Acoustic wave filter and electronic device

Abstract

The present disclosure belongs to the field of radio frequency technology. Provided are an acoustic wave filter and an electronic device. The acoustic wave filter in the present disclosure comprises an input end, an output end, and a series branch and a plurality of parallel branches, which are connected between the input end and the output end, wherein the parallel branches are electrically connected to the series branch; the series branch comprises at least one first bulk acoustic wave resonator, at least one capacitor and at least one inductor that are connected in series between the input end and the output end; the at least one inductor comprises an inductor connected to the input end and / or an inductor connected to the output end; and each parallel branch comprises at least one second bulk acoustic wave resonator.

Description

Acoustic filters and electronic devices Technical Field

[0001] This disclosure belongs to the field of radio frequency technology, and specifically relates to an acoustic filter and electronic device. Background Technology

[0002] In the field of mobile communications, due to the narrow total available frequency range and the large number of frequency bands used for mobile communications, the spacing between adjacent frequency bands is very narrow (approximately a few megahertz to tens of megahertz), and the bandwidth of a single frequency band is very narrow (tens of megahertz). Therefore, filters used in mobile phones must possess performance characteristics such as low in-band ripple, high out-of-band rejection, and good rectangularity. Conventional microstrip filters are too large, have insufficient out-of-band rejection, and poor rectangularity, making them unsuitable. Cavity filters are also too large, making them unsuitable. Dielectric filters have high in-band insertion loss and poor rectangularity, making them unsuitable. IPD filters have large in-band ripple and poor rectangularity, making them unsuitable.

[0003] As the basic structural unit of a bulk acoustic wave (BAW) filter, the existing BAW resonator uses a silicon wafer as the substrate material, with a sandwich structure consisting of a first electrode, a piezoelectric material, and a second electrode from bottom to top. The working principle is as follows: a radio frequency (RF) signal is input from one electrode of the resonator, and then converted into a mechanically vibrating acoustic signal at the interface between the piezoelectric material and the metal electrode through the inverse piezoelectric effect. This acoustic signal forms a resonant standing wave with a certain frequency within the sandwich structure of the first electrode, piezoelectric material, and second electrode. The frequency of the RF signal is equal to the resonant frequency of the resonator. The acoustic signal is then transmitted to the other electrode of the resonator, where it is converted back into an RF signal through the piezoelectric effect at the interface between the metal electrode and the piezoelectric material. A resonator has a fixed resonant frequency. When the frequency of the radio frequency signal is equal to the resonant frequency of the resonator, the conversion efficiency of radio frequency signal → sound wave signal → radio frequency signal is high. When the frequency of the radio frequency signal is not equal to the resonant frequency of the resonator, the conversion efficiency of radio frequency signal → sound wave signal → radio frequency signal is very low. Most of the radio frequency signal cannot be transmitted through the resonator. That is, the resonator is equivalent to a filter, filtering the radio frequency signal. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art, and to provide an acoustic filter and electronic device.

[0005] This disclosure provides an acoustic wave filter, which includes an input terminal and an output terminal, as well as a series branch and multiple parallel branches connected between the input terminal and the output terminal; the parallel branches are electrically connected to the series branch; wherein,

[0006] The series branch includes at least one first bulk acoustic resonator, at least one capacitor, and at least one inductor connected in series between the input terminal and the output terminal; the at least one inductor includes an inductor connected to the input terminal and / or an inductor connected to the output terminal.

[0007] The parallel branch includes at least one second body acoustic resonator.

[0008] Wherein, the number of parallel branches is one; the connection node between the parallel branch and the series branch is the first node; the capacitor is connected between the first bulk acoustic resonator and the first node; or, the capacitor is connected between the first bulk acoustic resonator and the input terminal.

[0009] The series branch includes a first bulk acoustic resonator, a capacitor, and an inductor, and the parallel branch includes a second bulk acoustic resonator.

[0010] The first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the second electrode of the second bulk acoustic wave resonator is connected to the first node, the first electrode of the second bulk acoustic wave resonator is connected to the reference electrode, the first end of the inductor is connected to the first node, and the second end of the inductor is connected to the output terminal.

[0011] The capacitance of the capacitor is 3-6pF; the inductance of the inductor is 1-3nH.

[0012] The series branch includes a first bulk acoustic resonator, a capacitor, and two inductors; the two inductors are a first inductor and a second inductor, respectively; the parallel branch includes a second bulk acoustic resonator.

[0013] The first end of the second inductor is connected to the input terminal, the second end of the second inductor is connected to the first electrode of the first bulk acoustic wave resonator, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the second electrode of the second bulk acoustic wave resonator is connected to the first node, the first electrode of the second bulk acoustic wave resonator is connected to the reference electrode, the first end of the first inductor is connected to the first node, and the second end of the first inductor is connected to the output terminal.

[0014] The capacitance of the capacitor is 1.5-4pF; the inductance of the first inductor and the second inductor is 0.3-1.5nH.

[0015] The series branch includes two first body acoustic resonators, a capacitor and an inductor, and the parallel branch includes a second body acoustic resonator.

[0016] The first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the second electrode of the second bulk acoustic wave resonator, the first electrode of the second bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the first electrode of the second bulk acoustic wave resonator is connected to the first node, the second electrode of the second bulk acoustic wave resonator is connected to the reference electrode, the first end of the inductor is connected to the first node, and the second end of the inductor is connected to the output terminal.

[0017] The capacitance of the capacitor is 2-4pF; the inductance of the inductor is 1-3nH.

