The invention concerns a resonator filter comprising a plurality of coupled resonators.

Furthermore, the invention concerns a method of operating a resonator filter.

Filters are known which are based on transforming an electrical input signal into an acoustic wave by means of a piezoelectric effect, after which the acoustic wave is transformed into an electrical output signal by means of a piezoelectric effect in order to achieve frequency-dependent filtering. In this way, bandpass filtering can be implemented.

For example, SAW filters (surface acoustic wave filters) are known, wherein an input transducer is formed on a piezoelectric layer with two interleaved metallic comb structures and an output transducer is formed with two interleaved metallic comb structures, wherein input transducer and output transducer are usually arranged spaced apart from each other on the piezoelectric layer. Typically, by applying an electrical input signal to the input transducer, surface acoustic waves of the piezoelectric layer can be generated, with the surface waves propagating to the output transducer and being transformed by the output transducer into an electrical output signal.

BAW filters (bulk acoustic wave filters) are also known, in which an acoustic wave is usually propagated in a layered structure. For example, a BAW filter can be formed by implementing a resonator on a substrate, formed with a piezoelectric layer arranged between two metal electrodes. Typically, by applying an electrical signal to the metal electrodes, acoustic waves can be generated in the piezoelectric layer, which acoustic waves are reflected at an interface of the piezoelectric layer. The acoustic waves typically form resonant oscillations or resonant states. Multiple resonators may be provided layered on top of each other to affect a filter effect.

SAW filters are usually used in a frequency range up to 1 GHz. BAW filters can be used in a frequency range of several GHz. It is an object of the invention to provide a resonator filter which has optimized passband characteristics and, in particular, enables a practical specification of a passband of the resonator filter.

A further object of the invention is to provide a method of operating a resonator filter which has optimized passband characteristics and, in particular, enables a passband of the resonator filter to be specified in a practicable manner.

To achieve the foregoing objects, the invention provides a resonator filter comprising a plurality of coupled resonators, wherein in a stacking direction the resonators each having a rib formed of piezoelectric material arranged between a first electrode and a second electrode so that an acoustic wave can be generated in the respective rib by applying an electrical input signal to the electrodes, wherein the ribs of the resonators are spaced apart from one another in a lateral direction oriented transversely, in particular orthogonally, to the stacking direction, wherein for transmission of acoustic waves between the ribs the resonators are coupled to each another via a coupling layer.

The invention is based on the idea of designing a resonator filter in such a way that a practical conversion of an input signal, in particular in a frequency range of several GHz, into acoustic waves for filtering the input signal is possible and a structure of the resonator filter enables a practical specification or adjustability of a bandwidth of the resonator filter. When it is provided that the resonators are coupled to each other in the lateral direction for transmission of acoustic waves between the resonators, a structure of the resonator filter can be flexibly adapted. The resonators are usually acoustically coupled. When it is provided that the resonators form laterally spaced ribs of piezoelectric material to form acoustic waves in the ribs, a structure, size, and spacing of the ribs can easily set a bandwidth or transfer function of the resonator filter. If acoustic coupling of the resonators or transmission of acoustic waves between the ribs takes place via a coupling layer, a pronounced functional separation of a transformation between an electrical input signal or electrical output signal and acoustic waves in the ribs and a transmission of acoustic waves between the resonators, in particular ribs, can be achieved. Thus, energy losses or signal losses can be minimized. Usually, the resonators for the transmission of acoustic waves between the ribs are connected to each other via the coupling layer. Usually, a respective resonator is implemented with a first electrode, a second electrode and a rib formed of piezoelectric material arranged between the first electrode and the second electrode. By applying an electrical signal to the electrodes, an elastic deformation, in particular elastic contraction or extension, of the rib can be generated by means of piezoelectric effect. By applying an electrical input signal to the respective resonator, an acoustic wave corresponding to the electrical input signal can be generated in the rib. The acoustic wave generated in the rib is typically a bulk acoustic wave (BAW) of the rib. The acoustic wave generated in the rib usually causes an acoustic wave propagating in the coupling layer, so that a plurality of ribs connected by the coupling layer, are acoustically coupled to each other. The wave propagating in the coupling layer is usually a SAW (surface acoustic wave) or Lamb wave of the coupling layer.

In this way, acoustic coupling between the ribs can be achieved via the coupling layer, with a frequency-dependent attenuation of the acoustic wave depending in particular on a shape, size and/or spacing of the ribs. Typically, the electrical input signal is applied to one or more of the resonators and/or an electrical output signal is taken at or from one or more other resonators. The electrical signals, in particular the electrical input signal or electrical output signal, is usually an alternating electrical signal, in particular an alternating electrical voltage. A supply of the electrical input signal to a respective resonator usually takes place via an input line, which is electrically connected to the first and/or second electrode of the respective resonator. An output of the electrical output signal from a respective resonator is usually done via an output line, which is electrically connected to the first and/or second electrode of the respective resonator. Resonators, which are designed for an input of an electrical input signal, are often referred to as input resonators and resonators, which are designed for an output of an electrical output signal, are often referred to as output resonators. Typically, the electrical output signal is an electrical input signal filtered by the resonator filter.

