Film bulk acoustic resonator and electronic equipment

Abstract

The utility model relates to a film bulk acoustic resonator and electronic equipment, and the film bulk acoustic resonator comprises a substrate which is internally provided with a cavity; the lower electrode is formed on the substrate and covers the cavity; a piezoelectric layer formed on the lower electrode; an upper electrode formed on the piezoelectric layer; the film bulk acoustic resonator has a thickness stretching mode and a thickness shearing mode, the thickness shearing mode is a main mode, and the cut-off frequency of the thickness shearing mode is lower than that of the thickness stretching mode.

Description

Technical Field

[0001] This utility model relates to a resonator, and more specifically, to a thin-film bulk acoustic resonator and electronic equipment. Background Technology

[0002] As a core component of the radio frequency (RF) front-end, filters possess superior performance characteristics, such as low insertion loss, steep filtering curves, high isolation, and smaller size. They are crucial for driving the development of next-generation communication standards and the miniaturization and multifunctionality of personal mobile terminals. The next-generation thin-film bulk acoustic wave (BAW) technology is effectively addressing these two aspects. BAW filters fabricated using BAW technology exhibit steeper filtering curves, lower insertion loss, and superior out-of-band rejection capabilities.

[0003] Thin-film bulk acoustic resonators (FBARs) play an important role in communication, sensors and other fields due to their advantages such as small size, high frequency, large power capacity and high sensitivity. They are gaining an increasing share in the radio frequency front-end field, especially in the radio frequency filter market, and also have significant development advantages in fields such as biosensing and medical measurement.

[0004] Please see Figure 1 , Figure 1 A schematic diagram of a thin-film bulk acoustic resonator in a thickness stretching mode is shown. Figure 1 As shown, a bottom electrode 10 is formed on a substrate (not shown), a piezoelectric layer 20 is formed on the bottom electrode 10, and a top electrode 30 is formed on the piezoelectric layer 20. For thin-film bulk acoustic resonators, the thickness extensional mode (TE mode) is often used. The TE mode is an important vibration mode in thin-film bulk acoustic resonators, referring to the mode in which the piezoelectric layer undergoes stretching or compression motion in the thickness direction when the sound wave propagates along the thickness direction of the piezoelectric layer 20.

[0005] However, when using a thin-film bulk acoustic resonator with a thickness stretching mode to construct a thin-film bulk acoustic filter with low frequency and small bandwidth, a very thick bottom electrode 10, a top electrode 30, and a very thin piezoelectric layer 20 are required. In this case, the thickness of the piezoelectric layer 20 accounts for less than 30% of the total thickness of the piezoelectric layer, the bottom electrode, and the top electrode. This often reduces the acoustic energy in the piezoelectric layer 20, lowers the conversion efficiency, and thus reduces the Q value of the thin-film bulk acoustic resonator. Therefore, providing a thin-film bulk acoustic resonator that can increase the acoustic energy conversion efficiency and improve the Q value is what the industry desires. Utility Model Content

[0006] This invention addresses the aforementioned technical problems by meticulously designing a thin-film bulk acoustic resonator, successfully developing a thin-film bulk acoustic resonator that increases sound energy conversion efficiency and improves Q value, as well as an electronic device incorporating the resonator.

[0007] A brief overview of the present invention will be given below to provide a basic understanding of certain aspects thereof. It should be understood that this overview is not an exhaustive summary of the present invention. It is not intended to identify key or essential parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0008] According to one aspect of the present invention, a thin-film bulk acoustic resonator is provided, comprising: a substrate having a cavity formed therein; a lower electrode formed on the substrate and covering the cavity; a piezoelectric layer formed on the lower electrode; and an upper electrode formed on the piezoelectric layer. The thin-film bulk acoustic resonator has a thickness stretching mode and a thickness shear mode, wherein the thickness shear mode is the dominant mode, and the cutoff frequency of the thickness shear mode is lower than the cutoff frequency of the thickness stretching mode.

[0009] Furthermore, the thin-film bulk acoustic resonator further includes a passivation layer and a protective layer; the passivation layer, the lower electrode, the piezoelectric layer, the upper electrode, and the protective layer together constitute the functional layer of the thin-film bulk acoustic resonator.

[0010] Furthermore, the piezoelectric layer thickness accounts for more than or equal to 50% of the total thickness of the functional layers.

[0011] Furthermore, the C-axis tilt angle of the piezoelectric layer is set to [30°, 90°].

[0012] Furthermore, the C-axis tilt angle of the piezoelectric layer can be set to [-30°, -90°].

[0013] Furthermore, the piezoelectric layer is aluminum nitride.

[0014] Furthermore, the piezoelectric layer is scandium-doped aluminum nitride.