[0018] The series branch includes two first-body acoustic resonators, a capacitor and an inductor, and the parallel branch includes two second-body acoustic resonators.

[0019] The first electrode of the first first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first first bulk acoustic wave resonator is connected to the second electrode of the second first bulk acoustic wave resonator, the first electrode of the second first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the first electrode of the first second bulk acoustic wave resonator is connected to the first node, the second electrode of the first second bulk acoustic wave resonator is connected to the second electrode of the second second bulk acoustic wave resonator, the first electrode of the second second bulk acoustic wave resonator is connected to the reference electrode, the first end of the inductor is connected to the first node, and the second end of the inductor is connected to the output terminal.

[0020] The capacitance of the capacitor is 2-4pF; the inductance of the inductor is 1-3nH.

[0021] The series branch includes N series sub-branches connected in series; N≥2, and N is a positive integer; the series sub-branch is electrically connected to one of the parallel branches; the series sub-branch includes at least one first bulk acoustic resonator and a capacitor connected in series with the first bulk acoustic resonator.

[0022] The connection node between the parallel branch and the series sub-branch is the first node; the capacitor in the series sub-branch is connected between the first bulk acoustic resonator and the first node.

[0023] Wherein, the capacitor in the first series sub-branch is connected between the input terminal and the first bulk acoustic resonator; the capacitor in the i-th series sub-branch is connected between the first bulk acoustic resonator therein and the (i-1)-th series sub-branch; i takes the value 2 to N.

[0024] Where N=2, the series sub-branch includes a first-body acoustic resonator and a capacitor; the parallel branch includes a second-body acoustic resonator.

[0025] For the first series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the second electrode of the second bulk acoustic wave resonator, and the second electrode of the first bulk acoustic wave resonator in the second series sub-branch is connected to the reference electrode.

[0026] For the second series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first electrode of the second bulk acoustic wave resonator and the first end of the inductor, and the second electrode of the second bulk acoustic wave resonator is connected to the reference electrode.

[0027] The second end of the inductor is connected to the output terminal.

[0028] The capacitance of the capacitor is 3-6pF; the inductance of the inductor is 1-3nH.

[0029] Where N=3, the series sub-branch includes a first body acoustic resonator and a capacitor; the parallel branch includes a second body acoustic resonator.

[0030] For the first series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the second electrode of the second bulk acoustic wave resonator, and the second electrode of the first bulk acoustic wave resonator in the second series sub-branch is connected to the reference electrode.

[0031] For the second series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first electrode of the second bulk acoustic resonator, and the first electrode of the first acoustic resonator in the third series sub-branch is connected to the reference electrode.

[0032] For the third series sub-branch and the parallel branch connected thereto, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first end of the inductor and the second electrode of the second bulk acoustic wave resonator, and the first electrode of the second bulk acoustic wave resonator is connected to the reference electrode.

[0033] The second end of the inductor is connected to the output terminal.

[0034] The capacitance values ​​of the capacitors in the first and third series sub-branch are both 3-6pF; the capacitance value of the capacitor in the second series sub-branch is 2-5pF; and the inductance value of the inductor is 1-3nH.

[0035] The first bulk acoustic wave resonator and the second bulk acoustic wave resonator each include a substrate, and a first electrode, a piezoelectric layer and a second electrode disposed on the substrate; the orthographic projections of any two of the first electrode, the piezoelectric layer and the second electrode on the substrate at least partially overlap.

[0036] The substrate has a first groove; the substrate includes a first surface and a second surface disposed opposite to each other along its thickness direction; the first groove includes a first opening located on the first surface; the first electrode is located on the first surface; the outline of the orthographic projection of the first opening on the second surface is within the outline of the orthographic projection of the first electrode on the second surface.

[0037] In some examples, both the first bulk acoustic wave resonator and the second bulk acoustic wave resonator include a substrate, and at least one mirror structure, a first electrode, a piezoelectric layer, and a second electrode disposed on the substrate; the orthographic projections of any two of the mirror structure, the first electrode, the piezoelectric layer, and the second electrode on the substrate at least partially overlap.

[0038] The reflector structure includes a first impedance layer and a second impedance layer arranged sequentially along the direction away from the substrate, wherein the acoustic impedance of the material of the first impedance layer is greater than the acoustic impedance of the material of the second impedance layer.

[0039] This disclosure provides an electronic device that includes any of the bulk acoustic wave resonators described above. Attached Figure Description

[0040] Figure 1 is a schematic diagram of a SAW resonator according to an embodiment of this disclosure.

[0041] Figure 2 is a schematic diagram of the FBAR resonator of this embodiment.

[0042] Figure 3 is a schematic diagram of the SMR resonator of this embodiment.

[0043] Figure 4 is a circuit diagram of an exemplary acoustic filter.

[0044] Figure 5 shows the transmission characteristics of introducing four inductors based on the acoustic filter shown in Figure 1.

[0045] Figure 6 is a circuit diagram of an acoustic filter according to a first example of an embodiment of this disclosure.

[0046] Figure 7 is a transmission characteristic diagram (wideband) of an acoustic filter without the introduction of capacitors and inductors in a first example of an embodiment of this disclosure.

[0047] Figure 8 shows the transmission characteristics (center band) of an acoustic filter without the introduction of capacitors and inductors in a first example of the embodiments of this disclosure.

[0048] Figure 9 is a circuit diagram of an acoustic filter according to a second example of an embodiment of this disclosure.

[0049] Figure 10 is a transmission characteristic diagram (wideband) of an acoustic filter according to a second example of an embodiment of this disclosure.

