Duplexer and communication device

Abstract

The application discloses a kind of duplexers and communication equipment.The duplexer includes the transmitting filter and the receiving filter formed by bulk acoustic wave resonator, and the duplexer includes stacked first wafer and second wafer, the first surface of first wafer and the second surface of second wafer are opposite, wherein, the series resonator of transmitting filter is located at the first side of first surface;Parallel resonator of receiving filter is located at the second side of first surface;Parallel resonator of transmitting filter is located at the first side of second surface;Series resonator of receiving filter is located at the second side of second surface.The duplexer can make full use of space, so as to reduce the size of duplexer, save manufacturing cost.The duplexer in the embodiment of the application can also improve the band roll-off, insertion loss and isolation of duplexer.

Description

Technical Field

[0001] This invention relates to the field of duplexer technology, and particularly to a duplexer and communication device. Background Technology

[0002] Bulk acoustic wave (BAW) resonators are widely used, especially in mobile communications, due to their high roll-off, low insertion loss, high suppression, and small size. BAW resonators generate resonance through mechanical waves, whose wavelengths are shorter than electromagnetic waves. Therefore, the size of BAW resonators and the filters they form are significantly smaller than traditional electromagnetic filters. Furthermore, the crystal orientation growth of piezoelectric crystals can now be well controlled, resulting in extremely low losses and a high quality factor, enabling them to meet complex design requirements such as steep transition bands and low insertion loss.

[0003] Currently, mobile communication is gradually entering the 5G era, and it is also developing towards multi-mode and multi-functionality. Mobile terminals need to integrate more and more modules, inevitably requiring each module to become smaller. Therefore, filters and duplexers, as indispensable components of radio frequency modules, also have a need for size reduction. Furthermore, for duplexers, the roll-off on the right side of the transmit filter passband and the roll-off on the left side of the receive filter passband are of particular concern, as these roll-offs directly affect adjacent band insertion loss and isolation. Currently, conventional duplexer packaging methods cannot simultaneously address these issues.

[0004] Therefore, how to utilize bulk acoustic resonator packaging design technology to reduce the size of the duplexer while improving the roll-off on the right side of the transmit filter passband and the left side of the receive filter passband, thereby improving the duplexer's adjacent band insertion loss and isolation, remains a technical problem to be solved. Summary of the Invention

[0005] In view of this, the present invention proposes a duplexer and communication device with small size and low manufacturing cost.

[0006] A first aspect of the present invention provides a duplexer comprising a transmit filter and a receive filter composed of bulk acoustic resonators. The duplexer comprises a stacked first wafer and a second wafer, with a first surface of the first wafer and a second surface of the second wafer facing each other. The series resonator of the transmit filter is located on a first side of the first surface; the parallel resonator of the receive filter is located on a second side of the first surface; the parallel resonator of the transmit filter is located on a first side of the second surface; and the series resonator of the receive filter is located on a second side of the second surface.

[0007] Optionally, the series resonator of the transmitting filter is aligned with the parallel resonator of the transmitting filter, and the series resonator of the receiving filter is aligned with the parallel resonator of the receiving filter.

[0008] Optionally, the projections of the series resonators of the transmitting filter and the series resonators of the receiving filter onto the horizontal plane do not overlap, and similarly, the projections of the parallel resonators of the transmitting filter and the parallel resonators of the receiving filter onto the horizontal plane do not overlap.

[0009] Optionally, the doping concentration of the piezoelectric layer in the first wafer and the doping concentration of the piezoelectric layer in the second wafer make the effective electromechanical coupling coefficient of the resonator on the second wafer greater than the effective electromechanical coupling coefficient of the resonator on the first wafer; or, the thickness of the piezoelectric layer in the first wafer and the thickness of the piezoelectric layer in the second wafer make the effective electromechanical coupling coefficient of the resonator on the second wafer greater than the effective electromechanical coupling coefficient of the resonator on the first wafer.

