Cavity type bulk acoustic wave resonator

Abstract

The cavity type bulk acoustic wave resonator comprises a load layer, a top electrode, a film structure layer, a bonding layer and a supporting substrate which are sequentially attached and connected from top to bottom, the film structure layer comprises a piezoelectric film and a bottom electrode, and the piezoelectric film is located between the top electrode and the bottom electrode to form a sandwich structure. The top electrode is internally provided with a recessed cavity, the center of the recessed cavity is provided with a boss, and two sides of the boss are respectively provided with a plurality of steps. According to the utility model, the generation of parasitic clutters is further inhibited through the combined action of the frame and the recessed structure, and the performance of the resonator is optimized.

Description

Technical Field

[0001] The utility model belongs to the field of third-generation semiconductor materials and devices, and relates to a cavity bulk acoustic wave resonator. Background Art

[0002] In recent years, the Film Bulk Acoustic Resonator (FBAR) has the advantages of high frequency, miniaturization, high performance, low power consumption, high power capacity, etc. Moreover, the manufacturing process of the FBAR filter is compatible with the IC process and can be integrated, which is beneficial to reducing the power consumption of the device and shrinking the device size. It is currently the only integrable radio frequency front-end filter. Therefore, the FBAR filter will become the core component of future 5G high-frequency communication. The working frequency range of the FBAR filter using microelectromechanical system (MEMS) technology can range from several hundred MHz to dozens of GHz, fully covering the requirements of the wireless communication frequency band. The traditional dielectric filter is too large in volume, and the insertion loss of the SAW filter is larger than that of the FBAR filter and cannot meet the high-frequency (>3 GHz) requirements. Therefore, the FBAR filter is the optimal solution for the high-frequency band above 3 GHz.

[0003] The thin film bulk acoustic wave resonator mainly consists of three parts: a substrate, an acoustic wave reflection layer, and a sandwich piezoelectric oscillation stack composed of upper and lower electrodes and a piezoelectric thin film sandwiched between the upper and lower electrodes. When a radio frequency (RF) voltage is applied between the two electrodes, an alternating electric field is generated in the piezoelectric oscillation stack. Through the inverse piezoelectric effect of the piezoelectric thin film, part of the electrical energy is converted into bulk acoustic waves propagating along the thickness direction of the thin film and reflected back and forth between the two electrodes. When the propagation of the bulk acoustic wave in the piezoelectric oscillation stack is exactly half a wavelength or an odd multiple of half a wavelength, resonance will occur, that is, the fundamental frequency wavelength of resonance is approximately equal to twice the thickness of the piezoelectric oscillation stack.

[0004] The cavity-type FBAR is divided into two structures: convex-up type and concave-down type, and their air cavities are both obtained by releasing the sacrificial layer. The convex-up type FBAR is to sequentially deposit the sacrificial layer and the functional layer material directly on the silicon substrate, and then release the sacrificial layer through the release hole structure reserved in the process to obtain a cavity structure; while the concave-down type FBAR is to first etch a cavity in the silicon substrate, fill the cavity with a sacrificial layer, polish it flat through a chemical mechanical polishing process, and then sequentially prepare the working layer and release the sacrificial layer to obtain an air cavity.

[0005] The cavity-type structure retains most of the substrate, has strong mechanical stability, and has a relatively high Q value and strong mechanical stability compared to other structures. It is the most mainstream structure currently used commercially. However, there are also parasitic effects, which generate parasitic capacitance and damage the core components of the thin-film bulk acoustic resonator during the production process, thereby resulting in a low quality factor of the produced thin-film bulk acoustic resonator. At the same time, parasitic capacitance will also be left in the thin-film bulk acoustic resonator, which often causes great energy damage when used in subsequent integrated circuits. In order to improve the above problems existing in the mainstream process, in the prior art, generally only a load layer is added on the top electrode to reduce parasitic capacitance, thereby improving the quality factor. However, there is still some parasitic capacitance during the production process. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a cavity-type bulk acoustic resonator.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A cavity-type bulk acoustic resonator includes a load layer, a top electrode, a thin-film structure layer, a bonding layer, and a support substrate that are sequentially bonded and connected from top to bottom. The thin-film structure layer includes a piezoelectric thin film and a bottom electrode, and the piezoelectric thin film is located between the top electrode and the bottom electrode to form a sandwich structure.

[0009] A concave cavity is provided in the top electrode, a convex platform is provided at the center of the concave cavity, and several steps are respectively provided on both sides of the convex platform.

