Bulk acoustic component and method for producing a bulk acoustic component

Abstract

The present invention relates to a bulk acoustic component (10) comprising: electrode contacts (120, 122); a piezoelectric element (100) with piezoelectric layers arranged between the electrode contacts, wherein a doping difference is present between the piezoelectric layers such that a two-dimensional electron gas can be formed at an interface between the piezoelectric layers, and these interfaces of the piezoelectric layers are each electrically contacted via an electrical contact; and further comprising a voltage source (SP), which is connected to the electrode contacts (120, 122) and to the electrical contact (EL1), and wherein an alternating voltage can be applied to these so that contacts with opposite polarity of the alternating voltage can be connected to each other, wherein the bulk acoustic component (10) further comprises a substrate (SB) and an acoustic reflector element (RE), wherein the acoustic reflector element (RE) is arranged in or on the substrate (SB) and the stacked arrangement is arranged on the substrate (SB) and / or on the reflector element (RE).

Description

[0001] Description

[0002] title

[0003] Volume acoustic component and method for producing a volume acoustic component

[0004] The present invention relates to a volume acoustic component and a method for producing a volume acoustic component.

[0005] State of the art

[0006] Bulk acoustic components can be used as resonators in filters and oscillators, with the operating frequencies being determined by the thickness of the piezoelectric layer and the speed of sound in the piezoelectric material. To achieve higher operating frequencies, the layer thickness can be reduced. However, this can increase the capacitance of the component. If the electromagnetic wave impedance is to be maintained, it may therefore be necessary to simultaneously reduce the component area. However, acoustic energy can be lost at the edge of the component, so that with a reduction in the size of the component, the edge losses can increase quadratically with the operating frequency. In this case, it may be desirable to increase the suitability of bulk acoustic components (BAW) for a range above 10 GHz.

[0007] An alternative to reducing the layer thickness could be the excitation of higher modes, which is collectively referred to as an overtoned bulk acoustic resonator (OBAR). However, this concept is prone to the oscillation of additional modes and is inefficient in its excitation (low piezoelectric coupling).

[0008] Another alternative is the use of thick cavities with alternating material polarization. The key advantage of these concepts is that an exciting electric field can directly excite an overtone, since the exciting force also changes direction with the changing material polarization. The fabrication of such alternating polarization layers is challenging, and their transfer to high-volume manufacturing processes is questionable.

[0009] To achieve the highest possible frequency resonance, the electrode thickness can play a crucial role. If the electrode thickness is not small compared to the acoustic wavelength, the mass of the electrode significantly reduces the resonance frequency. Furthermore, the electrode can degrade the quality of the resonator. The electrodes can be detached from the piezo material and capacitively coupled to the resonator via a gap, which can pose a technological challenge. Another possibility could be to replace the electrode with a two-dimensional electron gas, which can form, for example, in an AlGaN / GaN heterostructure.

[0010] With each new generation of mobile networks, higher frequencies and greater bandwidths are being released for mobile communications. Passive filter components made from bulk acoustic wave (BAW) resonators have become established in mobile communications due to their small form factor, low insertion losses, and steep slopes. BAW resonators are also used in oscillators. To achieve higher operating frequencies with the resonators, it may be necessary to reduce their energy losses. A dominant source of loss can be inherent material damping. AIN can exhibit comparatively high inherent material damping due to phonon-phonon interaction. The product f*Q of the operating frequency f and the quality factor Q is used as a measure of the inherent material damping. The larger the product, the lower the respective inherent material damping.

[0011] US 2018 / 085787 A1 describes a volume acoustic component.

[0012] Disclosure of the invention

[0013] The present invention provides a volume acoustic component according to claim 1 and a method for producing a volume acoustic component according to claim 12.

[0014] Preferred further training is the subject of the subclaims.

[0015] Advantages of the invention

[0016] The idea underlying the present invention is to provide a volume acoustic component and a method for manufacturing a volume acoustic component, whereby the suitability of the volume acoustic component for operation in high frequency ranges, particularly above 10 GHz, can be improved. Higher operating frequencies can be accessed and a simple technological implementation can be achieved.