[0010] Optionally, the doping concentration of the piezoelectric layer in the first wafer, the doping concentration of the piezoelectric layer in the second wafer, and the thickness of the piezoelectric layer in the first wafer and the thickness of the piezoelectric layer in the second wafer are such that the effective electromechanical coupling coefficient of the resonator on the second wafer is greater than the effective electromechanical coupling coefficient of the resonator on the first wafer.

[0011] Optionally, the effective electromechanical coupling coefficient of the parallel resonator of the transmitting filter is at least 0.015 greater than the effective electromechanical coupling coefficient of the series resonator of the transmitting filter.

[0012] Optionally, the effective electromechanical coupling coefficient of the series resonator of the receiving filter is at least 0.015 greater than the effective electromechanical coupling coefficient of the parallel resonator of the receiving filter.

[0013] Optionally, the first surface has a first metal strip located between the series resonator of the transmitting filter and the parallel resonator of the receiving filter, and the second surface has a second metal strip corresponding to the position of the first metal strip located between the parallel resonator of the transmitting filter and the series resonator of the receiving filter.

[0014] Optionally, the first metal strip is connected to a metal sealing ring on the first wafer, and the second metal strip is connected to a metal sealing ring on the second wafer.

[0015] A second aspect of the present invention provides a communication device comprising any of the duplexers disclosed herein.

[0016] According to the technical solution of the present invention, by setting a series resonator of the transmit filter and a parallel resonator of the receive filter on one of two opposing surfaces of two wafers, and setting a parallel resonator of the transmit filter and a series resonator of the receive filter on the other surface, resonators are fabricated on both wafers of the duplexer, which can make full use of space, thereby reducing the size of the duplexer and saving manufacturing costs. Furthermore, by fabricating the series resonator of the transmit filter and the parallel resonator of the receive filter on a wafer with a thinner piezoelectric layer, its effective electromechanical coupling coefficient can be made smaller than that of the resonator on the other wafer, which can improve the duplexer's adjacent band insertion loss, roll-off, and isolation. Moreover, by fabricating the parallel resonator of the transmit filter and the series resonator of the receive filter on a wafer with a thicker piezoelectric layer, its effective electromechanical coupling coefficient can be made larger than that of the resonator on the other wafer, which can maintain the filter bandwidth unchanged and provide good insertion loss. Attached Figure Description

[0017] For illustrative and not limiting purposes, the invention will now be described with reference to preferred embodiments thereof, particularly the accompanying drawings, in which:

[0018] Figure 1 This is a schematic diagram of a duplexer packaging structure in the prior art;

[0019] Figure 2 This is a typical topology diagram of a duplexer;

[0020] Figure 3 This is a schematic diagram of the duplexer packaging structure according to an embodiment of the present invention;

[0021] Figure 4 This is a plan view of the resonator distribution on wafer 1 and wafer 2 of the duplexer according to the first embodiment of the present invention;

[0022] Figure 5 A comparison diagram of the insertion loss of the transmit filter between a prior art duplexer and a duplexer according to an embodiment of the present invention;

[0023] Figure 6 A comparison diagram of the insertion loss of the receiving filter between a prior art duplexer and a duplexer according to an embodiment of the present invention;

[0024] Figure 7 A comparison diagram of the isolation degree between existing duplexers and duplexers according to embodiments of the present invention;

[0025] Figure 8 This is a plan view of the resonator distribution on wafer 1 and wafer 2 of the duplexer according to the second embodiment of the present invention. Detailed Implementation

[0026] Figure 1This is a schematic diagram of the packaging structure of a bulk acoustic wave duplexer in the prior art. The duplexer consists of filter 01 and filter 02. Filter 01 is composed of wafer 01 and wafer 02. All series resonators (resonator A) and parallel resonators (resonator B) that make up filter 01 are fabricated on wafer 01. No resonators are fabricated on wafer 02; it only serves as a protective cover. Similarly, filter 02 is composed of wafer 03 and wafer 04. All series resonators (resonator D) and parallel resonators (resonator C) that make up filter 02 are fabricated on wafer 03. No resonators are fabricated on wafer 04; it only serves as a protective cover.

