CN111342806B - Piezoelectric filter having lamb wave resonator, duplexer, and electronic device - Google Patents
Piezoelectric filter having lamb wave resonator, duplexer, and electronic device Download PDFInfo
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- CN111342806B CN111342806B CN201811550562.8A CN201811550562A CN111342806B CN 111342806 B CN111342806 B CN 111342806B CN 201811550562 A CN201811550562 A CN 201811550562A CN 111342806 B CN111342806 B CN 111342806B
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
- H03H9/545—Filters comprising resonators of piezo-electric or electrostrictive material including active elements
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/70—Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
- H03H9/703—Networks using bulk acoustic wave devices
- H03H9/706—Duplexers
Abstract
The present invention relates to a piezoelectric filter, comprising: a series-arm resonator unit having a plurality of series resonators; a parallel-arm resonator unit having a plurality of parallel resonators, each parallel resonator 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 inductance; and a lamb wave resonator, wherein: the lamb wave resonator shares a piezoelectric layer with the series resonator and 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 invention also relates to a duplexer and an electronic device with the structure.
Description
Technical Field
Embodiments of the present invention relate to the field of semiconductors, and more particularly, to a piezoelectric filter, a method of improving a filter suppression level, a duplexer having the piezoelectric filter, and an electronic device having the piezoelectric filter.
Background
With the rapid development of wireless communication technology nowadays, the application of miniaturized portable terminal equipment is also becoming wider, so that the demands for high-performance and small-sized radio frequency front-end modules and devices are also becoming urgent. In recent years, filter devices such as filters and diplexers based on thin film bulk acoustic resonators (Film Bulk Acoustic Resonator, abbreviated as FBAR) have been increasingly popular in the market. On the one hand, because of the excellent electrical properties of low insertion loss, steep transition characteristics, high selectivity, high power capacity, strong electrostatic discharge (ESD) resistance and the like, on the other hand, due to the small size and easy integration.
Currently, in order to meet the demand of increasingly stringent frequency resources, the suppression level of frequency selective devices such as filters, diplexers and the like at the front end of radio frequency to adjacent frequency bands is also increasingly high, and the thin film bulk acoustic resonator devices are also required to be improved and improved in this respect, so that the suppression level of stop band is improved, the insertion loss of pass bands cannot be greatly influenced, and meanwhile, the overall size of chips or devices is not increased as much as possible.
Common approaches are to increase inductance of the inductance on the series-parallel branch to change the resonator resonant frequency to increase the stop band rejection, or to increase the rejection point (notch) to improve the stop band rejection. However, these methods require the addition of additional reactive components, and the values of these components are often relatively large and difficult to implement on a chip. If this is achieved by winding wires on the substrate or adding discrete components off-chip, the number of layers and the size of the substrate must be increased, which inevitably results in an increase in the overall size of the filter or duplexer. Moreover, in practice, the added windings or discrete components are not ideal, and the loss introduced by the windings or discrete components is superimposed on the filter, resulting in deterioration of the insertion loss of the passband of the filter.
The method can improve stop band inhibition and simultaneously lead to the increase of chip loss and the large expansion of the whole size of the chip.
In addition, the passive integrated device (IPD) is fabricated on the filter chip, and special process steps are required to be added for the thin film bulk acoustic resonator device, which is disadvantageous in improving the production efficiency and reducing the cost. How to realize the improvement of the inhibition 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 alleviate or solve at least one of the above-mentioned problems occurring in 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-arm resonator unit having a plurality of parallel resonators, each parallel resonator 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 inductance; and a lamb wave resonator, wherein: the series resonators and the parallel resonators are film bulk acoustic resonators; and the lamb wave resonator shares a piezoelectric layer with the series resonator and 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.
In an alternative embodiment, the first end of the lamb wave resonator is connected to a port of one of the series resonators, the second end of the lamb wave resonator is connected to a non-grounded port of a corresponding grounded inductance of one of the parallel resonators, and the resonance frequency of the lamb wave resonator is different from the resonance frequencies of the series resonators and the parallel resonators.
