BAW COMPONENT, LAMINATION FOR A BAW COMPONENT, AND METHOD FOR MANUFACTURING A BAW COMPONENT, SAID BAW COMPONENT COMPRISING TWO

STACKED PIEZOELECTRIC MATERIALS THAT DIFFER

The present invention refers to BAW components, e.g. for use in RF filters for mobile communication devices, to lamina ^¬ tions for BAW components, and to methods for manufacturing BAW components.

The present trend towards miniaturization of mobile communi ^¬ cation devices demands for smaller electric and electro- acoustic components. BAW (BAW = bulk acoustic wave) compo ^¬ nents can be used in RF filters, e.g. in duplexers in front- end modules of mobile communication devices. A duplexer usu ^¬ ally comprises a TX (transmission) and an RX (reception) filter. The TX filter and the RX filter are band pass filters with adjacent but different pass bands. An important factor determining the pass band of a BAW pass band filter is the thickness of piezoelectric material arranged between two electrode layers of a resonator of the filter and the mass loading of a resonator.

One type of conventional BAW duplexers has different piezo- electric material thicknesses for the TX filter and for the

RX filter. Accordingly, the two filters are manufactured with different processes and on different carrier chips.

Another type of conventional BAW duplexers has additional mass, e. g. additional layers on the upper electrode, depos ^¬ ited on selected resonators to reduce their respective reso ^¬ nance frequency. The method for manufacturing for both types are relative complex, expensive and susceptible to errors. In particular, conventional duplexers have TX and RX filters on different carrier chips what is contrary to the miniaturization ef- forts.

What is needed is a BAW component where two BAW layer stacks can be easily arranged on the same chip to obtain a miniatur ^¬ ized BAW filter and where the composition of the component allows improved manufacturing methods to increase the gain of good components. What is further needed is a lamination for a BAW component and a method for manufacturing such a BAW component . It is, thus, an object of the present invention to provide an improved BAW component, a lamination for a BAW component, and a method for manufacturing a BAW component.

The independent claims provide a solution for the above-men- tioned problems. Dependent claims provide preferred embodi ^¬ ments .

A BAW component comprises a first BAW resonator with a bottom electrode, a top electrode, and a lamination between the bot- torn electrode and the top electrode. The lamination comprises a first layer with a first piezoelectric material and a sec ^¬ ond layer with a second piezoelectric material. The first piezoelectric material differs from the second piezoelectric material .

The two different materials of the lamination can have dif ^¬ ferent physical and/or chemical properties. The first BAW resonator can be arranged on a carrier chip next to a second BAW resonator comprising the first piezoelectric material or the second piezoelectric material between a bottom electrode and a top electrode. The thickness of the piezoelectric mate ^¬ rial of the second BAW resonator can be equal to the thick- ness of the layer of the first BAW resonator with the same piezoelectric material. Then, the first BAW resonator has a different resonance frequency and can provide a different pass band due to the presence of the respective other piezo ^¬ electric material of the lamination not comprised in the sec- ond BAW resonator.

Such a BAW component can be manufactured with a high quality of the materials atomic structure as described below. In one embodiment the first BAW resonator is arranged on a carrier chip next to a second BAW resonator comprising the first piezoelectric material a bottom electrode and a top electrode. The thicknesses of the layer with the first material in both resonators are equal.

In one embodiment, thus, the BAW component further comprises a carrier chip and a second BAW resonator. The first BAW resonator and the second BAW resonator are arranged on the same carrier chip.

In one embodiment thereof, the lamination of the first BAW resonator has a first thickness and the second BAW has a pie ^¬ zoelectric layer with a second thickness different from the first thickness.

The BAW resonator having the thicker piezoelectric layer can be utilized in a filter having the lower pass band and vice- versa. Thus, it is possible to utilize the first BAW resona- tor in a TX filter and the second BAW resonator in an RX filter .

In one embodiment, the first piezoelectric material and the second piezoelectric material have a different etching selec ^¬ tivity with respect to an etching agent.

This allows to deposit the piezoelectric material comprised by both resonators in the same manufacturing step and with the same layer thickness. The respective other piezoelectric material of the first BAW resonator can be deposited at the area of both BAW resonators. Then, the area of the first BAW resonator can be covered with a resist layer and an etching agent can etch the other piezoelectric material away from the area of the second resonator. The first piezoelectric mate ^¬ rial acts as an etch stop layer for the etching agent. After the etching process, the respective top electrodes can be ar ^¬ ranged on the piezoelectric materials of both resonators. In one embodiment, the etching agent is a wet etching agent.

