CN111434036A

CN111434036A - Electroacoustic resonator device and method for manufacturing the same

Info

Publication number: CN111434036A
Application number: CN201880078689.6A
Authority: CN
Inventors: M·希克; B·巴德
Original assignee: RF360 Europe GmbH
Current assignee: RF360 Singapore Pte Ltd
Priority date: 2017-12-07
Filing date: 2018-12-03
Publication date: 2020-07-17
Also published as: WO2019110504A1; EP3721556A1; DE102017129160B3

Abstract

The electroacoustic resonator device comprises a substrate (100), bottom and top electrodes (121, 122) and a piezoelectric layer (130) arranged therebetween. A Bragg mirror element (110) is disposed between the bottom electrode and the substrate. The thermally conductive material comprises amorphous or polycrystalline aluminum nitride (150, 151, 155), the thermally conductive material being in contact with the piezoelectric layer and the substrate to form a thermally conductive path to dissipate heat generated in an acoustically active region of the resonator device during operation of the resonator device.

Description

Electroacoustic resonator device and method for manufacturing the same

Technical Field

The present invention relates to an electroacoustic device and a method for manufacturing the same. In particular, the invention relates to an electro-acoustic resonator device having a piezoelectric layer arranged between a top electrode and a bottom electrode and a bragg mirror element arranged thereunder.

Background

The electro-acoustic device converts an electrical signal into an acoustic signal, and converts the acoustic signal into an electrical signal. In the electroacoustic resonator device, an electric signal is supplied to an electrode sandwiching a piezoelectric layer therebetween. An acoustic resonance wave is established between the electrodes, which performs a filtering function in a low loss and highly selective electrical domain. Electroacoustic resonator devices are commonly used in filter designs for mobile electronic devices such as cellular phones or smart phones. The interaction of electrical and acoustic operation allows the size of the device to be very compact, making many such devices useful in mobile devices to provide filters for various RF services.

One embodiment of the electroacoustic resonator device may be a solidly mounted bulk acoustic wave resonator (BAW-SMR). In BAW resonator devices, it is necessary to prevent the acoustic waves generated in the piezoelectric layer from propagating too far into the substrate, for example by means of a mirror element (in particular a bragg mirror element) arranged below the bottom electrode. The acoustic waves created in the resonator generate a significant amount of heat, thereby raising the temperature of the top and bottom electrodes and the piezoelectric layer between them. However, the temperature rise of these elements may affect the electrical parameters and reliability of the device. For example, an increase in the temperature of the electrodes may cause the metallic material of the electrodes to become viscous and may increase ohmic losses in the electrodes, so that their electro-acoustic behavior may change with an increase in temperature. Furthermore, an increase in the temperature of the piezoelectric layer may increase electrical and acoustic losses in the piezoelectric layer. Also, local hot spots in the material may lead to mechanical damage of such layers due to migration of the material. Due to the heat generated in the BAW resonator during operation of the BAW resonator, electrical parameters such as the resonant frequency and frequency bandwidth of the BAW resonator may be affected and may shift, such that e.g. the specifications of the RF filter may exceed the specifications of the mobile device. This is in contradiction to the requirements for sharp and deterministic filtering skirts (skirt) in present-day and future mobile devices. Therefore, it is desirable to avoid high temperatures in BAW devices during electro-acoustic operation.

Therefore, some BAW devices are supplied with a compensation layer for compensating for the shift of the electrical parameter due to the temperature increase. Another proposal disclosed in fig. 3 of DE 102014117238a1 suggests the use of thermal conduction to transfer heat generated in the electro-acoustic region towards the substrate. The piezoelectric layer is expanded so that it completely covers the stack of mirror layers and connects the electro-acoustic area with the substrate.

It is an object of the present disclosure to provide an electro-acoustic resonator device having stable electrical parameters during its operation and which can be easily manufactured. It is another object of the present disclosure to provide a method of manufacturing such an electro-acoustic resonator device.

