WO2021159881A1

WO2021159881A1 - Method for adjusting fbar parasitic component, filter, multiplexer, and communication device

Info

Publication number: WO2021159881A1
Application number: PCT/CN2020/141267
Authority: WO
Inventors: 庞慰; 柴竹青; 郑云卓
Original assignee: 诺思(天津)微系统有限责任公司
Priority date: 2020-02-12
Filing date: 2020-12-30
Publication date: 2021-08-19
Also published as: CN111211754A; CN111211754B

Abstract

A method for adjusting an FBAR parasitic component, a filter, a multiplexer, and a communication device. A position where a parasitic component appears in a frequency domain is changed, so that the passband performance is improved. In the method, a capacitor (42) and an FBAR (41) are connected in series to form a series connection (4), and in an amplitude-frequency curve of the series connection (4), a starting position of the parasitic component is moved to a frequency band below a series resonant frequency point.

Description

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

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 a communication device.

Background technique

In the radio frequency communication front-end, there are increasingly higher requirements for the performance of filters, duplexers and multiplexers, of which passband performance is particularly important, such as insertion loss, fluctuation, ripple, echo, etc. in the 5G era The requirements for passband indicators are becoming more and more stringent.

Since the film bulk acoustic resonator (FBAR) has parasitic components in the frequency band below the series resonance frequency, that is, the starting frequency of the parasitic component and the series resonance frequency of the FBAR resonator basically coincide, so the filter is formed Parasitic components also exist in the passband of the filter, duplexer, and multiplexer. This parasitic component causes the filter, duplexer and multiplexer's insertion loss, fluctuation, ripple, group delay fluctuation and other passband indicators. Negative Effects.

Summary of the invention

In view of this, the present invention provides a method, filter, multiplexer, and communication device for adjusting the parasitic component of FBAR to change the position of the parasitic component in the frequency domain, thereby improving the passband performance.

In order to achieve the above objective, according to one aspect of the present invention, a method for adjusting the parasitic component of a thin film bulk acoustic wave resonator FBAR is proposed.

In the method for adjusting the parasitic component of the film bulk acoustic wave resonator FBAR of the present invention, a 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 the series resonance frequency point The following frequency bands.

Optionally, the method further includes: 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 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, it further includes: 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, which is equivalent The acoustic impedance of the electrode material is equal to the acoustic impedance of the passivation layer.

Optionally, the method further includes: for using the FBRA to form a filter, replacing part or all of the FBAR in the filter with the series body, so that the parasitic component in the amplitude-frequency curve of the filter is outside the passband.

Optionally, all series FBARs in the filter are replaced with the series body. Since the series branch resonator adopts the resonator structure of the invention, the starting position of the parasitic ripple is far below Fs, so the first-order filter will not be affected by the parasitic ripple of the series branch resonator, thus Improve the passband performance indicators of the first-order filter such as insertion loss, ripple, ripple, and group delay ripple.

Optionally, all series FBARs and at least one parallel FBAR in the filter are replaced with the series body. When the associated FBAR is also replaced with the above-mentioned series body, it helps to further reduce the ripple of the transition band.

According to another aspect of the present invention, there is provided a filter including a film bulk acoustic wave resonator FBAR, and each series FBAR of the filter is connected in series with a capacitor.

Optionally, one or more parallel FBARs of the filter are connected in series with capacitors.

According to another aspect of the present invention, a multiplexer is provided, which includes the filter according to the present invention.

According to another aspect of the present invention, a communication device is provided, which includes the filter according to the present invention.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The new resonant unit structure provided by the present invention is obtained by connecting a capacitor and FBAR in series. The starting position of the parasitic component in the new resonant unit will move to a frequency band below the series resonance frequency, and the new resonant unit will form a filter In the case of filters, duplexers, and multiplexers, the parasitic components will be moved outside the passband, thereby improving the insertion loss, ripple, ripple, group delay fluctuations, etc. of the filter, duplexer, and multiplexer index;

(2) The filter composed of the new resonant unit in the present invention will not be affected by the parasitic ripple of the series branch resonator, thereby improving the insertion loss, fluctuation, ripple, group delay fluctuation, etc. of the filter. Band performance. Similarly, the use of duplexers and multiplexers composed of new filters will not be affected by the parasitic ripple of the series branch resonator, its insertion loss, fluctuation, ripple, group delay fluctuation, etc. The passband performance is also improved.