Optionally, there is an additional series resonator 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 alternative embodiment, the piezoelectric filter further comprises a coupling circuit unit comprising: an equipotential body; a first lamb wave resonator having a first end connected to the equipotential body and a second end connected to a port of one of the series resonators; and a second lamb wave resonator having a first end connected to the equipotential body and a second end connected to a non-ground port of a corresponding ground inductance of one of the parallel resonators. Optionally, there is an additional series resonator 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 alternative embodiment, the piezoelectric filter further comprises a coupling circuit unit comprising: an equipotential body; a first lamb wave resonator, a first end of the first lamb wave resonator is connected to the equipotential body, and a second end of the first lamb wave resonator is connected to a non-ground port of a corresponding ground inductance of one parallel resonator; and a second lamb wave resonator having a first end connected to the equipotential body and a second end connected to a non-ground port of a corresponding ground inductance 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. 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 the chip pattern region of the piezoelectric filter, the guard ring constituting 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 has a chip package portion 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 electrical connection via structures and the second electrical conductor constitute the equipotential body.
According to another aspect of the embodiments of the present invention, there is provided a method of increasing the above-mentioned filter suppression level, the piezoelectric filter further including a coupling circuit unit including: an equipotential body; a first lamb wave resonator having a first end connected to the equipotential body and a second end connected to a port of one of the series resonators; and a second lamb wave resonator having a first end connected to the equipotential body and a second end connected to a non-grounded port of a corresponding ground inductance of one of the parallel resonators, wherein the method comprises the steps of: by adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator, the transmission zero of the signal is shifted to a high frequency from the roll-off edge frequency at the right edge of the filter passband.
Embodiments of the present invention also relate to a method of increasing a filter rejection level, the piezoelectric filter further comprising a coupling circuit unit comprising: an equipotential body; a first lamb wave resonator, a first end of the first lamb wave resonator is connected to the equipotential body, and a second end of the first lamb wave resonator is connected to a non-ground port of a corresponding ground inductance of one parallel resonator; and a second lamb wave resonator having a first end connected to the equipotential body and a second end connected to a non-grounded port of a corresponding ground inductance of another parallel resonator, wherein the method comprises the steps of: by adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator, the transmission zero of the signal is shifted from the roll-off edge frequency at the left edge of the filter passband to a low frequency.
Embodiments of the present invention also relate to a duplexer including: a transmit filter; and a receive filter, wherein: at least one filter is the piezoelectric filter 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 resonator is connected to one filter and a second end is connected to the other filter. In a further alternative embodiment, the first end of the one lamb wave resonator is connected to a port of one series resonator of one filter and the second end is connected to a non-grounded port of a corresponding grounded inductance of one parallel resonator of the other filter; or the first end of the lamb wave resonator is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of one filter, and the second end is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of the other filter.
The diplexer may also have an equipotential, in which case the at least one lamb wave resonator comprises a first lamb wave resonator and a second lamb wave resonator, both first ends of the first and second lamb wave resonators being connected to the equipotential; and a second end of the first lamb wave resonator is connected to a port of one series resonator of one filter, and a second end of the second lamb wave resonator is connected to a non-grounded port of a corresponding ground inductance of one parallel resonator of the other filter; or the second end of the first lamb wave resonator is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of one filter, and the second end of the second lamb wave resonator is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of the other filter.
The embodiment of the invention also relates to an electronic device with the piezoelectric filter.
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 the several views, and wherein:
FIG. 1 is a schematic diagram of a prior art film bulk acoustic resonator based reminding architecture filter;
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 a lamb wave resonator, (c) a schematic cross-sectional view of a thin film bulk acoustic wave resonator, and (d) - (f) schematic cross-sectional views of other examples of a lamb wave resonator, respectively;
FIG. 4 is a schematic diagram of a filter according to an exemplary embodiment of the invention;
FIG. 5 is a graph of the amplitude-frequency response simulation 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 the first equivalent capacitance and the second equivalent capacitance are exemplarily shown, and the guard ring acts as an equipotential;
Fig. 12 schematically shows a resonator arrangement in a filter chip, wherein the first equivalent capacitance and the second equivalent capacitance are exemplarily shown, and the first electrical conductor acts as an equipotential;
FIG. 13a is a schematic perspective view of a package structure disposed on a chip, wherein the relationship between an equipotential body and a first equivalent capacitance and a second equivalent capacitance 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 view of a duplexer to which the filter structure of the present invention is applied as an exemplary embodiment of the present invention;
fig. 14b is a schematic diagram of a prior art duplexer;
fig. 15a exemplarily shows transmission characteristic curves of the transmission filters of the diplexers in fig. 14a and 14b, wherein a thick line corresponds to the transmission filter of the diplexer in fig. 14a and a thin line corresponds to the transmission characteristic curve of the transmission filter of the diplexer in fig. 14 b;
FIG. 15b is an enlarged view of the square frame portion of FIG. 15 a;
fig. 16a exemplarily shows transmission characteristics of the reception filter of the duplexer of fig. 14a and 14b, wherein a thick line corresponds to the reception filter of the duplexer of fig. 14a and a thin line corresponds to the transmission characteristics of the reception filter of the duplexer of fig. 14 b;
FIG. 16b is an enlarged view of a block portion of FIG. 16 a;
fig. 17 is a schematic diagram of a duplexer according to still another exemplary embodiment of the present invention;
fig. 18 is a schematic diagram of a diplexer according to 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 below through examples and with reference to the accompanying drawings. In the specification, the same or similar reference numerals denote the same or similar components. The following description of embodiments of the present invention with reference to the accompanying drawings is intended to illustrate the general inventive concept and should not be taken as limiting the invention.