[0050] Figure 11 is a transmission characteristic diagram (center frequency band) of an acoustic filter according to a second example of an embodiment of this disclosure.

[0051] Figure 12 is a circuit diagram of an acoustic filter according to a third example of an embodiment of this disclosure.

[0052] Figure 13 is a transmission characteristic diagram (wideband) of an acoustic filter according to a third example of an embodiment of this disclosure.

[0053] Figure 14 is a transmission characteristic diagram (center frequency band) of an acoustic filter according to a third example of an embodiment of this disclosure.

[0054] Figure 15 is a circuit diagram of an acoustic filter according to a fourth example of an embodiment of this disclosure.

[0055] Figure 16 is a transmission characteristic diagram (wideband) of an acoustic filter according to a fourth example of an embodiment of this disclosure.

[0056] Figure 17 is a transmission characteristic diagram (center frequency band) of an acoustic filter according to a fourth example of an embodiment of this disclosure.

[0057] Figure 18 is a circuit diagram of a fifth example of an acoustic filter according to an embodiment of this disclosure.

[0058] Figure 19 is a transmission characteristic diagram (wideband) of an acoustic filter according to a fifth example of an embodiment of this disclosure.

[0059] Figure 20 is a transmission characteristic diagram (center frequency band) of an acoustic filter according to a fifth example of an embodiment of this disclosure.

[0060] Figure 21 is a circuit diagram of an acoustic filter according to a sixth example of an embodiment of this disclosure.

[0061] Figure 22 is a transmission characteristic diagram (wideband) of an acoustic filter according to a sixth example of an embodiment of this disclosure.

[0062] Figure 23 is a transmission characteristic diagram (center frequency band) of an acoustic filter according to a sixth example of an embodiment of this disclosure. Detailed Implementation

[0063] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0064] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an,” “a,” or “the,” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “including,” “comprising,” or “containing,” and similar terms mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms “connected,” “linked,” or similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms “upper,” “lower,” “left,” and “right,” etc., are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0065] With the rapid development of mobile communication technology, the application of many radio frequency devices has increased significantly, among which the filter market is poised for explosive growth. Currently, the filtering devices used in personal mobile terminals (such as mobile phones) are mainly piezoelectric acoustic wave filters. The resonators constituting these filters are mainly: FBAR (Thin Film Bulk Acoustic Resonator), SMR (Solid State Mesh Resonator), and SAW (Surface Acoustic Wave Resonator), with FBAR and SMR collectively referred to as BAW (Bulk Acoustic Wave Resonator). The working principle of the SAW resonator is to convert electrical signals into sound waves propagating on the surface of the piezoelectric layer through interdigital transducers, as shown in Figure 1. Its resonant frequency is determined by the spacing between the IDT electrodes (interdigital electrodes), i.e., f1. p = v / p, where p is the spacing between the IDT electrodes and v is the velocity. The working principle of the BAW resonator is to convert the electrical signal into a bulk acoustic wave propagating along the thickness of the piezoelectric layer. The resonant frequency is determined by the thickness of the piezoelectric layer, i.e., f. p = v / 2t, where t is the thickness of the piezoelectric film and v is the speed of sound. Schematic diagrams of two commonly used BAW resonators, FBAR and SMR resonators, are shown in Figures 2 and 3. Specifically, as shown in Figure 2, the FBAR resonator includes a substrate 10, a first electrode 11 and a second electrode 12 disposed on the substrate 10, and a piezoelectric layer 13 sandwiched between the first electrode 11 and the second electrode 12; a first groove 101 is etched and formed on the substrate 10 below the first electrode 11 as an air gap; the first groove 101 includes a first opening located on the first surface of the substrate 10; the first electrode 11 is located on the first surface; the outline of the orthographic projection of the first opening on the second surface is within the outline of the orthographic projection of the first electrode 11 on the second surface. As shown in Figure 3, the SMR resonator differs from the FBAR resonator in that an acoustic reflector structure 14 is constructed below the first electrode 11, consisting of alternating layers of a first impedance layer 141 and a second impedance layer 142. The acoustic impedance of the material in the first impedance layer 141 is greater than that in the second impedance layer 142. While the FBAR resonator utilizes the near-zero acoustic impedance of air to achieve total reflection of acoustic waves at the interface, the SMR resonator achieves total reflection based on the Bragg reflector layer formed by alternating layers of the first and second impedance layers 141 and 142.

[0066] For radio frequency (RF) filters, key performance indicators include insertion loss, out-of-band rejection, and roll-off. Insertion loss is often represented by the parameter IL (Insert Loss). Because the signal cannot completely reach the output, energy loss will inevitably occur when passing through the filter. Insertion loss is defined as the input power P. in and output power P L The ratio, i.e., IL(dB) = 10lg(P) in / P L)=-S 21 S 21 The transmission coefficient from the input port to the output port can be measured by a vector network analyzer; out-of-band rejection is the attenuation outside the filter's passband range, representing the ability to suppress unwanted frequency signals; the roll-off factor, also known as the rectangular factor, describes the steepness of the filter's transition band. A steeper roll-off indicates better frequency selectivity, and can be expressed as the ratio of 60dB bandwidth to 3dB bandwidth. Compared to SAW, BAW has advantages such as lower insertion loss, higher Q value, steeper roll-off characteristics, and larger power capacity, but SAW is cheaper and has the advantage of impedance transformation.

