according to claim 1, wherein, The step of forming a bottom electrode on the substrate includes: A first metal layer is deposited on the substrate; Deposit space release material on the first metal layer and pattern it to form the first space release layer; A second metal layer covering the first space release layer is formed on the first metal layer; Etch the second metal layer and the first metal layer to form the bottom electrode body portion; The upper surface of the bottom electrode body is etched to form a first recessed frame, and a first raised frame is deposited on the upper surface of the bottom electrode body.

3. The manufacturing method according to claim 2, wherein: The material of the first metal layer is the same as the material of the second metal layer; or The material of the first metal layer is different from the material of the second metal layer.

4. The manufacturing method according to claim 1, wherein: The thickness of the heated or cooled second space release layer is greater than the depth of the groove, or the thickness of the heated or cooled second space release layer is equal to the depth of the groove, or the thickness of the heated or cooled second space release layer is less than the depth of the groove.

5. The manufacturing method according to claim 1, wherein, The portion of the top electrode connection located above the second air gap has a stepped upper surface.

6. The manufacturing method according to claim 1, wherein: The top electrode also includes a top electrode reflective portion, which includes a second recessed frame and / or a second protruding frame formed on the upper surface of the top electrode body at the edge of the effective area.

7. The manufacturing method of claim 1, further comprising, after providing the substrate and before forming the bottom electrode on the substrate: A seed layer is formed on the substrate.

8. A bulk acoustic resonator, the bulk acoustic resonator comprising: A substrate, a bottom electrode formed on the substrate, a piezoelectric layer formed on the bottom electrode, and a top electrode formed on the piezoelectric layer, wherein the bottom electrode includes a bottom electrode body portion and a bottom electrode reflective portion; The bottom electrode body comprises, from bottom to top, a first metal layer, a first space release layer after heating or cooling, a first air gap, and a second metal layer. The second metal layer is formed on the first metal layer and covers the first air gap and the first space release layer after heating or cooling. The first air gap is formed by the space released by the volume contraction of the first space release layer after heating or cooling, and the thickness of the first air gap is greater than 10 μm. The space release material of the first space release layer is a porous and loose material or a material containing volatile substances, and has volume stability after heating or cooling. The bottom electrode reflective portion includes a first recessed frame and a first protruding frame formed on the upper surface of the bottom electrode body portion at the edge of the effective region of the bulk acoustic resonator, wherein the first protruding frame is located outside the first recessed frame and is adjacent to the first recessed frame without any gap. The top electrode includes a top electrode body and a top electrode connecting part connected to the edge of the top electrode body, the top electrode connecting part including a suspended portion; A groove is formed on the upper surface of the piezoelectric layer at a position opposite to the suspended portion in the top electrode connection. A second space release layer after heating or cooling is formed in the groove. A second air gap is formed between the second space release layer after heating or cooling and the top electrode connection. The second air gap is formed by the space released by the volume contraction of the second space release layer after heating or cooling. The second space release layer is made of the same material as the first space release layer, and the materials of the first space release layer and the second space release layer have opposite temperature coefficients to the material of the piezoelectric layer. The horizontal projection overlap of the top electrode, the piezoelectric layer, the second metal layer, and the first air gap constitutes the effective region of the bulk acoustic resonator.

9. The bulk acoustic resonator according to claim 8, wherein: The material of the first metal layer is the same as the material of the second metal layer; or The material of the first metal layer is different from the material of the second metal layer.

10. The bulk acoustic resonator according to claim 8, wherein: The thickness of the heated or cooled second space release layer is greater than the depth of the groove, or the thickness of the heated or cooled second space release layer is equal to the depth of the groove, or the thickness of the heated or cooled second space release layer is less than the depth of the groove.

11. The bulk acoustic resonator according to claim 8, wherein, The portion of the top electrode connection located above the second air gap has a stepped upper surface.

12. The bulk acoustic resonator according to claim 8, wherein: The top electrode also includes a top electrode reflective portion, which includes a second recessed frame and / or a second protruding frame formed on the upper surface of the top electrode body at the edge of the effective area.

13. The bulk acoustic resonator according to claim 8, further comprising: A seed layer is formed between the substrate and the bottom electrode.

14. A filter comprising a bulk acoustic resonator, wherein, The bulk acoustic resonator is manufactured using the manufacturing method described in any one of claims 1 to 7, or implemented using the bulk acoustic resonator described in any one of claims 8 to 13.

15. A duplexer comprising a transmit filter and a receive filter, wherein, The transmit filter and / or the receive filter are implemented using the filter as described in claim 14.

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