Description of the drawings

The drawings are used to better understand the present invention, and do not constitute an improper limitation of the present invention. in:

Figure 1 is a topological structure diagram of an existing FBAR resonator;

FIG. 2 is a schematic diagram of the structure of an existing FBAR resonator;

Fig. 3 is a graph of an existing FBAR resonator;

Fig. 4 is a topological structure diagram of a new resonant unit involved in the first embodiment;

Fig. 5 is a graph of a new resonant unit involved in the first embodiment;

Fig. 6 is a topological structure diagram of an existing first-order filter;

Fig. 7 is a curve diagram of an existing first-order filter;

Fig. 8 is a frequency response curve diagram of a new resonant unit involved in the first embodiment;

9 is a topological structure diagram of the first-order filter involved in the second embodiment;

10 is a graph of the first-order filter involved in the second embodiment;

FIG. 11 is a topological structure diagram of a band pass filter composed of an existing FBAR resonator;

12 and 13 are the passband frequency response curve diagrams of the bandpass filter composed of the existing FBAR resonator;

14 is a topological structure diagram of the band pass filter involved in the third embodiment;

15 and 16 are the passband frequency response curve diagrams of the bandpass filter composed of the new resonant unit proposed by the embodiment of the present invention;

Figure 17 is a comparison diagram of the curves of two bandpass filters;

FIG. 18 is a structural diagram of a capacitor in a novel resonant unit involved in the first embodiment;

19 is a topological structure diagram of the novel resonant unit proposed in Embodiment 1 formed by cascading the interdigital capacitor and the existing FBAR resonator;

20 is a topological structure diagram of the novel resonant unit proposed in Embodiment 1 formed by cascading a plate capacitor and an existing FBAR resonator;

21 is a topological structure diagram 1 of a band pass filter composed of the new resonant unit proposed in the first embodiment;

22 is a topological structure diagram of a band pass filter composed of the new resonant unit proposed in the first embodiment;

FIG. 23 is a topological structure diagram 1 of a band-pass filter in which the series branch adopts the new resonant unit proposed in the first embodiment and the existing FBAR resonator is used in the three parallel branches;

24 is the topological structure diagram of the bandpass filter with the new resonant unit proposed in the first embodiment in the series branch and the existing FBAR resonator in the three parallel branches;

25 and FIG. 26 are frequency response curves of the band pass filter shown in FIG. 23.

Detailed ways

The present invention will be further described below in conjunction with the drawings and embodiments.

Figure 1 is a topological structure diagram of an existing 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 relationship curve between the Z parameter amplitude value and the frequency of the FBAR resonator 11 is obtained, as shown in FIG. 3. In Figure 3, the vertical axis represents the magnitude of the Z parameter, the horizontal axis represents the frequency, Fs represents the series resonance frequency, and Fp represents the parallel resonance frequency. Due to the inherent parasitic effects of the FBAR resonator, parasitic ripples will appear in the frequency range below Fs (that is, the starting position of the parasitic ripple starts from Fs, there are parasitic ripples below Fs, and none above Fs).

Fig. 2 is a schematic diagram of the structure of a conventional FBAR resonator. In FIG. 2, the typical FBAR resonator structure is composed of three stacked layers of a lower electrode 21, a piezoelectric layer 22 and an upper electrode 23. The FBAR resonator is located on a silicon substrate 24, and air is provided on the silicon substrate. Slot 25, the air slot 25 is used to pass in air, so that the upper electrode of the FBAR resonator and the lower electrode of the FBAR resonator are air. By adjusting the thickness 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. Its material can be a relatively stable non-metallic material, such as silicon dioxide. It is even possible to use the same material as the piezoelectric layer, such as aluminum nitride. The acoustic impedance of this layer of material is different from that of the electrode material, but it can be converted to an equal thickness with the same acoustic impedance as the upper electrode material and superimposed on the thickness of the upper electrode. Use this superimposed upper electrode thickness to be equivalent to the upper electrode and passivation The interaction of the layers, for simplicity, the passivation layer is omitted in the figure, but when adjusting the position of the parasitic component by adjusting the thickness of each layer of the resonator, the thickness of the passivation layer should also be considered.

