CN113615082A - SAW device and method of manufacturing the same - Google Patents

Abstract

The present invention relates to the field of Surface Acoustic Wave (SAW) devices. In particular, the SAW device of the present invention suppresses parasitic modes, in particular lateral modes. The SAW device of the present invention includes: a piezoelectric layer (101) for propagating SAW; at least one electrode (102) disposed on the piezoelectric layer and configured to couple an electrical signal to a SAW propagating in the piezoelectric layer (101). The SAW device further comprises at least one busbar (103) for routing the electrical signal to the electrode (102). The SAW device further comprises a decoupling layer (104), the decoupling layer (104) separating the piezoelectric layer (101) and the electrode (102) from the bus bar (103). The decoupling layer (104) has acoustic impedances different from the electrodes (102) and the bus bars (103), respectively.

Description

SAW device and method of manufacturing the same

Technical Field

The present invention relates to the field of Surface Acoustic Wave (SAW) device technology. The present invention specifically proposes a SAW device with a new design that suppresses lateral parasitic modes. Furthermore, the present invention relates to a method for manufacturing the SAW device.

Background

Acoustic wave devices are key components used in modern electronic circuits. Since such acoustic wave devices require high frequency selectivity while maintaining low electronic insertion loss, there is a need to couple high quality factor mechanical resonators in a filter topology.

SAW devices couple a time-varying electrical signal to a mechanical wave traveling on the surface of a piezoelectric material (layer). Conventional SAW resonators are produced on a piezoelectric layer with alternating metal interdigital transducer (IDT) electrodes on the surface of the piezoelectric layer.

When the desired vibration mode is triggered by the shock wave, the SAW resonator produces an in-band parasitic vibration mode. These are caused by the placement of the IDT electrodes above the piezoelectric layer, the geometry of the metal bus bars that route the electrical signals and confine the resonators, and the double-sided acoustic confinement of the Bragg mirrors. All of these reasons contribute to the growth of spurious modes in the frequency band of interest. The finite size of the lateral direction of wave propagation also contributes to the development of parasitic electroacoustic modes within the resonator.

Due to modal coupling, such parasitic modes having frequencies close to the desired operating frequency may affect the achievable mechanical quality factor Q. When SAW resonators are arranged in a filter configuration (e.g., ladder structure, lattice, dual-mode resonator, etc.), the presence of in-band parasitic modes can also affect the in-band ripple metric of these electrical filter circuits. Up to now, unwanted spurious modes have been addressed by:

IDT electrode apodization: this may reduce the excitation efficiency of the higher-order mode. Further, the lower order mode shapes can be matched by excitation. However, scattering at discontinuities can significantly increase losses.

Virtual electrode weighting: with the dummy electrodes, the parasitic mode can penetrate and leak in the bus bar region. However, the reflection at the gap creates strong wave confinement in the gap region, thereby guiding the vibration and again causing parasitic modes to occur.

Piston mode design: for example, devices on quartz (or highly coupled substrates), incorporate apodization of dummy electrodes to maintain a flat mode shape. The shape of the excitation remains constant along the aperture and the mode shape can be matched to the shape of the excitation. The electromechanical coupling to these parasitic modes is then greatly reduced. However, this approach makes the resonator design more complex.

Disclosure of Invention

In view of the above-described shortcomings, it is an object of embodiments of the present invention to improve upon conventional SAW devices and methods for addressing parasitic modes.

It is an object to provide a SAW device that suppresses lateral parasitic modes. It is therefore an object of the present invention to reduce passband ripple and increase the achievable out-of-band rejection. Spurious modes should be suppressed without requiring more complex SAW resonator/device designs. In addition, SAW devices should have low losses.

A first aspect of the present invention provides a SAW device comprising: a piezoelectric layer for propagating the SAW; at least one electrode disposed on the piezoelectric layer and configured to couple an electrical signal to a SAW propagating in the piezoelectric layer; at least one bus for routing the electrical signals to the electrodes; a decoupling layer separating the piezoelectric layer and the electrodes from the bus bars, wherein the decoupling layer has acoustic impedances different from the electrodes and the bus bars, respectively.

In particular, the decoupling layer may comprise a piezoelectric material, a dielectric material or any semiconductor material.

