DE102019102481B4 - Electroacoustic resonator with improved performance and increased service life, HF filter and multiplexer - Google Patents

Abstract

An improved electroacoustic resonator with good electrical, thermal and mechanical performance and with increased service life is provided. The resonator has an electrode structure comprising beryllium.

Description

The present invention relates to electroacoustic resonators which provide improved electrical, thermal and mechanical performance and which have an increased service life. Electroacoustic resonators can be used in electroacoustic filters, e.g. B. for use in wireless communication systems. Electroacoustic resonators include a piezoelectric material and an electrode structure that is coupled to the piezoelectric material. Due to the piezoelectric effect, an electroacoustic resonator can convert between electromagnetic RF signals and acoustic RF signals. Electroacoustic resonators can be combined to create RF filters; z. B. band pass filter or band stop filter. Such RF filters can be used in front end circuits of wireless devices, e.g. B. mobile communication devices can be used.

Such an electroacoustic resonator is disclosed, for example, by US 2017/0099040 A1 . The resonator disclosed there comprises a substrate, a resonator element with a base element with a first and a second surface and a pair of excitation electrodes as well as a first and a second connecting element.

Such electroacoustic resonators set up MEMS devices (MEMS: microelectromechanical system). Such electroacoustic resonators should accordingly provide good electrical properties together with good mechanical properties.

However, conventional electroacoustic resonators are not ideal electrical circuit components and accordingly have electrical losses. Furthermore, due to their mechanical nature, such resonators are exposed to electrical and mechanical stress, which can reduce the service life of corresponding devices.

Accordingly, an electroacoustic resonator is desired which provides good electrical, thermal and mechanical performance and which has an increased service life.

For this purpose an electroacoustic resonator according to independent claim 1 is provided. Dependent claims provide preferred embodiments.

The electroacoustic resonator includes a piezoelectric material and an electrode structure. The electrode structure is coupled to the piezoelectric material. The electrode structure includes an electrode core with Be (beryllium).

Accordingly, there is provided an electroacoustic resonator using beryllium in its electrode structure. The coupling between the electrode structure and the piezoelectric material can be an electrical coupling and a mechanical coupling. In particular, it is possible for the coupling to be implemented by bringing the electrode structure into direct contact with the piezoelectric material, so that the piezoelectric effect can be used to convert between electromagnetic and acoustic RF signals.

Conventional materials used for the electrode structures are e.g. B. Al (aluminum), Cu (copper), Ti (titanium), Ag (silver), Au (gold), Cr (chromium), Ni (nickel) and Co (cobalt) and similar metals. Metals for electrode structures should have a high conductivity in order to reduce electrical losses. However, conventionally used electrode materials, such as aluminum - which is preferred because of its high conductivity - have a low melting point and are very susceptible to electroacoustic migration. Titanium has a relatively low electrical and thermal conductivity.

The provision of beryllium in the electrode structure makes it possible to produce a stiff, lightweight, and highly conductive (both electrical and thermal) electrode structure with good electrical performance and excellent mechanical performance. In particular, its high resistance to electroacoustic migration and its stability in oxidizing environments can contribute to improving the longevity of the corresponding filter and multiplexer.

Beryllium can completely or partially replace one or more metals in conventional electrode structures. Beryllium has the highest specific stiffness, which is particularly important for electroacoustic applications. Furthermore, the rigidity parameters ensure that the electrode structure can maintain its shape even under high mechanical stress. Together with the relatively high melting point, a corresponding electrode structure is very resistant to electroacoustic migration. Furthermore, the high specific heat helps to maintain a low temperature level when the corresponding electrical circuit is exposed to high power levels. Accordingly, temperature-induced frequency shifts can also be reduced.

It should be noted that other metals may have higher thermal and electrical conductivity when the thermal and electrical conductivity of an electrode structure is considered with reference to the corresponding cross section of the conductor. However, in order to meet the requirements with regard to the mass coverage on the piezoelectric material in order to achieve a specific acoustic impedance, the low density of beryllium enables a significant increase in the cross section of the conductor. Accordingly, electrode structures comprising beryllium can have thermal and electrical resistances with respect to the mass coverage on the piezoelectric material which are considerably reduced compared to electrode structures without beryllium.

Accordingly, mechanical (acoustic), thermal and electrical losses can be obtained compared to electrode structures based on conventional materials.

It is possible that the electrode core - in addition to beryllium - comprises an alloy with one or more metals which is / are selected from aluminum, copper, titanium, silver and gold as additional metals.

It is also possible that the electrode core comprises one or more layers made of different materials.