Fig. 4 is a topological structure diagram of a new resonant unit involved in the first embodiment. As shown in FIG. 4, the resonance unit 4 as a series body includes a series capacitor 42 and an FBAR resonator 41. One end of the series capacitor 42 and the FBAR resonator 41 is connected to the signal input port 43, and the other end is grounded.

The Z parameter is measured from the signal input port 43, and the corresponding relationship curve between the Z parameter amplitude value and the frequency of the new resonant unit 4 is obtained. As shown in Figure 5, the vertical axis represents the amplitude value of the Z parameter, and the horizontal axis represents the frequency; Fs represents the series connection. The resonance frequency, Fp represents the parallel resonance frequency.

Compared with the conventional FBAR resonator 11, the frequency of Fp does not change much, and the frequency of Fs moves to high frequency. The starting position of the parasitic ripple has not changed much, and is still near 3650MHz. It can be seen from the figure that the new resonance unit 4 proposed in this embodiment can separate the starting position of the parasitic ripple from the position of Fs.

For an FBAR with a fixed thickness of each layer, when no capacitor is added, the starting position of the parasitic component of the resonator is the series resonance frequency Fs. After adding the series capacitor, the parallel resonance frequency Fp of the resonator does not move, and the starting position of the parasitic component is also Fs, which does not move. In fact, the Fs of the series body is moved, which is equivalent to becoming a resonator with a smaller Kt2. However, if the kt2 becomes smaller, the bandwidth of the filter will become smaller. Therefore, if necessary, re Take relevant measures to adjust kt2 back to the value required by the original design, and the location of the resonant frequency should also meet the requirements of the filter design.

The above measures are mainly considered: On the one hand, the resonant frequency of the resonator is related to the thickness of the layers (passivation layer, upper electrode, piezoelectric layer, and lower electrode) that make up the resonator. Under the condition that the thickness of other layers remains unchanged, a certain layer The thicker the thickness, the lower the resonance frequency, and the thinner the thickness, the higher the resonance frequency. On the other hand, when the resonant frequency is fixed, the Kt2 of the resonator is related to the thickness of the piezoelectric layer. Increase the thickness of the piezoelectric layer (in order to keep the resonance frequency basically unchanged, the thickness of the other layers needs to be adjusted accordingly), the Kt2 of the resonator becomes larger. On the contrary, reduce the thickness of the piezoelectric layer (in order to keep the resonant frequency basically unchanged, the thickness of the other layers needs to be adjusted accordingly), the Kt2 of the resonator becomes smaller.

In the embodiment of the present invention, a preferred design method of the filter can be carried out as follows: initial design is carried out according to the frequency and bandwidth of the original filter, the resonant frequency and Kt2 of each resonator are determined, and then some of the resonators ( Mainly a series resonator) add a series capacitor (can also be understood as replacing the resonator with the aforementioned series body). According to the above description, the Kt2 of the series body becomes smaller at this time, and the filter performance changes. In this case, the thickness of each layer of the resonator and the capacitance value can be further adjusted so that the resonant frequency Fs and Kt2 of the series body after replacement are the same as the resonator before replacement. At this time, the parasitic ripple is already at a position below Fs, that is, at Outside the passband. The design here can be completed with related software. Therefore, the above-mentioned "adjusting the thickness of each layer of the resonator and the capacitance value" mainly refers to the parameter adjustment during computer-aided design, although samples can also be made by trial production. The above method is illustrated below with examples.

Fig. 6 is a topological structure diagram of an existing first-order filter. As shown in FIG. 6, the first-order filter 6 includes a series branch resonator 61 and a parallel branch resonator 62. One end of the series branch resonator 61 is connected to the signal input port 63, and the other end is connected to the signal output port 64. The parallel branch resonator 62 is connected between the output port 64 and the ground terminal, and the thickness of the upper electrode of the parallel branch resonator is greater than the thickness of the upper electrode of the series branch resonator 61.

FIG. 7 is a graph of the filter 6. In Figure 7, 71 is the series branch resonator curve, 72 is the parallel branch resonator curve, and 73 is the first-order filter curve. It can be seen from FIG. 7 that because the series branch resonator 71 is affected by parasitic effects, the series branch resonator 71 will produce parasitic ripples below Fs, which leads to the formation of the first-order filter 7. Ripple is generated on the left side of the passband of the first-order filter 7, resulting in deterioration of the passband performance indicators of the first-order filter 7, such as insertion loss, ripple, ripple, and group delay fluctuation. Similarly, the insertion loss of the duplexer and multiplexer, Pass-band performance indicators such as fluctuations, ripples, and group delay fluctuations will also deteriorate.

