Bulk acoustic wave filter and method for manufacturing the same, and duplexer

Abstract

The present invention relates to the technical field of communication filter devices, and in particular to a bulk acoustic wave filter and a manufacturing method thereof and a duplexer, the manufacturing method comprising: forming a plurality of parallel resonators on the first surface of an upper wafer; forming a plurality of series resonators on the first surface of a lower wafer; connecting a first pin to the circuit of the parallel resonator, connecting a second pin to the circuit of the series resonator, arranging the first surface of the upper wafer and the first surface of the lower wafer parallel to each other, and bonding the first pin and the second pin to form a multi-stage series-parallel filter circuit, and forming a distributed capacitor; the parallel resonator and the series resonator forming the distributed capacitor are in the same level relationship, adjacent level relationship or across one level relationship in the multi-stage series-parallel filter circuit. The technical solution of the present invention reduces the volume of the filter by changing the structure of the filter without losing the filter performance.

Description

Technical Field

[0001] The present invention relates to the technical field of communication filter devices, and in particular to a bulk acoustic wave filter and a manufacturing method thereof, and a duplexer. Background Art

[0002] In recent years, with the rapid development of the market, wireless communication terminals and equipment are constantly developing in the direction of miniaturization, multi-mode and multi-band, and the number of duplexers used for FDD (frequency division duplexing) in wireless communication terminals has also increased. Five modes and thirteen bands, or even five modes and seventeen bands, have gradually become the standard requirements for mainstream mobile phones. Especially with the approaching commercial use of 5G, the demand for small-sized, high-performance duplexers such as Band 1, 2, 3, 5, 7, and 8 is also increasing.

[0003] refer to Figure 1 FIG. 1 is a front view of the upper wafer of the existing filter. Figure 1 As shown, the resonators in the filter are all arranged on the upper wafer 101. S1-S6 and P1-P6 in the figure are connected to the wafer through-holes located on the lower wafer through the wafer-level bonding area, and then connected to the pads located on the lower surface of the lower wafer, and interconnected with the pads on the upper surface of the packaging substrate through the solder balls. The two wafers are bonded to form a wafer-level packaging protection structure, and the structure and the packaging substrate are then covered with a plastic sealant of a resin compound to form a substrate-level packaging protection structure. The two-level packaging protection structure jointly protects the internal FBAR from being affected by the external environment to prevent the filter performance from deteriorating.

[0004] The area of ​​the wafer-level packaging protection structure is 1.3mm 2 As the area of ​​the resonator increases significantly as the frequency decreases, the size of this wafer-level packaging protection structure increases by about 1.5 to 2 times compared to similar filters in the S-band (2GHz to 4GHz). Combined with the size after substrate-level packaging, the overall size will reach 1.6mm x 1.2mm, which occupies too much area for use in mobile terminals, posing severe challenges to the high-density design of circuit layouts and the heat dissipation of devices and the entire machine.

[0005] It can be seen from this that providing a filter that can reduce the size of the filter without affecting its performance is a technical problem that urgently needs to be solved. Summary of the invention

[0006] In view of this, the main purpose of the present invention is to provide a bulk acoustic wave filter and a manufacturing method thereof and a duplexer, which can reduce the size of the filter and its occupied area without affecting the performance of the filter.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present invention, a method for manufacturing a bulk acoustic wave filter is provided, comprising the following steps: forming a plurality of parallel resonators on the first surface of an upper wafer; forming a plurality of series resonators on the first surface of a lower wafer; connecting a first pin to the circuit of the parallel resonator, connecting a second pin to the circuit of the series resonator, arranging the first surface of the upper wafer and the first surface of the lower wafer parallel to each other, and bonding the first pin and the second pin to form a multi-stage series-parallel filter circuit, and forming a distributed capacitor; wherein the parallel resonators and the series resonators forming the distributed capacitor are in the same level relationship, adjacent level relationship or cross-level relationship in the multi-stage series-parallel filter circuit.

[0008] Optionally, a plurality of the parallel resonators are arranged in a line, and a plurality of the series resonators are arranged in a line; and the distributed capacitance is formed between the parallel resonators and the series resonators of the same level.