The present invention proposes a filter having both a Film Bulk Acoustic Resonator (FBAR) and a lamb wave resonator (Lamb wave resonator, abbreviated LWR) that can improve the suppression level for adjacent band signals without causing an increase in passband insertion loss. In addition, the filter has no problems of large increase of the whole size of a chip, increase of complexity of a manufacturing process and the like caused by introducing additional discrete reactive devices, thereby saving space and reducing cost.
The lamb wave resonator has the working principle that: lamb waves generated by piezoelectric materials form standing waves inside the resonator, whose electrical properties manifest themselves as resonances 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 the thin film bulk acoustic resonator, the schematic diagram of the front structure is shown in (a) of fig. 3, and at least one side above or below the piezoelectric layer is provided with an electrode which receives an electrical signal and excites the resonator to work. The electrodes are typically in the shape of interdigital transducers (Interdigital transducer, abbreviated as IDT), the interdigital transducers of the same network are connected together at the finger roots, and the distance p between two adjacent electrodes is 1/2 of the lamb wave wavelength (lambda). In addition to the IDT structure on one side of the piezoelectric layer, the electrode on the other side of the piezoelectric layer may be fabricated in the following four structures: the cross-sectional views of the electrode-less, potential-less suspension electrode, ground electrode, and IDT electrode mirror-symmetrical to the opposite side IDT are shown in fig. 3 (d), (e), and (f), respectively, and the IDT electrode mirror-symmetrical to the opposite side IDT is shown in fig. 3 (b).
The LWR fabrication process is exactly the same as the FBAR. Taking LWR with IDT structures at the top and bottom as an example, a cross-sectional view of a lamb wave resonator is shown in fig. 3 (b). Etching an air cavity on a silicon substrate, and filling a sacrificial layer material in the air cavity; then depositing a lower electrode made of molybdenum, tungsten and other metals, and etching the lower electrode to form an IDT pattern; then depositing piezoelectric material (such as aluminum nitride) and upper electrode material (which is generally the same as the lower electrode material) in sequence; etching the upper electrode to form an IDT pattern; etching the piezoelectric layer material to form an air reflection grating, wherein the air reflection grating has the function of facilitating the reflection of sound waves, thereby forming standing waves and generating resonance; through the etched reflecting grating, 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 staggered and mirror-symmetrical in the upper and lower layers. In fig. 3 (c) is a schematic cross-sectional view of a thin film bulk acoustic resonator, it can be seen that the thin 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 under the sandwich structure. Unlike the lamb wave resonator, the thin film bulk acoustic resonator is generally formed of a planar top electrode and bottom electrode, and does not need to be formed in the shape of an IDT. The film bulk acoustic resonator has the same preparation process flow as the lamb wave resonator, and can be conveniently manufactured on a wafer.
Lamb waves are classified into symmetrical lamb waves (symmetric Lamb wave) and anti-symmetrical lamb waves (antisymmetric Lamb wave) according to their vibration characteristics. Solutions to the lamb wave equation due to periodicity, there are An infinite number of solutions, and the series of symmetric and anti-symmetric solutions are referred to as S0, S1, S2 … Sn, and A0, A1, A2 … An, respectively. The resonant frequency f=v/λ of the resonator, where v is the lamb wave velocity. Because each lamb wave can generate resonance and the wave speed of each lamb wave is different, a plurality of resonances can be detected in the same lamb wave resonator, and each resonance frequency is different, and a designer can select any resonance point to be utilized according to the requirement.
The electrical model of the lamb wave resonator is shown in fig. 2 (a), and its equivalent circuit can be represented by the 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. Because the lamb wave resonator and the film bulk acoustic wave resonator have different working modes, the lamb wave resonator and the film bulk acoustic wave resonator have different resonant frequencies under the same laminated structure. Thus, when the frequency is the resonant frequency of the thin film bulk acoustic resonator, the lamb wave resonator corresponds to a capacitance for the thin film bulk acoustic resonator.
