Acoustic resonator, and method for manufacturing an acoustic resonator

Abstract

The invention relates to an acoustic resonator comprising: a first electrode (10a) and a second electrode (10b); a layer stack (12) arranged between the first electrode (10a) and the second electrode (10b), the layers (14a-14c) of said stack having at least two piezoelectric layers (14a-14c); and an acoustic reflector device (18), wherein a working frequency (fw) of the acoustic resonator is defined as the frequency (fw) of an electromagnetic wave which is incoming through the first electrode (10a) and for which the acoustic resonator is transparent, this being achieved as a result of the at least two piezoelectric layers (14a-14c) of the layer stack (12) having an equal or specific layer thickness (d) along the direction extending from the first electrode (10a) to the second electrode (10b), where d = λa(fw) / 2, wherein λa(fw) is an acoustic wavelength of a sound wave (22) at the working frequency (fw) in the relevant piezoelectric layer (14a-14c).

Description

[0001] Description

[0002] title

[0003] Acoustic resonator and manufacturing method for an acoustic resonator

[0004] The invention relates to an acoustic resonator. The invention also relates to a manufacturing method for an acoustic resonator.

[0005] State of the art

[0006] US 2018 / 0085787 A1 describes acoustic resonator devices, each comprising a first electrode, a second electrode, a third electrode, a first piezoelectric layer arranged between the first electrode and the second electrode, and a second piezoelectric layer arranged between the second electrode and the third electrode. A polarization of the respective first piezoelectric layer is oriented opposite to a polarization of the respective second piezoelectric layer of the same acoustic resonator device.

[0007] Disclosure of the invention

[0008] The present invention provides an acoustic resonator having the features of claim 1 and a manufacturing method for an acoustic resonator having the features of claim 10.

[0009] Advantages of the invention

[0010] The present invention provides acoustic resonators which are advantageously suitable for filtering incoming electromagnetic waves. A frequency f of an incoming electromagnetic wave, for which an acoustic resonator according to the invention is permeable, i.e. a so-called operating frequency of the respective acoustic resonator, can be determined by means of the at least two piezoelectric layers of the respective acoustic resonator, wherein the layer stack comprising the at least two piezoelectric layers can be made comparatively high. Thus, a distance between a first electrode of the acoustic resonator according to the invention and a second electrode of the same acoustic resonator is also comparatively large, which ensures a relatively low capacitance of the acoustic resonator even with its comparatively large component area.Conventional problems associated with a relatively small component area, such as, in particular, the loss of comparatively large amounts of acoustic energy at the edge of an acoustic resonator device according to the prior art, therefore do not have to be accepted with the acoustic resonator according to the invention. Even if the acoustic resonator according to the invention has a comparatively high operating frequency, such as an operating frequency of over 10 GHz (gigahertz), its ohmic and acoustic losses are still relatively low. The present invention thus creates a possibility for developing higher frequency ranges with a higher k. t 2 * Q-product as the operating frequency of an acoustic resonator without significant loss of its acoustic energy.

[0011] As will also become clear from the following description, the present invention enables the development of higher operating frequencies for comparatively simple acoustic resonators, which can be manufactured relatively inexpensively. In such an acoustic resonator, its ohmic losses are reduced and the Q factor is increased. Furthermore, such an acoustic resonator ensures high electromechanical interaction, so that a high energy content of an acoustic wave occurring in the respective acoustic resonator is retained. Therefore, the k t 2 -value is high. A comparatively low capacitance density of the acoustic resonator according to the invention also enables relatively low acoustic energy losses in the lateral direction.

[0012] In an advantageous embodiment of the acoustic resonator, the first electrode and / or the second electrode each have an electrode thickness JE along the direction extending from the first electrode to the second electrode, for which JE = n* XaE(fw) / 2 applies, where X a E(fw) is an acoustic wavelength of the sound wave with the working frequency f w in the respective first or second electrode and n is a natural number greater than or equal to one. The working frequency f can also be determined by means of the design of the first electrode and / or the second electrode described here. w as frequency f w of electromagnetic waves for which the acoustic resonator is permeable.

[0013] Advantageously, the first electrode and / or the second electrode can be formed from aluminum and / or titanium. The first electrode and / or the second electrode can thus be formed from at least one material with a comparatively low density, which allows the respective electrode thickness d| to be an integer multiple of half an acoustic wavelength X a E(fw) / 2 facilitated.

