Filter chip and SAW resonator of the first kind

Abstract

Filter chip comprehensive - a continuous carrier substrate, - at least one electrical filter (1) of the first type is on the carrier substrate, which comprises at least one SAW resonator (10) of the first type, wherein - the SAW resonator (10) of the first type comprises a piezoelectric layer (11), an intermediate layer (12) on the piezoelectric layer (11) and an interdigital electrode structure (13) on the intermediate layer (12), - the interdigital electrode structure (13) is separated from the piezoelectric layer (11) by the intermediate layer (12), and wherein - the intermediate layer (12) is made of a dielectric, non-piezoelectric material; wherein the intermediate layer (12) is applied to the piezoelectric layer (11) in such a way that a distance between a resonance and an anti-resonance of the electrical filter of the first type is reduced; and - a plurality of electrical filters (2) of a second type on the carrier substrate, each comprising at least one SAW resonator (20) of a second type, wherein - the second type SAW resonator (20) comprises a piezoelectric layer (11) and an interdigital electrode structure (13) which is applied directly to the piezoelectric layer (11).

Description

[0001] A filter chip and a SAW resonator of the first kind are described.

[0002] From document DE 10 2018 109 833 A1, which is also prior art according to Section 3 (2) of the German Patent Act (PatentG), a SAW resonator is known that offers the possibility of adjusting the bandwidth of a bandpass filter or a bandstop filter. The described SAW resonator comprises a piezoelectric material, an electrode structure over the piezoelectric material, and a dielectric adjustment layer between the piezoelectric material and the electrode structure.

[0003] From document DE 11 2009 000 281 T5, an edge acoustic wave device is known, comprising a piezoelectric substrate having a top surface; a dielectric film formed on the top surface of the piezoelectric substrate and consisting of a first dielectric, an electrode formed on the dielectric film and comprising an IDT electrode, and a dielectric layer formed to cover the electrode and consisting of a second dielectric.

[0004] Document US 2008 / 0067891 A1 discloses an acoustic wave component comprising a piezoelectric substrate, a first dielectric film formed on the piezoelectric substrate, and electrodes provided on the first dielectric film for exciting an acoustic wave. The electrodes include electrode fingers. At least a portion of the first dielectric film is cut out between adjacent electrode fingers.

[0005] From the document US 2012 0200371 A1 an acoustic wave device is known which comprises a piezoelectric substrate, a dielectric layer formed on the piezoelectric substrate and first and second comb-tooth electrodes formed on the dielectric layer, wherein the dielectric layer has a first thickness between the first comb-tooth electrodes and the piezoelectric substrate and a second thickness between the second comb-tooth electrodes and the piezoelectric substrate, wherein the first and second thicknesses are different.

[0006] One problem to be solved is to provide a space-saving filter chip for communications applications. Another problem to be solved is to provide a SAW resonator of the first kind for such a filter chip.

[0007] These problems are solved, among other things, by the subject matter of the independent claim. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0008] According to at least one embodiment, the filter chip comprises a plurality of electrical filters. The filters are integrated into the filter chip. For example, each of the filters is a bandpass or bandstop filter. Preferably, the filters are RF filters. The filter chip comprises, for example, at least two or at least three or at least four or at least five electrical filters.

[0009] Each electrical filter includes an input terminal and an output terminal. The filters are configured so that an RF signal can be applied to the input terminal, then filtered by the filter, and the filtered signal can be tapped at the output terminal. Preferably, the input terminal or the output terminal of each filter is connected to an antenna terminal of the filter chip. Additionally, each electrical filter may have one or more ground terminals. Each electrical filter preferably includes one or more SAW (surface acoustic wave) resonators. For example, the electrical filters are ladder-type filters that include multiple series SAW resonators and multiple shunt SAW resonators, also called parallel SAW resonators. SAW resonators are electroacoustic resonators with an interdigital electrode structure on a piezoelectric layer.

[0010] The filter chip described here can be used particularly in communication devices such as mobile phones.

