WO2017184759A1

WO2017184759A1 - Multiplexer with filters realized in different technologies

Info

Publication number: WO2017184759A1
Application number: PCT/US2017/028403
Authority: WO
Inventors: Edgar Schmidhammer
Original assignee: Snaptrack, Incorporated
Priority date: 2016-04-20
Filing date: 2017-04-19
Publication date: 2017-10-26
Also published as: DE102016107309B3

Abstract

In a multiplexer configured for signal separation in carrier-aggregation mode, two filters of the multiplexer are designed in different technologies with different reflection behavior. The selection and assignment of the respective technology for one of the two filters respectively takes place such that the filter designed with the respective technology has a higher reflectivity for the respective counter band. The first filter (FEl) may be configured for band 8 and designed as an SAW filter on a lithium tantalate substrate, in which the second filter (FE2) may be configured for band 20 and designed as an SAW filter on a lithium niobate substrate and provided with a temperature compensation layer.

Description

MULTIPLEXER WITH FILTERS REALIZED IN DIFFERENT TECHNOLOGIES

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to German Application No. DE 102016107309.1 , filed April 20, 2016, which is incorporated herein by reference in its entirety.

DESCRIPTION

[0002] In order to manage the increasing demand for bandwidth in existing 4G and future 5G networks, what is known as "carrier aggregation" (CA) was introduced. In this aggregation, several mobile radio bands are operated simultaneously in one and the same communication link or data transmission in order to have more bandwidth available. So far, only bands for receive mode are aggregated for carrier aggregation (RX-CA); however, a plurality of band combinations that can also use the CA mode in transmit mode have already been proposed. In the process CA band combinations can combine several bands for Rx, Tx, or both Rx, Tx at the same time.

[0003] Two mobile radio bands to be combined with sufficient frequency spacing can use diplexers for signal separation (generally a high-pass/low- pass combination for separating 1 GHz and 2 GHz bands, for example). Band combinations with more than two different bands or with smaller frequency spacing require multiplexers that can separate several bands in the same frequency range, such as in the 1 GHz range, from one another.

[0004] In an n-fold multiplexer, n filters are connected to a common antenna connector. In doing so, however, the losses in the filters also increase with an increasing number n. So that the signals of the different bands or frequencies can be separated precisely and with low losses from one another in the individual filters, it is in particular important, in addition to the minimization of the electrical losses, to maximize the reflectivity of each individual filter for the frequencies of the other bands. [0005] An object to be achieved consists of specifying a multiplexer arrangement that has better properties, and in particular lower losses.

[0006] This object is achieved according to the invention by a multiplexer arrangement in accordance with claim 1. Advantageous embodiments of the invention can be taken from the dependent claims.

[0007] It was determined that the reflectivity behavior in the upper and lower stopband differs in different filters that differ in their substrate material or in their precise layer structure with respect to the selected material combinations. For example, filter structures are known, which have a high reflection in the lower stopband but a worse reflection in the upper stopband. Other filter technologies have a very good reflectivity reflection in the upper stopband but a worse reflectivity in the lower stopband than filters that are designed in the respective other technology.

[0008] The basic idea of the invention is therefore, for a multiplexer, to combine filters constructed from different material systems. The material systems are in this case selected such that the reflecivity in the respective counter band, i.e. in the band of the other filter, is maximal for the individual filter. The material system of a filter in the multiplexer according to the invention is thus selected depending on whether the counter band, i.e. the passband of the other filter of the multiplexer, is in the upper or lower stopband.

[0009] In this way, a multiplexer can be obtained which, compared respectively to a multiplexer designed in uniform technology, exhibits an overall improved reflecivity behavior and thus has a lower insertion loss.

[00010] A possible first technology that can be used in a duplexer according to the invention consists of acoustic filters on the basis of lithium niobate substrates. Such filters have a reflectivity that is approximately as good and acceptable in the upper as in the lower stopband. A second technology with which filters with a different reflectivity can be produced is acoustic filters on the basis of lithium tantalate substrates. Filters produced therefrom exhibit an improved reflectivity in the lower stopband compared to the technology mentioned first, but a worse reflectivity in the upper stopband.

[0011] If a first and a second filter are now combined in a multiplexer and if the frequency band with the higher frequencies is assigned to the first filter, the first filter is designed according to the invention in the second technology, the second filter on the other hand in the first technology. This has the advantage that the first filter has an improved reflectivity with respect to the frequencies of the second filter. However, if a filter designed in the second technology were selected for the band with the lower frequency, its reflectivity would be significantly worse with respect to the higher band. With the invention, the advantages and disadvantages of the two technologies are therefore advantageously combined so that the advantages essentially come into effect.

