Method for fabricating resonator structure and resonator structure

Methods for manufacturing resonator structures and corresponding resonator structures are described. A first wafer including a first piezoelectric material is singulated and bonded to a second wafer.

TECHNICAL FIELD

The present application relates to methods for manufacturing resonator structures and to corresponding resonator structures.

BACKGROUND

Filters are used in a variety of electronic circuits to filter out certain frequency components of a signal while letting other frequency components pass. For example, in communication circuits, filters may be used to block frequency components outside a frequency band or part of a frequency band used for communication and to be processed by further circuits.

To increase bandwidth, communication standards like wireless communication standards (for example LTE, Long Term Evolution) or also wire-based communication standards continually increase a used frequency range and a number of used frequency bands. In communication devices implementing such standards, often highly selective filters matching to the respective frequency bands are required. The frequency bands used may differ from country to country. Therefore, a plurality of filters having different filter characteristics (for example different passbands) are required. Furthermore, in what is referred to as carrier aggregation several frequency bands are operated at the same time. This requires specific filter designs for exactly those combinations. With a specific filter provided for each possible combination, the number of physical filters is actually much higher than the number of available bands. In order to reduce the number of different filters (2-port up to n-port filters) actually required in a communication device, tunable filters are highly desirable.

As highly selective bandpass filters in communication circuits and devices, surface acoustic wave (SAW) or bulk acoustic wave (BAW) technologies are frequently used. Conventional filters of such types are designed for fixed resonance or center frequencies. As a consequence, many filters are required to serve individual frequency bands or aggregated combinations of several frequency bands used in current communication standards like LTE or WiFi standards. Radio frequency (RF) switches are then used to select individual filters of the plurality of filters for example for desired signal paths between an antenna, a low noise amplifier or power amplifier. As such conventional approaches require a large number of mostly discrete components and as space is limited in mobile devices, tunable solutions are highly desirable.

One approach to provide tunability to BAW filters is to use coupled resonators with a first resonator and a second resonator, where the second resonator serves as the actual filter resonator and the first resonator, which is acoustically coupled to the second resonator, serves for tuning, for example by adjusting tunable capacitors coupled therewith. In some applications, different materials are desired for the first and second resonators. For example, for the second resonator, in many applications, a small resonator bandwidth is desired to provide small-band filters, while the second resonator should provide a large tuning range, which requirements may be implemented using different materials. However, such different materials may be difficult to integrate in a manufacturing process, for example due to different wafer sizes available and/or due to different material properties.

SUMMARY

A method as defined in claim1or6and a resonator structure as defined in claim19are provided. The dependent claims define further embodiments.

According to an embodiment, a method for manufacturing a coupled resonator structure is provided, comprising:

processing a first wafer to form a processed first wafer, the processed first wafer comprising a first piezoelectric material,

processing a second wafer to form a processed second wafer, the processed second wafer comprising a second piezoelectric material,

singulating the first wafer to form at least one singulated wafer chip,

bonding the at least one singulated wafer chip to the second wafer to form a joint wafer, and

processing the joint wafer to form a resonator structure comprising a first resonator including the first piezoelectric material and a second resonator including the second piezoelectric material such that the first and second resonators are acoustically coupled with each other.

According to another embodiment, a method for manufacturing a resonator structure is provided, comprising:

processing a first wafer to form a processed first wafer, the processed first wafer comprising a first piezoelectric material,

processing a second wafer to form a processed second wafer, the processed second wafer comprising an acoustic termination at a first side thereof,

singulating the first wafer to form at least one singulated wafer chip,

bonding the at least one singulated wafer chip to the second wafer such that the first side of the second wafer faces the singulated wafer chip to form a joint wafer, and

processing the joint wafer to form a resonator structure comprising a first resonator including the first piezoelectric material.

According to another embodiment, a resonator structure is provided, comprising:

a diced first wafer piece comprising a first piezoelectric material,

a substrate comprising an acoustic termination at a first side thereof, wherein the diced wafer piece is bonded to the second wafer such that the first side faces the diced wafer piece.

The above summary is merely intended to give a brief overview over some implementations and is not to be construed as limiting.

