CN111162752A

CN111162752A - Bulk acoustic wave filter

Info

Publication number: CN111162752A
Application number: CN202010036842.8A
Authority: CN
Inventors: 庞慰; 蔡华林
Original assignee: ROFS Microsystem Tianjin Co Ltd
Current assignee: ROFS Microsystem Tianjin Co Ltd
Priority date: 2020-01-14
Filing date: 2020-01-14
Publication date: 2020-05-15

Abstract

The invention relates to the technical field of filters, in particular to a bulk acoustic wave filter, which comprises a plurality of series resonators, wherein parallel resonators are arranged on each parallel branch between a connecting point of adjacent series resonators and a grounding end; a first branch and a second branch are connected in parallel on one series resonator; the first branch is provided with a first inductor, and the second branch is provided with a second inductor and a first capacitive element which are connected in series. The technical scheme of the invention ensures that the first capacitive element has reasonable area ratio, and can reduce the size of a chip and reduce the cost.

Description

Bulk acoustic wave filter

Technical Field

The invention relates to the technical field of filters, in particular to a bulk acoustic wave filter.

Background

The number of frequency bands in the communication system is gradually increased, and particularly in 4G and 5G communication systems, more frequency bands are applied to the system; therefore, when the multiband system works together, signals in other frequency bands need to be suppressed with certain amplitude. The filter plays a decisive role, and the out-band rejection performance of the filter determines the interference strength of each frequency band in the system and the overall performance, so that the improvement of the out-band rejection of the filter is crucial.

In the filter, for the filter with higher insertion loss requirement, the stage number of the filter is required to be reduced to reduce the loss of each stage; for filters with higher rejection requirements, the number of stages needs to be increased to improve rejection. Since increasing the number of stages affects the insertion loss performance of the filter, the suppression cannot be improved by increasing the number of stages.

In order to solve the above problems, an out-of-band transmission zero point is increased by connecting an inductor in parallel with a resonator, and an inductor is connected in parallel with a series resonator near an output end. The disadvantages of this method are:

1. the suppression of the frequency band far away from the filter passband is improved by using a larger inductor, and the integration of the large inductor in a substrate deteriorates the out-of-band suppression performance, increases the product size, lowers the Q value, deteriorates the insertion loss and the like by being coupled with other inductors; if the large inductor is not integrated with the substrate, the extra inductor can increase the cost outside the chip on the one hand, and on the other hand, the chip pin layout is changed, so that the chip pin layout is difficult to correspond to the mainstream chip pin, and the compatibility is poor;

2. when the inductance increases the out-of-band zero point, the adjacent band of the filter is restrained to be deteriorated to a certain extent, and when the filter is used in a duplexer or a multiplexer, the isolation degree is greatly deteriorated;

3. the echo matching of the passband after the inductor is added has certain deterioration, the position of echo difference, insertion loss and reflection are larger, and the overall performance of the system is also deteriorated.

At present, in order to avoid the above problems, as shown in fig. 1, a resonator is connected in parallel to the parallel inductor, but the area of the resonator is larger than that of the series resonator and the parallel resonator in the filter, and further, there is a reliability problem in manufacturing, which causes serious performance deterioration of resonators with different areas or damage of a part of the resonators, and at the same time, the overall size of the chip is increased due to the larger area, and further, the chip cost is increased.

Disclosure of Invention

In view of the above, the main objective of the present invention is to provide a bulk acoustic wave filter, which has a reasonable area ratio of the first capacitive element, and can reduce the size and cost of the chip.

In order to achieve the above object, according to one aspect of the present invention, there is provided a bulk acoustic wave filter comprising a plurality of series resonators, parallel resonators being provided on each parallel branch between a connection point of adjacent series resonators and a ground terminal; a first branch and a second branch are connected in parallel on one of the series resonators; the first branch is provided with a first inductor, and the second branch is provided with a second inductor and a first capacitive element which are connected in series.

Optionally, a parallel branch inductor is arranged on each parallel branch; and a second capacitive element is connected in series between the connecting point of the parallel resonator and the parallel branch inductor in one parallel branch and the output end of the bulk acoustic wave filter.

Optionally, the first and second capacitive elements are resonators having a frequency different from the frequency of the series resonators and the parallel resonators.

Optionally, a mass loading layer for adjusting the frequency of the resonator is disposed on the upper electrode of the resonator.

Optionally, the number of the series resonators is n, and n is greater than 3, wherein an nth series resonator is connected to the output end of the filter, and the first branch and the second branch are connected in parallel to the nth series resonator; one end of the second capacitive element is located in the parallel branch between the connection point of the 2 nd and 3 rd series resonators and ground.

Optionally, the area of the resonator is 10-100K um²。

Optionally, the inductance of the second inductor is 0-5 nH.

According to the technical scheme of the invention, the second inductor and the first capacitive element which are connected in series are arranged on the second branch, wherein the first capacitive element can be a capacitor or a resonator, the larger the area of the first capacitive element is, the size of the first inductor can be reduced, and the second inductor is connected in series with the first capacitive element to be equivalent to the first capacitive element, so that the size of the first capacitive element can be further reduced, and the first capacitive element is prevented from occupying a larger area.

