Electroacoustic component, RF filter, and manufacturing method

Abstract

Electroacoustic component, comprising - a carrier substrate (CS), - a first layer stack (BAWR) on or above the carrier substrate, - a second layer stack (EC) on or above the carrier substrate, wherein - the first layer stack comprises a first functional structure (IL) and a second functional structure arranged on or above the first functional structure, - the second layer stack comprises a raised structure (RS) and a third functional structure (BU, UBM, B) arranged on or above the raised structure, - the raised structure raises the third functional structure to the vertical height of the second functional structure.

Description

Technical Field

[0001] The present invention relates to electroacoustic components, and more particularly, to components having improved electrical contacts. Further, the present invention relates to corresponding RF filters and methods of manufacturing such components. Background Art

[0002] RF filters can be used in wireless communication devices, for example, in mobile terminals, to separate desired RF signals from undesired RF signals. RF filters can include electroacoustic components, such as electroacoustic resonators. In an electroacoustic resonator, an electrode structure is coupled to a piezoelectric material. Due to the piezoelectric effect, the electroacoustic resonator converts between electromagnetic RF signals and acoustic RF signals. The corresponding electroacoustic resonator can have a stacked configuration, in which a plurality of two or more layers are arranged one above the other.

[0003] Electroacoustic components can include electroacoustic resonators and other circuit elements, for example, active circuit elements or passive circuit elements and / or connecting means for electrically connecting the electroacoustic resonator to an external circuit environment.

[0004] There is generally a desire for an improved electroacoustic component, that is, an electroacoustic component having improved electrical and / or acoustic performance. Summary of the Invention

[0005] To this end, there is provided an electroacoustic component, an RF filter, and a method of manufacturing an electroacoustic component according to the claims. The dependent claims provide preferred embodiments.

[0006] The electroacoustic component includes a carrier substrate, a first layer stack, and a second layer stack. The first layer stack is disposed on or above the carrier substrate. The second layer stack is disposed on or above the carrier substrate. The first layer stack includes a first functional structure. Further, the first layer stack includes a second functional structure disposed on or above the first functional structure. Further, the second layer stack includes a raised structure and a third functional structure. The third functional structure is disposed on or above the raised structure. The raised structure raises the third functional structure to the vertical level of the second functional structure.

[0007] The carrier substrate provides a common carrier for the first layer stack and the second layer stack. The first layer stack and the second layer stack can be arranged one after another on the carrier substrate. The first layer stack and the second layer stack can be arranged directly adjacent to each other. However, a certain distance can also be arranged between the first layer stack and the second layer stack. More layer stacks can be arranged between the first layer stack and the second layer stack in the horizontal direction.

[0008] The first functional structure is a functional structure of the electroacoustic component. The functional structure can establish an electrical function and / or an acoustic function.

[0009] Furthermore, the second functional structure can establish the electrical and / or acoustic functions of the electroacoustic component. Similarly, the third functional structure can establish the electrical and / or acoustic functions.

[0010] The terms "upper" or "above" are valid for the orientation of the electroacoustic component, where the carrier substrate is below the first layer stack and the second layer stack. The vertical levels of the third functional structure and the second functional structure respectively refer to the vertical distances between the third functional structure and the second functional structure and the carrier substrate. Therefore, the raised structure is responsible for arranging the bottom part of the third functional structure at the vertical position of the bottom part of the second functional structure. Therefore, the bases of the second functional structure and the third functional structure have height positions relative to the carrier substrate.

[0011] Typical attempts to improve the performance of electroacoustic components refer to improving the performance of electroacoustic resonators. However, it has been observed that improved components can be obtained when the electrical connection to the external circuit environment is also improved. By positioning the second functional structure and the third functional structure at a common vertical position, the electrical connection to the external circuit environment can be improved, especially when the first layer stack and the second layer stack include multiple stacked layers.

[0012] The corresponding layer stack can include multiple layers of two or more, which are provided using layer deposition techniques, structuring techniques, and at least partially using material removal techniques. Specifically, a planarization step (such as a polishing step) can be used to provide a surface of one type of material on which another type of material, for example, another layer, can be deposited. For example, during the manufacture of a BAW resonator stack (BAW = bulk acoustic wave), an under-polishing step can be provided to prepare the material under the bottom electrode of the resonator. The polishing step can be a CMP step (CMP = chemical mechanical polishing).

[0013] By providing a raised structure below the third functional structure, the vertical position of the top part of the third functional structure can be obtained, such that the top part of the third functional structure can have an improved interconnection with the external circuit environment.