[0017] The aforementioned volume acoustic component can provide an alternative technology path for the development of higher frequency ranges.

[0018] According to the invention, the volume acoustic component comprises a first electrode contact and a second electrode contact; a piezoelement with a predetermined number n of piezoelectric layers, where n is greater than or equal to 2, which are arranged between the first electrode contact and the second electrode contact and stacked in a stack arrangement; where there is a doping difference between two adjacent piezoelectric layers such that a two-dimensional electron gas can be formed at an interface between the respective adjacent piezoelectric layers; and a first piezoelectric layer of the piezoelectric layers is electrically contacted via the first electrode contact and at least one i-th electrical contact for i from an interval [1;n-1] is present, with which the two-dimensional electron gas is electrically contacted at the i-th interface between the i-th and (i+1)-th piezoelectric layer and the n-th piezoelectric layer is electrically contacted with the second electrode contact at an upper side of the stack arrangement;and a voltage source which is connected to the first electrode contact and to the second electrode contact as well as to the i-th electrical contact and to which an alternating voltage can be applied, such that when n is an even number, the first electrode contact and the second electrode contact have the same polarity and when n is an odd number, the first electrode contact and the second electrode contact have opposite polarity and the i-th electrical contact has opposite polarity to the (i-1)-th and / or the (i+1)-th electrical contact or the i-th electrical contact has opposite polarity to the first electrode contact when i=1 and opposite polarity to the second electrode contact when i=n-1, wherein the volume acoustic component further comprises a substrate and an acoustic reflector element, wherein the acoustic reflector element is arranged in or on the substrate and the stack arrangement is arranged on the substrate and / or on the reflector element;

[0019] According to the invention, higher operating frequencies above, for example, 10 GHz can be achieved for volume acoustic components, for example resonators.

[0020] With the volume acoustic component according to the invention, inefficient excitation of higher modes can be avoided or at least reduced.

[0021] Furthermore, the reduction in the resonance frequency caused by the mass loading of the electrode on the resonator can be avoided or at least reduced. Furthermore, poor resonator quality can be avoided or at least reduced by thin layers.

[0022] Furthermore, poor resonator quality can be avoided or at least reduced by the electrode influence.

[0023] Furthermore, technologically challenging layers with alternating polarization can be avoided or at least reduced.

[0024] Furthermore, a simplified technological realization can be achieved by growing the structures instead of bonding two different material layers.

[0025] The number of piezoelectric layers can be two or more, whereby the piezoelectric layers arranged next to one another in a stacked arrangement can be highly and lightly doped (or undoped and doped).

[0026] The first doping and the third doping (or i-th and (i+2)-th) may be the same or different, wherein the second doping may be higher or lower than the first and / or third doping, wherein a predetermined difference in the doping may be present between the first and second piezoelectric layers and between the second and third piezoelectric layers in such a way as to form an interface with a two-dimensional electron gas there.

[0027] The first electrical contact and the second (or i-th) electrical contact can represent base points at the edge of the corresponding piezoelectric layer, each of which can be electrically connected to a via on the top side of the volume acoustic component. Laterally, the stack arrangement can be embedded in a dielectric.

[0028] According to a preferred embodiment of the volume acoustic component, this represents an acoustic resonator. According to a preferred embodiment of the volume acoustic component, the acoustic reflector element is an air or gas cavity in the substrate and / or in a dielectric or is arranged as an acoustic Bragg reflector on the substrate and / or in the stack arrangement.

[0029] According to a preferred embodiment of the volume acoustic component, the first piezoelectric layer comprises a first doping or no doping and the second piezoelectric layer comprises a second doping and the third piezoelectric layer comprises a third doping or no doping, wherein the first doping differs from the second doping and / or the second doping differs from the third doping such that the boundary layer can be formed from a two-dimensional electron gas at the interface between the first piezoelectric layer and the second piezoelectric layer and / or at the interface between the second piezoelectric layer and the third piezoelectric layer

[0030] According to a preferred embodiment of the volume acoustic component, a lateral trench is formed in the stack arrangement up to the first piezoelectric layer and delimits the stack arrangement from a lateral side, for example opposite the contact guide to the first and second electrical contacts.

