Electro-acoustic resonator device and method of manufacturing thereof

Technical Field

The invention relates to electro-acoustic devices and methods of manufacturing thereof. Specifically, the invention relates to an electro-acoustic resonator device having a

piezoelectric layer disposed between top and bottom

electrodes and a bragg mirror element disposed underneath.

Background

Electro-acoustic devices transform an electrical signal into an acoustic signal, and vice-versa. In an electro-acoustic resonator device, the electrical signal is supplied to the electrodes that sandwich a piezoelectric layer therebetween. An acoustical resonating wave is established between the electrodes that performs a filter function in the electrical domain of low loss and high selectivity. Electro-acoustic resonator devices are often used in filter designs of mobile electronic devices such as cell phones or smartphones. The interaction of electrical and acoustical operation allows a very compact size of the device so that many such devices may be used in mobile equipment to provide filters for a variety of RF services.

An embodiment of an electro-acoustic resonator device may be a solidly mounted bulk acoustic wave resonator (BAW-SMR) . In a BAW resonator device, the acoustical wave generated in the piezoelectric layer must be prevented from propagating too deep into the substrate, for example, by a mirror element, specifically a bragg mirror element disposed beneath the bottom electrode. The acoustic wave established in the resonator generates substantial heat that raises the

temperature of the top and bottom electrodes and the

piezoelectric layer therebetween. The increasing temperature of these elements, however, may affect the electrical

parameters and the reliability of the device. For example, a rising temperature of the electrodes may render the metal material of the electrodes viscous and may increase the ohmic losses in the electrodes so that their electro-acoustic behavior may change with rising temperature. Furthermore, a rising temperature of the piezoelectric layer may increase the electrical and acoustical losses in the piezoelectric layer. Also, local hot spots in the materials may lead to mechanical damage in such layers due to migration of

materials. As a consequence of the generation of heat in a BAW resonator during its operation, the electrical parameters such as the resonance frequency of the BAW resonator and the frequency bandwidth may be affected and may shift so that the specification of, for example, an RF filter in a mobile device may drift out of specification. This contradicts the requirement of sharp and defined filter skirts in nowadays and future mobile equipment. Therefore, there is a need to avoid a high temperature in the BAW device during the

electro-acoustical operation.

Some BAW devices are therefore supplied with compensation layers that compensate for the shift of electrical parameters due to increased temperature. Another proposal disclosed in FIG. 3 of DE 102014117238 A1 suggests to use a heat guide to transport the heat generated in the electro-acoustic area towards the substrate. The piezoelectric layer is expanded so that it covers the stack of the mirror layers completely and connects the electro-acoustic area with the substrate.

An object of the present disclosure is to provide an electro acoustic resonator device that has stable electrical

parameters during its operation and that can be easily manufactured. Another object of the present disclosure is to provide a method of manufacturing such an electro-acoustical resonator device.

Summary

According to the present disclosure, an electro-acoustic resonator device comprises a substrate; a bottom electrode, a top electrode and a piezoelectric layer, the piezoelectric layer disposed between the bottom and top electrodes;

a bragg mirror element disposed between the bottom electrode and the substrate; and a thermally conductive material comprising one of amorphous and polycrystalline aluminum nitride, wherein the thermally conductive material contacts the piezoelectric layer and the substrate.

According to an aspect of the present disclosure, a thermally conductive material which may comprise amorphous aluminum nitride contacts the piezoelectric layer and the substrate. Amorphous aluminum nitride has a thermal conductivity of about 180 W/Km so that a thermally conductive path is established between the area that generates the heat during the operation of the device and a heat sink such as the substrate. Instead of amorphous aluminum nitride,

polycrystalline aluminum nitride can be used for the

thermally conductive material. The thermal conductivity of polycrystalline aluminum nitride is higher than that of amorphous aluminum nitride. Whenever in this disclosure amorphous aluminum nitride is used, polycrystalline aluminum nitride may be used instead.