According to the invention, a lamb wave resonator is introduced into an FBAR filter device, so that the suppression degree and the isolation degree are improved.
A conventional ladder filter structure based on a film bulk acoustic resonator is shown in fig. 1. Port 131 is a signal input (or output) port, port 132 is a signal output (or input) port, and a signal to be filtered is input from port 131 (or 132) and output from port 132 (or 131). Series inductor 121 is connected between port 131 and resonator 101, and series inductor 122 is connected between port 132 and resonator 104. The series-arm resonators 101, 102, 103, 104 are connected in series between a series inductance 121 and a series inductance 122. One port of the parallel-arm resonator 111 is connected at a position between the series-arm resonators 101, 102, and the other port is connected to one port of the ground inductance 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 inductance 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 inductance 125. One port of the parallel-arm resonator 114 is connected between the series-arm resonator 104 and the series inductor 122, and the other port is connected to one port of the ground inductor 126. The other ports of the grounding inductors 123, 124, 125, 126 are 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, in which the lamb wave resonator LWR is connected across the input of the first series resonator 101 and the ground of the last parallel resonator 114, although other connection methods are also possible. The width of IDT electrode of LWR is 10um, the interval of electrode is 15um, the length of electrode is 100um, there are 5 pairs of mirror image electrodes on the upper and lower surfaces of piezoelectric layer respectively, its equivalent capacitance value that realizes is about 0.5pF.
Fig. 5 is a graph of the amplitude-frequency response simulation of the embodiment of fig. 4, which is a band 7 transmit filter, with a passband ranging from 2500MHz to 2570MHz (i.e., the transmit band of LTE band 7), requiring a better suppression level at 2620MHz to 2690MHz (i.e., the receive band of LTE band 7), and worse than-55 dB at worst. The thick solid line is the 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, while the inhibition near 2620MHz is slightly worse than the original inhibition, but still has-60 dB, the inhibition degree at 2690MHz is up to-56.8 dB, and 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, and the effective resonance area is far lower than the passband frequency of the filter, so that 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 resonator is provided in the filter, the filter can improve the suppression level for the adjacent band signals without causing an increase in passband insertion loss.
In addition, when the lamb wave resonator is arranged in the filter, the problems of great increase of the whole size of a chip, increase of the complexity of a manufacturing process and the like caused by introducing additional discrete reactive devices are avoided, so that the space is saved and the cost is reduced.
Fig. 6 is a schematic diagram of a filter capable of improving the high frequency near-stop band rejection level above the passband right roll-off edge frequency in accordance with another example embodiment of the invention.
In fig. 6, a port 131 is a signal input (or output) port, a 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 inductor 121 is connected between port 131 and resonator 101, and series inductor 122 is connected between port 132 and resonator 104. The series-arm resonators 101, 102, 103, 104 are connected in series between a series inductance 121 and a series inductance 122. One port of the parallel-arm resonator 111 is connected at a position between the series-arm resonators 101, 102, and the other port is connected to one port of the ground inductance 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 inductance 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 inductance 125. One port of the parallel-arm resonator 114 is connected between the series-arm resonator 104 and the series inductor 122, and the other port is connected to one port of the ground inductor 126. The other ports of the grounding inductors 123, 124, 125, 126 are grounded.
In fig. 6, a lamb wave resonator LWR1 is also added between the equipotential body U and the node S1; a lamb wave resonator LWR2 is added between the equipotential U and the node P4.
In fig. 6, the resonance frequencies fs of the series-arm resonators 101 to 104 may be the same or different from each other, and the resonance frequencies fs' of the parallel-arm resonators 111 to 114 may be the same or different from each other. The resonance frequency fs of each series-arm resonator is higher than the resonance frequency fs' of each parallel-arm.
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 point of the signal can move to high frequency from the roll-off edge frequency of the right side edge of the pass band of the filter, and the moving quantity can be controlled by adjusting the values of the equivalent capacitances of the two lamb wave resonators. Thus, the level of suppression around the frequency can be improved by adjusting the equivalent capacitance of the two lamb wave resonators to shift the transmission zero to the frequency required in the high-frequency near-stop band. 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 respectively adjusted, the realization flexibility is increased while the realizability is solved. The specific technical effects achieved with this construction will be described in detail in the following embodiments, referring to fig. 15a and 15b.