[0012] A filter designed in the first technology can also comprise a TCF compensation layer (TCF = temperature coefficient of frequency), which usually consists of a relatively thick silicon dioxide layer, in addition to the lithium niobate substrate and a metallization designed in multiple layers. The TCF compensation layer is usually also provided with a relatively thin passivation layer, for example made of silicon nitride. Other embodiments, such as a different material or additional layers, are also conceivable.

[0013] A multiplexer according to the invention is, however, independent of the two technologies mentioned and is always obtained when two technologies combined with one another or two filters combined with one another are designed in different technologies differing in their reflectivity behavior. The filters can thus also be realized independently of one another as SAW filters or as BAW filters. All transmit filters can also be designed in one technology, by contrast to which the receive filters are designed in a different technology. The invention can in this way already be used in a duplexer.

[0014] A multiplexer arrangement according to the invention can in addition be designed as diplexer, triplexer, quadplexer, or quintplexer. Such multiplexers can be constructed of individual filters. It is however also possible to use already pre-built duplexers in a multiplexer and to combine them with individual filters or additional duplexers. A pre-built duplexer has the advantage that the two filters of the duplexer, i.e. the RX filter and the TX filter, are already adjusted electrically to one another so well that the electrical losses are minimized in a pure duplex mode.

[0015] In an exemplary embodiment, the multiplexer arrangement comprises two duplexers that are respectively designed for operation in band 8 or band 20. In the simplest embodiment, such an exemplary multiplexer is then designed as a quadplexer, which combines the mobile radio bands B8 and B20 and respectively provides one RX and one TX filter for each of the two bands.

[0016] In principle, it is of course also possible to combine in one multiplexer filters and/or duplexers that cover the bands 8, 20 and one or more additional bands. It is only decisive that the technologies for the filter combinations are selected such that the reflectivity is maximized and the losses depending on it are thus minimized.

[0017] In the proposed exemplary band combination, which is also proposed for carrier-aggregation mode, the first filter can be configured for band 8 and is then designed as SAW filter on a lithium tantalate substrate. It is then advantageous to design the second filter, which is configured for band 20, as a SAW filter on a lithium niobate substrate and to provide it with an S1O2- containing TCF compensation layer.

[0018] While the selection of the suitable technology or the assignment of the suitable technology to the respective filter in the multiplexer arrangement according to the invention only minimizes material-related losses, other measures that minimize electrical losses resulting from the interconnection of several filters to form a multiplexer are additionally required in the multiplexer.

[0019] For this purpose, traditional multiplexer structures and multiplexer structures known per se can be drawn upon. In such multiplexers, several filters are connected to a common antenna connector. The electrical band separation is accomplished by connecting each of the filters to a phase shifter circuit with which the phase is changed by an amount suitable for an optimal adaptation, of, for example, 30°. Advantageously, each of these filters in a multiplexer is connected to a separate phase shifter circuit. Such a filter topology is, for example, known from US 7,495,529 B2.

[0020] According to another aspect, a multiplexer according to the invention is encapsulated in a TFAP package (TFAP = thin-film acoustic package). This technology is in particular suitable for MEMS structural elements, as they constitute acoustic structural elements or acoustic filters. With a TFAP package, the hollow space required for the undisturbed functioning of the electroacoustic transducers can be realized in a simple manner.

[0021] Such a TFAP package can be produced in an integrated process in which a sacrificial material is first applied and structured on top of the electrode structures where the hollow space must be provided. This sacrificial material is subsequently covered by a hard or mechanically stable layer. Openings are subsequently created in this layer in order to dissolve or dissolve away the sacrificial material through these openings. Subsequently, the opening is sealed again. In this way, packages can also be obtained which are characterized by a low structural shape in addition to their simple production. The production is furthermore possible in a fully integrated and therefore cost-effective manner.

[0022] In a multiplexer according to the invention, individual filter structures, individual filters, or individual duplexers can be separately encapsulated with a TFAP package under a respective separate hollow space. It is however also possible to encapsulate all components of the multiplexer together. Accordingly, a plurality of hollow spaces for respective individual electrode structures, or appropriately larger hollow spaces for one or more filters can be created, under which hollow spaces can be encapsulated one or more filters. [0023] The invention will be explained in greater detail below with reference to exemplary embodiments and accompanying Figures. The drawings in this respect can be schematic and can be shown enlarged, scaled down, or even distorted in individual dimensions for better illustration.