Aluminum nitride is a material that is often used in the manufacturing of electro-acoustic resonator devices so that the precursor materials to deposit aluminum nitride and the equipment for deposition and structuring of aluminum nitride are available in the manufacturing line. Aluminum nitride in columnar form may be used as the piezoelectric layer.

According to the present disclosure, it is useful to use amorphous or polycrystalline aluminum nitride as the

thermally conductive material outside of the piezoelectric layer because the amorphous or polycrystalline deposition of aluminum nitride is less complicated than the deposition of aluminum nitride having piezoelectric properties like

columnar aluminum nitride. Furthermore, the precursor

materials for the deposition of aluminum nitride are readily available in the manufacturing line. When the piezoelectric layer is made of columnar aluminum nitride and the thermally conductive path is made of amorphous/polycrystalline aluminum nitride, no change of material is necessary.

The microstructure of the columnar aluminum nitride is such that the columns in the layer itself may have crystalline form. On the other hand, polycrystalline aluminum nitride has a multitude of relatively small crystalline portions of different orientation so that the macroscopic polycrystalline aluminum material has substantially no piezoelectric

properties that could be used in an electro-acoustic

component . According to an aspect, the thermally conductive material being amorphous aluminum nitride is disposed between a bottom sidewall of the bragg mirror element and the substrate.

Accordingly, the acoustic mirror may be completely surrounded by thermally conductive material on its vertical and bottom sidewalls so that the thermal coupling to the substrate as a heat sink is very efficient. Furthermore, the coupling area between the amorphous aluminum nitride material and the substrate is enhanced, providing a low thermal coupling resistance between the aluminum nitride layer and the

substrate .

The BAW resonator device may be covered with a thin film package to provide efficient mechanical coverage at the top side. The thin film package encloses a cavity that is formed between the top electrode of the active region and a capping layer. The capping layer may comprise throughholes by which a sacrificial layer previously present between the top

electrode and the capping layer has been removed. A sealing layer is disposed on the capping layer to close the holes in the capping layer and to enhance the stability of the capping layer. According to an aspect of the present disclosure, the sealing layer may be further covered with the thermally conductive material of amorphous aluminium nitride to provide a thermally conductive path to heat sinks in the upper portion of the device, which may be, for example, ambient air around the upper aluminum nitride material or a carrier plate disposed on the upper aluminum nitride material or

electrically conductive bumps such as metal or solder bumps disposed in corresponding vias in the upper aluminum nitride layer. Such bumps provide electrical connection areas for the top and/or bottom electrodes at the upper surface of the device to external circuitry to which the resonator device is to be connected. On the other hand, this thermally conductive material of amorphous aluminum nitride serves as a

reinforcement layer on top of the device and enhances the mechanical stability of the device.

According to an aspect of the present disclosure, the

thermally conductive material of amorphous aluminum nitride may be further disposed between the piezoelectric layer and the lower end or surface of the capping layer and/or the lower end or surface of the sealing layer. Said lower ends of surface and sealing layers face in a direction to the

substrate of the device. The amorphous aluminum nitride material may contact the piezoelectric layer and the lower ends of the capping and/or sealing layers. According to the present disclosure, the amorphous aluminum nitride disposed between capping and sealing layers and the piezoelectric layer provides a good thermal path for the heat generated in the active area. In previous resonator devices, the lower ends of the capping and sealing layers contact either the piezoelectric layer or the top electrode or a top surface of the bragg mirror element so that thermal conductivity was limited .

According to a corresponding aspect of the present

disclosure, the thermally conductive material extends in the form of a continuous material which contacts surfaces of the top and bottom electrodes, surfaces of the bragg mirror element, and surfaces of the sealing and capping layers.

Therefore, the thermally conductive material achieves an integral encapsulation of the device and superior thermal conductivity to the heat sinks. The bragg mirror element may comprise a dielectric material and at least two or more layers of another material that has an acoustic impedance that is higher than the acoustic impedance of the dielectric material. The layers of the other material of higher acoustic impedance are spaced apart from each other so that the dielectric material is disposed between them. The bragg mirror element will be structured during the manufacturing process so that it has sidewalls that extend in a direction transversal to the substrate. The sidewalls may have vertical or substantially vertical orientation when compared to the surface of the substrate.