In one embodiment, the etching agent is a metal iron-free de ^¬ veloper that can also be used for photolithographic proc ^¬ esses. It is possible that the etching agent comprises 2,36% Tetramethyl amonium hydroxyl in combination with a wetting agent

In one embodiment the etching agent is a dry etching agent. In one embodiment, the first piezoelectric material is Sc (scandium) doped A1N (aluminum nitride) , and the second piezoelectric material is A1N. Thus, a lamination for a BAW component can have a first layer comprising Sc doped AIN and a second layer comprising AIN.

Other possible materials for the first piezoelectric material or for the second piezoelectric material are GaAs (gallium arsenide), ZnO (zinc oxide), PZT (lead zirconate titanate) , KNN ( (K( i- _x) Na _x ) Nb0 ₃ ) (with K: Kalium, Na : Sodium, Nb : Niobium, 0 : Oxygen) . The doping level of Sc _x Al( i- _y) N can be approx. 1% <= x <= 25% with y mainly equal to x. Especially a level of approx. 5% <= x <= 7% is possible.

In one embodiment, the component is a duplexer and the first resonator is a resonator of the TX filter of the duplexer.

The BAW component can be a Bragg-Mirror based component or or a FBAR component with a cavity under the lamination for confining acoustic energy.

Further variants, e.g. MEMS components comprising lever structures, are also possible. For instance, the component can comprise a piezo MEMS switch. A component with more than one switch is also possible. In an embodiment comprising two switches both switches can be made a single carrier chip. The first cantilever can have one piezoelectric layer while the second cantilever has two piezoelectric layers. Therefore, it is possible to process on the same chip two switches having two different closing voltages.

A method for manufacturing a BAW component comprises the steps :

- providing a bottom electrode, - arranging a first piezoelectric material on or above the bottom electrode,

- arranging a second piezoelectric material different from the first piezoelectric material on or above the first piezo- electric material,

- arranging a top electrode on or above the second piezoelec ^¬ tric material.

It is possible that these steps establish a first BAW resona- tor. A second BAW resonator can be established next to the first BAW resonator where the two steps:

- providing a bottom electrode;

- arranging a first piezoelectric material on or above the bottom electrode;

for establishing the first BAW resonator are also utilized to establish the second BAW resonator.

In order to arrange the second piezoelectric material on the first BAW resonator only, further photolithographic steps, e.g. via the use of a resist layer, can be applied.

In one embodiment, the method further comprises the step:

- selectively removing the second piezoelectric material at a previously specified area before arranging material of the top electrode on or above the first piezoelectric material in the specified area and on or above the second piezoelectric material in a further area located nearby the specified area. The previously specified area is the area of the second reso ^¬ nator and the further area is the area of the first resona ^¬ tor . Compared to other methods for manufacturing a BAW component and/or a BAW duplexer, the present method yields layer sys ^¬ tems with a higher layer quality resulting in improved electro-acoustic properties as parameters, e.g. the electro- acoustic coupling coefficient κ ² , are enhanced.

Such a BAW component can be utilized to obtain a BAW resona ^¬ tor having a different resonance frequency than other resona ^¬ tors. Different resonance frequencies can be needed for TX and RX filters in duplexers . However, such differences in resonance frequencies can also be needed in ladder type fil ^¬ ter structures where series resonators need to have a differ ^¬ ent frequency compared to parallel branch resonators. When the anti-resonance frequency of parallel resonators mainly match the resonance frequency of serial branch resonators in a ladder type structure, then a band pass filter is obtained. When the resonance frequency of parallel branch resonators matches the anti-resonance frequency of serial branch resona ^¬ tors, then a band stop filter of a notch filter can be ob- tained.

The two deposition steps relating to the first piezoelectric material and to the second piezoelectric material respec ^¬ tively can be done in situ or with a vacuum break. Even with a vacuum break during the different deposition steps good layer quality is obtained.

Examples of BAW components, laminations and methods for manu ^¬ facturing and the respective working principles are shown in the schematic figures.

