CN111342806A

CN111342806A - Piezoelectric filter having lamb wave resonator, duplexer, and electronic device

Info

Publication number: CN111342806A
Application number: CN201811550562.8A
Authority: CN
Inventors: 庞慰; 郑云卓
Original assignee: Tianjin University; ROFS Microsystem Tianjin Co Ltd
Current assignee: Tianjin University; ROFS Microsystem Tianjin Co Ltd
Priority date: 2018-12-18
Filing date: 2018-12-18
Publication date: 2020-06-26
Anticipated expiration: 2038-12-18
Also published as: CN111342806B

Abstract

The present invention relates to a piezoelectric filter including: a series-arm resonator unit having a plurality of series resonators; a parallel-branch resonator unit having a plurality of parallel resonators, each of the parallel resonators having one end connected to a port of a corresponding series resonator and the other end adapted to be connected to a ground terminal through a corresponding ground inductor; and a lamb wave resonator, wherein: the lamb wave resonator, the series resonator and the parallel resonator share a piezoelectric layer, or the piezoelectric layer of the lamb wave resonator, the piezoelectric layer of the series resonator and the piezoelectric layer of the parallel resonator are in the same layer. The invention also relates to a duplexer and an electronic device with the structure.

Description

Piezoelectric filter having lamb wave resonator, duplexer, and electronic device

Technical Field

Embodiments of the present invention relate to the field of semiconductors, and in particular, to a piezoelectric filter, a method of improving a suppression level of a filter, a duplexer having the piezoelectric filter, and an electronic device having the piezoelectric filter.

Background

With the rapid development of wireless communication technology, the application of miniaturized portable terminal equipment is becoming more and more extensive, and thus the demand for high-performance and small-size radio frequency front-end modules and devices is becoming more and more urgent. In recent years, filters such as filters and duplexers based on Film Bulk Acoustic Resonators (FBARs) are becoming more popular in the market. On one hand, the material has excellent electrical properties such as low insertion loss, steep transition characteristic, high selectivity, high power capacity, strong anti-static discharge (ESD) capability and the like, and on the other hand, the material has the characteristics of small volume and easy integration.

Currently, in the face of increasingly severe frequency resources, the suppression level of frequency selective devices such as filters and duplexers at the front end of radio frequency to adjacent frequency bands is required to be higher and higher, and thin film bulk acoustic resonator devices also need to be improved and improved in this respect, so that the suppression level of stop band is improved, the insertion loss of pass band cannot be greatly influenced, and the overall size of a chip or a device is not increased as much as possible.

A common method is to increase the stop-band rejection by increasing the inductance of the large inductance in the series-parallel branch to change the resonant frequency of the resonator, or to increase the rejection point (notch) to improve the stop-band rejection. However, these methods require additional reactive elements, and these elements are usually large and difficult to implement on a chip. If the method is implemented by winding wires on a substrate or adding discrete components outside a chip, the number of layers and the size of the substrate are inevitably increased, thereby inevitably resulting in an increase in the overall size of the filter or duplexer. Moreover, the added winding or discrete components are not ideal in practice, and the loss introduced by the winding or discrete components is superposed on the filter, so that the insertion loss of the pass band of the filter is deteriorated.

The method can improve the stop band suppression, and simultaneously, the loss of the chip is increased and the overall size of the chip is greatly enlarged.

In addition, the fabrication of passive integrated devices (IPDs) on the filter chip requires additional special processing steps for the thin film bulk acoustic resonator device, which is not favorable for improving the production efficiency and reducing the cost. How to achieve the improvement of the suppression degree and the isolation degree in a low-cost mode becomes a problem to be solved urgently by device manufacturers.

Disclosure of Invention

The present invention has been made to mitigate or solve at least one of the above-mentioned problems with the prior art.

According to an aspect of an embodiment of the present invention, there is provided a piezoelectric filter including: a series-arm resonator unit having a plurality of series resonators; a parallel-branch resonator unit having a plurality of parallel resonators, each of the parallel resonators having one end connected to a port of a corresponding series resonator and the other end adapted to be connected to a ground terminal through a corresponding ground inductor; and a lamb wave resonator, wherein: the series resonators and the parallel resonators are film bulk acoustic resonators; and the lamb wave resonator, the series resonator and the parallel resonator share the piezoelectric layer, or the piezoelectric layer of the lamb wave resonator, the piezoelectric layer of the series resonator and the piezoelectric layer of the parallel resonator are in the same layer.

In an alternative embodiment, the first end of the lamb wave resonator is connected to a port of a series resonator, the second end of the lamb wave resonator is connected to a non-grounded port of a corresponding grounded inductance of a parallel resonator, and the resonance frequency of the lamb wave resonator is different from the resonance frequencies of the series resonator and the parallel resonator.

Optionally, another series resonator is further provided between the parallel resonator to which the second end of the lamb wave resonator is connected and the series resonator to which the first end of the lamb wave resonator is connected.

In a further optional embodiment, the piezoelectric filter further comprises a coupling circuit unit, the coupling circuit unit comprising: an equipotential body; a first lamb wave resonator, a first end of which is connected to the equipotential body and a second end of which is connected to a port of one series resonator; and a second lamb wave resonator, a first end of the second lamb wave resonator is connected to the equipotential body, and a second end of the second lamb wave resonator is connected to a non-grounded port of a corresponding grounded inductor of one parallel resonator. Optionally, another series resonator is further provided between the parallel resonator to which the second end of the second lamb wave resonator is connected and the series resonator to which the second end of the first lamb wave resonator is connected.