[0009] Another aspect of the present invention provides a bulk acoustic wave filter, comprising: an upper wafer, a first surface of which is provided with a plurality of parallel resonators and a first pin; a lower wafer, a first surface of which is provided with a plurality of series resonators and a second pin; the upper wafer and the lower wafer are stacked to form a packaging structure, inside the packaging structure, the first surface of the upper wafer and the first surface of the lower wafer are arranged parallel to each other, the first pin and the second pin are bonded to form a multi-stage series-parallel filter circuit, and a distributed capacitor is formed; wherein the parallel resonators and the series resonators forming the distributed capacitor are in the same level relationship, adjacent level relationship, or cross-level relationship in the multi-stage series-parallel filter circuit.

[0010] Optionally, the parallel resonator and the series resonator are thin film bulk acoustic wave resonators, solid state assembly resonators or surface acoustic wave resonators.

[0011] Optionally, the parallel resonator and the series resonator have different electromechanical coupling coefficients.

[0012] Optionally, the electromechanical coupling coefficient of the series resonator is at least 2% greater than the electromechanical coupling coefficient of the parallel resonator.

[0013] Optionally, a material of the parallel resonator piezoelectric layer is different from a material of the series resonator piezoelectric layer.

[0014] Optionally, a vertical interval between an upper electrode of the parallel resonator and an upper electrode of the series resonator is 5 um.

[0015] Optionally, the capacitance of the distributed capacitor is 0.1 pF.

[0016] Another aspect of the present invention provides a duplexer comprising two of the above-mentioned BAW filters.

[0017] According to the technical solution of the present invention, a parallel resonator is arranged on the upper wafer, and a series resonator is arranged on the lower wafer, and a relatively superimposed structural form is adopted, which can effectively reduce the volume of the filter; wherein, under this structural form, a distributed capacitance will be generated between the parallel resonator and the series resonator. If the distributed capacitance exists between the parallel resonator and the series resonator separated by more than 2 levels, it will have a greater impact on the performance of the filter, including deterioration of out-of-band suppression, deterioration of insertion loss, etc. Therefore, in the packaging structure, by adjusting the position of the parallel resonator / series resonator, the distributed capacitance formed does not span more than 2 levels, and is formed by parallel resonators and series resonators of the same level, adjacent level, or spanning one level.

[0018] The technical solution of the present invention reduces the volume of the filter by changing its structure without losing the performance of the filter, thereby reducing the space occupied by the filter in the communication terminal, thereby facilitating the miniaturization of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For purposes of illustration and not limitation, the present invention will now be described in terms of preferred embodiments thereof, with particular reference to the accompanying drawings, in which:

[0020] Figure 1 is a front view of an upper wafer of a filter in the prior art;

[0021] Figure 2 A flowchart of a method for manufacturing a bulk acoustic wave filter provided by an embodiment of the present invention;

[0022] Figure 3 is a side view of a filter according to an embodiment of the present invention;

[0023] Figure 4A is a front view of a wafer in an embodiment of the present invention;

[0024] Figure 4B is a front view of a wafer according to an embodiment of the present invention;

[0025] Figure 5 is a circuit diagram of a distributed capacitor non-cross-stage filter according to an embodiment of the present invention;

[0026] Fig. 6A is a comparison diagram of out-of-band suppression curves of an embodiment of the present invention;

[0027] Figure 6B is a comparison diagram of insertion loss curves of embodiments of the present invention;

[0028] Figure 7 is a circuit diagram of a distributed capacitor cross-stage filter according to an embodiment of the present invention;

[0029] Fig. 8A 1 is a comparison diagram of out-of-band suppression curves of cross-level distributed capacitors according to an embodiment of the present invention;

[0030] Figure 8B 1 is a comparison diagram of insertion loss curves of cross-level distributed capacitors according to an embodiment of the present invention;

[0031] Fig. 9 is a circuit diagram of a filter according to an embodiment of the present invention;

[0032] Fig. 10A is a comparison diagram of out-of-band suppression curves of an embodiment of the present invention;

[0033] Fig. 10B is a comparison diagram of insertion loss curves of embodiments of the present invention;

[0034] Fig. 10C is a comparison diagram of roll-off curves of embodiments of the present invention;

[0035] Fig.11 is a comparison diagram of the electromechanical coupling coefficients of the resonators in the filter of the embodiment of the present invention;

[0036] Fig.12 It is a schematic structural diagram of a duplexer according to an embodiment of the present invention.

