A single-crystal AlN thin film bulk acoustic duplexer and its fabrication method

Abstract

This application discloses a single-crystal AlN thin-film bulk acoustic wave duplexer and its fabrication method. The bulk acoustic wave duplexer includes a receiving filter and a transmitting filter. The receiving filter includes a first substrate, a first resonator unit, a dielectric layer, and a first bonding structure. The transmitting filter includes a second substrate, a second resonator unit, and a second bonding structure. The first bonding structure and the second bonding structure are bonded to each other, and the second top electrode layer of the second resonator unit is bonded to the first top electrode layer or dielectric layer of the first resonator unit. This application uses flip-chip bonding to connect the receiving filter and the transmitting filter together, resulting in a compact structure and eliminating the need for partitioning different filters. Simultaneously, the flip-chip bonding method makes it possible to use a single-crystal AlN thin film as the piezoelectric material for both the first and second piezoelectric layers, improving the isolation, insertion loss, and other performance characteristics of the thin-film bulk acoustic wave duplexer. This application relates to the field of semiconductor manufacturing.

Description

Technical Field

[0001] This application relates to the field of semiconductor manufacturing, and in particular to a single-crystal AlN thin-film bulk acoustic duplexer and its preparation method. Background Technology

[0002] Bulk acoustic wave (BAW) resonators offer advantages such as high frequency, miniaturization, high performance, low power consumption, and high power capacity. Furthermore, BAW filters are compatible with and can be integrated into IC processes, enabling them to reduce device power consumption and size. Micromachining (MEMS) BAW filters can operate in frequencies from hundreds of MHz to tens of GHz, covering the requirements of wireless communication bands. Traditional dielectric filters are too bulky, and surface acoustic wave (SAW) filters have higher insertion losses compared to BAW filters and cannot meet high-frequency (>3 GHz) requirements. Therefore, BAW filters are the optimal solution for high-frequency bands above 3 GHz.

[0003] A thin-film bulk acoustic resonator is a device that converts electrical signals into acoustic signals for propagation, and then back into electrical signals for output. A single resonator cannot be used as a filter; multiple resonators must be cascaded to form a filter. In frequency division multiplexing (FDM) systems, a duplexer shares signal transmission and reception through a single antenna, utilizing internal transmitter filters (Tx) and receiver filters (Rx) for signal filtering and selection.

[0004] Thin-film bulk acoustic wave (BAS) filters / duplexers possess superior filtering characteristics, such as high Q-value, low insertion loss, high power capacity, good rectangularity coefficient, good directional selectivity, and excellent zero depth and out-of-band rejection. However, traditional BAS resonators, due to structural defects, are susceptible to corrosion from the sacrificial layer release solution, leading to poor performance. Simultaneously, some acoustic waves leak through the piezoelectric material into the surrounding substrate, resulting in a low quality factor and ultimately poor duplexer isolation and loss. Because traditional BAS filters require AlN growth on a polycrystalline electrode structure, their piezoelectric material is polycrystalline AlN. This polycrystalline AlN piezoelectric material has a high defect density, which also reduces the resonator's quality factor, thus affecting duplexer performance. Furthermore, because the transmitter and receiver filters in traditional BAS filters operate at different frequencies, frequency modulation requires adjusting the film thickness. This makes it impossible to deposit frequency modulation layers of different thicknesses on the same wafer; the transmitter and receiver filters must be fabricated on two separate wafers, integrated after initial packaging. This method makes the transmitter and receiver filters independent of each other and requires reserved spacing, which is not conducive to reducing the overall duplexer module area. Meanwhile, to improve reliability, existing thin-film bulk acoustic wave (TFT) filters typically use an additional cap wafer for wafer-level packaging to ensure that the TFT filter is not affected by external environmental interference. Wafer-level packaging is not only more difficult and has a lower device yield, but it also increases the thickness of the TFT filter, leading to a larger size and additional cost. Summary of the Invention

[0005] The purpose of this application is to at least solve one of the technical problems existing in the prior art, and to provide a single-crystal AlN thin film bulk acoustic duplexer and its preparation method, which can save the volume of the thin film bulk acoustic duplexer and make the structure more compact.

