Bulk acoustic wave resonator structure

Abstract

A bulk acoustic wave resonator structure provided by the present invention comprises a substrate, a bottom electrode, a piezoelectric layer and a top electrode, the bottom electrode is located above the substrate, the piezoelectric layer is located above the bottom electrode, and the piezoelectric layer comprises first ferroelectric film layers and second ferroelectric film layers which are alternately stacked from bottom to top. The polarization directions of the adjacent first ferroelectric film layers and second ferroelectric film layers are opposite to excite N-order mode resonance, and N is an integer not lower than the total number of the first ferroelectric film layers and the second ferroelectric film layers; the top electrode is over the piezoelectric layer. The polarities of the adjacent first ferroelectric film layer and the second ferroelectric film layer are opposite, the high-order resonance mode of the resonator is excited under the condition that the thick piezoelectric layer is maintained, and the resonance frequency of the bulk acoustic wave resonator is remarkably improved. Besides, the adjacent first ferroelectric film layer and the second ferroelectric film layer are in direct contact, an electrode material layer does not need to be inserted between the first ferroelectric film layer and the second ferroelectric film layer, and the device is simple in structure and high in performance.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology and relates to a bulk acoustic resonator structure. Background Technology

[0002] Currently, wireless data transmission requires radio frequency (RF) filters with operating frequencies of 5 GHz or higher. The filters used in 5G communication are mainly bulk acoustic wave (BAW) filters and surface acoustic wave (SAW) filters. BAW devices have extremely high Q values ​​(above 4000), operate in frequency bands from 100 MHz to 20 GHz, and offer advantages such as high operating frequency, low insertion loss, high frequency selectivity, high power capacity, and strong electrostatic discharge (ESD) immunity, making them the best solution for future RF front-ends.

[0003] With increasing application demands, microwave acoustics not only needs to extend its operating frequency range to the Ku, Ka bands, and even the millimeter-wave (mm-Wave) band, but also needs to meet the requirements of ultra-wideband applications. In traditional single-layer piezoelectric thin-film resonators, since the resonant frequency of the bulk acoustic resonator is positively correlated with the ratio of longitudinal sound velocity to film thickness, this means that the thickness of the piezoelectric film used in filters at higher frequency bands such as 5G will be even smaller. For example, the piezoelectric film thickness for operating frequencies above 10 GHz must be less than 100 nm, which would severely degrade the quality of the piezoelectric film crystal and cause a sharp decrease in the resonator's power handling capability, electromechanical coupling coefficient, and Q value.

[0004] Therefore, how to provide a bulk acoustic resonator structure that can improve the resonant frequency of the resonator while maintaining the thickness of the piezoelectric layer and thus improve the device performance has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a bulk acoustic wave resonator structure to solve the problem of performance degradation of the bulk acoustic wave resonator when the resonant frequency is increased in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a bulk acoustic resonator structure, comprising:

[0007] Substrate;

[0008] The bottom electrode is located above the substrate;

[0009] A piezoelectric layer is located above the bottom electrode. The piezoelectric layer includes alternating layers of first and second ferroelectric thin films stacked from bottom to top. The interfaces of adjacent first and second ferroelectric thin films are in direct contact, and the polarization directions of adjacent first and second ferroelectric thin films are opposite to excite N-order mode resonance, where N is an integer not less than the total number of the first and second ferroelectric thin films.

[0010] The top electrode is located above the piezoelectric layer.

[0011] Optionally, the total number of layers of the first ferroelectric thin film layer and the second ferroelectric thin film layer is 3, which suppresses the first-order thickness-extended mode resonance and excites the third-order thickness-extended mode resonance.

[0012] Optionally, the material of the first ferroelectric thin film layer includes Al. 1-x Sc x The material of the second ferroelectric thin film layer is one or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3, and the material of the second ferroelectric thin film layer includes Al. 1-x Sc x One or more of N (0.2≤x≤0.5), BST, PZT and PbTiO3.

[0013] Optionally, the thickness of the first ferroelectric thin film layer is not less than 0.01 μm, and the thickness of the second ferroelectric thin film layer is not less than 0.01 μm.

[0014] Optionally, the material of the bottom electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and the material of the top electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf.

[0015] Optionally, the thickness of the bottom electrode does not exceed 0.3 μm, and the thickness of the top electrode does not exceed 0.3 μm.

[0016] Optionally, the substrate has an upward-opening groove, and the bottom electrode and the groove together form a cavity.