The decoupling layer decouples the bus bar from the SAW resonator (piezoelectric layer and one or more electrodes). Accordingly, parasitic modes can be suppressed in the SAW device of the first aspect, and an improved low-loss SAW device is provided.

In one implementation of the first aspect, the at least one bus bar is at least partially disposed above the piezoelectric layer and the electrode, and the decoupling layer vertically separates the piezoelectric layer and the electrode from the bus bar.

The vertical decoupling effectively suppresses the lateral parasitic modes.

In one implementation form of the first aspect, the SAW device further comprises: a Vertical Interconnect Access (VIA) formed through the decoupling layer for electrically connecting the bus bar to the electrode.

The VIA may control one or more SAW resonators. Multiple VIAs may be provided. Multiple VIAs may also be used to form a periodic arrangement in the decoupling layer, for example to form a phononic crystal.

In one implementation form of the first aspect, the decoupling layer is a patterned layer and/or a passivation layer.

In particular, if the SAW resonator includes an optional passivation layer (e.g., above the IDT arrangement), it is not used to reduce parasitic modes in this case.

In one implementation of the first aspect, one or more material elements are embedded in the decoupling layer, the embedded elements having acoustic impedance and/or having different electrical and/or optical properties than the surrounding material of the decoupling layer.

In one implementation form of the first aspect, a plurality of the material elements is embedded in the decoupling layer in a periodic arrangement.

In one implementation of the first aspect, the spatial periodicity of the periodic arrangement of embedded elements is approximately the wavelength of the SAW propagating in the decoupling layer at the operating frequency of the SAW device.

The embedded elements may be identical or may include one or more of the above-described VIAs that contact the bus bars to one or more of the electrodes.

In one implementation of the first aspect, a plurality of embedded elements form a phononic crystal in the decoupling layer.

In particular, the dimensions of the members of the plurality of embedded elements are selected according to bloch's theorem, the operating frequency of the resonator, and the operating bandwidth of the filter.

Thus, an acoustic bandgap can be formed, supporting decoupling and suppression of parasitic modes. In addition, the size of the phononic crystal may be such that the acoustic energy is partially permeated within the frame structure to produce "piston" vibration modes in the core resonator. This greatly reduces the triggering of spurious modes.

In one implementation of the first aspect, the phononic crystal in the decoupling layer has a bandgap centered around an operating frequency of the SAW device.

Parasitic modes are therefore particularly suppressed close to the desired operating frequency and therefore have no influence on the achievable mechanical quality factor Q due to modal coupling.

In one implementation of the first aspect, the length of the phononic crystal (which may also be referred to as a phononic crystal framework structure) at the operating frequency of the acoustic wave that it is capable of supporting is in the range of a quarter wavelength.

In one implementation form of the first aspect, a sign of a temperature coefficient of the decoupling layer is opposite to a sign of a temperature coefficient of the piezoelectric layer.

The precise geometry and implementation of the phononic crystal (e.g., described below with reference to the figures) is merely illustrative and an asymmetric periodic arrangement may be implemented in different parts of a SAW device.

Ideally, the temperature coefficients of the decoupling layer and the piezoelectric layer have the same absolute value and opposite signs. Thus, temperature compensation is achieved.

In one implementation of the first aspect, the decoupling layer comprises a dielectric material.

In one implementation form of the first aspect, the SAW device further comprises: a plurality of SAW resonators, each SAW resonator formed from at least one IDT electrode and at least a portion of the piezoelectric layer.

In one implementation form of the first aspect, the SAW device further comprises: one or more Bragg reflectors disposed adjacent to the SAW resonator, wherein a plurality of embedded elements in the decoupling layer are used to direct acoustic energy from the SAW resonator to the one or more Bragg reflectors.

This implementation prevents diffraction scattering in the lateral direction.

In one implementation form of the first aspect, the decoupling layer is configured to acoustically couple at least two SAW resonators, wherein the coupling direction is perpendicular to the SAW propagation direction.

The strength of coupling between SAW resonators can be tuned by changing the geometry and structure of the decoupling layer. The SAW propagation direction (in an implementation, the longitudinal direction) refers to the primary propagation direction.

In one implementation of the first aspect, the distance between adjacent SAW resonators is selected to be between a quarter wavelength and a half wavelength of the induced acoustic wave at the operating frequency of the resonator.