[0011] A chip is to be understood here and below as a separately operable and electrically contactable element. A chip is formed in particular by singulation from a wafer. The chip can comprise a continuous carrier substrate. The carrier substrate can be formed from a semiconductor material, e.g., crystalline Si, or from a ceramic such as Al2O3. Lateral surfaces of the carrier substrate can have traces of material removal resulting from the singulation of the chip from the wafer. A lateral extent of the chip is, for example, at most 1%, at most 5%, or at most 10% larger than the lateral extent of the carrier substrate. All electrical functional regions of the filter chip are preferably carried by the carrier substrate. A lateral extent is an extent measured parallel to the main extension plane of the chip.

[0012] According to at least one embodiment, at least one of the plurality of electrical filters is a first-type electrical filter. A first-type electrical filter is defined here as a filter that comprises at least one first-type SAW resonator, which is defined below. An first-type electrical filter may comprise a plurality of first-type SAW resonators. Preferably, a first-type filter comprises only first-type SAW resonators. It is possible for the filter chip to comprise only one first-type filter or to comprise a plurality of first-type filters.

[0013] A first-type SAW resonator is defined here as a SAW resonator comprising a piezoelectric layer, an intermediate layer on the piezoelectric layer, and an interdigital electrode structure on the intermediate layer. Thus, the intermediate layer is located between the interdigital electrode structure and the piezoelectric layer. In particular, both the interdigital electrode structure and the piezoelectric layer are in direct contact with the intermediate layer.

[0014] The piezoelectric layer can be a thin film. The piezoelectric layer is preferably applied to the carrier substrate of the filter chip.

[0015] One or more dielectric, non-piezoelectric layers can be located between the carrier substrate and the piezoelectric layer. Alternatively, the piezoelectric layer itself can form the carrier substrate. For example, the piezoelectric layer is made of lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, or another suitable piezoelectric material for SAW resonators. The interdigital electrode structure and the intermediate layer are applied to a side of the piezoelectric layer facing away from the carrier substrate.

[0016] The interdigital electrode structure comprises, for example, two electrodes, each with several fingers. The fingers of the two electrodes interdigitate with each other. The electrodes are preferably formed from or comprise a metal or a metal layer stack. The electrodes of the interdigital electrode structure are preferably applied directly to the intermediate layer. Each electrode can comprise at least ten, or at least 50, or at least 100 fingers. In particular, the intermediate layer extends continuously, preferably without interruptions, across all fingers of the electrode structure.

[0017] According to at least one embodiment, in the SAW resonator of the first type, the interdigital electrode structure is separated from the piezoelectric layer by the intermediate layer, preferably only by the intermediate layer. Thus, a distance between the interdigital electrode structure and the piezoelectric layer, in particular a distance between the electrodes of the electrode structure and the piezoelectric layer, is defined by the thickness of the intermediate layer.

[0018] According to at least one embodiment, the intermediate layer of the first type of SAW resonator comprises a dielectric, non-piezoelectric material. The intermediate layer can be made of only one material or comprise multiple layers of different materials.

[0019] The properties specified here and below for a first-type SAW resonator apply to each first-type SAW resonator of the filter chip. In a first-type filter comprising multiple first-type SAW resonators, the piezoelectric layer and / or the intermediate layer preferably extend contiguously across all first-type SAW resonators of the filter.

[0020] In at least one embodiment, the filter chip comprises a plurality of electrical filters, wherein at least one of the plurality of electrical filters is a first-type electrical filter comprising at least one first-type SAW resonator. The first-type SAW resonator comprises a piezoelectric layer, an intermediate layer on the piezoelectric layer, and an interdigital electrode structure on the intermediate layer. The interdigital electrode structure is separated from the piezoelectric layer by the intermediate layer. The intermediate layer comprises a dielectric, non-piezoelectric material.

[0021] The present invention is based, among other things, on the discovery that by using a thin, dielectric, and non-piezoelectric intermediate layer between the electrode structure and the piezoelectric layer of a SAW resonator, the coupling factor of the SAW resonator and thus the pole-zero spacing, i.e., the distance between the resonance and the antiresonance of the SAW resonator, can be reduced. This makes it possible, for example, to reduce the bandwidth of the filter in which such a SAW resonator is used. In fact, the bandwidth of a filter is largely determined by the pole-zero spacing of the resonator(s) used. As a first approximation, the pole-zero spacing of a resonator corresponds to approximately half the bandwidth of the filter.

