DE102019113797A1 - BAW resonator with reduced losses, RF filter, multiplexer and method for manufacturing a BAW resonator - Google Patents

Abstract

A BAW resonator with reduced losses is provided. The BAW resonator has a first gap which is arranged between the piezoelectric material and a first electrode selected from the lower electrode and the upper electrode of the resonator.

Description

The present invention relates to a BAW resonator with reduced losses and a corresponding RF filter, a multiplexer and a manufacturing method.

RF filters can be used in wireless communication devices to separate wanted RF signals from unwanted RF signals. RF filters are parts of multiplexers in a front-end circuit, e.g. B. a mobile communication device. Parameters such as insertion loss, out-of-band suppression, roll-off, isolation, linearity, service life, etc. determine the quality of an RF filter. The filter insertion loss parameter is directly influenced by the losses of the individual components that are cascaded to construct the filter. Such components in an RF filter are resonators, with some being detuned with respect to others to form an overall bandpass or bandstop filter function after they have been cascaded. Therefore, the resonator quality factor is a typical key performance indicator of filter performance.

Resonators used in RF filters can be electroacoustic using acoustic waves and comprising a piezoelectric material. Due to the piezoelectric effect, a transducer in a resonator converts between electromagnetic and acoustic RF signals. For this purpose, a BAW resonator (BAW: Bulk Acoustic Wave) typically comprises a piezoelectric material which is arranged between a lower electrode and an upper electrode, which are in direct mechanical contact with the piezoelectric dielectric. The total conductivity losses of the resonator are determined by the conductivity of the upper and lower electrode material and the thickness. You can't just increase the electrode thickness and expect the acoustic performance to stay the same. In practice there is a compromise - the effective electrode conductivity can be improved at the expense of the acoustic quality factor, the electromechanical coupling coefficient (in connection with the pole / zero point spacing and the achievable filter bandwidth) and the interference mode component / level. As the filter passband frequency increases, this trade-off becomes more of a problem, as the electrode thickness should be reduced for acoustic reasons in order to have similar acoustic properties as a device with a low frequency, while in order to have a similar effective conductivity as a device with a lower frequency , the electrode film thickness should be about the same.

A method of decoupling this conductivity / acoustic performance tradeoff is provided which allows a simultaneous improvement in the acoustic performance and the effective electrical conductivity of the resonator and the overall filter performance. A BAW resonator and a method for producing a BAW resonator according to the independent claims are provided. Dependent claims provide preferred embodiments.

The BAW resonator with reduced losses comprises a piezoelectric material. The piezoelectric material is arranged in a piezoelectric layer. The resonator furthermore comprises a lower electrode which is arranged and structured in a lower electrode layer. The BAW resonator further comprises an upper electrode which is structured and arranged in an upper electrode layer. The piezoelectric layer is arranged on or above the lower electrode layer. The upper electrode layer is arranged on or above the piezoelectric layer. A first gap is arranged between the piezoelectric material and a first electrode. The first electrode is selected from the lower electrode and the upper electrode.

Accordingly, a BAW resonator is provided which has a stacked layer structure which is different from the sandwich structure of conventional BAW resonators, wherein the piezoelectric material is sandwiched between the lower electrode and the upper electrode. In particular, the first gap, which is arranged between the piezoelectric material and the first electrode (which can be the lower electrode or the upper electrode), enables a significant reduction in losses, since conductivity can be improved by an increased thickness without the acoustic To influence loading of the piezoelectric material with high quality (low acoustic loss).

A reduction in losses can be obtained because ohmic losses and acoustic losses can be reduced. The first gap can reduce acoustic losses because the confinement of acoustic energy to the resonator area comprising the piezoelectric material is improved because no acoustic energy can be dissipated via the gap.

Furthermore, the RF signal can be coupled into the piezoelectric material over a wide range via the first electrode and via the gap, so that currents, eddy currents and ohmic losses are reduced.

Furthermore, the acoustic decoupling of the piezoelectric material from the first electrode reduces the number of possible interference modes. Accordingly, the number of acoustic channels that derive acoustic energy from the resonator is further reduced.

The BAW resonator provided accordingly has significantly reduced losses and therefore a higher quality factor. Such a BAW resonator enables HF filters with reduced losses and corresponding HF filter components, such as multiplexers with reduced losses and with improved electrical properties.