[0014] Specifically, the raised structure can be used to prevent residual dielectric material on the contact pad through which the electroacoustic component should be electrically connected to the external circuit environment.

[0015] The first functional structure may include elements of an acoustic mirror. Furthermore, the second functional structure may include elements of an electroacoustic resonator. The raised structure can include elements of a pseudo-acoustic mirror.

[0016] Thus, an electroacoustic resonator can be implemented in the first layer stack. For example, a BAW resonator is implemented. The BAW resonator can include an active structure and an acoustic mirror. The active structure can be used to excite acoustic waves. The acoustic mirror can be used to confine acoustic energy to the region of the resonator. Correspondingly, an element of the acoustic mirror (e.g., a mirror layer) forms at least one element of the first functional structure. For example, an electrode of the active part of the resonator forms an element of the second functional structure.

[0017] An acoustic mirror generally includes two or more layers having different acoustic impedances. At the interface between the layers of different acoustic impedances, acoustic waves are at least partially reflected. The multiple corresponding stacked mirrors form a Bragg mirror to confine acoustic energy to the active region of the resonator disposed above the mirror. Providing the layered elements of the mirror at a specific location in the electroacoustic component locally disrupts the symmetry of the layer structure of the electroacoustic component. As an undesired effect, compared with the position of the acoustic mirror itself, the polishing step may locally remove more material at the environment of the mirror. Therefore, such a polishing step may result in a non-planar top surface with a local elevation at the position of the acoustic mirror. Near the structured region, the step height is very low, while in the unstructured region, the step height can reach more than 100 nm, which may cause problems for subsequent layers. For example, subsequent steps of providing materials for other functional structures (e.g., the bottom element of the BAW resonator in the first layer stack and the metallization for contacting the external circuit environment in the second layer stack) may have different vertical positions. Another step of depositing a dielectric material in the first layer stack and the second layer stack may result in a different thickness of the dielectric material at the position of the acoustic mirror compared to the position of the structure where contact with the external circuit environment should be allowed. In another subsequent step of removing the material of the dielectric material, the different thicknesses will cause the material of the dielectric material to remain on the electrode structure, making it possible to obtain a non-ideal contact with the external circuit environment.

[0018] However, by providing a raised structure, the metallization of the BAW resonator serving as the third functional structure for contacting the external circuit environment and the bottom electrode of the BAW resonator serving as the second functional structure can be vertically planar and no additional dielectric material will be left on the third functional structure, so that a good electrical contact with the external circuit environment can be obtained.

[0019] Correspondingly, the phrase "pseudo-acoustic mirror" refers to an acoustic mirror used as a raised structure because the raised structure also causes a local elevation at the second layer stack. However, in the second layer stack of this electroacoustic component, there is no need for a pseudo-acoustic mirror for acoustic reasons.

[0020] Correspondingly, the third functional structure may include elements for electrical connection (e.g., electrical connection with the external circuit environment).

[0021] It is possible and / or preferable that the first functional structure and the raised structure have the same height.

[0022] The common height of the first functional structure and the raised structure preferably, together with the same vertical level of the first functional structure and the raised structure, improves the provision of the common level of the top portions of the first functional structure and the lifting structure, such that the provision of the common vertical position of the second functional structure and the third functional structure is simplified.

[0023] Furthermore, it is possible and / or preferable that the first functional structure and the raised structure have the same layer configuration.

[0024] Thus, the first functional structure and the raised structure can have the same number of layers. The thicknesses and materials of the corresponding layers of the first functional structure and the raised structure can also be equal.

[0025] The first layer stack can include a BAW resonator.

[0026] Furthermore, the second layer stack can include a pseudo-acoustic mirror and an electrical connection to the external circuit environment. Further, the first functional structure can be an SMR-type BAW resonator (SMR = solidly mounted resonator). The second functional structure is an active element of the SMR-type BAW resonator. The raised structure is a pseudo-acoustic mirror of the SMR-type BAW resonator, and the third functional structure is a bump connection, which can include solder bumps electrically connected to the external circuit environment or solder bumps not yet electrically connected to the external circuit environment, where the bump connection can include more layers (e.g., UBM (underbump metallurgy) layer, adhesive layer, etc.).

[0027] Although the raised structure may provide an acoustic function that is not necessarily required at that particular location, one or more elements of the raised structure may provide an electrical function. The electrical function can be electrical shielding or protection against ESD (ESD = electrostatic discharge) search, etc.