In one implementation of the first aspect, the piezoelectric layer (which may also be referred to as a substrate) includes at least one of a piezoelectric material lithium tantalate oxide (LiTaO3) or lithium niobate (LiNbO 3).

In one implementation of the first aspect, the at least one IDT electrode includes a metal material (e.g., at least one of copper (Cu), tungsten (W), silver (Ag), platinum (Pt), titanium (Ti), or aluminum (Al)).

In an implementation of the first aspect, the decoupling layer may comprise a dielectric material (e.g. at least one of SiO2, SiCOH).

In one implementation of the first aspect, the at least one electrode is an interdigital transducer (IDT) electrode.

A second aspect of the present invention provides a method for manufacturing a SAW device, the method comprising: providing a piezoelectric layer for propagating SAW; forming at least one electrode on the piezoelectric layer, wherein the electrode is configured to couple an electrical signal to a SAW propagating in the piezoelectric layer; forming a decoupling layer; forming a bus bar for routing the electrical signal to the electrode; wherein the decoupling layer separates the piezoelectric layer and the electrode from the bus bar, wherein the decoupling layer has acoustic impedances different from the electrode and the bus bar, respectively.

The method of the second aspect may further be implemented according to an implementation of the device of the first aspect. Accordingly, the method of the second aspect and its implementations achieve all the effects and advantages of the first aspect and its respective implementations.

It should be noted that all devices, elements, units and modules described in the present application may be implemented in software or hardware elements or any type of combination thereof. All steps performed by the various entities described in the present application, as well as the functions described to be performed by the various entities, are intended to indicate that the respective entities are adapted or used to perform the respective steps and functions. Although in the following description of specific embodiments specific functions or steps performed by an external entity are not reflected in the description of specific elements of the entity performing the specific steps or functions, it should be clear to a skilled person that these methods and functions may be implemented in corresponding hardware elements or software elements or any type of combination thereof.

Drawings

The following description of specific embodiments, taken in conjunction with the accompanying drawings, set forth the above-described aspects of the invention and the manner of attaining them.

FIG. 1 illustrates a SAW device provided in accordance with embodiments of the present invention;

fig. 2 illustrates a SAW device provided by an embodiment of the present invention in (a) a top view and (b) a side view;

FIG. 3 illustrates steps provided by embodiments of the present invention for fabricating a SAW device;

FIG. 4 illustrates steps provided by embodiments of the present invention for fabricating a SAW device;

FIG. 5 illustrates a SAW device provided in accordance with embodiments of the present invention;

FIG. 6 illustrates components of a SAW device provided in accordance with embodiments of the present invention;

FIG. 7 illustrates a SAW device provided in accordance with embodiments of the present invention;

fig. 8 illustrates a method for fabricating a SAW device according to an embodiment of the present invention.

Detailed Description

In particular, embodiments of the present invention propose to form a decoupling layer (also referred to as a "resonator frame") around the core electrode by using a specific deposition material. The frame decouples the SAW resonator electrodes from the metal wiring and bus bars of the SAW device. The frame may be patterned (e.g., apodized geometry may be formed). In addition, the frame may embed a region of material to form a vocal cord gap near the operating frequency of the SAW device. The frame frequency Temperature Coefficient (TCF) may be selected to reduce the overall TCF of the SAW device. Furthermore, two different SAW resonators can be mechanically coupled in a lateral direction by the frame, wherein the acoustic coupling strength can be optimized by modifying the geometry of the frame. The following aspects and implementations describe embodiments of the invention.

Fig. 1 illustrates a cross-section of a SAW device 100 provided by an embodiment of the present invention. SAW device 100 includes a piezoelectric layer 101 for propagating SAW and includes at least one electrode 102 disposed on piezoelectric layer 101, wherein electrode 102 is for coupling an electrical signal to SAW propagating in piezoelectric layer 101. Electrode 102 and piezoelectric layer 101 or at least a portion of piezoelectric layer 101 can form a SAW resonator of SAW device 100. The plurality of electrodes 102 and piezoelectric layer 101 may form a plurality of SAW resonators.

Further, the SAW device 100 of fig. 1 includes at least one bus bar 103, the bus bar 103 for routing electrical signals to the electrodes 102. Further, the SAW device 100 includes a decoupling layer 104, which decoupling layer 104 separates the piezoelectric layer 101 and the electrode 102 from the bus bar 103. The decoupling layer 104 has different acoustic impedances than the electrode 102 and the bus bar 103, respectively.

