CN111211754B

CN111211754B - Method for adjusting FBAR parasitic component, filter, multiplexer and communication equipment

Info

Publication number: CN111211754B
Application number: CN202010088346.7A
Authority: CN
Inventors: 庞慰; 柴竹青; 郑云卓
Original assignee: ROFS Microsystem Tianjin Co Ltd
Current assignee: ROFS Microsystem Tianjin Co Ltd
Priority date: 2020-02-12
Filing date: 2020-02-12
Publication date: 2021-02-26
Anticipated expiration: 2040-02-12
Also published as: WO2021159881A1; CN111211754A

Abstract

The invention provides a method for adjusting FBAR parasitic components, a filter, a multiplexer and communication equipment, which change the positions of the parasitic components appearing in a frequency domain so as to improve the performance of a pass band. In this method, a capacitor is connected in series with the FBAR to form a series body, and the start position of a parasitic component in an amplitude-frequency curve of the series body is shifted to a frequency band below a series resonance frequency.

Description

Method for adjusting FBAR parasitic component, filter, multiplexer and communication equipment

Technical Field

The invention relates to the technical field of radio frequency communication, in particular to a method for adjusting FBAR parasitic components, a filter, a multiplexer and communication equipment.

Background

In the front end of radio frequency communication, there are increasingly high requirements for the performance of filters, duplexers and multiplexers, wherein the passband performance is especially important, for example, the requirements for passband indexes such as insertion loss, fluctuation, ripple, echo and the like in the 5G era are increasingly stringent.

Because a Film Bulk Acoustic Resonator (FBAR) has a parasitic component in a frequency band below a series resonance frequency point, that is, the starting frequency point of the parasitic component is basically coincident with the series resonance frequency point of the FBAR Resonator, the filter, the duplexer and the multiplexer formed also have a parasitic component in a passband, and the parasitic component causes adverse effects on passband indexes such as insertion loss, fluctuation, ripple, group delay fluctuation and the like of the filter, the duplexer and the multiplexer.

Disclosure of Invention

Accordingly, the present invention provides a method, a filter, a multiplexer, and a communication device for adjusting parasitic components of FBARs, so as to change the positions of the parasitic components appearing in the frequency domain, thereby improving the performance of the pass band.

To achieve the above object, according to one aspect of the present invention, a method of adjusting parasitic components of a film bulk acoustic resonator FBAR is provided.

In the method for adjusting the parasitic component of the FBAR of the film bulk acoustic resonator, a capacitor is connected with the FBAR in series to form a series connection body, so that the initial position of the parasitic component in an amplitude-frequency curve of the series connection body moves to a frequency band below a series resonance frequency point, and the method further comprises the following steps: adjusting the thickness of one or more of the upper electrode, the lower electrode and the piezoelectric layer of the FBAR, and/or adjusting the capacitance value of the capacitor, so that the series resonance frequency and the parallel resonance frequency of the series body are respectively located in the neighborhood of the preset width of the series resonance frequency and the parallel resonance frequency of the FBAR.

Optionally, the method further comprises: the upper electrode is composed of an electrode material and a passivation layer above the electrode material; the thickness of the upper electrode is the sum of the thickness of the electrode material and the thickness of an equivalent electrode material, and the acoustic impedance of the equivalent electrode material is equal to that of the passivation layer.

Optionally, the method further comprises: for constructing a filter using the FBARs, part or all of the FBARs in the filter are replaced by the series, so that the spurious components in the amplitude-frequency curve of the filter are located outside the pass band.

Optionally, all of the series FBARs in the filter are replaced with the series. Because the series-arm resonator adopts the resonator structure of the invention, the starting position of the parasitic ripple is far below Fs, so that the first-order filter is not influenced by the parasitic ripple of the series-arm resonator, thereby improving the pass-band performance indexes of the first-order filter, such as insertion loss, fluctuation, ripple, group delay fluctuation and the like.

Optionally, all of the series FBARs and at least 1 shunt FBARs in the filter are replaced with the series body. In the case where the associated FBAR is also replaced with the tandem, it contributes to further reducing the ripple of the transition band.