Disclosure of Invention

According to the present disclosure, an electroacoustic resonator device includes: a substrate; a bottom electrode, a top electrode, and a piezoelectric layer disposed between the bottom electrode and the top electrode; 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 one aspect of the disclosure, a thermally conductive material, which may include amorphous aluminum nitride, contacts the piezoelectric layer and the substrate. The thermal conductivity of amorphous aluminum nitride is about 180W/Km, such that a thermal conduction path is established between the region where heat is generated during device operation and the heat sink (e.g., substrate). Instead of amorphous aluminum nitride, polycrystalline aluminum nitride may be used as the heat conductive material. The thermal conductivity of polycrystalline aluminum nitride is higher than that of amorphous aluminum nitride. Whenever amorphous aluminum nitride is used in the present disclosure, polycrystalline aluminum nitride may be used instead.

Aluminum nitride is a material commonly used in the fabrication of electroacoustic resonator devices, making available precursor materials for deposition of aluminum nitride and deposition and structuring equipment for aluminum nitride in production lines. Columnar aluminum nitride may be used as the piezoelectric layer. In accordance with the present disclosure, the use of amorphous or polycrystalline aluminum nitride as a thermally conductive material external to the piezoelectric layer is useful because amorphous or polycrystalline deposition of aluminum nitride is simpler than deposition of aluminum nitride having piezoelectric properties (e.g., columnar aluminum nitride). Furthermore, precursor materials for depositing aluminum nitride are readily available in the production line. When the piezoelectric layer is made of columnar aluminum nitride and the heat conduction path is made of amorphous/polycrystalline aluminum nitride, no material change is required.

The microstructure of the columnar aluminum nitride allows the columns in the layer itself to have a crystalline form. On the other hand, polycrystalline aluminum nitride has a plurality of relatively small crystal portions that are oriented differently, such that macroscopic polycrystalline aluminum materials have substantially no piezoelectric properties that can be used in electro-acoustic assemblies.

According to one aspect, a thermally conductive material of amorphous aluminum nitride is disposed between the bottom sidewall of the bragg mirror element and the substrate. Thus, the acoustic mirror can be completely surrounded by a thermally conductive material on its vertical and bottom side walls, so that it is very efficiently thermally coupled to the substrate as a heat sink. In addition, the coupling area between the amorphous aluminum nitride material and the substrate is increased, thereby 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 encapsulation to provide an efficient mechanical coverage at the top side. A thin film encapsulation surrounds the cavity formed between the top electrode of the active region and the cladding layer. The cladding layer may include a via through which a sacrificial layer previously existing between the top electrode and the cladding layer is removed. A sealing layer is disposed on the clad layer to close pores in the clad layer and enhance the stability of the clad layer. According to an aspect of the present disclosure, the sealing layer may be further covered with a thermally conductive material of amorphous aluminum nitride to provide a thermally conductive path to a heat sink 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 a conductive bump, e.g., a metal or solder bump, disposed in a corresponding via of 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 an external circuit to which the resonator device is connected. On the other hand, such a thermally conductive material of amorphous aluminum nitride serves as a reinforcing layer on top of the device and enhances the mechanical stability of the device.

According to one aspect of the disclosure, a thermally conductive material of amorphous aluminum nitride may be further disposed between the piezoelectric layer and the lower end or surface of the cladding layer and/or the lower end or surface of the sealing layer. The surface and said lower end of the sealing layer face in the direction of the substrate of the device. The amorphous aluminum nitride material may contact the piezoelectric layer and the lower end of the cladding layer and/or the sealing layer. According to the present disclosure, the amorphous aluminum nitride disposed between the cladding layer and the sealing layer and the piezoelectric layer provides a good thermal path for heat generated in the active region. In previous resonator devices, the lower ends of the cladding layer and the sealing layer were in contact with the top surface of the piezoelectric layer or the top electrode or the bragg mirror element, so that the thermal conductivity was limited.

According to a corresponding aspect of the invention, the thermally conductive material extends in the form of a continuous material, the thermally conductive material contacting surfaces of the top and bottom electrodes, surfaces of the bragg mirror element, and surfaces of the encapsulation layer and the cladding layer. Thus, the thermally conductive material enables an integral packaging of the device and excellent thermal conductivity to the heat sink.