[0006] According to a first aspect of this application, a single-crystal AlN thin-film bulk acoustic duplexer is provided, comprising a receiving filter and a transmitting filter:

[0007] The receiving filter includes:

[0008] A first substrate, wherein a first air cavity is formed in the first substrate;

[0009] The first resonator unit includes a first bottom electrode layer, a first piezoelectric layer and a first top electrode layer that are sequentially deposited. The first bottom electrode layer is formed on the surface of the first substrate and covers the first air cavity. The first piezoelectric layer uses a single-crystal AlN thin film as the piezoelectric material.

[0010] A dielectric layer is formed on the surface of the first substrate;

[0011] A first bonding structure is formed on the surface of the first substrate;

[0012] The transmit filter includes:

[0013] A second substrate, wherein a second air cavity is formed in the second substrate;

[0014] The second resonator unit includes a second bottom electrode layer, a second piezoelectric layer and a second top electrode layer that are sequentially deposited. The second bottom electrode layer is formed on the surface of the second substrate and covers the second air cavity. The second piezoelectric layer uses a single-crystal AlN thin film as the piezoelectric material.

[0015] The second bonding structure is formed on the surface of the second substrate;

[0016] Wherein, the first bonding structure is bonded to the second bonding structure, and the second top electrode layer is bonded to the first top electrode layer or the dielectric layer.

[0017] According to a first aspect embodiment of this application, the first substrate further includes a TSV via.

[0018] According to a first aspect of the present application, the receiving filter further includes an inductor mounted in the TSV via.

[0019] According to a first aspect of this application, the receiving filter further includes a metal connector connected to the TSV via.

[0020] According to a first aspect of the present application, the metal connector is further spherical.

[0021] According to a first aspect of the present application, the materials of the first substrate and the second substrate further include at least one selected from single-crystal silicon, sapphire, quartz, silicon carbide, gallium nitride, and diamond.

[0022] According to a first aspect embodiment of this application, the first bottom electrode layer, the first top electrode layer, the second bottom electrode layer, and the second top electrode layer are made of one of Mo, Al, W, Ru, and Cu.

[0023] According to a second aspect of this application, a method for fabricating the above-mentioned single-crystal AlN thin-film bulk acoustic duplexer is provided, including a method for fabricating a receiving filter, a method for fabricating a transmitting filter, and a bonding method:

[0024] The method for preparing the receiving filter includes:

[0025] A first air cavity is formed on the first substrate, and a first lower bonding structure is formed on the surface of the first substrate;

[0026] Prepare a first temporary substrate, and form the first piezoelectric layer, the dielectric layer and the first upper bonding structure on the surface of the first temporary substrate;

[0027] A first bottom electrode layer is formed on the surface of the first piezoelectric layer;

[0028] The first temporary substrate is flipped onto the first substrate, such that the first bottom electrode layer is bonded to the first substrate, and the first upper bonding structure and the first lower bonding structure are bonded to each other to form the first bonding structure.

[0029] Remove the first temporary substrate to expose the first piezoelectric layer;

[0030] The first top electrode layer is formed on the surface of the first piezoelectric layer;

[0031] The method for manufacturing the transmission filter includes:

[0032] A second air cavity is formed on the second substrate, and a second lower bonding structure is formed on the surface of the second substrate;

[0033] Prepare a second temporary substrate, and form the second piezoelectric layer and the second upper bonding structure on the surface of the second temporary substrate;

[0034] A second bottom electrode layer is formed on the surface of the second piezoelectric layer;

[0035] The second temporary substrate is flipped onto the second substrate, such that the second bottom electrode layer is bonded to the second substrate, and the second upper bonding structure and the second lower bonding structure are bonded to each other to form the second bonding structure;

[0036] Remove the second temporary substrate to expose the second piezoelectric layer;

[0037] A second top electrode layer is formed on the surface of the second piezoelectric layer;

[0038] The bonding method includes:

[0039] The transmitting filter is flipped onto the receiving filter, the first bonding structure and the second bonding structure are bonded to each other, and the second top electrode layer is bonded to the first top electrode layer or the dielectric layer.