[0067] Figure 4 shows an exemplary acoustic filter. As shown in Figure 4, the acoustic filter has a typical third-order ladder topology, which includes an input terminal 1, an output terminal 2, a series branch connecting the input terminal 1 and the output terminal 2, and three parallel branches. The series branch includes three first acoustic resonators, each using S... 11 S 12 S 13 S indicates that 11 S 12 S 13 Connected sequentially between input port 1 and output port 2, each of the three parallel branches includes a second-body acoustic resonator. The three second-body acoustic resonators in the three parallel branches are respectively connected in series between input port 1 and output port 2. 11 P 12 P 13 Indicated. Among them, P 11 One end is connected to S 11 and S 12 Between them, one end is grounded; P 12 One end is connected to S 12 and S 13 Between them, one end is grounded; P 13 One end is connected to S 14 Between output port 2 and the ground, one end is connected. All first-stage acoustic resonators, i.e., S... 11 S 12 and S 13 All parallel resonators, i.e., P, have the same structure. 11 P 12 and P 13The structures are the same. For each band in mobile communication, there will be two bands that are relatively close to each other, which puts higher demands on the out-of-band rejection of the filter. Usually, an inductor is connected in series in the parallel branch to increase the out-of-band rejection, but this will increase the bandwidth of the filter and affect the selectivity of the band edge. If the inductance value is not set properly, it may also cause a decrease in the out-of-band rejection at a certain frequency, as shown in Figure 5. Figure 5 introduces four inductors based on the filter shown in Figure 4, and its out-of-band rejection increases near 5 GHz and in the 6-7 GHz range.

[0068] Based on the above-mentioned technical problems, the following technical solutions are provided in the embodiments of this disclosure.

[0069] This disclosure provides an acoustic wave filter, which includes an input terminal and an output terminal, as well as a series branch and multiple parallel branches connected between the input terminal and the output terminal; one end of the parallel branch is connected to the series branch, and the other end is connected to a reference electrode; wherein, the series branch includes at least one first bulk acoustic wave resonator, at least one capacitor, and at least one inductor connected in series between the input terminal and the output terminal; the at least one inductor includes an inductor connected to the input terminal and / or an inductor connected to the output terminal; the parallel branch includes at least one second bulk acoustic wave resonator.

[0070] In this embodiment of the acoustic filter, a capacitor and an inductor are introduced into the series branch. Introducing the capacitor improves out-of-band rejection, while introducing the inductor reduces in-band ripple and improves insertion loss. In other words, this embodiment of the acoustic filter can maintain high out-of-band rejection over a wide frequency range without changing the bandwidth.

[0071] The acoustic filter in the embodiments of this disclosure will be described in detail below with reference to specific examples.

[0072] In some examples, the acoustic filter of this disclosure can be a first-order circuit or a multi-order circuit. When the acoustic filter is a first-order circuit, there is one parallel branch, and the series branch can include a series sub-branch; the series sub-branch is connected to the parallel branch; the series sub-branch can consist of at least one first-body acoustic resonator and a capacitor. When the acoustic filter is a multi-order circuit, there are multiple parallel branches, and the series branch can include N series-connected sub-branches; N≥2, and N is a positive integer. Each series sub-branch is connected to a parallel branch to form a first-order circuit, and the N series sub-branches and their respective connected parallel branches form an Nth-order circuit.

[0073] Specifically, when the acoustic filter is a first-order circuit, the capacitor is connected between the first bulk acoustic resonator and the first node; or the capacitor is connected between the first bulk acoustic resonator and the input terminal. When the acoustic filter is a multi-order circuit, i.e., N≥2, the capacitor in the first series sub-branch is connected between the input terminal and the first bulk acoustic resonator; the capacitor in the i-th series sub-branch is connected between the first bulk acoustic resonator therein and the (i-1)-th series sub-branch; i takes values ​​from 2 to N. To make the acoustic filter of this embodiment clearer, specific examples will be described below.

[0074] First Example: Figure 6 is a circuit diagram of an acoustic filter according to a first example of this disclosure. As shown in Figure 6, the acoustic filter is a first-order circuit, specifically including a first bulk acoustic resonator, a second bulk acoustic resonator, a capacitor, and an inductor. The first bulk acoustic resonator is represented by S... 11 This indicates that the second-body acoustic resonator uses P 11 In this diagram, capacitors are represented by C1, and inductors by L1. Specifically, S... 11 The first electrode is connected to input terminal 1, S 11 The second electrode is connected to the first plate of C1, and the second plate of C1 is connected to P. 11 The second electrode and the first end of L1 are connected, and the connection node of the three is the first node 3, P 11 The first electrode of L1 is connected to the reference electrode, and the second terminal of L1 is connected to the output terminal 2.

[0075] It should be noted that the reference electrode in this embodiment can specifically be a ground electrode, and this embodiment only uses the reference electrode as a ground electrode as an example.

[0076] In this example, the introduction of capacitor C1 can improve out-of-band rejection. At the same time, capacitor C1 will also cause some deterioration to in-band insertion loss. However, in this example, not only capacitor C1 is added, but inductor L1 is also added. The introduction of inductor L1 can reduce in-band ripple and improve insertion loss.

[0077] In some examples, the capacitance of capacitor C1 is between 2-4 pF, and the inductance of inductor L1 is between 1-3 nH. The values ​​of capacitor C1 and inductor L1 can be specifically set based on simulation results.

[0078] Simulations were performed on the acoustic filter of the first example. Figure 7 shows the transmission characteristics (wideband) of the acoustic filter of the first example of this disclosure and without the introduction of capacitors and inductors; Figure 8 shows the transmission characteristics (center band) of the acoustic filter of the first example of this disclosure and without the introduction of capacitors and inductors. Referring to Figures 7 and 8, the transmission characteristics of the acoustic filter in this example and the first-order circuit without the introduction of capacitors and inductors were compared. It can be seen that the out-of-band rejection level remains stable in a wide frequency range of 1-7 GHz, and the out-of-band rejection is improved by 0.7-5 dB compared with the first-order circuit without the introduction of capacitors and inductors.