[0024] Elements that are the same or have the same function are denoted by the same reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 a multiplexer configuration known per se,

[0026] Figure 2 the reflectivity and the associated additional losses depending on the degree of a multiplexer,

[0027] Figure 3 a SAW filter constructed in a first technology in a schematic cross section,

[0028] Figure 4 a SAW filter constructed in a second technology in a schematic cross section,

[0029] Figure 5 the curves of the reflectivities of two diplexers designed in different technologies,

[0030] Figure 6 a multiplexer according to the invention in a schematic block diagram,

[0031] Figure 7 the superimposed passband curves of four filters connected to form a quadplexer according to the invention,

[0032] Figures 8A to 8C different process steps in the production of a TFAP encapsulation, [0033] Figures 9A and 9B a structural element with TFAP encapsulation in a top view and in a schematic cross section,

[0034] Figure 10 a module in SESUB technology, in which a multiplexer according to the invention is integrated into the laminate structure.

DETAILED DESCRIPTION

[0035] Figure 1 shows a schematic block diagram of a multiplexer MPX known per se. This multiplexer comprises a number of n individual filters FE1 , FE2, FEn which are respectively connected via a phase shifter circuit PS1 , PS2, PSn to a common node and in particular to a common antenna connector AT. Since each filter can only be realized with a limited and therefore not optimal reflectivity, losses result which further increase with an increasing number n of the filters connected in the multiplexer.

[0036] A simple formula can be created which specifies the dependence of the added additional losses ll__add on the number n of the filters combined in the multiplexer and their reflection factor p, wherein it is assumed that the reflection factor p is the same for all filters. The variable m is determined as m = n - 1 ;

[0038] Figure 2 shows the dependency of the additional losses on the reflectivity of the filters used for the multiplexer. The different graphs represent multiplexers of different degrees, wherein n varies from two to five filters.

[0039] It is shown that, with optimal reflectivity 1 , no additional losses occur. With decreasing reflectivity, the losses strongly increase with the degree of the multiplexer. For a multiplexer with still acceptable losses, a reflectivity of at least 0.8 should therefore be sought. [0040] Figure 3 shows a schematic cross section of a SAW filter designed in a first technology, in which filter a lithium niobate crystal LiNb0₃ serves as substrate. The electrode fingers EF of the transducer electrodes are designed as a multi-layer structure, which can at least comprise aluminum- and/or copper- containing sublayers. On top of the substrate and the finger electrodes FE, a TCF compensation layer CL is applied whose thickness is dimensioned such that a minimal temperature coefficient of the center frequency of the filter results.

[0041] In order to protect the TCF combination layer TCL, a passivation layer PL, such as a thin silicon nitride layer, is in this case additionally applied on top of the entire structure.

[0042] Figure 4 shows a schematic cross section of the structure of a SAW filter designed in a second technology. This filter comprises aluminum-containing transducer electrodes with individual electrode fingers EF on a substrate SU made of lithium tantalate.

[0043] Figure 5 shows the different reflectivity behavior of two filters which are designed in the two aforementioned technologies and are optimized for the same passband, in this case band 8. Plotted is the dependence of the reflectivity on the frequency, wherein a first curve 1 specifies the reflectivity for a filter according to the first technology (LN or HQTCF), while curve 2 represents the reflectivity for a filter in the second technology (LT).

[0044] It is shown that curve 2 for a filter according to the second technology has a high reflectivity in the lower stopband SBu but a worse reflectivity in the upper stopband SB₀. The reflectivity of a filter according to the first technology (curve 1) is completely different. This technology has only a slightly worse reflectivity in the lower stopband SPu but a significantly improved reflectivity in the upper stop band SP₀, compared to the second technology.

[0045] By means of a block diagram, Figure 6 shows how a multiplexer according to the invention can be constructed with a number of n = 2 filters. A first filter FE1 is configured for a first frequency f1 . A second filter FE2 is configured for a second frequency f2. Both filters FE1 , FE2 are respectively connected via a phase shifter PS1 , PS2 to a common node, in this case an antenna connector AT. The first filter FE1 is designed as a passband filter in the first technology. The second filter FE2 is designed as a passband filter in the second technology. According to the invention, significant improvements with respect to reflectivity and the associated losses can then be obtained if the first frequency f1 is lower than the second frequency f2. The improved reflectivity of a filter of the second technology in the lower stopband SPu then precisely affects the passband of the first filter FE2 and generates less losses.

