A wide passband thin film bulk acoustic wave notch filter structure

Abstract

The application discloses a wide-passband thin film bulk acoustic resonator (FBAR) wave trap structure, and relates to the field of microwave passive chips, comprising: a FBAR wave trap chip capable of introducing an external matching inductance at a middle-stage series resonator and a wide-passband matching circuit structure; the application introduces two or more external matching inductances at the position of the middle-stage series resonator of the FBAR wave trap chip, the matching inductances can introduce one or more transmission poles at the two ends of the stop band of the FBAR wave trap, the position of the transmission poles can be flexibly adjusted, the insertion loss and the standing wave characteristics of the far end of the passband can be optimized, the problem of the mutual contradiction between the stop band suppression and the insertion loss and the standing wave of the passband can be effectively solved, and the passband bandwidth is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of microwave passive chips, specifically to a wide-passband thin-film bulk acoustic notch filter structure. Background Technology

[0002] The statements in this section are provided only as background information in connection with this disclosure and may not constitute prior art.

[0003] According to the working principle of passive filters, their size is usually positively correlated with wavelength, and both wavelength and frequency follow the physical relationship "v = λf", where v is the wave speed of electromagnetic waves or sound waves. Therefore, for a specific frequency filter, the smaller the wave speed, the smaller the wavelength, and correspondingly the smaller the filter size. Since electromagnetic waves have a relatively large wave speed, the wavelength is relatively large at lower frequencies. Traditional band-stop filters or notch filters use the electromagnetic wave resonance principle, with the length of a single resonator being about one-quarter of the wavelength, and the resonator spacing being about one-quarter of the wavelength. For example, in the P / L band, the resonator size can even reach the centimeter level. Acoustic filters use the acoustic wave resonance principle. With the advantage that the wave speed of sound is 4 to 5 orders of magnitude lower than that of electromagnetic waves, the size of filters in the P / L / S / C bands can be reduced by hundreds or even thousands of times to the level of hundreds of micrometers, which has obvious advantages in miniaturization and integration.

[0004] Acoustic filters include surface acoustic wave (SAW) filters and thin-film bulk acoustic wave (FBAR) filters. When FBAR resonators are used as notch filters, a contradictory phenomenon exists between passband insertion loss and standing wave ratio (SWR) and stopband rejection. When the passband bandwidth reaches a third harmonic and the stopband rejection exceeds 35 dB, the passband insertion loss and SWR deteriorate significantly, especially at the far end of the passband. To optimize SWR and insertion loss while increasing stopband rejection for FBAR notch filter applications, the current conventional technique involves connecting external matching inductors to the input / output ports and ground port. Although this optimizes insertion loss and SWR to some extent, they still deteriorate significantly at lower frequencies, limiting the passband range. Summary of the Invention

[0005] The purpose of this invention is to address the contradiction between passband insertion loss and standing wave ratio (SWR) and stopband suppression in current FBAR notch filters. This invention breaks through traditional matching methods and provides a wide-passband thin-film bulk acoustic wave (BAS) notch filter structure. By introducing an external matching inductor into the intermediate-stage series resonator, the contradiction between passband insertion loss and SWR and stopband suppression in FBAR notch filters can be effectively resolved. Simultaneously, it avoids the defects of increased low-frequency far-end insertion loss and deteriorated SWR caused by conventional port matching methods. In particular, introducing an external matching inductor into the series resonator at the center position allows for the introduction of one or more transmission poles on both sides of the stopband. Adjusting the inductance value of the matching inductor can change the position of the transmission poles, thereby optimizing insertion loss and SWR while significantly increasing the passband bandwidth. This effectively solves the problem of narrow passband bandwidth caused by severe far-end insertion loss and SWR deterioration in the FBAR notch filter.