[0031] According to a preferred embodiment of the volume acoustic component, the first electrical contact and / or the second electrical contact extend as through-contacts through the stack arrangement.

[0032] According to a preferred embodiment of the volume acoustic component, the first electrode contact and / or the second electrode contact comprises an electrode layer or an electrical contact material with an electrode doping.

[0033] According to a preferred embodiment of the volume acoustic component, the first electrode contact and / or the second electrode contact comprises the electrical contact material with the electrode doping and the electrode doping differs from the respective doping of the adjacent piezoelectric layer in such a way that a boundary layer of a two-dimensional electron gas can be formed at an interface between the first piezoelectric layer and the adjacent electrode contact and / or at an interface between the n-th piezoelectric layer and the adjacent electrode contact.

[0034] According to a preferred embodiment of the volume acoustic component, the voltage source can be connected to the two-dimensional electron gas at the interface between the first piezoelectric layer and the adjacent electrode contact and / or to the interface between the n-th piezoelectric layer and the adjacent electrode contact.

[0035] According to a preferred embodiment of the volume acoustic component, this is a MEMS component and represents an acoustic filter.

[0036] According to a preferred embodiment of the volume acoustic component, it is designed for operation as a resonator at an acoustic frequency of greater than or equal to 10 GHz.

[0037] The volume acoustic component can be advantageously used for or as volume acoustic resonator component(s), for example as resonators / oscillators, RF filters in the transmit and receive path of a communication system or radar system, gravimetric sensors or others and can relate to or represent MEMS sensors.

[0038] The volume acoustic component according to the invention can therefore be used to create a high-frequency acoustic resonator for frequencies >10 GHz with electrical excitation. The piezoelectric element can be doped, undoped, or lightly doped with a donor material in each of the respective piezoelectric layers (first, second, and third, or more or fewer). This can create doped and undoped or less doped regions that alternate in the stacking direction. A two-dimensional electron gas (2DEG) can form at the transitions and interfaces between these dopants (undoped-doped or less doped-highly doped), or more precisely, in one of the two materials at the interface. The heights of these respective piezoelectric layers can be selected so that half an acoustic wavelength can fit into them at the desired resonance frequency.

[0039] If each individual layer of the two-dimensional electron gas is subjected to an electrical potential via an electrical contact (first or second), which can be an ohmic contact or Schottky contact, for example, a location-dependent electric field strength is formed across the entire piezoelectric layer, the field lines of which can run at right angles from one layer of the two-dimensional electron gas to its neighboring / further layers of the two-dimensional electron gas (or electrodes, if applicable).An alternating voltage can be applied to these and the electrode contacts using the voltage source, such that the upper electrode contact and every second (from top to bottom) layer of the two-dimensional electron gas have a positive potential, while the lower and remaining layers of the two-dimensional electron gas have a negative (or ground with OV) potential (the potentials can also be reversed accordingly and change with the alternating signal). A resulting locally alternating, frequency-dependent electric field can lead to a significant increase in piezoelectric coupling at the resonant frequency. This resonant frequency can be a higher harmonic than the resonant frequency of a resonator without doped regions, which allows the aforementioned volume acoustic component to be classified as an OBAR.