The sidewalls of the bragg mirror element and the sidewalls of the dielectric material have a common contact surface with the amorphous aluminum nitride material. Accordingly, the vertical and the bottom sidewalls of the bragg mirror element may be completely covered by amorphous aluminum nitride material so that any heat in the bragg mirror element is guided to the heat sink portions of the device. Furthermore, the active area has a wide thermal path to the heat sinks.

In another embodiment, the transversal sidewalls of the bragg mirror element may have an inclinded direction with regard to the surface of the substrate. A cross-sectional diameter of the bragg mirror may be larger close to the substrate than close to the bottom electrode. The contact surface between the insulation material of the bragg mirror element and the amorphous AIN is larger with non-vertical, inclinded

sidewalls when compared to vertical sidewalls so that the heat sinking effect may be increased with inclined sidwalls.

According to an aspect of the present disclosure, the other material of higher acoustic impedance may be a metal such as tungsten or an alloy of tungsten. Alternatively, the other material of higher acoustic impedance may be made of aluminum nitride, preferably amorphous aluminum nitride. In this case, the amorphous aluminum nitride material may extend from one sidewall of the bragg mirror structure to another opposing sidewall of the bragg mirror structure so that the amorphous aluminum nitride layers within the bragg mirror element are spaced apart by layers of the dielectric material.

According to an aspect of the present disclosure, the top electrode may be further covered by a layer or a layer stack that has the function of tuning and/or trimming and/or passivation on top of the top electrode. This layer of tuning, trimming and passivation may comprise or may also be made of amorphous aluminum nitride so that heat generated in the top electrode is uniformly distributed. This avoids hot spots in the top electrode.

A compact electro-acoustic resonator device according to the present disclosure comprises a first amorphous aluminum nitride layer disposed on the substrate, a stack of layers of the bragg mirror element disposed on the first aluminum nitride layer, wherein the bottom electrode is disposed on the bragg mirror element. A second amorphous aluminum nitride layer is disposed around sidewalls of the bragg mirror element. The piezoelectric layer is disposed on the bottom electrode, and the top electrode is disposed on the

piezoelectric layer. A third amorphous aluminum nitride layer is disposed around sidewalls of the top electrode, capping and sealing layers are disposed above the top electrode enclosing a cavity between the top electrode and the capping layer. A fourth amorphous aluminum nitride layer is disposed around and on sidewalls of the sealing layer to form a reinforcement layer. Such a compact design of the resonator device has a complete encapsulation of the device by

amorphous aluminum nitride so that the device has a small size and exhibits good heat dissipating properties.

The object of the present disclosure may be further achieved by a method of manufacturing an electro-acoustic resonator that comprises the steps of: providing a substrate;

depositing a bragg mirror layer stack on the substrate;

depositing an electrode layer on the bragg mirror layer stack to form a bottom electrode; structuring the bragg mirror layer stack and the bottom electrode; depositing aluminum nitride; performing a polishing step to expose a polished surface of the bottom electrode and a polished surface of the deposited aluminum nitride; depositing a piezoelectric material layer on the surface of the bottom electrode;

depositing another electrode layer on the piezoelectric layer to form a top electrode.

According to an aspect of the disclosed method of

manufacturing, aluminum nitride may be deposited after providing the substrate and before depositing the bragg mirror layer stack. Accordingly, the thermally conductive aluminum nitride material is disposed between the bottom sidewall of the bragg mirror element and the substrate, providing for a good thermal contact between the bragg mirror element and the substrate.

According to another aspect of the method, aluminum nitride is deposited on the top electrode. The top electrode and said deposited aluminum nitride are polished together to generate a uniform surface of the device for the deposition of a thin film package which includes a capping layer and a sealing layer. Aluminum nitride is further deposited to cover the previously deposited structures such as previously deposited aluminum nitride and the sealing layer to achieve a

reinforcement layer on top of the sealing layer to enhance the stability of the top portion of the device.