In the SAW device 100, the actuation electrode 102, which may be an IDT electrode, and the routing bus bar 103 are decoupled by a decoupling layer 104. The decoupling layer 104 may in particular be a passivation layer and may be referred to as "resonator frame". The decoupling layer 104 may also be engineered/patterned, for example, to modify the acoustic environment of one or more electrodes 102(IDT structure). Thus, additional "optimization" of SAW device 100 may be made, particularly as compared to conventional 1D metal designs.

For example, the decoupling layer 104 (which preferably has a different inherent surface wave reflectivity than the metal electrode 102) can be patterned to obtain a particular band gap shape/acoustic mirror, e.g., except at the center resonant frequency. The decoupling layer 104 can also be designed to specifically leak energy in lateral modes.

In terms of process complexity, good quality of the electrode metallization is maintained. The patterned decoupling layer 104 is less dependent on process variations (i.e., it does not require as precise lithography as required by conventional methods). Decoupling layer 104 also has the advantage of modifying the temperature characteristics of SAW device 100, for example, in the case of TC-SAW designs.

Fig. 2 shows a SAW device 100 provided by an embodiment of the present invention, and the SAW device 100 is based on the SAW device 100 shown in fig. 1. Like elements are labeled with like reference numerals and the function is the same. The SAW device 100 of fig. 2 is particularly shown in a top view in (a) and a side view in longitudinal section in (b).

SAW device 100 of fig. 2 also includes one or more VIA 200, which VIA 200 are formed through decoupling layer 104, e.g., from metal. The one or more VIA's are used to electrically connect the bus bar 103 to the one or more electrodes 102 so that electrical signals can be routed from the bus bar 103 to the one or more electrodes 102. Fig. 2 also shows that SAW device 100 may be disposed on a bulk wafer or substrate 201.

As further illustrated in fig. 2, one or more electrodes 102 may be IDT electrodes formed by/in first metal layer M1, M1. The decoupling layer 104 may be a passivation layer. The bus bar 103 may be formed of/in the second metal layer M2 from/to the second metal layer M2. The passivation layer 104 serves to reduce the generation of parasitic modes. This is achieved by decoupling the electrode(s) 102/SAW resonator(s) from the boundary of the SAW device 100 (where one or more busbars 103 are typically located). The passivation layer 104 with one or more VIA 200 may be formed by depositing a particular material (e.g., a dielectric material).

Fig. 3 and 4 show how the SAW device 100 of fig. 2 is manufactured. Fig. 3 and 4 thus show the SAW device 100 in (a) a side view, (b) a front view (at the boundary where the bus bar 103 is located), and (c) a rear view (where the SAW resonator is located). Fig. 8 also illustrates a general method 800 of manufacturing a SAW device 100. Steps I/IV to IV/IV will be described below.

The general manufacturing method 800 shown in FIG. 8 includes: step 801, providing a piezoelectric layer, wherein the piezoelectric layer is used for transmitting SAW; forming at least one electrode 102 on the piezoelectric layer 101, wherein the electrode 102 is used for coupling an electrical signal to a SAW propagating in the piezoelectric layer 101; step 803, forming a decoupling layer 104; step 804, forming a bus 103, the bus 103 for routing electrical signals to the electrode 102; wherein a decoupling layer 104 separates the piezoelectric layer 101 and the electrode 102 from the bus bar 103, wherein the decoupling layer 104 has an acoustic impedance different from the electrode 102 and the bus bar 103, respectively.

In fig. 3, in step I/IV, a piezoelectric layer 101 is provided on a wafer 201, and a plurality of electrodes 102 are formed on the piezoelectric layer. This step I/IV therefore involves steps 801 and 802 of fig. 8. Then, in step II/IV, a decoupling layer 104 is deposited on the piezoelectric layer 101 and the electrode 102, respectively, and the VIA 200 is formed. Thus, this step II/IV involves step 803 of FIG. 8.

In fig. 4, in step III/IV, the decoupling layer 104 is removed over portions of the electrodes where the core SAW resonators are formed. In step IV/IV, a bus bar 103 is formed on the remaining decoupling layer 104. These steps therefore involve step 804 of fig. 8.