[0040] According to a second aspect of the present application, the first air cavity and the second air cavity are further formed using photolithography, nanoimprinting, dry etching, or wet etching processes.

[0041] According to a second aspect of the present application, the bonding process in the receiving filter preparation method, the transmitting filter preparation method, and the bonding method is performed using bonding bumps.

[0042] The beneficial effects of the embodiments of this application include at least the following: This application connects the receiving filter and the transmitting filter together by flip-chip bonding, resulting in a compact structure and eliminating the need for partitioning different filters; at the same time, the flip-chip bonding method also makes it possible to use single-crystal AlN thin films as piezoelectric materials for the first and second piezoelectric layers, thereby improving the isolation, insertion loss and other performance of the thin-film bulk acoustic duplexer. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly explained below. Obviously, the described drawings are only a part of the embodiments of this application, and not all of them. Those skilled in the art can obtain other design schemes and drawings based on these drawings without creative effort.

[0044] Figure 1 This is a circuit diagram of a single-crystal AlN thin-film bulk acoustic duplexer according to the first aspect of this application;

[0045] Figure 2 This is a schematic diagram of the structure of a single-crystal AlN thin film bulk acoustic duplexer according to the first aspect of this application;

[0046] Figure 3 This is a schematic diagram of step S110 in the preparation method of the second aspect embodiment of this application;

[0047] Figure 4 This is a schematic diagram of step S120 in the preparation method of the second aspect embodiment of this application;

[0048] Figure 5 This is a schematic diagram of step S140 in the preparation method of the second aspect embodiment of this application;

[0049] Figure 6 This is a schematic diagram of step S150 in the preparation method of the second aspect embodiment of this application;

[0050] Figure 7 This is a schematic diagram of step S160 in the preparation method of the second aspect embodiment of this application;

[0051] Figure 8 This is a schematic diagram of the bonding method in the preparation method of the second aspect embodiment of this application.

[0052] Reference numerals: 100-Receiver filter, 110-First substrate, 111-First air cavity, 112-TSV via, 120-First resonator unit, 121-First bottom electrode layer, 122-First piezoelectric layer, 123-First top electrode layer, 130-Dielectric layer, 140-First bonding structure, 141-First lower bonding structure, 142-First upper bonding structure, 150-Inductor, 160-Metal connector, 170-First temporary substrate, 200-Emitter filter, 210-Second substrate, 211-Second air cavity, 220-Second resonator unit, 221-Second bottom electrode layer, 222-Second piezoelectric layer, 223-Second top electrode layer, 230-Second bonding structure, 300-Bonding bump. Detailed Implementation

[0053] This section will describe in detail the specific embodiments of this application. Preferred embodiments of this application are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of this application, but they should not be construed as limiting the scope of protection of this application.

[0054] In the description of this application, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0055] In the description of this application, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0056] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0057] Traditional thin-film bulk acoustic wave (TFT) resonators are susceptible to corrosion from the sacrificial layer solution due to structural defects, resulting in poor performance. Simultaneously, some acoustic waves leak into the surrounding substrate through the piezoelectric material, leading to a low quality factor and ultimately poor duplexer isolation and loss. Because traditional TFT filters require AlN growth on a polycrystalline electrode structure, their piezoelectric material is polycrystalline AlN, which has a high defect density, further reducing the resonator's quality factor and affecting duplexer performance. Furthermore, traditional TFT filters require frequency tuning by adjusting the film thickness because the transmitter and receiver filters operate at different frequencies. This prevents the deposition of frequency tuning layers of varying thicknesses on the same wafer, necessitating the fabrication of transmitter and receiver filters on separate wafers, followed by initial packaging and integration. This method makes the transmitter and receiver filters independent and requires pre-allocated spacing, hindering the reduction of the overall duplexer module area. Meanwhile, to improve reliability, existing thin-film bulk acoustic wave (TFT) filters typically employ additional cap wafers for wafer-level packaging to ensure they are unaffected by external environmental interference. Wafer-level packaging is not only more complex and results in lower device yields, but it also increases the thickness of the TFT filter, leading to a larger size and additional cost.