It is usually provided that the ribs are arranged at a distance from each other, projecting from a reference surface, in particular a reference plane. The reference surface is usually oriented essentially parallel to the lateral direction and essentially orthogonal to the stacking direction. Typically, a longitudinal extent of the coupling layer is oriented parallel to the lateral direction, in particular parallel to the reference surface, so that the coupling layer overlaps with the resonators in the stacking. Typically, the ribs are spaced from each other in the lateral direction such that an interspace is formed between the ribs, with essentially no acoustic signal transmission occurring between the ribs via the interspace. Usually, no solid material is arranged in the lateral direction between the ribs or the interspace at least in sections, in particular predominantly, preferably substantially. The ribs may be spaced substantially equidistantly from each other in the lateral direction. However, the ribs can also be spaced at different distances from one another in the lateral direction. The distances between the ribs usually refer to two directly adjacent ribs.

The resonator filter may comprise a substrate on which the resonators and the coupling layer are arranged, wherein the coupling layer is arranged between the substrate and the resonators in the stacking direction. The substrate, coupling layer and resonators are typically arranged on each other in the stacking direction. The substrate is typically oriented substantially parallel to the reference surface.

It is advantageous if an acoustic reflector is arranged between the coupling layer and the substrate in order to acoustically isolate the substrate from the coupling layer. With the acoustic reflector, an entry of acoustic waves into the substrate can be minimized. The acoustic reflector may be formed as a cavity and/or a Bragg reflector. The Bragg reflector typically comprises an alternating arrangement of layers with different acoustic impedances to cause reflection by interference of acoustic waves reflected at interfaces between the layers. In this regard, in a simple implementation, the layers may have, for example, a layer thickness of substantially one-quarter of a wavelength of acoustic waves. The acoustic reflector typically extends in a lateral direction along a plurality, preferably a majority, of the reflectors.

Usually, an average acoustic impedance of the coupling layer is smaller than an average acoustic impedance of the ribs and/or smaller than an average acoustic impedance of the substrate. This allows acoustic waves to be transmitted efficiently in the coupling layer, in particular with little loss.

Typically, a longitudinal direction of the ribs is oriented transversely, in particular orthogonally, to the stacking direction and transversely, in particular orthogonally, to the lateral direction. The ribs are usually formed separated from each other or represent elevations separated from each other. This is especially the case in a plane parallel to the reference surface, in particular reference plane. The longitudinal directions of the ribs are usually oriented parallel to each other. The ribs are often designated as pillars. The respective rib usually represents an elevation. Typically, a length of the respective rib is greater than a width and greater than a height of the respective rib. The length of the rib is typically measured orthogonal to the lateral direction and orthogonal to the stacking direction. The width of the rib is typically measured in the lateral direction. The height of the rib is typically measured in the stacking direction. Typically, the length of the rib is at least twice, in particular at least three times, as large as the width of the rib. Usually, the length of the rib is between 5 times and 500 times, in particular between 10 times and 250 times, preferably between 20 times and 150 times, in particular preferably between 40 times and 100 times as large as the width of the rib. Typically, the rib is at least twice as large as the height of the rib. Usually, the width of the rib is between 2 times and 5 times, in particular between 2 times and 3 times, as large as the height of the rib. In a cross-section orthogonal to the length of the respective rib, the rib may be rectangular or trapezoidal in shape.

Typically, the respective resonator represents a piezoelectric element formed with the first electrode, second electrode and the rib of piezoelectric material arranged between the electrodes. The first electrode and/or the second electrode is usually formed in a layered manner. Several, in particular a majority, particularly preferably all, of the resonators may each have their own first electrode and/or their own second electrode. The first electrode and/or the second electrode may be applied directly to the respective rib. The first and/or second electrode may extend along a predominant portion, preferably substantially along an entire extent, of the respective rib. A plurality, in particular a majority, of the resonators may have a common first electrode and/or a common second electrode. If an electrode is associated with only a single resonator, it may be convenient if the electrode does not extend beyond an extent of the rib of the resonator in the lateral direction, in particular in a plane orthogonal to the stacking direction. A plurality, in particular a majority, of the resonators may each have their own first electrode and/or their own second electrode. It is preferred if a plurality, in particular a majority, especially preferably substantially all of the resonators have their own first electrode.

Usually, the first electrode is arranged on a side of the rib of the respective resonator facing away from the substrate and/or the second electrode is arranged on a side of the rib of the respective resonator facing towards the substrate. The second electrode is typically arranged between the rib of the respective resonator and the coupling layer. In an analogous manner, however, the arrangement of the first electrode and second electrode can also be reversed.

Several, in particular a majority, especially preferably all, of the resonators can have a common second electrode. Several of the resonators, in particular a majority, especially preferably all, of the resonators can each have their own first electrode.