[0014] As an advantageous development, the layers of the layer stack can comprise at least one intermediate layer in addition to the at least two piezoelectric layers, wherein the at least one intermediate layer of the layer stack has a respective intermediate layer thickness d along the direction extending from the first electrode to the second electrode, for which di_ = m* X a L(f w ) / 2, where aL(fw) is an acoustic wavelength of the sound wave with the working frequency f win the respective intermediate layer and m is a natural number greater than or equal to one. As will become clear from the following description, the insertion of at least one intermediate layer into the layer stack enables additional optimization of the embodiment of the acoustic resonator described here.

[0015] For example, the individual intermediate layer or at least one of the intermediate layers of the layer stack can be formed from silicon oxide, silicon nitride, silicon carbide, aluminum oxide, and / or diamond-like carbon. Such an intermediate layer can increase the quality factor of acoustic vibrations within the layer stack and ensure better parasitic mode suppression in the layer stack. Furthermore, a thermal expansion coefficient of such an intermediate layer can be easily adapted to the at least one thermal expansion coefficient of the at least one adjacent piezoelectric layer.

[0016] Alternatively or additionally, the individual intermediate layer or at least one of the intermediate layers of the layer stack can each be a reflector layer sequence of reflector layers, wherein the reflector layers of the respective reflector layer sequence have a respective reflector layer thickness d Ralong the direction extending from the first electrode to the second electrode, for which d R = (2R - 1 ) * aR.(fw) / 4, where X a R.(fw) is an acoustic wavelength of the sound wave with the working frequency f w in the respective reflector layer and R is a natural number greater than or equal to one. The advantages described in the previous paragraph can also be realized using such an intermediate layer.

[0017] Preferably, the layer stack has a total number G of layers equal to 2Z + 1 and Z is a natural number greater than or equal to one, wherein a respective layer thickness d or d of each of the G layers of the layer stack is equal to X a (f w ) / 2, provided that the respective layer is a piezoelectric layer, or equal to m * X a L(f w) / 2, provided that the respective layer is not a piezoelectric layer, but an intermediate layer. Such a layer stack realizes a reliable and precise determination of the operating frequency f w of the acoustic resonator.

[0018] Preferably, the at least two piezoelectric layers of the layer stack comprise the same base material. This facilitates the formation of the layer stack.

[0019] For example, the at least two piezoelectric layers of the layer stack can be formed from aluminum nitride, scandium aluminum nitride, zinc oxide, lithium niobate, and / or lithium tantalate. Thus, a variety of advantageous piezoelectric materials can be used for the at least two piezoelectric layers of the layer stack.

[0020] Implementing a corresponding manufacturing method for an acoustic resonator also provides the advantages described above. It is expressly noted that the manufacturing method can be further developed according to the above-described embodiments of the acoustic resonator.

[0021] Short description of the drawings

[0022] Further features and advantages of the present invention are explained below with reference to the figures. Figure 1 shows a schematic representation of a first embodiment of the acoustic resonator;

[0023] Fig. 2 is a schematic representation of a second embodiment of the acoustic resonator;

[0024] Fig. 3 is a schematic representation of a third embodiment of the acoustic resonator;

[0025] Fig. 4 is a schematic representation of a fourth embodiment of the acoustic resonator; and

[0026] Fig. 5 is a flowchart for explaining an embodiment of the

[0027] Manufacturing process for an acoustic resonator.

[0028] Embodiments of the invention

[0029] Fig. 1 shows a schematic representation of a first embodiment of the acoustic resonator.

[0030] The acoustic resonator schematically illustrated in Fig. 1 has a first electrode 10a and a second electrode 10b. The first electrode 10a and the second electrode 10b can, in particular, be aligned parallel to one another. Between the first electrode 10a and the second electrode 10b there is a layer stack 12, which can also be referred to as a piezoelectric layer stack. The layer stack 12 is arranged between the first electrode 10a and the second electrode 10b such that its layers 14a to 14c are arranged one after the other along a direction extending from the first electrode 10a to the second electrode 10b. In addition, the layers 14a to 14c of the layer stack 12 comprise at least two piezoelectric layers 14a to 14c, of which at least two piezoelectric layers 14a to 14c directly adjoin one another.