According to another aspect of the method, the thermally conductive aluminum nitride may be amorphous or

polycrystalline aluminum nitride, and the piezoelectric material may be columnar aluminum nitride so that both materials are different states of the same material. The use of the same material provides good controllability of the manufacturing process and low manufacturing costs.

According to another aspect of the method, a metal bump is provided in a via in the aluminum nitride of the

reinforcement layer so that an external electrical contact surface is provided at the bump's surface. A corresponding metal bump may be connected to the top and/or the bottom electrode .

Brief Description of the Drawings

Embodiments of the present invention are hereinbelow

described in more detail in connection with the figures of the drawings. Corresponding elements in different figures are denoted with the same reference numerals. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and operation of the various embodiments. In the drawings:

FIG. 1 shows a cross-section of an embodiment of an

electro-acoustic resonator device; FIG. 2 shows an embodiment with a metallic bump;

FIGs. 3A through 3F show several stages of a workpiece during the manufacturing of an electro-acoustic resonator device; and

FIG. 4 shows a flowchart of the manufacturing process of the device of FIG. 3.

Detailed Description of Embodiments

Both the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework to understand the nature and character of the claims.

The electro-acoustic resonator device of FIG. 1 may be a solidly-mounted resonator bulk acoustic wave device (BAW- SMR) . The device is mounted on a substrate 100 as its bottom layer. Suitable substrates can be made of various materials. In one embodiment, the substrate may be made of doped

crystalline silicon. The doping is such that the silicon is substantially not electrically conductive.

The BAW device includes an electro-acoustic resonator which is comprised of a bottom electrode 121 and a top electrode 122 and a piezoelectric layer 130 disposed therebetween. Top and bottom electrodes may each be made of a layer of metal. The metal layer may be made of tungsten (W) or a tungsten alloy. The piezoelectric layer 130 is made of a piezoelectric material. In this embodiment, the piezoelectric material is made of aluminum nitride (AIN) in a form that has

piezoelectric properties. Preferably, the piezoelectric layer is columnar AIN which exhibits good piezoelectric characteristics .

During operation of the device, a high-frequency electrical signal in the range of several GHz is supplied to the top and bottom electrodes. An acoustical oscillation is excited by the interaction between the electrodes and the piezoelectric layer. The oscillation has a defined frequency and a narrow, sharp spectrum. An electronic filter using the BAW device, therefore, has defined, relatively sharp skirts.

The acoustical oscillation takes mainly place in the

piezoelectric layer 130 and the electrodes 121, 122, however, expands also into the surrounding area so that the active area of the device needs to be shielded towards the substrate 100 by bragg mirror element 110. The bragg mirror element 110 as shown comprises a dielectric material 111 in which, in the present case, two layers 112, 113 are embedded which have an acoustical impedance higher than the acoustical impedance of the dielectric material 110. In one embodiment, the

dielectric material 110 may be silicon dioxide (SiCk) , and the material of higher acoustical impedance 112, 113 may be a metal such as tungsten (W) . With the bragg mirror 110 beneath the bottom electrode 121, the acoustical wave is reflected back to the active area and is thereby shielded from

substrate 100.

In order to fine-tune the characteristics of the device, a layer 125 on top of the top electrode 122 may be disposed for tuning, trimming and passivation. The layer 125 may be made of a composite layer comprising silicon oxide and silicon nitride (SiCk/SiN), which is suitably structured to achieve the required characteristics of the device. During operation of the BAW device, substantial losses are generated in the active area where the electrical and

acoustical oscillation takes place. The area of substantial loss during device operation is primarily the piezoelectric layer 130 and top and bottom metal electrodes 122, 121. Other loss will occur in the bragg mirror 110. The dissipation losses generate substantial heat in the piezoelectric layer 130 and the electrodes 122, 121.