[0027] The existing packaging structure has the following two disadvantages: (1) For each filter, all resonators are fabricated on only one wafer, and no resonators are fabricated on the other wafer, which serves as a protective cover. This results in low space utilization and a large overall duplexer size, which is not conducive to device miniaturization or cost control. (2) For each filter, all resonators are fabricated on only one wafer, which inevitably leads to a similar effective electromechanical coupling coefficient between the series resonators and the parallel resonators. This is detrimental to roll-off. For the transmitting filter of the duplexer, based on isolation considerations, users prefer a steeper roll-off on the right side of the transmitting filter. This requires the series resonators of the transmitting filter to have a smaller effective electromechanical coupling coefficient, while the parallel resonators of the transmitting filter have a larger effective electromechanical coupling coefficient. Similarly, for the receiving filter of the duplexer, based on isolation considerations, users prefer a steeper roll-off on the left side of the receiving filter. This requires the parallel resonators of the receiving filter to have a smaller effective electromechanical coupling coefficient, while the series resonators of the receiving filter have a larger effective electromechanical coupling coefficient. Figure 1 The packaging structure cannot independently control the effective electromechanical coupling coefficient of the series and parallel resonators of the filter.

[0028] In view of this, in order to solve the above problems, this application aims to propose a new duplexer that can distribute the resonators on two wafers and control the effective electromechanical coupling coefficients of the series resonators and parallel resonators of the filter separately. This can reduce the size of the duplexer, save costs, and improve the adjacent band insertion loss, roll-off and isolation of the duplexer.

[0029] The duplexer of this invention includes a transmit filter and a receive filter composed of bulk acoustic wave resonators. The duplexer comprises a first wafer and a second wafer stacked (for example, stacked vertically, the same below), with a first surface of the first wafer and a second surface of the second wafer facing each other. Specifically, the series resonator of the transmit filter is located on the first side of the first surface; the parallel resonator of the receive filter is located on the second side of the first surface; the parallel resonator of the transmit filter is located on the first side of the second surface; and the series resonator of the receive filter is located on the second side of the second surface. For example, the first wafer and the second wafer can be stacked vertically, with the first wafer below and the second wafer above. The upper surface of the first wafer is the first surface, and the lower surface of the second wafer is the second surface. The first side and the second side can refer to the left and right sides, respectively.

[0030] In this configuration, the series resonator and parallel resonator of the transmitting filter are aligned, and the series resonator and parallel resonator of the receiving filter are also aligned. "Alignment" means that the series resonator of the transmitting filter is located directly above or below the parallel resonator of the transmitting filter, and the series resonator of the receiving filter is located directly above or below the parallel resonator of the receiving filter. Optionally, the projections of the series resonators of the transmitting and receiving filters onto the horizontal plane do not overlap, and the projections of the parallel resonators of the transmitting and receiving filters onto the horizontal plane do not overlap.

[0031] When the piezoelectric materials of the first and second wafers have the same doping concentration, the thickness of the piezoelectric layer on the first wafer can be set to be less than that on the second wafer. When there is a thickness difference between the piezoelectric layers of the first and second wafers, the effective electromechanical coupling coefficients of the resonators on the different wafers also have a difference. For example, the effective electromechanical coupling coefficient of the parallel resonator of the transmitting filter can be at least 0.015 greater than that of the series resonator of the transmitting filter, and the effective electromechanical coupling coefficient of the series resonator of the receiving filter can be at least 0.015 greater than that of the parallel resonator of the receiving filter. If the piezoelectric materials of the first and second wafers have different doping concentrations, the piezoelectric layer thicknesses of the two wafers need to be adjusted simultaneously to ensure that the effective electromechanical coupling coefficient of the resonator on the second wafer is greater than that of the resonator on the first wafer. At the same time, it is ensured that the effective electromechanical coupling coefficient of the parallel resonator of the transmitting filter is at least 0.015 greater than that of the series resonator of the transmitting filter, and the effective electromechanical coupling coefficient of the series resonator of the receiving filter is at least 0.015 greater than that of the parallel resonator of the receiving filter.

