A broadband poc integration structure for an FBAR notch filter

Abstract

The application provides a broadband POC integrated structure of an FBAR wave trap, which comprises an FBAR wave trap chip and a broadband matching circuit structure, wherein the broadband matching circuit structure comprises a dielectric substrate, a metal pattern area for bonding the FBAR device, two radio frequency interfaces, at least one ground pad and at least two two-dimensional planar spiral matching inductors; the FBAR wave trap chip is mounted on the metal pattern area, the radio frequency ports of the FBAR wave trap chip are connected with the radio frequency interfaces respectively, and the ground port of the FBAR wave trap chip is connected with the ground pad; the two radio frequency interfaces are connected with the ground pad through the matching inductors respectively. The application effectively solves the problem of the mutual contradiction between the stop band suppression and the pass band standing wave, optimizes the insertion loss standing wave characteristics, greatly improves the pass band bandwidth, and realizes the FBAR wave trap performance of miniaturization, low insertion loss, low standing wave and 3.5 times frequency wide pass band.

Description

Technical Field

[0001] This invention relates to the field of microwave circuits, and in particular to a broadband POC integrated structure for an FBAR notch filter. Background Technology

[0002] The size of passive filters is one of the key factors limiting high-density integration in RF front-ends. Therefore, miniaturization has always been a major trend in filter development. The stringent requirements for weight reduction and low profile in electronic equipment necessitate miniaturization of passive filters while maintaining high performance. Traditional microwave notch filters use electromagnetic waves as the transmission medium and generally employ a suspended wire structure. The spacing between resonators is approximately one-quarter of a wavelength. The lower the frequency, the larger the device size, especially in the P-band and L-band, where traditional electrical notch filters are even larger and more difficult to integrate. LTCC filters also use electromagnetic waves as the transmission medium. Although researchers have reduced the design size to the millimeter level, meeting the requirements of general integration applications, it still cannot meet the requirements of SIP-level high-density integration applications. Furthermore, planar microstrip filters, widely used in RF and microwave bands, have reduced their size to the millimeter level, but in the P / L band, their size reaches tens of millimeters, still failing to meet the increasingly strong demand for high-density integration.

[0003] Unlike traditional microwave notch filters, FBAR technology is an acoustic notch filter technology. Using acoustic resonance, it can directly reduce the size of the chip at the same frequency by tens of times, even down to the hundred-micrometer scale for high-frequency bare chips. However, because the stopband suppression and high- and low-end standing wave ratios of FBAR notch filters are mutually restrictive, the greater the stopband suppression, the closer the insertion loss at the far end of the passband will be to the stopband position, making it difficult to apply in broadband applications.

[0004] To increase the passband bandwidth of an FBAR notch filter, an external matching circuit is required. This is typically achieved by using a matching inductor to increase the resonant point. Because the matching inductor has a high inductance, even reaching the 10nH range, a common method is to assemble it within the component using an enameled wire coil inductor. This inductor needs to be soldered to ground using spacers. While this assembly is simple, the spacers are prone to detaching during environmental testing, such as vibration tests, leading to low process reliability. Furthermore, this assembly method is sensitive to inductor accuracy and the matching distance between the inductor and the RF interface. Figure 1 As shown, the performance results of the notch filter obtained with different matching inductors and different matching distances for the same matching inductor are presented. It can be seen that the performance of the FBAR notch filter is significantly dependent on the number of turns of the inductor coil. In addition, when matching the same number of turns of the inductor, the performance of the FBAR notch filter will also change when the matching distance is changed. It can be seen that the FBAR notch filter obtained by this matching inductor method has poor performance and consistency. Summary of the Invention

[0005] To address the problems existing in the prior art, a broadband POC (Passive On Ceramics) integrated structure for FBAR notch filters is provided. This structure can adjust the position of the transmission poles by flexibly adjusting the number, position, and inductance value (up to tens of nH) of the matching inductors in the broadband matching circuit. It can effectively solve the contradiction between passband insertion loss VSWR and stopband suppression in FBAR notch filters, optimize passband insertion loss and VSWR while ensuring stopband suppression, and significantly improve the application passband bandwidth of FBAR notch filters.