The electrodes, in particular the first electrodes and/or second electrodes, are typically electrically connected to signal lines for applying an electrical input signal to the respective resonator(s) or for discharging an electrical output signal from the respective resonator(s). Expediently, a signal line for applying an electrical input signal to a resonator, in particular its first and/or second electrode, may be referred to as an input line, and a signal line for discharging an electrical output signal from a resonator, in particular its first and/or second electrode, may be referred to as an output line. Usually, the signal lines are electrical lines. The input line and output line are usually different signal lines.

A plurality of the resonators may be electrically connected to a common input line to apply an equal input signal to the resonators. A plurality of the resonators may be electrically connected to a common output line to discharge an equal output signal from the resonators. The input line and/or output line is typically electrically connected to the first electrodes and/or second electrodes of the respective resonators to apply the input signal or to output the output signal. For example, the first electrodes of a plurality of the resonators may be electrically connected to a common input line to input a signal to the resonators. There may then be the first electrodes of several others of the resonators electrically connected to a common output line to output an output signal from the resonators. A plurality of the resonators having a common input line may have a common second electrode, and/or a plurality of the resonators having a common output line may have a common second electrode. These may be different common second electrodes or the same common second electrode.

Usually, the first electrode and the second electrode of the respective resonator are connected to signal lines, in particular electrical signal lines, to apply an input signal or to discharge an output signal. Often one of the electrodes, usually the second electrode, is defined as electrical ground. Typically, a defined electrical potential is generated between the electrodes of the respective resonator. It may be provided that one of the electrodes, often the second electrode, forms a floating electrical potential. This electrode is then usually not electrically connected to a signal line, in particular electrical signal line, for input or output of an electrical signal. The signal lines are usually part of the resonator filter.

The ribs may be substantially parallelepipedal in shape. The ribs may project from an intermediate layer formed of piezoelectric material, which intermediate layer is disposed between the first electrode and the second electrode. The ribs can be formed integrally with the intermediate layer. The intermediate layer and the ribs may be formed with a different or preferably a same piezoelectric material.

An input group formed with one or more resonators can be provided, wherein the resonators of the input group can be supplied with the same, in particular the identical, input signal in order to generate acoustic waves in the ribs of the resonators. An output group, formed with one or more resonators, can be provided, wherein an output signal can be taken from the electrodes of the resonators of the output group, which output signal corresponds to acoustic waves that can be transmitted to the resonators of the output group via the coupling layer. Usually, the acoustic waves are transmitted from the resonators of the input groups via the coupling layer to the resonators of the output groups. The resonators of the input group may be electrically connected to a common input line, in particular as described in this document, to apply an input signal to the resonators. The resonators of the output group may be electrically connected, particularly as described in this document, to a common output line for outputting an output signal from the resonators. Multiple input groups and/or multiple output groups may be provided. The resonators of different input groups can be supplied with different input signals. Different output signals can be taken from the electrodes of the resonators of different output groups. The resonators of different input groups are usually electrically connected to different common input lines. This allows different electrical input signals to be applied to resonators of different input groups. The resonators of different output groups are usually electrically connected to different common output lines. This allows different electrical output signals to be output from resonators of different output groups. Usually, one subset of the resonators is assigned to one or more input groups and another subset of the resonators is assigned to one or more output groups.

Usually, resonators assigned to an input group are arranged in the lateral direction according to a repeating order scheme, in particular alternating with each other. For example, a resonator of an input group and a resonator of an output group may be arranged alternately in the lateral direction. In particular, if a single input group and a single output group are provided, such an arrangement may be advantageous.

Resonators from different input groups and/or resonators from different output groups can each be arranged in the lateral direction according to a repeating order scheme, in particular alternating with each other. For example, resonators from different input groups can be arranged alternately in the lateral direction. Resonators from different output groups can be arranged alternately in the lateral direction.

Resonators of input groups may be arranged in a first region and resonators of output groups in a second region, wherein a distance between the regions in the lateral direction is at least 2 times, in particular at least 3 times, as large as an average distance between the resonators of the input groups or an average distance between the resonators of the output groups. These may be resonators of one or more input groups and/or resonators of one or more output groups. The distance between the regions may be between 2 times to 10 times as large as the average distance between the resonators of the input groups or output groups. The resonators of the input groups and/or resonators of the output groups can each be arranged in accordance with a repeating order scheme, in particular as described above, especially alternating with one another. The distance between the regions may be, in particular in the lateral direction, a minimum distance between edges of the regions, for example in lateral direction a distance between a last of the resonators associated with an input group and a first of the resonators associated with an output group. Here, usually no distinction is made between resonators of different input groups or output groups. A distance, especially average distance, between resonators usually refers to the distances between immediately adjacent resonators in the lateral direction.

The resonators of input groups and/or the resonators of output groups may have a common electrode, usually a second electrode. This is particularly advantageous if resonators of input groups and resonators of output groups are arranged in different, aforementioned regions.