In the shown embodiment, the heat generated in the active region of the BAW device is guided to heat sinking structures of the device through thermally conductive paths. The

thermally conductive paths are comprised of thermally

conductive material that is aluminum nitride (AIN) in

amorphous form, amorphous AIN. While the embodiments shown in the drawings use amorphous AIN, alternatively,

polycrystalline AIN can be used for the thermally conductive paths. The amorphous or polycrystalline AIN is substantially the same material as the columnar AIN in piezoelectric layer 130, however, it has a different structure, because it is amorphous/polycrystalline rather than columnar. Amorphous AIN is preferred for the thermally conductive material as it is easier to deposit than columnar AIN. Polycrystalline AIN may also be used for the thermally conductive paths. Using the same basic material AIN for the piezoelectric layer 130 and the thermally conductive layer 150 ensures that these

components of the device have substantially the same

mechanical characteristics so that the device is mechanically stable even during its operation while generating substantial heat. Manufacturing is cost effective because the same manufacturing equipment and the same chemical precursor materials can be used for the deposition of the piezoelectric layer and the thermally conductive material.

A thin layer of thermally conductive material 151 is

deposited on top of the upper surface of the substrate 100. The thin layer 151 of amorphous AIN is disposed between substrate 100 and the bottom side of bragg mirror element 110. Layer 151 has a large contact area to substrate 100 so that the thermal resistance of the surface between AIN layer 151 and substrate 100 is rather low.

Thermally conductive material AIN 150 is grown on thin layer

151 to surround the sidewalls 113 of the dielectric material 111 of bragg mirror element 110. The sidewall 113 shown as two sections of the sidewalls in the cross-sectional view in FIG. 1 has a direction which is transversal or inclined relative to the surface of substrate 100. The sidewalls 113 of bragg mirror element 110 are obtained by a structuring process such as a dry etch.

The thermally conductive material AIN 150 further surrounds the sidewalls of the piezoelectric layer 130 and the top and bottom electrodes 122, 121 that have also been obtained by a structuring process. The material 150 reaches a surface level

152 which is common with the upper surface of top electrode 122. The surface level 152 has been obtained by a polishing process that polishes top electrode 122 and aluminum nitride 150. The polishing process may be a chemical mechanical polishing (CMP) process. Surface 152 carries a thin film package 165, 166 which encloses a cavity 160 above top electrode 122 and tuning, trimming and passivation layer 125. Cavity 160 may be obtained by the deposition of a sacrificial layer (not shown in the drawings) that has been removed after the deposition of a capping layer 165. The capping layer 165 is provided with at least one opening 1651 through which the sacrificial layer was removed to obtain cavity 160. Cavity 160 is filled, for example, with air. The capping layer 165 is covered with a sealing layer 166 to enhance the mechanical stability and close the hole 1651. The lower surfaces 1652, 1661 of capping and sealing layers 165, 166 are in contact with and stand on surface 152 of the thermally conductive AIN material. This means that thermally conductive amorphous AIN material contacts the piezoelectric layer 130 and extend such that it reaches the lower surfaces 1652, 1661 of the capping and sealing layers. The lower surfaces 1652, 1661 of layers 165, 166 face towards the substrate 100. Finally, the sealing layer 166 is covered again with thermally conductive material of amorphous AIN 155. Material 155 has also a reinforcement function which enhances the mechanical stiffness and

stability of the BAW device. The outer surfaces of the AIN material which comprise the top surface of reinforcement layer 155 and the sidewall surfaces of the AIN material 150, 155, 151 may face to ambient air so that these surfaces have the function of a heat sink. Aluminum nitride has relatively good thermal conductivity in the range of about 180 W/Km so that the guidance of heat out of the acoustically active areas into the bulk material of AIN 150, 155, 151 to the corresponding outer surfaces enables a good dissipation of a high amount of heat.

The top and bottom electrodes 121, 122 are preferably made of a metal or a composition of different metals. For example, these electrodes may be made of tungsten or of aluminum or a sandwich of at least one of tungsten and aluminum. Other materials useful for the bottom and top electrodes may be copper, molybdenum, ruthenium or platinum, or a sandwich of one or more of these metals.