[0032] Preferably, the first surface has a first metal strip located between the series resonator of the transmitting filter and the parallel resonator of the receiving filter, and the second surface has a second metal strip corresponding to the position of the first metal strip located between the parallel resonator of the transmitting filter and the series resonator of the receiving filter. The metal strips improve the isolation between the transmitting and receiving filters. The first metal strip can also be connected to a metal sealing ring on the first wafer, and the second metal strip can also be connected to a metal sealing ring on the second wafer; this design facilitates heat dissipation.

[0033] Figure 2 This is a typical duplexer topology diagram. As shown, the duplexer consists of filter 1 and filter 2, where filter 1 is the transmitting filter and filter 2 is the receiving filter. The passband frequency covered by filter 1 is lower than that covered by filter 2. One end of filter 1 is connected to the common port A and the other end is connected to the transmitting port TX. One end of filter 2 is connected to the common port A and the other end is connected to the receiving port RX. The common port A is connected to an antenna, and a grounding inductor L1 is connected in parallel to the common port A. This inductor L1 mainly adjusts the impedance of the common port A, serving a matching function.

[0034] The topology of filter 1 is as follows Figure 2 As shown, the overall structure adopts a trapezoidal shape, specifically a 4-4 structure (not limited to a 4-4 structure; it could be an MN structure, where M and N are natural numbers; here, only the 4-4 structure is used as an example). It includes one series branch and four parallel branches. The series branch consists of series resonators S11, S12, S13, and S14 connected in series between the common port A and the transmitting port TX. Each of the four parallel branches includes one parallel resonator. Parallel resonators P11 and P12 are connected at one end between series resonators S11 and S12, and between S12 and S13, respectively; their other ends are interconnected and grounded through inductor L11. Similarly, parallel resonators P13 and P14 are connected at one end between series resonators S13 and S14, and between S14 and port TX, respectively; their other ends are interconnected and grounded through inductor L12. It should be noted that the parallel resonators do not necessarily have to be interconnected in pairs and grounded through an inductor; they can also be grounded individually through an inductor.

[0035] The topology of filter 2 is also as follows Figure 2As shown, the overall structure adopts a trapezoidal shape, specifically a 4-4 structure (not limited to 4-4; it could be an MN structure, where M and N are natural numbers; here, only the 4-4 structure is used as an example). It includes one series branch and four parallel branches. The series branch consists of series resonators S21, S22, S23, and S24 connected in series between the common port A and the receiving port RX. Each of the four parallel branches includes one parallel resonator. Parallel resonators P21 and P22 are connected at one end between series resonators S21 and S22, and between S22 and S23, respectively; their other ends are interconnected and grounded through inductor L21. Similarly, parallel resonators P23 and P24 are connected at one end between series resonators S23 and S24, and between S24 and port RX, respectively; their other ends are interconnected and grounded through inductor L22. It should be noted that the parallel resonators do not necessarily have to be interconnected in pairs and grounded through an inductor; they can also be grounded independently through an inductor.

[0036] First embodiment:

[0037] Figure 3 This is a schematic diagram of the packaging of a duplexer according to an embodiment of the present invention. The duplexer is formed by bonding wafer 1, wafer 2, and a substrate, wherein wafer 1 is located below wafer 2 and above the substrate. The upper surface of wafer 1 is opposite to the lower surface of wafer 2. Resonators A and C are fabricated on the upper surface of wafer 1. Resonator A is a series resonator of filter 1 (transmitting filter), and resonator C is a parallel resonator of filter 2 (receiving filter).

[0038] For duplexers, considering isolation and roll-off, a high roll-off is desired on the right side of the transmit filter passband and the left side of the receive filter passband. Therefore, both the series resonator of the transmit filter and the parallel resonator of the receive filter require a low effective electromechanical coupling coefficient. Thus, the series resonator of the transmit filter and the parallel resonator of the receive filter can be fabricated on the same wafer using a thinner piezoelectric layer, which helps improve isolation and optimize roll-off performance. Resonators B and D are fabricated on the lower surface of wafer 2. Resonator B is the parallel resonator of filter 1 (transmit filter), and resonator D is the series resonator of filter 2 (receive filter). Furthermore, for duplexers, the roll-off requirements for the left side of the transmit filter passband and the right side of the receive filter passband are relatively low. Therefore, these resonators can use a larger effective electromechanical coupling coefficient, keeping the bandwidth of the two filters essentially constant. Fabricating the parallel resonator of the transmit filter and the series resonator of the receive filter on the same wafer using a thicker piezoelectric layer helps maintain a relatively constant bandwidth.