[0058] In response, this application proposes a single-crystal AlN thin-film bulk acoustic duplexer and its fabrication method. The receiving filter 100 and the transmitting filter 200 are connected together by flip-chip bonding, resulting in a compact structure that eliminates the need for partitioning different filters. At the same time, the flip-chip bonding method also makes it possible to use single-crystal AlN thin film as the piezoelectric material for the first piezoelectric layer 122 and the second piezoelectric layer 222, thereby improving the isolation, insertion loss, and other performance characteristics of the thin-film bulk acoustic duplexer.

[0059] Reference Figure 1 The single-crystal AlN thin film bulk acoustic duplexer in the first aspect embodiment of this application includes a receiving filter 100 and a transmitting filter 200, which respectively filter the received electrical signal and the transmitted electrical signal.

[0060] Specifically, refer to Figure 2 The receiving filter 100 includes a first substrate 110, a first resonator unit 120, a dielectric layer 130, and a first bonding structure 140. The first substrate 110 has a first air cavity 111. The first resonator unit 120 includes a first bottom electrode layer 121, a first piezoelectric layer 122, and a first top electrode layer 123, which are sequentially deposited. The first bottom electrode layer 121 is formed on the surface of the first substrate 110 and covers the first air cavity 111. The first piezoelectric layer 122 uses a single-crystal AlN thin film as the piezoelectric material. The dielectric layer 130 and the first bonding structure 140 are both formed on the surface of the first substrate 110.

[0061] The emission filter 200 includes a second substrate 210, a second resonator unit 220, and a second bonding structure 230. The second substrate 210 has a second air cavity 211. The second resonator unit 220 includes a second bottom electrode layer 221, a second piezoelectric layer 222, and a second top electrode layer 223, which are sequentially deposited. The second bottom electrode layer 221 is formed on the surface of the second substrate 210 and covers the second air cavity 211. The second piezoelectric layer 222 uses a single-crystal AlN thin film as the piezoelectric material. The second bonding structure 230 is formed on the surface of the second substrate 210.

[0062] The first bonding structure 140 and the second bonding structure 230 are bonded to each other in an inverted manner. The second top electrode layer 223 can be bonded to the first top electrode layer 123 or to the dielectric layer 130. The dielectric layer 130 is used to block the movement of charge between the electrodes.

[0063] Furthermore, the first substrate 110 also has a TSV via 112, and the receiving filter 100 also includes an inductor 150, which is installed in the TSV via 112 for detecting the inductance in the TSV via 112.

[0064] Furthermore, the receiving filter 100 also includes a metal connector 160, which is connected to the TSV through hole 112. The metal connector 160 is spherical and is used for welding and fixing to the external structure.

[0065] Specifically, for the first substrate 110 and the second substrate 210, both are made of at least one of single-crystal silicon, sapphire, quartz, silicon carbide, gallium nitride, and diamond. For the electrode materials, the first bottom electrode layer 121, the first top electrode layer 123, the second bottom electrode layer 221, and the second top electrode layer 223 are made of one of Mo, Al, W, Ru, and Cu.

[0066] The method for fabricating the above-mentioned single-crystal AlN thin film bulk acoustic duplexer in the second aspect of this application includes a receiving filter fabrication method, a transmitting filter fabrication method, and a bonding method.

[0067] The method for preparing the receiving filter includes the following steps:

[0068] S110. (Refer to) Figure 3 A first air cavity 111 and a TSV via 112 are formed on the first substrate 110, an inductor 150 is embedded in the via 112, and a first lower bonding structure 141 is formed on the surface of the first substrate 110.