[0031] As schematically shown by the arrows 16a and 16b, the at least two piezoelectric layers 14a to 14c of the layer stack 12 are polarized. The respective polarization 16a or 16b of the at least two directly adjacent piezoelectric layers 14a to 14c of the layer stack 12 is determined such that a respective polarization 16a or 16b of each of the at least two directly adjacent piezoelectric layers 14a to 14c of the layer stack 12 is oriented opposite to a respective polarization 16a or 16b of the at least one directly adjacent piezoelectric layer 14a to 14c of the layer stack 12. For example, in the example of Fig. 1, the piezoelectric layer 14b lying between the piezoelectric layers 14a and 14c has a polarization 16b which is oriented opposite to a polarization 16a of the directly adjacent piezoelectric layers 14a and 14c.

[0032] The acoustic resonator also comprises an acoustic reflector device 18, which is located on a side of the first electrode 10a facing away from the layer stack 12 or on a side of the second electrode 10b facing away from the layer stack 12. For example, in the embodiment described here, the acoustic reflector device 18 is arranged / configured on the side of the second electrode 10b facing away from the layer stack 12. The design of the acoustic reflector device 18 as an acoustic Bragg reflector stack, illustrated in Fig. 1, is not to be interpreted as exhaustive. Likewise, the arrangement of the acoustic reflector device 18 between the second electrode 10b and a substrate surface 20a of a substrate 20 is only an example. The substrate 20 can, for example, be a semiconductor substrate, specifically a silicon substrate. In the embodiment of Fig.1, the first electrode 10a is thus located on a side of the layer stack 12 facing away from the substrate, while the second electrode 10b is arranged on a side of the layer stack 12 facing the substrate.

[0033] As will become clear from the following description, the acoustic resonator shown in Fig. 1 is designed for an electromagnetic wave with a specific frequency f arriving via the first electrode 10a. w , which is referred to as the working frequency f w of the acoustic resonator is permeable. The acoustic resonator can therefore be used to filter out electromagnetic waves whose frequencies are different from the operating frequency f wcan be used advantageously. An electromagnetic wave arriving via the first electrode 10a is converted at the first electrode 10a by at least the adjacent first piezoelectric layer 14a into a schematically reproduced sound wave / acoustic wave 22, wherein a frequency of the sound wave 22 is equal to a frequency of the incoming electromagnetic wave. (The pictorial representation of the sound wave 22 with the operating frequency f w in Fig. 1 is to be interpreted only as an example.) By means of the acoustic reflector device 18, the acoustic resonator is largely acoustically decoupled from the substrate 20, while at the first electrode 10a an impedance jump to air for the necessary acoustic inclusion of the sound wave 22 with the working frequency f w A sound wave 22 transmitted through the layer stack 12 with the working frequency f wis converted back into an electromagnetic wave at the second electrode 10b. The electrodes 10a and 10b can therefore also be referred to as electrodes 10a and 10b that acoustically resonate with the layer stack 12. However, if the electromagnetic wave arriving via the first electrode 10a has a frequency different from the operating frequency f w , the respective electromagnetic wave is reflected. The acoustic resonator described here therefore represents a volume acoustic resonator element, which is advantageously suited for a variety of applications listed below.

[0034] The operating frequency f w, for which the acoustic resonator is permeable, is determined in that the at least two piezoelectric layers 14a to 14c of the layer stack 12 each have an equal or specific layer thickness d along the direction extending from the first electrode 10a to the second electrode 10b, for which d = X a (f w ) / 2 applies. X a (f w ) is an acoustic wavelength of the sound wave 22 with the working frequency f w in the respective piezoelectric layer 14a to 14c. The acoustic wavelength X a (f w ) of the sound wave with the working frequency f w is defined according to equation (Eq. 1) with:

[0035] (Eq. 1) X a (f w ) = c a (f w ) / f w , where c a (f w) is a speed of sound of the sound signal 22 in the respective piezoelectric layer 14a to 14c. The respective layer thickness d of the at least two piezoelectric layers 14a to 14c of the layer stack 12 along the direction extending from the first electrode 10a to the second electrode 10b can therefore also be specified using equation (Eq. 2): Below the acoustic wavelength X a (f w ) and the speed of sound c a (f w ) of the sound signal 22 in the respective piezoelectric layer 14a to 14c are to be understood as variables that depend (also) on the material properties of the respective piezoelectric layer 14a to 14c. The respective layer thickness d of the at least two piezoelectric layers 14a to 14c of the layer stack 12 thus also depends on the material from which the respective piezoelectric layer 14a to 14c is formed.