According to another aspect of the present invention, there is provided a filter comprising thin film bulk acoustic resonators FBARs, each series FBAR of the filter having a capacitance in series; the thickness of one or more of the upper electrode, lower electrode, piezoelectric layer of the FBAR and/or the capacitance value of the capacitor are such that the series and parallel resonant frequencies of the series body are within the vicinity of a preset width of the series and parallel resonant frequencies of the FBAR, respectively.

Optionally, one or more shunt FBARs of the filter are connected in series with a capacitor.

According to another aspect of the present invention, there is provided a multiplexer including the filter of the present invention.

According to yet another aspect of the present invention, there is provided a communication device comprising the filter of the present invention.

Compared with the prior art, the invention has the beneficial effects that:

(1) the novel resonance unit structure provided by the invention is obtained by connecting the capacitor and the FBAR in series, the initial position of the parasitic component in the novel resonance unit can move to the frequency band below the series resonance frequency point, and when the novel resonance unit forms the filter, the duplexer and the multiplexer, the parasitic component can be moved out of the passband, so that the indexes of insertion loss, fluctuation, ripple, group delay fluctuation and the like of the filter, the duplexer and the multiplexer are improved;

(2) the filter composed of the new resonance units is not influenced by parasitic ripples of the series-branch resonators, so that the passband performances of the filter, such as insertion loss, fluctuation, ripples, group delay fluctuation and the like, are improved.

Drawings

The drawings are included to provide a better understanding of the invention and are not to be construed as unduly limiting the invention. Wherein:

fig. 1 is a topological structure diagram of a conventional FBAR resonator;

fig. 2 is a schematic structural view of a conventional FBAR resonator;

FIG. 3 is a graph of a conventional FBAR resonator;

FIG. 4 is a diagram of a topology of a novel resonating unit according to an embodiment;

FIG. 5 is a graph of a novel resonant cell according to an embodiment;

FIG. 6 is a prior art topology diagram of a first order filter;

FIG. 7 is a graph of a prior art first order filter;

FIG. 8 is a graph of the frequency response of the novel resonant cell according to an embodiment;

FIG. 9 is a topology diagram of a first-order filter according to the second embodiment;

FIG. 10 is a graph of a first order filter according to the second embodiment;

fig. 11 is a topological structure diagram of a band pass filter composed of conventional FBAR resonators;

fig. 12 and 13 are graphs showing the pass band response of a band pass filter composed of conventional FBAR resonators;

FIG. 14 is a topology diagram of a band pass filter according to a third embodiment;

fig. 15 and 16 are graphs showing the pass band response of the band pass filter composed of the novel resonant unit according to the embodiment of the present invention;

FIG. 17 is a graph comparing curves of two band pass filters;

fig. 18 is a structural view of a capacitor in the novel resonance unit according to the first embodiment;

fig. 19 is a topology diagram of a novel resonant cell according to an embodiment formed by cascading interdigital capacitors with conventional FBAR resonators;

fig. 20 is a topology diagram of a novel resonant unit according to an embodiment formed after a plate capacitor is cascaded with an existing FBAR resonator;

fig. 21 is a first topological structure diagram of a band-pass filter composed of the novel resonant unit according to the first embodiment;

fig. 22 is a second topology diagram of a bandpass filter composed of the novel resonant cells proposed in the first embodiment;

fig. 23 is a first topological structure diagram of a band pass filter using existing FBAR resonators in three parallel branches using the novel resonance unit proposed in the first embodiment of the series branch;

fig. 24 is a second topology diagram of a band pass filter in which a series branch employs the novel resonance unit proposed in the first embodiment and existing FBAR resonators are employed in three parallel branches;

fig. 25 and 26 are frequency response graphs of the band pass filter shown in fig. 23.

Detailed Description

The invention is further described with reference to the following figures and examples.