[0028] Specifically, when the raised structure includes a plurality of mirror layers, good electrostatic shielding can be provided. Further, additional circuit elements of the electro-acoustic component (such as inductive elements, capacitive elements, and / or resistive elements) can be elements of the raised structure. Thus, the raised structure not only improves the electrical connection to the external circuit environment, but also improves the signal quality and miniaturization.

[0029] The RF filter includes an electro-acoustic component, e.g., the electro-acoustic component as described above. Further, the RF filter can include one or more additional electro-acoustic resonators, which can be electrically connected to the components as described above.

[0030] The RF filter can be a filter of a mobile communication device, e.g., a filter of a wireless terminal. Specifically, the filter can be a filter of the front-end circuit of the corresponding device.

[0031] Furthermore, such a filter can be used to build a multiplexer, e.g., a duplexer.

[0032] Such a filter can have a ladder-like circuit topology or a lattice-like circuit topology. In the ladder-like circuit topology, two or more series resonators are electrically connected in series in the signal path. The parallel paths include parallel resonators and electrically connect the signal path to ground.

[0033] A method of manufacturing an electroacoustic component (e.g., the electroacoustic component as described above) includes the following steps:

[0034] - Providing a carrier substrate,

[0035] - Arranging a first functional structure and a raised structure on or above the carrier substrate,

[0036] - Arranging a second functional structure on or above the first functional structure,

[0037] - Arranging a third functional structure on or above the raised structure at the vertical level of the second functional structure.

[0038] Furthermore, a method can include the step of at least partially removing the material of the intermediate layer below the third functional structure.

[0039] Thus, an electroacoustic resonator with improved performance (especially with improved interconnection with the external circuit environment) is provided.

[0040] For example, the implementation of pseudo-structures in the layer below the material layer after the material removal step (e.g., the CMP under-polishing step) provides improved electrical connection and avoids connection problems with the external circuit environment.

[0041] The carrier substrate can include silicon or be composed of silicon.

[0042] The mirror layer (e.g., with high acoustic impedance) can contain tungsten (W) or be composed of W. The acoustic mirror layer with low acoustic impedance can include silicon oxide or be composed of silicon oxide (e.g., silicon dioxide). The piezoelectric material between the two electrode layers in the active region of the resonator can include aluminum nitride or scandium-doped aluminum nitride or be composed of aluminum nitride or scandium-doped aluminum nitride. The electrode layer of the active structure of the resonator can include tungsten, aluminum, gold, silver, copper, or their alloys or be composed of tungsten, aluminum, gold, silver, copper, or their alloys. Description of the Drawings

[0043] The central aspects, working principles, and details of the preferred embodiments are shown in the drawings.

[0044] In the drawings:

[0045] Figure 1 Cross-sections of corresponding components are shown;

[0046] Figure 2 An acoustic mirror as the first functional structure is shown;

[0047] Figure 3 The metallization structures of the second and third functional structures are shown;

[0048] Figure 4 A pseudo-acoustic mirror as a raised structure is shown;

[0049] Figure 5 The first layer stack for establishing the BAW resonator and the second layer stack for establishing the external connections are shown;

[0050] Figure 6 Problems that may occur during the polishing process and local disturbances in the component symmetry are illustrated; and

[0051] Figure 7 A duplexer including two band-pass filters with a circuit topology based on a similar trapezoid is shown. Detailed Description

[0052] Figure 1 A cross-section of a schematic electro-acoustic component is shown. The component has a carrier substrate CS, and other structures are arranged on the carrier substrate. The carrier substrate CS serves as a common carrier for additional structures of the electro-acoustic component. The first layer stack LS 1 and the second layer stack LS 2 are arranged one after another on the carrier substrate CS. The first layer stack LS 1 includes the first functional structure FS 1 and the second functional structure FS 2 . The second layer stack LS 2 includes a raised structure RS and the third functional structure FS 3 .

[0053] The first functional structure FS 1 and the raised structure RS can be embedded in the matrix material. Providing the raised structure RS allows the second functional structure FS 3 to be provided at the same vertical position as the third functional structure FS 2 . Thus, the distance between the carrier substrate CS and the second functional structure FS 2 is substantially equal to the distance between the carrier substrate CS and the third functional structure FS 3The distance therebetween. The substrate material may have a planar surface. Specifically, the surface of the substrate material may be parallel to the top surface of the carrier substrate CS. However, the thickness of the substrate material may vary locally. Specifically, the vertical level of the substrate material at the location where the first functional structure FS 1 is located may be higher than the vertical level in the region surrounding the first functional structure FS 1 . However, by providing the raised structure RS, the corresponding height level of the surface of the substrate material is substantially equal to the height level of the substrate material at the location of the first functional structure FS 1 .