The reduced insertion loss of the corresponding RF filter, e.g. B. a bandpass filter, corresponds to an improved signal-to-noise ratio and requires a lower signal amplification, which leads to an overall longer battery life of the corresponding communication device due to the simultaneous improvement of the acoustic and electrical properties of the resonator.

The lower electrode and / or the upper electrode can be conventional electrode materials for BAW resonators, e.g. B. gold, molybdenum, silver, tungsten, copper, aluminum or alloys thereof, comprise or consist thereof.

The piezoelectric material in the piezoelectric layer can comprise conventional piezoelectric materials used for electroacoustic active devices of electroacoustic filter components. Accordingly, the piezoelectric material can comprise or consist of lithium tantalate, lithium niobate, aluminum nitride, scandium-doped aluminum nitride, quartz or combinations thereof.

The first gap is a vertical gap between a material below and a material above the gap. Accordingly, the gap has an extension in horizontal (x, y) directions and is substantially orthogonal to the vertical (z) direction. The gap has a thickness in the vertical direction that can be 10 nm or larger and 100 nm or smaller.

The lower electrode and / or the upper electrode may have dimensions in horizontal directions that are on the order of 100 μm. The gap accordingly also has horizontal dimensions. Accordingly, the gap has a very large aspect ratio of approximately 100,000 × 10 to 100,000 × 100.

In order to obtain such a gap in such a way that the acoustics of the piezoelectric material are undisturbed by the first electrode, special conditions must be followed during manufacture. Accordingly, buckling or other disturbances that locally reduce the vertical thickness of the gap must be avoided.

The steps during the production of the corresponding stack of layers must be controlled with high precision.

Then an interface free from mechanical stress and optionally free from charges is possible on one or both sides of the piezoelectric material, which leads to the above-mentioned advantages of the BAW resonator provided.

It is not only possible to provide a gap between the piezoelectric material and the first electrode. It is also possible to provide a corresponding second gap on the respective other side of the piezoelectric material between the piezoelectric material and the corresponding other electrode, which is selected from the lower electrode and the upper electrode, so that the piezoelectric material has a corresponding gap is isolated from both electrodes. The piezoelectric material is separated from the first electrode via the first gap and from the second electrode via the second gap.

Accordingly, all technical features that are described with reference to this first gap can also - mutatis mutandis - be applied to the second gap, if this is present.

In particular, with regard to the arrangement of the piezoelectric material and the gaps, the structures in the vicinity of the piezoelectric material - at least with regard to the layer construction - can have a mirror symmetry, the expansion of the piezoelectric material in the horizontal directions establishing a mirror plane.

It is possible for the gap (e.g. the first gap and / or the second gap) to mechanically and / or electrically isolate the piezoelectric material from the first (and / or second) electrode.

The mechanical isolation improves the acoustics of the transducer, because energy loss channels are removed and the possibilities for the excitation of interference modes - due to the simplified geometry and the symmetry of the transducer structure - are reduced.

The electrical insulation reduces the possibilities of ohmic losses as its thickness increases without affecting the acoustics. The RF signal can be capacitively coupled into the piezoelectric material from the corresponding electrode via the gap. A charge transfer from the piezoelectric material to the corresponding first (and / or second) electrode or vice versa is prevented, so that the total ohmic losses of the BAW resonator are reduced.

Accordingly, it is possible for the first gap to be provided and suitable for capacitive coupling of the first electrode to the piezoelectric material. Accordingly, the first electrode and the piezoelectric material are also provided and suitable for capacitive coupling of the transducer structure, which comprises the piezoelectric material, with a signal path that is electrically coupled to the BAW resonator.

It is possible that the first electrode (and / or the second electrode), the first gap (and / or the second gap, if this is present) and the corresponding interface between the gap and the piezoelectric material establish a series capacitance element.

The provision of the series capacitance element establishes an additional degree of freedom for adapting the electroacoustic coupling, which corresponds to the coupling coefficient K ^{2 of} the BAW resonator.

Similarly, if there are two gaps, then the transducer structure comprising the piezoelectric material is electrically connected in series between the two series capacitance elements established across the gaps.

It is possible that the BAW resonator comprises a first (and / or second) coupling layer between the piezoelectric material and the first (and / or second) gap.

In particular, the first (and / or second) coupling layer can be arranged on the upper or lower surface of the piezoelectric material.