[0010] The several steps on both sides of the convex platform extend from the bottom surface of the concave cavity to the upper surface of the convex platform.

[0011] A cavity is provided in the support substrate, and the bonding layer is provided with an opening corresponding to the cavity, so that the bottom of the bottom electrode corresponds to the cavity.

[0012] The material of the support substrate is one of a silicon substrate, a sapphire substrate, a LiGaO2 substrate, and a metal single-element substrate.

[0013] The number of steps on both sides of the convex platform in the top electrode is 1-5.

[0014] The piezoelectric thin film is a single-crystal AlN thin film, and the electrode material is one of metals Pt, Mo, W, Ti, and Au.

[0015] Compared with the prior art, the present invention has the following technical effects:

[0016] The generation of parasitic capacitance can be suppressed by a single-stage load layer, and the parasitic effect can be further reduced by multi-stage top electrodes with different structures. At the same time, the leakage of acoustic waves can be reduced, the acoustic wave energy can be constrained, and the Q value can be further improved. The subsequent filters, duplexers, sensors and other related devices prepared on this basis have more excellent performance. At the same time, due to the smaller lattice mismatch between the AlN crystal and the sapphire substrate compared with the silicon substrate, the quality of the AlN crystal grown on the sapphire substrate is better. Compared with the existing preparation methods, the crystal quality of the piezoelectric thin film is greatly improved, and the quality factor and effective electromechanical coupling coefficient of the resonator are improved by improving the crystal quality of the piezoelectric thin film. Brief Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram after sequentially depositing a piezoelectric layer and a bottom electrode on a preparation substrate;

[0018] Figure 2 It is a schematic structural diagram after bonding a support substrate and a preparation substrate through a silicon layer;

[0019] Figure 3 It is a schematic cross-sectional structural diagram of the present invention.

[0020] Reference Signs:

[0021] Load layer 1, top electrode 2, piezoelectric thin film 3, bottom electrode 4, bonding layer 5, support substrate 6, cavity 7, preparation substrate 8, step 9. Detailed Embodiments

[0022] The following describes in detail the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0023] In the description of the present utility model, it should be understood that if there are terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present utility model. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise specifically defined.

[0024] In the description of the present utility model, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection. It may be a mechanical connection or an electrical connection. It may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0025] As Figure 3 shown, a cavity bulk acoustic wave resonator includes a load layer 1, a top electrode 2, a thin film structure layer, a bonding layer 5, and a support substrate 6 that are sequentially bonded and connected from top to bottom. The thin film structure layer includes a piezoelectric thin film 3 and a bottom electrode 4. The piezoelectric thin film 3 is located between the top electrode 2 and the bottom electrode 4 to form a sandwich structure. A recessed cavity is provided in the top electrode 2, a convex platform is provided at the center of the recessed cavity, and a plurality of steps 9 are respectively provided on both sides of the convex platform. The number of the steps is specifically set to be 1 - 5. By using the step structure, the generation of parasitic capacitance can be suppressed by a single-stage load layer, and the parasitic effect can be further reduced by a multi-stage top electrode with different structures. At the same time, the leakage of acoustic waves can be reduced, the acoustic wave energy can be constrained, and the Q value can be further improved. The subsequent filters, duplexers, sensors and other related devices prepared based on this have more excellent performance.

[0026] A cavity 7 is provided in the support substrate 6, and the bonding layer 5 is provided with an opening corresponding to the cavity, so that the bottom of the bottom electrode 4 corresponds to the cavity 7. The generation of parasitic clutter is further suppressed by the combined action of the overall frame and the recessed structure, optimizing the performance of the resonator.

[0027] The material of the support substrate 6 is one of a silicon substrate, a sapphire substrate, a LiGaO2 substrate, and a metallic element substrate.

[0028] The piezoelectric thin film is a single-crystal AlN thin film, and the electrode material is one of metals Pt, Mo, W, Ti, and Au.

[0029] The following is an illustration with specific preparation.

[0030] I. Growing a thin film structure layer on a preparation substrate.

[0031] 1. Preparing the substrate.

[0032] Deposit an oriented single-crystal aluminum nitride layer on the surface of a sapphire preparation substrate 8 that has been subjected to standard RCA cleaning, drying, and annealing in a nitrogen atmosphere at 850 °C for 1 h, serving as the piezoelectric thin film 3. The thickness of this aluminum nitride layer is determined according to the frequency range of actual applications.