[0046] In parallel with this, the improved reflectivity of the second filter in the upper stopband SP₀ of the second filter F2 produces an improved reflectivity in the passband of the first filter FE1 . In Figure 6 it is indicated that the multiplexer according to the invention can be expanded by additional individual filters or pairs of filters, wherein the respectively suitable technology depending on the frequency is used for each pair.

[0047] Figure 7 shows a combined representation of four passbands of a quadplexer, i.e. a multiplexer with n = 4. The multiplexer comprises a total of four Rx and Tx filters for the bands B8 and B20. At the outlets of the individual filters, a corresponding passband curve with the respective passband is respectively obtained. A first passband PB1 corresponds to the RX filter for band 20. A second passband PB2 corresponds to a TX filter for band 20. Passband 3 PB3 and passband 4 PB4 are assigned to the TX and the RX filter of band 8. The passband curves show that a multiplexer according to the invention only shows low losses in the individual filters.

[0048] The multiplexer shown in Figure 7 can be realized according to the invention by designing both the RX and TX filters of band 8 in accordance with the passbands PB3 and PB4 in the second technology, with which a filter with high reflectivity with respect to the frequencies in the lower stopband respectively results. The filters for band 20 with the first and second passband PB1 and PB2 are then designed in the first technology, which has an improved reflectivity in the upper stopband. Accordingly, the filters for the two bands 8 and 20 are insulated well against one another in the respective counter band. This is shown in the low insertion loss as Figure 7 clearly shows.

[0049] It is, however, also possible to design the filters for a multiplexer, such as for a quadplexer according to Figure 7, in a different manner in a first and second technology so that a respective RX filter and a TX filter, each of a first and second band, in pairs have an improved isolation or reflectivity in the respective counter band.

[0050] For the selected quadplexer, which can operate the bands 20 and 8, the RX filter can, for example, be designed for band 8 in the second technology, by contrast to which the TX filter for band 8 can be designed in the first technology. Accordingly, the TX filter for band 20 can then be designed in the second technology, the RX filter for band 20 in the first technology.

[0051] For multiplexers with other band combinations in which the frequencies of the Tx filters respectively lie above the respective Rx frequencies, the Tx filters can also be designed in the second technology, by contrast to which the Rx filters can be designed in the first technology.

[0052] If the Rx frequencies lie above the Tx frequencies, the assignment can also take place vice versa.

[0053] In a higher multiplexer, the filters can be assigned arbitrarily in a corresponding manner on the assumption that a filter with the higher frequency is respectively assigned to the second technology and a filter with the lower frequency is respectively assigned to the first technology. The filters assigned to one another must not operate the same band. The pair assignment can be intermittent. It is however also possible that a first filter for a passband with the highest frequency is designed in the second technology and a filter with the lowest frequency is then designed in the first technology, wherein two additional bands are located between the first and the second band, of which additional bands the upper band can again respectively be designed in the second technology and the lower band in the first technology.

[0054] By means of schematic cross sections, Figures 8A to 8C show different process steps in the production of a TFAP package which is in particular suitable for acoustic structural elements.

[0055] Figure 8A shows an acoustic filter as used in a multiplexer according to the invention. It is, for example, constructed on a substrate SU and comprises transducer structures, of which only individual electrode fingers EF are shown in Figure 8A in longitudinal cross section. On top of the transducer structures, a sacrificial layer SL is now applied and structured such that all transducer structures or electrode fingers are covered by a common sacrificial layer SL. The structuring can also take place such that individual substructures of the filter are covered separately by a separate sacrificial layer SL.

[0056] On top of the sacrificial layer, a first cover layer CL1 is now applied as shown in Figure 8B.

[0057] Openings OE are subsequently introduced into this first cover layer, for example by etching. In this way, the sacrificial layer SL can now be dissolved with a suitable solvent or etchant and removed through the openings. Subsequently, the openings OE are sealed again, e.g. by applying a second cover layer CL2 as shown in Figure 8C.

[0058] Each of the two cover layers CL1 , CL2 can itself consist of a layer combination of different layers in order to ensure the respective requirements for the cover layer with respect to mechanical stability and etchability.

[0059] Since a TFAP package can be optimized and dimensioned with respect to structures to be covered in a precisely fitting manner, an extremely space-saving encapsulation of the acoustic structural elements is achieved, which acoustic structural elements can serve as filters for the multiplexer according to the invention. It is also possible to design the entire multiplexer as a module and to encapsulate the filters individually with a TFAP package.

[0060] Figure 9A shows, for example in a schematic top view, a structural element BE whose components or electroacoustic substructures are encapsulated with a TFAP package both individually and in groups. The dashed line indicates a section plane which is illustrated schematically in Figure 9B. This illustration shows that the soldered joints for the transducer structures are provided outside the TFAP package. The cover layers CL1 , CL2 are limited to the space between the solder pads and structured appropriately.