[0006] The technical solution adopted in this invention is as follows: A broadband POC integrated structure for an FBAR notch filter includes an FBAR notch filter chip and a broadband matching circuit structure. The broadband matching circuit structure includes a dielectric substrate. The surface of the dielectric substrate is provided with a metal pattern area for bonding the FBAR device, two radio frequency interfaces, at least one ground pad, and at least two two-dimensional planar spiral matching inductors. The FBAR notch filter chip is mounted in the metal pattern area, and its radio frequency ports are respectively connected to the radio frequency interfaces, and its ground ports are connected to the ground pads. The two radio frequency interfaces are respectively connected to the ground pads through matching inductors.

[0007] Furthermore, the RF port of the FBAR notch filter chip is connected to the RF interface via gold wire bonding, and the ground port of the FBAR notch filter chip is connected to the ground pad via gold wire bonding; the RF interface is connected to the matching inductor via gold wire bonding.

[0008] Furthermore, the ground port of the FBAR notch filter chip is also connected to the ground pad through a matching inductor. One end of the matching inductor is connected to the ground port by gold wire bonding, and the other end is connected to the ground pad.

[0009] Furthermore, the radio frequency interface is provided with a transition structure, which is connected to one end of the matching inductor.

[0010] Furthermore, the matching inductor is centered at one end and spirally wound around the center at the other end to form a two-dimensional planar spiral matching inductor, which is square, circular or regular polygonal in shape. The center end of the matching inductor is provided with a metal pad, which is connected to the transition structure through the metal pad, and the other end is connected to the grounding pad.

[0011] Furthermore, the line width, line spacing, and number of coil turns of the matching inductor are adjusted according to actual needs to obtain the required inductance value.

[0012] Furthermore, the grounding pad has a grounding through hole connected to the back of the dielectric substrate, and the back of the dielectric substrate is a full-surface metal ground; the inner wall of the grounding through hole is metallized.

[0013] Furthermore, the radio frequency interface is implemented using an impedance-matched microstrip line structure.

[0014] Furthermore, the size of the metal pattern area is achieved by expanding the size of the FBAR notch filter by 0-0.2mm on one side. Its material is suitable for bonding conductive adhesive or red glue, and the notch filter chip is bonded to the metal pattern area by conductive adhesive or red glue.

[0015] Furthermore, the dielectric substrate is a dielectric substrate suitable for thin film processes, and is made of alumina ceramic, zirconia ceramic, ordinary glass or quartz glass.

[0016] Compared with existing technologies, the advantages of the above technical solution are as follows: The structure of this application introduces a pair of transmission poles at the far end of the passband of the FBAR notch filter, and the position of the transmission poles can be adjusted more flexibly to move them further away from the stopband. This not only effectively solves the contradiction between stopband suppression and passband standing wave ratio, but also optimizes the insertion loss standing wave characteristics, significantly improves the passband bandwidth, and achieves FBAR notch filter performance with miniaturization, low insertion loss, low standing wave ratio, and a 3.5 times bandwidth passband. This structure is small in size and has high process reliability. It is not only suitable for RF hybrid integrated circuits, but also for high-density integrated applications such as RF micro-modules and 3D stacked reconstruction. Compared with existing solutions, it has better broadband performance and higher consistency; it is smaller and has higher integration density; and it is simpler to implement and has higher process reliability and stability. Attached Figure Description

[0017] Figure 1 This diagram illustrates the performance results of the FBAR notch filter obtained with different matching inductance values ​​and different matching distances for the same matching inductance value in the existing scheme.

[0018] Figure 2 This is a diagram of the broadband POC integrated structure of the FBAR notch filter in one embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the device bonding and interconnection structure in a broadband matching circuit structure according to an embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of a matching inductor in one embodiment of the present invention.

[0021] Figure 5 This is a schematic diagram of a broadband matching circuit structure in one embodiment of the present invention.

[0022] Figure 6 This is a performance diagram of an FBAR notch filter without a matching circuit structure in one embodiment of the present invention.

[0023] Figure 7This is a performance diagram of an FBAR notch filter with a broadband POC integrated structure in one embodiment of the present invention.