[0036] The formation of the at least two piezoelectric layers 14a to 14c of the layer stack 12 such that their respective layer thickness d is equal to half an acoustic wavelength k a (f w ) / 2 allows the layer stack 12 to be formed with a relatively large height h along the direction extending from the first electrode 10a to the second electrode 10b. This results in a lower capacitance density than in conventional BAW resonators with only one piezo layer. Thus, even at an operating frequency f w in a range greater than or equal to 10 GHz (gigahertz), there is a need to downscale the lateral dimensions of the acoustic resonator (ie dimensions perpendicular to the direction extending from the first electrode 10a to the second electrode 10b) in order to achieve a reduction in the operating frequency f wThis compensates for the increase in capacitance caused by the increase in capacitance. Even with the comparatively large lateral dimensions of the acoustic resonator shown in Fig. 1, an electrical target impedance value of approximately 50 ohms can be easily achieved. Due to the comparatively large lateral dimensions of the acoustic resonator, the ratio of the periphery of the acoustic resonator to the area of ​​the acoustic resonator remains advantageous, so that only relatively low acoustic energy losses occur at the acoustic resonator. Finally, the energy density in the resonator decreases, allowing the resonator to be subjected to higher power without nonlinearities occurring.

[0037] The alternating polarization of the piezoelectric layers 14a to 14c in the layer stack 12 ensures good fulfillment of the resonance conditions and good suppression of secondary modes. Due to the alternating polarities 16a and 16b of the piezoelectric layers 14a to 14c along the direction extending from the first electrode 10a to the second electrode 10b, it is also reliably ensured that each sound wave 22 at the operating frequency f wcan be excited in phase by an electric field applied to the electrodes 10a and 10b. This can also be described as ensuring efficient simultaneous excitation of positive and negative acoustic half-waves in the respective piezoelectric layers 14a to 14c due to the opposite polarities 16a and 16b of the layer stack. Consequently, the loss of electromechanical coupling resulting from the smaller electric field can be reliably compensated by the increased height h of the layer stack 12.

[0038] In addition, the capacitance density is reduced by forming at least two piezoelectric layers 14a to 14c of the layer stack 12. The formation of at least two piezoelectric layers 14a to 14c of the layer stack 12 is equivalent to a "series connection of several capacitances," in which the height of the individual capacitances only "slightly influences" the capacitance density of the layer stack 12 (since only the reciprocals of the individual capacitances are added). Therefore, the acoustic resonator can be dimensioned larger laterally, which minimizes its edge losses.

[0039] Preferably, the at least two piezoelectric layers 14a to 14c of the layer stack 12 comprise (substantially) the same base material. In this case, the at least two piezoelectric layers 14a to 14c have the same thermal expansion coefficient and a similar crystal lattice, which is advantageous for thermal expansion of the layer stack 12 upon temperature change and for growth of the layers during the production of the layer stack 12.

[0040] The at least two piezoelectric layers 14a to 14c of the layer stack 12 can be formed, for example, from aluminum nitride (AlN), scandium aluminum nitride (ScAlN), zinc oxide (ZnO), lithium niobate (LiNbOs), and / or lithium tantalate (LiTaOs). Aluminum nitride and scandium aluminum nitride have a comparatively high speed of sound c awhich enables a comparatively large layer thickness d of piezoelectric layers 14a to 14c formed from at least one of these materials.

[0041] Preferably, the first electrode 10a and / or the second electrode 10b each have an electrode thickness ds along the direction extending from the first electrode 10a to the second electrode 10b, for which d| = n* X aE (f w ) / 2. Where X a E(fw) is an acoustic wavelength of the sound wave 22 with the working frequency f w in the respective first or second electrode 10a or 10b, and n is a natural number greater than or equal to one. The respective electrode thickness d| of the first and / or second electrode 10a or 10b along the direction extending from the first electrode 10a to the second electrode 10b can also be specified using equation (Eq. 3): where CaE(fw) is a speed of sound of the sound signal 22 with the working frequency f w in the first or second electrode 10a or 10b.

[0042] By making the electrode thickness d| of the first electrode 10a and / or the second electrode 10b equal to a multiple of half the acoustic wavelength X a E(fw) / 2, ohmic losses at the acoustic resonator are improved. Therefore, in the acoustic resonator of Fig. 1, the first electrode 10a and / or the second electrode 10b are preferably significantly thicker than in the prior art. (Conventionally, an electrode thickness of at most 4 electrode layers is preferred in order to achieve the greatest possible electromechanical coupling k t 2between acoustic and electromagnetic waves and thus to achieve a high bandwidth of a corresponding filter device.) The increase in the electrode thickness d| compared to the prior art is achieved in the acoustic resonator of Fig. 1 by increasing the height h of the layer stack 12 to a multiple of half the acoustic wavelength X a (f w ) / 2, so that a relatively higher proportion of acoustic energy remains in the layer stack 12.