The first and / or second coupling layer can comprise a conductive or dielectric material. The corresponding first and / or second coupling layer improves the capacitive coupling of the RF signal into and out of the transducer, which comprises the piezoelectric material.

The capacitive coupling can essentially be a quasi-electrostatic coupling.

Furthermore, the material of the coupling layer can be used during manufacture to act as an etch stop layer, e.g. B. when the gap is provided using a sacrificial material that is removed during manufacture.

As stated above, it is possible for the BAW resonator to include a second gap in addition to the first gap. The second gap is arranged between the piezoelectric material and a second electrode. The second electrode is selected from the lower electrode and the upper electrode, and the second electrode is the respective other electrode of the lower electrode and the upper electrode compared to the first electrode. Accordingly, if the first electrode is the lower electrode, then the second electrode is the upper electrode. If the first electrode is the top electrode, then the second electrode is the bottom electrode.

It is possible that the BAW resonator comprises a second coupling layer between the piezoelectric material and the second gap.

It is possible that the BAW resonator comprises a horizontal acoustic reflection structure which is arranged on the upper side and / or the lower side of the piezoelectric material.

The horizontal acoustic reflection structure reflects acoustic energy that would otherwise emit from the transducer area along a lateral, i. horizontal direction, would be derived. The horizontal acoustic reflection structure is different from a vertical Bragg mirror structure that prevents acoustic energy from being dissipated in a vertical direction, as known, and can, from SMR-type BAW resonators (SMR: Solidly Mounted Resonator) in addition to this.

It is possible that the horizontal acoustic reflection structure comprises a vertical interface between areas of different acoustic impedances.

Acoustic energy is reflected at an interface between materials of different acoustic impedance. The acoustic impedance of a material depends on the stiffness parameters of the material and the density of the material. If some such interfaces are iteratively arranged in a horizontal direction, especially if the horizontal distance is an integral multiple of λ / 2 (where λ is the acoustic wavelength), then a Bragg mirror structure can be obtained which has a large proportion of the reflecting acoustic energy.

Such a horizontal reflection structure can have structures on the upper side of the piezoelectric material and structures on the lower side of the piezoelectric material.

It is possible that the horizontal acoustic reflection structure comprises one or more depressions in the piezoelectric material. Additionally or as an alternative, it is possible that the horizontal acoustic reflection structure comprises one or more locations of an additional material, which are arranged on an upper or at a lower side of the piezoelectric material.

In addition to the horizontal acoustic reflection structure, the BAW resonator can comprise a Bragg reflector which is arranged below or above the piezoelectric material. The Bragg reflector can be acoustically coupled to the piezoelectric material.

Then the BAW resonator is a resonator of the SMR type (SMR: permanently mounted resonator).

The Bragg reflector can comprise two or more iteratively stacked layers made of materials of different acoustic impedances.

A conventional SMR-type BAW resonator mirror material, such as tungsten for high acoustic impedance and silicon oxide for low acoustic impedance, are possible.

Furthermore, the BAW resonator can also be a resonator of the TF-BAR type. A TF-BAR (Thin-Film-Bulk Acoustic Resonator) has a cavity which is arranged above or below the piezoelectric material in order to limit the acoustic energy to the transducer area.

The BAW resonator as described above has at least one gap between an electrode and the piezoelectric material, which creates acoustic insulation and which limits acoustic energy by preventing the discharge of acoustic energy. If the BAW resonator has a second gap on the other side, good insulation is already included.

However, if the BAW resonator has only one gap, as described above, then the respective other side of the piezoelectric material can be acoustically different from its surroundings using the Bragg mirror of an SMR-type resonator or using a cavity of a TF-BAR to be isolated.

It is also possible that the BAW resonator comprises a first and / or a second additional layer. The first and / or second additional layer is selected from a carrier material layer and a cap material layer. The carrier material layer can be arranged below the piezoelectric material. The cap material layer can be arranged above the piezoelectric material. The first additional layer or the second additional layer or the first and the second additional layer may contain a via.

The carrier material layer can then establish a layer of the carrier material on which the stacked layer structure of the BAW resonator is arranged. The carrier material establishes a physical carrier and provides protection for the sensitive electroacoustic transducer at the bottom of the BAW resonator.