[0079] The second example: Figure 9 is a circuit diagram of the acoustic filter according to the second example of the present disclosure. As shown in Figure 9, this example has a structure that is largely the same as the first example, except that the acoustic filter in this example introduces not only inductor L1 (first inductor) but also inductor L2 (second inductor). Specifically, the first end of L2 is connected to input terminal 1, and the second end of L2 is connected to S. 11 The first electrode, S 11 The second electrode is connected to the first plate of C1, and the second plate of C1 is connected to the first node 3, P 11 The second electrode is connected to the first node 3, P 11 The first electrode is connected to the reference electrode, the first end of L1 is connected to the first node 3, and the second end of L1 is connected to the output terminal 2.

[0080] In this example, inductors L1 and L2 work together to reduce in-band ripple.

[0081] In some examples, capacitor C1 is between 1.5-4pF, inductor L1 is between 0.3-1.5nH, and inductor L2 is between 0.3-1.5nH. The values ​​of capacitor C1, inductor L1, and inductor L2 can be specifically set based on simulation results.

[0082] The acoustic filter of the second example was simulated. Figure 10 is a transmission characteristic diagram (wideband) of the acoustic filter of the second example of the present disclosure embodiment; Figure 11 is a transmission characteristic diagram (center band) of the acoustic filter of the second example of the present disclosure embodiment. As shown in Figures 10 and 11, it can be seen that the out-of-band suppression level remains stable in a wide frequency range of 1-7 GHz.

[0083] Third Example: Figure 12 is a circuit diagram of an acoustic filter according to a third example of the present disclosure. As shown in Figure 12, this example has a structure that is largely the same as the first example, except that the acoustic filter in this example includes two first-body acoustic resonators, and the two first-body acoustic resonators are respectively connected by S... 11 and S 12 Indicates. Specifically, S 11The first electrode is connected to the input terminal 1, S 11 The second electrode is connected to S 12 The second electrode, S 12 The first electrode is connected to the first plate of C1, and the second plate of C1 is connected to the first node 3. 11 The first electrode is connected to the first node 3, P 11 The second electrode is connected to the reference electrode, the first end of L1 is connected to the first node 3, and the second end of L1 is connected to the output terminal 2.

[0084] In this example, the acoustic filter's series branch includes two first-body acoustic resonators connected in series, i.e., it includes S... 11 and S 12 Compared to the first example which only includes S 11 The area of ​​the first-body acoustic resonator is twice that of the first example, thus increasing the power capacity.

[0085] In some examples, capacitor C1 is between 2-4 pF, and inductor L1 is between 1-3 nH. The values ​​of capacitor C1 and inductor L1 can be specifically set through simulation results.

[0086] The acoustic filter of the third example was simulated. Figure 13 is a transmission characteristic diagram (wideband) of the acoustic filter of the third example of the present disclosure embodiment; Figure 14 is a transmission characteristic diagram (center band) of the acoustic filter of the third example of the present disclosure embodiment. As shown in Figures 13 and 14, it can be seen that the out-of-band suppression level remains stable in a wide frequency range of 1-7 GHz.

[0087] Fourth Example: Figure 15 is a circuit diagram of the acoustic filter of the fourth example of the present disclosure; as shown in Figure 15, this example has a structure that is largely the same as the first example, except that the acoustic filter of this example includes two first bulk acoustic resonators and two second bulk acoustic resonators, and the two first bulk acoustic resonators are respectively connected by S 11 and S 12 This indicates that the two second-body acoustic resonators are respectively equipped with P 11 and P 12 Indicates. Specifically, S 11 The first electrode is connected to the input terminal 1, S 11 The second electrode is connected to S 12 The second electrode, S 12 The first electrode is connected to the first plate of C1, and the second plate of C1 is connected to the first node 3. 11 The first electrode is connected to the first node 3, P 11 The second electrode is connected to P 12 The second electrode P 12The first electrode is connected to the reference electrode, the first end of L1 is connected to the first node 3, and the second end of L1 is connected to the output terminal 2.

[0088] In this example, the acoustic filter's series branch includes two first-body acoustic resonators connected in series, i.e., it includes S... 11 and S 12 The parallel branch includes two second-body acoustic resonators connected in series, that is, it includes P 11 and P 12 Compared to the first example which only includes S 11 and P 11 The area of ​​the first bulk acoustic resonator is twice that of the first example, and the area of ​​the second bulk acoustic resonator is twice that of the first example, thereby increasing the power capacity.

[0089] In some examples, the capacitance of capacitor C1 is 2-4 pF, and the inductance of inductor L1 is 1-3 nH. The values ​​of capacitor C1 and inductor L1 can be specifically set through simulation results.

[0090] Simulations were performed on four examples of acoustic filters. Figure 16 shows the transmission characteristics (wideband) of the fourth example acoustic filter of the present disclosure embodiment; Figure 17 shows the transmission characteristics (center band) of the fourth example acoustic filter of the present disclosure embodiment. As shown in Figures 16 and 17, it can be seen that the out-of-band rejection level remains stable in a wide frequency range of 1-7 GHz.