In a further optional embodiment, the piezoelectric filter further comprises a coupling circuit unit, the coupling circuit unit comprising: an equipotential body; the first end of the first lamb wave resonator is connected to the equipotential body, and the second end of the first lamb wave resonator is connected to a non-grounding port of a corresponding grounding inductor of one parallel resonator; and a second lamb wave resonator, a first end of the second lamb wave resonator is connected to the equipotential body, and a second end of the second lamb wave resonator is connected to a non-grounded port of the corresponding grounded inductor of the other parallel resonator. Further optionally, the one parallel resonator is not adjacent to the other parallel resonator; and the one parallel resonator and the other parallel resonator do not share the same ground terminal. Further, the ground inductance to which the one parallel resonator is connected is not adjacent to the ground inductance to which the other parallel resonator is connected.

Optionally, the piezoelectric filter has a guard ring located at the periphery of a chip pattern region of the piezoelectric filter, and the guard ring constitutes the equipotential body; or the piezoelectric filter has a first conductor provided in a chip pattern region of the piezoelectric filter, the first conductor constituting the equipotential body; or the piezoelectric filter is provided with a chip packaging part, and the chip packaging part is provided with a second conductor; the piezoelectric filter is provided with two electric connection through hole structures which are respectively and electrically connected with the second electric conductor; the two electric connection through hole structures and the second electric conductor form the equipotential body.

According to another aspect of embodiments of the present invention, there is provided a method of improving a suppression level of the above-described filter, the piezoelectric filter further including a coupling circuit unit including: an equipotential body; a first lamb wave resonator, a first end of which is connected to the equipotential body and a second end of which is connected to a port of one series resonator; and a second lamb wave resonator, a first end of the second lamb wave resonator being connected to the equipotential body, and a second end of the second lamb wave resonator being connected to a non-ground port of a corresponding ground inductance of one of the parallel resonators, wherein the method comprises the steps of: and adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator to enable the transmission zero point of the signal to move from the roll-off edge of the right side edge of the passband of the filter to a high frequency along the frequency.

Embodiments of the present invention also relate to a method of increasing a suppression level of a filter, the piezoelectric filter further including a coupling circuit unit, the coupling circuit unit including: an equipotential body; the first end of the first lamb wave resonator is connected to the equipotential body, and the second end of the first lamb wave resonator is connected to a non-grounding port of a corresponding grounding inductor of one parallel resonator; and a second lamb wave resonator, a first end of the second lamb wave resonator being connected to the equipotential body, and a second end of the second lamb wave resonator being connected to a non-ground port of a corresponding ground inductance of another parallel resonator, wherein the method comprises the steps of: and adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator to enable the transmission zero point of the signal to move from the roll-off edge of the left edge of the passband of the filter to the low frequency.

Embodiments of the present invention also relate to a duplexer, including: a transmit filter; and a receive filter, wherein: at least one of the filters is a piezoelectric filter as described above.

Embodiments of the present invention also relate to a duplexer, including: a transmit filter; a receiving filter; and at least one lamb wave resonator, wherein: the series resonators and the parallel resonators of the transmitting filter and the receiving filter are film bulk acoustic resonators; the at least one lamb wave resonator shares a piezoelectric layer with the series resonator, or the piezoelectric layer of the at least one lamb wave resonator and the piezoelectric layer of the series resonator are in the same layer.

Further optionally, a first end of one of the at least one lamb wave resonators is connected to one filter, and a second end is connected to another filter. In a further alternative embodiment, the first end of said one lamb wave resonator is connected to the port of one series resonator of one filter, and the second end is connected to the non-grounded port of the corresponding grounded inductance of one shunt resonator of the other filter; or the first end of one lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of one filter, and the second end of the one lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of the other filter.

The duplexer may further have an equipotential body, in which case the at least one lamb wave resonator includes a first lamb wave resonator and a second lamb wave resonator, and first ends of the first lamb wave resonator and the second lamb wave resonator are both connected to the equipotential body; the second end of the first lamb wave resonator is connected to the port of one series resonator of one filter, and the second end of the second lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of the other filter; or the second end of the first lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of one filter, and the second end of the second lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of the other filter.

Embodiments of the present invention also relate to an electronic device having the piezoelectric filter described above.

Drawings

These and other features and advantages of the various embodiments of the disclosed invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate like parts throughout, and in which:

fig. 1 is a schematic structural diagram of a reminder-frame filter based on a film bulk acoustic resonator in the prior art;

fig. 2 (a) is an electrical model diagram of a lamb wave resonator, and (b) is an equivalent circuit of the lamb wave resonator represented by a BVD model;

in fig. 3, (a) a schematic top view of a lamb wave resonator, (b) a schematic cross-sectional view of one example of the lamb wave resonator, (c) a schematic cross-sectional view of a thin film bulk acoustic resonator, and (d) - (f) schematic cross-sectional views of other examples of the lamb wave resonator, respectively;

FIG. 4 is a schematic diagram of a filter according to an exemplary embodiment of the present invention;

FIG. 5 is a simulation plot of the amplitude-frequency response of the filter of FIG. 4;

FIG. 6 is a schematic diagram of a filter according to another exemplary embodiment of the present invention;

FIGS. 7a, 7b, 8a-8f are schematic diagrams of alternative embodiments of the filter of FIG. 6, respectively;

FIG. 9 is a schematic diagram of a filter according to another exemplary embodiment of the present invention;

FIGS. 10a-10d are schematic diagrams of alternative embodiments of the filter of FIG. 9, respectively;

fig. 11 schematically shows a resonator arrangement in a filter chip, wherein a first equivalent capacitance and a second equivalent capacitance are exemplarily shown, and a guard ring is used as an equipotential body;

fig. 12 schematically shows a resonator arrangement in a filter chip, wherein a first equivalent capacitance and a second equivalent capacitance are exemplarily shown, and a first electrical conductor is acting as an equipotential body;

fig. 13a is a schematic perspective view of a chip on which a package structure is disposed, wherein a relationship between an equipotential body and first and second equivalent capacitors is exemplarily shown;