The cap material layer establishes a cap that protects the sensitive transducer from harmful influences on the upper side of the BAW resonator. In particular, the cap material layer can set up a cap which covers a cavity in which the piezoelectric material and the first and / or gap are arranged, so that the transducer structure, which comprises the piezoelectric material, is hermetically sealed from its surroundings.

Spacer elements can be used to mechanically separate the carrier material layer and / or the cap material layer from the piezoelectric material.

The plated-through hole through the carrier material layer and / or through the cap material layer enables electrical contact to be made with the corresponding lower or upper electrode in order to electrically couple the converter structure to a signal path of the corresponding HF filter. The cross section of the via can be of the order of magnitude of the lower or the upper electrode, so that ohmic losses - due to the large cross section of the conductor - are reduced. Correspondingly, the through-hole plating uses a material with a high conductivity, such as silver, gold, aluminum, copper or similar metals or alloys.

Correspondingly, it is possible for an HF filter to include a BAW resonator, as described above.

The RF filter may have a branch-type circuit topology or a cross-link-type circuit topology.

In a branch type circuit topology, series resonators are electrically connected in series between a first port and a second port. Parallel resonators can be arranged in one or more shunt paths that electrically connect the signal path to ground.

In a crosslink topology, electroacoustic resonators are electrically connected between a first port that includes two connections and a second port that includes two connections. At least one circuit element is connected between a first connection of the first port and a first connection of the second port and one circuit element is electrically connected between one connection of the first port and the corresponding other connection of the second port so that a cross connection is obtained between connections of the two ports becomes.

It is of course possible for two or more or all of the resonators of the RF filter to have the technical features described above.

It is also possible for a multiplexer to include an RF filter, as described above.

The multiplexer can be a duplexer, a triplexer, a quadplexer or a multiplexer of a higher order. In particular, the multiplexer can be provided for working in a carrier aggregation operating mode.

A method for producing a BAW resonator comprises the step of arranging a first gap between a piezoelectric material and a first electrode. The piezoelectric material can be the piezoelectric material as described above and the first electrode can be one of the first electrodes as described above.

The provision of the piezoelectric material may include steps from thin film layer deposition techniques, e.g. B. sputtering. The provision of the piezoelectric material using thin film layer deposition techniques is particularly possible when aluminum nitride or scandium-doped aluminum nitride is used as the piezoelectric material.

If the piezoelectric material is lithium niobate or lithium tantalate, then techniques such as Smart Cut ™ or similar techniques are possible. The carrier material layer can be provided via a carrier wafer and the cap material layer can be provided via a cap wafer. Wafer bonding process for connecting the cap wafer and / or the carrier wafer to one another or to the piezoelectric material, e.g. B. via spacer elements are possible.

The coupling layers can be used to control the lateral wave dispersion properties of the piezoelectric material. In particular, placing an electrically short-circuiting film on top of the piezoelectric reduces the lateral mode cutoff frequency and can reduce spurious mode components around the device resonance frequency - especially for Type II dispersion, where modes show areas of negative group velocity (typically just below the cutoff frequency).

The coupling layers can comprise or consist of aluminum, molybdenum or tungsten or other materials that have a low acoustic loss and are electrically conductive. The thickness in a vertical direction of the coupling layers may be 20 nm or more and 500 nm or less.

The piezoelectric material can consist of a single crystal material or comprise multiple grains and domains. However, it is preferred that the piezoelectric material has substantially a piezoelectric axis that is oriented parallel to the vertical direction.

Central aspects and functional principles of the BAW resonator and details of preferred embodiments are shown by the accompanying schematic figures.

• 1 bis 3 zeigen Konstruktionsmöglichkeiten grundlegender Resonatorstrukturen;
• 4 zeigt einen Resonator mit zwei Spalten und mit einem Träger und einer Kappe;
• 5 zeigt die Verwendung eines Hohlraums unterhalb des piezoelektrischen Materials;
• 6 zeigt die Verwendung eines Bragg-Spiegels unterhalb des piezoelektrischen Materials;
• 7 zeigt die Verwendung eines leitenden Bragg-Spiegels unterhalb des piezoelektrischen Materials;
• 8 zeigt mögliche Strukturen horizontaler akustischer Reflexionsstrukturen;
• 9 zeigt zusätzliche oder alternative mögliche Einzelheiten horizontaler akustischer Reflexionsstrukturen.
• 10 und 11 zeigen mögliche Einzelheiten horizontaler akustischer Reflexionsstrukturen; und
• 12 veranschaulicht eine mögliche Schaltkreistopologie eines Duplexers.