Fig. 1 is a topological structure diagram of a conventional FBAR resonator. As shown in fig. 1, one end of the FBAR resonator 11 is connected to the signal input port 12, and the other end is grounded. The Z parameter is measured from the signal input port 12, and the corresponding relation curve of the Z parameter amplitude value and the frequency of the FBAR resonator 11 is obtained, as shown in fig. 3. In fig. 3, the vertical axis represents the amplitude value of the Z parameter, the horizontal axis represents the frequency, Fs represents the series resonance frequency, and Fp represents the parallel resonance frequency. Spurious ripples occur in the frequency range below Fs due to the effects of the inherent parasitics of the FBAR resonator (i.e., spurious ripples start at a starting location from Fs, spurious ripples below Fs, and none above Fs).

Fig. 2 is a schematic structural view of a conventional FBAR resonator. In fig. 2, the typical FBAR resonator structure is composed of three stacked layers, i.e., a lower electrode 21, a piezoelectric layer 22 and an upper electrode 23, the FBAR resonator is located on a silicon substrate 24, an air slot 25 is opened on the silicon substrate, and the air slot 25 is used for introducing air, so that air is located above the upper electrode and below the lower electrode of the FBAR resonator. By adjusting the thicknesses of the lower electrode 21, the piezoelectric layer 22, and the upper electrode 23, the positions of the series resonance frequency Fs and the parallel resonance frequency Fp can be controlled. It should be noted that, in order to protect the resonator from oxidation due to environmental influences, a passivation layer is usually formed above the upper electrode, and the passivation layer may be made of a non-metallic material with relatively stable properties, such as silicon dioxide, or even the same material as the piezoelectric layer, such as aluminum nitride. The material of the layer has different acoustic impedance from the electrode material, but can be converted into equal thickness with the same acoustic impedance as the upper electrode material, and is superposed on the thickness of the upper electrode, the superposed upper electrode thickness is used to be equivalent to the combined action of the upper electrode and the passivation layer, the passivation layer is omitted in the figure for the sake of simplicity, but when the parasitic component position is adjusted by adjusting the thickness of each layer of the resonator, the thickness influence of the passivation layer should also be considered.

Fig. 4 is a topological structure diagram of a novel resonance unit according to the present embodiment. As shown in fig. 4, the resonant unit 4 includes a capacitor 42 and an FBAR resonator 41 connected in series as a series body, one end of the capacitor 42 and the FBAR resonator 41 connected in series is connected to a signal input port 43, and the other end is grounded.

Measuring the Z parameter from the signal input port 43 to obtain a new corresponding relationship curve between the Z parameter amplitude value and the frequency of the resonance unit 4, as shown in fig. 5, where the vertical axis represents the amplitude value of the Z parameter, and the horizontal axis represents the frequency; fs represents the series resonance frequency and Fp represents the parallel resonance frequency.

The frequency of Fp does not change much compared to the conventional FBAR resonator 11, and the frequency of Fs moves to a high frequency. The starting position of the parasitic ripple does not change much and is still near 3650 MHz. As can be seen from the figure, the new resonance unit 4 proposed by the present embodiment can separate the start position of the parasitic ripple from the position of Fs.

For an FBAR with fixed thickness of each layer, the starting position of the parasitic component of the resonator is the series resonance frequency Fs when no capacitance is applied. After the series capacitance is added, the parallel resonance frequency Fp of the resonator does not move, and the starting position of the parasitic component is also Fs and does not move. In fact, it is the Fs of the series body that is moved, which is equivalent to a resonator with a smaller Kt2, but the resonator with the smaller Kt2 makes the bandwidth of the filter smaller, so that if necessary, relevant measures are taken to adjust Kt2 back to the value required by the original design, and the position of the resonant frequency also meets the requirement of the filter design.

The above measures are mainly considered: on the one hand, the resonance frequency of a resonator is related to the thickness of each layer (passivation layer, upper electrode, piezoelectric layer, lower electrode) constituting the resonator, and under the condition that the thickness of other layers is unchanged, the thicker a certain layer is, the lower the resonance frequency is, and the thinner the thickness is, the higher the resonance frequency is. On the other hand, when the resonant frequency is fixed, Kt2 of the resonator is related to the piezoelectric layer thickness. Increasing the thickness of the piezoelectric layer (and correspondingly decreasing the thickness of the other layers to maintain the resonant frequency) increases the Kt2 of the resonator. Conversely, by reducing the thickness of the piezoelectric layer (and by correspondingly increasing the thickness of the other layers to maintain the resonant frequency substantially constant), the Kt2 of the resonator is reduced.