It should be noted that, the connection manner of the two lamb wave resonators connected to the equipotential conductor U in fig. 6 is not only, for example, one port of the lamb wave resonator LWR2 may be connected to another node other than P4.
In a further embodiment, the lamb wave resonator LWR1 is connected between one port node of a certain series resonator and an equipotential body, and the lamb wave resonator LWR2 is connected between a connection node of a corresponding grounding inductance of a certain parallel resonator and an equipotential body, the parallel resonator not being adjacent to the series resonator; in a further embodiment, the parallel resonator is not grounded to a 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 should be 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 LWR2. In other words, in these figures, although shown as equivalent capacitances, they are corresponding lamb wave resonators.
The example given in fig. 6 is a case where 4 parallel-arm resonators are respectively grounded through corresponding grounding inductances, and some parallel-arm resonators may be combined and grounded through a common grounding inductance according to design requirements. Some variant embodiments in this case are given in fig. 8a-8f, which can achieve an effect of improving the level of inhibition.
Based on the structure of fig. 1, the invention also proposes a filter structure capable of improving the rejection level in fig. 9, which can improve the low-frequency near-stop band rejection level below the passband left roll-off edge frequency.
In fig. 9, a port 131 is a signal input (or output) port, a 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 inductor 121 is connected between port 131 and resonator 101, and series inductor 122 is connected between port 132 and resonator 104. The series-arm resonators 101, 102, 103, 104 are connected in series between a series inductance 121 and a series inductance 122. One port of the parallel-arm resonator 111 is connected at a position between the series-arm resonators 101, 102, and the other port is connected to one port of the ground inductance 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 inductance 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 inductance 125. One port of the parallel-arm resonator 114 is connected between the series-arm resonator 104 and the series inductor 122, and the other port is connected to one port of the ground inductor 126. The other ports of the grounding inductors 123, 124, 125, 126 are grounded, respectively.
As shown in fig. 9, an equivalent capacitance Ca is also added between the equipotential body U and the node P1; an equivalent capacitance Cb is added between the equipotential body U and the node P4.
In fig. 9, the resonance frequencies fs of the series-arm resonators 101 to 104 may be the same or different from each other, and the resonance frequencies fs' of the parallel-arm resonators 111 to 114 may be the same or different from each other. The resonance frequency fs of each series-arm resonator is higher than the resonance frequency fs' of each parallel-arm.
The equipotential body U and the equivalent capacitors Ca and Cb form a signal coupling circuit structure or a coupling circuit unit, and in fig. 9, the signal coupling circuit structure is added to enable the transmission zero point of the signal to move from the roll-off edge frequency of the left edge of the passband of the filter to low frequency, and the moving amount can be controlled by adjusting the values of the equivalent capacitors Ca and Cb. Thus, by adjusting the equivalent capacitances Ca and Cb to shift 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 flexibility of implementation is increased while solving the realisation. The specific technical effects that can be achieved with this particular structure will be described in detail in the following embodiments, referring to fig. 16a and 16b.
It should be noted that, in fig. 9, the equivalent capacitors Ca and Cb coupled to the equipotential body U are not limited to the same connection, and the ports of the equivalent capacitor Cb may be connected to other nodes except the P4 node. 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 grounding inductor, and the equivalent capacitor Cb may be connected between the equipotential body U and a node between the other parallel resonator and the corresponding grounding inductor. In an alternative embodiment, the two parallel resonators are not adjacent or commonly grounded through a common ground inductance, and in a further alternative embodiment, the corresponding ground inductances of the two parallel resonators are not adjacent.
Fig. 10a-10d show several variant embodiments of fig. 9, respectively, which can also achieve an improved level of inhibition.
What needs to be specifically stated here is: each series resonator such as 101 in combination with a parallel resonator such as 111 adjacent thereto is referred to as a stage, so figures 6-10 d and the like all show examples of a 4-stage FBAR ladder filter. The present invention is merely used as an example to facilitate detailed description of the details of the invention, and the application scope of the present invention is not limited to the case of the 4-level ladder architecture, but may be applied to any case of more or less levels, and may be other architectures.
The implementation of equipotential bodies in the above-described filter structure is exemplified below.
In practice, a guard ring around the periphery of the pattern area of the FBAR chip may be used as the equipotential body U. In the first special structure of fig. 6, the resonator arrangement in one FBAR chip is shown in fig. 11, and a peripheral guard ring is used as the equipotential body U.