In the figures:

• 1 to 3 show construction possibilities of basic resonator structures;
• 4th shows a resonator with two columns and with a carrier and a cap;
• 5 Figure 3 shows the use of a cavity beneath the piezoelectric material;
• 6th shows the use of a Bragg mirror beneath the piezoelectric material;
• 7th Figure 3 shows the use of a conductive Bragg mirror beneath the piezoelectric material;
• 8th shows possible structures of horizontal acoustic reflection structures;
• 9 shows additional or alternative possible details of horizontal acoustic reflection structures.
• 10 and 11 show possible details of horizontal acoustic reflection structures; and
• 12th illustrates one possible circuit topology of a duplexer.

1 illustrates one way of providing a BAW resonator BAWR with a first crack G1 between the piezoelectric material PM and the first electrode EL1 . In particular, the BAW resonator has a piezoelectric material with reduced losses PM in a piezoelectric layer PL on. The resonator also has an upper electrode TE in an upper electrode layer TEL on. A lower electrode BE is in a lower electrode layer BEL arranged and structured.

The piezoelectric material PM is between the lower electrode BE and the top electrode TE arranged. The first crack G1 is between the piezoelectric material PM and the top electrode TE than the first electrode EL1 arranged. Accordingly, there is capacitive coupling of an RF signal to the piezoelectric material from the top of the piezoelectric material PM provided. The provision of the first gap G1 between the first electrode EL1 and the piezoelectric material allows a reduction in ohmic losses (through thickened electrodes) without impairing the acoustic performance.

2 illustrates the possibility of arranging the first gap G1 below the piezoelectric material. The first electrode is accordingly EL1 and the piezoelectric material PM , between which the first gap is arranged, the lower electrode BE .

3 illustrates the possibility of providing a gap above and a gap below the piezoelectric material PM . The top electrode TE aligns the first electrode EL1 one. The lower electrode BE aligns the second electrode EL2 one. The first crack G1 is between the piezoelectric material PM and the top electrode TE arranged. The second gap G1 is between the piezoelectric material and the lower electrode BE arranged.

In 1 aligns the first gap in combination with the top electrode and the piezoelectric material PM a capacitive element that is electrically between the top of the BAW resonator BAWR and the piezoelectric material is connected in series.

In 2 straighten the first gap G1 in combination with the first electrode EL1 and the piezoelectric material PM a capacitance element on the lower side of the resonator BAWR is arranged.

In 3 the first gap in combination with the top electrode and the piezoelectric material establishes a first series capacitance element. The second gap G2 sets up - in combination with the lower electrode and the piezoelectric material - a second capacitance element, so that the electroacoustic transducer, the piezoelectric material PM is electrically connected in series between the two capacitance elements.

The coupling of the RF signal from an external circuit environment, e.g. B. an RF filter, in the piezoelectric material PM takes place over the first gap G1 and / or over the first and the second gap G1 , G2 .

4th illustrates the use of coupling layers CL1, CL2 in order to enable a tuning of the lateral mode dispersion properties of the active region as well as a resonator frequency tuning. In particular, a first coupling layer CL1 is arranged on the upper side of the piezoelectric material. The second coupling layer CL2 is arranged on the lower side of the piezoelectric material. The first coupling layer CL1 reinforces the coupling across the first gap G1 . The second coupling layer CL2 reinforces the coupling across the second gap G2 .

Furthermore, schematically illustrates in 4th BAW resonator shown BAWR the use of spacer elements SP surrounding the electroacoustic transducer area and the necessary gaps G1 , G2 maintained between the piezoelectric material and the environment in order to limit the acoustic energy to the piezoelectric material and the coupling layer CL1, CL2. The resonator BAWR has a cap material layer CPML and a substrate layer CRML on. The cap material CPML sets up a cap and the substrate layer CRML sets up a carrier substrate so that the transducer structure can be hermetically sealed in a closed volume, so that the sensitive transducer structure is protected from damaging influences from the environment of the BAW resonator BAWR is protected.

Electrical connections are made using vias TC through the cap material layer CPML and through the carrier material layer CRML provided. About the vias TC is the transducer that makes the piezoelectric material PM includes, electrically with signal lines SL coupled to the BAW resonator BAWR electrical with an external circuit environment, z. B. with other circuit elements or resonators of an RF filter connect.