[0015] Furthermore, the thin-film bulk acoustic resonator operates at a frequency of approximately 900 MHz.

[0016] Furthermore, the excitation intensities of the thickness tensile mode and the thickness shear mode are determined by the thickness of each layer in the functional layer.

[0017] According to another aspect of the present invention, an electronic device is provided, the electronic device comprising the thin-film bulk acoustic resonator of any of the above claims.

[0018] The thin-film resonator provided by the utility model is suitable for application environments that operate at low frequencies, and its effective electromechanical constant Kt2 is less than 3%. By using scandium-doped aluminum nitride for the piezoelectric layer of the thin-film resonator, the piezoelectric coefficient can be increased, thereby increasing the effective electromechanical constant Kt2. Attached Figure Description

[0019] The specific details of this utility model are described below with reference to the accompanying drawings, which will help to more easily understand the above and other objects, features, and advantages of this utility model. The drawings are only for illustrating the principle of this utility model. The dimensions and relative positions of the units are not necessarily drawn to scale in the drawings.

[0020] Figure 1 A schematic diagram of a thin-film bulk acoustic resonator in the thickness stretching mode is shown.

[0021] Figure 2 This diagram shows a thin-film bulk acoustic resonator provided by the present invention.

[0022] Figure 3 This diagram illustrates the first-order thickness shear mode vibration of a piezoelectric thin film.

[0023] Figure 4 This diagram illustrates the vibration of the first-order thickness tensile mode of a piezoelectric thin film.

[0024] Figure 5 The dispersion curve of a thin-film bulk acoustic resonator with ALN as the piezoelectric layer is shown.

[0025] Figure 6a The impedance curves corresponding to different modes in a thin-film bulk acoustic resonator with ALN as the piezoelectric layer are shown.

[0026] Figure 6b The Q-value curves corresponding to different modes in the thin-film bulk acoustic resonator are shown when ALN ​​is used as the piezoelectric layer. Detailed Implementation

[0027] The exemplary disclosure of this utility model will be described below with reference to the accompanying drawings. For clarity and brevity, not all features implementing this utility model are described in the specification. However, it should be understood that many utility model-specific decisions can be made in the development of any such implementation of this utility model in order to achieve the developer's specific objectives, and these decisions may vary depending on the specific implementation of this utility model.

[0028] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the device structure closely related to the solution according to the present invention is shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0029] It should be understood that this invention is not limited to the described embodiments by reference to the accompanying drawings. In this invention, features may be substituted or borrowed between different embodiments where feasible, and one or more features may be omitted in one embodiment.

[0030] Please see Figure 2 , Figure 2 A schematic diagram of the thin-film bulk acoustic resonator provided by this utility model is shown. Figure 2 As shown, the thin-film bulk acoustic resonator includes a substrate 101, a cavity 102 formed in the substrate 101, a lower electrode 103, an upper electrode 105, and a piezoelectric layer 104 sandwiched between the upper and lower electrodes.

[0031] Those skilled in the art will understand that the substrate 101 may be, for example, a semiconductor-compatible material such as silicon (Si), gallium arsenide (GaAs), indium phosphide (InP), glass, sapphire, alumina, or SiC. A cavity 102 is formed in the substrate 101.

[0032] A lower electrode 103 covering the cavity 102 is formed on the substrate 101. The lower electrode 102 can be formed of one or more conductive materials, such as various metals compatible with semiconductor processes, including copper (Cu), tungsten (W), molybdenum (Mo), iridium (Ir), aluminum (Al), platinum (Pt), ruthenium (Ru), niobium (Nb), or hafnium (Hf).

[0033] A passivation layer may further be included between the substrate 101 and the lower electrode 103. The passivation layer may be a single layer or multiple layers, and the material of the passivation layer may, for example, be silicon dioxide (SiO2), silicon nitride (Si3N4), silicon dioxide / silicon nitride / silicon dioxide (ONO), aluminum oxide (Al2O3), etc.

[0034] A piezoelectric layer 104 is formed on the lower electrode 103. The piezoelectric layer 104 can be made of a piezoelectric material compatible with semiconductor processes, such as aluminum nitride (AlN) or scandium-doped aluminum nitride.

[0035] An upper electrode 104 is formed on the piezoelectric layer 103. The upper electrode 104 can be formed of one or more conductive materials, such as various metals compatible with semiconductor processes, including tungsten, molybdenum, iridium, aluminum, platinum, ruthenium, niobium, or hafnium. The materials of the upper electrode 105 and the lower electrode 103 can be the same or different. The upper electrode 105 and the lower electrode 103 can be formed as a circle, a regular pentagon, or a polygon with an interior angle greater than 90 degrees. Furthermore, a protective layer can be provided on the upper electrode 105. The passivation layer, the lower electrode, the piezoelectric layer, the upper electrode, and the protective layer constitute the functional film layers of the thin-film bulk acoustic resonator.

