Radio frequency front end for 5G millimeter wave communication

Abstract

The invention provides a radio frequency front end for 5G millimeter wave communication, the radio frequency front end comprises at least one bulk acoustic wave resonator structure, the bulk acoustic wave resonator structure comprises a substrate, a first electrode, a piezoelectric layer and a second electrode, and the first electrode is located above the substrate; the piezoelectric layer is located above the first electrode, the piezoelectric layer comprises a first thin film layer and a second thin film layer which are alternately stacked, at least one of the first thin film layer and the second thin film layer is a ferroelectric thin film layer, and the polarities of the adjacent first thin film layer and second thin film layer are opposite so as to suppress a first-order resonance mode and excite an N-order resonance mode; the second electrode is over the piezoelectric layer. The polarities of the adjacent first thin film layer and second thin film layer are opposite, a high-order resonance mode is excited under the condition that the thick piezoelectric layer is maintained, the resonance frequency is remarkably improved, and the communication frequency band is within the n257 frequency band and the n258 frequency band. In addition, there is no need to insert an electrode material layer between the first film layer and the second film layer, the structure is simple, and the device performance is high.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology and relates to a radio frequency front-end for 5G millimeter-wave communication. Background Technology

[0002] 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 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] Currently, 5G communication commonly uses the sub-6GHz (3.3-4.2GHz) frequency band. With increasing application demands, microwave acoustics not only needs to extend its operating frequency range to Ku, Ka bands, and even millimeter-wave (mm-Wave) frequencies, but also must meet the requirements of ultra-wideband applications. In existing technologies, the resonators in the RF front-end use single-layer piezoelectric materials. Since the resonant frequency of a bulk acoustic wave resonator is positively correlated with the ratio of longitudinal sound velocity to film thickness, this means that the thickness of the piezoelectric film in filters used at higher frequency bands will be even smaller. For example, the piezoelectric film thickness for operating frequencies above 10GHz must be less than 100nm, which severely degrades the crystal quality of the piezoelectric film and leads to a sharp decrease in the resonator's power handling capability, electromechanical coupling coefficient, and Q value.

[0004] Therefore, how to provide a radio frequency front-end for 5G millimeter-wave communication that can increase the resonant frequency while maintaining the thickness of the piezoelectric layer, so that the communication frequency band is in the n257 (26.5-29.5GHz) band and the n258 (24.25-27.5GHz) band, 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 radio frequency front-end for 5G millimeter-wave communication, which solves the problem of performance degradation when increasing the resonant frequency in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a radio frequency front-end for 5G millimeter-wave communication, with the communication frequency bands being the n257 and n258 bands. The radio frequency front-end includes at least one bulk acoustic wave resonator structure, the bulk acoustic wave resonator structure comprising:

[0007] Substrate;

[0008] A first electrode is located above the substrate, and an acoustic mirror is disposed between the substrate and the first electrode;

[0009] A piezoelectric layer is located above the first electrode. The piezoelectric layer includes alternating stacked first and second thin film layers. At least one of the first and second thin film layers is a ferroelectric thin film layer. The polarities of adjacent first and second thin film layers are opposite to suppress the first-order resonant mode and excite the Nth-order resonant mode, where N is an integer greater than 1.

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

[0011] Optionally, the piezoelectric layer comprises alternating stacked ferroelectric thin film layers / piezoelectric thin film layers.

[0012] Optionally, the material of the ferroelectric thin film layer includes Sc. x Al 1-x The material of the piezoelectric thin film layer includes one or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3, and the material of the piezoelectric thin film layer includes AlN, Al x Ga 1-x N(0 < x < 1), Al 1-x Sc x One or more of N (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, and Ga2O3.

[0013] Optionally, the piezoelectric layer comprises alternating stacked ferroelectric thin film layers / ferroelectric thin film layers.

[0014] Optionally, the total number of layers of the first thin film layer and the second thin film layer is three, which suppresses the first-order thickness-spreading mode resonance and excites the third-order thickness-spreading mode resonance.