[0069] S120. Reference Figure 4Prepare a first temporary substrate 170, and form a first piezoelectric layer 122, a dielectric layer 130 and a first upper bonding structure 142 on the surface of the first temporary substrate 170.

[0070] S130. A first bottom electrode layer 121 is formed on the surface of the first piezoelectric layer 122;

[0071] S140. Reference Figure 5 The first temporary substrate 170 is flipped onto the first substrate 110, so that the first bottom electrode layer 121 is bonded to the first substrate 110, the first bottom electrode layer 121 covers the first air cavity 111, and the first upper bonding structure 142 and the first lower bonding structure 141 are bonded to each other to form the first bonding structure 140.

[0072] S150. (Refer to) Figure 6 Remove the first temporary substrate 170 to expose the first piezoelectric layer 122;

[0073] S160. (Refer to) Figure 7 A first top electrode layer 123 is formed on the surface of the first piezoelectric layer 122, and the receiving filter 100 is fabricated.

[0074] The method for fabricating a transmitting filter includes the following steps (see attached diagram for a schematic diagram of the method for fabricating a receiving filter):

[0075] S210. A second air cavity 211 is formed on the second substrate 210, and a second lower bonding structure is formed on the surface of the second substrate 210;

[0076] S220. Prepare a second temporary substrate, and form a second piezoelectric layer 222 and a second upper bonding structure on the surface of the second temporary substrate;

[0077] S230. A second bottom electrode layer 221 is formed on the surface of the second piezoelectric layer 222;

[0078] S240. The second temporary substrate is flipped onto the second substrate 210, so that the second bottom electrode layer 221 is bonded to the second substrate 210, the second bottom electrode layer 221 covers the second air cavity 211, and the second upper bonding structure and the second lower bonding structure are bonded to each other to form the second bonding structure 230.

[0079] S250. Remove the second temporary substrate 240 to expose the second piezoelectric layer 222;

[0080] S260. A second top electrode layer 223 is formed on the surface of the second piezoelectric layer 222, and the emission filter 200 is fabricated.

[0081] The bonding method includes the following steps:

[0082] Reference Figure 8The transmitting filter 200 is flipped onto the receiving filter 100, the first bonding structure 140 and the second bonding structure 230 are bonded to each other, and the second top electrode layer 223 is bonded to the first top electrode layer 123 or the dielectric layer 130.

[0083] Specifically, the first air cavity 111 and the second air cavity 211 are formed by photolithography, nanoimprinting, dry etching or wet etching processes.

[0084] The bonding process in the receiving filter fabrication method, the transmitting filter fabrication method, and the bonding method is carried out through bonding bumps 300. The material of the bonding bumps 300 is Au or other bonding materials.

[0085] The above is a detailed description of the preferred embodiments of this application. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of this application. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A single-crystal AlN thin-film bulk acoustic duplexer, characterized in that, Includes a receive filter (100) and a transmit filter (200): The receiving filter (100) includes: A first substrate (110) has a first air cavity (111). The first resonator unit (120) includes a first bottom electrode layer (121), a first piezoelectric layer (122) and a first top electrode layer (123) sequentially deposited. The first bottom electrode layer (121) is formed on the surface of the first substrate (110) and covers the first air cavity (111). The first piezoelectric layer (122) uses a single-crystal AlN thin film as the piezoelectric material. A dielectric layer (130) is formed on the surface of the first substrate (110); A first bonding structure (140) is formed at the surface edge of the first substrate (110); The transmit filter (200) includes: The second substrate (210) has a second air cavity (211). The second resonator unit (220) includes a second bottom electrode layer (221), a second piezoelectric layer (222), and a second top electrode layer (223) sequentially deposited. The second bottom electrode layer (221) is formed on the surface of the second substrate (210) and covers the second air cavity (211). The second piezoelectric layer (222) uses a single-crystal AlN thin film as the piezoelectric material. The second bonding structure (230) is formed at the surface edge of the second substrate (210); The first bonding structure (140) and the second bonding structure (230) are bonded to each other, the transmit filter (200) is flipped onto the receive filter (100), a portion of the second top electrode layer (223) is bonded to the first top electrode layer (123), and a portion of the second top electrode layer (223) is bonded to the dielectric layer (130).