DETAILED DESCRIPTION

In the following, various embodiments will be described in detail referring to the attached drawings. It should be noted that these embodiments serve illustrative purposes only and are not to be construed as limiting. For example, while embodiments may be described as comprising a plurality of features, elements or details, in other embodiments, some of these features, elements or details may be omitted and/or may be replaced by alternative features, elements or details. In addition to the features, elements or details explicitly described or shown in the drawings, other features, elements or details, for example components conventionally used in bulk acoustic wave (BAW) resonators or BAW-based filters, may be provided.

Features from different embodiments may be combined to form further embodiments unless noted to the contrary. Variations or modifications described with respect to one of the embodiments may also be applicable to other embodiments unless noted otherwise.

Embodiments discussed in the following relate to manufacturing of bulk acoustic wave (BAW) resonator structures, which may be used to build a BAW-based filter. For forming acoustic resonators like BAW resonators, generally a piezoelectric layer is provided between two electrodes (e.g. top and bottom electrodes), and acoustic waves propagate through the bulk of the piezoelectric material. The application of an electric field between the two electrodes generates a mechanical stress that is further propagated through the bulk of the structure as an acoustic wave. A resonance condition is established when the acoustical path in thickness direction of the structure corresponds to integer multiples of half the acoustic wave length.

In embodiments, at least two resonators are used which are acoustically coupled to each other to form a resonator structure. The at least two resonators comprise a first resonator using a first piezoelectric material and a second resonator using a second piezoelectric material. In some embodiments, the first piezoelectric material is provided as or on a first wafer, which is processed, diced and then provided to a second wafer. This way, by first dicing the first wafer and then providing the diced portions (also referred to as chips herein) to the second wafer enables the use of different materials which are provided in different wafer sizes.

For example, embodiments used herein may be used to integrate a thin lithium niobate (LiNbO3) crystal film into such a coupled resonator structures, for example based on silicon wafers. LiNbO3 crystals are usually available as wafers having a diameter of about 100 mm, while silicon (Si) wafers are available in larger sizes, for example as 200 mm or even 300 mm wafers. Using larger wafers for building resonator structures in many applications is preferable, as it enables parallel processing of more structures on a single wafer and may therefore serve to increase production yield. By using techniques disclosed herein, e.g. 100 mm LiNbO3 wafers may be used to form resonator structures on larger Si wafers like 200 mm wafers or 300 mm wafers. While LiNbO3 is used as an example material herein, other materials may also be used, for example lithium tantalate (LiTaO3).

Turning now to the figures,FIG. 1is a flowchart of a method for manufacturing a resonator structure according to some embodiments. While the method ofFIG. 1is depicted as a series of acts or events, the order in which the events are described is not to be construed as limiting. For example, some acts or events may be performed in different orders, or some acts or events may be performed simultaneously. Examples of such varying orders will be given when describing the method ofFIG. 1.

At10, the method ofFIG. 1comprises providing a first wafer. The first wafer may be made of a piezoelectric material, for example of monocrystalline piezoelectric material like lithium niobate (LiNbO3), intended as piezoelectric material for a first resonator of a coupled resonator structure. In other embodiments, the first wafer may be a wafer carrying a first piezoelectric material. Processing the first wafer may for example include providing an electrode, for example by metal deposition.

At11, the method comprises processing a second wafer. The second wafer in some embodiments may be a semiconductor wafer, and processing the second wafer may comprise forming a resonator comprising a second piezoelectric material on the second wafer. In some embodiments, the second wafer is a silicon wafer, and processing the second wafer may comprise depositing for example aluminum nitride as second piezoelectric material on the second wafer, and/or may comprise forming electrodes or other components of the second resonator.

At12, the method comprises singulating the first wafer, also referred to as dicing, i.e. cutting individual pieces (also referred to as chips, chip dies or dies) from the first wafer, each piece being intended for one or more individual resonator structures. In other words, each piece may have a size to comprise one or more structures intended for one or more resonators structures in a final device.

It should be noted that the acts described with reference to numeral10-12may also be performed in a different order. For example, the second wafer may be processed prior to processing the first wafer, or may be processed in parallel to processing and/or singulating the first wafer.

At13, the pieces singulated at12are transferred to the second wafer and bonded to the second wafer. It should be noted that pieces from more than one first wafer may be transferred to a single second wafer, for example to use a larger area of the second wafer for device manufacturing compared to an area of the first wafer. For example, in some implementations, the first wafer may be a LiNbO3 wafer, with sizes typically up to 100 mm diameter, while the second wafer may be a silicon wafer having a diameter of 200 mm or 300 mm.