FIG. 13b is a schematic top view of the chip of FIG. 13a with the package structure removed;

fig. 14a is a schematic structural diagram of a duplexer to which a filter structure of the present invention is applied as an exemplary embodiment of the present invention;

fig. 14b is a schematic structural diagram of a duplexer in the prior art;

fig. 15a illustrates transmission characteristic curves of the transmit filters of the duplexers in fig. 14a and 14b, wherein the thick lines correspond to the transmit filters of the duplexer in fig. 14a and the thin lines correspond to the transmission characteristic curves of the transmit filters of the duplexer in fig. 14 b;

FIG. 15b is an enlarged view of the boxed portion of FIG. 15 a;

fig. 16a exemplarily shows transmission characteristic curves of the receiving filter of the duplexer in fig. 14a and 14b, wherein the thick line corresponds to the receiving filter of the duplexer in fig. 14a and the thin line corresponds to the transmission characteristic curve of the receiving filter of the duplexer in fig. 14 b;

FIG. 16b is an enlarged view of the box portion of FIG. 16 a;

fig. 17 is a schematic diagram of a duplexer in accordance with still another exemplary embodiment of the present invention;

fig. 18 is a schematic diagram of a duplexer in accordance with an exemplary embodiment of the present invention;

fig. 19 is a simulation result of the duplexer circuit diagram in fig. 18.

Detailed Description

The technical scheme of the invention is further specifically described by the following embodiments and the accompanying drawings. In the specification, the same or similar reference numerals denote the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the general inventive concept of the present invention and should not be construed as limiting the invention.

The invention provides a filter simultaneously provided with a Film Bulk Acoustic Resonator (FBAR) and a Lamb Wave Resonator (LWR), which can improve the suppression level of adjacent frequency band signals and does not cause the increase of pass band insertion loss. In addition, the filter does not have the problems of large increase of the whole size of a chip, increase of complexity of a manufacturing process and the like caused by introducing an additional discrete reactive device, so that the space is saved, and the cost is reduced.

The working principle of the lamb wave resonator is as follows: lamb waves generated by the piezoelectric material form standing waves inside the resonator, and the electrical characteristics of the standing waves are represented as resonance due to the piezoelectric effect. The lamb wave resonator is mainly composed of electrode materials and piezoelectric materials, the manufacturing process is completely compatible with that of the film bulk acoustic resonator, the schematic diagram of the front structure of the lamb wave resonator is shown in (a) in fig. 3, at least one side above or below the piezoelectric layer is provided with an electrode, and the electrode receives an electrical signal and excites the resonator to work. The electrodes are typically in the shape of Interdigital transducers (IDTs), with the fingers of the same network connected together at the finger roots, with the spacing p between two adjacent electrodes being 1/2 of the lamb wavelength (λ). Besides the IDT structure on one side of the piezoelectric layer, the electrode on the other side of the piezoelectric layer can be made into the following four structures: the cross-sectional views of the electrode structures of the first three electrode structures are shown as (d), (e) and (f) in fig. 3, and the cross-sectional view of the electrode structure of the IDT electrode that is mirror-symmetrical to the opposite IDT is shown as (b) in fig. 3.

The LWR process is exactly the same as the FBAR process. Taking LWR with IDT structure at both top and bottom as an example, a sectional view of a lamb wave resonator is shown in fig. 3 (b). Firstly, etching an air cavity on a silicon substrate, and then filling a sacrificial layer material in the air cavity; then, depositing a lower electrode made of metal such as molybdenum and tungsten, and etching the lower electrode to form an IDT pattern; then sequentially depositing a piezoelectric material (such as aluminum nitride) and an upper electrode material (generally the same as the lower electrode material); etching the upper electrode to form an IDT pattern; etching the piezoelectric layer material to form an air reflection grid, wherein the air reflection grid is used for facilitating the reflection of the sound wave, so that standing waves can be formed and resonance can be generated; by etching the reflective gate, the liquid can etch the sacrificial layer material in the cavity, and after the sacrificial layer is released, the resonator finally forms a suspended structure. In fig. 3 (b), the upper and lower sides of the piezoelectric layer are fabricated with interdigital structures, which are respectively connected with signal input and signal output, and the input and output electrodes are arranged in a staggered manner and are in mirror symmetry with the upper and lower layers. Fig. 3 (c) is a schematic cross-sectional view of the film bulk acoustic resonator, and it can be seen that the film bulk acoustic resonator is provided with a sandwich structure having a top electrode, a piezoelectric layer and a bottom electrode on a silicon substrate, and also has an air cavity located below the sandwich structure. Unlike lamb wave resonators, thin film bulk acoustic resonators are typically formed from planar top and bottom electrodes and do not need to be formed in the shape of an IDT. As can be seen from the figure, the process flow of the thin film bulk acoustic resonator is completely the same as that of the lamb wave resonator, and the thin film bulk acoustic resonator and the lamb wave resonator can be conveniently manufactured on one wafer at the same time.

Lamb waves are divided into symmetric Lamb waves (symmet Lamb waves) and anti-symmetric Lamb waves (anti-symmet Lamb waves) according to Lamb wave vibration characteristics. Solutions to lamb wave equations, due to periodicity, exist in infinite numbers, and this series of symmetric and antisymmetric solutions are referred to as S0, S1, S2 … Sn, and a0, a1, a2 … An, respectively. The resonance frequency f of the resonator is v/λ, where v is the lamb wave velocity. Because every kind of lamb wave can all produce the resonance, and every kind of lamb wave velocity of wave is different, consequently in same lamb wave syntonizer, can detect a plurality of resonances, and every kind of resonant frequency all is different, and the designer can select arbitrary resonance point to utilize according to the demand.