[0006] The technical solution of the present invention is as follows:

[0007] A wide-passband thin-film bulk acoustic notch filter structure includes:

[0008] An FBAR notch filter chip and a wide-band matching circuit structure can be introduced at the intermediate-stage series resonator;

[0009] The FBAR notch filter chip includes three types of ports: an input / output port, a ground port, and two or more pad ports. The input / output port, ground port, and pad ports are all located on the surface of the FBAR notch filter chip. The pad ports are led out from the lower or upper electrode of the intermediate series resonator inside the FBAR notch filter chip and are used to connect to an external wideband matching circuit.

[0010] The wide passband matching circuit structure includes a dielectric substrate for supporting the FBAR notch filter chip and the wide passband matching circuit; the wide passband matching circuit includes several POC or POG two-dimensional and three-dimensional spiral inductors, which can be matched with four or more external circuits with three types of ports on the surface of the FBAR notch filter chip; the FBAR notch filter chip is located entirely on the surface of the dielectric substrate, and the back of the dielectric substrate is a metal ground.

[0011] Furthermore, each intermediate-stage series resonator inside the FBAR notch filter chip can lead out at least one pad port.

[0012] Furthermore, the pad ports on the surface of the FBAR notch filter chip appear in pairs;

[0013] Each pair of pad ports is led out from the same intermediate-stage series resonator and is located at both ends of the same series resonator. One pad port is connected to the upper electrode of the intermediate-stage series resonator, and the other pad port is connected to the lower electrode of the series resonator through an etched hole.

[0014] Furthermore, the pad ports on the surface of the FBAR notch filter chip appear individually;

[0015] Each pad port is led out by a different intermediate-stage series resonator. The pad port is directly connected to the upper electrode of the intermediate-stage series resonator or connected to the lower electrode of the series resonator through an etched hole.

[0016] Furthermore, the wide passband matching circuit structure includes a metal pattern for bonding the FBAR notch filter chip, the size of which is larger than the size of the FBAR notch filter chip.

[0017] Furthermore, the wideband matching circuit includes: an input / output interface, a ground interface, and a matching inductor.

[0018] Furthermore, the input / output interface is implemented using an impedance-matched microstrip line structure;

[0019] The input / output interface is connected to the input / output port of the FBAR notch filter chip via gold wire bonding, realizing physical cascading and weak circuit matching.

[0020] Furthermore, the grounding interface includes a grounding pad, which is connected to the metal ground on the back of the dielectric substrate through a through-hole;

[0021] The grounding pad is connected to the grounding port of the FBAR notch filter chip via gold wire bonding, realizing physical cascading of the ground port and weak circuit matching.

[0022] Furthermore, one end of the matching inductor is connected to the grounding pad;

[0023] The input and output ports of the FBAR notch filter chip serve as access terminals for the wide passband matching circuit, and are connected to the matching inductor of the wide passband matching circuit to achieve strong circuit matching.

[0024] The FBAR notch filter chip's pad ports are connected to the matching inductor via gold wire bonding, achieving strong circuit matching.

[0025] Furthermore, the inner diameter of the through hole is 100μm to 500μm, and the inner wall of the through hole is metallized.

[0026] Compared with existing technologies, the advantages of this invention are:

[0027] A wide-passband thin-film bulk acoustic wave (FBAR) notch filter structure is disclosed. Two or more external matching inductors are introduced at the intermediate-stage series resonator position of the FBAR notch filter chip. These matching inductors can introduce one or more transmission poles at each end of the stopband of the FBAR notch filter, and the positions of these transmission poles can be flexibly adjusted. This not only optimizes the insertion loss and standing wave characteristics at the far end of the passband but also effectively solves the contradiction between stopband suppression and passband insertion loss / standing wave, significantly improving the passband bandwidth. The position of the intermediate-stage series resonator has a significant impact on the matching effect. Especially when external inductors are used for matching at both ends of the series resonator in the center position, three transmission poles can be achieved, resulting in superior notch filter performance. Compared with conventional port matching methods in existing technologies, introducing external matching inductors at the port of the intermediate-stage series resonator of the notch filter can significantly improve insertion loss, standing wave, and passband bandwidth performance, enabling a miniaturized, low-insertion-loss, low-standing-wave, and 4th-harmonic passband bandwidth wide-passband FBAR notch filter structure. Attached Figure Description

[0028] Figure 1 A schematic diagram of a wide-passband thin-film bulk acoustic notch filter structure;

[0029] Figure 2 Performance diagram of FBAR notch filter without external matching inductor;

[0030] Figure 3 A schematic diagram of a conventional FBAR notch filter topology with an external matching inductor.