In practice, a conductive or first conductive body (pad) with an equipotential difference may be added as the equipotential body U in the pattern region of the FBAR chip. In the first special structure of fig. 6, the resonator arrangement in one FBAR chip may also be as shown in fig. 12, i.e. a first electric conductor added separately is used as the equipotential body U.
In practice, a through hole via connected to the same conductive pad on the chip package cap may be used as the equipotential body U. 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 electrical conductor pad on the package structure as an equipotential body U, thereby introducing equivalent capacitances Ca and Cb. Fig. 13b is a top plan view of the chip portion from above looking down with the package structure cap omitted.
Fig. 11-13b illustrate the implementation of the equipotential body U in practice by taking the filter structure in fig. 6 as an example, and all these implementations can be used to implement the second specific structure in fig. 9 as well, which is not repeated here.
Fig. 14a is a schematic diagram of a duplexer 100, in which: 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 with external equipment such as a radio frequency signal generating circuit and the like, and is used for transmitting radio frequency signals generated by the external equipment into the transmitting filter 101; the other port of the transmission filter 101 is connected to a matching network (match network) 103 for sending the filtered signal to the matching network; one port of the reception filter 102 is connected to a port 106, which can be connected to a post-stage circuit such as a low noise amplifier or the like; the other port of the receiving filter 102 is connected to the matching network 103, and is used for transmitting the signal received by the antenna into the receiving filter 102; a matching network 103 is connected between the antenna 104 and the transmit and receive filters 101, 102 for adjusting the impedance matching of the antenna ports. 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 a filter structure proposed by the present invention, for example as shown in fig. 5.
For comparison, a duplexer 110 is also provided, the structure of which is shown in fig. 14b, and the components and functions are the same as those of fig. 14a, so that the description thereof will not be repeated. The difference is that the transmit filter (TX filter) 111 and the receive filter (RX filter) 112 use the general ladder-shaped architecture given in fig. 1 instead of the specific structure given in the present invention, and no special signal coupling circuit structure consisting of the equipotential body U and the equivalent capacitances Ca and Cb is used.
Fig. 15a and 16a show transmission characteristics of the receive and transmit filters of the diplexers 100 and 110, respectively. The passband frequency of the duplexer in this example, the transmit filter, is in the range 1710MHz-1785MHz, the center frequency can be considered to be approximately 1749MHz; the passband frequency of the receive filter is in the range 1805MHz-1880MHz, and the center frequency can be considered to be about 1844MHz. In order to minimize the interaction between the two filters, it is desirable in the design to maximize the degree of rejection of the two filters within the passband of the pair, particularly around the center frequency. In this embodiment, only the duplexer in this frequency band is used for illustration, and the filter structure of this patent is also applicable to the duplexers and filters in other frequency bands.
Fig. 15a shows exemplary transmission characteristic curves of the transmission filters 101 and 111, wherein 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 structure of the transmit filter 101 is shown in fig. 2, in which a special coupling circuit structure consisting of an equipotential body U and equivalent capacitances Ca, cb is used, and the structure functions to shift the transmission zero of the signal from the roll-off point on the right side edge of the passband to a position of about 1844MHz toward the high frequency, and substantially coincides with the center frequency of the receive filter 102. It can be seen from fig. 15a that the shifted transmission zero forms a deeper suppression point at 1844MHz, the suppression level reaches around-78 dB (marked m1 in the figure), and the suppression level in the range around this point is significantly improved. Without the use of the equipotential U and the equivalent capacitance Ca, cb structure of the transmit filter 111, the transmission characteristic is shown as a thin line, the suppression level at 1844MHz is only about-56 dB (indicated by m2 in the figure), and the suppression level in the range around this point is significantly worse.
In addition, fig. 15b is an enlarged view of the portion in the square frame in fig. 15a, and it can be seen that the two curves in the passband are completely overlapped, illustrating that no degradation of the insertion loss of the passband occurs while improving the out-of-band rejection after using the structure proposed by the present invention, such as that shown in fig. 6.
Fig. 16a shows an exemplary transmission characteristic of the reception 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 of an equipotential body U and equivalent capacitances Ca, cb is used, and the configuration functions to shift the transmission zero point of the signal from the roll-off position at the left edge of the passband to a position of about 1749MHz toward a low frequency, 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, the suppression level reaches around-78 dB (marked m1 in the figure), and the suppression level in the range around this point is significantly improved. Without the use of the equipotential U and the equivalent capacitance Ca, cb structure of the transmit filter 112, the transmission characteristic is shown as a thin line, the suppression level at 1749MHz is only about-59 dB (marked m2 in the figure), and the suppression level in the range around this point is significantly worse.