[0043] Preferably, the first electrode 10a and / or the second electrode 10b are made of at least one material with a comparatively low mass density. For example, the first electrode 10a and / or the second electrode 10b can be formed from aluminum (Al) and / or titanium (Ti). The materials listed here have a comparatively low acoustic material damping, which allows the conversion of an electromagnetic wave with a comparatively high operating frequency f w into the respective sound wave 22 is facilitated, since in this case only a relatively small mass needs to be moved during the oscillation. The first electrode 10a and / or the second electrode 10b can also be formed from several layers of different materials, such as aluminum, titanium, and / or copper. The acoustic resonator explained above can be described as an SMR (surface-mounted resonator) type.

[0044] Fig. 2 shows a schematic representation of a second embodiment of the acoustic resonator.

[0045] The acoustic resonator schematically illustrated in Fig. 2, in contrast to the embodiment of Fig. 1, has, in addition to the at least two piezoelectric layers 14a and 14b, at least one intermediate layer / replacement layer 24 (as layers 14a, 14b, and 24 of the layer stack 12). The at least one intermediate layer 24 of the layer stack 12 has a respective intermediate layer thickness d along the direction extending from the first electrode 10a to the second electrode 10b, for which di = m * X aL (f w ) / 2. Where k a L(fw) is an acoustic wavelength of the sound wave 22 with the working frequency f win the respective intermediate layer 24. m is a natural number greater than or equal to one. The respective intermediate layer thickness d of the at least one intermediate layer 24 of the layer stack 12 along the direction extending from the first electrode 10a to the second electrode 10b can also be specified using equation (Eq. 4): where Ca (fw) is a speed of sound of the sound signal 22 with the working frequency f w in the respective intermediate layer 24.

[0046] By means of the at least one intermediate layer 24 of the layer stack 12, a quality factor of acoustic vibrations can be increased and better parasitic mode suppression can be achieved. Furthermore, by means of the at least one intermediate layer 24 of the layer stack 12, a reduced temperature coefficient of expansion (TCE) of the layer stack 12 can be achieved. Since the intermediate layer thickness d of the at least one intermediate layer 24 is adapted to the operating frequency fw of the acoustic resonator, ie a multiple of half the acoustic wavelength X aL(fw) / 2, the advantageous “filter properties” of the acoustic resonator are retained despite the insertion of the at least one intermediate layer 24 in the layer stack 12. The at least one intermediate layer 24 of the layer stack 12 can be designed in a variety of ways, for example as a high-f*Q layer, as a reflector layer sequence made up of reflector layers (as a Bragg reflector pair layer), as an electrode layer and / or as a temperature compensation layer. The individual intermediate layer 24 or at least one of the intermediate layers of the layer stack 12 can be formed, for example, from a dielectric, i.e. an electrically insulating material. In particular, the individual intermediate layer 24 or at least one of the intermediate layers of the layer stack 12 can be formed from silicon oxide, silicon nitride, silicon carbide, aluminum oxide and / or diamond-like carbon.The materials listed here have low dielectric and / or acoustic losses and an adapted thermal expansion coefficient.

[0047] Alternatively or additionally, the at least one intermediate layer 24 or at least one of the intermediate layers of the layer stack 12 can each be a reflector layer sequence composed of reflector layers. Optionally, the reflector layers of the respective reflector layer sequence have a respective reflector layer thickness dR along the direction extending from the first electrode 10a to the second electrode 10b, for which dR = (2R-1) * X a R(fw) / 4 applies. Where X a R(fw) is an acoustic wavelength of the sound wave 22 with the working frequency f win the respective reflector layer. R is a natural number greater than or equal to one. The reflector layers of the respective reflector layer sequence thus each have a reflector layer thickness dR equal to an odd multiple of aR(f w ) / 4. The respective reflector layer thickness dR of the respective reflector layer of the reflector layer sequence formed thereby along the direction extending from the first electrode 10a to the second electrode 10b can also be given by equation (Eq. 5): where CaR(fw) is a speed of sound of the sound signal 22 with the working frequency f w in the respective reflector layer of the reflector layer sequence formed thereby.