One or more of the resonators can be switchably connected, in particular reversibly, to an input line for supplying an electrical input signal and/or one or more of the resonators can be switchably connected, in particular reversibly, to an output line for discharging an electrical output signal. In this way, a bandwidth and/or transfer function of the resonator filter can be varied. A switching of one or more resonators can be implemented with one or more switches. The switch may be designed to establish or interrupt an electrical connection between an input line or output line and one or more resonators. For example, several resonators of an input group can be electrically connectable, in particular reversibly, by a switch to an input line. A plurality of resonators of an output group may be electrically connectable to a switch with an output line, in particular reversibly. Each resonator can be assigned its own switch. Several resonators may be electrically connectable by a common switch with a respective signal line, in particular electrical signal line. The electrical connection is usually established or interrupted between one of the electrodes, for example the first electrode, of the respective resonator and a respective signal line, in particular input line or output line, leading to the electrode, by the switch. The switches are typically part of the resonator filter. The input line and/or output line may each comprise a main signal line, from which a plurality of secondary signal lines each branch to one of the resonators, for supplying the input signal to the respective resonators or for discharging the output signal from the respective resonators via the main signal line and secondary signal lines. A respective switch may be configured to reversibly connect or interrupt one of the secondary signal lines for a transmission of the input signal or output signal. The switch may be an electrical or electronic switch.

Due to the spatial confinement of the acoustic waves, for example in the ribs and/or the coupling layer, resonance states or resonance frequencies of the acoustic wave are formed, typically by interaction with boundary layers. In particular, depending on a shape, size and/or spacing of the ribs, desired resonance states and/or a transfer function of the resonator filter can be set.

Resonant frequencies of the acoustic wave in the respective rib usually depend on a width b, length w and height t of the rib. The width b of the respective rib is usually measured in the lateral direction. The length w of the respective rib is usually measured orthogonal to the lateral direction and orthogonal to the stacking direction. The height t of the rib is usually measured in the stacking direction. A resonant frequency of the acoustic wave in the piezoelectric material between the electrodes, in particular between the first electrode and second electrode, of the respective resonator usually depend on a height h of the piezoelectric material between the electrodes. The height of the piezoelectric material between the electrodes is usually measured in the stacking direction. If the entire piezoelectric material between the electrodes of the respective resonator is formed by the rib of the resonator, the height h is equivalent to the height t. A distance d between immediately adjacent ribs is usually measured in the lateral direction.

Usually, the height h of the piezoelectric material between the electrodes of the respective resonator is 0.3 times to 1 times as large as a wavelength AR ₆ S of the acoustic wave, in particular the BAW (bulk acoustic wave), in the piezoelectric material of the respective resonator. Usually, the distance d between directly adjacent ribs is 0.5 times to 1 times, preferably about 0.5 times, as large as a wavelength Ac of the acoustic wave, in particular the SAW (surface acoustic wave) or Lamb wave, of the coupling layer.

For the height h of the piezoelectric material between the electrodes of the respective resonator can be defined: h = 0,5 AR ₆ S - 0,2 AR ₆ S. The height h is preferably from 2 pm to 0.3 pm.

For the height t of the rib of the respective resonator can be defined: t = 0,5 h - 0,7 h. The height t is preferably from 0.6 pm to 0.1 pm.

For the distance d between immediately adjacent ribs can be defined: d = 0,5 Ac. The distance d is preferably from 2 pm bis 0,6 pm.

For the length w of the rib of the respective resonator can be defined: w = 20 - 40 Ac. The length w is preferably from 160 pm bis 40 pm.

For the width b of the rib of the respective resonator can be defined: b = 0,6 d - 0,4 d. The width b is preferably from 1 pm bis 0,3 pm. In the, in particular above, specifications AR ₆ S denotes the wavelength of the acoustic wave, in particular the BAW (bulk acoustic wave), in the piezoelectric material of the respective resonator and Ac denotes the wavelength of the acoustic wave, in particular the SAW (surface acoustic wave) or Lamb wave, of or in the coupling layer.

By applying a, in particular high-frequency, electrical input signal to several of the resonators, acoustic waves can be generated depending on a geometry of the piezoelectric material, in particular the rib, between the electrodes of the respective resonator. Typically, the acoustic waves in the piezoelectric material of the respective resonator generate acoustic waves in the coupling layer, in particular depending on a distance between the ribs, and vice versa, so that the ribs are acoustically coupled to each other via the coupling layer. Usually, several modes or resonant frequencies of the acoustic waves are generated simultaneously. As a result, a wide passband is achievable.

One, in particular several, resonant frequencies and/or a number of resonant frequencies can be set by varying a size, in particular height, length and/or width, of the respective rib. This applies accordingly to the transfer function or the passband of the resonator filter. A passband width of the passband is usually dependent on a number of excited modes, the distances between the ribs of the resonators, the acoustic impedance of the coupling layer and/or the number of resonators which are acoustically coupled to each other, in particular via the coupling layer.

Several of the ribs may have a different height and/or width. Alternatively or cumulatively, distances between directly adjacent ribs can be different in the lateral direction. In this way, a bandpass filtering can be adjusted efficiently. This can apply to resonators of input groups and/or resonators of output groups. For example, the ribs of resonators of input groups can have a different height and/or width than the ribs of resonators of output groups.