In the embodiment of the present invention, a preferable design method of the filter may be performed as follows: the initial design is carried out according to the frequency and bandwidth of the original filter, the resonance frequency and Kt2 of each resonator are determined, then series capacitance is added to part of the resonators (mainly series resonators) (it can also be understood that the resonators are replaced by the series body), according to the above description, at this time, Kt2 of the series body becomes smaller, the performance of the filter changes, in this case, the thickness of each layer of the resonators and the capacitance value can be further adjusted, so that the resonance frequency Fs and Kt2 of the series body after the replacement are the same as the resonators before the replacement, and at this time, the parasitic ripple is already located below Fs, namely outside the passband. The design can be performed by using relevant software, so that the above-mentioned "adjusting the thicknesses of the layers of the resonator and the capacitance value" mainly refers to the parameter adjustment in the computer aided design, although the sample can also be made in a trial production manner. The above method is exemplified below.

Fig. 6 is a topology diagram of a conventional first-order filter. As shown in fig. 6, the first-order filter 6 includes a series-arm resonator 61 and a parallel-arm resonator 62, one end of the series-arm resonator 61 is connected to a signal input port 63, the other end is connected to a signal output port 64, the parallel-arm resonator 62 is connected between the signal output port 64 and the ground, and the upper electrode thickness of the parallel-arm resonator is larger than that of the series-arm resonator 61.

Fig. 7 is a graph of the filter 6. In fig. 7, 71 is a series-arm resonator curve, 72 is a parallel-arm resonator curve, and 73 is a first-order filter curve. As can be seen from fig. 7, since the series-arm resonators 71 are affected by the parasitic effect, the series-arm resonators 71 generate parasitic ripples below Fs, so that when the first-order filter 7 is formed, ripples are generated on the left side of the passband of the first-order filter 7, which causes deterioration of passband performance indexes of the first-order filter 7, such as insertion loss, fluctuation, ripples, group delay fluctuation, and the like, and deterioration of passband performance indexes of the duplexer and the multiplexer, such as insertion loss, fluctuation, ripples, group delay fluctuation, and the like.

In order to improve the influence of the parasitic ripple on the first-order filter 6, the new resonant unit 4 proposed in the first embodiment may be used to form the first-order filter. In order to obtain the same performance as the first order filter 6, it is necessary to obtain a frequency response curve of the resonator having an approximate shape as in fig. 3. By adjusting the thickness of the stack of FBAR resonator 41 and the capacitance of capacitor 42 of the new resonant cell 4 of fig. 4, a frequency response curve of the new resonant cell 4 can be obtained that is similar to the curve of fig. 3. As can be seen from fig. 8, Fs and Fp of the new resonance unit 4 are the same as Fs and Fp of the resonator 11 in fig. 3, and the start position of the parasitic ripple of the new resonance unit 4 starts from 3580MHz, and the start position of the parasitic ripple of the resonator 11 in fig. 3 starts from 3650 MHz.

Fig. 9 is a topology structural diagram of a first-order filter according to the second embodiment. As shown in fig. 9, the first-order filter includes a series resonant unit 95 and a parallel resonant unit 96, one end of the series resonant unit 95 is connected to a signal input port 97, the other end is connected to a signal output port 98, the parallel resonant unit 96 is connected in parallel between the signal output port 98 and a ground terminal,

in the present embodiment, the structure of the series resonant unit 95 is identical to the topology and the composition structure of the resonant unit 4 proposed in the first embodiment. The series resonant unit 95 includes a capacitor 92 and an FBAR resonator 91 connected in series, and one end of the capacitor 92 and the FBAR resonator 91 connected in series is connected to a signal input port 97, and the other end is connected to a signal output port 98.

The structure of the parallel resonant unit 96 is the same as the topology of the resonant unit 4 proposed in the first embodiment. The capacitor 94 and the FBAR 93 are connected in series, one end of the capacitor 94 and the FBAR 93 are connected with the signal output port 98, and the other end is grounded.