[0036] For piezoelectric layer 103, the piezoelectric coefficient, dielectric constant, elastic modulus, and other parameters of piezoelectric layer 104 change with the tilt angle of the C-axis of piezoelectric layer 104, thus affecting the electromechanical coupling coefficient (k2) of the thin-film bulk acoustic resonator. Therefore, different vibration modes can be excited by changing the tilt angle of the C-axis of the piezoelectric layer. The C-axis of the piezoelectric layer refers to the axis parallel to the edge line of the regular hexahedron in the piezoelectric crystal.

[0037] Please see Figure 3 , Figure 3 A schematic diagram of the first-order thickness shear mode vibration of a piezoelectric thin film is shown. Figure 3 As shown, the solid line represents the piezoelectric film not exhibiting first-order thickness shear mode (TS mode) vibration, while the dashed line represents the piezoelectric layer exhibiting first-order thickness shear mode vibration. When first-order TS mode vibration occurs, its direction is parallel to the surface of the piezoelectric layer, i.e., it vibrates along the horizontal direction (xy plane). Within one vibration cycle, the relative displacement along the horizontal direction (xy plane) at the upper and lower surfaces of the piezoelectric layer is the largest, while the piezoelectric layer remains constant along its thickness at the center plane. The resonant frequency of the first-order TS mode is determined by the thickness of the piezoelectric layer and the shear wave velocity of the material.

[0038] Please see Figure 4 , Figure 4 A schematic diagram of the first-order thickness tensile mode vibration of a piezoelectric thin film is shown. Figure 4 As shown, the solid line represents the piezoelectric layer without first-order thickness tensile mode vibration, while the dashed line represents the piezoelectric layer with first-order thickness tensile mode vibration. When first-order TE mode vibration occurs, the vibration direction of the TE mode is perpendicular to the surface of the piezoelectric layer; that is, the TE mode vibration is a stretching vibration along the thickness direction of the piezoelectric layer (i.e., the z-axis). Within one vibration cycle, the relative displacement between the upper and lower surfaces of the piezoelectric layer is the largest along the direction perpendicular to the piezoelectric layer surface, while the center plane of the piezoelectric film remains unchanged. The resonant frequency of the first-order TE mode is determined by the thickness of the piezoelectric layer and the longitudinal wave velocity of the material.

[0039] Please see Figure 5 , Figure 5 The dispersion curves of a thin-film bulk acoustic wave resonator using ALN as the piezoelectric layer are shown. The TS1 curve represents the dispersion curve of the thin-film bulk acoustic wave resonator in the first-order TS mode, and the TE curve represents the dispersion curve of the thin-film bulk acoustic wave resonator in the TE mode. Figure 5 It can be seen that, at the same thickness, the fundamental frequency of the first-order TS mode is less than that of the first-order TE mode. Therefore, at lower frequencies, the thin-film bulk acoustic resonator of the first-order TE mode requires a smaller piezoelectric layer thickness, while the thin-film bulk acoustic resonator of the first-order TS mode requires a larger piezoelectric layer thickness.

[0040] Please refer to the table below, which shows the thickness values ​​of each layer in the functional film of a thin-film bulk acoustic resonator (FCAS) at a low frequency of around 900MHz when ALN ​​is used as the piezoelectric layer, with TE mode and TS mode as the dominant modes. As shown in Table 1, if a very small bandwidth is desired for the FCAS at a low frequency of around 900MHz, for example, an effective Kt2 of around 2.2%, when TE mode is used as the dominant mode, the piezoelectric layer accounts for only about 17% of the thickness of the functional film of the FCAS. This results in most of the acoustic energy being concentrated in the upper and lower electrodes, leading to very low acoustic energy conversion efficiency. However, when TS mode is used as the dominant mode, the piezoelectric layer accounts for about 50% to achieve a similar frequency and bandwidth, significantly improving acoustic energy utilization.

[0041]

[0042] Please see Figures 6a-6b , Figure 6a The impedance curves corresponding to different modes in a thin-film bulk acoustic resonator with ALN as the piezoelectric layer are shown. Figure 6b The Q-value curves corresponding to different modes in the thin-film bulk acoustic resonator are shown when ALN ​​is used as the piezoelectric layer.

[0043] Depend on Figures 6a-6b It can be seen that when using the TS mode, increasing the proportion of piezoelectric layer thickness can effectively improve the Q value of the resonator.