[0017] Optionally, a Bragg reflector layer is disposed between the substrate and the bottom electrode, the Bragg reflector layer comprising a stacked high acoustic impedance material layer and a low acoustic impedance material layer.

[0018] Optionally, the substrate includes a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate, or a diamond substrate.

[0019] As described above, in the bulk acoustic wave resonator of the present invention, the adjacent first and second ferroelectric thin film layers have opposite polarities, breaking the inverse relationship between the resonant frequency and the piezoelectric layer thickness of traditional bulk acoustic wave resonators. This allows for the excitation of higher-order resonant modes of the resonator while maintaining a relatively thick piezoelectric layer, significantly increasing the resonant frequency of the bulk acoustic wave resonator. Furthermore, the adjacent first and second ferroelectric thin film layers are in direct contact, eliminating the need for an electrode material layer between them, resulting in a simple device structure and high device performance. Attached Figure Description

[0020] Figure 1 The diagram shown is a structural schematic of a bulk acoustic resonator according to an embodiment of the present invention.

[0021] Figure 2 The diagram shown is a schematic diagram of a piezoelectric layer consisting of three thin film layers in an embodiment of the present invention.

[0022] Figure 3 The diagram shown is a comparative example of a piezoelectric layer consisting of three thin film layers.

[0023] Figure 4 The figure shown is a simulation result diagram of an embodiment of the present invention.

[0024] Figure 5 The simulation results are shown as a scale diagram.

[0025] Component designation explanation

[0026] 1 Substrate

[0027] 2 Bottom electrode

[0028] 3 Piezoelectric layer

[0029] 3A First Ferroelectric Thin Film Layer

[0030] 3B Second Ferroelectric Thin Film Layer

[0031] 4. Polarization direction

[0032] 5 Top Electrodes

[0033] 6. Cavity

[0034] 7 Resonance Modes Detailed Implementation

[0035] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] Please see Figures 1 to 5 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0037] This embodiment provides a bulk acoustic resonator structure. Please refer to [link / reference]. Figure 1 The bulk acoustic wave resonator structure includes a substrate 1, a bottom electrode 2, a piezoelectric layer 3, and a top electrode 5. The bottom electrode 2 is located above the substrate 1. The piezoelectric layer 3 is located above the bottom electrode 2. The piezoelectric layer 3 includes alternating layers of first ferroelectric thin film 3A and second ferroelectric thin film 3B stacked from bottom to top. The interfaces of adjacent first ferroelectric thin film layers 3A and second ferroelectric thin film layers 3B are in direct contact, and the polarization directions 4 of adjacent first ferroelectric thin film layers 3A and second ferroelectric thin film layers 3B are opposite to excite N-order mode resonance, where N is an integer not less than the total number of layers of first ferroelectric thin film layers 3A and second ferroelectric thin film layers 3B. The top electrode 5 is located above the piezoelectric layer 3.

[0038] As an example, the substrate 1 includes a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate, or a diamond substrate. The substrate 1 has an upward-facing groove. The bottom electrode 2 and the groove together form a cavity 6, which serves as an acoustic wave reflection structure. In other examples, a Bragg reflector layer is disposed between the substrate 1 and the bottom electrode 2 as an acoustic wave reflection structure. The Bragg reflector layer includes stacked high acoustic impedance material layers and low acoustic impedance material layers. The high acoustic impedance material layer is made of one or more of W, Mo, Pt, Au, Ni, and Ir. The low acoustic impedance material layer is made of one or more of AlN, Si3N4, and SiO2. The thickness of each layer in the Bragg reflector layer is 1 / 4 or 3 / 4 of the wavelength of the acoustic wave corresponding to the resonant frequency of the resonator.

[0039] As an example, the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B refer to thin film layers that simultaneously possess piezoelectric and ferroelectric properties.

[0040] As an example, the material of the first ferroelectric thin film layer includes Al. 1-x Sc x The material of the first ferroelectric thin film layer 3A is one or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3, and the thickness of the single-layer first ferroelectric thin film layer 3A is not less than 0.01μm; the material of the second ferroelectric thin film layer includes Al. 1-x Sc xOne or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3 are used, and the thickness of the single-layer second ferroelectric thin film layer 3B is not less than 0.01 μm; the total thickness of the piezoelectric layer 3 is not greater than 2 μm. In this embodiment, the first ferroelectric thin film layer 3A is made of Al. 1-x Sc x N layer, the second ferroelectric thin film layer 3B is made of Al 1-x Sc x N layers.