The thickness of the piezoelectric layer is in the range of about 1 pm. For example, the thickness of the piezoelectric AIN layer 130 may be in the range of 300 nm to 2500 nm, more preferably in the range of 700 nm to 2000 nm. The overall thickness of the device reaching from the lower surface of the substrate to the upper outer surface of the reinforcement layer 155 may be in the range of about 10 pm. Even with the thermally conductive AIN material in place, the device has still rather small dimensions.

Substantially all elements of the BAW resonator are

encapsulated by amorphous AIN material 150, 155 so that the generated operational heat can be effectively transported to several heat sinks to ensure the desired electrical

specifications. The device is relatively easy to manufacture, because the use of amorphous AIN can be well controlled. The material 150, 155 is a continuous material that integrally and completely surrounds the device. There is no substantial material change from the piezoelectric layer 130 to the corresponding heat sinks such as substrate 100 and the outer surfaces of the AIN material.

FIG. 2 shows a another embodiment in which the BAW resonator device of FIG. 1 is further equipped with an electrical input/output terminal for the top electrode 122. Although FIG. 2 shows only the connection to the top electrode 122, another connection to bottom electrode 121 can be provided in a similar way. Top electrode 122 in FIG. 2 is provided with a metal strip 210 which extends on substantially the same level beyond the sealing and capping layers 165, 166. Metal strip 210 extends beyond the lower surfaces of capping and sealing layers 165, 166 within the amorphous AIN material 150 as shown on the left-hand side of the device depicted in FIG. 2. A via hole

201 is etched into the upper portion 155 of the AIN material. The via 201 is filled with a metallic material 202 which forms a bump that protrudes above the top surface of the reinforcement layer 155. The outer surface 203 of the bump

202 is a connection terminal for an electrical signal to be supplied or outputted to/from the top electrode 122. The bump material 202 may be a metallic solder material which is electrically and thermally highly conductive so that bump 202 serves also as a heat sink for the heat generated in the active region of the device. The amorphous AIN material 155 is electrically non-conductive so that metallic bump 202 is electrically isolated from the rest of the device, except for the wiring strip 210 and the top electrode 122. The long contact surface of bump 202 along the length of via 201 allows for an easy transfer of the heat guided in the AIN material 150, 155 to the bump 202. Bump 202 has a combined function of a thermal heat sink and an electrical connection from the top electrode 122 to the external of the device at the surface 203 of the bump 202.

As a variation of the BAW resonator devices of FIGs. 1 and 2, the amorphous aluminum nitride of the thermally conductive materials 150, 155 may be used in additional places. For example, the tuning, trimming and passivation layer 125 may comprise amorphous AIN. Accordingly, the top surface of top electrode 122 has a thermally conductive cover 125 of

amorphous AIN so that potential hot spots in the top electrode 122 are avoided. The risk of damaging the top electrode by potential hot spots is therefore substantially reduced. On the other hand, the heat generated in the top electrode is further removed from the top electrode through the thermally conductive tuning, trimming and passivation layer 125 being AIN in that this heat will be dissipated into the air present in the cavity 160.

As another variation, the dielectric material 111 of the bragg mirror element 110, which may be made of SiCk in one embodiment, may be replaced by AIN, preferably amorphous AIN, according to the variation. In this case, the material 111 is also amorphous AIN as is the surrounding material 150. In this case, the AIN material 111 of the bragg mirror element 110 embeds the layers 112, 113 of a metal such as tungsten or aluminum or an alloy thereof. Otherwise stated, the metal material of higher acoustic impedance is completely enclosed in material of amorphous AIN.

As another variation, the piezoelectric layer 130 can also be made of aluminum scandium nitride or otherwise doped aluminum nitride which, in each case, exhibit piezoelectric

properties .