[0048] Preferably, the reflector layers of the same reflector layer sequence arranged one after the other along the direction extending from the first electrode 10a to the second electrode 10b have significant differences in the acoustic impedance of the acoustic signal 22 with the operating frequency f w(The acoustic impedance is the square root of the product of mass density and sound speed of a material.) In particular, a reflector layer with a comparatively low acoustic impedance can be arranged between two reflector layers of the same reflector layer sequence with a relatively high acoustic impedance and / or a reflector layer with a comparatively high acoustic impedance can be arranged between two reflector layers of the same reflector layer sequence with a relatively low acoustic impedance. Possible materials for the respective reflector layer with a low acoustic impedance are, for example, titanium (Ti), silicon oxide (SiC>2) and / or aluminum (Al). The respective reflector layer with a high acoustic impedance can be made of, for example, tantalum (Ta), tungsten (W) and / or molybdenum (Mo). However, combinations of dielectric and semiconducting / metallic reflector layers in a reflector layer sequence are also possible.

[0049] As a further difference from the previously described embodiment, in the acoustic resonator of Fig. 2, the acoustic reflector device 18 is realized by means of a recess 26 structured into the substrate surface 20a of the substrate 20 and filled with air, which is spanned by the second electrode 10b. The recess 26 can also be referred to as a (partial) undercut of the acoustic resonator, a so-called FBAR type (Film Bulk Acoustic Resonator). The recess 26 enables an impedance jump at the surface of the second electrode 10b. The acoustic resonator of Fig. 2 thus has an impedance jump on both sides, both on its side of the first electrode 10a facing away from the substrate and at the recess 26. The recess 26 thus contributes to preventing a loss of acoustic energy into the substrate 20, which is noticeable in smaller insertion losses.

[0050] For further properties and features of the acoustic resonator of Fig. 2 and their advantages, reference is made to the description of the embodiment of Fig. 1.

[0051] Fig. 3 shows a schematic representation of a third embodiment of the acoustic resonator.

[0052] The acoustic resonator schematically illustrated in Fig. 3 has, as a supplement to the embodiment of Fig. 1, a further acoustic reflector device 28 on a side of the first electrode 10a facing away from the layer stack 12. The further acoustic reflector device 28 can also be an acoustic Bragg reflector stack.

[0053] As can also be seen in Fig. 3, the acoustic resonator can be embedded / integrated as a mesa structure in a dielectric layer environment 30. This can facilitate integration of the acoustic resonator with other relevant components on the same chip. The first electrode 10a can be electrically contacted / connected via a first lead 32a, while the second electrode 10b can be electrically contacted / connected via a second lead 32b. Vias 34a and 34b through the dielectric layer environment 30 as parts of the leads 32a and 32b can be easily formed.

[0054] For further properties and features of the acoustic resonator of Fig. 3 and their advantages, reference is made to the description of the embodiment of Fig. 1.

[0055] Fig. 4 shows a schematic representation of a fourth embodiment of the acoustic resonator.

[0056] As can be seen in Fig. 4, a layer stack 12 equipped with at least one intermediate layer 24 can also be embedded / integrated into the dielectric layer environment 30 as part of the mesa structure. By way of example only, the layer stack 12 has five piezoelectric layers 14a to 14e, wherein, in the layer stack 12, two piezo layers 14a-b are located on a side facing the first electrode and three piezo layers 14c-e are located on a side of the intermediate layer facing the second electrode, separated by an intermediate layer 24. This asymmetry makes it possible to suppress unwanted parasitic secondary modes even better.

[0057] For further properties and features of the acoustic resonator of Fig. 4 and their advantages, reference is made to the description of the embodiments of Figs. 1 to 3.

[0058] All of the acoustic resonators explained above comprise a layer stack 12 with a total of G layers between their first electrode 10a and their second electrode 10b. The total number G of layers of the respective layer stack 12 is preferably equal to 2Z + 1, where Z is a natural number greater than or equal to one. Preferably, a respective layer thickness / interlayer thickness d or d i of each of the G layers of the respective layer stack 12 is also equal to X. a (f w ) / 2, provided that the respective layer is a piezoelectric layer 14a to 14e, where X a (f w ) the acoustic wavelength of the sound wave 22 with the working frequency f w in the respective intermediate layer 24, or equal to m * X aL (f w ) / 2, provided that the respective layer is not a piezoelectric layer but an intermediate layer, where X a L(f w) the acoustic wavelength of the sound wave 22 with the working frequency f w in the respective intermediate layer 24 and m is a natural number greater than or equal to one. (The layer thickness / interlayer thickness d or d of each of the G layers of the respective layer stack 12 can also be represented accordingly using equations (Eq. 2) and (Eq. 4).) The height h of the layer stack 12 extending from the first electrode 10a to the second electrode 10b is then defined according to equation (Eq. 6) with:

[0059] (Eq.1.6) h = ^ =1 d i , where di is the layer thickness / interlayer thickness d or di of the i-th layer of the layer stack.