[0031] Figure 4 Performance diagram of FBAR notch filter with conventional external matching inductor;

[0032] Figure 5 The topology of the FBAR notch filter is a series resonator connected to an external matching inductor at the center position;

[0033] Figure 6 The implementation method of leading out the pad port of the lower electrode of the intermediate stage series resonator;

[0034] Figure 7 The implementation method of leading out the pad port of the upper electrode of the intermediate stage series resonator;

[0035] Figure 8 This is a schematic diagram of the FBAR notch filter chip port.

[0036] Figure 9 The diagram shows the performance of the wide-passband thin-film bulk acoustic notch filter proposed in Example 3.

[0037] Reference numerals: 100 - Wide passband matching circuit structure, 101 - Matching inductor, 102 - Input / output interface, 103 - Ground interface, 104 - Through hole, 105 - Metal pattern, 106 - Dielectric substrate, 107 - Gold wire, 201 - Pad port one, 202 - Piezoelectric layer etched hole, 203 - Lower electrode one of resonator, 204 - Upper electrode one of resonator, 301 - Pad port two, 302 - Upper electrode two of resonator, 303 - Lower electrode two of resonator, 401 - Pad port three, 402 - Pad port four, 403 - Ground port, 404 - Input / output port, 400 - FBAR notch filter chip. Detailed Implementation

[0038] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0039] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0040] Example 1

[0041] When thin-film bulk acoustic wave (FBAR) resonators are used as notch filters, a contradictory phenomenon exists between passband insertion loss VSWR and stopband rejection. When the passband bandwidth reaches a third harmonic and the stopband rejection exceeds 35 dB, the passband insertion loss VSWR deteriorates significantly, especially at the far end of the passband. Figure 2 As shown; to optimize VSWR and insertion loss while increasing stopband rejection and enabling the application of FBAR notch filters, the current conventional technique is to connect external matching inductors to the input / output ports and ground port, such as... Figure 3 The black circle indicates the notch filter performance after inductor matching. Figure 4 As shown, with a stopband suppression of 40dB, insertion loss and standing wave ratio are optimized to a certain extent. However, as the frequency approaches the lower and more distant frequencies, insertion loss and standing wave ratio still deteriorate significantly, and the passband range is limited.

[0042] This embodiment addresses the aforementioned problems by proposing a wide-passband thin-film bulk acoustic wave (FBAR) notch filter structure. Introducing an external matching inductor into the intermediate-stage series resonator effectively solves the contradiction between passband insertion loss, standing wave ratio (SWR), and stopband suppression in FBAR notch filters. It also avoids the drawbacks of conventional port matching methods, such as increased low-frequency far-end insertion loss and deteriorated SWR. In particular, introducing an external matching inductor into the central series resonator allows for the introduction of one or more transmission poles on both sides of the stopband. Adjusting the inductance value of the matching inductor changes the position of these transmission poles, thereby significantly improving the passband bandwidth while optimizing insertion loss and SWR. This effectively solves the problem of narrow application passband bandwidth caused by severe far-end insertion loss and SWR deterioration in FBAR notch filters.