At14, the method then comprises processing of the joint wafers (second wafer with singulated pieces of first wafer bonded thereto) to finalize resonator structures.

FIG. 2, in a simplified way, illustrates a resonator device according to an embodiment. The resonator device ofFIG. 2comprises a portion20based on a singulated piece of a first wafer, comprising a first piezoelectric material, bonded to a second portion21based on a second wafer, with a second piezoelectric material for forming a second resonator. The first and second resonators are acoustically coupled in the device ofFIG. 2, and for example a first resonator including the first piezoelectric material may serve for tuning the resonator structure, while a second resonator including the second piezoelectric material is the resonator directly incorporated (for example by connecting its electrodes) in a filter device.

Next, a more specific example for the general method and device described with reference toFIGS. 1 and 2will be given referring toFIGS. 3 and 4.

FIG. 3is a flowchart illustrating a detailed method for manufacturing a resonator structure according to an embodiment.FIGS. 4A-4Millustrate the resonator structure in various stages of the manufacturing process. The specific example ofFIGS. 3 and 4is given for further illustrating the general method and device discussed with reference toFIGS. 1 and 2, but is not to be construed as limiting. In particular, while specific materials and structures are given inFIGS. 3 and 4for illustration purposes, other materials and structures may also be used. While inFIG. 3a plurality of acts or events are shown, in other embodiments some of the acts or events may be omitted, depending on a particular processing used and a particular resonator structure to be manufactured.

At30ofFIG. 3, the method comprises providing a lithium niobate (LiNbO3) wafer, which is shown as a LiNbO3 wafer40inFIG. 4A. LiNbO3 wafer40may for example be a 100 mm diameter wafer, but is not limited to this wafer size. Such LiNbO3 wafers are commercially available.

At31, the method comprises depositing a metal layer as a conductive material on the LiNbO3 wafer, which metal layer will later form a bottom electrode of a first resonator. InFIG. 4B, as an example a metal layer41is shown provided on LiNbO3 wafer40. Any conventional metal deposition techniques like sputtering may be used. Usable metals include tungsten or aluminum, but are not limited thereto. Combinations of metals or sandwich electrodes made of different metals are also possible as conductive material.

At32, optionally the method ofFIG. 3comprises structuring the bottom electrode, for example defining a size for the electrode. An example is shown inFIG. 4C, where metal layer41is structured to form an electrode of a certain size. Any conventional metal structuring technique may be used, for example lithography techniques in combination with dry (plasma) or wet etch processes.

At33, the method comprises deposition an oxide (or other isolation layer) on the LiNbO3 wafer, and subsequently planarizing the oxide. An example for a suitable oxide is silicon dioxide. The planarization may for example be performed by a standard CMP process (chemical mechanical polishing). An example result of the planarization is illustrated inFIG. 4D, where an oxide layer covers LiNbO3 wafer40and metal layer41, the oxide layer42having a planar surface (immediately after deposition, the steps between metal layer41and LiNbO3 wafer40would at least partially be reflected in the surface of oxide layer42).

It should be noted thatFIGS. 4A-4Cshow only a portion of wafer40, and in mass production of resonator devices a plurality of electrodes may be formed from metal layer41intended for a plurality of resonator structures, of which only a single electrode is shown inFIGS. 4A-4C.

At34, the method ofFIG. 3comprises a singulation of the LiNbO3 wafer, for example by sawing or etching. This is illustrated inFIG. 4E, where a portion comprising the structured metal layer41is singled out along cut lines43. It should be noted that the provision of a single electrode41is only an example, and in embodiments chips comprising a plurality of electrodes for a plurality of resonators may be singulated. The result is shown inFIG. 4F, for a singulated chip44(flipped top-side down).