2. The single-crystal AlN thin-film bulk acoustic duplexer according to claim 1, characterized in that: The first substrate (110) also has a TSV via (112).

3. The single-crystal AlN thin-film bulk acoustic duplexer according to claim 2, characterized in that: The receiving filter (100) also includes an inductor (150) mounted in the TSV via (112).

4. The single-crystal AlN thin-film bulk acoustic duplexer according to claim 2, characterized in that: The receiving filter (100) also includes a metal connector (160) connected to the TSV via (112).

5. The single-crystal AlN thin film bulk acoustic duplexer according to claim 4, characterized in that: The metal connector (160) is spherical.

6. The single-crystal AlN thin-film bulk acoustic duplexer according to claim 1, characterized in that: The materials of the first substrate (110) and the second substrate (210) include at least one of single-crystal silicon, sapphire, quartz, silicon carbide, gallium nitride and diamond.

7. The single-crystal AlN thin-film bulk acoustic duplexer according to claim 1, characterized in that: The first bottom electrode layer (121), the first top electrode layer (123), the second bottom electrode layer (221) and the second top electrode layer (223) are made of one of Mo, Al, W, Ru and Cu.

8. A method for fabricating a single-crystal AlN thin-film bulk acoustic duplexer according to any one of claims 1 to 7, characterized in that, This includes methods for fabricating receiver filters, methods for fabricating transmitter filters, and bonding methods: The method for preparing the receiving filter includes: A first air cavity (111) is formed on the first substrate (110), and a first lower bonding structure (141) is formed on the surface of the first substrate (110). Prepare a first temporary substrate (170), and form the first piezoelectric layer (122), the dielectric layer (130), and the first upper bonding structure (142) on the surface of the first temporary substrate (170). A first bottom electrode layer (121) is formed on the surface of the first piezoelectric layer (122); The first temporary substrate (170) is flipped onto the first substrate (110) so that the first bottom electrode layer (121) is bonded to the first substrate (110), and the first upper bonding structure (142) and the first lower bonding structure (141) are bonded to each other to form the first bonding structure (140). Remove the first temporary substrate (170) to expose the first piezoelectric layer (122). The first top electrode layer (123) is formed on the surface of the first piezoelectric layer (122); The method for manufacturing the transmission filter includes: A second air cavity (211) is formed on the second substrate (210), and a second lower bonding structure is formed on the surface of the second substrate (210); Prepare a second temporary substrate, and form the second piezoelectric layer (222) and the second upper bonding structure on the surface of the second temporary substrate; A second bottom electrode layer (221) is formed on the surface of the second piezoelectric layer (222); The second temporary substrate is flipped onto the second substrate (210) so that the second bottom electrode layer (221) is bonded to the second substrate (210), and the second upper bonding structure and the second lower bonding structure are bonded to each other to form the second bonding structure (230). Remove the second temporary substrate (240) to expose the second piezoelectric layer (222). The second top electrode layer (223) is formed on the surface of the second piezoelectric layer (222); The bonding method includes: The transmitting filter (200) is flipped onto the receiving filter (100), the first bonding structure (140) and the second bonding structure (230) are bonded to each other, and the second top electrode layer (223) is bonded to the first top electrode layer (123) or the dielectric layer (130).

9. The preparation method according to claim 8, characterized in that: The first air cavity (111) and the second air cavity (211) are formed by photolithography, nanoimprinting, dry etching or wet etching processes.

10. The preparation method according to claim 8, characterized in that: The bonding process in the receiving filter preparation method, the transmitting filter preparation method, and the bonding method is performed through bonding bumps (300).

Images