An electrical model of the lamb wave resonator is shown in fig. 2 (a), and an equivalent circuit thereof can be represented by a BVD model, as shown in fig. 2 (b). When the signal frequency is far from the resonance frequency, the lamb wave resonator can be equivalent to a capacitor with a capacitance value of C0 and a high quality factor. The lamb wave resonator and the film bulk acoustic resonator have different resonant frequencies under the same laminated structure because of different working modes. Therefore, when the frequency is the resonant frequency of the film bulk acoustic resonator, the lamb wave resonator corresponds to a capacitor for the film bulk acoustic resonator.

The lamb wave resonator is introduced into the FBAR filter device and is used for improving the suppression degree and the isolation degree.

A conventional ladder-structured filter structure based on film bulk acoustic resonators is shown in fig. 1. The port 131 is a signal input (or output) port, the port 132 is a signal output (or input) port, and a signal to be filtered is input from the port 131 (or 132) and output from the port 132 (or 131). Series inductance 121 is connected between port 131 and resonator 101, and series inductance 122 is connected between port 132 and resonator 104. The series-

arm resonators

101, 102, 103, 104 are connected in series between the series inductance 121 and the series inductance 122. One port of the parallel-arm resonator 111 is connected to a position between the series-

arm resonators

101 and 102, and the other port is connected to one port of the ground inductor 123. One port of the parallel-arm resonator 112 is connected at a position between the series-

arm resonators

102, 103, and the other port is connected to one port of the ground inductor 124. One port of the parallel-arm resonator 113 is connected at a position between the series-

arm resonators

103, 104, and the other port is connected to one port of the ground inductor 125. One port of the parallel-arm resonator 114 is connected at a position between the series-arm resonator 104 and the series inductance 122, and the other port is connected to one port of the ground inductance 126. The other ports of the

ground inductors

123, 124, 125, 126 are all grounded. Wherein the resonance frequency fs of the series-

arm resonators

101, 102, 103, 104 is higher than the resonance frequency fs' of the parallel-arm resonators.

Fig. 4 shows an embodiment of the present invention, and the lamb wave resonator LWR is connected across the input end of the first series resonator 101 and the ground end of the last parallel resonator 114, but other connection methods are also possible. Wherein LWR's IDT electrode width is 10um, and the interval of electrode is 15um, and electrode length is 100um, respectively has 5 pairs of mirror image electrodes on the upper and lower surface of piezoelectric layer, and the equivalent capacitance value of its realization is about 0.5 pF.

Fig. 5 is an amplitude-frequency response simulation curve of the embodiment in fig. 4, which is a band (band)7 transmission filter, the passband of which is 2500MHz-2570MHz (i.e. the transmission band of LTE band 7), and which is required to have a better suppression degree at 2620MHz-2690MHz (i.e. the reception band of LTE band 7), and at worst, cannot be worse than-55 dB. The thick solid line is a curve without the lamb wave resonator, the inhibition at 2690MHz is only 49.5dB, the thin dotted line is the design with the lamb wave resonator, although the inhibition near 2620MHz is slightly worse than the original one, but still has-60 dB, which far exceeds the index requirement, and the inhibition degree at 2690MHz reaches-56.8 dB, so that the performance is greatly improved. The effective resonance area of the lamb wave resonator adopted in the circuit is 1500um2, the resonance frequency point is 1500MHz, which is far lower than the passband frequency of the filter, therefore, the lamb wave resonator is equivalent to a capacitive device with high Q value in the working frequency band of the filter.

It can be seen that, in the case where the lamb wave resonators are provided in the filter, the filter can improve the suppression level for the adjacent band signals without causing an increase in the passband insertion loss.

In addition, when the lamb wave resonator is arranged in the filter, the problems of large increase of the whole size of a chip, increase of complexity of a manufacturing process and the like caused by introducing an additional discrete reactive device do not exist, so that the space is saved, and the cost is reduced.

Fig. 6 is a schematic diagram of a filter according to another exemplary embodiment of the present invention, which is capable of improving the high frequency near stop band rejection level above the roll-off edge frequency on the right side of the pass band.

In fig. 6, the port 131 is a signal input (or output) port, the port 132 is a signal output (or input) port, and a signal to be filtered is input from the port 131 (or 132) and output from the port 132 (or 131). Series inductance 121 is connected between port 131 and resonator 101, and series inductance 122 is connected between port 132 and resonator 104. The series-

arm resonators

ground inductors

123, 124, 125, 126 are all grounded.

In fig. 6, also between the equipotential body U and the node S1, a lamb wave resonator LWR1 is added; a lamb wave resonator LWR2 is added between the equipotential body U and the node P4.

In FIG. 6, the resonant frequencies fs of the series-arm resonators 101-104 may or may not be identical, and the resonant frequencies fs' of the parallel-arm resonators 111-114 may or may not be identical. The resonant frequency fs of each series-arm resonator is higher than the resonant frequency fs' of each parallel-arm resonator.

The equipotential body U and the two lamb wave resonators form a signal coupling circuit structure or a coupling circuit unit. In fig. 6, the signal coupling circuit structure is added, so that the transmission zero of the signal is moved from the roll-off edge at the right edge of the filter passband to a high frequency, and the amount of movement can be controlled by adjusting the values of the equivalent capacitances of the two lamb wave resonators. Thus, by adjusting the equivalent capacitances of the two lamb wave resonators to move the transmission zero to a frequency required in the high-frequency near-stop band, the suppression level in the vicinity of the frequency can be improved. In the invention, two lamb wave resonators and an equipotential body U form a complete signal coupling circuit. In addition, because the equivalent capacitances of the two lamb wave resonators can be adjusted respectively, the realizability is solved, and meanwhile, the realization flexibility is increased. The specific technical effects achieved by using this structure will be described in detail in the following embodiments, which can be seen in fig. 15a and 15 b.