[0060] All acoustic resonators explained above implement volume acoustic (wave) components that can be used in a variety of applications in RF technology, for example, as resonators in filters and oscillators. As is clear from the above explanations, the operating frequency f w of such an acoustic resonator is relatively high compared to the state of the art. An electromagnetic wave with the operating frequency f w , for which the acoustic resonator is permeable, can therefore also be understood as a high-frequency signal.

[0061] Several such acoustic resonators can also be interconnected in circuits to form so-called conductor and / or grid configurations. In this way, filter components can be realized that are permeable to defined frequency ranges. Such filter components can be used advantageously, for example, in mobile communications for (essentially) any frequency band. With such a filter component, signal interference between transmit and receive channels can be avoided, both in the communication modules of mobile devices and in the base stations. Applications requiring high power processing are also conceivable, for example, in base stations and in the transmission path.

[0062] A volume acoustic resonator component according to the invention can be used in particular as a high-precision timing oscillator, in filter components for frequencies above 10 GHz, or as a gravimetric resonance sensor. Further possible applications for the acoustic resonators described above are in the mobile communications and radar sectors.

[0063] Fig. 5 shows a flowchart for explaining an embodiment of the manufacturing method for an acoustic resonator.

[0064] Using the manufacturing process described below, all of the acoustic resonators discussed above can be produced. However, the feasibility of the manufacturing process is not limited to the production of these acoustic resonators.

[0065] In a method step S1 of the manufacturing method, a layer stack is arranged or formed between a first electrode and a second electrode such that its layers are arranged one after the other along a direction extending from the first electrode to the second electrode. The layer stack comprises at least two piezoelectric layers as its layers, of which at least two piezoelectric layers are directly adjacent to one another. The at least two piezoelectric layers are polarized, wherein the at least two directly adjacent piezoelectric layers of the layer stack are polarized such that a respective polarization of each of the at least two directly adjacent piezoelectric layers of the layer stack is oriented opposite to a respective polarization of the at least one directly adjacent piezoelectric layer of the layer stack.

[0066] Additionally, in a method step S2, (at least) one acoustic reflector device is arranged or formed on a side of the first electrode facing away from the layer stack or on a side of the second electrode facing away from the layer stack. A first acoustic reflector device may also be arranged or formed on a side of the first electrode facing away from the layer stack, and a second acoustic reflector device may also be arranged or formed on a side of the second electrode facing away from the layer stack. Method steps S1 and S2 are described in the order presented here only for the sake of clarity. However, method steps S1 and S2 may be performed in any order, at an overlapping time, or at least partially simultaneously.

Claims

Claims 1 . Acoustic resonator comprising: a first electrode (10a) and a second electrode (10b); a layer stack (12) arranged between the first electrode (10a) and the second electrode (10b), the layers (14a - 14e, 14b) of which are arranged one after the other along a direction extending from the first electrode (10a) to the second electrode (10b) and comprise at least two piezoelectric layers (14a - 14e), of which at least two piezoelectric layers (14a - 14e) are directly adjacent to one another, wherein the at least two piezoelectric layers (14a - 14e) are polarized, and wherein the at least two directly adjacent piezoelectric layers (14a - 14e) of the layer stack (12) are polarized such that a respective polarization (16a, 16b) of each of the at least two directly adjacent piezoelectric layers (14a - 14e) of the layer stack (12) is oriented opposite to a respective polarization (16a,16b) the at least one immediately adjacent piezoelectric layer (14a - 14e) of the layer stack (12); and an acoustic reflector device (18) on a side of the first electrode (10a) directed away from the layer stack (12) or on a side of the second electrode (10b) directed away from the layer stack (12); characterized in that an operating frequency f, w of the acoustic resonator as frequency (f w ) an electromagnetic wave arriving via the first electrode 10a, for which the acoustic resonator is permeable, is determined by the at least two piezoelectric layers (14a - 14e) of the layer stack (12) having an equal or specific layer thickness d along the direction extending from the first electrode (10a) to the second electrode (10b), for which d = X a (f w ) / 2, where X a (f w) an acoustic wavelength of a sound wave (22) with the working frequency f w in the respective piezoelectric layer (14a - 14e).