[0033] Among them, the piezoelectric thin film 3 of the single-crystal aluminum nitride layer can be obtained by MOCVD (Metal-Organic Chemical Vapor Deposition) deposition under the parameters of a trimethylaluminum (TMA) flow rate of 45 - 60 sccm (standard-state milliliters per minute), an NH3 flow rate of 2 - 5 slm (standard-state liters per minute), an Ar flow rate of 0.5 - 1.5 slm, a substrate temperature of 750 - 1000 °C, and a total reaction chamber pressure of 35 - 45 Torr. Its deposition is divided into two steps. First, deposit a 5 - 10 nm single-crystal AlN nucleation layer, and then deposit a relatively thick AlN layer, the thickness of which is determined by the operating frequency.

[0034] Use a radio frequency magnetron sputtering system to sputter-deposit a layer of metallic molybdenum as the bottom electrode 4 on the surface of the single-crystal aluminum nitride layer, with a thickness of 100 - 400 nm using a pure molybdenum target (purity 99.999%).

[0035] Prepare a 30 - 200 nm Si thin film on the bottom electrode for subsequent bonding processes.

[0036] 2. Support substrate: Prepare a 30 - 200 nm Si thin layer on a silicon substrate that has been subjected to standard RCA cleaning and drying, and dry-etch a cavity 7 corresponding to the pattern.

[0037] II. Flip-chip bonding.

[0038] Through non-metallic Si - Si bonding, bond the obtained preparation substrate 8 and the thin film structure layer grown thereon together, with non-metallic Si as the bonding surface, to bond with the Si thin layer of the support substrate 6. As Figure 2 shown.

[0039] III. Removing the preparation substrate.

[0040] The preparation substrate 8 is removed through two steps of mechanical thinning and dry etching to expose the single-crystal aluminum nitride piezoelectric thin film 3.

[0041] IV. Post-process.

[0042] 1. A layer of metal molybdenum is sputter-deposited on the exposed piezoelectric thin film 3 as the top electrode 2, with a thickness of 100 - 400 nm.

[0043] 2. Through photolithography and etching processes, the patterns of the aluminum nitride layer and the top electrode are obtained successively.

[0044] 3. A layer of load molybdenum thin film is sputtered on the top electrode, with a thickness of 5 - 20 nm, and a ring pattern is obtained through etching, with a width of 2 - 7 nm.

[0045] 4. Further, according to the order, the top electrode is etched multiple times to obtain a multi-order ring-shaped concave structure, with each order having a thickness of 2 - 20 nm and a width of 1 - 7 nm.

[0046] Finally, a structure with a cavity 7, a support substrate 6, a bonding layer 5, a bottom electrode 4, a piezoelectric thin film 3, a top electrode 2, and a load layer 1 stacked in sequence is formed to obtain a cavity bulk acoustic wave resonator, as Figure 3 shown.

[0047] It should be noted that the above is only the preferred embodiment of the present utility model and is not used to limit the present utility model. Although the present utility model has been described in detail with reference to the embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present utility model shall be included within the protection scope of the present utility model.

Claims

1. A cavity bulk acoustic wave resonator, characterized in that, It includes a load layer, a top electrode, a thin film structure layer, a bonding layer, and a support substrate that are sequentially bonded and connected from top to bottom. The thin film structure layer includes a piezoelectric thin film and a bottom electrode, and the piezoelectric thin film is located between the top electrode and the bottom electrode to form a sandwich structure.

2. The cavity bulk acoustic wave resonator according to claim 1, wherein The top electrode is provided with a recessed cavity, and a boss is provided at the center of the recessed cavity, and a plurality of steps are respectively provided on both sides of the boss.

3. The cavity bulk acoustic wave resonator according to claim 2, wherein The plurality of steps on both sides of the boss extend from the bottom surface of the recessed cavity to the upper surface of the boss.

4. The cavity bulk acoustic wave resonator according to claim 1, characterized in that, The support substrate is provided with a cavity, and the bonding layer is provided with an opening corresponding to the cavity, so that the bottom of the bottom electrode corresponds to the cavity.

5. The cavity bulk acoustic wave resonator according to claim 1, wherein, The material of the support substrate is one of a silicon substrate, a sapphire substrate, a LiGaO2 substrate, and a metal single-element substrate.

6. The cavity bulk acoustic wave resonator according to claim 2, wherein The number of steps on both sides of the boss in the top electrode is 1-5.

7. The cavity bulk acoustic wave resonator according to claim 1, characterized in that The piezoelectric thin film is a single-crystal AlN thin film, and the electrode material is one of metals Pt, Mo, W, Ti, and Au.

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