For example, the property of titanium to provide good adhesion properties can be used to provide a thin layer of titanium as an adhesion layer, e.g. B. between the piezoelectric material and one or more further layers of the electrode core of the electrode structure to be used.

Accordingly, it is possible that the electrode core comprises a central segment, which comprises or consists of beryllium, and an adhesive layer, which comprises or consists of titanium, between the central segment and the piezoelectric material.

In addition, the use of layers, e.g. B. copper, possible to prevent electroacoustic migration.

Accordingly, taking advantage of the stiffness and low density of beryllium and advantageous properties of other metals, e.g. B. in thin additional layers, can be used to combine preferred properties in a single component.

It is also possible that the electrode structure comprises a dielectric coating layer.

The dielectric coating layer can consist of or comprise a dielectric material. The material of the dielectric coating layer can be arranged on the core of the electrode structure, so that the electrode core is arranged between the coating layer and the piezoelectric material. In particular, it is possible that the coating layer is provided in such a way that the core of the electrode structure is prevented from being in contact with an atmosphere. Accordingly, each surface of the electrode structure can be in contact with either the piezoelectric material or the material of the dielectric coating.

In particular, it is possible for the dielectric coating layer to be a passivation layer. Possible materials for the passivation layer are metal oxides, e.g. B. Oxides of the elements of the core. Other materials are aluminum nitride, aluminum oxide, silicon oxide and the like.

It is possible for the electroacoustic resonator to further comprise one or more additional layers. The one or more additional layers can be selected from a passivation layer, a TCF layer (TCF: Temperature Coefficient of Frequency) and / or a trimming growth layer. A passivation layer can be used in order to protect the electrode structure or the core of the electrode structure from a corrosive influence of the atmosphere of the device. The passivation layer can be arranged such that free surfaces of the piezoelectric material and the electrode structure are covered.

The passivation layer can comprise the above-mentioned materials of the dielectric coating layer.

A TCF layer can be used to compensate for temperature-induced frequency shifts of characteristic frequencies of the resonator or a corresponding filter, e.g. B. a center frequency of a pass band or a stop band or resonance frequencies or anti-resonance frequencies of the resonator to reduce or eliminate.

For this purpose, the thickness of the TCF layer and the material of the TCF layer can be selected so that the temperature-induced frequency of the device without the TCF layer and the temperature-induced frequency shifts of the TCF layer have the same magnitude but opposite signs, so that a total temperature-induced frequency shift is reduced to essentially zero.

A trimming layer can be implemented as an additional layer covering the other structures of the device. During the production of the resonators, the thickness of the trimming layer can be adjusted (e.g. by local removal of material) so that inhomogeneities during a layer deposition can be compensated for during production and each resonator of several resonators that are produced simultaneously have the same characteristic frequencies having.

It is possible that the resonator consists of a SAW resonator (SAW: Surface Acoustic Wave), a GBAW resonator (GBAW: Guided Bulk Acoustic Wave) and a BAW resonator (BAW: Bulk Acoustic Wave - bulk acoustic wave) is selected.

A SAW resonator operates with surface acoustic waves which essentially propagate in the surface area of the piezoelectric material, especially in the interface area where the piezoelectric material and the electrode structure are coupled to one another. Propagation in this area is problematic for electrode structures because the existence of acoustic waves corresponds to a continuous deformation of the electrode structure. Accordingly, the provision of beryllium exhibiting high rigidity values has an excellent advantage for the longevity of the device.

GBAW resonators employ acoustic waves that propagate at an interface between the piezoelectric material and a waveguide structure above the piezoelectric material such that the electrode structure is essentially sandwiched between the waveguide layers and the piezoelectric material therebetween.

A BAW resonator uses bulk acoustic waves that propagate as longitudinal waves between two electrode layers, between which the piezoelectric material is provided as a piezoelectric layer.

BAW resonators use acoustic longitudinal waves, whereas SAW resonators and GBAW resonators use acoustic transverse waves or acoustic waves which have wave modes which at least partially include transverse wave modes. Accordingly, the electrode structure of a BAW resonator essentially comprises two flat electrode areas, between which the piezoelectric material is provided in a piezoelectric layer.

In contrast to this, SAW resonators and GBAW resonators have electrode structures which include interdigitated electrode fingers which extend in a direction orthogonal to the direction of propagation of the acoustic waves and parallel to the surface of the piezoelectric material.

An electroacoustic resonator is obtained by placing an electroacoustic excitation structure in such a way that acoustic energy can be confined to the area of the resonator. Typically this is obtained by placing the IDT (IDT: Interdigital Transducer) structure of SAW resonators and GBAW resonators between reflector fingers on the surface of the piezoelectric material.