Usually, ribs of resonators of the same input group or output group have equal heights and/or widths. It can be provided that ribs of resonators of different input groups have a different height and/or a different width. Alternatively or cumulatively, ribs of resonators of different output groups may have a different height and/or a different width. Typically, distances between immediately adjacent ribs are equal in the lateral direction. This can apply to the resonators of input groups and/or output groups. However, it may also be favorable if distances of different sizes are thereby provided. In particular, the ribs of resonators of input groups can have different distances to each other than the resonators of output groups to each other. Usually, ribs of resonators of the same input group or output group are arranged with equal distances to each other in lateral direction. Ribs of resonators of different input groups or output groups can have different distances to each other in lateral direction. The aforementioned distances usually refer to the distances in the lateral direction of directly adjacent ribs.

If an intermediate layer, in particular the aforementioned one, is provided from which the resonators protrude, a recess in or elevation of the intermediate layer can be present between directly adjacent resonators. A recess or elevation of the intermediate layer can be present between several directly adjacent resonators respectively. The elevation or recess usually refers to the stacking direction. The elevation and/or recess may each extend in the lateral direction to the immediately adjacent resonators. Sections of the intermediate layer between the resonators can be considered as piezoelectric bridges between the ribs, which piezoelectric bridges can be varied by the recesses and/or elevations. In this way, resonance frequencies of the acoustic waves can be influenced, in particular tuned. The elevation or recess usually has a height in the stacking direction of less than 0.6 times, in particular from 0.1 times to 0.5 times, of an average height of the ribs between which the elevation or recess is located.

The coupling layer can be formed with, in particular of, an arrangement of several coupling sublayers. In this way, transmission of the acoustic waves between the ribs can be adjusted in a fine-tuned manner. The coupling sublayers can have different acoustic impedances. The coupling sublayers can be arranged according to a repeating order scheme, in particular alternating. Generally, it is provided that at least one of the coupling sublayers has a small acoustic impedance and at least one of the coupling sublayers has a large acoustic impedance compared to an acoustic impedance of the piezoelectric material of the resonators, in particular the ribs, and/or an acoustic impedance of the substrate. The coupling sublayers are usually arranged on each other in the lateral direction. The transfer function or passband describes the passability or attenuation of the filter for a signal, in particular the electrical input signal, as a function of a frequency. The transfer function or passband can be adjusted in particular with variation of a size, in particular a height, of the ribs and/or a distance between the, in particular directly adjacent, ribs and depending on an acoustic impedance of the coupling layer. A bandwidth of the passband can be adjusted in particular with a number of the resonators.

The resonators can be acoustically coupled such that the transfer function or passband of the resonator filter forms a flat plateau in a frequency range. This is referred to as critical coupling of the resonators, in particular the ribs. The flat plateau usually represents a maximum of the transfer function or passband. The transfer function is then often referred to as a critical coupled curve. Usually, signal losses are minimal with critical coupling. Alternatively, the resonators can be acoustically coupled such that the transfer function or passband of the resonator filter has a single maximum, in particular without a pronounced plateau. This is referred to as under-coupling of the resonators, in particular the ribs. This is usually associated with a narrow passband and/or increased signal losses. The transfer function is then often referred to as an under-coupled curve. Alternatively, the resonators can be acoustically coupled in such a way that the transfer function or the passband of the resonator filter has several maxima, usually exactly two maxima. This is referred to as over-coupling of the resonators, especially the ribs. This usually represents a split passband condition. The transfer function is then often referred to as an over-coupled curve.

The resonator filter usually has a layered structure. The coupling layer, the intermediate layer, the ribs and/or the electrodes can each be layered. These can be arranged on each other, in particular rigidly, in the stacking direction, in particular as described in this document. The substrate may be formed in a layered manner. The electrodes are usually formed with, in particular from, an electrically conductive material, usually metal. The coupling layer, intermediate layer and/or electrodes are usually oriented substantially parallel to the reference surface, in particular reference plane.

The piezoelectric material, in particular the ribs, of the resonators can be realized with etching, in particular anisotropic etching, of piezoelectric basic material, in particular a piezoelectric basic layer. In this way, the ribs can be formed efficiently. The substrate can be formed with, in particular, silicon, sapphire, fused quartz and/or SiC. The coupling layer can be formed with, in particular, SiC>2, SiOC, or Sisl^ . The coupling layer can be an elastic layer. A coupling sublayer with small acoustic impedance, in particular as described above, may be formed with, in particular from, SiC>2, SiOC, Sisl^ , and/or a polymer. A coupling sublayer with high acoustic impedance, in particular as described above, can be formed with, in particular, tungsten, platinum, SiC, diamond and/or AI2O3.