[0015] Optionally, the thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

[0016] Optionally, the material of the first electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and the material of the second electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf.

[0017] Optionally, the substrate has an upward-opening groove, and the first electrode and the groove together form a cavity.

[0018] Optionally, a Bragg reflector layer is disposed between the substrate and the first electrode, the Bragg reflector layer comprising a stacked high acoustic impedance material layer and a low acoustic impedance material layer.

[0019] Optionally, a support layer is provided between the substrate and the first electrode, and an opening is provided in the support layer, wherein the substrate, the opening and the first electrode together form a cavity.

[0020] As described above, in the RF front-end for 5G millimeter-wave communication of the present invention, the adjacent first and second 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 while maintaining a thicker piezoelectric layer, significantly increasing the resonant frequency, and enabling communication within the n257 and n258 frequency bands. Furthermore, the adjacent first and second thin film layers are in direct contact, eliminating the need for an electrode material layer between them, resulting in a simple structure and high device performance. Attached Figure Description

[0021] Figure 1 The diagram shown is a schematic diagram of the bulk acoustic resonator structure according to an embodiment of the present invention.

[0022] 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.

[0023] Figure 3 The diagram shown is a comparative example of a piezoelectric layer consisting of three thin film layers.

[0024] Figure 4 The figure shown is a simulation result diagram of an embodiment of the present invention.

[0025] Figure 5 The simulation results are shown as a scale diagram.

[0026] Component designation explanation

[0027] 1 Substrate

[0028] 2 First electrode

[0029] 3 Piezoelectric layer

[0030] 3A First Thin Film Layer

[0031] 3B Second Thin Film Layer

[0032] 4. Polarization direction

[0033] 5 Second electrode

[0034] 6. Cavity

[0035] 7 Resonance Modes Detailed Implementation

[0036] 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.

[0037] 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.

[0038] This embodiment provides a radio frequency front-end for 5G millimeter-wave communication, with communication frequency bands in the n257 (26.5-29.5GHz) and n258 (24.25-27.5GHz) bands. The radio frequency front-end includes at least one bulk acoustic resonator structure. Please refer to [link to relevant documentation]. Figure 1 The bulk acoustic wave resonator structure includes a substrate 1, a first electrode 2, a piezoelectric layer 3, and a second electrode 5. The first electrode 2 is located above the substrate 1. The piezoelectric layer 3 is located above the first electrode 2. The piezoelectric layer 3 includes alternating stacked first thin film layers 3A and second thin film layers 3B. At least one of the first thin film layers 3A and the second thin film layers 3B is a ferroelectric thin film layer. The polarities of adjacent first thin film layers 3A and second thin film layers 3B are opposite to suppress the first-order resonant mode and excite the Nth-order resonant mode, where N is an integer greater than 1. The second electrode 5 is located above the piezoelectric layer 3.

[0039] 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, and the first electrode 2 and the groove together form a cavity 6, which serves as an acoustic mirror. In another example, a support layer can be provided between the substrate 1 and the first electrode 2. The support layer has an opening, and the substrate 1, the opening, and the first electrode 2 together form the cavity 6. In another example, a Bragg reflector layer can also be provided between the substrate 1 and the first electrode 2 as an acoustic mirror. The Bragg reflector layer includes a stacked high acoustic impedance material layer and a low acoustic impedance material layer. The high acoustic impedance material layer is made of one or more of W, Mo, Pt, Au, Ni, and Ir, and 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 sound wave corresponding to the resonant frequency of the resonator.

[0040] As an example, at least one of the first thin film layer 3A and the second thin film layer 3B is a ferroelectric thin film layer, and the piezoelectric layer 3 can be an alternating stack of ferroelectric thin film layers / piezoelectric thin film layers, or an alternating stack of ferroelectric thin film layers / ferroelectric thin film layers.