[0043] Please see Figure 1 A wide-passband thin-film bulk acoustic notch filter structure, specifically comprising:

[0044] An FBAR notch filter chip and a wide-band matching circuit structure can be introduced at the intermediate-stage series resonator;

[0045] The FBAR notch filter chip includes three types of ports: an input / output port, a ground port, and two or more pad ports. All three ports are located on the surface of the FBAR notch filter chip. The pad ports are led out from the lower or upper electrode of the intermediate-stage series resonator inside the FBAR notch filter chip and are used to connect to an external wide-passband matching circuit. Preferably, a wide-passband matching circuit is added at both ends of the resonator at the center position to achieve three transmission poles and obtain a better matching effect. The pad ports can be square, rectangular, or irregular in shape, with a large area of ​​gold plating on the surface for gold wire bonding.

[0046] The wide-passband matching circuit structure includes a dielectric substrate for supporting the FBAR notch filter chip and the wide-passband matching circuit. The wide-passband matching circuit includes several POC or POG two-dimensional or three-dimensional spiral inductors, which can be implemented by square, circular or regular polygonal inductors. The wide-passband matching circuit can match four or more external circuits with three types of ports on the surface of the FBAR notch filter chip. The FBAR notch filter chip is located entirely on the surface of the dielectric substrate, and the back of the dielectric substrate is a metal ground. Preferably, the dielectric substrate can be alumina ceramic, zirconia ceramic, ordinary glass, quartz glass or other dielectric substrates suitable for thin film processes.

[0047] In this embodiment, specifically, each intermediate-stage series resonator inside the FBAR notch filter chip can lead out at least one pad port.

[0048] In this embodiment, specifically, the pad ports on the surface of the FBAR notch filter chip appear in pairs;

[0049] Each pair of pad ports is led out from the same intermediate-stage series resonator and is located at both ends of the same series resonator. One pad port is connected to the upper electrode of the intermediate-stage series resonator, and the other pad port is connected to the lower electrode of the series resonator through an etched hole. Preferably, when the paired pad ports are located at both ends of the series resonator in the center position, the external wide-bandwidth matching circuit can achieve a better matching effect.

[0050] In this embodiment, specifically, the pad ports on the surface of the FBAR notch filter chip appear separately;

[0051] Each pad port is led out by a different intermediate-stage series resonator. The pad port is directly connected to the upper electrode of the intermediate-stage series resonator or connected to the lower electrode of the series resonator through an etched hole.

[0052] In this embodiment, specifically, the wide passband matching circuit structure includes a metal pattern for bonding the FBAR notch filter chip, the size of which is larger than the size of the FBAR notch filter chip.

[0053] In this embodiment, specifically, the wide passband matching circuit includes: an input / output interface, a ground interface, and a matching inductor.

[0054] In this embodiment, specifically, the input / output interface is implemented using an impedance-matched microstrip line structure;

[0055] The input / output interface is connected to the input / output port of the FBAR notch filter chip via gold wire bonding, realizing physical cascading and weak circuit matching.

[0056] In this embodiment, specifically, the grounding interface includes: a grounding pad, which is connected to the back metal ground of the dielectric substrate through a through hole with an inner diameter of 100μm to 500μm, wherein the inner wall of the through hole is metallized;

[0057] The grounding pad is connected to the grounding port of the FBAR notch filter chip via gold wire bonding, realizing physical cascading of the ground port and weak circuit matching.

[0058] In this embodiment, specifically, one end of the matching inductor is connected to the grounding pad;

[0059] The input and output ports of the FBAR notch filter chip serve as access terminals for the wide passband matching circuit, and are connected to the matching inductor of the wide passband matching circuit to achieve strong circuit matching.

[0060] The FBAR notch filter chip's pad ports are connected to the matching inductor via gold wire bonding, achieving strong circuit matching.

[0061] In this embodiment, specifically, the FBAR notch filter chip implemented above has a size of less than 1.3mm × 1.3mm × 0.3mm;

[0062] The wide passband FBAR notch filter structure implemented above has a volume of less than 3mm × 3mm × 0.7mm.

[0063] Example 2

[0064] To realize the wide passband FBAR notch filter structure proposed in Embodiment 1, the location of the intermediate stage series resonator with the external matching inductor must first be determined.