[0037] In the figure:

[0038] 1. Bulk acoustic wave filter; 11. Upper wafer; 12. Lower wafer. DETAILED DESCRIPTION

[0039] like Figure 2 As shown, an embodiment of the present invention provides a method for manufacturing a bulk acoustic wave filter, comprising:

[0040] S1: forming a plurality of parallel resonators on a first surface of an upper wafer; forming a plurality of series resonators on a first surface of a lower wafer;

[0041] S2: Connect a first pin to the circuit of the parallel resonator, connect a second pin to the circuit of the series resonator, arrange the first surface of the upper wafer and the first surface of the lower wafer parallel to each other, and bond the first pin and the second pin to form a multi-stage series-parallel filter circuit, and form a distributed capacitor; wherein the parallel resonator and the series resonator forming the distributed capacitor are in the same level relationship, adjacent level relationship or cross-level relationship in the multi-stage series-parallel filter circuit.

[0042] Wherein, in step S2, preferably, a plurality of the parallel resonators are arranged in a row, and a plurality of the series resonators are arranged in a row; the distributed capacitor is formed between the parallel resonators and the series resonators of the same level. When arranging the positions of the parallel resonators and the series resonators, the parallel resonators and the series resonators of the same level are preferably arranged relative to form a distributed capacitor, which has a lower impact on the performance of the filter than the distributed capacitor across levels (especially the distributed capacitor across more than 2 levels).

[0043] like Figure 3-12 The embodiment of the present invention further provides a bulk acoustic wave filter, including an upper wafer 11, a first surface of the upper wafer 11 is provided with a plurality of parallel resonators and a first pin; a lower wafer 12, a first surface of the lower wafer 12 is provided with a plurality of series resonators and a second pin; the upper wafer 11 and the lower wafer 12 are superimposed to form a packaging structure, inside the packaging structure, the first surface of the upper wafer 11 and the first surface of the lower wafer 12 are arranged parallel to each other, the first pin and the second pin are bonded to form a multi-stage series-parallel filter circuit, and a distributed capacitor is formed; wherein the parallel resonators and the series resonators forming the distributed capacitor are in the same level relationship, adjacent level relationship, or a cross-level relationship in the multi-stage series-parallel filter circuit.

[0044] In the embodiment of the present invention, the parallel resonator and the series resonator are thin film bulk acoustic wave resonators, solid state assembly resonators or surface acoustic wave resonators.

[0045] The upper wafer 11 and the lower wafer 12 form a superimposed structure, wherein a distributed capacitance is generated between the upper electrodes of the parallel resonator and the series resonator. If the distributed capacitance exists between the parallel resonator and the series resonator separated by more than 2 levels, the BAW filter will suffer from out-of-band suppression deterioration, insertion loss deterioration, etc. Therefore, it is necessary to arrange the positions of the parallel resonator and the series resonator reasonably. In the embodiment of the present invention, the position requirements of the parallel resonator and the series resonator are that the parallel resonator and the series resonator generating the distributed capacitance are at least in the same level relationship, adjacent level relationship, or across one level relationship.

[0046] Among them, the bulk acoustic wave filter also includes structures such as solder balls, solder pads, and packaging substrates. Such structures are similar to existing structures and are not improved in this embodiment, so they will not be described in detail.

[0047] like Figure 3 As shown, FBAR resonators are fabricated on the upper wafer 11 and the lower wafer 12 at the same time, wherein all series resonators are fabricated on the lower wafer 12 and all parallel resonators are fabricated on the upper wafer 11. The layout designs on the two wafers are as follows: Figure 4A and 4BAs shown in the figure, all of them are views from the same direction, so the position of the bonding area is the same. In the figure, P1-P6 are parallel resonators, S1-S6 are series resonators, VIN is the input pin, VOUT is the output pin, VG1 and VG2 are ground pins. Since the series resonator is made on the lower wafer 12, it can be understood vividly as follows: for the wafer that originally contains all the resonators of the filter (similar to Figure 1 The layout of the series resonator and the parallel resonator is distributed separately), along the dividing line between the series resonator and the parallel resonator, the wafer is "folded in half" and "broken" into two wafers, and the series resonator and the parallel resonator overlap each other. And at this time, the two wafers are arranged with four bonding areas, namely VIN, VG1, VG2, and VOUT. At the same time, new bonding areas are added to the "folding line" position of the above-mentioned "fold" (below the view), namely J1, J2, and J3 in the figure. This new bonding area is only used to connect the upper wafer 11 and the lower wafer 12 together, and there is no need to connect to the outside of the chip through vias. Therefore, its shape is different from the bonding area connected to the vias, and the area is only one-half. The dotted circle indicates the position of the chip solder ball connected to the nearest wafer via.