[0040] The loss of acoustic energy into the substrate should also be avoided as much as possible in order to keep insertion losses to a minimum. Two approaches have been established in this regard: one or more acoustic (Bragg) reflector layers can be inserted between the substrate and the piezo element (resonator) as a reflector element (so-called SM R architecture - surface mounted resonator), or the resonator (piezo element with electrodes) can be undercut and a cavity can be formed in a dielectric or in the substrate (so-called FBAR architecture - film bulk acoustic resonator). According to the invention, the method for producing a volume acoustic component comprises providing a substrate and arranging a first electrode contact and a second electrode contact;wherein a piezoelectric element with a predetermined number n of piezoelectric layers, where n is greater than or equal to 2, is arranged between the first electrode contact and the second electrode contact and is stacked in a stack arrangement; wherein a doping difference is present between two mutually adjacent piezoelectric layers such that a two-dimensional electron gas can be formed at an interface between the respective adjacent piezoelectric layers; and a first piezoelectric layer of the piezoelectric layers is electrically contacted via the first electrode contact and at least one i-th electrical contact for i from an interval [1;n-1] is provided, with which the two-dimensional electron gas is electrically contacted at the i-th interface between the i-th and (i+1)-th piezoelectric layer and the n-th piezoelectric layer is electrically contacted at an upper side of the stack arrangement with the second electrode contact;and a voltage source is provided which is connected to the first electrode contact and to the second electrode contact as well as to the i-th electrical contact and to which an alternating voltage can be applied such that, when n is an even number, the first electrode contact and the second electrode contact have the same polarity and, when n is an odd number, the first electrode contact and the second electrode contact have opposite polarity and the i-th electrical contact has opposite polarity to the (i-1)-th and / or the (i+1)-th electrical contact or the i-th electrical contact has opposite polarity to the first electrode contact if i=1 and opposite polarity to the second electrode contact if i=n-1, wherein the volume acoustic component further comprises a substrate and an acoustic reflector element, wherein the acoustic reflector element is arranged in or on the substrate and the stack arrangement is arranged on the substrate and / or on the reflector element;

[0041] The piezoelectric element can be a layer stack composed of a plurality of piezoelectric layers with alternating opposite polarity and a thickness of half an acoustic wavelength. The resonator component (bulk acoustic component) can be configured such that a main mode with substantially at least a multiple of half an acoustic wavelength occurs in the piezoelectric layer stack and substantially a multiple of another half an acoustic wavelength. The frequency of the main mode can be greater than 10 GHz.

[0042] Thus, and among other things, according to the invention, a reduction of acoustic energy losses due to material damping in volume acoustic resonator components and / or an opening up of higher frequency ranges can be advantageously achieved.

[0043] The invention can be used advantageously for volume acoustic resonator components such as resonators / oscillators, RF filters, or others and can relate to MEMS components for RF systems in the mobile radio (filters) or in the radar range (oscillators).

[0044] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings.

[0045] Short description of the drawings

[0046] The present invention is explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing.

[0047] They show:

[0048] Fig. 1 is a schematic sectional view of a volume acoustic component according to an embodiment of the present invention;

[0049] Fig. 2 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention; Fig. 3 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0050] Fig. 4 is a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0051] Fig. 5 is a block diagram of method steps of the method for producing a volume acoustic component according to an embodiment of the present invention.

[0052] In the figures, the same reference symbols denote the same or functionally identical elements.

[0053] Fig. 1 shows a schematic sectional view of a volume acoustic component according to an embodiment of the present invention.

[0054] The sectional view shows a schematic section through the layers of the volume acoustic component 10.

[0055] The volume acoustic component 10 comprises a first electrode contact 120 and a second electrode contact 122; a piezoelectric element 100 with a first piezoelectric layer 101 and a second piezoelectric layer 102 and a third piezoelectric layer 103, which are arranged between the first electrode contact 120 and the second electrode contact 122 and stacked in a stack arrangement;wherein a doping difference is present between the first piezoelectric layer 101 and the second piezoelectric layer 102 and / or between the second piezoelectric layer 102 and the third piezoelectric layer 103, such that a two-dimensional electron gas can be formed at an interface G12 between the first piezoelectric layer 101 and the second piezoelectric layer 102 and / or a two-dimensional electron gas can be formed between the second piezoelectric layer 102 and the third piezoelectric layer 103 at an interface G23 there;and the first piezoelectric layer 101 is electrically contacted via the first electrode contact 120 and the second piezoelectric layer 102 is electrically contacted at the interface to the first piezoelectric layer 101 via a first electrical contact EL1 and the third piezoelectric layer 103 is electrically contacted at the interface to the second piezoelectric layer 102 via a second electrical contact EL2 and the third piezoelectric layer 103 is electrically contacted at an upper side of the stack arrangement with the second electrode contact 122;and a voltage source SP, which is connected to the first electrode contact 120 and to the second electrode contact 122 as well as to the first electrical contact EL1 and the second electrical contact EL2 and to which an alternating voltage can be applied, such that the first electrode contact 120 and the second electrical contact EL2 can be connected with an identical polarity of the alternating voltage and the second electrode contact 122 and the first electrical contact EL1 can be connected with a different identical polarity of the alternating voltage, wherein the volume acoustic component 10 further comprises a substrate SB and an acoustic reflector element RE, wherein the acoustic reflector element RE is arranged in or on the substrate SB and the stack arrangement is arranged on the substrate SB and / or on the reflector element RE.;