5 illustrates the use of a cavity CAV that is below the piezoelectric material PM is arranged. In particular, the cavity CAV below the lower electrode BE arranged directly mechanically with the piezoelectric material PM can be connected. The cavity CAV provides an improved decoupling of the piezoelectric material PM from its surroundings so that acoustic energy is limited to the transducer area in order to further reduce losses. Accordingly shows 5 a BAW resonator of the TF-BAR type.

In contrast, illustrated 6th a BAW resonator of the SMR type with a Bragg mirror BM that is below the piezoelectric material PM is arranged to confine acoustic energy to the resonator structure. The piezoelectric material on its lower side can connect directly to the lower electrode BE be connected. Then non-conductive materials can be in the Bragg mirror BM be used.

The Bragg mirror BM comprises iteratively arranged layers of different acoustic impedance to maintain a high degree of energy reflection back into the piezoelectric material.

In contrast shows 7th the use of a Bragg mirror BM that is part of the lower electrode BE set up. This is possible if each of the layers of the Bragg mirror BM comprises a conductive material.

8th shows - in a cross-sectional view that 1 to 11 corresponds to - structures of a horizontal acoustic reflection structure HARS . The horizontal acoustic reflection structure includes structures on the top of the piezoelectric material. However, the structures can also be on the lower side of the piezoelectric material PM be mirrored. The structure HARS includes vertical interfaces between areas of different acoustic impedances. In particular, the in 8th Embodiments shown on two wells. A first deepening R1 is structured in the piezoelectric material. An additional second recess R2 a smaller lateral dimension is additionally structured into the upper side of the piezoelectric material, so that the vertical interfaces between air or vacuum and the piezoelectric material at the lateral positions LP2 and LP3 can be obtained. The lateral position LP1 is defined by the lateral end of the electrode and / or the coupling layer CL1. The second lateral position LP2 is defined by the vertical section corresponding to the second recess. The third lateral position LP3 in the in 8th The cross section shown is defined by the vertical interface which is the perimeter of the first recess R1 corresponds. The fourth lateral position LP4 is through the lateral end of the piezoelectric material PM Are defined. It can be preferred that the distance between the second lateral position LP2 and the third lateral position LP3 and / or the distance between the third lateral position LP3 and the fourth lateral position LP4 is an integer multiple of A / 4, where λ is the corresponding acoustic wavelength, so that a Bragg mirror-like structure is obtained which reflects acoustic energy back to the active transducer structure. Correspondingly, the horizontal acoustic reflection structure HRAS directs a horizontal acoustic mirror HAM one.

Furthermore, the depth of the first and the second recess R1 , R2 provided by the height differences of the first, second and third vertical positions. In particular, it is the depth of the first depression R1 by the height difference of the third vertical position VP3 and the second vertical position VP2 Are defined. The depth of the second recess R2 is by the difference in height between the first vertical position VP1 and the second vertical position VP2 Are defined.

9 illustrates a possible alternative to the one in 8th shown structure, which is based on wells. In contrast to the in 8th The structures shown are based on the embodiment shown HARS out 9 on the provision of additional material in the corresponding sections between the second, third and fourth lateral positions LP2 , LP3 , LP4 . In particular, the material which is arranged in the layer of the first coupling layer CL1 can have a different acoustic impedance compared to that of the first coupling layer CL1 between the second and the third lateral position. An additional level of acoustic impedance can be applied at the third lateral position, ie between the material between the second and third lateral positions and the material between the third and fourth lateral positions LP3 , LP4 is arranged, so that a horizontal acoustic mirror is obtained which reflects acoustic energy back in a horizontal direction towards the transducer structure.

10 illustrates the possibility of providing a fifth lateral position LP5 where the thickness of the material is between the third and fourth lateral positions LP3 , LP4 changes with respect to the lateral direction.

11 shows the possibility of adding a sixth lateral position LP6 at which a thickness of the material in the section between the second lateral position LP2 and the third lateral position LP3 provides a stage for improving the reflection of acoustic energy back to the active transducer structure.

