ELECTRO ACOUSTIC COMPONENT, RF FILTER AND METHOD OF MANUFACTURING

Abstract

Electro acoustic 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 (TE, BM, PE) arranged on or above the first functional structure, —the second layer stack comprises a raising structure (RS) and a third functional structure (BU, UBM, B) arranged on or above the raising structure, —the raising structure raises the third functional structure to the vertical level of the second functional structure.

Claims

1. An electro acoustic component, comprising a carrier substrate, a first layer stack on or above the carrier substrate, a second layer stack on or above the carrier substrate, wherein the first layer stack comprises a first functional structure and a second functional structure arranged on or above the first functional structure, the second layer stack comprises a raising structure and a third functional structure arranged on or above the raising structure, the raising structure raises the third functional structure to the vertical level of the second functional structure.

2. The electro acoustic component of claim 1, wherein the first functional structure comprises an element of an acoustic mirror, the second functional structure comprises an element of an electro acoustic resonator, the raising structure comprises an element of a dummy acoustic mirror.

3. The electro acoustic component of one of claim 1, wherein the third functional structure comprises an element of an electrical connection.

4. The electro acoustic component of one of claim 1, wherein the first functional structure and the raising structure have the same height.

5. The electro acoustic component of claim 1, wherein the first functional structure and the raising structure have the same layer construction.

6. The electro acoustic component of claim 1, wherein the first functional structure and the raising structure have the same construction.

7. The electro acoustic component of claim 1, wherein the first layer stack comprises a BAW resonator.

8. The electro acoustic component of claim 1, wherein the first functional structure is an SMR-type BAW resonator, the second functional structure is the active element of the SMR-type BAW resonator. the raising structure is a dummy acoustic mirror of an SMR-type BAW resonator and the third functional structure is a bump connection.

9. The electro acoustic component of claim 1, wherein the raising structure provides an electrical functionality.

10. The electro acoustic component of claim 1, wherein the electro acoustic component is part of an RF filter, the RF filter including one or more additional electro acoustic resonators.

11. A method of manufacturing an electro acoustic component, comprising: providing a carrier substrate, arranging a first functional structure and a raising structure on or above the carrier substrate, arranging a second functional structure on or above the first functional structure, and arranging a third functional structure on or above the raising structure at the vertical level of the second functional structure.

12. The method of claim 11, further comprising partially removing material of an intermediate layer below the third functional structure.

Description

[0044] In the figures:

[0045] FIG. 1 shows a cross-section of a corresponding component;

[0046] FIG. 2 shows an acoustic mirror as the first functional structure;

[0047] FIG. 3 shows metallization structures for the second and the third functional structures;

[0048] FIG. 4 shows a dummy acoustic mirror as the raising structure;

[0049] FIG. 5 shows the first layer stack establishing a BAW resonator and the second layer stack establishing an external connection;

[0050] FIG. 6 illustrates possible problems with polishing processes and a local disturbance of the component's symmetry; and

[0051] FIG. 7 shows a duplexer comprising two bandpass filters based on a ladder-type like circuit topology.

[0052] FIG. 1 shows a cross-section through a schematic electro acoustic component. The component has a carrier substrate CS on which the further structures are arranged. The carrier substrate CS acts as a common carrier for the additional structures of the electro acoustic component. A first layer stack LS1 and a second layer stack LS2 are arranged one next to another on the carrier substrate CS. The first layer stack LS1 comprises a first functional structure FS1 and a second functional structure FS2. The second layer stack LS2 comprises the raising structure RS and the third functional structure FS3. It is possible that the first functional structure FS1 and the raising structure RS are embedded in a matrix material. The provision of the raising structure RS allows to provide the second functional structure FS2 at the same vertical position as the third functional structure FS3. Thus, the distance between the carrier substrate CS and the second functional structure FS2 essentially equals the distance between the carrier substrate CS and the third functional structure FS3. The matrix material can have a plane surface. Specifically, the surface of the matrix material can be parallel to the top surface of the carrier substrate CS. However, it is possible that the thickness of the matrix material locally varies. Specifically, it is possible that the vertical level of the matrix material at the position where the first functional structure FS1 is arranged is higher than in an area surrounding the first functional structure FS1. However, by providing the raising structure RS the corresponding height level of the surface of the matrix material essentially equals the height level of the matrix material at the place of the first functional structure FS1.

[0053] FIG. 2 shows the possibility of realizing the first functional structure FS1 as an acoustic mirror AM. An acoustic mirror comprises two or more layers. Adjacent layers—with respect to the vertical direction—have different acoustic impedances. Correspondingly, FIG. 2 illustrates an acoustic mirror comprising two layers of high acoustic impedance being embedded in material of a lower acoustic impedance. The material of high acoustic impedance can be tungsten. The matrix material establishing the material of the low acoustic impedance can be realized as a silicon dioxide.