The respective signal line, in particular input line and/or output line, is usually implemented to conduct a signal, in particular an electrical signal. The signal line is usually an electrical signal line. In particular, the input line is an electrical input line and/or the output line is an electrical output line. The signal, in particular the input signal and/or the output signal, is usually an electrical signal, in particular an electrical input signal and/or an electrical output signal. The signal, in particular input signal and/or output signal, is usually an electrical signal, which is usually a high frequency signal, in particular with a frequency range between 1 GHz and 20 GHz, preferably between 1 GHz and 15 GHz, more preferably between 2 GHz and 6 GHz. The skilled person understands that the respective signal line, in particular input line and/or output line, can be designed in an analogous manner to transmit a respective signal at least in sections in another customary manner, for example electromagnetically, with the signal line, as long as the signal can be applied or output as an electrical signal to or from the respective electrodes of the resonators. This is therefore to be seen as an analog implementation.

Furthermore, the invention concerns a method of operating a resonator filter, wherein an electrical input signal is applied to the electrodes of one or more resonators so that an acoustic wave is generated in the ribs of the resonators, wherein by a transmission of acoustic waves via the coupling layer to ribs of one or more further resonators an output signal is generated at the electrodes of the further resonators. In this way, an input signal can be filtered with a high degree of practicability, and in particular with an optimized passband and/or an optimized transfer function. In particular, the method is implementable with a resonator filter as described in this document.

It is understood that the method of operating a resonator filter can be implemented analogously to the features and effects which are described in the context of a resonator filter, in particular above, in this document. The same applies analogously to the resonator filter with regard to the method of operating a resonator filter.

Typically, the resonator filter is operated in a frequency range between 1 GHz and 20 GHz, especially between 1 GHz and 15 GHz, preferably between 2 GHz and 6 GHz, more preferably between 3 GHz and 4 GHz. Accordingly, an input signal can have frequencies in a corresponding frequency range in order to filter the input signal with the resonator filter.

It is advantageous if at least one of the resonators for a supply of the electrical input signal or discharge of the electrical output signal is connected or disconnected with a switch. The switch can be designed to establish an electrical connection between an electrode of the resonator and the input line or output line, in particular reversibly. Thus, a passband, in particular a bandwidth, of the resonator filter can be changed after a fabrication, in particular during operation, of the resonator filter. Preferably, several of the resonators are designed to be switchable in this way. Preferably, several of the resonators can be switched separately from each other.

It is advantageous if at least one of the resonators for a supply of the electrical input signal or discharge of the electrical output signal is connected or disconnected by a switch. Expediently, the switch can be used to establish an electrical connection between an electrode of the resonator and the input line or output line, in particular reversibly, by switching the switch. Thus, a passband or bandwidth of the resonator filter can be adjusted after a fabrication, in particular during operation, of the resonator filter.

Preferably, several of the resonators are connected by switches in this way. Preferably, several of the resonators are switched separately from each other in this way.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic illustration of a resonator filter;

Fig. 2 shows a transfer function of resonator filters with different acoustic coupling of resonators;

Fig. 3 shows a cross section of a resonator filter with common second electrode; Fig. 4 shows a cross section of a resonator filter, where input resonators and output resonators are located in different regions;

Fig. 5 shows a cross section of the resonator filter of Fig. 4, where the input resonators and the output resonators have a separate common second electrode;

Fig. 6 shows a cross section of a resonator filter with balanced input lines and unbalanced output lines;

Fig. 7 shows a cross section of a resonator filter with balanced input lines and balanced output lines;

Fig. 8 shows a cross section of a resonator filter, wherein resonators can be switchably connected to an input line or output line by switches;

Fig. 9 shows a cross section of a resonator filter, where resonators have different widths; Fig. 10 shows a cross section of a resonator filter, wherein the piezoelectric intermediate layer has an elevation and/or recess between immediately adjacent resonators.

Fig. 1 shows a schematic diagram of a resonator filter 1. The resonator filter 1 has a plurality of resonators 2, each of the resonators 2 being formed in a stacking direction S arranged on each other, with a first electrode 3, a second electrode 4 and piezoelectric material arranged between the first electrode 3 and the second electrode 4. The respective resonator 2 thereby forms a piezoelectric element. The piezoelectric material of the respective resonator 2 is formed with an intermediate layer 6 and a rib 5 projecting from the intermediate layer 6. The ribs 5 of the resonators 2 are spaced apart from each other in a lateral direction L oriented transversely, in particular orthogonally, to the stacking direction S. A plurality of the resonators 2 are electrically connected to an input line 8, so that by applying an electrical input signal to the electrodes of the respective resonator 2, an acoustic wave can be generated in the piezoelectric material, in particular the rib 5, of the respective resonator 2. These resonators 2 are referred to as input resonators 21. A plurality of further ones of the resonators 2 are electrically connected to an output line 9 for outputting an electrical output signal caused by an acoustic wave in the piezoelectric material, in particular the rib 5, of the respective resonator 2 at the electrodes of the respective resonator 2 via the output line 9. These resonators 2 are referred to as output resonators 22. Typically, the first electrode 3 of the respective resonator 2 is electrically connected to the input line 8 for transmitting the electrical input signal or to the output line 9 for outputting the electrical output signal. For transmission of acoustic waves between the ribs 5 of the resonators 2, the resonators 2 are arranged on a coupling layer 7 in the stacking direction S. In this way, the resonators 2, in particular input resonators 21 and output resonators 22, are acoustically coupled to each other by the coupling layer 7. By applying an electrical input signal via the input line 8 to the input resonators 21 , acoustic waves, usually BAW waves, can be generated in the ribs 5 of the input resonators 21 , which cause acoustic waves, usually SAW waves or Lamb waves, in the coupling layer 7. The acoustic waves in the coupling layer 7 cause acoustic waves, usually BAW waves, in the ribs 5 of the output resonators 22, so that an electrical output signal is provided from the output resonators 22 via the output line 9. Due to the transmission by means of acoustic waves, especially by interference of the acoustic waves, a filtering can be implemented so that the output signal represents the filtered input signal. Typically, the input line 8 and output line 9 are signal lines, in particular electrical signal lines.