[0022] Typically, the maximum achievable pole-to-zero spacing of a SAW resonator is defined by the stacking properties of the SAW technology used. The pole-to-zero spacing can be reduced either by adding a capacitance parallel to the resonator or by selecting a SAW stack or a SAW technology with a smaller inherent pole-to-zero spacing. In both cases, however, the area required by the resonator and thus the filter is increased. Consequently, such a filter cannot usually be implemented together with other filters in a single chip.

[0023] With the present invention, a filter with a narrow bandwidth and low area consumption can be realized using one or more SAW resonators of the first type with an intermediate layer. A capacitor connected in parallel with the SAW resonator is no longer required, or the area of ​​the parallel capacitor is significantly reduced. Such a filter can be integrated together with other filters in a filter chip.

[0024] According to at least one embodiment, a main acoustic mode wave of the first-type SAW resonator of the filter has a wavelength λ. The main acoustic mode wave is the acoustic wave for which the resonator is designed. During operation, a surface acoustic wave with such a wavelength is generated in the SAW resonator. In particular, the pitch between two adjacent fingers of the interdigital electrode structure is λ / 2.

[0025] According to at least one embodiment, the thickness of the intermediate layer is at least 0.001 λ or at least 0.005 λ. Additionally or alternatively, the thickness of the intermediate layer is at most 0.05 λ or at most 0.02 λ or at most 0.01 λ. In absolute values, the thickness of the intermediate layer can be at least 2 nm or at least 10 nm. Additionally or alternatively, the thickness may be at most 100 nm or at most 40 nm or at most 20 nm. With increasing thickness of the intermediate layer, the coupling factor of the SAW resonator of the first type decreases. By adjusting the thickness of the intermediate layer, the pole-zero distance can be adjusted. Such a thin intermediate layer has only a minor influence on the temperature-frequency coefficient of the resonator.

[0026] Preferably, the above-mentioned thickness for the intermediate layer applies to all SAW resonators of the first type, where λ is the wavelength of the main mode of the respective resonator.

[0027] A layer thickness is defined here as the average thickness of the layer, averaged over the entire lateral extent of the layer.

[0028] According to at least one embodiment, the intermediate layer has a lower relative permittivity er than the piezoelectric layer. Preferably, the relative permittivity er is at most 10, or at most 8, or at most 5, or at most 3. A low relative permittivity er is preferred because the lower the relative permittivity εr, the greater the reduction in the coupling factor and thus also the reduction in the pole-zero distance.

[0029] According to at least one embodiment, the intermediate layer comprises or consists of one or more of the following materials: Al2O3, MgO, ZrO2.

[0030] According to at least one embodiment, each filter of the filter chip is a bandpass filter. Two filters of the filter chip preferably have different bandwidths and / or different center frequencies.

[0031] According to at least one embodiment, the at least one filter of the first type is a bandpass filter with a bandwidth of at most 20 MHz or at most 10 MHz.

[0032] According to at least one embodiment, the filter chip is a multiplexer, for example, a duplexer, a quadplexer, or a pentaplexer. In particular, the filter chip comprises one or more transmit filters (Tx filters) and / or one or more receive filters (Rx filters). The at least one filter of the first type can be a transmit filter or a receive filter.

[0033] According to at least one embodiment, the intermediate layer is deposited by atomic layer deposition (ALD). Atomic layer deposition allows for the production of particularly thin and homogeneous layers. A maximum deviation of the layer thickness from the average thickness is, for example, at most 10%, at most 5%, or at most 2%.

[0034] According to at least one embodiment, each filter comprises at least one, i.e., one or more, SAW resonators. Each SAW resonator comprises an interdigital electrode structure on a piezoelectric layer. The interdigital electrode structure can be applied directly to the piezoelectric layer or separated from the piezoelectric layer by an intermediate layer (SAW resonator of the first type). The features of the piezoelectric layer and the interdigital electrode structure disclosed here in connection with the SAW resonator of the first type are also disclosed for each SAW resonator of the filter chip.

[0035] According to at least one embodiment, the piezoelectric layers of all SAW resonators of all filters are formed by a continuous piezoelectric layer. This means that all SAW resonators of the filter chip share the same piezoelectric layer. The piezoelectric layer preferably extends over the entire lateral extent or almost the entire lateral extent of the filter chip. The piezoelectric layer is preferably simply connected, i.e., it is free of holes or interruptions.