[0041] As an example, the piezoelectric thin film layer refers to a thin film layer with piezoelectric properties, and the ferroelectric thin film layer refers to a thin film layer that has both piezoelectric and ferroelectric properties.

[0042] As an example, when the piezoelectric layer 3 employs alternating stacked ferroelectric thin film layers / piezoelectric thin film layers, the material of the piezoelectric thin film layers includes AlN, Al x Ga 1-x N(0 < x < 1), Al 1-x Sc x The ferroelectric thin film layer is made of one or more of the following materials: N (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, and Ga2O3, and the material of the ferroelectric thin film layer includes Sc. x Al 1-x One or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3.

[0043] As an example, when the piezoelectric layer 3 employs alternating stacked ferroelectric thin film layers / ferroelectric thin film layers, the material of the ferroelectric thin film layers includes Sc. x Al 1-x One or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3.

[0044] As an example, in this embodiment, the first thin film layer 3A is a ferroelectric thin film layer, the second thin film layer 3B is a piezoelectric thin film layer, the thickness of a single layer of the first thin film layer 3A is not less than 0.01 μm, the thickness of a single layer of the second thin film layer 3B is not more than 0.01 μm, and the total thickness of the piezoelectric layers 3 is not greater than 2 μm. The first thin film layer 3A is made of Al. 1-x Sc x The N layer, and the second thin film layer 3B, is an AlN layer.

[0045] Specifically, please refer to Figure 2 The piezoelectric layer 3 is configured with a total of 3 layers, including the first thin film layer 3A and the second thin film layer 3B. The piezoelectric layer 3 is composed of stacked first thin film layer 3A, second thin film layer 3B, and first thin film layer 3A. The first thin film layer 3A is made of Al. 0.7 Sc 0.3 The second thin film layer 3B is an AlN layer, meaning the piezoelectric layer 3 is a stacked Al layer. 0.7 Sc 0.3N-layer / AlN-layer / Al 0.7 Sc 0.3 N layers, single-layer Al 0.7 Sc 0.3 The thickness of the N layer is 50 nm, and the thickness of a single AlN layer is 150 nm. Adjacent Al... 0.7 Sc 0.3 The N layer and the AlN layer have opposite polarities (polarization directions 4 are opposite), and both the first electrode 2 and the second electrode 5 use a Mo metal layer with a thickness of 100 nm. Also, please refer to... Figure 3 A comparative example is provided. The comparative example has the same material and thickness for the first electrode 2, piezoelectric layer 3, and second electrode 5 as the example, but differs in that adjacent first thin film layers 3A and 3B have the same polarity (same polarization direction 4). The example and the comparative example have different resonance modes 7. Please refer to [link to relevant documentation]. Figure 4 and Figure 5 The simulation results are shown in the figures for the embodiments and comparative examples, respectively. Figure 4 It can be seen that when the polarization directions of adjacent first thin film layer 3A and second thin film layer 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 thin film layer 3A and second thin film layer 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. The operating frequency band is 28GHz, which makes the communication frequency band within the n257 band. Figure 5 It can be seen that when the polarization directions of the adjacent first thin film layer 3A and the second thin film layer 3B are the same, the excited resonant mode is the first-order thickness extension mode (TE1), and the operating frequency band is 7GHz.

[0046] In another example, by adjusting the thickness of the piezoelectric layer 3, the communication frequency band can be selected in the n258 band as needed.

[0047] As an example, this invention employs a thicker piezoelectric layer 3 to achieve ultra-high frequencies in the resonator. 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 device, making it more suitable for low-power mobile communications 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 communications, 5G millimeter-wave bands, and 6G ultra-high-frequency bands.

[0048] As an example, compared with existing dielectric resonators such as low-temperature co-fired ceramic (LTCC) resonators and integrated passive device (IPD) resonators used for high and ultra-high frequencies, the present invention has excellent out-of-band rejection and in-band insertion loss characteristics, and significantly reduces signal interference and operating power in wireless communication.