The bragg mirror element may comprise a dielectric material and at least two or more layers of another material having an acoustic impedance higher than that of the dielectric material. Another layer of material having a higher acoustic impedance is spaced apart from each other such that a dielectric material is disposed therebetween. The bragg mirror element will be structured in the manufacturing process such that it has sidewalls extending in a direction transverse to the substrate. The sidewalls may have a vertical or substantially vertical orientation when compared to the surface of the substrate. The sidewalls of the bragg mirror elements and the sidewalls of the dielectric material have a common contact surface with the amorphous aluminum nitride material. Thus, the vertical sidewalls and bottom sidewalls of the bragg mirror elements may be completely covered by the amorphous aluminum nitride material such that any heat in the bragg mirror elements is directed to the heat sink portion of the device. Furthermore, the active area has a wide thermal path to the heat sink.

In another embodiment, the lateral sidewalls of the bragg mirror elements may have an inclined orientation with respect to the surface of the substrate. The cross-sectional diameter of the bragg mirror may be larger near the substrate than near the bottom electrode. With non-vertically sloping sidewalls, the contact surface between the insulating material of the bragg mirror element and the amorphous AlN is larger than with vertical sidewalls, so that the sloping sidewalls can be utilized to improve the heat dissipation effect.

According to one aspect of the present disclosure, the other material having a higher acoustic impedance may be a metal such as tungsten or a tungsten alloy. Alternatively, the further material with 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 the other, opposite sidewall of the bragg mirror structure, such that the amorphous aluminum nitride layers within the bragg mirror elements are spaced apart by the dielectric material layer.

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

The compact electroacoustic resonator device according to the present disclosure includes: a first amorphous aluminum nitride layer disposed on the substrate; a stack of Bragg mirror elements disposed on the first aluminum nitride layer, wherein the bottom electrode is disposed on the Bragg mirror elements. A second amorphous aluminum nitride layer is disposed around the sidewalls of the bragg mirror elements. A piezoelectric layer is disposed on the bottom electrode, and a top electrode is disposed on the piezoelectric layer. A third amorphous aluminum nitride layer is disposed around the sidewalls of the top electrode, and a cladding layer and a sealing layer are disposed over the top electrode, surrounding a cavity between the top electrode and the cladding layer. A fourth amorphous aluminum nitride layer is disposed around and on the sidewalls of the sealing layer to form a reinforcement layer. This compact design of the resonator device has the device fully encapsulated by amorphous aluminum nitride, so that the device has a small size and exhibits good heat dissipation properties.

The object of the present disclosure may be further achieved by a method of manufacturing an electro-acoustic resonator, the method comprising the steps of: providing a substrate; depositing a bragg mirror stack on a substrate; depositing an electrode layer on the bragg mirror stack to form a bottom electrode; structuring the bragg mirror 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 layer of piezoelectric material on a surface of the bottom electrode; another electrode layer is deposited on the piezoelectric layer to form a top electrode.

According to one aspect of the disclosed fabrication method, aluminum nitride may be deposited after providing the substrate and before depositing the bragg mirror stack. Thus, the thermally conductive aluminum nitride material is disposed between the bottom sidewall of the bragg mirror element and the substrate, thereby providing 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 the deposited aluminum nitride are polished together to create a uniform surface for depositing a thin film package in the device, the thin film package including a cladding layer and a sealing layer. Aluminum nitride is further deposited to cover previously deposited structures (e.g., previously deposited aluminum nitride) and the sealing layer to achieve a reinforcing layer on top of the sealing layer to enhance the stability of the top 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 such that the two materials are different states of the same material. The use of the same material may provide good manufacturing process controllability and lower manufacturing costs.

According to another aspect of the method, a metal bump is provided in a via in the aluminum nitride of the enhancement layer such that an external electrical contact surface is provided at a surface of the bump. Corresponding metal bumps may be connected to the top and/or bottom electrodes.