It should be noted that the connection mode of the two lamb wave resonators connected to the equipotential conductor U in fig. 6 is not exclusive, and for example, one port of the lamb wave resonator LWR2 may be connected to a node other than the P4.

In a further embodiment, the lamb wave resonator LWR1 is connected between a port node of a certain series resonator and the equipotential body, the lamb wave resonator LWR2 is connected between a connection node of a certain parallel resonator, which is not adjacent to the series resonator, and the corresponding ground inductance and the equipotential body; in a further embodiment, the parallel resonator is not grounded to the parallel resonator adjacent to the series resonator through a common ground inductance.

Fig. 7a, 7b show two variants of the embodiment of fig. 6. It is specifically noted that in fig. 7a-10d of the present invention, lamb wave resonator LWR1 is replaced with equivalent capacitance Ca of lamb wave resonator LWR1 and lamb wave resonator LWR2 is replaced with equivalent capacitance Cb of lamb wave resonator LWR 2. In other words, in these drawings, although shown as equivalent capacitance, it is a corresponding lamb wave resonator.

The example shown in fig. 6 is a case where 4 parallel-arm resonators are grounded through corresponding grounding inductors, and some parallel-arm resonators may be grounded through a common grounding inductor after being combined according to design requirements. Some variant embodiments of this case are given in figures 8a-8f, which can achieve an improved level of suppression.

On the basis of the structure of fig. 1, the invention also provides a filter structure capable of improving the suppression level in fig. 9, which can improve the low-frequency near-stop-band suppression level below the roll-off edge frequency on the left side of the pass band.

In fig. 9, the port 131 is a signal input (or output) port, the port 132 is a signal output (or input) port, and a signal to be filtered is input from the port 131 (or 132) and output from the port 132 (or 131). Series inductance 121 is connected between port 131 and resonator 101, and series inductance 122 is connected between port 132 and resonator 104. The series-

arm resonators

ground inductors

123, 124, 125, 126 are grounded, respectively.

As shown in fig. 9, between the equipotential body U and the node P1, the equivalent capacitance Ca is also increased; an equivalent capacitance Cb is added between the equipotential body U and the node P4.

In FIG. 9, the resonant frequencies fs of the series-arm resonators 101-104 may or may not be identical, and the resonant frequencies fs' of the parallel-arm resonators 111-114 may or may not be identical. The resonant frequency fs of each series-arm resonator is higher than the resonant frequency fs' of each parallel-arm resonator.

The equipotential body U and the equivalent capacitors Ca and Cb constitute a signal coupling circuit structure or a coupling circuit unit, and in fig. 9, the signal coupling circuit structure is added to move the transmission zero of the signal from the roll-off edge of the left edge of the filter passband to a low frequency, and the amount of movement can be controlled by adjusting the values of the equivalent capacitors Ca and Cb. Thus, by adjusting the equivalent capacitances Ca and Cb to move the transmission zero to a frequency required in the low-frequency near-stop band, the suppression level in the vicinity of the frequency can be improved.

In addition, since the equivalent capacitances Ca and Cb can be adjusted separately, the realizability is solved and the flexibility of implementation is increased. The specific technical effects achieved by using this particular structure will be described in detail in the following embodiments, which can be seen in fig. 16a and 16 b.

It should be noted that the connection of the equivalent capacitors Ca and Cb coupled to the equipotential body U in fig. 9 is not exclusive, and the port of the equivalent capacitor Cb may be connected to a node other than the node P4. Specifically, the equivalent capacitor Ca may be connected between the equipotential body U and a node between one of the parallel resonators and the corresponding ground inductor, and the equivalent capacitor Cb may be connected between the equipotential body U and a node between the other one of the parallel resonators and the corresponding ground inductor. In an alternative embodiment, the two parallel resonators are not adjacent or are commonly grounded through a common grounding inductor, and in a further alternative embodiment, the grounding inductors of the two parallel resonators are not adjacent.

Fig. 10a-10d show several variations of fig. 9, respectively, which also achieve an improved level of suppression.

Here, it should be specifically noted that: the combination of each series resonator, e.g., 101, and a parallel resonator, e.g., 111, adjacent to it is referred to as a stage, so figures 6-10 d, etc., all give an example of a 4-stage FBAR ladder architecture filter. The present invention is used as an example to facilitate the detailed description of the details of the invention, and the application scope of the present invention is not limited to the 4-level ladder architecture, but can be applied to any more or less levels, and can also be other architectures.

The implementation of the equipotential bodies in the above-described filter structure is exemplarily described below.

In practice, a guard ring around the FBAR chip pattern area may be used as the equipotential body U. The first special structure in fig. 6, the resonator arrangement in one FBAR chip is shown in fig. 11, i.e. the peripheral guard ring is used as the equipotential body U.

In practice, a conductive or first conductor (pad) of equal potential difference may be added as the equipotential body U in the FBAR chip pattern region. In the first special structure of fig. 6, the resonator arrangement in one FBAR chip can also be as shown in fig. 12, i.e. a first conductor added separately is used as the equipotential body U.

In practice, the through hole via connected to the same conductive pad on the chip package structure cap may be used as the equipotential body U. In the filter structure shown in fig. 6, the resonator arrangement in one FBAR chip may also be as shown in fig. 13a, using two vias via a, via B connected to the same conductive pad on the package structure as the equipotential body U, so as to introduce equivalent capacitances Ca and Cb. Fig. 13b is a top plan view of the chip part from above looking down after omitting the package structure cap.