[0039] Therefore, in the first embodiment, when stacking the two wafers, to ensure short connections between resonator A (the series resonator of the transmit filter) on wafer 1 and resonator B (the parallel resonator of the transmit filter) on wafer 2, and to avoid coupling between the resonators of the transmit filter and the receive filter, the series resonator (resonator A) and the parallel resonator (resonator B) of the transmit filter are positioned on the same side of wafers 1 and 2, respectively. That is, during stacking, the series resonator of the transmit filter is directly below the parallel resonator. Similarly, the series resonator (resonator D) and the parallel resonator (resonator C) of the receive filter are positioned on the same side of wafers 2 and 1, respectively. That is, during stacking, the series resonator of the receive filter is directly above the parallel resonator. The connector pins on top of wafer 1 and the connector pins on bottom of wafer 2 are bonded together for hermetical packaging or signal connection. The projections of the series resonators of the transmitting filter and the series resonators of the receiving filter onto the horizontal plane do not overlap, and the projections of the parallel resonators of the transmitting filter and the parallel resonators of the receiving filter onto the horizontal plane also do not overlap.

[0040] To more intuitively explain the distribution and connection relationship of the resonators on wafer 1 and wafer 2, Figure 4 A plan view of the resonator distribution of wafer 1 and wafer 2 in the duplexer 40 of the first embodiment of the present invention is given. Figure 4The upper half shows the resonator layout of wafer 2, and the lower half shows the resonator layout of wafer 1. Both the upper and lower half diagrams are front views of the resonators. A-A1 is a fold line; during bonding, wafers 1 and 2 are folded along A-A1 and then bonded and packaged. Looking at the lower half diagram, which shows the resonator distribution on wafer 1, the series resonators (i.e., resonators A) S11, S12, S13, and S14 of the emitter filter are located on the right half of wafer 1. Next to resonator S11 is the input pin TX_in of the emitter filter. Also next to these series resonators are adapter pins J11, J12, J13, and J14, which are used to connect to the parallel resonators on wafer 2. The parallel resonators (i.e., resonators C) P21, P22, P23, and P24 of the receiving filter are located on the left half of wafer 1. Adjacent to these parallel resonators are adapter pins J21, J22, J23, and J24, which are used to connect to the series resonators on wafer 2. Ground pins G21 and G22 are located on both sides of the parallel resonators (i.e., resonators C) of the receiving filter. The antenna pin Ant is located between resonators S14 and P24. A metal ring 11 surrounds wafer 1; this metal ring is bonded to a metal ring 22 on wafer 2 and is connected to ground on the substrate. Metal rings 11 and 22 serve a sealing function. Looking at the upper half of the diagram, which shows the resonator distribution on wafer 2, the parallel resonators (i.e., resonators B) P11, P12, P13, and P14 of the emitter filter are located on the right half of wafer 2. Next to these parallel resonators are adapter pins J11, J12, J13, and J14. These pins are used to connect the series resonators S11, S12, S13, and S14 on wafer 1. The ground pins G11 and G12 are located on both sides of the parallel resonators (i.e., resonators B) of the emitter filter. The series resonators (i.e., resonators D) S21, S22, S23, and S24 of the receiving filter are distributed on the left half of wafer 2. Next to these series resonators are adapter pins J21, J22, J23, and J24, which are used to connect to the parallel resonators P21, P22, P23, and P24 on wafer 1. The input pin RX_in of the receiving filter is located next to resonator S21. The antenna pin Ant is located between resonators S24 and P14. There is a metal ring 22 around wafer 2.