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 can 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 the frequency response curve of the resonator with a shape similar to that in FIG. 3. By adjusting the laminated thickness of the FBAR resonator 41 of the new resonance unit 4 in FIG. 4 and the capacitance value of the capacitor 42, the frequency response curve of the new resonance unit 4 similar to the curve in FIG. 3 can be obtained. It can be seen from FIG. 8 that the Fs and Fp of the new resonant unit 4 are the same as the Fs and Fp of the resonator 11 in FIG. The starting position of the parasitic ripple of the resonator 11 in 3 starts from 3650MHz.

FIG. 9 is a topological structure diagram of the first-order filter involved in 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 the signal input port 97, the other end is connected to the signal output port 98, and the signal output port 98 is connected to the ground terminal. Parallel resonance unit 96 is connected in parallel,

In this embodiment, the structure of the series resonant unit 95 is completely the same as the topology and composition 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. One end of the capacitor 92 and the FBAR resonator 91 connected in series is connected to the signal input port 97 and the other end is connected to the signal output port 98.

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

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

FIG. 10 is a graph of the first-order filter involved in the second embodiment. It can be seen from Fig. 10 that since the series branch resonator adopts the resonant unit structure proposed in the first embodiment, the starting position of the parasitic ripple is far below Fs, so the first-order filter will not be subject to series branch resonance. The influence of parasitic ripple of the first-order filter, thereby improving the passband performance indicators such as insertion loss, ripple, ripple, and group delay fluctuation of the first-order filter. Similarly, the insertion loss, ripple, and ripple of the duplexer and multiplexer Pass-band performance indicators such as wave and group delay fluctuations will also be improved.

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

It should be noted that if the influence of the parasitic ripple of the new resonant unit on the performance of the transition band is acceptable, then the series resonant unit 95 can adopt the new resonant unit proposed in the first embodiment; the parallel resonant unit 96 can adopt the existing Some parallel branch resonators have ripples in the transition.

FIG. 11 is a topological structure diagram of a band pass filter composed of an existing FBAR resonator. As shown in Figure 11, the band-pass filter includes four series-connected FBAR resonators 111-114 connected between the signal input port and the signal output port; parallel FBAR resonators 115-117 connected in multiple series Between the connection point of the FBAR resonator and the ground terminal. An inductance is connected between each parallel FBAR resonator and the ground terminal.

Figures 12 and 13 are the passband frequency response curves of the bandpass filter composed of the existing FBAR resonator. From Figure 12 and Figure 13, we can see that there is a significant ripple on the left side of the passband.

FIG. 14 is a topological structure diagram of the band pass filter involved in the third embodiment. As shown in Fig. 14, the band-pass filter includes: four series resonant units 141-144 connected between the signal input port and the signal output port; parallel resonant units 145-147 connected to multiple series FBAR resonance Between the connection point of the device and the ground terminal. An inductance is connected between each of the parallel resonance units 145-147 and the ground terminal.

In this embodiment, the structures of the series-connected resonant units 141 to 144 and the parallel-connected resonant units 145 to 147 are the same as the structure of the resonant unit 4 proposed in the first embodiment, and will not be repeated.

Figures 15 and 16 are the passband frequency response curves of the bandpass filter composed of the new resonant unit proposed in this embodiment. It can be seen from Figure 15 and Figure 16 that the curve on the left side of the passband is very smooth, no ripple appears, and there is no ripple in the transition band (between 3600MHz and 3630MHz), and the ripple appears around 3580MHz.

Figure 17 is a comparison diagram of the two curves. The dotted line is the passband frequency response curve of the bandpass filter composed of the new resonant unit proposed in this embodiment, and the solid line is the passband frequency response curve of the bandpass filter composed of the existing FBAR resonator. It can be seen from FIG. 17 that the left side of the passband of the curve of this embodiment is relatively full and smooth, and there is no ripple jitter, thereby improving the passband performance such as insertion loss, ripple, ripple, and group delay fluctuation.