Fig. 11-13b illustrate an implementation of the equipotential body U in practice by taking the filter structure in fig. 6 as an example, and all of these implementations may also be used to implement the second special structure in fig. 9, which is not described herein again.

Fig. 14a is a schematic structural diagram of a duplexer 100, wherein: 101 is a transmit filter (TX filter), 102 is a receive filter (RX filter); one port of the transmitting filter 101 is connected to the port 105, and the port can be connected to an external device such as a radio frequency signal generating circuit, and is used for transmitting a radio frequency signal generated by the external device into the transmitting filter 101; the other port of the transmission filter 101 is connected to a matching network (match network)103, and is used for feeding the filtered signal into the matching network; a port of the receiving filter 102 is connected to a port 106, which may be connected to a subsequent circuit such as a low noise amplifier; the other port of the receiving filter 102 is connected to a matching network 103 for transmitting the signal received by the antenna into the receiving filter 102; the matching network 103 is connected between the antenna 104 and the transmission filter 101 and the reception filter 102, and adjusts impedance matching of the antenna port. In this embodiment: the transmit filter 101 uses a filter structure proposed by the present invention, for example, as shown in fig. 2. The receive filter 102 uses the filter structure proposed by the present invention, for example, as shown in fig. 5.

For comparison, a duplexer 110 is also shown, and a schematic structural diagram thereof is shown in fig. 14b, and the components and functions are the same as those in fig. 14a, so that the details are not repeated. The difference is that the transmitting filter (TX filter)111 and the receiving filter (RXfilter)112 use the general ladder structure shown in fig. 1 instead of the specific structure shown in the present invention, and do not use a special signal coupling circuit structure composed of an equipotential body U and equivalent capacitors Ca and Cb.

Fig. 15a and 16a show transmission characteristic curves of the reception filter and the transmission filter of the

duplexers

100 and 110, respectively. In the duplexer of this example, the passband frequency range of the transmit filter is 1710MHz-1785MHz, and the center frequency can be considered to be about 1749 MHz; the passband of the receive filter has a frequency in the range of 1805MHz to 1880MHz, and the center frequency can be considered to be approximately 1844 MHz. In order to minimize the mutual influence between the two filters, it is necessary to design the degree of suppression of the two filters in the opposite pass band, particularly in the vicinity of the center frequency, as large as possible. In this embodiment, the duplexer in this frequency band is used for illustration only, and the filter structure of this patent is also applicable to duplexers and filters in other frequency bands.

Fig. 15a illustrates the transmission characteristic curves of the transmission filters 101 and 111, where the thick line is the performance of the transmission filter 101 and the thin line is the performance of the transmission filter 111. The circuit configuration of the transmission filter 101 is shown in fig. 2, in which a special coupling circuit configuration composed of an equipotential body U and equivalent capacitors Ca and Cb is used, and the function of the configuration is to move the transmission zero of the signal from the roll-off at the right edge of the passband to a high frequency to a position of about 1844MHz, which is substantially identical to the center frequency of the reception filter 102. It can be seen from fig. 15a that the shifted transmission zero forms a deeper suppression point at 1844MHz, and the suppression level reaches about-78 dB (marked as m1 in the figure), and the suppression level in the range near the point is obviously improved. Without the use of the emitter filter 111 of the structure of the equipotential body U and the equivalent capacitances Ca and Cb, the transmission characteristic curve is shown as a thin line, the suppression level at 1844MHz is only around-56 dB (marked m2 in the figure), and the suppression level in the range around this point is significantly worse.

Fig. 15b is an enlarged view of a part of the frame in fig. 15a, and it can be seen that the two curves in the pass band completely overlap, and the structure proposed by the present invention, for example, as shown in fig. 6, is used to explain that the out-of-band rejection is improved without any deterioration in the pass band insertion loss.

Fig. 16a shows an example of the transmission characteristic of the receive

filters

102 and 112. Where the thick line is the performance of the receive filter 102 and the thin line is the performance of the receive filter 112. The circuit configuration of the receiving filter 102 is shown in fig. 9, in which a special coupling circuit configuration composed of an equipotential body U and equivalent capacitors Ca and Cb is used, and the function of the configuration is to move the transmission zero of the signal from the roll-off at the left edge of the pass band to a low frequency to a position of about 1749MHz, which is substantially identical to the center frequency of the transmitting filter 101. It can be seen from fig. 16a that the shifted transmission zero forms a deeper suppression point at 1749MHz, and the suppression level reaches about-78 dB (marked as m1 in the figure), and the suppression level in the range near the point is obviously improved. Without the use of the emitter filter 112 of the structure of the equipotential body U and the equivalent capacitances Ca and Cb, the transmission characteristic curve is shown as a thin line, the suppression level at 1749MHz is only around-59 dB (marked m2 in the figure), and the suppression level in the range around this point is significantly worse.

Fig. 16b is an enlarged view of a part of a square frame in fig. 16a, and it can be seen that two curves in the pass band completely overlap, and the filter structure proposed by the present invention, such as that shown in fig. 9, is used to improve the out-of-band rejection without any deterioration of the pass-band insertion loss.

Fig. 17 is a schematic diagram of a duplexer according to still another exemplary embodiment of the present invention. The duplexer is composed of two filters with lamb wave resonators, and is a duplexer of an LTE frequency band 7, wherein a transmitting frequency band is 2500MHz-2570MHz, a receiving frequency band is 2620MHz-2690MHz, the transmitting filter is the embodiment shown in FIG. 4, but the technical effects of the two are similar to each other, and the embodiment shown in FIG. 6 can also be used.

Fig. 18 is a schematic diagram of a duplexer in accordance with an exemplary embodiment of the present invention. The duplexer is a duplexer composed of two FBAR filters, and is different in that a lamb wave resonator LWR is bridged between the two filters.