[0054] Figure 2 Illustrates the possibility of implementing the first functional structure FS 1 as an acoustic mirror AM. The acoustic mirror includes two or more layers. Adjacent layers with respect to the vertical direction have different acoustic impedances. Correspondingly, Figure 2 illustrates an acoustic mirror including two layers with a high acoustic impedance layer embedded in a material with a lower acoustic impedance. The high acoustic impedance material may be tungsten. The substrate material for establishing the material with a low acoustic impedance may be implemented as silicon dioxide.

[0055] The second functional structure FS 2 may be implemented as an electroacoustic active structure EAS, which includes (not explicitly shown) two electrodes in two electrode layers and a piezoelectric material in a piezoelectric layer sandwiched between the two electrode layers. The electroacoustic active structure excites sound waves, and since the acoustic mirror AM acts as a Bragg mirror and reflects acoustic energy to prevent energy dissipation in the carrier substrate CS, the energy of the sound waves is confined to the resonant structure.

[0056] Figure 3 Illustrates the possibility of providing the second functional structure FS 2 as a bottom electrode (the lower electrode of the two electrodes of the BAW resonator) arranged above the acoustic mirror. The bottom electrode BE provides a basis for further material deposition of the piezoelectric material of the resonator.

[0057] In the second layer stack, metallization is provided, which establishes the third functional structure FS 3 , and this third functional structure FS 3 becomes the base of a connection structure for electrically connecting the electroacoustic component to the external circuit environment. The bottom electrode BE and the third functional structure FS 3 may have the same layer structure, the same layer thickness, and the same number and material of layers.

[0058] Figure 4Illustrates the (preferred) possibility of providing the raised structure RS as a structure having the same configuration as the acoustic mirror stacked with the first layer. Thus, although the position of the raised structure does not require an acoustic function, the raised structure RS is provided as the acoustic mirror AM.

[0059] However, by implementing the acoustic mirror of the electroacoustic resonator and the raised structure RS as acoustic mirrors such that the two mirrors have the same configuration, the design and manufacture of the components are simplified, and since the structure of the raised structure can be implemented together with the structure of the acoustic mirror stacked with the first layer without additional processing steps, and the same vertical level can be obtained for the second functional structure and for the third functional structure.

[0060] Figure 5 Illustrates the possibility of providing the piezoelectric material PM in the piezoelectric layer and the top electrode TE in the top electrode layer on the bottom electrode BE in the first layer stack to establish the BAW resonator BAWR. In the second layer stack, the under bump metal UBM and the bump connection BU are arranged on the base B of the electrical connection EC to the external circuit environment (not shown).

[0061] Figure 6 Illustrates the origin of possible contact problems when the raised structure RS is not provided. To establish an acoustic mirror on the carrier substrate CS in the first layer structure, multiple interfaces between materials with different acoustic impedances are provided. For example, silicon dioxide is used as the material with a low acoustic impedance. Tungsten can be used as the material with a high acoustic impedance. A tungsten layer is locally applied on the silicon dioxide material layer. Then, the space next to the tungsten element is filled with silicon dioxide to form a matrix element composed of silicon dioxide. To have a planar surface for other layer deposition and structuring steps, a polishing step is performed. However, during polishing, for example, during CMP, the removal rate at positions far from the tungsten element is higher than that at positions close to the tungsten element. Correspondingly, a small vertical offset Δh is obtained. 1 If the corresponding steps are repeated to build multiple layers of the acoustic mirror, multiple corresponding small vertical steps Δh 1 sum up to the vertical offset Δh 2 In the final polishing step at the position of the later electrical contact EC, more material is removed again compared to the material at the position of the later BAW resonator. However, a certain amount of matrix material with a height of Δh 3 remains above the third functional structure. Especially when the matrix material is a dielectric material, contact problems occur.

[0062] Therefore, by providing the raised structure RS, the vertical level differences Δh 1 、Δh 2 and Δh 3 can be prevented, and the second functional structure FS at the same vertical position can be obtained.2 and a parallel alignment with the top surface of the third functional structure FS 3 without adding an undesired additional dielectric material above the third functional structure FS 3

[0063] Figure 7 The basic circuit topology of the duplexer DU is illustrated. The duplexer DU includes a transmit filter TXF and a receive filter RXF. The transmit filter TXF is typically connected between the transmit port and the antenna port connected to the antenna AN. The receive filter RXF is typically connected between the receive port and the antenna port. The transmit filter TXF and the receive filter RXF based on a similar ladder-shaped circuit topology have signal paths in which series resonators SR are connected in series electrically between the input port and the output port. Further, the parallel path includes parallel resonators PR that electrically connect the signal path to the ground potential.