Resonant frequencies of the acoustic wave in the respective rib 5 usually depend on a width b, length w and height t of the rib 5. A resonant frequency of the acoustic wave in the piezoelectric material between the electrodes, in particular between the first electrode 3 and second electrode 4, of the respective resonator 2 usually depend on a height h of the piezoelectric material between the electrodes. If the entire piezoelectric material between the electrodes of the respective resonator 2 is formed by the rib 5 of the resonator 2, the height h is equivalent to the height t. A passband of the resonator filter 1 depends in particular on a distance d between immediately adjacent ribs 5.

Typically, input resonators 21 and output resonators 22 are arranged alternately in the lateral direction L according to a repeating order scheme. For example, input resonators 21 and output resonators 22 can be arranged alternately in the lateral direction L.

Usually, the first electrode 3 of the respective resonator 2 is arranged on a side of the rib 5 of the respective resonator 2 facing away from the coupling layer 7, and the second electrode 4 is arranged between the coupling layer 7 and the rib 5 of the respective resonator 2. The second electrode 4 may be a common second electrode 4 of a plurality of the resonators 2. Typically, the resonators 2 each have their own first electrode 3. The resonator filter 1 can have a substrate 10, on which substrate 10 in the stacking direction S the coupling layer 7, the second electrode 4, the intermediate layer 6, the ribs 5 and the first electrodes 3 can be arranged on each other, in particular in layers. The resonator filter 1 , in particular the respective resonator 2, can also be implemented without the intermediate layer 6.

In particular, depending on a size, especially height, of the ribs 5, a distance of the ribs 5 from each other and/or an acoustic impedance of the coupling layer 7, a different acoustic coupling of the resonators 2 can be achieved. Fig. 2 shows a graph with different transfer functions which a resonator filter 1 , in particular a resonator filter 1 of Fig. 1 , can have depending on the acoustic coupling of the resonators 2. The transfer function can have a maximum with a plateau, denoted as critical coupling of the resonators 2. This is shown in Fig. 2 with the transfer function 18. The transfer function may have a single maximum without a plateau, denoted under-coupling of the resonators 2. This is shown in Fig. 2 with the transfer function 19. The transfer function may have multiple maxima, denoted over-coupling of the resonators 2. This is shown in Fig. 2 with the transfer function 20. Usually, a bandwidth of the passband in particular can be adjusted with a number of the resonators 2.

Fig. 3 schematically shows a cross-section of a resonator filter 1 with a common second electrode 4 of the resonators 2. The resonator filter 1 can be designed according to the features of the resonator filter 1 of Fig. 1 and vice versa. A plurality of input resonators 21 are electrically connected to an input line 8, and a plurality of output resonators 22 are electrically connected to an output line 9. The input resonators 21 and output resonators 22 are arranged alternately with each other in the lateral direction L. The common second electrode 4 is electrically connected to an electrical ground potential 14.

Fig. 4 schematically shows a cross-section of a resonator filter 1 , with input resonators 21 and output resonators 22 arranged in different regions 11. The resonator filter 1 can be designed according to the features of the resonator filter 1 of Fig. 1 and/or Fig. 3 and in an analogous manner vice versa. A distance between the regions 11 is preferably at least twice as large as an average distance between the rips d, in particular rips of input resonators 21. Resonators, in particular input resonators 21 , to which the same electrical input signal can be applied via a common input line 8 form an input group 12. Resonators, in particular output resonators 22, which are electrically connected to a common output line 9 in order to output an electrical output signal from the output resonators 22 via the output line 9, form an output group 13. A plurality of input groups 12 and/or a plurality of output groups 13 may be provided. The input resonators 21 are preferably arranged such that input resonators 21 of different input groups 12 are arranged alternately with each other in the lateral direction L. The output resonators 22 are preferably arranged such that in the lateral direction L output resonators 22 of different output groups 13 are arranged alternately. It may be convenient if the second electrode 4 forms a flowing electrical potential. The second electrode 4 is then usually not electrically contacted with a signal line, especially electrical signal line, for the supply or discharge of an electrical signal.

In Fig. 5, a cross-section of the resonator filter 1 according to Fig. 4 is shown schematically, wherein the input resonators 21 and the output resonators 22 each have a separate common second electrode 4, i.e. , the input resonators 21 have one common second electrode 4 and the output resonators 22 have another common second electrode 4.