Drawings

Embodiments of the present invention are described in more detail below with reference to the accompanying drawings. Corresponding elements in different figures are denoted by the same reference numerals. The drawings illustrate one or more embodiments and, together with the description, serve to explain the principles and operations of the various embodiments. In the drawings:

figure 1 shows a cross section of an embodiment of an electro-acoustic resonator device;

FIG. 2 illustrates one embodiment having metal bumps;

figures 3A to 3F show stages of a workpiece in the manufacturing process of an electroacoustic resonator device; and

fig. 4 shows a flow chart of a manufacturing process of the device of fig. 3.

Detailed Description

Both the foregoing general description and the following detailed description are exemplary only, and are intended to provide an overview or framework for understanding the nature and character of the claims.

The electroacoustic 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 a variety of materials. In one embodiment, the substrate may be made of doped crystalline silicon. The doping renders the silicon substantially non-conductive.

The BAW device comprises an electro-acoustic resonator comprising a bottom electrode 121 and a top electrode 122 with a piezoelectric layer 130 disposed therebetween. The top electrode and the bottom electrode may each be made of a metal layer. 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 (AlN) in the form of piezoelectric properties. Preferably, the piezoelectric layer is a columnar AlN exhibiting good piezoelectric characteristics.

During operation of the device, high frequency electrical signals in the several GHz range are supplied to the top and bottom electrodes. The interaction between the electrodes and the piezoelectric layer excites acoustic oscillations. The oscillations have a defined frequency and a narrow and sharp frequency spectrum. Thus, electronic filters using BAW devices have a defined, relatively sharp skirt.

The acoustic oscillations occur primarily in the piezoelectric layer 130 and the

electrodes

121, 122, but the acoustic oscillations also extend into the surrounding area, so the active area of the device needs to be oriented through the bragg mirror element 110The substrate 100 is shielded. The bragg mirror element 110 as shown comprises a dielectric material 111, in the present case two

layers

112, 113 having a higher acoustic impedance than the acoustic impedance of the dielectric material 110 being embedded in the dielectric material 111. In one embodiment, the dielectric material 110 may be silicon dioxide (SiO)₂) And the

material

112, 113 having a higher acoustic impedance may be a metal such as tungsten (W). The acoustic wave is reflected back to the active region, shielded from the substrate 100, by the bragg mirror 110 under the bottom electrode 121.

To fine tune the characteristics of the device, a layer 125 may be provided on top of the top electrode 122 for trimming, trimming and passivation. Layer 125 may be formed of a material including silicon oxide and silicon nitride (SiO)₂SiN), which is appropriately structured to achieve the desired characteristics of the device.

During operation of BAW devices, a large amount of loss is generated in the active area where electrical and acoustic oscillations occur. During operation of the device, the areas of substantial loss are primarily the piezoelectric layer 130 and the top and

bottom metal electrodes

122 and 121. Other losses will occur in the bragg mirror 110. The dissipation losses generate a large amount of heat in the piezoelectric layer 130 and the

electrodes

122, 121.

In the illustrated embodiment, heat generated in the active region of the BAW device is directed through a thermal conduction path to the heat dissipating structure of the device. The thermally conductive path includes a thermally conductive material that is amorphous form of aluminum nitride (AlN), amorphous AlN. Although the embodiment shown in the figures uses amorphous AlN, alternatively, polycrystalline AlN may be used for the heat conduction path. The amorphous or polycrystalline AlN is substantially the same material as the columnar AlN in the piezoelectric layer 130, but has a different structure because it is amorphous/polycrystalline rather than columnar. Amorphous AlN is preferred for thermally conductive materials because it is easier to deposit than columnar AlN. Polycrystalline AlN may also be used for the thermal conduction path. The use of the same base material AlN for the piezoelectric layer 130 and the thermally conductive layer 150 ensures that these components of the device have substantially the same mechanical properties, so that the device has mechanical stability even when a large amount of heat is generated during its operation. Fabrication is cost effective because the piezoelectric layer and the thermally conductive material can be deposited using the same fabrication equipment and the same chemical precursor materials.