Fig. 19 is a simulation result of the circuit diagram of the duplexer shown in fig. 18, and it can be seen from fig. 19 that the isolation of the duplexer is improved by 4dB at 2500MHz, while the isolation of other locations is not significantly deteriorated.

It is to be noted that fig. 18 merely shows that one lamb wave resonator is disposed between two independent FBAR filters. In an alternative embodiment, a plurality of lamb wave resonators may also be provided. In fig. 18, one end of the lamb wave resonator is connected to the port of one series resonator of one filter and the other end is connected to the non-ground port of the corresponding ground inductance of one parallel resonator of the other filter, but the connection manner of the lamb wave resonator is not limited to this, and for example, one end of the lamb wave resonator is connected to the non-ground port of the corresponding ground inductance of one parallel resonator of one filter and the other end is connected to the non-ground port of the corresponding ground inductance of one parallel resonator of the other filter.

Furthermore, similar to the embodiment of the invention in which equipotential bodies are provided in fig. 5-10d, it is also possible to connect two filters by means of two lamb wave resonators and an equipotential body.

Based on the above, the present invention provides a piezoelectric filter, including: a series-arm resonator unit having a plurality of series resonators; a parallel-branch resonator unit having a plurality of parallel resonators, each of the parallel resonators having one end connected to a port of a corresponding series resonator and the other end adapted to be connected to a ground terminal through a corresponding ground inductor; and a lamb wave resonator, wherein: the lamb wave resonator and the series resonator share the piezoelectric layer through the parallel resonator, or the piezoelectric layer of the lamb wave resonator is in the same layer as the piezoelectric layers of the series resonator and the parallel resonator.

The piezoelectric filter based on the invention has no problems of great increase of the whole size of a chip, increase of complexity of a manufacturing process and the like caused by introducing an additional discrete reactive device, thereby saving space and reducing cost.

For example, referring to fig. 4, a first end of the lamb wave resonator is connected to a port of a series resonator and a second end of the lamb wave resonator is connected to a non-ground port of a corresponding ground inductor of a parallel resonator. Further, another series resonator is provided between the parallel resonator to which the second end of the lamb wave resonator is connected and the series resonator to which the first end of the lamb wave resonator is connected.

For example, referring to fig. 6, the piezoelectric filter may further include a coupling circuit unit including: an equipotential body; a first lamb wave resonator, a first end of which is connected to the equipotential body and a second end of which is connected to a port of one series resonator; and a second lamb wave resonator, a first end of the second lamb wave resonator is connected to the equipotential body, and a second end of the second lamb wave resonator is connected to a non-grounded port of a corresponding grounded inductor of one parallel resonator. Further, another series resonator is provided between the parallel resonator to which the second end of the second lamb wave resonator is connected and the series resonator to which the second end of the first lamb wave resonator is connected.

For example, referring to fig. 9, the piezoelectric filter may further include a coupling circuit unit including: an equipotential body; the first end of the first lamb wave resonator is connected to the equipotential body, and the second end of the first lamb wave resonator is connected to a non-grounding port of a corresponding grounding inductor of one parallel resonator; and a second lamb wave resonator, a first end of the second lamb wave resonator is connected to the equipotential body, and a second end of the second lamb wave resonator is connected to a non-grounded port of the corresponding grounded inductor of the other parallel resonator. Further, the one parallel resonator is not adjacent to the other parallel resonator; and the one parallel resonator and the other parallel resonator do not share the same ground terminal.

For example, referring to fig. 14a and 17, the present invention also proposes a duplexer comprising: a transmit filter; and a receive filter, wherein: at least one of the filters is a piezoelectric filter as described above.

For another example, referring to fig. 18, the present invention also provides a duplexer, comprising: a transmit filter; a receiving filter; and at least one lamb wave resonator, wherein: the series resonators and the parallel resonators of the transmitting filter and the receiving filter are film bulk acoustic resonators; the at least one lamb wave resonator shares a piezoelectric layer with the series resonator, or the piezoelectric layer of the at least one lamb wave resonator and the piezoelectric layer of the series resonator are in the same layer.

Accordingly, the present invention proposes a method for increasing the suppression level of a filter, such as a band-pass filter shown in fig. 6, the method comprising the steps of: and adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator to enable the transmission zero point of the signal to move from the roll-off edge of the right side edge of the passband of the filter to a high frequency along the frequency.

The present invention also proposes a method of increasing the suppression level of a filter, such as a band-pass filter as shown in fig. 9, the method comprising the steps of: and adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator to enable the transmission zero point of the signal to move from the roll-off edge of the left edge of the passband of the filter to the low frequency.

Embodiments of the invention also relate to an electronic device comprising a bandpass filter as described above. It should be noted that the electronic device herein includes, but is not limited to, intermediate products such as a radio frequency front end and a filtering and amplifying module, and terminal products such as a mobile phone, WIFI, and an unmanned aerial vehicle.

Although embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims

1. A piezoelectric filter comprising:

a series-arm resonator unit having a plurality of series resonators;

a parallel-branch resonator unit having a plurality of parallel resonators, each of the parallel resonators having one end connected to a port of a corresponding series resonator and the other end adapted to be connected to a ground terminal through a corresponding ground inductor; and

the resonator of the lamb wave is provided with a plurality of resonators,

wherein:

the series resonators and the parallel resonators are film bulk acoustic resonators; and is

The lamb wave resonator, the series resonator and the parallel resonator share a piezoelectric layer, or the piezoelectric layer of the lamb wave resonator, the piezoelectric layer of the series resonator and the piezoelectric layer of the parallel resonator are in the same layer.