[0036] According to claim 1, the filter chip comprises a plurality of second-type electrical filters. A second-type electrical filter is defined here as a filter that includes at least one second-type SAW resonator. A second-type SAW resonator is defined below. A second-type filter may include a plurality of second-type SAW resonators. In particular, a second-type filter includes only second-type SAW resonators and no first-type SAW resonators.

[0037] A second-type SAW resonator is defined herein as a SAW resonator comprising a piezoelectric layer and an interdigital electrode structure applied directly to the piezoelectric layer. The features disclosed for the interdigital electrode structure and the piezoelectric layer in connection with the first-type SAW resonator are also disclosed for the second-type SAW resonator. Second-type SAW resonators thus differ from first-type SAW resonators in that they do not comprise the intermediate layer between the electrode structure and the piezoelectric layer. The electrodes of the electrode structure, in particular the metal layers of the electrodes, are therefore applied directly to the piezoelectric material of the piezoelectric layer in a second-type SAW resonator.

[0038] According to at least one embodiment, the at least one second-type filter is a bandpass filter with a bandwidth of at least 30 MHz or at least 50 MHz. Such a bandpass filter does not require an intermediate layer.

[0039] According to at least one embodiment, the filter chip is a pentaplexer for LTE applications.

[0040] According to at least one embodiment, the filter chip comprises a filter of the first type and four filters of the second type. In particular, the filter chip comprises exactly one filter of the first type and exactly four filters of the second type.

[0041] According to at least one embodiment, the first type filter is an Rx filter configured for frequency band 30 (bandwidth = 10 MHz).

[0042] According to at least one embodiment, two of the second-type filters are Tx filters. One of these Tx filters is configured for frequency band 25 (bandwidth = 65 MHz) and one of these Tx filters is configured for frequency band 66 (bandwidth = 70 MHz).

[0043] According to at least one embodiment, two of the second-type filters are Rx filters. One of these Rx filters is configured for frequency band 25 (bandwidth = 65 MHz) and one of these Rx filters is configured for frequency band 66 (bandwidth = 90 MHz).

[0044] The SAW resonators mentioned here may be TCF SAW resonators (TCF = temperature-compensated filter). These SAW resonators comprise a TCF compensation layer, for example, made of SiO2, on the interdigital electrode structure.

[0045] Alternatively, the SAW resonators mentioned here can also be thin-film SAW resonators. In this case, a TCF compensation layer, e.g., made of SiO2, can be located between the piezoelectric layer and the carrier substrate.

[0046] In addition to the filter chip, the present invention also relates to a SAW resonator of the first type as described herein, as well as a filter of the first type as described herein.

[0047] Further preferred embodiments and developments of the filter chip and the SAW resonator of the first type are described below in conjunction with the figures. Identical or similar elements, as well as elements with the same function, are designated by the same reference numerals in the figures. The figures and the proportions of the elements depicted in the figures are not considered to scale. Rather, individual elements, particularly layers, may be exaggerated for the sake of better illustration and / or understanding.

[0048] In the figures: Fig. 1 shows an exemplary embodiment of the filter chip, Fig. 2 shows a section of an exemplary embodiment of the filter of the first type in a cross-sectional view, Fig. 3 shows a section of an example of a filter of the second type in a cross-sectional view, Fig. 4 shows a section of another exemplary embodiment of a filter of the first type in a cross-sectional view, Fig. Figure 5 shows the simulated admittance curves of different SAW resonators.

[0049] Fig. Figure 1 shows an exemplary embodiment of the filter chip. The filter chip comprises four filters 1, 2. One filter 1 is a first-type filter, and four filters are each a second-type filter. The filters 1, 2 are all connected to an antenna 3. The antenna 3 is not part of the filter chip.

[0050] The filter chip of the Fig. 1 is a pentaplexer suitable for communication applications. The filter chip of the Fig. 1 can be used, for example, in mobile phones. For example, the first-type filter 1 is an Rx filter configured for LTE frequency band 30, two of the second-type filters 2 are Tx filters configured for LTE frequency bands 25 and 66, respectively, and the two remaining second-type filters 2 are Rx filters configured for LTE frequency bands 25 and 66, respectively.