The technical scheme of the invention ensures that the first capacitive element has reasonable area ratio, and can reduce the size of a chip and reduce the cost. In actual production, the area ratio of all resonators is reasonable, the performance of the resonators is guaranteed not to be deteriorated in the production and manufacturing process, the reliability is higher, in addition, the small inductance can enable the impedance matching to be better, and the return loss and the insertion loss are improved.

Drawings

For purposes of illustration and not limitation, the present invention will now be described in accordance with its preferred embodiments, particularly with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a prior art filter circuit;

fig. 2 is a schematic diagram of a bulk acoustic wave filter circuit provided in the present embodiment;

FIGS. 3 and 4 are graphs comparing the performance without the addition of a second capacitive element;

FIGS. 5 and 6 are graphs comparing the performance of the second capacitive element when added;

fig. 7 is a sectional view of a resonator provided in the present embodiment;

FIG. 8 is a graph comparing frequency change after addition of a mass loading layer;

FIG. 9 is a graph comparing equivalent capacitance changes corresponding to FIG. 8;

FIG. 10 is a graph comparing the impedance of the present embodiment with that of the prior art;

FIG. 11 is a Q-value comparison graph;

FIG. 12 is a comparison graph of the echo improvement of the present embodiment and the prior art;

fig. 13 is a comparison diagram of the insertion loss improvement between the embodiment and the related art.

In the figure:

1: a series resonator; 2: a parallel resonator; 3: a first inductor; 4: a first capacitive element; 5: a second inductor; 6: shunt circuit inductance; 7: a second capacitive element; 8: a mass loading layer.

Detailed Description

As shown in fig. 2, the present invention provides a bulk acoustic wave filter, which includes a plurality of series resonators 1, and parallel resonators 2 are disposed on each parallel branch between a connection point of adjacent series resonators 1 and a ground terminal; a first branch and a second branch are connected in parallel on one series resonator 1; wherein, a first inductor 3 is arranged on the first branch, and a second inductor 5 and a first capacitive element 4 which are connected in series are arranged on the second branch. Parallel branch inductors 6 are arranged on each parallel branch, and a second capacitive element 7 is connected in series between the connecting point of the parallel resonance 2 and the parallel branch inductor 6 in one parallel branch and the output end of the bulk acoustic wave filter.

In this embodiment, the first capacitive element 4 and the second capacitive element 7 may be resonators, the frequency of the resonators is different from the frequency of the series resonator 1 and the frequency of the parallel resonator 2, the resonators are integrally disposed on a wafer of the filter, and meanwhile, the first capacitive element 4 and the second capacitive element 7 may also be capacitors, and the capacitors are externally disposed outside the package structure. Preferably, the first capacitive element 4 and the second capacitive element 7 employ resonators, which are more convenient for the integrated arrangement operation. Wherein, the area of the resonator is 10-100K um²(ii) a The inductance of the second inductor 5 is 0-5 nH.

Fig. 3 and 4 show a comparison of the performance without the addition of the second capacitive element 7, in which the dashed line indicates the performance of the prior art solution and the solid line indicates the solution of the present embodiment; in fig. 3, the filter is the filter at the transmitting end of B25, and the right box is the frequency range of the filter at the receiving end of B25, so it can be seen that the adjacent band rejection is better than the prior art solution. In fig. 4, the far rejection is also substantially equivalent, and an increase in transmission zero is also achieved at 1.55 GHz. The same effect as the large inductance solution can be achieved using the small inductance plus resonator solution.

Fig. 5 and 6 show a comparison of the performance when the second capacitive element 7 is added, in which the dashed line indicates the performance of the prior art solution and the solid line indicates the solution of the present embodiment; in fig. 5, the filter is a filter at the transmitting end of B25, and the right-side box is the frequency range of the filter at the receiving end of B25. In fig. 6, a transmission zero is also formed at 1.55GHz, and the suppression of this frequency is improved; meanwhile, the inhibition is obviously improved compared with the prior art scheme in the vicinity of 2.1-2.2 GHz.

When a resonator is used, the frequency of the resonator is adjusted by providing the mass loading layer 8 on the upper electrode of the resonator, as shown in fig. 7, which is a cross-sectional view of the first capacitive element 4 (resonator) (the cross-sectional view of the second capacitive element 7 is the same as that in fig. 7), wherein the frequency of the resonator can be adjusted by the area and/or thickness of the mass loading layer 8. In the manufacture of the filter, a relatively thick gold layer is generally deposited at the PAD position, and the gold layer can be deposited on the resonator so as to adjust the frequency, and the resonance frequency is adjusted to a position far away from the passband of the filter, and the resonator is equivalent to a capacitor.