2. The piezoelectric filter of claim 1, wherein:

the first end of the lamb wave resonator is connected to a port of a series resonator, the second end of the lamb wave resonator is connected to a non-grounded port of a corresponding grounded inductor of a parallel resonator, and the resonance frequency of the lamb wave resonator is different from the resonance frequencies of the series resonator and the parallel resonator.

3. The piezoelectric filter of claim 2, wherein:

there are further said series resonators between the parallel resonator to which the second end of the lamb wave resonator is connected and the series resonator to which the first end of the lamb wave resonator is connected.

4. The piezoelectric filter structure of claim 3, wherein:

the piezoelectric filter has at least two grounded terminals to which the second terminals of the lamb wave resonators are connected or which correspond to different grounded terminals than the grounded terminals to which the parallel resonators adjacent to the series resonator to which the first terminals of the lamb wave resonators are connected or which correspond to the grounded terminals.

5. The piezoelectric filter of claim 4, wherein:

at least two of the plurality of parallel resonators share a common ground terminal.

6. The piezoelectric filter of claim 1, wherein:

the piezoelectric filter further includes a coupling circuit unit including:

an equipotential body;

a first lamb wave resonator, a first end of which is connected to the equipotential body and a second end of which is connected to a port of one series resonator; and

and the first end of the second lamb wave resonator is connected to the equipotential body, and the second end of the second lamb wave resonator is connected to a non-grounding port of the corresponding grounding inductor of one parallel resonator.

7. The piezoelectric filter of claim 6, wherein:

there are further said series resonators between the parallel resonator to which the second end of the second lamb wave resonator is connected and the series resonator to which the second end of the first lamb wave resonator is connected.

8. The piezoelectric filter of claim 1, wherein:

the piezoelectric filter further includes a coupling circuit unit including:

an equipotential body;

the first end of the first lamb wave resonator is connected to the equipotential body, and the second end of the first lamb wave resonator is connected to a non-grounding port of a corresponding grounding inductor of one parallel resonator; and

and a first end of the second lamb wave resonator is connected to the equipotential body, and a second end of the second lamb wave resonator is connected to a non-grounded port of the corresponding grounded inductor of the other parallel resonator.

9. The piezoelectric filter of claim 8, wherein:

the one parallel resonator is not adjacent to the other parallel resonator; and is

The one parallel resonator and the other parallel resonator do not share the same ground terminal.

10. The piezoelectric filter of claim 9, wherein:

the ground inductance to which the one parallel resonator is connected is not adjacent to the ground inductance to which the other parallel resonator is connected.

11. The piezoelectric filter according to any one of claims 6-10, wherein:

the piezoelectric filter is provided with a protection ring positioned at the periphery of a chip pattern area of the piezoelectric filter, and the protection ring forms the equipotential body; or

The piezoelectric filter has a first conductor disposed in a chip pattern region of the piezoelectric filter, the first conductor constituting the equipotential body; or

The piezoelectric filter is provided with a chip packaging part, and the chip packaging part is provided with a second conductor; the piezoelectric filter is provided with two electric connection through hole structures which are respectively and electrically connected with the second electric conductor; the two electric connection through hole structures and the second electric conductor form the equipotential body.

12. A method of increasing the suppression level of a filter, the filter being a piezoelectric filter according to claim 6 or 7, wherein the method comprises the steps of:

and adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator to enable the transmission zero point of the signal to move from the roll-off edge of the right side edge of the passband of the filter to a high frequency along the frequency.

13. A method of increasing the suppression level of a filter, the filter being a piezoelectric filter according to any one of claims 8-10, wherein the method comprises the steps of:

and adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator to enable the transmission zero point of the signal to move from the roll-off edge of the left edge of the passband of the filter to the low frequency.

14. A duplexer, comprising:

a transmit filter; and

the reception of the filter is carried out by a filter,

wherein:

at least one filter is a piezoelectric filter according to any one of claims 1-11.

15. The duplexer of claim 14 wherein:

the transmission filter comprises a piezoelectric filter according to claim 6 or 7;

the receive filter comprising a piezoelectric filter according to any one of claims 8-10.

16. A duplexer, comprising:

a transmit filter;

a receiving filter; and

at least one of the lamb wave resonators is,

wherein:

the series resonators and the parallel resonators of the transmitting filter and the receiving filter are film bulk acoustic resonators;

the at least one lamb wave resonator shares a piezoelectric layer with the series resonator, or the piezoelectric layer of the at least one lamb wave resonator and the piezoelectric layer of the series resonator are in the same layer.

17. The duplexer of claim 16 wherein:

one of the at least one lamb wave resonators has a first end connected to one of the filters and a second end connected to the other of the filters.

18. The duplexer of claim 17 wherein:

the first end of one lamb wave resonator is connected to the port of one series resonator of one filter, and the second end of the lamb wave resonator is connected to the non-grounding port of the corresponding grounding inductor of one parallel resonator of the other filter; or

The first end of one lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of one filter, and the second end of the one lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of the other filter.

19. The duplexer of claim 16 wherein:

the duplexer also comprises an equipotential body;

the at least one lamb wave resonator comprises a first lamb wave resonator and a second lamb wave resonator, and the first ends of the first lamb wave resonator and the second lamb wave resonator are connected to the equipotential body; and is

The second end of the first lamb wave resonator is connected to a port of a series resonator of one filter, and the second end of the second lamb wave resonator is connected to a non-grounded port of a corresponding grounded inductor of a parallel resonator of the other filter; or the second end of the first lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of one filter, and the second end of the second lamb wave resonator is connected to the non-ground port of the corresponding ground inductor of one parallel resonator of the other filter.

20. An electronic device having a piezoelectric filter according to any one of claims 1 to 11.