Short description of the figures: FIG. 1 shows a basic BAW resonator stack with a lamination L,

FIG. 2 shows a BAW component with two BAW resonator

stacks,

FIG. 3 shows elements of a BAW component comprising acous ^¬ tic mirrors, FIG. 4 shows a stage of a manufacturing process,

FIG. 5 shows a stage of a manufacturing process,

FIG. 6 shows a stage of a manufacturing process,

FIG. 7 shows a final stage of a manufacturing process,

FIG. 8 shows a component with piezoelectric switches with different closing voltages.

FIG. 1 shows a BAW component BAWC comprising a lamination L between a bottom electrode BE and a top electrode TE . The lamination comprises a first layer with a first piezoelectric material PMl and a second layer with a second piezoelectric material PM2. The second piezoelectric material PM2 is ar ^¬ ranged between the first piezoelectric material PMl and the top electrode TE . The first piezoelectric material PMl is different from the second piezoelectric material PM2. This allows high quality BAW components with more than one BAW resonators on a common carrier chip where different resona ^¬ tors have different resonance frequencies. FIG. 2 shows a BAW component BAWC where a first BAW resonator BAWR1 is arranged next to a second BAW resonator BAWR2. Both resonators can be arranged on or above a carrier substrate CS . Both resonators comprise a bottom electrode BE and a top electrode TE and the first piezoelectric material PM1. Only the first BAW resonator BAWR1 comprises a second piezoelec ^¬ tric material PM2. The piezoelectric material of the first BAW resonator BAWR1 is thicker than the piezoelectric material of the second resonator BAWR2. Thus, both resonators have different resonance frequencies although they can be manufactured with easy to perform manufacturing steps one next to the other on or above a common carrier substrate CS .

FIG. 3 shows main components of a BAW component BAWC where mainly the top electrode is omitted. Two resonator stacks are arranged on respective acoustic mirrors AM. The acoustic mir ^¬ rors AM comprise a layer system with alternating high and low acoustic impedance. The acoustic mirror AM confines acoustic energy and allows to establish a resonance mode of the re- spective resonator.

FIG. 4 shows a stage during one of several possible

manufacturing processes where two resonator stacks are arranged next to another on a common carrier substrate CS . After depositing and structuring a bottom electrode BE, the first piezoelectric material PM1 is deposited and structured on the bottom electrode BE for both resonator stacks.

It may not be necessary to structure one or more layers.

FIG. 5 shows a further stage of a manufacturing process where a second piezoelectric material PM2 is arranged on the first piezoelectric material. However, the second piezoelectric ma- terial PM2 is only needed in one of the resonator stacks and needs to be removed in the respective other resonator stack.

Accordingly, FIG. 6 shows a stage where a resist film RES is arranged on the lamination of the first resonator. The resist film RES protects the lamination of the later first resonator BAWR1 but the piezoelectric material PM2 is removed from the second resonator stack, the later second resonator BAWR2, shown on the left. Different properties of the different pie- zoelectric materials ensure that an etching agent etches the second piezoelectric material in such a way that the etching process stops when the second piezoelectric material PM2 is completely removed. The upper surface of the first piezoelec ^¬ tric material of the left resonator stack establishes an etch stop zone for the process.

FIG. 7 shows a final manufacturing stage where a top elec ^¬ trode TE has been deposited and structured on both resonator stacks .

FIG. 8 shows a BAW component where a lamination comprising a first piezoelectric material PM1 and a second piezoelectric material PM2 are arranged between a bottom electrode BE and a top electrode TE to establish a cantilever shaped switch SW1. The switch is arranged next to a switch SW2 without the second piezoelectric material PM2. The different

constructions of the two switches allow different closing voltages . Neither the BAW component nor the lamination for a BAW component nor the method for manufacturing a BAW component are limited to the embodiments described in the specification or shown in the figures. Components, laminations and methods comprising further materials or layers or components compris ^¬ ing further resonators or methods comprising further deposition steps or etching steps or combinations thereof are also comprised by the present invention.

List of reference signs:

AM: acoustic mirror

BAWC: BAW component

BAWR1 : first BAW resonator

BAWR2 : second BAW resonator

BE: bottom electrode

CS : carrier substrate

L: lamination

PM1 : first piezoelectric material

PM2 : second piezoelectric material

RES: resist film

SW1, SW2 : switch

TE : top electrode