[0024] Figure 8 This is a standing wave characteristic diagram of the FBAR notch filter of a broadband POC integrated structure in one embodiment of the present invention.

[0025] Reference numerals: 10-Dielectric substrate, 100-FBAR device bonding and interconnection structure, 200-Matching inductor, 300-FBAR notch filter chip, 101-Metal pattern area, 102-RF interface, 103-Ground pad, 104-Ground via, 105-Transition structure, 106-Square inductor, 107-Metal pad, 108-Gold wire bonding. Detailed Implementation

[0026] The embodiments of this application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar modules or modules having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, the embodiments of this application include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0027] This embodiment proposes a broadband POC integrated structure for FBAR notch filters. The broadband matching circuit in this POC integrated structure is simple and compatible with traditional thin-film and micro-assembly processes. The fabricated broadband POC structure has a small size, large passband bandwidth, high stopband suppression, and excellent high and low end VSWR. It effectively solves the problem of limited application and narrow passband bandwidth caused by the contradiction between stopband suppression and high and low end VSWR in FBAR notch filters. The specific solution is as follows:

[0028] A broadband point-of-concept (POC) integrated structure for an FBAR notch filter includes an FBAR notch filter chip and a broadband matching circuit structure. The broadband matching circuit structure includes a dielectric substrate with a metal patterned area for bonding the FBAR device, two radio frequency (RF) interfaces, at least one ground pad, and at least two two-dimensional planar spiral matching inductors on its surface. The FBAR notch filter chip is mounted in the metal patterned area, with its RF ports connected to the RF interfaces and its ground ports connected to the ground pads. Both RF interfaces are connected to the ground pads via matching inductors.

[0029] In this embodiment, the RF port of the FBAR notch filter chip is connected to the RF interface of the broadband matching circuit structure via gold wire bonding, and the ground port of the FBAR notch filter chip is connected to the ground pad of the broadband matching circuit structure via gold wire bonding; the RF interface is connected to the matching inductor via gold wire bonding. The gold wire, acting as a small matching inductor, can work with the spiral matching inductor to adjust the position of the notch filter's transmission pole.

[0030] In practical applications, the two RF interfaces must be connected to the ground pad via matching inductors. Additionally, matching inductors can be added between the ground port of the FBAR notch filter chip and the ground pad, depending on design requirements. One end of the matching inductor is connected to the ground port via gold wire bonding, and the other end is connected to the ground pad. The number of matching inductors is selected based on requirements.

[0031] In this embodiment, the RF interface is provided with a transition structure, which is connected to one end of the matching inductor. In a preferred embodiment, the RF interface is implemented using a microstrip line structure with 50-ohm impedance matching, and the transition structure has a size of 100μm×500μm, which is used for subsequent gold wire bonding with the inductor.

[0032] Specifically, the matching inductor is centered at one end, with the other end spirally wound around the center to form a two-dimensional planar spiral shape. The overall shape is square, circular, or a regular polygon. A metal pad is located at the center of the matching inductor, connecting it to a transition structure, while the other end is connected to a ground pad. When a matching inductor needs to be placed between the ground port of the FBAR notch filter chip and the ground pad, the metal pad at the center of the matching inductor is connected to the ground port of the FBAR notch filter chip via gold wire bonding, and the other end is connected to the ground pad. In practical applications, the inductance value of the matching inductor can be adjusted by adjusting the line width, line spacing, and number of coil turns, thereby flexibly adjusting the position of the transmission poles.

[0033] The grounding pad has a grounding through hole connected to the back of the dielectric substrate, and the back of the dielectric substrate is a whole metal ground. The grounding pad can be square, round or other irregular shape. The diameter of the grounding through hole is 100μm to 500μm and the inner wall is metallized.

[0034] In this embodiment, the size of the metal pattern area is achieved by expanding the size of the FBAR notch filter by 0 to 0.2 mm on one side. The material is suitable for bonding conductive adhesive or red glue. The FBAR notch filter chip is bonded to the metal pattern area with conductive adhesive or red glue.

[0035] In a preferred embodiment, the dielectric substrate is a dielectric substrate suitable for thin film processes, and is made of alumina ceramic, zirconia ceramic, ordinary glass or quartz glass.