In a BAW resonator, the acoustic energy is limited by arranging the excitation structure, which comprises two electrode areas and the piezoelectric material between the two electrode areas, on an acoustic mirror (SMR-type resonator, SMR: Solidly Mounted Resonator) or by arranging the excitation structure above a cavity (FBAR-type resonator, FBAR: Film Bulk Acoustic Resonator).

Accordingly, it is possible for one or more of the electroacoustic resonators, as described above, to be used to set up an RF filter.

The RF filter may comprise one or more electroacoustic resonators, e.g. In a branch-type circuit configuration or in a cross-link-type circuit configuration.

In a laddertype-like (branch-type) circuit topology, series resonators are electrically connected in series between an input port and an output port. Shunt paths include one or more resonators that are coupled between the signal path with the series resonators and a ground potential.

In a latticetype-like (cross-link type) circuit topology, an input port comprises two connections and an output port comprises two connections and is at least one electroacoustic resonator in a signal path arranged, which electrically connects a first connection of the input port to a second connection of the output port or a second connection of the input port electrically connects to a first connection of the output port (whereby a conductor crossing is accordingly established).

It is also possible for one or more such RF filters to be used to set up a multiplexer. A multiplexer can be a duplexer, a triplexer, a quadplexer or a multiplexer of a higher order. Multiplexers can be used to transfer signals of different frequencies to a common port, e.g. B. at a common antenna port to separate and / or combine.

The piezoelectric material of resonators that work with surface acoustic waves can be lithium niobate or lithium tantalate. The piezoelectric material of resonators that work with bulk acoustic waves can be aluminum nitride, e.g. B. aluminum nitride doped with scandium.

Solid beryllium is generally safe, but airborne particles of beryllium or material containing beryllium are toxic health hazards if inhaled. Exposure to beryllium particles should be avoided as much as possible by using appropriate personal protective equipment, such as a respirator or full face mask respirator. Very sensitive beryllium detection methods are available and should be used to monitor the workplace to avoid harmful worker exposure to beryllium dust and smoke.

The electroacoustic resonator, the RF filter and the multiplexer are not limited to the technical details described above. Resonators can include other acoustic active or electrical circuit elements such as waveguide structures and impedance matching circuits. RF filters can also include conventional resonators. Multiplexers can also include conventional RF filters.

The use of beryllium is not limited to the electrode structure. In particular, the use of beryllium is not limited to electrode fingers. Busbars and / or reflector fingers can be of the same construction and also use beryllium to achieve the above benefits. In particular, each element of the resonator that is acoustically active, i. H. exposed to acoustic waves have a construction as described above.

Central aspects, functional principles and details of preferred embodiments are shown in the accompanying schematic figures.

• 1 zeigt eine Draufsicht auf die Elektrodenstruktur eines SAW-Resonators;
• 2 zeigt eine Querschnittsansicht eines BAW-Resonators;
• 3 zeigt einen Querschnitt durch den IDT eines SAW-Resonators, der eine Beschichtungsschicht umfasst;
• 4 zeigt die Möglichkeit, dass der Elektrodenkern einige Unterschichten umfasst; und
• 5 zeigt einen Duplexer, der zwei Bandpassfilter basierend auf einer abzweigtypartigen Schaltkreistopologie umfasst.

In the figures:

• 1 Fig. 13 shows a plan view of the electrode structure of a SAW resonator;
• 2 Figure 3 shows a cross-sectional view of a BAW resonator;
• 3 shows a cross section through the IDT a SAW resonator including a coating layer;
• 4th shows the possibility that the electrode core includes some sub-layers; and
• 5 Figure 11 shows a duplexer that includes two bandpass filters based on a branch type circuit topology.

1 illustrates the basic construction of a SAW resonator SAWR . The electrode structure includes an IDT structure IDT with finger-like interlaced electrode fingers EFI . Every electrode finger EFI is electrical with one of two busbars BB connected. Of the IDT sets up the excitation element of the SAW resonator. Of the IDT is between reflector fingers RFI arranged to confine the acoustic energy to the acoustic track. The electrode fingers EFI set up a Bragg mirror to deflect the acoustic waves onto the area of the IDT to limit.

Of the IDT and the reflector fingers RFI are on a piezoelectric material PM arranged. The surface of the piezoelectric material PM is arranged in the xy plane. The direction of propagation of the acoustic waves is parallel to the x direction. The extension of the electrode fingers EFI is parallel to the y-direction.

The extension of the electrode fingers is corresponding EFI parallel to the direction of propagation of the acoustic waves and parallel to the normal to the surface of the piezoelectric material PM .