At35, the method then comprises providing a silicon substrate wafer with a resonator structure processed thereon. An example is shown inFIG. 4Gfor a processed silicon wafer45. Processed wafer45comprises a silicon substrate wafer46. On wafer46, a BAW resonator is formed comprising an acoustic mirror stack48, for example made of alternating layers of an oxide like silicon dioxide and a metal like tungsten, a bottom electrode49, a piezoelectric material410, for example aluminum nitride (AlN) or scandium aluminum nitride (ScAlN), and a top electrode411. This structure is surrounded by planarized oxide47. In another embodiment, the layer stack48forming the acoustic mirror may also be embedded into silicon wafer46. Instead of acoustic mirror stack48, another acoustic termination like a cavity may be provided. Such a cavity may be provided on silicon substrate wafer46or in silicon substrate wafer46at the side facing singulated chip44inFIG. 4G.

The resonator structure of processed wafer45serves only as an example, and other conventional BAW resonator structures may also be used.

At36, the chips of the LiNbO3 wafer generated by singulation are then transferred to the processed silicon wafer and bonded thereto. This is also illustrated inFIG. 4G, where chip44is placed above and aligned to processed wafer45such that electrode41is aligned with the resonator in processed wafer45and oxide42faces oxide47.

It should be noted that a plurality of chips44may be placed on processed wafer45to be aligned with different resonator structured on processed wafer45for a production of a plurality of resonator structures or a plurality of devices with resonator structures on a single wafer. In this case,FIG. 4Gshows only a part of a larger wafer structure. After the chip transfer onto the Si substrate wafer, the transferred chips are bonded to the substrate wafer by means of a conventional oxide-to-oxide bonding process. For example, by applying heat and pressure, oxide layers42,47bond to form a single oxide layer413.

At37, after the chips44are bonded to processed wafer45, the entire wafer35with the bonded chips44is then encapsulated for example by a compression molding process. This is illustrated inFIG. 4H, where a numeral412inFIG. 4Hillustrates a molding material like a plastic mold compound material, which may be provided in liquid form onto the wafer and then pressed in form and cured by the compression molding. Through the molding, acoustic mirror stack48or another acoustic termination is encapsulated in the structure.

Next, in the embodiment ofFIG. 3at38mechanical grinding is performed to thin the LiNbO340to a layer having a desired thickness. With usual mechanical grinding, an accuracy of about +/−10 μm may be obtained. To increase accuracy, spacers with a well-defined height may serve to stop or slow down the grinding. Two or more different kinds of spacers may be used to provide a multistep grinding process. In some embodiments, a final thickness of the order of 5 to 20 μm may be reached. After single or multi-step grinding, additional thickness correction may be obtained by subsequent wet etching or dry etching or ion milling processes.

At39, the method comprises structuring of the LiNbO3 layer, electrode deposition and structuring. This is illustrated inFIGS. 4J and 4K. InFIG. 4J, LiNbO3 layer40has been structured (brought to a desired lateral size), gaps have been filled with oxide material414, for example silicon dioxide, followed by a planarization process (for example CMP process). Additionally, if needed some final thickness adjustments for the LiNbO3 layer may be performed, for example by polishing and etching.

InFIG. 4K, electrode deposition and structuring is shown. A metal layer is deposited and structured to form a top electrode416and a connection415for the bottom electrode41, which is electrically coupled to bottom electrode41via a vertical interconnect (via)414.

At310, the method comprises providing connections for the electrode to a desired location. For example, as shown inFIG. 4L, electrodes416,415may be electrically provided to terminals at a backside of wafer46via connections417, or as shown inFIG. 4Mto terminals419on wafer46via connections418. Such terminals419may be interconnects being formed as a part of a metallization layer. Such a metallization layer may be part of circuitry formed on or in wafer46. The variation ofFIG. 4Mmay for example be employed when wafer46has also electronic or electric structures formed thereon which provide signals to electrodes416,41and/or receive signals from them. For example, tuning circuitry to be coupled to electrodes416,41may be provided in case the first resonator formed by LiNbO3 layer40sandwiched between electrodes416,41serves as a tuning resonator for tuning a resonance frequency, while a second resonator formed by piezoelectric material410and electrodes49,411serves as a filter resonators, with the electrodes connected in a filter structure. In a similar way, electrodes49and411of the second resonator (on the Si substrate wafer) may be connected to terminals being part of circuitry formed on or in wafer46or by means of vias to the wafer frontside or wafer backside.

Substrate wafer46may then be diced to form individual devices with parts of wafer46serving as substrate.

Just for better illustrating the purpose of resonator structures as discussed previously having two resonators stacked upon each other, operation and application of such resonator structures will now be explained using non-limiting examples referring toFIGS. 5-8.