[0041] To verify the effectiveness of the technical solution of this invention, the inventors conducted a duplexer simulation comparison between the comparative example and the first embodiment. The comparative example is as follows: Figure 1The existing technology structure shown has a duplexer whose transmitting filter covers a frequency range of 880 to 915 MHz and whose receiving filter covers a frequency range of 925 to 960 MHz. In the comparative example, the piezoelectric layer thickness of the transmitting filter is 0.74 micrometers, and correspondingly, the effective electromechanical coupling coefficient of its series resonator (50 ohms) is 0.088, and the effective electromechanical coupling coefficient of its parallel resonator (50 ohms) is 0.083. The piezoelectric layer thickness of the receiving filter is 0.75 micrometers, and correspondingly, the effective electromechanical coupling coefficient of its series resonator (50 ohms) is 0.093, and the effective electromechanical coupling coefficient of its parallel resonator (50 ohms) is 0.087. In the first embodiment, the piezoelectric layer thickness of wafer 1 (on which a series resonator of the transmitting filter and a parallel resonator of the receiving filter are arranged) is 0.725 micrometers, the effective electromechanical coupling coefficient of the series resonator (50 ohms) of the transmitting filter is 0.075, and the effective electromechanical coupling coefficient of the parallel resonator (50 ohms) of the receiving filter is 0.078. The piezoelectric layer thickness of wafer 2 (on which a parallel resonator of the transmitting filter and a series resonator of the receiving filter are arranged) is 0.765 micrometers, the effective electromechanical coupling coefficient of the parallel resonator (50 ohms) of the transmitting filter is 0.09, and the effective electromechanical coupling coefficient of the series resonator (50 ohms) of the receiving filter is 0.1. It must be ensured that the difference between the effective electromechanical coupling coefficients of the series and parallel resonators of the transmitting filter or the receiving filter is greater than 0.015.

[0042] Figure 5 The graph shows a comparison of the insertion loss of the transmit filter. The solid line represents the insertion loss curve of the transmit filter in the comparative example, and the dashed line represents the insertion loss curve of the transmit filter in the first embodiment. As can be seen from the graph, compared with the comparative example, the first embodiment has a 0.2dB improvement in the insertion loss on the right side of the transmit filter passband, and the right roll-off is also better. Figure 6 The graph shows a comparison of insertion loss of the receiving filter. The solid line (thick line) is the insertion loss curve of the receiving filter in the comparative example, and the dashed line (thin line) is the insertion loss curve of the receiving filter in the first embodiment. As can be seen from the graph, compared with the comparative example, the insertion loss on the right side of the passband of the receiving filter in this embodiment is improved by 0.3dB, and the insertion loss on the left side of the passband of the receiving filter is improved by 0.2dB. At the same time, the left roll-off is better. Figure 7 The graph shows a comparison of isolation levels. The solid line represents the isolation level curve for the comparative embodiment, while the dashed line represents the isolation level curve for the first embodiment. The graph shows a 3dB improvement in isolation. It should also be noted that, theoretically, since both wafer 1 and wafer 2 in the first embodiment have resonators, the space utilization is higher, and the duplexer size can be reduced by half. However, considering that the first embodiment has additional connection pins that occupy some area, the actual duplexer size can be reduced by approximately 35%.

[0043] Second embodiment:

[0044] Figure 8 A plan view of the resonator distribution on wafers 1 and 2 in the duplexer 80 according to the second embodiment of the present invention is provided. The second embodiment is similar to the first embodiment, with wafer 1 at the bottom and wafer 2 on top. The main difference between the second and first embodiments is that each of the two wafers has an additional metal strip, and these two metal strips are positioned correspondingly. This metal strip can be connected to a metal sealing ring, which serves both as a heat dissipation function and as a way to reduce coupling between the transmit and receive filters, thereby improving isolation. Specifically, as shown... Figure 8 On wafer 1, an additional metal strip 12 is added, which is connected to a metal sealing ring 11. Because the metal sealing ring needs to be connected to the ground of the substrate, metal strip 12 is also equivalent to grounding. Similarly, on wafer 2, an additional metal strip 21 is added, which is connected to a metal sealing ring 22. After wafer 1 and wafer 2 are bonded, metal strip 21 and metal strip 12 are in complete contact as a whole.

[0045] The communication device of the embodiments of the present invention may include any of the duplexers disclosed herein.