In contrast, illustrated 2 a basic construction of a BAW resonator of the SMR type. A piezoelectric material PM is sandwiched between two electrode areas Tbsp between. The electrode areas Tbsp and the piezoelectric material PM set up the excitation element of the BAW resonator BAWR one. To limit the acoustic energy is an acoustic mirror AT THE between the excitation element and a carrier substrate CS arranged. The direction of propagation of the acoustic waves - which are longitudinal waves - is parallel to the z-direction, correspondingly parallel to the normal the area of the electrodes Tbsp . To limit the acoustic energy, the acoustic mirror can AT THE can be set up as a Bragg mirror, which comprises two or more sub-layers with different acoustic impedances, which are arranged one above the other.

3 illustrates the possibility of setting up the electrode structure IT with an electrode structure core EC going through a coating layer CL is covered. The material of the coating layer CL can be a dielectric material. The dielectric material can be used to make the core EC to protect against harmful influences. The core EC includes or consists of beryllium. The electrode structure IT is on the surface of the piezoelectric material PM arranged. The direction of propagation of the surface waves is parallel to the x-direction and orthogonal to the z-direction. 3 Fig. 13 shows a cross section orthogonal to the y-direction which is the extension direction of the electrode fingers.

4th illustrates the possibility of providing the core of the electrode structure as a layer construction comprising three sublayers. A first underclass ECL1 may comprise or consist of titanium and establish an adhesive layer. One of the upper layers ECL2 and ECL3 or both top layers may comprise beryllium to provide the improved properties described above. An additional layer, e.g. B. ECL2 and or ECL3 , can include other materials and provide additional functionality.

Furthermore, one or more additional layers, e.g. B. a passivation layer PL and / or a TCF layer TCF, above the piezoelectric material PM and the electrode structure.

5 illustrates a basic circuit topology of a duplexer YOU . The duplexer YOU includes a transmission filter TXF and a receive filter RXF . The transmission filter TXF is usually between a transmission port and an antenna port with an antenna ON connected, connected. The reception filter RXF is typically connected between a receiving port and the antenna port. The transmission filter TXF and the receive filter RXF are based on a branch-type circuit topology, which has a signal path with series resonators SR electrically connected in series between an input port and an output port. Furthermore, parallel paths include parallel resonators PR that electrically connect the signal path to a ground potential.

About the frequency-dependent impedances of the receiving filter RXF , the transmission filter TXF and / or to adapt the antenna, the impedance matching circuit IMC between the transmission filter TXF and the receive filter RXF , e.g. B. at the antenna port.

List of reference symbols

AT THE:

acoustic mirror

ON:

antenna

BAWR:

Bulky acoustic wave resonator

BB:

Busbar

CL:

Coating layer

CS:

Carrier substrate

YOU:

Duplexer

EC:

Electrode core

ECL1, ECL2, ECL3:

Underlayers of the electrode core

EFI:

Electrode finger

EL:

Electrode areas

IT:

Electrode structure

IDT:

Interdigital converter

IMC:

Impedance matching circuit

PM:

piezoelectric material

PR:

Parallel resonator

RFI:

Reflector finger

RXF:

Receive filter

SAWR:

SAW resonator

SR:

Series resonator

TXF:

Transmission filter

x:

Direction of propagation of surface acoustic waves

y:

Extension direction of electrode fingers

z:

Direction of propagation of bulk acoustic waves

Claims (8)

An electroacoustic resonator comprising: - a piezoelectric material (PM), - An electrode structure (ES) which is coupled to the piezoelectric material (PM), the electrode structure (ES) comprising an electrode core (EC) with Be; and wherein the electrode structure (ES) comprises a dielectric coating layer (CL). Electroacoustic resonator according to the preceding claim, wherein the electrode core (EC) comprises an alloy with Be and one or more metals selected from Al, Cu, Ti, Ag, Au, Cr, Ni, Co. Electroacoustic resonator according to one of the preceding claims, wherein the electrode core (EC) comprises one or more layers (ECL1, ECL2, ECL3) made of different materials. Electroacoustic resonator according to one of the preceding claims, wherein the dielectric coating layer (CL) is a passivation layer. An electroacoustic resonator according to any one of the preceding claims, further comprising one or more additional layers selected from a passivation layer, a TCF layer, a trimming layer. Electroacoustic resonator according to one of the preceding claims, which is selected from a SAW resonator, a GBAW resonator, a BAW resonator. RF filter comprising one or more electroacoustic resonators according to one of the preceding claims. Multiplexer comprising one or more RF filters according to the preceding claim.

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