FIG. 5schematically illustrates a resonator structure as discussed above together with a tuning circuit55. The resonator structure of the embodiment ofFIG. 1comprises a second resonator50that may correspond to the resonator formed in the second wafer, for example a resonator using aluminum nitride (410inFIG. 4) as a piezoelectric material having a relatively low piezoelectric coupling, allowing for filters having a small bandwidth. Second resonator50is coupled with a first resonator54via an acoustic coupling53. First resonator54may for example comprise a piezoelectric material having a comparatively high piezoelectric coupling, for example the lithium niobate discussed above (for example40inFIG. 4). Acoustic coupling53is provided by a material between the first and second resonators, for example the oxide material inFIG. 4. Acoustic coupling means in this context that acoustic waves of second resonator50may at least partially propagate to first resonator54and vice versa.

Second resonator50has a first terminal51and a second terminal52. Using first and second terminals51,52which may for example correspond to or be coupled to electrodes of second resonator50, the resonator structure ofFIG. 5may be incorporated in a filter structure like a ladder filter structure or a lattice filter structure.

Furthermore, tuning circuit55is coupled to first resonator54. Tuning circuit55may comprise an impedance network, which may comprise variable elements like variable impedances, for example a variable capacitor, or switches like radio frequency (RF) switches. By changing a value of the variable element(s) of tuning circuit55, resonances of the resonator structure ofFIG. 5may be shifted. This may be used for building a tunable filter using one or more filter structures as shown inFIG. 5.

In such an approach with first and second resonators, tuning circuit55is electrically decoupled from second resonator50and acts on second resonator50only via first resonator54and acoustic coupling53. In some embodiments, this avoids adverse effects compared to tuning circuits directly coupled to second resonator50. Second resonator50may also be referred to as a filter resonator, as it is to be incorporated into a filter structure using first and second terminals51,52. First resonator54may also be referred to as a frequency tuning resonator, as it is used for tuning resonance frequencies of the resonator structure ofFIG. 1using tuning circuit55.

As mentioned, second resonator50, acoustic coupling53and first resonator54may be implemented in a process flow as discussed above.

For further illustration,FIG. 6illustrates an equivalent circuit of the resonator structures discussed above. Numeral60denotes a second resonator, formed for example inFIG. 4by electrodes411,49and piezoelectric material410. Numeral61denotes the first resonator formed for example by electrodes416,41and piezoelectric material40(lithium niobate in the example ofFIG. 4) inFIG. 6. Terminals63,64contact the electrodes of second resonator60, and terminals65,66contact the electrodes of first resonator61. A parasitic capacitor62with a capacitance C12represents the dielectric material between both resonators, for example oxide material42,47or413inFIG. 4. In embodiments, terminals63,64then serve to incorporate the resonator structure ofFIG. 6into a filter structure. To provide frequency tuning, a tuning circuit may be coupled to terminals65and66.

FIG. 7illustrates an example topology of a ladder filter, in this case a 3½ stage ladder filter. Numeral70denotes a signal input, numeral71denotes a signal output and numeral72denotes ground. The ladder filter ofFIG. 7comprises four series resonators73A to73D and three shunt resonators74A to74C. Typically all series resonators73A to73D have the same resonance frequencies, and all shunt resonators74A to74C have the same resonance frequencies, but the resonance frequencies of the series and the shunt resonators are detuned with respect to each other. The amount of detuning roughly corresponds to the bandwidth of the individual resonators or to half the bandwidth of the resulting filters. The resonance frequencies of the shunt resonators74A to74C in typical cases are lower than the resonance frequencies of the series resonators73A to73D.

Each of resonators73A to73D,74A to74C may be a first resonator of a resonator structure as discussed previously with respect toFIGS. 1-6. Via a tuning circuit coupled to the respective second resonators of the resonator structures, frequency tuning of the filter may be performed. The ladder filter structure ofFIG. 7serves only as an example, and any conventional ladder or lattice filter structures used with BAW resonators in the art may be used and modified by replacing resonators conventionally used by resonator structures comprising first and second resonators as explained with reference toFIGS. 1-6. A plurality of such filters may be combined to form an n-port filter structure, for example for filtering a plurality of frequency bands used in communication applications.