[0065] like Figure 5 As indicated by the black circle, a matching inductor is introduced at each end of the fourth-order series resonator, and the inductance value is determined based on the frequency band of the notch filter and the matching effect.

[0066] Furthermore, it is necessary to determine the implementation method of the external matching inductor for the intermediate-stage series resonator, such as... Figure 6 and Figure 7 As shown;

[0067] in, Figure 6 The implementation method for leading out a pad port on the lower electrode of a series resonator includes: a pad port 201, a piezoelectric layer etched hole 202, a lower electrode of the resonator 203, and an upper electrode of the resonator 204.

[0068] Figure 7 The implementation method of leading out the pad structure on the upper electrode of the series resonator includes: pad port 2 301, upper electrode 2 302 of the resonator, and lower electrode 2 303 of the resonator.

[0069] The solder pads are plated with a large area of ​​gold to ensure the gold wire bonding requirements are met.

[0070] The three port structures of the implemented FBAR notch filter chip 400 are as follows: Figure 8 As shown, it includes: pad port 3 401 and pad port 402, ground port 403, and input / output port 404, which are respectively led out from both ends of the series resonator at the center position.

[0071] Furthermore, implement a wide passband matching circuit, such as... Figure 1 As shown, it includes: a matching inductor 101, one end of which is connected to a grounding interface 103. The grounding interface 103 is connected to the metal ground on the back of the dielectric substrate 106 through a through hole 104, and the inner wall of the through hole 104 is metallized.

[0072] Furthermore, it also includes: a metal pattern 105, which realizes the physical integration structure of the FBAR notch filter chip 400 on the wide passband matching circuit structure 100.

[0073] Furthermore, the FBAR notch filter chip 400 is interconnected with the input / output and ground ports of the wide passband matching circuit through the input / output interface 102 and the ground interface 103.

[0074] Furthermore, the FBAR notch filter chip 400 is integrated on the wide passband matching circuit structure 100. By bonding with gold wire 107, pad port 3 401 and pad port 402 are connected to the corresponding matching inductor 101, and the input / output interface 102 is connected to the corresponding matching inductor 101. This enables the input / output port 404 of the FBAR notch filter chip 400 to serve as the access terminal of the wide passband matching circuit, and is connected to the matching inductor 101 of the wide passband matching circuit to achieve strong circuit matching.

[0075] To achieve a wide passband FBAR notch filter structure, such as Figure 1 As shown, by introducing an external matching inductor into the intermediate stage series resonator, one or more transmission poles can be introduced at both ends of the stopband, which can effectively solve the contradiction between the stopband suppression and passband insertion loss standing wave of the FBAR notch filter, and effectively increase the application passband bandwidth of the FBAR notch filter chip.

[0076] Example 3

[0077] In radio frequency systems, notch filters are typically required to ensure that normal signals pass through with low attenuation while notching a specific frequency band. Therefore, notch filters usually need to have characteristics such as high stopband rejection, wide passband range, low passband insertion loss, and low passband standing wave ratio.

[0078] Using the above techniques, simulation design was performed for, for example Figure 5 The FBAR topology shown implements Figure 8 The layout shown realizes the wide passband matching circuit structure of the FBAR notch filter on a 0.381mm thick alumina ceramic substrate. The wide passband FBAR notch filter structure is realized through physical integration and gold wire bonding.

[0079] By combining electrical simulation and hardware-in-the-loop electromagnetic coupling simulation, the frequency response curve was obtained as follows: Figure 9 As shown, the stopband bandwidth is ±10MHz, the stopband rejection is >35dB, the passband insertion loss is <2.5dB, the passband VSWR is <2.2, and the passband bandwidth reaches more than 4 times the frequency.