[0061] On top of the solder pads, a suitable soldered connection BU, such as a bump as illustrated, can be provided which allows for a flip-chip assembly of the structural element BE on a circuit carrier, for example.

[0062] Figure 10 shows another possibility of integrating a structural element BE as well as a multiplexer according to the invention in a space-saving manner in a circuit environment by means of what is known as the SESUB technology (SESUB = semiconductor embedded in substrate). In doing so, the production of a hollow space, in which a structural element BE can already be arranged during the construction of the laminate and can be installed in the laminate LM by means of additional layers functioning as cover layers, is integrated into a production process of a multi-layer laminate LM comprising metallization levels ML1 and ML2.

[0063] In this case, each of the numerous metallization levels ML comprises metallizations, which metallization levels in turn form wiring levels, or the metallizations of which metallization levels can implement passive components such as resistors, capacitors, and inductors, partially even in a cross-layer manner. In the end, a laminate is obtained which in turn can serve as circuit carrier for additional components, such as for ICs or additional passive components PC. [0064] By combining the two structures TFAP and SESUB, very thin but nonetheless highly integrated structural elements can be obtained in a cost- effective manner.

[0065] A thin TFAP structural element (such as a multiplexer according to the invention) can be integrated easily into a SESUB structure.

[0066] Although the invention was explained with reference to only a few exemplary embodiments, it is not limited to these embodiments. Each new feature in itself is considered to be in accordance with the invention, as are combinations of new features with known features as described in the claims and the description.

List of reference signs

[0067] MPX Multiplexer arrangement

[0068] AT Node point / antenna connector

[0069] FE Filter

[0070] n Number of filters

[0071] f1 ...fn Frequency

[0072] PSL .PSn Phase shifter

[0073] CL TCF compensation layer

[0074] EF Transducer electrodes

[0075] SU Substrate

[0076] TFAP TFAP package

[0077] PB Passband

[0078] PL Passivation layer

[0079] SBo Upper stopband

[0080] SBu Lower stopband

[0081] SL Sacrificial layer

[0082] CL1 , CL2 First and second cover layer

[0083] OE Openings in CL1

[0084] BE Structural element

[0085] BU Soldered connection

[0086] LM Laminate [0087] ML Metallization levels

[0088] IC Integrated circuit

[0089] PC Passive component

Claims

1. A multiplexer arrangement (MPX) for signal separation in CA band combinations,

comprising a number of n filters (FE1 , FE2) for n bands connected to a common node point,

wherein at least two filters are realized in different technologies exhibiting a different reflectivity behavior for frequencies in the band of the respective other filter,

wherein for each of these at least two filters, the technology that has the higher reflectivity with respect to the respective counter band is selected.

2. The multiplexer arrangement according to claim 1 ,

in which a first of the filters (FE1) is constructed on a lithium niobate substrate and is additionally provided with a TCF compensation layer arranged on top of transducer electrodes,

in which a second of the filters (FE2) is constructed on a lithium tantalate substrate.

3. The multiplexer arrangement according to the preceding claim,

in which the first filter (FE1 ) is assigned to a band, the frequencies of which lie below the frequencies of the band assigned to the second filter (FE2).

4. The multiplexer arrangement according to one of the preceding claims, in which the filters are realized independently of one another as SAW filters or as BAW filters.

5. The multiplexer arrangement according to one of the preceding claims, in which the multiplexer arrangement is designed as diplexer, triplexer, quadplexer, or quintplexer.

6. The multiplexer arrangement according to one of the preceding claims, wherein the multiplexer arrangement comprises duplexers for bands that are selected for a carrier aggregation mode.

7. The multiplexer arrangement according to one of the preceding claims, wherein the multiplexer arrangement is a quadplexer comprising duplexers designed for the mobile radio bands B8 and B20.

8. The multiplexer arrangement according to one of the preceding claims, in which the first filter is configured for band 8 and designed as an SAW filter on an LT substrate,

in which the second filter is configured for band 20 and designed as an SAW filter on an LN substrate and provided with a TCF compensation layer,

9. The multiplexer arrangement according to one of the preceding claims, wherein each of the filters or of the duplexers is connected to a phase shifter.

10. The multiplexer arrangement according to one of the preceding claims, wherein at least one of the filters or of the duplexers is encapsulated in a TFAP package.

1 1 The multiplexer arrangement according to one of the preceding claims, in which the filter is embedded into a multi-layer substrate.