[0036] Furthermore, this embodiment provides a specific scenario to illustrate the broadband POC integrated structure of the FBAR notch filter:

[0037] To realize the broadband POC integrated structure of the FBAR notch filter mentioned above, the broadband matching circuit structure must first be realized. This broadband matching circuit structure needs to ensure that the bare FBAR notch filter chip can be integrated on the substrate, and at the same time, it needs to enable interconnection between the FBAR device and the substrate, such as interconnection between RF ports and interconnection between ground pads.

[0038] like Figure 3 As shown, a planar metal structure is used to realize the FBAR device bonding and interconnection structure 100. This structure is set on the surface of the dielectric substrate 10 and consists of one FBAR device bonding metal pattern area 101, two RF interfaces 102, four ground pads 103, four circular vias 104, and two transition structures 105. The back of the dielectric substrate 10 is a full metal ground. In this application scenario, a matching inductor is only set between the RF interface and the ground pad. No matching inductor is set between the ground port of the FBAR notch filter chip and the ground pad. If it is necessary to set one, the layout can be changed and a matching inductor can be set between the ground port and the ground pad.

[0039] The overall size of the metal pattern area 101 is 1.3mm × 1.3mm, which needs to surround the FBAR device and can be adjusted according to the size of the device; the RF interface 102 is implemented using a 50Ω impedance matching microstrip line structure; the ground pad 103 is connected to the metal ground on the back of the dielectric substrate 10 through a grounding via 104 with an internal diameter of 100-500μm. The size of the ground pad 103 is larger than the diameter of the grounding via 104, and its position can be flexibly adjusted according to the layout; the transition structure 105 has a size of 100μm × 500μm and is used for subsequent gold wire bonding with the inductor.

[0040] Furthermore, to realize this broadband matching circuit structure, a high-precision and easily integrated inductor is also required. In this embodiment, a square spiral matching inductor 200 is used. The matching inductor structure consists of a planar spiral square inductor 106 and a metal pad 107. The center end of the planar spiral square inductor 106 is connected to the metal pad 107, and the other end is connected to the ground pad 103. Figure 4 , Figure 5 As shown. The metal pad 107 is used for subsequent gold wire bonding, the inductance of the square inductor 106 can be flexibly adjusted according to the matching parameters, and its relative position to the ground pad 103 can be flexibly adjusted according to the circuit layout.

[0041] Finally, the FBAR notch filter chip is mounted on the dielectric substrate and interconnected to realize the broadband POC integrated structure of the FBAR notch filter, such as... Figure 2As shown, the FBAR notch filter chip 300 is bonded to the metal pattern area 101 on the surface of the dielectric substrate using conductive adhesive. A transition structure 105 is connected to the metal pad 107 of the matching inductor via gold wire bonding 108, introducing a matching inductor at the RF interface location. Furthermore, gold wire bonding 108 interconnects the FBAR notch filter RF port and the RF interface 102 on the surface of the dielectric substrate 10. Gold wire bonding 108 also interconnects the FBAR notch filter ground port and the ground pad 103 on the surface of the dielectric substrate 10.

[0042] The matching inductor structure of the FBAR notch filter proposed in this embodiment is mainly divided into two parts. Structure 1 consists of two planar spiral inductors, which, compared with commonly used enameled wire coil inductors, not only have significant advantages in notch filtering performance and consistency but also have higher process reliability. Structure 2 is a gold wire bonding structure, where the gold wire can be equivalent to a small-value inductor. This equivalent inductance has a significant impact on insertion loss and standing wave ratio (SWR), but its adjustable range is extremely small, thus ensuring high process stability. By adding inductor structure 2 and adjusting inductor structure 1, the position of the transmission poles can be flexibly adjusted, effectively solving the contradiction between stopband suppression and passband SWR insertion loss in the FBAR notch filter, and effectively increasing the application bandwidth of the FBAR notch filter.