A thin layer 151 of thermally conductive material is deposited on top of the upper surface of the substrate 100. An amorphous AlN thin layer 151 is provided between the substrate 100 and the bottom side of the bragg mirror element 110. The layer 151 has a large contact area with the substrate 100, so that the thermal resistance of the surface between the AlN layer 151 and the substrate 100 is considerably low.

A thermally conductive material, AlN150, is grown on the thin layer 151 to surround the sidewalls 113 of the dielectric material 111 of the bragg mirror element 110. The sidewalls 113, which are shown as two portions of sidewalls in the cross-sectional view of fig. 1, have a lateral or oblique orientation with respect to the surface of the substrate 100. The sidewalls 113 of the bragg mirror elements 110 are obtained by a structuring process such as dry etching.

A thermally conductive material AlN150 further surrounds the sidewalls of the piezoelectric layer 130 and the top electrode 122 and the bottom electrode 121, which are also obtained by the structuring process. The material 150 reaches a common surface level 152 with the upper surface of the top electrode 122. The surface level 152 has been obtained by a polishing process that polishes the top electrode 122 and the aluminum nitride 150. The polishing process may be a Chemical Mechanical Polishing (CMP) process. The surface 152 carries a

thin film encapsulation

165, 166, the

thin film encapsulation

165, 166 enclosing the cavity 160 and the conditioning, trimming and passivation layer 125 over the top electrode 122. The cavity 160 may be obtained by depositing a sacrificial layer (not shown in the figures) which is removed after the deposition of the cladding layer 165. The cladding layer 165 is provided with at least one opening 1651 through which the sacrificial layer is removed to obtain the cavity 160. The cavity 160 is filled with air, for example. The cladding 165 is covered with a sealing layer 166 to enhance mechanical stability and close the hole 1651.

Lower surfaces

1652, 1661 of the cladding and sealing

layers

165, 166 are in contact with and stand on the surface 152 of the thermally conductive AlN material. This means that the thermally conductive amorphous AlN material contacts the piezoelectric layer 130 and extends so that it reaches the

lower surfaces

1652, 1661 of the cladding and encapsulation layers.

Lower surfaces

1652, 1661 of

layers

165, 166 face substrate 100. Finally, the encapsulation layer 166 is again covered by the thermally conductive material of amorphous AlN 155. Material 155 also has an enhanced function of enhancing the mechanical stiffness and stability of the BAW device. The outer surfaces of the AlN material, including the top surface of the enhancement layer 155 and the sidewall surfaces of the

AlN material

150, 155, 151, may face ambient air, such that these surfaces function as heat sinks. Aluminum nitride has a relatively good thermal conductivity in the range of about 180W/Km, so that directing heat from the acoustically active region into the bulk material of AlN150, 155, 151 and to the corresponding outer surface can dissipate a significant amount of heat well.

The top and

bottom electrodes

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

The thickness of the piezoelectric layer is in the range of about 1 μm. For example, the thickness of the piezoelectric AlN layer 130 may be in the range of 300nm to 2500nm, and more preferably in the range of 700nm to 2000 nm. The total thickness of the device from the lower surface of the substrate to the upper outer surface of the reinforcing layer 155 may be in the range of about 10 μm. Even with the use of thermally conductive AlN materials, the size of the device remains small.

Essentially all elements of the BAW resonator are encapsulated by the

amorphous AlN material

150, 155 so that the generated operating heat can be efficiently transferred to several heat sinks to ensure the desired electrical specifications. The device is relatively easy to manufacture because the use of amorphous AlN is well controlled. The

materials

150, 155 are continuous materials that integrally and completely surround the device. There is no substantial material change from the piezoelectric layer 130 to the corresponding heat sink (e.g., the outer surface of the substrate 100 and AlN material).

Fig. 2 shows another embodiment, wherein the BAW resonator device of fig. 1 is further equipped with an electrical input/output terminal for the top electrode 122. Although fig. 2 only shows a connection to the top electrode 122, another connection to the bottom electrode 121 may be provided in a similar manner.