[0041] As an example, the bottom electrode 2 is made of one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and its thickness does not exceed 0.3 μm; the top electrode 5 is made of one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and its thickness does not exceed 0.3 μm. In this embodiment, the bottom electrode 2 is made of a Mo metal layer, and the top electrode 5 is made of a Mo metal layer.

[0042] Specifically, please refer to Figure 2 The piezoelectric layer 3 is configured with a total of 3 layers, including the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B. The piezoelectric layer 3 is composed of stacked layers of the first ferroelectric thin film layer 3A, the second ferroelectric thin film layer 3B, and the first ferroelectric thin film layer 3A. The first ferroelectric thin film layer 3A is made of Al. 0.7 Sc 0.3 N layer, the second ferroelectric thin film layer 3B is made of Al 0.7 Sc 0.3 The N-layer has the following characteristics: the first ferroelectric thin film layer 3A has a thickness of 50 nm, the second ferroelectric thin film layer 3B has a thickness of 100 nm, and the polarization directions 4 of the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are opposite. Both the bottom electrode 2 and the top electrode 5 are made of a 100 nm thick Mo metal layer. Please also refer to... Figure 3 A comparative example is provided, which has the same material and thickness for the bottom electrode 2, piezoelectric layer 3, and top electrode 5 as the example. The difference lies in that the polarization directions 4 of the adjacent first ferroelectric thin film layer 3A and second ferroelectric thin film layer 3B are the same, and the example and the comparative example have different resonance modes 7. Please refer to... Figure 4 and Figure 5 The simulation results are shown in the figures for the embodiments and comparative examples, respectively. Figure 4It can be seen that when the polarization directions of adjacent first ferroelectric thin film layers 3A and second ferroelectric thin film layers 3B are opposite, there is a 180° phase difference in the piezoelectric response to the electrical signal. The inverse piezoelectric effect causes one of the adjacent first ferroelectric thin film layers 3A and second ferroelectric thin film layers 3B to be subjected to compressive stress, and the other to be subjected to tensile stress, suppressing the first-order asymmetric thickness spread mode and exciting the corresponding higher-frequency third-order (TE3) thickness spread mode, with an operating frequency band of 28GHz; from Figure 5 It can be seen that when the polarization directions of the adjacent first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are the same, the excited resonance mode is the first-order thickness extension mode (TE1), and the operating frequency band is 7GHz.

[0043] It should be noted that in this embodiment, the total number of layers of the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B is three. In other examples, more layers of the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B can be set. The thickness of the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B can be adjusted until the first-order thickness extension mode is almost completely suppressed. The order of the excited thickness extension mode is equal to the total number of layers of the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B.

[0044] As an example, this invention employs a thicker piezoelectric layer 3 to achieve ultra-high frequencies in the filter. The piezoelectric layer 3 has high crystal quality and low defect density, resulting in a higher Q value, lower loss, and higher power capacity for the corresponding device, making it more suitable for low-power mobile communication and wireless communication applications requiring low interference. Furthermore, to ensure the manufacturing yield of the resonator, the thickness uniformity of the piezoelectric layer 3 needs to be better than 0.5%, and a thicker piezoelectric layer 3 can significantly improve the manufacturing yield and manufacturing stability. In addition, it is not necessary to reduce the thickness of the piezoelectric layer 3 to achieve frequency increases in the resonator, making it particularly suitable for new high-frequency bands in 5G, high-frequency satellite communication, 5G millimeter-wave bands, and 6G ultra-high-frequency bands.

[0045] As an example, compared with existing dielectric filters such as low-temperature co-fired ceramic (LTCC) filters and integrated passive device (IPD) filters used for high and ultra-high frequencies, the resonator of the present invention has excellent out-of-band rejection and in-band insertion loss characteristics, which significantly reduces signal interference and operating power in wireless communication.

[0046] As an example, in traditional bulk acoustic resonators made of single-layer piezoelectric materials, the electromechanical coupling coefficient of the excited high-frequency modes is inversely proportional to the order of the higher-order modes. Therefore, the electromechanical coupling coefficient of the resonator at higher orders is very small, resulting in a small bandwidth for the corresponding filter, which is difficult to meet the requirements of practical communication applications. In the present invention, the electromechanical coupling coefficient of the higher-order modes of the device is independent of the order, and it can maintain a high electromechanical coupling coefficient and a large bandwidth at high frequencies, making it very suitable for high-frequency, high-bandwidth applications.