[0048] Figure 5 It is a circuit diagram of an embodiment of the present invention, wherein the circuit in the lower wafer 12 is in the upper dotted box, and the circuit in the upper wafer 11 is in the lower dotted box. Since the series-parallel resonators are overlapped after being folded, there is a distributed capacitance formed by electrodes facing each other between the multiple series resonators and parallel resonators (indicated by the dotted capacitance symbol); in this embodiment, when the number of the first resonator and the second resonator is different, the series resonators and the parallel resonators are aligned as one by one as possible to ensure that the symmetry of the resonators is maximized. For example, when the filter includes 5 parallel resonators and 6 series resonators, it is necessary to ensure that the 5 parallel resonators are symmetrically arranged with the 5 series resonators; the distributed capacitance formed by the upper electrode of the symmetrical parallel resonator and the upper electrode of the series resonator will not exist between resonators separated by more than 2 levels, such as between S1 and P3. The "level" here refers to the alignment of the series resonator and the parallel resonator, which can be referred to. Figure 4A and 4BAfter the upper wafer 11 and the lower wafer 12 are packaged, the resonator S1 and the resonator P1 are aligned vertically, which are in the same level relationship; the resonator and the adjacent resonators of the same level are in the adjacent level relationship, such as resonator P1 and resonator S2, resonator S1 and resonator P2, resonator P3 and resonator S4, etc.; the resonator and the resonator of the same level separated by one resonator are in the spanning level relationship, such as resonator P1 and resonator P3 are separated by one resonator P2, resonator S3 and resonator P3 are in the same level, then resonator P1 and resonator S3 span one level. Similarly, resonator S1 and resonator P3, resonator P2 and resonator S4, etc., are also spanning one level.

[0049] like Fig. 6A and 6B As shown in the figure, it is a comparison of the BAW filter curves with and without distributed capacitance. In the figure, the dotted line is the BAW filter response curve without distributed capacitance, and the solid line is the BAW filter response curve after adding distributed capacitance. From the comparison chart, it can be seen that this level of distributed capacitance has almost no effect on the performance of the BAW filter, except that the frequency of the right roll-off edge moves slightly inward by less than 1MHz.

[0050] In the embodiment of the present invention, preferably, the interval between the upper electrode of the parallel resonator and the upper electrode of the series resonator is 5 um; and the capacitance of the distributed capacitor is 0.1 pF.

[0051] In this embodiment, all / part of the parallel resonators and the series resonators are arranged in the above-mentioned structure, and the generated distributed capacitance will not have a significant impact on the performance of the BAW filter. However, if the layout of the parallel resonators and the series resonators is unreasonable, the distributed capacitance may exist between the resonators of the interval order, such as Figure 7 As shown in Figure 2, the distributed capacitance will have a significant impact on the performance of the BAW filter. Fig. 8A and 8B The out-of-band suppression in the range of 925MHz to 960MHz deteriorated by more than 10dB, and the insertion loss on the right side of the passband also deteriorated by 0.1dB.

[0052] Due to the adoption of the technical solution of the embodiment of the present invention, the FBAR resonator that could only be made on one wafer can be made on two wafers respectively, and finally wafer-level bonding is achieved. Compared with the prior art, the size of the filter in the embodiment of the present invention can be significantly reduced, for example, it can be reduced from the original 1300um×1000um to 1300um×650um, and the area is reduced from the original 1.3mm 2 Reduced to 0.845mm 2 At the same time, because the filter size is reduced, the 1.6mm×1.2mm duplexer, which was originally difficult to achieve, has also become easier to achieve in engineering.