2. Acoustic resonator according to claim 1, wherein the first electrode (10a) and / or the second electrode (10b) each have an electrode thickness dE along the direction extending from the first electrode (10a) to the second electrode (10b), for which dE = n* X aE (f w ) / 2, where X aE (f w ) an acoustic wavelength of the sound wave (22) with the working frequency f w in the respective first or second electrode (10a, 10b) and n is a natural number greater than or equal to one.

3. Acoustic resonator according to claim 1 or 2, wherein the first electrode (10a) and / or the second electrode (10b) are formed of aluminum and / or titanium.

4. Acoustic resonator according to one of the preceding claims, wherein the layers (14a - 14e, 24) of the layer stack (12) comprise, in addition to the at least two piezoelectric layers (14a - 14e), at least one intermediate layer (24), and wherein the at least one intermediate layer (24) of the layer stack (12) has a respective intermediate layer thickness d along the direction extending from the first electrode (10a) to the second electrode (10b), for which d = m* X aL (f„) / 2, where X aL (f„) an acoustic wavelength of the sound wave (22) with the working frequency f w in the respective intermediate layer (24) and m is a natural number greater than or equal to one.

5. Acoustic resonator according to claim 4, wherein the single intermediate layer (24) or at least one of the intermediate layers of the layer stack (12) is formed from silicon oxide, silicon nitride, silicon carbide, aluminum oxide and / or diamond-like carbon.

6. Acoustic resonator according to claim 4 or 5, wherein the individual intermediate layer (24) or at least one of the intermediate layers of the layer stack (12) is in each case a reflector layer sequence of reflector layers, and wherein the reflector layers of the respective reflector layer sequence have a respective reflector layer thickness dR along the direction extending from the first electrode (10a) to the second electrode (10b), for which d = (2R - 1) * X aR (f w ) / 4, where X aR (f w ) an acoustic wavelength of the sound wave (22) with the working frequency f w in the respective reflector layer and R is a natural number greater than or equal to one 7. Acoustic resonator according to one of the preceding claims, wherein the layer stack (12) has a total number G of layers (14a - 14e, 24) equal to 2Z + 1 and Z is a natural number greater than or equal to one, and wherein a respective layer thickness d or di of each of the G layers (14a - 14e, 24) of the layer stack (12) is equal to X a (f w ) / 2, provided that the respective layer (14a - 14e, 24) is a piezoelectric layer (14a - 14e), or equal to m * X aL (f w ) / 2, provided that the respective layer (14a - 14e, 24) is not a piezoelectric layer but an intermediate layer (24).

8. Acoustic resonator according to one of the preceding claims, wherein the at least two piezoelectric layers (14a - 14e) of the layer stack (12) comprise the same base material.

9. Acoustic resonator according to one of the preceding claims, wherein the at least two piezoelectric layers (14a - 14e) of the layer stack (12) are formed from aluminum nitride, scandium aluminum nitride, zinc oxide, lithium niobate and / or lithium tantalate.

10. Manufacturing method for an acoustic resonator with the steps: Arranging or forming a layer stack (12) between a first Electrode (10a) and a second electrode (10b) such that its Layers (14a - 14e, 24) one after the other along a line extending from the first Electrode (10a) are arranged in a direction extending from the second electrode (10b) and comprise at least two piezoelectric layers (14a - 14e), of which at least two piezoelectric layers (14a - 14e) are directly adjacent to one another, wherein the at least two piezoelectric layers (14a - 14e) are polarized, and wherein the at least two directly adjacent piezoelectric layers (14a - 14e) of the layer stack (12) are polarized such that a respective polarization (16a, 16b) of each of the at least two directly adjacent piezoelectric layers (14a - 14e) of the layer stack (12) is oriented opposite to a respective polarization (16a, 16b) of the at least one directly adjacent piezoelectric layer (14a - 14e) of the layer stack (12)(S1); and Arranging or forming an acoustic reflector device (18) on a side of the first electrode (10a) directed away from the layer stack (12) or on a side of the second electrode (10b)(S2) directed away from the layer stack (12); characterized in that an operating frequency f w of the acoustic resonator as frequency (f w ) of an electromagnetic wave arriving via the first electrode (10a), for which the acoustic resonator is permeable, is determined by forming the at least two piezoelectric layers (14a - 14e) of the layer stack (12) with an identical or specific layer thickness d along the direction extending from the first electrode (10a) to the second electrode (10b), for which d = X a (f w ) / 2, where X a (f w ) an acoustic wavelength of a sound wave (22) with the working frequency f win the respective piezoelectric layer (14a - 14e).

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