In addition, fig. 16b is an enlarged view of the portion in the square frame in fig. 16a, and it can be seen that the two curves in the passband are completely overlapped, which illustrates that no degradation of the insertion loss of the passband occurs while improving the out-of-band rejection after using the filter structure proposed by the present invention, such as that shown in fig. 9.
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, is a duplexer with an LTE frequency band 7, wherein the transmitting frequency band is 2500MHz-2570MHz, the receiving frequency band is 2620MHz-2690MHz, and the transmitting filter is an embodiment shown in fig. 4, but can also be an embodiment shown in fig. 6, and the technical effects of the two are similar.
Fig. 18 is a schematic diagram of a duplexer according to an exemplary embodiment of the present invention. The duplexer is a duplexer composed of two FBAR filters, except that a lamb wave resonator LWR is connected across 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 without significant deterioration of the isolation at other positions.
It should be noted that fig. 18 only shows one lamb wave resonator disposed between two separate FBAR filters. In alternative embodiments, multiple lamb wave resonators may also be provided. In fig. 18, one end of the lamb wave resonator is connected to a port of one series resonator of one filter and the other end is connected to a non-grounded port of a corresponding ground inductance of one parallel resonator of the other filter, but the connection manner of the lamb wave resonator is not limited thereto, for example, one end of the lamb wave resonator is connected to a non-grounded port of a corresponding ground inductance of one parallel resonator of one filter and the other end is connected to a non-grounded port of a corresponding ground inductance of one parallel resonator of the other filter.
Furthermore, similar to the embodiment of the invention in which an equipotential is provided in fig. 5-10d, two filters may also be connected by two lamb wave resonators and an equipotential.
Based on the above, the present invention proposes a piezoelectric filter including: a series-arm resonator unit having a plurality of series resonators; a parallel-arm resonator unit having a plurality of parallel resonators, each parallel resonator 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 inductance; and a lamb wave resonator, wherein: the lamb wave resonator and the series resonator share a piezoelectric layer by a parallel resonator, or the piezoelectric layer of the lamb wave resonator is positioned on 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 the chip, increase of the complexity of the manufacturing process and the like caused by introducing additional discrete reactive devices, thereby saving space and reducing cost.
Referring to fig. 4 for example, the first end of the lamb wave resonator is connected to a port of one series resonator and the second end of the lamb wave resonator is connected to a non-grounded port of a corresponding ground inductance of one parallel resonator. Further, there is an additional series resonator 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.
Referring to fig. 6, for example, the piezoelectric filter may further include a coupling circuit unit including: an equipotential body; a first lamb wave resonator having a first end connected to the equipotential body and a second end connected to a port of one of the series resonators; and a second lamb wave resonator having a first end connected to the equipotential body and a second end connected to a non-ground port of a corresponding ground inductance of one of the parallel resonators. Further, there is an additional series resonator 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.
Referring to fig. 9 for example, the piezoelectric filter may further include a coupling circuit unit including: an equipotential body; a first lamb wave resonator, a first end of the first lamb wave resonator is connected to the equipotential body, and a second end of the first lamb wave resonator is connected to a non-ground port of a corresponding ground inductance of one parallel resonator; and a second lamb wave resonator having a first end connected to the equipotential body and a second end connected to a non-ground port of a corresponding ground inductance 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.
For example, referring to fig. 14a, 17, the present invention also proposes a diplexer comprising: a transmit filter; and a receive filter, wherein: at least one filter is the piezoelectric filter described above.
As another example, referring to fig. 18, the present invention further provides 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.
Accordingly, the present invention proposes a method of increasing the suppression level of a filter, such as the bandpass filter shown in fig. 6, comprising the steps of: by adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator, the transmission zero of the signal is shifted to a high frequency from the roll-off edge frequency at the right edge of the filter passband.
The invention also proposes a method of increasing the suppression level of a filter, such as the bandpass filter shown in fig. 9, comprising the steps of: by adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator, the transmission zero of the signal is shifted from the roll-off edge frequency at the left edge of the filter passband to a low frequency.