[0047] As an example, in the prior art, when high-frequency modes are excited by piezoelectric thin film layers and ferroelectric thin film layers with opposite polarities, an electrode material layer needs to be inserted between the piezoelectric thin film layer and the ferroelectric thin film layer. The polarity reversal is achieved by applying a very high bias voltage to the electrode material layer. However, inserting an electrode material layer will seriously affect the crystal quality of the piezoelectric thin film layer and the ferroelectric thin film layer, deteriorate the out-of-band suppression and in-band loss characteristics of the device, and pose great challenges to cost, controllability and integration. In this application, the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B are in direct contact. The ferroelectricity of the ferroelectric thin film layer causes spontaneous polarization within it. The polarization reversal voltage between different ferroelectric thin films varies due to deposition conditions, material type, doping concentration, etc. By applying an external voltage between the bottom electrode 2 and the top electrode 5, the polarization state of one of the adjacent first ferroelectric thin film layers 3A and the second ferroelectric thin film layer 3B remains unchanged, while the polarization state of the other layer is reversed. This achieves opposite polarity control between adjacent first ferroelectric thin film layers 3A and the second ferroelectric thin film layer 3B. There is no need to insert an electrode material layer between the first ferroelectric thin film layer 3A and the second ferroelectric thin film layer 3B, resulting in a simple device structure and high device performance.

[0048] In another example, by adjusting the thickness of the bottom electrode 2, the piezoelectric layer 3, and the top electrode 5, it is possible to suppress the third-order thickness extension mode and excite the fourth-order overtone thickness mode resonance.

[0049] In summary, in the bulk acoustic wave resonator of this invention, the adjacent first and second ferroelectric thin film layers have opposite polarities, breaking the inverse relationship between the resonant frequency and the piezoelectric layer thickness in traditional bulk acoustic wave resonators. This allows for the excitation of higher-order resonant modes while maintaining a relatively thick piezoelectric layer, significantly increasing the resonant frequency of the bulk acoustic wave resonator. Furthermore, the adjacent first and second ferroelectric thin film layers are in direct contact, eliminating the need for an electrode material layer between them, resulting in a simple device structure and high performance. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0050] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A bulk acoustic resonator structure, characterized in that, include: Substrate; The bottom electrode is located above the substrate; A piezoelectric layer is located above the bottom electrode. The piezoelectric layer includes alternating layers of first and second ferroelectric thin films stacked from bottom to top. The interfaces of adjacent first and second ferroelectric thin films are in direct contact, and the polarization directions of adjacent first and second ferroelectric thin films are opposite to excite N-order mode resonance, where N is an integer not less than the total number of the first and second ferroelectric thin films. The top electrode is located above the piezoelectric layer.

2. The bulk acoustic resonator structure according to claim 1, characterized in that: The first ferroelectric thin film layer and the second ferroelectric thin film layer have a total of 3 layers, which suppress the first-order thickness-extended mode resonance and excite the third-order thickness-extended mode resonance.

3. The bulk acoustic resonator structure according to claim 1, characterized in that: The material of the first ferroelectric thin film layer includes Al 1-x Sc x The material of the second ferroelectric thin film layer is one or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3, and the material of the second ferroelectric thin film layer includes Al. 1-x Sc x One or more of N (0.2≤x≤0.5), BST, PZT and PbTiO3.

4. The bulk acoustic resonator structure according to claim 1, characterized in that: The thickness of the first ferroelectric thin film layer is not less than 0.01 μm, and the thickness of the second ferroelectric thin film layer is not less than 0.01 μm.

5. The bulk acoustic resonator structure according to claim 1, characterized in that: The bottom electrode is made of one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and the top electrode is made of one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf.

6. The bulk acoustic resonator structure according to claim 1, characterized in that: The thickness of the bottom electrode does not exceed 0.3 μm, and the thickness of the top electrode does not exceed 0.3 μm.

7. The bulk acoustic resonator structure according to claim 1, characterized in that: The substrate has an upward-opening groove, and the bottom electrode and the groove together form a cavity.

8. The bulk acoustic resonator structure according to claim 1, characterized in that: A Bragg reflector layer is disposed between the substrate and the bottom electrode, the Bragg reflector layer comprising a stacked high acoustic impedance material layer and a low acoustic impedance material layer.

9. The bulk acoustic resonator structure according to claim 1, characterized in that: The substrate includes a Si substrate, a SiC substrate, a Ge substrate, a sapphire substrate, or a diamond substrate.

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