The top electrode 122 in fig. 2 is provided with a metal strip 210, the metal strip 210 extending at substantially the same level beyond the sealing layer and the

cladding layer

165, 166. As depicted on the left side of the device in fig. 2, the metal strap 210 extends beyond the lower surfaces of the cladding and sealing

layers

165, 166 within the amorphous AlN material 150. A via 201 is etched into the upper portion 155 of AlN material. The vias 201 are filled with a metallic material 202, the metallic material 202 forming 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 supplying/outputting an electrical signal to/from the top electrode 122. The bump material 202 may be a metal solder material that is highly electrically and thermally conductive, such that the bump 202 also acts as a heat sink for heat generated in the active area of the device. Amorphous AlN material 155 is non-conductive, such that metal bump 202 is electrically isolated from the rest of the device, except for wiring strap 210 and top electrode 122. The long contact surface of bump 202 along the length of via 201 allows for easy transfer of heat directed in

AlN material

150, 155 to bump 202. The bump 202 has the combined function of a heat sink and an electrical connection from the top electrode 122 to the outside of the device at the surface 203 of the bump 202.

As a variation of the BAW resonator device of fig. 1 and 2, amorphous aluminum nitride of thermally

conductive material

150, 155 may be used in addition. For example, the tuning, trimming and passivation layer 125 may include amorphous AlN. Thus, the top surface of the top electrode 122 has a thermally conductive cap 125 of amorphous AlN, so that potential hot spots in the top electrode 122 are avoided. Thus, the risk of damaging the top electrode by potential hot spots is significantly reduced. On the other hand, the heat generated in the top electrode is further removed from the top electrode by the thermal conductivity modification, trimming and passivation layer 125 of AlN, as the heat will dissipate into the air present in the cavity 160.

As another variation, according to this variation, the dielectric material 111 (which may be SiO in one embodiment) of the Bragg mirror element 110₂Made) may be replaced by AlN, optionally amorphous AlN. In this case, material 111 is also amorphous AlN, as is surrounding material 150. In this case, the AlN material 111 of the bragg mirror element 110

embeds layers

112, 113 of a metal such as tungsten or aluminum, or alloys thereof. Unless otherwise specified, metallic materials with higher acoustic impedance are fully encapsulated in an amorphous stateAlN material.

As another variation, the piezoelectric layer 130 may also be made of aluminum scandium nitride or other doped aluminum nitride each exhibiting piezoelectric properties.

An embodiment of a method of manufacturing an electroacoustic resonator device is described below in connection with fig. 3A to 3F and 4. Fig. 4 shows a flow chart of a sequence of method steps, and fig. 3A to 3F show corresponding states of workpiece processing. As a starting point of the manufacturing process according to this embodiment, the substrate 100 (fig. 3A) is provided according to step 401 (fig. 4). A relatively thin amorphous aluminum nitride layer 151 is deposited on the substrate 100 (step 402 of fig. 4). Subsequently, a bragg mirror stack 110 is deposited comprising a dielectric material 111 embedded in

tungsten layers

112, 113. Thereafter, a metal layer of the bottom electrode 121 is deposited. The bragg mirror stack and the bottom electrode layer are structured (step 403) by photolithography and dry etching to achieve substantially vertical sidewalls as shown in fig. 3B. As another embodiment (not shown), the dry etch parameters may be set such that the sidewalls of the bragg mirror stack achieve a tilted orientation relative to the substrate surface, rather than a vertical orientation. The diameter of the bragg mirror stack further from the substrate surface is smaller than the diameter close to the substrate.

Amorphous aluminum nitride is then deposited to fill all valleys and trenches present in the current structure. The top surface of the workpiece is now polished, for example, using a Chemical Mechanical Polishing (CMP) process. The CMP operation generates a uniform top surface 1211 of the top electrode 121 and a polished top surface 1501 of the AlN layer 150 (step 404). The resulting workpiece is shown in fig. 3C.