Embodiments of a method of manufacturing an electro-acoustic resonator device are described hereinbelow in connection with FIGs. 3A to 3F and 4. While FIG. 4 shows a flowchart of the sequence of method steps, FIGs. 3A to 3F show corresponding states of the treatment of the workpiece. As a starting point of the manufacturing process according to the embodiment, a substrate 100 (FIG. 3A) is provided in accordance with step 401 (FIG. 4) . A relatively thin layer of amorphous aluminum nitride 151 is deposited on the substrate 100 (step 402, FIG. 4) . Subsequently, the bragg mirror layer stack 110 is

deposited, including the dielectric material 111 in the embedded tungsten layers 112, 113. Thereafter, the metal layer of the bottom electrode 121 is deposited. By means of lithography and dry etching, the bragg mirror layer stack and the bottom electrode layer are structured (step 403) to achieve substantially vertical sidewalls as shown in FIG. 3B. As another embodiment (not shown) , the dry etching parameters can be set such that the sidewalls of the bragg mirror stack achieve an inclined orientation relative to the surface of the substrate, rather than vertical. A diameter of the bragg mirror stack more distant from the surface of the substrate is smaller than closer to the substrate.

Then, amorphous aluminum nitride is deposited to fill all valleys and trenches present in the current structure. The top surface of the workpiece is now polished, for example, with a chemical mechanical polishing (CMP) process. The CMP operation generates a uniform top surface 1211 of the top electrode 121 together with a polished top surface 1501 of the AIN layer 150 (step 404) . The resulting workpiece is shown in FIG. 3C.

As the next step, a piezoelectric layer is deposited on the uniform surfaces 1211 and 1501 of the bottom electrode 121 and the AIN 150. In the embodiment, the piezoelectric

material is columnar AIN. In order to achieve the columnar structure, it is useful to deposit a suitable seed layer on the polished surface 1211 (step 405) . Suitable alternative materials for the piezoelectric layer may be deposited instead of piezoelectric AIN, such as aluminum scandium nitride or otherwise doped aluminum nitride. Then, a metal layer for the top electrode 122 is deposited. The top electrode layer and the piezoelectric layer are structured to obtain a width that is substantially the same as the width of the bottom electrode 121 (step 406) . It is to be noted that, alternatively, the deposited piezoelectric layer may be structured first to obtain already the proper width of the piezoelectric material 130 so as to deposit the metal layer for the top electrode thereafter and structure that metal layer to obtain the proper width of the top electrode 122.

The resulting structure is shown in FIG. 3D

Then, aluminum nitride 154 is deposited to fill all valleys and trenches present in the workpiece. A CMP process is performed on the top surface of the workpiece to obtain a flattened uniform top surface as shown in FIG. 3E, having a polished surface 1221 of top electrode 121 and 1541 of deposited aluminum nitride 154 (step 407) .

On the workpiece shown in FIG. 3E, a layer for the tuning, trimming and passivation function is deposited and structured to have a width substantially the same as the top electrode 122 (step 408) . The layer 125 may be a layer stack comprising Si0 ₂ /SiN or, alternatively, amorphous AIN. Then, a thin film top package is manufactured, including capping layer 165 and sealing layer 166. The capping layer 165 covers a cavity 160 that has been achieved by depositing a sacrificial layer, structuring the sacrificial layer and capping it with the capping layer 165. The capping layer 165 is provided with one or more holes through which the sacrificial oxide is removed to obtain the cavity. The resulting structure is shown in FIG. 3F (step 409) .

Finally, the amorphous AIN is deposited on top of the

workpiece shown in FIG. 3F to achieve the top reinforcement layer 155. The top surface may be polished by CMP to obtain a substantially flat top surface. The resulting device is depicted in FIG. 1.

As an option, a solder bump can be manufactured into the top reinforcement layer 155 as described in connection with FIG.

2 to achieve the structure shown in FIG. 2.

The above given disclosure describes an electro-acoustic resonator device such as a SMR-BAW resonator device and a corresponding method of manufacturing, wherein the device is enclosed in thermally conductive material such as amorphous AIN which provides a thermal path for the operational heat generated in the acoustically active area to the heat sinks such as ambient air, solder bumps and silicon substrate. With the sinking of heat, the electrical characteristics of the BAW device are maintained even if high power loss is

generated in the acoustically active region.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosure as laid down in the appended claims. Since modifications, combinations, sub combinations and variations of the disclosed embodiments incorporating the spirit and substance of the disclosure may occur to persons skilled in the art, the disclosure should be construed to include everything within the scope of the appended claims.