[0046] In summary, the technical solution of the present invention provides a series resonator for the transmit filter and a parallel resonator for the receive filter on one of the two opposite surfaces of the two wafers, and a parallel resonator for the transmit filter and a series resonator for the receive filter on the other surface. This allows resonators to be fabricated on both wafers of the duplexer, making full use of space, thereby reducing the size of the duplexer and saving manufacturing costs.

[0047] Furthermore, by fabricating the series resonator of the transmitting filter and the parallel resonator of the receiving filter on a wafer with a thinner piezoelectric layer, their effective electromechanical coupling coefficient can be made smaller than that of the resonator on another wafer, thus improving the duplexer's adjacent-band insertion loss, roll-off, and isolation. Conversely, by fabricating the parallel resonator of the transmitting filter and the series resonator of the receiving filter on a wafer with a thicker piezoelectric layer, their effective electromechanical coupling coefficient can be made larger than that of the resonator on another wafer, maintaining the filter's bandwidth and ensuring good insertion loss.

[0048] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A duplexer, comprising a transmitting filter and a receiving filter composed of bulk acoustic resonators, characterized in that, The duplexer includes a stacked first wafer and a second wafer, with a first surface of the first wafer and a second surface of the second wafer facing each other. The series resonator of the emission filter is located on the first side of the first surface; The parallel resonator of the receiving filter is located on the second side of the first surface; The parallel resonator of the emission filter is located on the first side of the second surface; The series resonator of the receiving filter is located on the second side of the second surface.

2. The duplexer according to claim 1, characterized in that, The series resonator of the transmitting filter is aligned with the parallel resonator of the transmitting filter, and the series resonator of the receiving filter is aligned with the parallel resonator of the receiving filter.

3. The duplexer according to claim 1, characterized in that, The projections of the series resonators of the transmitting filter and the series resonators of the receiving filter onto the horizontal plane do not overlap. At the same time, the projections of the parallel resonators of the transmitting filter and the parallel resonators of the receiving filter onto the horizontal plane do not overlap.

4. The duplexer according to claim 1, characterized in that, The doping concentration of the piezoelectric layer in the first wafer and the doping concentration of the piezoelectric layer in the second wafer make the effective electromechanical coupling coefficient of the resonator on the second wafer greater than that of the resonator on the first wafer. Alternatively, the thickness of the piezoelectric layer in the first wafer and the thickness of the piezoelectric layer in the second wafer are such that the effective electromechanical coupling coefficient of the resonator on the second wafer is greater than the effective electromechanical coupling coefficient of the resonator on the first wafer.

5. The duplexer according to claim 1, characterized in that, The doping concentration of the piezoelectric layer in the first wafer and the doping concentration of the piezoelectric layer in the second wafer, as well as the thickness of the piezoelectric layer in the first wafer and the thickness of the piezoelectric layer in the second wafer, make the effective electromechanical coupling coefficient of the resonator on the second wafer greater than the effective electromechanical coupling coefficient of the resonator on the first wafer.

6. The duplexer according to claim 4 or 5, characterized in that, The effective electromechanical coupling coefficient of the parallel resonator of the transmitting filter is at least 0.015 greater than the effective electromechanical coupling coefficient of the series resonator of the transmitting filter.

7. The duplexer according to claim 4 or 5, characterized in that, The effective electromechanical coupling coefficient of the series resonator of the receiving filter is at least 0.015 greater than the effective electromechanical coupling coefficient of the parallel resonator of the receiving filter.

8. The duplexer according to claim 1, characterized in that, The first surface has a first metal strip located between the series resonator of the transmitting filter and the parallel resonator of the receiving filter. The second surface has a second metal strip corresponding to the position of the first metal strip, and the second metal strip is located between the parallel resonator of the transmitting filter and the series resonator of the receiving filter.

9. The duplexer according to claim 8, characterized in that, The first metal strip is connected to a metal sealing ring on the first wafer, and, The second metal strip is connected to a metal sealing ring on the second wafer.

10. A communication device, characterized in that, The duplexer includes any one of claims 1 to 9.

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