In the present embodiment, the upper electrode thickness of the FBAR resonator 93 is greater than that of the FBAR resonator 91.

Fig. 10 is a graph of a first-order filter according to the second embodiment. As can be seen from fig. 10, since the series-arm resonator adopts the resonant unit structure proposed in this embodiment, and the start position of the parasitic ripple is far below Fs, the first-order filter is not affected by the parasitic ripple of the series-arm resonator, so that the pass-band performance indexes of the first-order filter, such as insertion loss, fluctuation, ripple, group delay fluctuation, and the like, are improved, and the pass-band performance indexes of the duplexer and the multiplexer, such as insertion loss, fluctuation, ripple, group delay fluctuation, and the like, are also improved.

The series resonant unit 95 and the parallel resonant unit 96 of this embodiment respectively adopt the new resonant unit proposed in this embodiment, and the transition band (3590-3610 MHz) has no ripple, and the ripple appears in the stop band.

It should be noted that, if the influence of the parasitic ripple of the new resonant unit on the transition band performance is acceptable, the series resonant unit 95 may adopt the new resonant unit proposed in the first embodiment; the parallel resonance unit 96 may employ an existing parallel-arm resonator, and the transition has a ripple.

Fig. 11 is a schematic diagram of a bandpass filter including conventional FBAR resonators. As shown in fig. 11, the band pass filter includes: four FBAR resonators 111-114 connected in series are connected between the signal input port and the signal output port; the parallel FBAR resonators 115-117 are connected between the connection point of the plurality of series FBAR resonators and the ground. An inductor is connected between each FBAR resonator connected in parallel and the ground terminal.

Fig. 12 and 13 are passband frequency response curves of a bandpass filter including conventional FBAR resonators. From fig. 12 and 13, it can be seen that a ripple appears clearly on the left side of the pass band.

Fig. 14 is a topology diagram of a bandpass filter according to the third embodiment. As shown in fig. 14, the band pass filter includes: four resonance units 141-144 connected in series and connected between the signal input port and the signal output port; the parallel resonance units 145 to 147 are connected between the connection point of the plurality of series FBAR resonators and the ground terminal. An inductor is connected between each of the parallel resonance units 145-147 and a ground terminal.

In this embodiment, the structures of the series resonant units 141-144 and the parallel resonant units 145-147 are the same as the structure of the resonant unit 4 in the first embodiment, and are not described again.

Fig. 15 and 16 are passband frequency response curves of a bandpass filter composed of the novel resonance unit proposed in the present embodiment. As can be seen from fig. 15 and 16, the left side curve of the pass band is very smooth, no ripple occurs, and no ripple occurs in the transition band (between 3600MHz and 3630 MHz), which occurs around 3580 MHz.

FIG. 17 is a graph comparing two curves. The dotted line is the passband response curve of the bandpass filter composed of the novel resonant units proposed in this embodiment, and the solid line is the passband response curve of the bandpass filter composed of the existing FBAR resonators. As can be seen from fig. 17, the left side of the passband of the curve of the present embodiment is relatively full and smooth, and there is no ripple jitter, so that passband performances such as insertion loss, ripple, group delay ripple, and the like are improved.

Fig. 18 is a structural diagram of a capacitor in the novel resonance unit according to the first embodiment. Fig. 18 is a kind of capacitor, called an interdigital capacitor, in which 182 and 183 are metal electrodes, and 181 and 184 are external connection terminals of the interdigital capacitor.

Fig. 19 is a topology diagram of a novel resonant cell according to an embodiment of the present invention, which is formed by cascading an interdigital capacitor with a conventional FBAR resonator. The resonant unit comprises an interdigital capacitor 192 and an FBAR resonator 193 which are connected in series, one end of the interdigital capacitor 192 and the FBAR resonator 193 which are connected in series is connected with a signal input port 191, and the other end of the interdigital capacitor 192 and the FBAR resonator 193 is connected with a signal output port 194.