[0064] To match the frequency-dependent impedance of the receive filter RXF, the transmit filter TXF, and / or the antenna, an impedance matching circuit IMC can be connected between the transmit filter TXF and the receive filter RXF, for example, at the antenna port.

[0065] List of reference numerals

[0066] AM: Acoustic mirror

[0067] AN: Antenna

[0068] B: Electrically connected base

[0069] BAWR: BAW resonator

[0070] BE: Bottom electrode

[0071] BU: Bump

[0072] CS: Carrier substrate

[0073] DU: Duplexer

[0074] EAS: Electroacoustic active structure

[0075] FS 1 、FS 2 、FS 3 : First functional structure, second functional structure, third functional structure IMC: Impedance matching circuit

[0076] LS 1 、LS 2 : First layer stack, second layer stack

[0077] M 1 : High acoustic impedance material, for example, tungsten ​

[0078] M 2 : Substrate material, low acoustic impedance material, e.g., silicon dioxide

[0079] PM: Piezoelectric material

[0080] PR: Parallel resonator

[0081] RS: Raised structure

[0082] RXF: Receive filter

[0083] SR: Series resonator

[0084] TE: Top electrode

[0085] TXF: Transmission filter

[0086] UBM: Under bump metallization

Claims

1. An electroacoustic component, comprising - a carrier substrate; - a first layer stack located on or above the carrier substrate; - a second layer stack located on or above the carrier substrate; wherein - the first layer stack includes a first functional structure and a second functional structure disposed on or above the first functional structure, - the second layer stack includes a raised structure and a third functional structure disposed on or above the raised structure, wherein the raised structure is designed such that the bottom surface of the third functional structure and the bottom surface of the second functional structure are in the same horizontal plane, wherein the raised structure includes elements of a pseudo-acoustic mirror, wherein the pseudo-acoustic mirror is an acoustic mirror configured to achieve local elevation and electrostatic shielding at the second layer stack, wherein: the first functional structure is an SMR-type BAW resonator; the second functional structure is an active element of the SMR-type BAW resonator; the raised structure is the pseudo-acoustic mirror of the SMR-type BAW resonator; and the third functional structure is a bump connection.

2. The electroacoustic component according to claim 1, wherein - the first functional structure includes elements of an acoustic mirror, - the second functional structure includes elements of an electroacoustic resonator.

3. The electroacoustic component according to claim 1 or 2, wherein - the third functional structure includes elements of an electrical connection.

4. The electroacoustic component according to claim 1 or 2, wherein the first functional structure and the raised structure have the same height.

5. The electroacoustic component according to claim 1 or 2, wherein the first functional structure and the raised structure have the same layer structure.

6. The electroacoustic component according to claim 1 or 2, wherein the first functional structure and the raised structure have the same configuration.

7. The electroacoustic component according to claim 1 or 2, wherein the first layer stack includes a BAW resonator.

8. The electroacoustic component according to claim 1 or 2, wherein the raised structure provides an electrical function.

9. An RF filter, comprising an electroacoustic component according to any one of claims 1-8, and further comprising additional electroacoustic resonators.

10. A method of manufacturing an electroacoustic component, comprising the steps of: - providing a carrier substrate; - disposing a first functional structure and a raised structure on or above the carrier substrate; - disposing a second functional structure on or above the first functional structure; - disposing a third functional structure on or above the raised structure such that the bottom surface of the third functional structure and the bottom surface of the second functional structure are in the same horizontal plane, wherein the second layer stack of the electroacoustic component includes the raised structure and the third functional structure, wherein the raised structure includes elements of a pseudo-acoustic mirror, wherein the pseudo-acoustic mirror is an acoustic mirror configured to achieve local elevation and electrostatic shielding at the second layer stack, wherein: the first functional structure is an SMR-type BAW resonator; the second functional structure is an active element of the SMR-type BAW resonator; the raised structure is the pseudo-acoustic mirror of the SMR-type BAW resonator; and The third functional structure is bump connection.

11. The method according to claim 10, further comprising: Partially removing the material of the intermediate layer under the third functional structure.

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