[0091] It should be noted that the first to fourth examples only provide several exemplary structures for acoustic filters using first-order circuits, but these examples do not constitute a limitation on the scope of protection of this embodiment. For example, capacitor C1 is connected to input terminals 1 and 2. 11 Between them, the number of the first body acoustic resonator and the second body acoustic resonator can be more than that, all within the protection scope of the embodiments of this disclosure. The values ​​of capacitor C1, inductor L1 and L2 can be specifically set by simulation according to the specific structure of the acoustic filter.

[0092] Fifth Example: Figure 18 is a circuit diagram of the acoustic filter of the fifth example of this disclosure. As shown in Figure 18, the acoustic filter in this example adopts a second-order circuit. Specifically, the acoustic filter in this example includes a series branch, two series sub-branches, and an inductor L1. Each series sub-branch includes a first bulk acoustic resonator and a capacitor connected in series. Each series sub-branch is connected to a parallel branch to form a first-order circuit. The parallel branch is composed of a second bulk acoustic resonator. The first bulk acoustic resonator, the second bulk acoustic resonator, and the capacitor in the first first-order circuit are respectively represented by S... 11 P 11C1 represents the first bulk acoustic resonator, the second bulk acoustic resonator, and the capacitor in the second first-order circuit, respectively represented by S. 12 P 12 C2 represents.

[0093] Specifically, S 11 The first electrode is connected to input terminal 1, S 11 The second electrode is connected to the first plate of C1, and the second plate of C1 is connected to P. 11 The second electrode, and S 12 The second electrode, P 11 The first electrode is connected to the reference electrode; S 12 The first electrode is connected to the first plate of C2, and the second plate of C2 is connected to P. 12 The first electrode and the first terminal of L1, P 12 The second electrode of L1 is connected to the reference electrode; the second terminal of L1 is connected to the output terminal 2.

[0094] In this example, the introduced capacitors C1 and C2 can improve out-of-band rejection, but will cause some deterioration to in-band insertion loss, while the introduced inductor L1 can reduce in-band ripple and improve insertion loss.

[0095] In some examples, the capacitance values ​​of capacitors C1 and C2 are both 3-6pF; the inductance value of inductor L1 is 1-3nH. The values ​​of capacitors C1 and C2, as well as inductor L1, can be set according to the simulation results.

[0096] Simulations were performed on the acoustic filter of the fifth example. Figure 19 shows the transmission characteristics (wideband) of the acoustic filter of the fifth example of this disclosure. Figure 20 shows the transmission characteristics (center band) of the acoustic filter of the fifth example of this disclosure. As shown in Figures 19 and 20, it can be seen that within a wide frequency range of 1-7 GHz, the absolute value of S21 remains stable at an out-of-band suppression level greater than 14 dB in both the 1-7 GHz and 2.5-8 GHz bands.

[0097] Sixth Example: Figure 21 is a circuit diagram of the acoustic filter of the sixth example of the present disclosure. As shown in Figure 21, the acoustic filter of this example adopts a third-order circuit. Specifically, the acoustic filter in this example includes three series-connected sub-branches and an inductor L1. Each series-connected sub-branch includes a first bulk acoustic resonator and a capacitor connected in series. Each series-connected sub-branch is connected to a parallel branch to form a first-order circuit. The parallel branch is composed of a second bulk acoustic resonator. The first bulk acoustic resonator, the second bulk acoustic resonator, and the capacitor in the first first-order circuit are respectively represented by S... 11 P 11 C1 represents the first bulk acoustic resonator, the second bulk acoustic resonator, and the capacitor in the second first-order circuit, respectively represented by S.12 P 12 C2 represents the first bulk acoustic resonator, the second bulk acoustic resonator, and the capacitor in the third first-order circuit, respectively represented by S. 13 P 13 C3 represents.

[0098] Specifically, the first-body acoustic resonator S 11 The first electrode is connected to the input terminal 1, S 11 The second electrode is connected to the first plate of capacitor C1, and the second plate of C1 is connected to P. 11 The second electrode, and S 12 The second electrode, P 11 The first electrode is connected to the reference electrode; S 12 The first electrode is connected to the first plate of C2, and the second plate of C2 is connected to P. 12 The first electrode, and S 13 The first electrode, P 12 The second electrode is connected to the reference electrode; S 13 The second electrode is connected to the first plate of C3, and the second plate of C3 is connected to the first end of L1 and P. 13 The second electrode P 13 The first electrode of L1 is connected to the reference electrode; the second end of L1 is connected to the output terminal 2.

[0099] In this example, capacitors C1, C2, and C3 can improve out-of-band rejection, but they will cause some deterioration to in-band insertion loss. Inductor L1 can reduce in-band ripple and improve insertion loss.

[0100] In some examples, capacitors C1 and C3 have capacitance values ​​of 3-6pF; capacitor C2 has a capacitance value of 2-5pF; and inductor L1 has an inductance value of 1-3nH. The values ​​of capacitors C1, C2, and C3, as well as inductor L1, can be set according to the simulation results.

[0101] The acoustic filter of the sixth example was simulated. Figure 22 is a transmission characteristic diagram (wideband) of the acoustic filter of the sixth example of the present disclosure embodiment; Figure 23 is a transmission characteristic diagram (center band) of the acoustic filter of the sixth example of the present disclosure embodiment. As shown in Figures 22 and 23, it can be seen that the out-of-band suppression level remains stable in a wide frequency range of 1-7 GHz.