FIG. 8illustrates a resonator structure according to an embodiment comprising a tuning circuit and usable as shunt resonator element, for example to implement shunt resonators74A to74C of the ladder filter structure ofFIG. 7.

The resonator structure ofFIG. 8comprises a first resonator85and a second resonator82. First resonator85and second resonator82are electrically isolated (but not acoustically decoupled) e.g. by a dielectric material represented by a parasitic capacitor84with capacitance C12. This dielectric material provides an acoustic coupling between the resonators82,85as indicated by an arrow83. Implementation of first resonator85and second resonator82may be as explained previously with respect toFIGS. 1-6.

One electrode of the second resonator82is connected to ground (e.g.88inFIG. 8), whereas the other electrode is connected to terminals80and81. Terminals80,81serve for connection with further resonators or signal input/output terminals to build filter structures. For example, when the shunt resonator element ofFIG. 6is used for implementing the shunt resonator74A ofFIG. 7, first terminal80is connected with series resonator73A and second terminal81is connected with series resonator73B.

In the example filter structure ofFIG. 7, the ground connection88inFIG. 8corresponds to the coupling of any one of shunt resonators74A to74C to ground line72.

Furthermore, a tuning circuit is coupled between the electrodes of first resonator85. In the example ofFIG. 8, the tuning circuit comprises a variable capacitor87coupled in parallel to an inductance86. Inductance86in some embodiments may be implemented as a high Q (Quality-factor) inductor or other reactance, e.g. having a Q-factor of more than 10, more than 50 or more than 100. An inductivity L1of the inductor may for example be between 0.5 and 200 nH, for example below 50 nH, e.g. between 1 and 10 nH. Variable capacitor87may be implemented in any conventional manner using for example varactors or switched capacitors. By changing the capacitance value of variable capacitor87, resonances (series resonance and parallel resonance) of the resonator element ofFIG. 8may be tuned. The tuning circuit ofFIG. 8is only an example, and various combinations of capacitances, inductors and/or resistors may be used, one or more of these capacitances, inductors and/or resistors being variable to provide a tuning. In some embodiments, the tuning circuit may also comprise switches like radio frequency (RF) switches that may be selectively opened and closed to tune the resonator element. In such tuning circuits, capacitances or inductivities may be connected in series or parallel to the switch or switches, (e.g. RF switch or switches).

An inductance86, e.g. an inductor, may increase a tuning range compared to a case where only a variable capacitor is used.

FIG. 9is a circuit diagram of a resonator element suitable as a series resonator in filter structures like the filter structure ofFIG. 7, for example for implementing series resonators73A to73D. The resonator element ofFIG. 9comprises a first resonator95and a second resonator92which are electrically separated as indicated by a (parasitic) capacitance93, having a capacitance value C12. Capacitance93is associated with some dielectric layer(s) that acoustically couples the first resonator95and the second resonator92, as indicated by an arrow94. First and second resonators95and92may be implemented as explained with reference toFIGS. 1-6above.

The electrodes of second resonator92are coupled with a first terminal90and a second terminal91, respectively. Via first and second terminals90,91, the resonator element ofFIG. 9may be incorporated in a filter structure. For example, to implement series resonator73A ofFIG. 7, first terminal90would be coupled to signal input70, and second terminal91would be coupled to resonators74A and73B. In case resonator74A is implemented as inFIG. 7, for example second terminal91ofFIG. 9would be coupled with first terminal80ofFIG. 8, and second terminal81ofFIG. 8would then be coupled with a corresponding terminal90of resonator73B.

Furthermore, a tuning circuit is coupled to the electrodes of first resonator95comprising for example an inductance96and a variable capacitor97. Inductance96and variable capacitance97may be implemented in a similar manner as explained for inductance86and variable capacitance87ofFIG. 8, respectively. Furthermore, inductance96and capacitance97are merely one example for a tuning circuit coupled to first resonator95, and as also explained forFIG. 8other tuning circuit configurations are also possible.

With the shunt resonator element ofFIG. 8and the series resonator element ofFIG. 9, various filter structures like lattice filters and ladder filters, for example the ladder filter structure ofFIG. 7, may be built.

It should be noted that the above filter structures and explanations only serve for further illustrating applications of the resonator structures discussed referring toFIGS. 1-6, but are not to be construed as limiting in any way.