Next, a piezoelectric layer is deposited on the

uniform surfaces

1211 and 1501 of the bottom electrode 121 and AlN 150. In this embodiment, the piezoelectric material is columnar AlN. To obtain a columnar structure, it is useful to deposit a suitable seed layer on the polishing surface 1211 (step 405). Suitable alternative materials for the piezoelectric layer may be deposited instead of piezoelectric AlN (e.g., 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 substantially the same width as the width of the bottom electrode 121 (step 406). Note that alternatively, the deposited piezoelectric layer may be first structured to obtain the appropriate width of the piezoelectric material 130, to subsequently deposit a metal layer for the top electrode, and to structure the metal layer to obtain the appropriate width of the top electrode 122. The resulting structure is shown in fig. 3D.

Aluminum nitride 154 is then deposited to fill all valleys and trenches present in the workpiece. As shown in fig. 3E, a CMP process is performed on the top surface of the workpiece to obtain a flat uniform top surface having a polished surface 1221 of the

top electrode

121 and 1541 of the deposited aluminum nitride 154 (step 407).

On the workpiece shown in fig. 3E, a layer for the trimming, trimming and passivation functions is deposited and structured to have substantially the same width as the top electrode 122 (step 408). Layer 125 may be a layer comprising SiO₂A stack of/SiN or alternatively amorphous AlN. A thin film top package comprising a cladding layer 165 and a sealing layer 166 is then fabricated. The cladding layer 165 covers the cavity 160, and the cavity 160 is realized by depositing a sacrificial layer, structuring the sacrificial layer, and covering with the cladding layer 165. The cladding layer 165 is provided with one or more holes through which the sacrificial oxide is removed, thereby obtaining a cavity. The resulting structure is shown in fig. 3F (step 409).

Finally, amorphous AlN is deposited on top of the workpiece shown in fig. 3F to implement a top enhancement layer 155. The top surface may be polished by CMP to obtain a substantially flat top surface. The resulting device is shown in fig. 1.

Alternatively, the structure shown in fig. 2 may be implemented by fabricating solder bumps into the top enhancement layer 155 as described in connection with fig. 2.

The disclosure given above describes electro-acoustic resonator devices (e.g., SMR-BAW resonator devices) and corresponding methods of manufacture, in which the devices are encased in a thermally conductive material (e.g., amorphous AlN) that provides a thermal path to a heat sink (e.g., ambient air, solder bumps, and silicon substrate) for the operating heat generated in the acoustically active region. With heat dissipation, the electrical characteristics of the BAW device are maintained even if high power losses are 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 defined 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.

Claims

1. An electro-acoustic resonator device comprising:

a substrate (100);

a bottom electrode (121), a top electrode (122), and a piezoelectric layer (130) disposed between the bottom electrode and the top electrode;

a Bragg mirror element (110) disposed between the bottom electrode and the substrate; and

a thermally conductive material comprising one of amorphous aluminum nitride and polycrystalline aluminum nitride (150, 151, 155), wherein the thermally conductive material contacts the piezoelectric layer and the substrate.

2. The electro-acoustic resonator device according to claim 1, wherein said thermally conductive material (151) is further arranged between a bottom sidewall of said bragg mirror element (110) and said substrate (100).

3. The electro-acoustic resonator device according to claim 1 or 2, further comprising: a cladding layer (165) covering a cavity (160) disposed over the top electrode; and an encapsulation layer (165) covering the cladding layer, wherein the thermally conductive material (155) is further disposed over the encapsulation layer.

4. The electroacoustic resonator device of claim 3, wherein the thermally conductive material (150) is further disposed between the piezoelectric layer (130) and at least one of a lower end (1652) of the cladding layer (165) and a lower end (1661) of the encapsulation layer (166).

5. The electro-acoustic resonator device of claim 3 or 4, wherein the thermally conductive material (150, 151, 155) extends in the form of a continuous material in contact with each of the surfaces of the top and bottom electrodes (121, 122), the Bragg mirror element (110) and the sealing layer and the cladding layer (165, 166).