[0080] and Figure 4Compared to conventional matching techniques, the wide passband FBAR notch filter structure implemented using the above technique adds three transmission poles in the passband. This is due to the matching effect of the external inductor introduced by the resonator at the center position. Two transmission poles are located at the left end of the stopband, and one transmission pole is located at the right end of the stopband. The two transmission poles located near the stopband effectively reduce the insertion loss and standing wave ratio (SWR) in the passband. The transmission pole located far to the left of the stopband significantly optimizes the insertion loss and SWR at the far end of the passband, resulting in a passband bandwidth of more than four times the frequency. This effectively meets the requirements of low insertion loss, low SWR, high stopband suppression, and wide passband applications, and outperforms existing technologies in terms of performance.

[0081] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

[0082] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects described in this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.

Claims

1. A wide-passband thin-film bulk acoustic notch filter, characterized in that, include: An FBAR notch filter chip and a wide-band matching circuit structure can be introduced at the intermediate-stage series resonator; The FBAR notch filter chip includes three types of ports: an input / output port, a ground port, and two or more pad ports. The input / output port, ground port, and pad ports are all located on the surface of the FBAR notch filter chip. The pad ports are led out from the lower or upper electrode of the intermediate series resonator inside the FBAR notch filter chip and are used to connect to an external wideband matching circuit. The wide passband matching circuit structure includes a dielectric substrate for supporting the FBAR notch filter chip and the wide passband matching circuit; the wide passband matching circuit includes several POC or POG two-dimensional and three-dimensional spiral inductors, which can achieve more than four external inductor matching with three types of ports on the surface of the FBAR notch filter chip; the FBAR notch filter chip is located entirely on the surface of the dielectric substrate, and the back of the dielectric substrate is a metal ground. The FBAR notch filter chip has a pair of pad ports on its surface. Each pair of pad ports is led out from the same intermediate-stage series resonator and is located at both ends of the same series resonator. One pad port is connected to the upper electrode of the intermediate-stage series resonator, and the other pad port is connected to the lower electrode of the series resonator through an etched hole. When the paired pad ports are located at both ends of the series resonator in the center position, an external wide-bandwidth matching circuit is used to realize three transmission poles. The wide passband matching circuit structure includes a metal pattern for bonding the FBAR notch filter chip, the size of which is larger than the size of the FBAR notch filter chip. The wide-band matching circuit includes: an input / output interface, a ground interface, and a matching inductor.

2. The wide-passband thin-film bulk acoustic notch filter according to claim 1, characterized in that, Each intermediate-stage series resonator inside the FBAR notch filter chip can lead out at least one pad port.

3. A wide-passband thin-film bulk acoustic notch filter according to claim 2, characterized in that, The pad ports on the surface of the FBAR notch filter chip appear individually; Each pad port is led out by a different intermediate stage series resonator. The pad port is directly connected to the upper electrode of the intermediate stage series resonator or connected to the lower electrode of the series resonator through an etched hole.

4. A wide-passband thin-film bulk acoustic notch filter according to claim 3, characterized in that, The input / output interface is implemented using an impedance-matched microstrip line structure. The input / output interface is connected to the input / output port of the FBAR notch filter chip via gold wire bonding, realizing physical cascading and weak circuit matching.

5. A wide-passband thin-film bulk acoustic notch filter according to claim 4, characterized in that, The grounding interface includes: a grounding pad, which is connected to the metal ground on the back of the dielectric substrate through a through hole; The grounding pad is connected to the grounding port of the FBAR notch filter chip via gold wire bonding, realizing physical cascading of the ground port and weak circuit matching.

6. A wide-passband thin-film bulk acoustic notch filter according to claim 5, characterized in that, One end of the matching inductor is connected to the grounding pad; The input and output ports of the FBAR notch filter chip serve as access terminals for the wide passband matching circuit, and are connected to the matching inductor of the wide passband matching circuit to achieve strong circuit matching. The FBAR notch filter chip's pad ports are connected to the matching inductor via gold wire bonding, achieving strong circuit matching.

7. A wide-passband thin-film bulk acoustic notch filter according to claim 5, characterized in that, The inner diameter of the through hole is 100μm~500μm, and the inner wall of the through hole is metallized.

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