Fig. 6 schematically shows a cross-section of a resonator filter 1 with balanced input lines 8 and unbalanced output lines 9. In this way, a balun filter can be implemented for conversion between a balanced line system and an unbalanced line system. The resonator filter 1 of Fig. 6 may be implemented according to the features of the resonator filter 1 of Fig. 1 , Fig. 3, Fig. 4 and/or Fig. 5 and vice versa in an analogous manner. There are input resonators 21 of a plurality of input groups 12. Output resonators 2 of a plurality of output groups 13 may be present. Usually, phase-shifted, in particular opposite-phase, electrical input signals are applied to the input resonators 21 of different input groups 12. The second electrode 4 of the input resonators 21, which may be a common second electrode 4, can be electrically connected to an electrical ground potential 14. The second electrode 4 of the output resonators 22, which is typically a common second electrode 4, may have a floating electrical potential, wherein the second electrode 4 is typically not electrically contacted with a signal line, especially electrical signal line, for supplying or discharging an electrical signal.

Fig. 7 schematically shows a cross-section of a resonator filter 1 with balanced input lines 8 and balanced output lines 9. There are input resonators 21 of a plurality of input groups 12 and output resonators 22 of a plurality of output groups 13. The resonator filter 1 of Fig. 7 may be implemented according to the features of the resonator filter 1 of Fig. 1 , Fig. 3, Fig. 4, Fig. 5 and/or Fig. 6 and vice versa in an analogous manner. Usually, phase-shifted, in particular opposite-phase, electrical input signals are applied to the input resonators 21 of the different input groups 12. Phase-shifted, in particular opposite-phase, electrical output signals are usually output from the output resonators 22 of the different output groups 13. The second electrode 4 of the input resonators 21 , which may be a common second electrode 4, can be electrically connected to an electrical ground potential 14. The second electrode 4 of the output resonators 22, which may be a common second electrode 4, can be electrically connected to an electrical ground potential 14.

Fig. 8 schematically shows a cross section of a resonator filter 1 , wherein resonators 2 can be reversibly switchably connected by switches 15 to an input line 8 and/or resonators 2 can be reversibly switchably connected by switches 15 to an output line 9. One or more of the input resonators 21 , in particular their respective first electrode 3, can be electrically switchably connectable to the input line 8 via a switch 15. One or more of the output resonators 22, in particular their respective first electrode 3, can be electrically switchably connectable to the output line 9 via a switch 15. By switching the respective switch 15, an electrical connection can be established between the respective resonator 2, in particular its first electrode 3, and the associated signal line, in particular reversibly. In this way, a number of resonators 2 involved can be varied, in particular in operation of the resonator filter 1 . In this way, a transfer function or passband of the resonator filter 1 can be controllably changed. Resonators of different input groups 12 and/or resonators 2 of different output groups 13 can each be electrically switchably connectable by a switch 15 to an associated signal line, in particular input line 8 or output line 9. The second electrode 4 can be electrically connected to an electrical ground potential 14. A corresponding implementation with switches 15 for switchable connection of a respective resonator 2 with an input line 8 or output line 9 can be implemented in an analogous manner with a respective resonator filter 1 of Fig. 1 and/or Fig. 3 to Fig. 7.

In Fig. 9, a cross-section of a resonator filter 1 is shown schematically, with ribs 5 of resonators 2 having different widths. For example, input resonators 21 from different input groups 12 and/or output resonators 22 from different output groups 13 may have ribs 5 with different widths. Alternatively or cumulatively, input resonators 21 of different input groups 12 and/or output resonators 22 of different output groups 13 may have ribs 5 with different heights. A corresponding implementation may be implemented in an analogous manner for a respective resonator filter 1 of Fig. 1 and/or Fig. 3 to Fig. 10.

In Fig. 10, a cross-section of a resonator filter 1 is shown schematically, wherein the intermediate layer 6 between directly adjacent resonators 2 has an elevation 16 and/or recess 17. For example, an elevation 16 of the intermediate layer 6 can be arranged between immediately adjacent input resonators 21, in particular of different input groups 12. For example, a recess 17 of the intermediate layer 6 can be arranged between immediately adjacent output resonators 22, in particular of different output groups 13. In an analogous manner, a recess 17 can be provided instead of the elevation 16 or vice versa. In this way, resonance frequencies of the acoustic waves can be tuned. A corresponding implementation can be implemented in an analogous manner in a respective resonator filter 1 of Fig. 1 and/or Fig. 3 to Fig. 9.

In the aforementioned exemplary implementations of a respective resonator 2 of Fig. 1 and Fig. 2 to Fig. 10, different aspects of a configuration of a resonator filter 1 are considered in each case, which can be combined with one another comprehensibly to the skilled person. In particular, it is comprehensible to the skilled person that in the respective resonator filters 1 , several of the resonators 2 can each have their own second electrode 4 and/or several of the resonators 2 can have a common second electrode 4.