[0053] In addition, in order to achieve a faster roll-off characteristic, it is generally necessary to reduce the electromechanical coupling coefficient of the resonator in the BAW filter. In the prior art, since the series and parallel resonators are both arranged on the same wafer, the electromechanical coupling coefficients will not differ too much. In this embodiment, since the parallel resonator and the series resonator are distributed on the upper and lower wafers, the electromechanical coupling coefficients of the parallel resonator and the parallel resonator can be set to be different. Fig. 9 and 11 As shown, the resonant frequency of the series resonator in the circuit diagram is around 896MHz. The resonant frequencies of the series resonators can be the same or different, but they have almost the same electromechanical coupling coefficient, which is about 7.5%. The resonant frequency of the parallel resonator is around 858MHz. The resonant frequencies of the parallel resonators can be the same or different, but they have almost the same electromechanical coupling coefficient, which is about 9.5%. It can be seen that the electromechanical coupling coefficient of the series resonator is at least 2% greater than that of the parallel resonator; by increasing the types of mass loads, more resonant frequencies can be achieved.

[0054] A specific way to achieve different electromechanical coupling coefficients between the parallel resonator and the series resonator is to set the piezoelectric layer of the parallel resonator and the piezoelectric layer of the series resonator to be different materials.

[0055] like Fig. 10A As shown in Figure C, the dotted line in the figure is the performance parameter curve of the existing BAW filter, and the solid line is the performance parameter curve of the BAW filter of the embodiment of the present invention; it can be seen that without sacrificing the passband insertion loss, the frequency position of the right side is rolled off to 50dB, which is reduced by 1.5MHz from the original 924MHz to 922.5MHz, thereby greatly improving the roll-off characteristics of the filter.

[0056] Another aspect of the present invention provides a duplexer, such as Fig.12 As shown, it includes two BAW filters 1. Since the volume of the BAW filter 1 is reduced, the volume of the duplexer can also be reduced, making the product miniaturized.

[0057] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for manufacturing a bulk acoustic wave filter, characterized in that: The following steps are involved: Forming a plurality of parallel resonators on the first surface of the upper wafer; forming a plurality of series resonators on the first surface of the lower wafer; A first pin is connected to the circuit of the parallel resonator, and a second pin is connected to the circuit of the series resonator. The first surface of the upper wafer and the first surface of the lower wafer are arranged parallel to each other, and the first pin and the second pin are bonded to form a multi-stage series-parallel filter circuit. The positions of the parallel resonator and the series resonator are arranged so that the parallel resonator and the series resonator forming the distributed capacitor are in the same level relationship, adjacent level relationship or cross-level relationship in the multi-stage series-parallel filter circuit.

2. The method for manufacturing a bulk acoustic wave filter according to claim 1, wherein: A plurality of the parallel resonators are arranged in a line, and a plurality of the series resonators are arranged in a line; The distributed capacitance is formed between the parallel resonator and the series resonator in a same-level relationship.

3. A bulk acoustic wave filter, characterized in that: include: An upper wafer, wherein a plurality of parallel resonators and a first pin are disposed on a first surface of the upper wafer; A lower wafer, wherein a first surface of the lower wafer is provided with a plurality of series resonators and a second pin; The upper wafer and the lower wafer are stacked to form a packaging structure, and inside the packaging structure, the first surface of the upper wafer and the first surface of the lower wafer are arranged parallel to each other, and the first pin and the second pin are bonded to form a multi-stage series-parallel filter circuit, and a distributed capacitor is formed; The positions of the parallel resonator and the series resonator are such that the parallel resonator and the series resonator forming the distributed capacitor are in the same level relationship, adjacent level relationship, or across-level relationship in the multi-stage series-parallel filter circuit.

4. The bulk acoustic wave filter according to claim 3, characterized in that The parallel resonator and the series resonator are thin film bulk acoustic wave resonators or solid state assembly resonators or surface acoustic wave resonators.

5. The bulk acoustic wave filter according to claim 3, characterized in that The parallel resonator and the series resonator have different electromechanical coupling coefficients.

6. The bulk acoustic wave filter according to claim 3, characterized in that The electromechanical coupling coefficient of the series resonator is at least 2% greater than the electromechanical coupling coefficient of the parallel resonator.

7. The bulk acoustic wave filter according to claim 3, characterized in that The material of the parallel resonator piezoelectric layer is different from the material of the series resonator piezoelectric layer.

8. The bulk acoustic wave filter according to claim 3, characterized in that A vertical interval between the upper electrode of the parallel resonator and the upper electrode of the series resonator is 5 um.

9. The bulk acoustic wave filter according to claim 3, characterized in that The capacitance of the distributed capacitor is 0.1 pF.

10. A duplexer, characterized in that: The invention comprises two BAW filters as claimed in any one of claims 3 to 9.

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