As shown in fig. 8, the horizontal axis of the graph is frequency, the vertical axis is impedance, the dotted line is an impedance curve of a general resonator, and the solid line is an impedance curve after the gold layer mass load is added, and it can be seen from the graph that the frequency of the filter can be effectively reduced by the mass loading layer 8. As shown in fig. 9, which is the equivalent capacitance change for fig. 8, the dashed line indicates that the resonator resonates around 1.87GHz, and the solid line indicates that a capacitance is equivalent in this region after the mass loading layer 8 is added.

In this embodiment, it is preferable to implement that the number of the series resonators 1 is n, where the nth series resonator 1 is connected to the output terminal of the filter, and the first branch and the second branch are connected in parallel to the nth series resonator 1 near the output terminal of the filter circuit, and in this embodiment, as shown in fig. 2, the number of the series resonators 1 is 5; one end of the second capacitive element 7 is located in the parallel branch between the connection point of the 2 nd and 3 rd series resonators 1 and ground.

By the above arrangement, the out-of-band rejection of the filter can be improved, and fig. 10 is an impedance comparison graph of the technical solution of the present embodiment and the prior art. As shown in fig. 10, the dotted line is a prior art solution, the solid line is a technical solution of the present embodiment, and as can be seen from fig. 10, the impedance curve in the technical solution of the present embodiment has a high impedance value at 1.93GHz, because the structure is on the series resonator 1, after a signal near the frequency of 1.93GHz passes through the structure, there is an attenuation, and the frequency corresponds to the out-of-band of the filter, so that the out-of-band rejection is improved. The inductance in the technical scheme of the embodiment is about 1.6nH, while the inductance in the technical scheme of the prior patent is 3.3nH, the area of the increased resonator is about 0.015mm2, and the overall layout of the filter is negligible. Therefore, the inductance is obviously reduced, and the integral packaging is also obviously reduced after integration; the high impedance point in the vicinity of 1.55GHz in the figure is formed by the first inductor 3, i.e. the out-of-band transmission zero is formed.

As shown in fig. 11, the Q values of the 1.6nH inductor and the 3.3nH inductor are compared, and the solid line shows the Q value of 1.6nH and the dotted line shows the Q value of 3.3nH, so that a larger Q value has smaller loss and less influence on the insertion loss of the filter.

FIG. 12 is a comparison graph of the echo improvement of the present embodiment and the prior art, in which the dotted line corresponds to the prior art and the solid line corresponds to the present embodiment; as can be seen from fig. 12, a larger inductance changes the impedance more, so that matching is more difficult, while a smaller inductance can match the impedance better, so that the echo is better.

As shown in fig. 13, which is a graph of the insertion loss improvement comparison, the dashed line in the graph indicates the performance of the prior art solution, and the solid line indicates the solution of the present embodiment; from this figure, it can be seen that the echo is better on the one hand, and the small inductance Q value is higher on the other hand, so the insertion loss is better.

The filter can reduce the inductance of the first inductor to 50% by combining the inductance and the resonator (or the capacitance) in parallel and in series and adding the coupling resonator (or the capacitance) between the inductances to the ground, realizes the integration of the inductance, has higher Q value, and simultaneously does not deteriorate the suppression of adjacent bands and return loss. Further, by adding a second inductor inductance in series with the first capacitive element (resonator), the area of the resonator can be reduced, ensuring that the area ratio of all resonators is within a certain reasonable range.

The above-described embodiments should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions can occur, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A bulk acoustic wave filter, the filter comprises a plurality of series resonators (1), and parallel resonators ( 2); it is characterized in that,

A first branch and a second branch are connected in parallel on one of the series resonators (1);

Wherein, a first inductance (3) is arranged on the first branch, and a second inductance (5) and a first capacitive element (4) in series are arranged on the second branch.

2. Bulk acoustic wave filter according to claim 1, is characterized in that,

Each of the parallel branches is provided with a parallel branch inductance (6);

A second capacitive element (7) is connected in series between the connection point of the parallel resonator (2) in one parallel branch and the parallel branch inductor (6) and the output end of the bulk acoustic wave filter.

3. The bulk acoustic wave filter according to claim 2, wherein the first capacitive element (4) and the second capacitive element (7) are resonators, and the frequency of the resonator is the same as that of the series resonator (1). ) and the frequency of the parallel resonator (2) are different.

4. The bulk acoustic wave filter according to claim 3, characterized in that, a mass load layer (8) for adjusting the frequency of the resonator is provided on the upper electrode of the resonator.

5. Bulk acoustic wave filter according to claim 1, is characterized in that,

The number of the series resonators (1) is n, and n>3, wherein the nth series resonator (1) is connected to the output end of the filter, the first branch and the second The branch is connected in parallel on the nth series resonator (1);

One end of the second capacitive element (7) is located on the parallel branch between the connection point of the second and third series resonators (1) and the ground terminal.

6 . The bulk acoustic wave filter according to claim 3 , wherein the area of the resonator is 10-100 Kum ² .

7 . The bulk acoustic wave filter according to claim 1 , wherein the inductance value of the second inductor ( 5 ) is 0˜5 nH. 8 .