12th shows a possible implementation of the BAW resonator as a series resonator SR and / or as a parallel resonator PR a multiplexer MUL as indicated by the in 12th duplexer shown is specified. The duplexer includes a transmission filter TXF that is between an input port and a common port CP is arranged, and a reception filter RXF that is between the common port CP and an output port is arranged. The transmission filter TXF and the receive filter RXF have a branch-type circuit topology with series resonators SR that are electrically connected in series in the signal path between the ports. Parallel resonators PR are arranged in parallel paths that electrically connect the signal path to ground. Between the common port CP and the receive filter RXF is an impedance matching circuit IMC provided to the frequency-dependent impedances of the ports of the transmission filter TXF and the reception filter RXF adapt to each other. One antenna AT can be electrical with the common port CP be connected.

The BAW resonator, the HF filter, the multiplexer and the method for producing a BAW resonator are not limited to the technical details that are described above or shown in the figures. The resonator can also comprise acoustic and / or electrical means for optimization.

List of reference symbols

AT:

antenna

BAWR:

BAW resonator

BE:

lower electrode

BEL:

lower electrode layer

BM:

Bragg mirror

CAV:

cavity

CP:

common port

CPML:

Cap material layer

CRML:

Carrier material layer

EL1, EL2:

first, second electrode

G1, G2:

first, second gap

HAM:

horizontal acoustic mirror

HARS:

horizontal acoustic reflection structure

IMC:

Impedance matching circuit

LP1, LP2, LP3,

first, second, ..., sixth lateral

LP4, LP5, LP6:

position

MUL:

multiplexer

PL:

piezoelectric layer

PM:

piezoelectric material

PR:

Parallel resonator

R1, R2:

first, second recess

RXF:

Receive filter

SL:

Signal line

SP:

Spacer element

SR:

Series resonator

TC:

Via

TE:

upper electrode

TEL:

upper electrode layer

TXF:

Transmission filter

VP1, VP2, VP3:

first, second, third vertical position

Claims (17)

BAW resonator with reduced losses, which includes: - a piezoelectric material in a piezoelectric layer, - a lower electrode in a lower electrode layer, - an upper electrode in an upper electrode layer, wherein - the piezoelectric layer is arranged on or above the lower electrode layer, - the upper electrode layer is arranged on or above the piezoelectric layer, - A first gap is arranged between the piezoelectric material and a first electrode, - the first electrode is selected from the lower electrode and the upper electrode. BAW resonator according to the preceding claim, wherein the first gap mechanically and / or electrically isolates the piezoelectric material from the first electrode. BAW resonator according to one of the preceding claims, wherein the first gap is provided and suitable for capacitive coupling of the first electrode to the piezoelectric material. BAW resonator according to one of the preceding claims, wherein the first electrode, the first gap and the interface between the first gap and the piezoelectric material establish a series capacitance element. BAW resonator according to one of the preceding claims, which further comprises a first coupling layer between the piezoelectric material and the first gap. BAW resonator according to one of the preceding claims, further comprising a second gap which is arranged between the piezoelectric material and a second electrode, the second electrode being the respective other electrode selected from the lower electrode and the upper electrode. BAW resonator according to the preceding claim, which further comprises a second coupling layer between the piezoelectric material and the second gap. BAW resonator according to one of the preceding claims, which comprises a horizontal acoustic reflection structure which is arranged on the upper side and / or the lower side of the piezoelectric material. BAW resonator according to the preceding claim, wherein the horizontal acoustic reflection structure comprises a vertical interface between regions of different acoustic impedances. BAW resonator according to one of the two preceding claims, wherein the horizontal acoustic reflection structure comprises: - One or more indentations in the piezoelectric material and / or one or more locations of an additional material which is arranged on the upper side and / or at the lower side of the piezoelectric material. BAW resonator according to one of the preceding claims, which further comprises a Bragg reflector below or above the piezoelectric material and acoustically coupled to the piezoelectric material. BAW resonator according to the preceding claim, wherein the Bragg reflector comprises conductive layers of different acoustic impedances. BAW resonator according to one of the preceding claims, which comprises a cavity above or below the piezoelectric material. BAW resonator according to one of the preceding claims, further comprising: - A first and / or a second additional layer which is selected from a carrier material layer below the piezoelectric material and a cap material layer above the piezoelectric material, wherein - The first and / or second additional layer contains a via. HF filter comprising a BAW resonator according to one of the preceding claims. Multiplexer comprising an RF filter according to the preceding claim. A method of manufacturing a BAW resonator comprising the step of arranging a first gap between a piezoelectric material and a first electrode.

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