[0043] In radio frequency (RF) systems, notch filters are typically required to filter specific frequencies while avoiding attenuation of normal signals and ensuring that the operating signal remains unaffected. Therefore, notch filters are generally required to have low insertion loss, low VSWR, high stopband rejection, and wide passband characteristics. First, circuit simulation is used to obtain the performance of an FBAR notch filter without external matching circuitry. Figure 6 As shown, the insertion loss is relatively large, and the return loss is poor. Furthermore, the further away from the stopband, the more severe the deterioration in insertion loss and VSWR. Using the above technology, a broadband matching circuit structure for an FBAR notch filter is realized on a 0.381mm thick alumina ceramic substrate, as shown... Figure 3 As shown, the area is 3mm × 2.1mm. The frequency response curve was obtained through circuit simulation combined with semi-physical electromagnetic simulation, as shown below. Figure 7 , Figure 8 As shown, the maximum insertion loss is 1.2dB, the passband VSWR is <2, the stopband rejection reaches 33dBc, and the passband bandwidth reaches more than 3.5 times the frequency. It effectively meets the requirements of low insertion loss, low VSWR, high stopband rejection and broadband applications, and is superior to existing technologies in terms of size and performance.

[0044] The optimization of insertion loss and standing wave ratio, as well as the significant increase in bandwidth, are attributed to the dual matching effect of the planar matching inductor and the gold wire equivalent inductance. This allows a transmission pole to be generated at both the high and low ends of the passband. In this embodiment, the poles are mainly generated around 1.2 GHz and 2.4 GHz. While ensuring stopband suppression, the passband standing wave ratio and insertion loss are significantly optimized, effectively solving the problem of the contradiction between stopband suppression and passband insertion loss standing wave ratio in FBAR notch filters, enabling its application bandwidth to reach more than 3.5 times the frequency.

[0045] It should be noted that, in the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances. The accompanying drawings in the embodiments are used to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0046] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A broadband POC integrated structure for an FBAR notch filter, characterized in that, This includes the FBAR notch filter chip and broadband matching circuit structure; The broadband matching circuit structure includes a dielectric substrate. The surface of the dielectric substrate has a metal pattern area for bonding FBAR devices, two RF interfaces, at least one ground pad, and at least two two-dimensional planar spiral matching inductors. The size of the metal pattern area is achieved by expanding the size of the FBAR notch filter by 0-0.2mm on one side. The RF interfaces have a transition structure that connects to one end of the matching inductors. The center end of the matching inductor has a metal pad that connects to the transition structure, and the other end is connected to the ground pad. The ground pad has a grounding via that connects to the back of the dielectric substrate, which is a solid metal ground. The inner wall of the grounding via is metallized. The FBAR notch filter chip is mounted in the metal pattern area, with its RF ports connected to the RF interfaces respectively, and its ground port connected to the ground pad; both RF interfaces are connected to the ground pad through matching inductors.

2. The broadband POC integrated structure of the FBAR notch filter according to claim 1, characterized in that, The RF port of the FBAR notch filter chip is connected to the RF interface via gold wire bonding. The RF interface is implemented using an impedance-matched microstrip line structure and is connected to the matching inductor via gold wire bonding. The ground port of the FBAR notch filter chip is connected to the ground pad via gold wire bonding.

3. The broadband POC integrated structure of the FBAR notch filter according to claim 2, characterized in that, The ground port of the FBAR notch filter chip is connected to the ground pad through a matching inductor. One end of the matching inductor is connected to the ground port by gold wire bonding, and the other end is connected to the ground pad.

4. The broadband POC integrated structure of the FBAR notch filter according to claim 1, characterized in that, The matching inductor is centered at one end and spirally wound around the center at the other end, forming a two-dimensional planar spiral matching inductor, which is square, circular or regular polygonal in shape.

5. The broadband POC integrated structure of the FBAR notch filter according to claim 4, characterized in that, The line width, line spacing, and number of coil turns of the matching inductor are adjusted according to actual needs to obtain the required inductance value.

6. The broadband POC integrated structure of the FBAR notch filter according to claim 1, characterized in that, The metal pattern area is made of a material suitable for bonding conductive adhesive or red glue, and the notch filter chip is bonded to the metal pattern area using conductive adhesive or red glue.

7. The broadband POC integrated structure of the FBAR notch filter according to claim 1, characterized in that, The dielectric substrate is a dielectric substrate suitable for thin film processes, and is made of alumina ceramic, zirconia ceramic, ordinary glass or quartz glass.

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