FIG. 18 is a structural diagram of the capacitor in the new resonant unit involved in the first embodiment. Figure 18 is a type of capacitor called an interdigital capacitor, where 182 and 183 are metal electrodes, and 181 and 184 are the external connection terminals of the interdigital capacitor.

19 is a topological structure diagram of the novel resonant unit proposed in Embodiment 1 formed by cascading the interdigital capacitor and the existing FBAR resonator. The resonance unit includes a series-connected interdigital capacitor 192 and an FBAR resonator 193. One end of the series-connected interdigital capacitor 192 and FBAR resonator 193 is connected to the signal input port 191, and the other end is connected to the signal output port 194.

Another form of capacitor is called plate capacitor. 20 is a topological structure diagram of the novel resonant unit proposed in Embodiment 1 formed by cascading a plate capacitor and an existing FBAR resonator. The resonance unit includes a plate capacitor 202 and an FBAR resonator 203 connected in series. One end of the plate capacitor 202 and the FBAR resonator 203 connected in series is connected to the signal input port 201 and the other end is connected to the signal output port 204.

The FBAR resonator is composed of upper and lower electrodes and a piezoelectric film in the middle. The FBAR resonator is above the upper electrode and below the lower electrode is air. If there is no air groove under the lower electrode of the FBAR resonator, the FBAR resonator becomes a plate capacitor. The plate capacitor 202 can be realized in the above-mentioned manner. Adjusting the area of the plate capacitor or the thickness of the piezoelectric film can change the capacitance of the capacitor.

FIG. 21 is a topological structure diagram of a band pass filter composed of the new resonant unit proposed in this embodiment. As shown in FIG. 21, the series branch and three parallel branches of the band-pass filter adopt the new resonant unit shown in FIG. 19.

FIG. 22 is a topological structure diagram of a band pass filter composed of the new resonant unit proposed in this embodiment. As shown in Fig. 22, the series branch and three parallel branches of the band-pass filter adopt the new resonant unit shown in Fig. 20.

As shown in Figure 23, the series branch of the band-pass filter uses the new resonant unit shown in Figure 19, and the three parallel branch resonators use the existing FBAR resonator; as shown in Figure 24, The series branch of the band-pass filter uses the new resonant unit shown in FIG. 20, and the three parallel branch resonators use the existing FBAR resonator.

Figure 25 and Figure 26 are the frequency response curves of the band-pass filter produced by the design structure shown in Figure 23. There will be ripples in the transition band (between 3600MHz and 3630MHz), but there is no ripple in the passband.

In the embodiment of the present invention, a new band-pass filter is used to form a multiplexer (including a duplexer), so that the multiplexer will not be affected by the parasitic ripple of the series branch resonator, thereby improving the performance of the multiplexer. Pass-band performance indicators such as insertion loss, fluctuation, ripple, and group delay fluctuation.

Although the specific embodiments of the present invention are described above in conjunction with the accompanying drawings, they do not limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solutions of the present invention, those skilled in the art do not need to make creative efforts. Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims

The method for adjusting the parasitic component of the film bulk acoustic wave resonator FBAR is characterized by:

A 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.
The method according to claim 1, further comprising:

The thickness of one or more of the upper electrode, lower electrode, and piezoelectric layer of the FBAR is adjusted, and/or the capacitance value of the capacitor is adjusted so that the series resonance frequency of the series body is equal to The parallel resonant frequencies are respectively located in the neighborhood of the preset width of the series resonant frequency and the parallel resonant frequency of the FBAR.
The method of claim 2, 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.
The method according to claim 2, further comprising:

For using the FBRA to form a filter, part or all of the FBAR in the filter is replaced with the series body, so that the parasitic component in the amplitude-frequency curve of the filter is outside the passband.
The method according to claim 4, wherein all series FBARs in the filter are replaced with the series body.
The method according to claim 4, wherein all series FBARs and at least one parallel FBAR in the filter are replaced with the series body.
A filter includes a thin film bulk acoustic wave resonator FBAR, which is characterized in that each series FBAR of the filter is connected in series with a capacitor.
The filter according to claim 7, wherein one or more parallel FBARs of the filter are connected in series with capacitors.
A multiplexer characterized by comprising the filter according to claim 6 or 7.
A communication device, characterized by comprising the filter according to claim 6 or 7.