Fig. 5 shows a SAW device 100 provided by an embodiment of the present invention, and the SAW device 100 is based on the SAW device 100 shown in fig. 1 and 2. Like elements are labeled with like reference numerals and the function is the same. The SAW device 100 of fig. 5 is shown in a side view.

The SAW device 100 of fig. 5 illustrates that the decoupling layer 104 ("resonator frame") can be patterned by embedding one or more material elements 500 within the decoupling layer 104. The embedded element 500 may have acoustic impedance and/or may have different electrical and/or optical properties than the surrounding material of the decoupling layer 104. A plurality of material elements 500 may be embedded in the decoupling layer 104 in a periodic arrangement. In particular, the decoupling layer 104 may be provided with periodic replicas of a metal structure (e.g. VIA 200) (or with any other material deposition in the decoupling layer 104 with acoustic impedance lower or higher than that of the decoupling layer 104). The islands of material embedded in decoupling layer 104 may have a unit length, e.g., on the order of the acoustic wavelength/fraction thereof at the frequency of SAW device 100. Thus, a plurality of embedded elements/islands 500 may form a phononic crystal in the decoupling layer 104.

Fig. 6 shows a part of a SAW device 100 provided by an embodiment of the present invention, the SAW device 100 being based on the SAW device 100 shown in fig. 1 and 5. Like elements are labeled with like reference numerals and the function is the same. The SAW device 100 of fig. 5 is shown in a top view.

In the SAW device 100 of fig. 6, an external bragg reflector 600 is used to confine acoustic energy within one or more core SAW resonators. In this case, one or more metal busbars 103 may be removed and the decoupling layer 104 may be patterned into a two-dimensional periodic replica structure 500 (e.g., using metal VIA 200 or other material) to effectively direct acoustic vibrations in the longitudinal direction and prevent diffraction scattering in the lateral direction.

Fig. 7 shows a SAW device 100 provided by an embodiment of the present invention, and the SAW device 100 is based on the SAW device 100 shown in fig. 1 and 6. Like elements are labeled with like reference numerals and the function is the same. The SAW device 100 of fig. 7 is shown in a top view.

The SAW device 100 of fig. 7 has in particular a layered design of mechanically coupled SAW resonators (i.e. the electrode 102 and the piezoelectric layer 101 forming part of the SAW resonator) which are located in close proximity to each other, e.g. for filter applications. In this case, the decoupling layer 104 (which may be patterned and optimized as described above) may act as a lateral acoustic coupler between adjacent SAW resonators. Varying the geometry and structure of decoupling layer 104 can adjust the strength of acoustic coupling between adjacent SAW resonators.

In the above-described embodiments of SAW device 100, the substrate (bulk wafer 201) may be a substrate comprising silicon, glass, ceramic, or the like. The piezoelectric layer 101 may be a thin film piezoelectric layer comprising one of lithium niobate, lithium tantalate, or the like. One or more of the electrodes 102 may be a low resistivity layer comprising a metal and/or metal alloy (e.g., copper, titanium, etc.) layer, or may be a highly doped silicon layer.

In the above-described embodiments of SAW device 100, decoupling layer 104 may comprise or may be made of a dielectric material. For example, the dielectric material of the decoupling layer 104 may include: an oxide or nitride of SiCOH, phosphosilicate glass, aluminum, silicon, germanium, gallium, indium, tin, antimony, tellurium, bismuth, titanium, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, palladium, cadmium, helium, tantalum, or tungsten, or any combination thereof.

In the above-described embodiments of SAW device 100, metallization layers M1 and M2 (for one or more bus bars 103 and/or one or more electrodes 102, respectively) may include: copper, aluminum, tungsten, titanium, and the like. The BEOL dielectric layer may include: copper Capping Layer (CCL), Etch Stop Layer (ESL), Diffusion Barrier (DB), anti-reflection coating (ARC), and low-k dielectrics such as SiCOH, SiOCN, SiCN, SiOC, SiN. Materials that may be used in CMOS BEOL layers may include: copper metallization, tungsten, low-k dielectrics, silicon dioxide, copper capping layers, etch stop layers, anti-reflective coatings, and the like.

In the above-described embodiments of SAW device 100, the substrate may comprise silicon, SOI technology substrates, gallium arsenide, gallium phosphide, gallium nitride and/or indium phosphide or other example substrates, alloy semiconductors including GaAsP, AlInAs, GaInAs, GaInP, or GaInAsP, or combinations thereof.