[0051] Fig. 2 shows a section of an exemplary embodiment of the filter 1 of the first type, for example the filter chip of the Fig. 1 used filter 1 of the first type. The filter 1 of the first type comprises a carrier substrate 14, for example made of Si. The carrier substrate 14 is preferably self-supporting and mechanically supports all structures applied to the carrier substrate 14. A piezoelectric layer 11 is applied to an upper side of the carrier substrate 14. The piezoelectric layer 11 is made of, for example, LiTaO3 or LiNbO3. An intermediate layer 12 is applied to a side of the piezoelectric layer 11 facing away from the carrier substrate 14. The intermediate layer 12 is in direct contact with the piezoelectric layer 11. The intermediate layer 12 comprises a dielectric, non-piezoelectric material. The intermediate layer 12 is made of, for example, Al2O3. The intermediate layer 12 was deposited, for example, using atomic layer deposition (ALD).

[0052] Interdigital electrode structures 13 are applied to a side of the intermediate layer 12 facing away from the piezoelectric layer 11. The electrode structures 13 each comprise electrodes, preferably made of a metal such as Al and / or Cu. The electrodes are in direct contact with the intermediate layer 12. The electrodes comprise fingers, with the fingers of the various electrodes interdigitating with each other.

[0053] In Fig. 2, two electrode structures 13, each with intermeshing electrodes, are applied to the intermediate layer 12. Each of the electrode structures 13, together with the piezoelectric layer 11 and the intermediate layer 12, forms a SAW resonator 10 of the first type. The two SAW resonators 10 of the first type of Fig. 2 are connected in series. The filter 1 of the first type in Fig. 2 may comprise further SAW resonators 10 of the first type, e.g., SAW resonators 10 of the first type connected in parallel to the shown SAW resonators 10 of the first type. The filter of the first type 1 in Fig. 1 is, for example, a ladder-type filter.

[0054] A TCF compensation layer 15, for example made of SiO2, is applied to the electrode structures 13.

[0055] As in Fig. As can be seen in Figure 2, the two SAW resonators 10 of the first type share the same piezoelectric layer 11, which extends contiguously across both SAW resonators 10 of the first type. Likewise, the intermediate layer 12 extends adjacently across the two SAW resonators 10 of the first type.

[0056] The SAW resonators 10 of the first type of Fig. 1 are each configured for the excitation of a main acoustic mode wave with a wavelength λ. In particular, the distance between two adjacent fingers of the electrode structures 13 is λ / 2. The thickness of the intermediate layer 12 is preferably at least 0.001·λ and at most 0.02·λ. Such a thin intermediate layer 12 reduces the pole-zero distance in each of the SAW resonators 10 of the first type. For example, the filter 1 of the first type in Fig. 2 a bandwidth of no more than 20 MHz.

[0057] Fig. 3 shows an excerpt from an example of a filter of the second type 2. For example, the filter of the second type 2 is the Fig. 3 one of the second type filters 2, which are located in the filter chip of the Fig. 1. The second type filter 2 comprises two second type SAW resonators 20. The second type SAW resonators 20 are constructed similarly to the first type SAW resonators 10 in Fig. 2, with the difference that no intermediate layer 12 is used. Instead, the electrodes of the electrode structures 13 are applied directly to the piezoelectric layer 11.

[0058] In Fig. 1, a piezoelectric layer of the various filters 1, 2 preferably extends continuously over all filters 1, 2.

[0059] Fig. 4 shows a further exemplary embodiment of the filter 1 of the first type. This filter 1 of the first type could also be the filter 1 of the first type of Fig. 1. The filter of the first kind 1 of the Fig. 4 is constructed similarly to the filter of the first type 1 of the Fig. 2. In this case, however, no TCF compensation layer is applied to the electrode structures 13. Instead, a TCF compensation layer 16, e.g. made of SiO2, is located between the carrier substrate 14 and the piezoelectric layer 11. The piezoelectric layer 11 in Fig. 4 is preferably a thin film.

[0060] Fig. Figure 5 shows the simulated admittance curves of various SAW resonators. The x-axis represents the frequency in MHz. The y-axis represents the imaginary part of the admittance in arbitrary units.

[0061] Graph C1 shows the simulation results for a second-type SAW resonator, in which the interdigital electrode structure is applied directly to the piezoelectric layer without a dielectric, non-piezoelectric intermediate layer. The pole-zero distance, i.e., the distance between the resonance and antiresonance, is comparatively large.