Another form of capacitor is called a plate capacitor. Fig. 20 is a topology diagram of a novel resonant unit according to an embodiment of the present invention, in which a plate capacitor is cascaded with an existing FBAR resonator. The resonant unit comprises a plate capacitor 202 and an FBAR resonator 203 which are connected in series, wherein one end of the plate capacitor 202 and one end of the FBAR resonator 203 which are connected in series are connected with a signal input port 201, and the other end of the plate capacitor 202 and the other end of the FBAR resonator 203 which are connected in series are connected with a signal output port 204.

The FBAR resonator is composed of upper and lower electrodes and a piezoelectric film in the middle. Above the upper electrode and below the lower electrode of the FBAR resonator is air. Without the air slot under the lower electrode of the FBAR resonator, the FBAR resonator becomes a plate capacitor. The plate capacitor 202 may be implemented as described above. The capacitance value of the capacitor can be changed by adjusting the area of the plate capacitor or the thickness of the piezoelectric film.

Fig. 21 is a topological structure diagram of a band pass filter composed of the novel resonance unit proposed in the present embodiment. As shown in fig. 21, the series branch and the three parallel branches of the band pass filter employ the novel resonance unit shown in fig. 19.

Fig. 22 is a topological structure diagram of a band pass filter composed of the novel resonance unit proposed in the present embodiment. As shown in fig. 22, the series branch and the three parallel branches of the band pass filter employ the novel resonance unit shown in fig. 20.

As shown in fig. 23, the series branch of the band-pass filter employs the novel resonance unit shown in fig. 19, and the three parallel branch resonators employ the existing FBAR resonators; as shown in fig. 24, the series arm of the band pass filter employs the novel resonance unit shown in fig. 20, and the three parallel arm resonators employ the existing FBAR resonators.

Fig. 25 and 26 are graphs of bandpass filter frequency responses generated using the design of fig. 23. Ripples are generated in the transition band (between 3600MHz and 3630 MHz) region, but no ripples are generated within the pass band.

In the embodiment of the invention, the new band-pass filter is adopted to form the multiplexer (including the duplexer), so that the multiplexer is not influenced by the parasitic ripple of the series-branch resonator, and the pass-band performance indexes of the multiplexer, such as insertion loss, fluctuation, ripple, group delay fluctuation and the like, are improved.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims

1. the method for adjusting film bulk acoustic wave resonator FBAR parasitic component, is characterized in that,

The capacitor is connected in series with the FBAR to form a series body, so that in the amplitude-frequency curve of the series body, the starting position of the parasitic component is moved to a frequency band below the series resonance frequency;

Adjust the thickness of one or more of the upper electrode, the lower electrode and the piezoelectric layer of the FBAR, and/or adjust the capacitance value of the capacitor, so that the series resonance frequency of the series body and The parallel resonant frequency is located in the neighborhood of the preset width of the series resonant frequency and the parallel resonant frequency of the FBAR, respectively.

2. The method according to claim 1, wherein

The upper electrode is composed of an electrode material and a passivation layer above the electrode material;

The thickness of the upper electrode is the sum of the thickness of the electrode material and the thickness of the equivalent electrode material, and the acoustic impedance of the equivalent electrode material is equal to the acoustic impedance of the passivation layer.

3. The method of claim 1, further comprising:

For forming a filter using the FBAR, part or all of the FBAR in the filter is replaced with the series body, so that in the amplitude-frequency curve of the filter, the spurious components are located outside the passband.

4. The method of claim 3, wherein all series FBARs in the filter are replaced by the series.

5 . The method according to claim 3 , wherein all series-connected FBARs and at least one parallel-connected FBAR in the filter are replaced by the series body. 6 .

6. A filter comprising a thin-film bulk acoustic resonator FBAR, wherein each series-connected FBAR of the filter is connected in series with a capacitor to form a series body;

The thickness of one or more of the upper electrode, the lower electrode, and the piezoelectric layer of the FBAR and/or the capacitance value of the capacitor, so that the series resonance frequency and the parallel resonance frequency of the series body are respectively located in the The FBAR's series resonant frequency and parallel resonant frequency are in the neighborhood of preset widths.

7 . The filter according to claim 6 , wherein a capacitor is connected in series with one or more parallel FBARs of the filter. 8 .

8. A multiplexer comprising the filter according to claim 6 or 7.

9. A communication device comprising the filter according to claim 6 or 7.