Above, methods for manufacturing coupled resonator structures have been discussed. In other embodiments, techniques as discussed above, in particular the singulating of a wafer made of a piezoelectric material followed by a bonding of one or more singulated pieces to another wafer, may be used to manufacture single resonator structures. In this way, for example a LiNbO3-based resonator may be integrated in a silicon environment, where for example an acoustic termination is provided in or on a silicon wafer as discussed above.

For such a manufacturing, the same process flow as discussed above may be used, where only the formation of a resonator in the second wafer is omitted. To illustrate this,FIG. 10shows a cross-sectional view corresponding toFIG. 4Kfor such a process. Compared toFIG. 4K, inFIG. 10electrodes49,411and piezoelectric material410are not provided, resulting in a single resonator structure. Apart from this difference, all variations and details discussed for manufacturing of coupled resonator structures may also be applied to the manufacturing of single resonator structures. In this case, oxide layer413between layer stack48and bottom electrode414becomes a part of the acoustic mirror, and in embodiments is taken into account for the design of the individual layer thicknesses of the acoustic mirror.

At least some embodiments are defined by the examples given below:

A method for manufacturing a coupled resonator structure, comprising:

processing a first wafer to form a processed first wafer, the processed first wafer comprising a first piezoelectric material,

processing a second wafer to form a processed second wafer, the processed second wafer comprising a second piezoelectric material,

singulating the first wafer to form at least one singulated wafer chip,

bonding the at least one singulated wafer chip to the second wafer to form a joint wafer, and

processing the joint wafer to form a resonator structure comprising a first resonator including the first piezoelectric material and a second resonator including the second piezoelectric material such that the first and second resonators are acoustically coupled with each other.

The method of example 1, wherein processing the second wafer comprises forming the second resonator on the second wafer.

The method of example 1, wherein the second piezoelectric material comprises at least one of aluminum nitride or scandium aluminum nitride.

The method of example 1, wherein the second piezoelectric material has a lower piezoelectric coupling constant than the first piezoelectric material.

The method of example 1, wherein the processed second wafer comprises an acoustic termination at a first side thereof, wherein said bonding is performed such that the first side of the second wafer faces the singulated wafer chip.

A method for manufacturing a resonator structure, comprising:

processing a first wafer to form a processed first wafer, the processed first wafer comprising a first piezoelectric material,

processing a second wafer to form a processed second wafer, the processed second wafer comprising an acoustic termination at a first side thereof,

singulating the first wafer to form at least one singulated wafer chip,

bonding the at least one singulated wafer chip to the second wafer such that the first side of the second wafer faces the singulated wafer chip to form a joint wafer, and

processing the joint wafer to form a resonator structure comprising a first resonator including the first piezoelectric material.

The method of example 6, wherein said acoustic termination comprises at least one of a cavity or an acoustic mirror.

The method of example 6, wherein the acoustic termination is encapsulated in the resonator structure.

The method of example 1, wherein the first wafer is made of the first piezoelectric material.

The method of example 1, wherein the first piezoelectric material is monocrystalline.

The method of example 1, wherein processing the first wafer comprises depositing a conductive material on the first wafer, at least part of the conductive material forming an electrode of the first resonator.

The method of example 11, further comprising structuring the conductive material.

The method of example 1, wherein the first piezoelectric material comprises at least one of lithium niobate or lithium tantalate.

The method of example 1, wherein processing the first wafer comprises providing a first dielectric layer on the first wafer, and wherein processing the second wafer comprises providing a second dielectric layer on the second wafer, wherein said bonding comprises bonding the first and second dielectric layers.

The method of example 14, wherein said first and second dielectric layers comprise an oxide.

The method of example 1, further comprising encapsulating the joint wafer.

The method of example 1, wherein said processing of the joint wafer comprises thinning the first piezoelectric layer.

The method of example 1, wherein said processing of the joint wafer comprises at least one of electrode deposition, electrode structuring or providing electrode connections.

a diced first wafer piece comprising a first piezoelectric material,

a substrate comprising an acoustic termination at a first side thereof, wherein the diced wafer piece is bonded to the second wafer such that the first side faces the diced wafer piece.

The resonator structure of example 19, wherein the resonator structure is manufactured by the method of example 1.