[0044] Therefore, the thin-film bulk acoustic resonator provided by this invention adjusts the excitation intensity of the TS mode and TE mode by adjusting the angle of the C-axis of the piezoelectric layer, and uses the TS mode as the dominant mode of the thin-film bulk acoustic resonator. This is because the excitation intensity of the TS mode is the greatest when the C-axis is parallel to the thickness direction of the piezoelectric layer, and the excitation intensity of the TE mode increases when the C-axis is at a certain angle to the thickness direction of the piezoelectric layer.

[0045] Preferably, the thin-film bulk acoustic resonator provided by this utility model sets the C-axis tilt angle of the piezoelectric layer 104 to 30°-90° or -30°--90°, and uses the TS mode as the main mode of the thin-film bulk acoustic resonator. The cutoff frequency of the TS mode is lower than that of the thickness stretching mode (TE mode). The expected frequency and bandwidth can be achieved by increasing the thickness of the piezoelectric layer 104 and decreasing the thickness of the upper electrode 105 and / or the lower electrode 103.

[0046] For example, in this invention, AlN exhibits a strong piezoelectric effect along its C-axis, and a piezoelectric layer is constructed using it. Based on the excitation intensities of the TE and TS modes, the crystal orientation of the piezoelectric layer can be adjusted by controlling the growth conditions (such as temperature, pressure, and gas composition) during the deposition process, thereby changing the angle of the C-axis. Furthermore, the angle of the C-axis relative to the substrate surface can be changed by rotating the substrate during deposition. This can be achieved by using a tilted substrate or dynamically adjusting the substrate position during deposition. The excitation intensities of the TS and TE modes can be further optimized by adjusting the thickness of the piezoelectric layer 104 and the thickness of the upper electrode 105 and / or the lower electrode 103.

[0047] Alternatively, the piezoelectric layer of the thin-film resonator provided by this invention can be made of scandium-doped aluminum nitride. Since the piezoelectric coefficient of the TS mode is relatively small, the thin-film resonator provided by this invention is suitable for applications operating at low frequencies, and its effective electromechanical constant Kt2 is less than 3%. By using scandium-doped aluminum nitride for the piezoelectric layer of the thin-film resonator, the piezoelectric coefficient can be increased, thereby increasing the effective electromechanical constant Kt2.

[0048] The thin-film bulk acoustic resonator of this invention can be widely used in electronic devices, such as mobile phones, personal digital assistants, video game devices, and wearable terminals.

[0049] The present invention has been described above with reference to specific embodiments. However, those skilled in the art should understand that these descriptions are exemplary and not intended to limit the scope of protection of the present invention. Those skilled in the art can make various modifications and variations to the present invention based on its spirit and principles, and these modifications and variations are also within the scope of the present invention.

Claims

1. A thin-film bulk acoustic resonator, characterized in that, include: Substrate, in which cavities are formed; The lower electrode is formed on the substrate and covers the cavity; A piezoelectric layer is formed on the lower electrode; The upper electrode is formed on the piezoelectric layer; The thin-film bulk acoustic resonator has a thickness stretching mode and a thickness shear mode, with the thickness shear mode being the dominant mode. The cutoff frequency of the thickness shear mode is lower than that of the thickness stretching mode.

2. The thin-film bulk acoustic resonator as described in claim 1, characterized in that: The thin-film bulk acoustic resonator further includes a passivation layer and a protective layer; the passivation layer, the lower electrode, the piezoelectric layer, the upper electrode, and the protective layer together constitute the functional layer of the thin-film bulk acoustic resonator.

3. The thin-film bulk acoustic resonator as described in claim 2, characterized in that: The piezoelectric layer thickness accounts for more than or equal to 50% of the total thickness of the functional layer.

4. The thin-film bulk acoustic resonator as described in claim 3, characterized in that: The C-axis tilt angle of the piezoelectric layer is set to [30°, 90°].

5. The thin-film bulk acoustic resonator as described in claim 3, characterized in that: Alternatively, the C-axis tilt angle of the piezoelectric layer can be set to [-30°, -90°].

6. The thin-film bulk acoustic resonator as described in claim 4 or 5, characterized in that: The piezoelectric layer is aluminum nitride.

7. The thin-film bulk acoustic resonator as described in claim 4 or 5, characterized in that: The piezoelectric layer is scandium-doped aluminum nitride.

8. The thin-film bulk acoustic resonator as described in claim 7, characterized in that: The thin-film bulk acoustic resonator operates at a frequency of 900MHz.

9. The thin-film bulk acoustic resonator as described in claim 8, characterized in that: The excitation intensities of the thickness tensile mode and the thickness shear mode are determined by the thickness of each layer in the functional layer.

10. An electronic device, characterized in that, include: The thin-film bulk acoustic resonator according to any one of claims 1-9.

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