[0102] It should be noted that the fifth and sixth examples only provide exemplary structures for acoustic filters using second-order and third-order circuits, but these examples do not constitute a limitation on the scope of protection of this embodiment. For example, inductor L1 is connected to input terminals 1 and 2. 11 Between input terminals 1 and S, capacitor C1 is connected. 11Similarly, capacitor C2 can be connected to S. 11 and S 12 Between, capacitor C3 can be connected to S 12 and S 13 Within the scope of this disclosure, the number of first-order and second-order acoustic resonators in each first-order circuit can be multiple. The values ​​of the inductors and capacitors can be specifically set through simulation based on the specific structure of the acoustic filter. Furthermore, the number of first-order circuits in the acoustic filter can be even greater; for example, a fourth-order or fifth-order circuit can be used. A higher order results in better out-of-band suppression and a larger bandwidth; third- to fifth-order circuits are preferred for acoustic filters.

[0103] In some examples, the bulk acoustic resonators in the embodiments of this disclosure, namely the first bulk acoustic resonator and the second bulk acoustic resonator, can both be the bulk acoustic resonators shown in Figures 2 and 3.

[0104] Furthermore, the substrate 10 is preferably Si, but can also be made of glass, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, etc. The thickness of the substrate 1010 ranges from 0.1 μm to 10 mm.

[0105] In some examples, the first electrode 11 is preferably molybdenum, but it can also be made of Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, or Se. It can also be an alloy of these metals or a stack of metal layers. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0106] The piezoelectric layer 12 is preferably AlN, followed by AlN doped with Sc, or other materials such as BN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, and La3Ga5SiO2. 14 Materials such as BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, and PVDF are used. It can be a single piezoelectric material or a stack of these piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10 nm to 100 μm.

[0107] The second electrode 13 is preferably molybdenum, but can also be made of Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, or Se. It can also be an alloy of these metals or a stack of metal layers. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0108] The acoustic reflector structure 14 is composed of alternating high acoustic impedance layers 141 and low acoustic impedance layers 142. The acoustic impedance of a material is equal to the speed of sound propagation in the material multiplied by the material's density. Theoretically, when the thickness of the high acoustic impedance layer 141 is equal to one-quarter of the wavelength of the sound wave at the resonant frequency of the bulk acoustic resonator propagating in the high acoustic impedance layer 141, and the thickness of the low acoustic impedance layer 142 is equal to one-quarter of the wavelength of the sound wave at the resonant frequency of the bulk acoustic resonator propagating in the low acoustic impedance layer 142, the alternating arrangement of high and low acoustic impedance layers 142 (high / low / high / low... or low / high / low / high...) acts as an acoustic reflector, reflecting the sound wave signal leaking from above back. A reflector structure 14 consisting of high acoustic impedance layers 141 and low acoustic impedance layers 142 typically requires 3 to 4 sets to achieve a good acoustic reflection effect; more sets are better, but this increases the cost. The number of layers is not limited, and the range of selectable reflector structures 14 is from 1 to 100. There is also no restriction on whether the layer is equal to one-quarter of the wavelength; any thickness is acceptable. Materials for the high acoustic impedance layer 141 can include W, Ir, Pt, Ru, Au, Mo, Ta, Ti, Cu, Ni, Zn, Al, Al2O3, Ag, etc. Commonly used materials for the low acoustic impedance layer 142 include SiO2, Si3N4, Mg, rubber, nylon, polyimide, polyethylene, polystyrene, Teflon, etc. Depending on the resonant frequency and the sound velocity of different materials, the thickness range of a single high acoustic impedance layer 141 and a single low acoustic impedance layer 142 is from 1 nm to 10 μm.

[0109] This disclosure also provides an electronic device that may include any of the above-described acoustic resonators.

[0110] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. An acoustic wave filter, comprising an input terminal and an output terminal, and a series branch and multiple parallel branches connected between the input terminal and the output terminal; wherein, The series branch includes at least one first bulk acoustic resonator, at least one capacitor, and at least one inductor connected in series between the input terminal and the output terminal; the at least one inductor includes an inductor connected to the input terminal and / or an inductor connected to the output terminal. The parallel branch includes at least one second body acoustic resonator.

2. The acoustic filter according to claim 1, wherein, The number of parallel branches is one; the connection node between the parallel branch and the series branch is the first node; the capacitor is connected between the first bulk acoustic resonator and the first node; or, the capacitor is connected between the first bulk acoustic resonator and the input terminal.

3. The acoustic filter according to claim 2, wherein, The series branch includes a first bulk acoustic resonator, a capacitor, and an inductor, and the parallel branch includes a second bulk acoustic resonator. The first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the second electrode of the second bulk acoustic wave resonator is connected to the first node, the first electrode of the second bulk acoustic wave resonator is connected to the reference electrode, the first end of the inductor is connected to the first node, and the second end of the inductor is connected to the output terminal.

4. The acoustic filter according to claim 3, wherein, The capacitance of the capacitor is 3-6pF; the inductance of the inductor is 1-3nH.

5. The acoustic filter according to claim 2, wherein, The series branch includes a first bulk acoustic resonator, a capacitor, and two inductors; the two inductors are a first inductor and a second inductor, respectively; the parallel branch includes a second bulk acoustic resonator. The first end of the second inductor is connected to the input terminal, the second end of the second inductor is connected to the first electrode of the first bulk acoustic wave resonator, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the second electrode of the second bulk acoustic wave resonator is connected to the first node, the first electrode of the second bulk acoustic wave resonator is connected to the reference electrode, the first end of the first inductor is connected to the first node, and the second end of the first inductor is connected to the output terminal.

6. The acoustic filter according to claim 5, wherein, The capacitance of the capacitor is 1.5-4pF; the inductance of the first inductor and the second inductor is 0.3-1.5nH.