[0054] The second functional structure FS2 can be realized as an electro acoustically active structure EAS comprising (not explicitly shown) two electrodes in two electrode layers and a piezoelectric material in a piezoelectric layer sandwiched between the two electrode layers. The electro acoustically active structure excites acoustic waves, the energy of which is confined to the resonating structure due to the acoustic mirror AM acting as a Bragg mirror and reflecting the acoustic energy to prevent energy dissipation in the carrier substrate CS.

[0055] FIG. 3 illustrates the possibility of providing the second functional structure FS2 as the bottom electrode (the lower of the two electrodes of a BAW resonator) arranged above the acoustic mirror. The bottom electrode BE establishes the base for further material deposition of the piezoelectric material of the resonator.

[0056] In the second layer stack a metallization is provided establishing the third functional structure FS3 that will be the base for the connection structure for electrically connecting the electro acoustic component to an external circuit environment. The bottom electrode BE and the third functional structure FS3 can have the same layer construction, the same layer thickness and the same number of layers and the same layer materials.

[0057] FIG. 4 shows the (preferred) possibility of providing the raising structure RS as a structure having the same construction like the acoustic mirror of the first layer stack. Thus, the raising structure RS is provided as an acoustic mirror AM although the position of the raising structure no acoustic functionality is necessary.

[0058] However, by realizing the acoustic mirror of the electro acoustic resonator and the raising structure RS as an acoustic mirror such that both mirrors have the same construction, designing and manufacturing of the component is simplified and as the structures of the raising structure can be realized together with the structures of the acoustic mirror of the first layer stack no additional processing steps are needed and a same vertical level for the second functional structure and for the third functional structure can be obtained.

[0059] FIG. 3 illustrates the possibility of providing the piezoelectric material PM in a piezoelectric layer and the top electrode TE in a top electrode layer on the bottom electrode BE in the first layer stack to establish a BAW resonator BAWR. In the second layer stack an under bump metallurgy UBM and a bump connection BU are arranged on the base B of the electrical connection EC to an external circuit environment (not shown).

[0060] FIG. 6 illustrates the origin of a possible contact problem when no raising structure RS would be provided. To establish the acoustic mirror on the carrier substrate CS in the first layer structure a plurality of interfaces between materials of different acoustic impedances are provided. For example silicon dioxide is used as the material of the low acoustic impedance. Tungsten can be used as the material of the high acoustic impedance. On a layer of silicon oxide material of a tungsten layer is locally applied. Then, the space next to the tungsten element is filled with silicon dioxide to proceed with the matrix element consisting of the silicon dioxide. To have a plane surface for further layer deposition and structuring steps a polishing step is performed. However, during the polishing, e.g. during CMP, the removal rate at a position far from the tungsten element is higher than at a position near the tungsten. Correspondingly, a small vertical offset Δh1 is obtained. If the corresponding steps are repeated to establish the plurality of layers of the acoustic mirror then the plurality of corresponding small vertical steps Δh1 sum up to a vertical offset Δh2. In a last polishing step at the position of the later electrical contact EC, again, more material is removed than at the position of the later BAW resonator. However, a certain amount of matrix material having a height of Δh3 remains above the third functional structure. Especially when the matrix material is a dielectric material, then contacting problems would arise.

[0061] Thus, by providing the raising structure RS the vertical level differences Δh1, Δh2 and Δh3 can be prevented and a parallel alignment of the top surfaces of the second functional structure FS2 and of the third functional structure FS3 at the same vertical position can be obtained without unwanted additional dielectric material above the third functional structure FS3.

[0062] FIG. 7 illustrates a basic circuit topology of a duplexer DU. The duplexer DU comprises a transmission filter TXF and a reception filter RXF. The transmission filter TXF usually is connected between a transmission port and an antenna port connected to an antenna AN. The reception filter RXF is typically connected between a reception port and the antenna port. The transmission filter TXF and the reception filter RXF base on a ladder-type like circuit topology having a signal path with series resonators SR electrically connected in series between an input port and an output port. Further, parallel paths comprise parallel resonators PR electrically connecting the signal path to a ground potential.

[0063] In order to match the frequency-dependent impedances of the reception filter RXF, the transmission filter TXF and/or the antenna, an impedance matching circuit IMC can be connected between the transmission filter TXF and the reception filter RXF, e.g. at the antenna port.

LIST OF REFERENCE SIGNS

[0064] AM: acoustic mirror [0065] AN: antenna [0066] B: base of electric connection [0067] BAWR: BAW resonator [0068] BE: bottom electrode [0069] BU: bump [0070] CS: carrier substrate [0071] DU: duplexer [0072] EAS: electro acoustically active structure [0073] FS1, FS2, FS3: first, second, third functional structure [0074] IMC: impedance matching circuit [0075] LS1, LS2: first, second layer stack [0076] M1: material of high acoustic impedance, e.g. tungsten [0077] M2: matrix material, material of low acoustic impedance, e.g. silicon dioxide [0078] PM: piezoelectric material [0079] PR: parallel resonator [0080] RS: raising structure [0081] RXF: reception filter [0082] SR: series resonator [0083] TE: top electrode [0084] TXF: transmission filter [0085] UBM: under bump metallurgy