6. The electro-acoustic resonator device according to any one of claims 1-5, wherein a via (201) is comprised in said thermally conductive material (155) and at least one bump (202) made of electrically conductive material is provided at an upper end of said via, said at least one bump being connected to one of said top and bottom electrodes (122) to provide an electrical terminal to the outside of said electro-acoustic resonator device.

7. The electro-acoustic resonator device according to any one of claims 1-6, the Bragg mirror (110) element comprising a dielectric material (111) and two or more layers of a further material (112, 113), the acoustic impedance of the two or more layers of the further material (112, 113) being higher than the acoustic impedance of the dielectric material, wherein the two or more layers of the further material (112, 113) having higher acoustic impedance are spaced apart from each other, wherein the dielectric material (111) is arranged between the further material having higher acoustic impedance, the dielectric material having sidewalls (113), the sidewalls (113) extending in a direction transverse to the substrate (100), wherein the sidewalls of the dielectric material contact the thermally conductive material (150).

8. The electroacoustic resonator device of claim 7, wherein the further material (112, 113) of the Bragg mirror element having a higher acoustic impedance comprises a metal and the dielectric material (113) comprises aluminum nitride.

9. The electro-acoustic resonator device according to any one of claims 1 to 8, further comprising a layer of one of amorphous aluminum nitride and polycrystalline aluminum nitride (125) arranged on top of said top electrode for at least one of trimming, trimming and passivating.

10. The electro-acoustic resonator device of claim 1, comprising:

a first amorphous aluminum nitride layer (151) disposed on the substrate (100);

-the stack of bragg mirror elements (110) is arranged on the first amorphous aluminum nitride layer (151);

a bottom electrode (121) disposed on the Bragg mirror element;

a second amorphous aluminum nitride layer (150) disposed around a sidewall (113) of the Bragg mirror element;

the piezoelectric layer (130) disposed on the bottom electrode (121) and the top electrode (122) disposed on the piezoelectric layer;

a third amorphous aluminum nitride layer (150) disposed around sidewalls of the top electrode (122);

a cavity (160) disposed over the top electrode (122) and a cladding layer (165) and a sealing layer (166) disposed over the cavity;

a fourth amorphous aluminum nitride layer (155) disposed around and on sidewalls of the sealing layer.

11. A method of manufacturing an electroacoustic resonator device, comprising the steps of:

providing a substrate (100);

depositing a bragg mirror stack (110) on the substrate;

depositing an electrode layer on the Bragg mirror stack to form a bottom electrode (121);

structuring the Bragg mirror stack and the bottom electrode;

depositing aluminum nitride (150);

performing a polishing step to expose a polished surface (1211) of the bottom electrode and a polished surface (1510) of the deposited aluminum nitride;

depositing a layer of piezoelectric material (130) on the surface of the bottom electrode; and

another electrode layer (122) is deposited on the piezoelectric layer to form a top electrode.

12. The method of claim 11, further comprising:

after the step of providing a substrate and before the step of depositing a bragg mirror stack, depositing aluminum nitride (151) to form an aluminum nitride layer disposed between the substrate (100) and the bragg mirror stack (110).

13. The method according to claim 11 or 12, comprising:

further depositing aluminum nitride on the top electrode (122);

performing a polishing step to expose a polished surface (1221) of the top electrode and a polished surface (1541) of further deposited aluminum nitride;

depositing a cladding layer (165) and a sealing layer (166) to obtain a cavity (160) disposed between the top electrode and the cladding layer;

aluminum nitride (155) is then deposited to cover the further deposited aluminum nitride and the sealing layer.

14. The method of any one of claims 11 to 13, wherein the step of depositing aluminum nitride comprises, in each case: depositing one of amorphous aluminum nitride and polycrystalline aluminum nitride (150, 151, 154, 155); and the step of depositing the layer of piezoelectric material (130) comprises depositing a column of aluminium nitride.

15. The method of claim 11, further comprising providing at least one via (201) in the deposited aluminum nitride (155) and providing a metal bump (202) at an upper end of the via to provide an external electrical contact for at least one of the top and bottom electrodes (122) at the bump.