[0062] Graphs C2 to C4 represent the simulation results for first-type SAW resonators. The design of the first-type SAW resonators is almost identical to that of the simulated second-type SAW resonator used in Graph C1. The only difference is that a dielectric, non-piezoelectric interlayer was used between the interdigital electrode structures and the piezoelectric layer for the first-type SAW resonators. For Graph C2, the interlayer thickness was simulated to be 2.5 nm. For Graph C3, a thickness of 5 nm was simulated. For Graph C4, a thickness of 10 nm was simulated. As can be seen, with increasing the thickness of the interlayer, the pole-zero distance can be significantly reduced. Thus, a first-type SAW resonator can be used in filters where a narrow bandwidth is desired.

[0063] The invention described here is not limited by the description in conjunction with the exemplary embodiments. Rather, the invention encompasses any novel feature and any combination of features, in particular any combination of features in the claims, even if this feature or combination is not explicitly mentioned as such in the claims or exemplary embodiments. List of reference symbols: 1 first type filter 2 second type filters 3 Antenna 10 SAW resonator of the first kind 11 piezoelectric layer 12 Intermediate layer 13 interdigital electrode structure 14 Carrier substrate 15 TCF compensation layer 16 TCF compensation layer 20 SAW resonator of the second type C1, C2, C3, C4 simulated admittance curves

Claims

[1] Filter chip comprising - a continuous carrier substrate, - at least one electrical filter (1) of the first type is on the carrier substrate, which comprises at least one SAW resonator (10) of the first type, wherein - the SAW resonator (10) of the first type comprises a piezoelectric layer (11), an intermediate layer (12) on the piezoelectric layer (11) and an interdigital electrode structure (13) on the intermediate layer (12), - the interdigital electrode structure (13) is separated from the piezoelectric layer (11) by the intermediate layer (12), and wherein - the intermediate layer (12) is made of a dielectric, non-piezoelectric material; wherein the intermediate layer (12) is applied to the piezoelectric layer (11) in such a way that a distance between a resonance and an anti-resonance of the electrical filter of the first type is reduced; and - a plurality of electrical filters (2) of a second type on the carrier substrate, each comprising at least one SAW resonator (20) of a second type, wherein - the second type SAW resonator (20) comprises a piezoelectric layer (11) and an interdigital electrode structure (13) which is applied directly to the piezoelectric layer (11). [2] Filter chip according to claim 1, wherein - a main acoustic mode wave of the first type SAW resonator (10) of the first type filter (1) has a wavelength λ, - the thickness of the intermediate layer (12) is between 0.001·λ and 0.05·λ inclusive. [3] Filter chip according to one of the preceding claims, wherein the intermediate layer (12) has a lower relative permittivity than the piezoelectric layer (11). [4] Filter chip according to one of the preceding claims, wherein the intermediate layer (12) comprises or consists of: Al2O3, MgO, ZrO2. [5] Filter chip according to one of the preceding claims, wherein each filter (1, 2) is a bandpass filter. [6] Filter chip according to one of the preceding claims, wherein the at least one filter (1) of the first type is a bandpass filter with a bandwidth of at most 20 MHz. [7] Filter chip according to one of the preceding claims, wherein the filter chip is a multiplexer. [8] Filter chip according to one of the preceding claims, wherein the intermediate layer (12) is deposited by atomic layer deposition. [9] Filter chip according to one of the preceding claims, wherein - each filter (1, 2) comprises at least one SAW resonator (10, 20), - each SAW resonator (10, 20) comprises an interdigital electrode structure (13) on a piezoelectric layer (11), - the piezoelectric layers (11) of all SAW resonators (10, 20) of all filters (1, 2) are formed by a continuous piezoelectric layer (11). [10] Filter chip according to one of claims 1 to 9, wherein the at least one filter of the second type (2) is a bandpass filter with a bandwidth of at least 30 MHz. [11] Filter chip according to one of claims 1 to 10, wherein - the filter chip is a pentaplexer for LTE applications, - the filter chip comprises a filter of the first type (1) and four filters of the second type (2), - the filter of the first type (1) is an Rx filter configured for the frequency band 30 - two of the second type filters (2) are Tx filters, one configured for the frequency band 25 and one configured for the frequency band 66, - two of the second type filters (2) are Rx filters, one configured for frequency band 25 and one configured for frequency band 66.

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