[0049] 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 this invention, the electromechanical coupling coefficient of the higher-order modes is independent of the order, and a high electromechanical coupling coefficient and a large bandwidth can be maintained at high frequencies, making it very suitable for high-frequency, high-bandwidth applications.

[0050] As an example, in existing technologies, when high-frequency modes are excited using piezoelectric and ferroelectric thin film layers with opposite polarities, an electrode material layer needs to be inserted between the piezoelectric and ferroelectric thin film layers. Polarity reversal is achieved by applying a very high bias voltage to the electrode material layer. However, inserting the electrode material layer severely affects the crystal quality of the piezoelectric and ferroelectric thin film layers, deteriorating the device's out-of-band rejection and in-band loss characteristics, while also posing significant challenges to cost, controllability, and integration. In this application, the first thin film layer 3A and the second thin film layer 3B are in direct contact. The ferroelectricity of the ferroelectric thin film layer results in spontaneous polarization. By applying an external voltage between the first electrode 2 and the second electrode 5, the polarization state can be changed, and the polarization state can be maintained after the external voltage is removed. This achieves opposite polarity control between adjacent first thin film layers 3A and second thin film layers 3B, eliminating the need to insert an electrode material layer between the first thin film layer 3A and the second thin film layer 3B. This results in a simple structure and high performance.

[0051] In summary, in the RF front-end for 5G millimeter-wave communication of the present invention, the adjacent first and second 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 while maintaining a relatively thick piezoelectric layer, significantly increasing the resonant frequency within the n257 and n258 frequency bands. Furthermore, the adjacent first and second thin film layers are in direct contact, eliminating the need for an electrode material layer between them, resulting in a simple structure and high device performance. Therefore, the present invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0052] 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 radio frequency front-end for 5G millimeter-wave communication, wherein the communication frequency band is in the n257 and n258 frequency bands, characterized in that, The radio frequency front end includes at least one bulk acoustic wave resonator structure, the bulk acoustic wave resonator structure comprising: Substrate; A first electrode is located above the substrate, and an acoustic mirror is disposed between the substrate and the first electrode; A piezoelectric layer is located above the first electrode. The piezoelectric layer includes alternating stacked first and second thin film layers. At least one of the first and second thin film layers is a ferroelectric thin film layer. The polarities of adjacent first and second thin film layers are opposite to suppress the first-order resonant mode and excite the Nth-order resonant mode, where N is an integer greater than 1. The second electrode is located above the piezoelectric layer.

2. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: The piezoelectric layer comprises alternating stacked ferroelectric thin film layers / piezoelectric thin film layers.

3. The radio frequency front-end for 5G millimeter-wave communication according to claim 2, characterized in that: The ferroelectric thin film layer is made of Sc. x Al 1-x The material of the piezoelectric thin film layer includes one or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3, and the material of the piezoelectric thin film layer includes AlN, Al x Ga 1-x N(0 < x < 1), Al 1-x Sc x One or more of N (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, and Ga2O3.

4. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: The piezoelectric layer comprises alternating stacked ferroelectric thin film layers / ferroelectric thin film layers.

5. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: The first and second thin film layers together have a total of three layers, which suppresses the first-order thickness-spreading mode resonance and excites the third-order thickness-spreading mode resonance.

6. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: The thickness of the first single-layer film layer is not less than 0.01 μm, and the thickness of the second single-layer film layer is not less than 0.01 μm.

7. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: The material of the first electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, and the material of the second electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf.

8. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: The substrate has an upward-opening groove, and the first electrode and the groove together form a cavity.

9. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: A Bragg reflector layer is disposed between the substrate and the first electrode, the Bragg reflector layer comprising a stacked high acoustic impedance material layer and a low acoustic impedance material layer.

10. The radio frequency front-end for 5G millimeter-wave communication according to claim 1, characterized in that: A support layer is provided between the substrate and the first electrode, and an opening is provided in the support layer. The substrate, the opening and the first electrode together form a cavity.

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