7. The acoustic filter according to claim 2, wherein, The series branch includes two first-body acoustic resonators, a capacitor and an inductor, and the parallel branch includes a second-body acoustic resonator. The first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the second electrode of the second bulk acoustic wave resonator, the first electrode of the second bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the first electrode of the second bulk acoustic wave resonator is connected to the first node, the second electrode of the second bulk acoustic wave resonator is connected to the reference electrode, the first end of the inductor is connected to the first node, and the second end of the inductor is connected to the output terminal.

8. The acoustic filter according to claim 7, wherein, The capacitance of the capacitor is 2-4pF; the inductance of the inductor is 1-3nH.

9. The acoustic filter according to claim 2, wherein, The series branch includes two first-body acoustic resonators, a capacitor and an inductor, and the parallel branch includes two second-body acoustic resonators. The first electrode of the first first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first first bulk acoustic wave resonator is connected to the second electrode of the second first bulk acoustic wave resonator, the first electrode of the second first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first node, the first electrode of the first second bulk acoustic wave resonator is connected to the first node, the second electrode of the first second bulk acoustic wave resonator is connected to the second electrode of the second second bulk acoustic wave resonator, the first electrode of the second second bulk acoustic wave resonator is connected to the reference electrode, the first end of the inductor is connected to the first node, and the second end of the inductor is connected to the output terminal.

10. The acoustic filter according to claim 9, wherein, The capacitance of the capacitor is 2-4pF; the inductance of the inductor is 1-3nH.

11. The acoustic filter according to claim 1, wherein, The series branch includes N series sub-branches connected in series; N≥2, and N is a positive integer; the series sub-branches are electrically connected to one of the parallel branches; the series sub-branches include at least one first bulk acoustic resonator and a capacitor connected in series with the first bulk acoustic resonator.

12. The acoustic filter according to claim 11, wherein, The connection node between the parallel branch and the series sub-branch is the first node; the capacitor in the series sub-branch is connected between the first bulk acoustic resonator and the first node.

13. The acoustic resonator according to claim 11, wherein, The capacitor in the first series sub-branch is connected between the input terminal and the first bulk acoustic resonator; the capacitor in the i-th series sub-branch is connected between the first bulk acoustic resonator therein and the (i-1)-th series sub-branch; i takes values ​​from 2 to N.

14. The acoustic filter according to claim 11, wherein, N=2, the series sub-branch includes a first-body acoustic resonator and a capacitor; the parallel branch includes a second-body acoustic resonator. For the first series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the second electrode of the second bulk acoustic wave resonator, and the second electrode of the first bulk acoustic wave resonator in the second series sub-branch is connected to the reference electrode. For the second series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first electrode of the second bulk acoustic wave resonator and the first end of the inductor, and the second electrode of the second bulk acoustic wave resonator is connected to the reference electrode. The second end of the inductor is connected to the output terminal.

15. The acoustic filter according to claim 14, wherein, The capacitance of the capacitor is 3-6pF; the inductance of the inductor is 1-3nH.

16. The acoustic filter according to claim 11, wherein, N=3, the series sub-branch includes a first bulk acoustic resonator and a capacitor; the parallel branch includes a second bulk acoustic resonator; For the first series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic wave resonator is connected to the input terminal, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the second electrode of the second bulk acoustic wave resonator, and the second electrode of the first bulk acoustic wave resonator in the second series sub-branch is connected to the reference electrode. For the second series sub-branch and the parallel branch connected thereto, the first electrode of the first bulk acoustic resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first electrode of the second bulk acoustic resonator, and the first electrode of the first acoustic resonator in the third series sub-branch is connected to the reference electrode. For the third series sub-branch and the parallel branch connected thereto, the second electrode of the first bulk acoustic wave resonator is connected to the first plate of the capacitor, the second plate of the capacitor is connected to the first end of the inductor and the second electrode of the second bulk acoustic wave resonator, and the first electrode of the second bulk acoustic wave resonator is connected to the reference electrode. The second end of the inductor is connected to the output terminal.

17. The acoustic filter according to claim 16, wherein, The capacitance values ​​of the capacitors in the first and third series sub-branch are both 3-6pF; the capacitance value of the capacitor in the second series sub-branch is 2-5pF; and the inductance value of the inductor is 1-3nH.

18. The acoustic filter according to any one of claims 1-17, wherein, Both the first bulk acoustic wave resonator and the second bulk acoustic wave resonator include a substrate, and a first electrode, a piezoelectric layer and a second electrode disposed on the substrate; the orthographic projections of any two of the first electrode, the piezoelectric layer and the second electrode on the substrate at least partially overlap. The substrate has a first groove; the substrate includes a first surface and a second surface disposed opposite to each other along its thickness direction; the first groove includes a first opening located on the first surface; the first electrode is located on the first surface; the outline of the orthographic projection of the first opening on the second surface is within the outline of the orthographic projection of the first electrode on the second surface.

19. The acoustic filter according to any one of claims 1-17, wherein, Both the first bulk acoustic wave resonator and the second bulk acoustic wave resonator include a substrate, and at least one reflector structure, a first electrode, a piezoelectric layer and a second electrode disposed on the substrate; the orthographic projections of any two of the reflector structure, the first electrode, the piezoelectric layer and the second electrode on the substrate at least partially overlap. The reflector structure includes a first impedance layer and a second impedance layer arranged sequentially along the direction away from the substrate, wherein the acoustic impedance of the material of the first impedance layer is greater than the acoustic impedance of the material of the second impedance layer.

20. An electronic device comprising the bulk acoustic resonator according to any one of claims 1-19.

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