The invention has been described in connection with various embodiments and implementations as examples. However, other variations will become apparent to those skilled in the art and may be made in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims as well as in the description, the word "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims (16)

1. A Surface Acoustic Wave (SAW) device (100), comprising:

a piezoelectric layer (101) for propagating SAW;

at least one electrode (102) disposed on the piezoelectric layer (101) and configured to couple an electrical signal to a SAW propagating in the piezoelectric layer (101);

at least one bus (103) for routing the electrical signals to the electrodes (102);

a decoupling layer (104) separating the piezoelectric layer (101) and the electrode (102) from the bus bar (103),

wherein the decoupling layer (104) has acoustic impedances different from the electrodes (102) and the bus bars (103), respectively.

2. A SAW device (100) as claimed in claim 1, wherein:

the at least one busbar (103) is arranged at least partially above the piezoelectric layer (101) and the electrode (102),

the decoupling layer (104) vertically separates the piezoelectric layer (101) and the electrode (102) from the bus bar (103).

3. A SAW device (100) as claimed in claim 1 or 2, comprising:

a Vertical Interconnect Access (VIA) (200) formed through the decoupling layer (104) for electrically connecting the bus bar (103) to the electrode (102).

4. A SAW device (100) as claimed in any one of claims 1 to 3, wherein:

the decoupling layer (104) is a patterned layer and/or a passivation layer.

5. A SAW device (100) according to any of claims 1-4, wherein:

one or more material elements (500) are embedded in the decoupling layer (104), the embedded elements (500) having an acoustic impedance and/or having different electrical and/or optical properties than the surrounding material of the decoupling layer (104).

6. A SAW device (100) according to claim 5, wherein:

a plurality of the material elements (500) are embedded in the decoupling layer (104) in a periodic arrangement.

7. A SAW device (100) according to claim 6, wherein:

the spatial periodicity of the periodic arrangement of the embedded elements (500) is approximately the wavelength of the SAW propagating in the decoupling layer (104) at the operating frequency of the SAW device (100).

8. A SAW device (100) according to any of claims 5 to 7, wherein:

a plurality of embedded elements (500) form phononic crystals in the decoupling layer (104).

9. A SAW device (100) as claimed in claim 8, wherein:

the phononic crystal in the decoupling layer has a bandgap centered at an operating frequency of the SAW device (100).

10. A SAW device (100) as claimed in any one of claims 1 to 9, wherein:

the sign of the temperature coefficient of the decoupling layer (104) is opposite to the sign of the temperature coefficient of the piezoelectric layer (101).

11. A SAW device (100) as claimed in any one of claims 1 to 10, wherein:

the decoupling layer (104) comprises a dielectric material.

12. A SAW device (100) as claimed in any one of claims 1 to 11, comprising:

a plurality of SAW resonators, each SAW resonator being formed from at least one electrode (102) and at least a portion of the piezoelectric layer (101).

13. A SAW device (100) as claimed in claim 12, comprising:

one or more Bragg reflectors (600) disposed adjacent to the SAW resonator,

wherein a plurality of embedded elements (500) in the decoupling layer (104) are used to direct acoustic energy from the SAW resonator to the one or more Bragg reflectors (600).

14. A SAW device (100) as claimed in claim 12 or 13, wherein:

the decoupling layer (104) is used for acoustically coupling at least two SAW resonators, wherein the coupling direction is perpendicular to the SAW propagation direction.

15. A SAW device (100) as claimed in any one of the preceding claims, wherein the at least one electrode (102) is an interdigital transducer (IDT) electrode.

16. A method (800) for fabricating a Surface Acoustic Wave (SAW) device (100), the method (800) comprising:

providing (801) a piezoelectric layer (101), the piezoelectric layer (101) for propagating SAW;

forming (802) at least one electrode (102) on the piezoelectric layer (101), wherein the electrode (102) is for coupling an electrical signal to a SAW propagating in the piezoelectric layer (101);

forming (803) a decoupling layer (104);

forming (804) a bus bar (103), the bus bar (103) for routing the electrical signals to the electrodes (102);

wherein the decoupling layer (104) separates the piezoelectric layer (101) and the electrode (102) from the bus bar (103),

wherein the decoupling layer (104) has acoustic impedances different from the electrodes (102) and the bus bars (103), respectively.

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