The embodiment of the invention also relates to electronic equipment comprising the band-pass filter. It should be noted that, the electronic devices herein include, but are not limited to, intermediate products such as a radio frequency front end, a filtering and amplifying module, and end products such as a mobile phone, a 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 (18)
1. A piezoelectric filter, comprising:
a series-arm resonator unit having a plurality of series resonators;
a parallel-arm resonator unit having a plurality of parallel resonators, each parallel resonator 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 inductance; and
a lamb wave resonator is provided which has a plurality of resonators,
wherein:
the series resonators and the parallel resonators are film bulk acoustic resonators; and is also provided with
The lamb wave resonator shares a piezoelectric layer with the series resonator and the parallel resonator, or the piezoelectric layer of the lamb wave resonator is positioned on the same layer as the piezoelectric layers of the series resonator and the parallel resonator;
The first end of the lamb wave resonator is connected to a port of one series resonator, the second end of the lamb wave resonator is connected to a non-grounded port of a corresponding grounded inductance of one 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.
2. A piezoelectric filter according to claim 1, wherein:
there is also an additional series resonator 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.
3. A piezoelectric filter structure according to claim 2, wherein:
the piezoelectric filter has at least two ground terminals, and the second terminal of the lamb wave resonator is connected to or corresponds to a ground terminal different from that of a parallel resonator adjacent to the series resonator to which the first terminal of the lamb wave resonator is connected.
4. A piezoelectric filter according to claim 3, wherein:
at least two parallel resonators of the plurality of parallel resonators share a same ground.
5. A piezoelectric filter according to claim 1, wherein:
The piezoelectric filter further includes a coupling circuit unit including:
an equipotential body;
a first lamb wave resonator having a first end connected to the equipotential body and a second end connected to a port of one of the series resonators; 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 a corresponding grounding inductor of one parallel resonator.
6. A piezoelectric filter according to claim 5, wherein:
there is also an additional series resonator 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.
7. A piezoelectric filter according to 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 the first lamb wave resonator is connected to the equipotential body, and a second end of the first lamb wave resonator is connected to a non-ground port of a corresponding ground inductance of one parallel 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 a corresponding grounding inductor of the other parallel resonator.
8. A piezoelectric filter according to claim 7, wherein:
the one parallel resonator is not adjacent to the other parallel resonator; and is also provided with
The one parallel resonator and the other parallel resonator do not share the same ground.
9. A piezoelectric filter according to claim 8, 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.
10. A piezoelectric filter according to any one of claims 5 to 9, wherein:
the piezoelectric filter has a guard ring located at the periphery of a chip pattern region of the piezoelectric filter, the guard ring constituting the equipotential body; or alternatively
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 alternatively
The piezoelectric filter has a chip package portion 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 electrical connection via structures and the second electrical conductor constitute the equipotential body.
11. A method of increasing the suppression level of a filter, which is a piezoelectric filter according to claim 5 or 6, wherein the method comprises the steps of:
by adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator, the transmission zero of the signal is shifted to a high frequency from the roll-off edge frequency at the right edge of the filter passband.
12. A method of increasing the suppression level of a filter, which is a piezoelectric filter according to any one of claims 7-9, wherein the method comprises the steps of:
by adjusting at least one of the equivalent capacitance of the first lamb wave resonator and the equivalent capacitance of the second lamb wave resonator, the transmission zero of the signal is shifted from the roll-off edge frequency at the left edge of the filter passband to a low frequency.
13. A diplexer, comprising:
a transmit filter; and
the frequency of the reception filter is set to be the same as the frequency of the reception filter,
wherein:
at least one filter is a piezoelectric filter according to any one of claims 1-10.
14. The diplexer of claim 13, wherein:
the transmission filter comprising a piezoelectric filter according to claim 5 or 6;
The receiving filter comprising a piezoelectric filter according to any one of claims 7-9.
15. A diplexer, comprising:
a transmit filter;
a receiving filter; and
at least one lamb wave resonator is provided,
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;
one lamb wave resonator of the at least one lamb wave resonator has a first end connected to one filter and a second end connected to the other filter;
the first end of the 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 ground inductance of one parallel resonator of the other filter.
16. The diplexer of claim 15, wherein:
the first end of the lamb wave resonator is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of one filter, and the second end is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of the other filter.
17. The diplexer of claim 15, wherein:
the duplexer further comprises an equipotential body;
the at least one lamb wave resonator comprises 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 connected to the equipotential body; and is also provided with
The second end of the first lamb wave resonator is connected to a port of one 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 grounding inductance of one parallel resonator of the other filter; or the second end of the first lamb wave resonator is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of one filter, and the second end of the second lamb wave resonator is connected to the non-grounded port of the corresponding grounded inductance of one parallel resonator of the other filter.
18. An electronic device having the piezoelectric filter according to any one of claims 1 to 10.
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