[0056] The acoustic reflector element RE may be formed as a cavity in a dielectric DI and below the stack arrangement, wherein the dielectric DI may be located between the substrate SB and the first electrode contact 120.

[0057] Furthermore, the first piezoelectric layer 101 may comprise a first doping or no doping, and the second piezoelectric layer 102 may comprise a second doping, and the third piezoelectric layer 103 may comprise a third doping or no doping, wherein the first doping differs from the second doping and / or the second doping differs from the third doping such that the boundary layer can be formed from a two-dimensional electron gas at the interface between the first piezoelectric layer 101 and the second piezoelectric layer 102 and / or at the interface between the second piezoelectric layer 102 and the third piezoelectric layer 103.

[0058] Furthermore, a lateral trench TR can be formed in the stack arrangement up to the first piezoelectric layer 101 and delimit the stack arrangement from a lateral side.

[0059] Furthermore, the first electrical contact EL1 and / or the second electrical contact EL2 can be located at the lateral edge of the associated piezoelectric layer, for example as a contact pad, and from the top side of the stack arrangement, a respective through contact K (with a respective contact pad on the top side, which can be connected to the voltage source SP) can be electrically connected to the associated electrical contact and thus to the boundary layer and the two-dimensional electron gas and can have a polarity currently specified by the voltage source at this associated terminal of the voltage source.

[0060] The first and second electrode contacts may comprise an electrode material and be formed as an electrode per se or as an electrode layer, which may be connected to respective terminals of the voltage source.

[0061] The first electrode contact 120 can be electrically contacted laterally at a side region with a through contact FK through the dielectric, for example also laterally outside the trench TR, from the top side of the volume acoustic component 10 via a contact pad K there and through the dielectric DI.

[0062] In other words, a cavity RE can be located beneath the lower electrode 120, which can fully or partially reflect the acoustic wave that can propagate vertically in the piezoelectric element 100. Likewise, an air transition can be located above the upper electrode 122, so that partial or full reflection of the acoustic wave can also occur there. The doped and undoped (or less doped) piezoelectric layers can exhibit piezoelectricity, so that the entire piezoelectric element 100 can be piezoelectric. At the transitions between the doped and undoped (or less doped) regions, boundary layers of the two-dimensional electron gas can form, which can be the case, for example, with AlxGa1-xN / GaN, Aln / AlxGa1-xN, AlxGa1-xN / AlyGa1-yN (x <> y), or ZnO / MgxZn1-xO transitions.

[0063] In order to confine the two-dimensional electron gas in a lateral direction, one or more trenches TR can be etched laterally into the dielectric or into the piezo element 100.

[0064] The above materials can be structured using physical ion beam etching or plasma etching with CI2 and / or BCI3 chemistry.

[0065] The voltage source SP can output an RF signal as an alternating signal, especially at multiple terminals (so that different polarities can be delivered to the respective layers over time).

[0066] The voltage source SP can therefore be applied to the corresponding electrodes and the boundary layers G12 and G23 with the wiring shown. The resulting alternating electric field is indicated by the arrow. Due to the inverse piezoelectric effect, this field leads to a location-dependent deflection that can be described by acoustic waves. If the piezoelectric layers (101, 102, 103) are dimensioned at resonance such that their height corresponds to half an acoustic wavelength, the coupling due to the applied electric field increases significantly. In the simplest sense, the piezoelectric coupling can be proportional to the integral over the piezoelectric layer of the product of electric field strength and strain. With the inventive impression of the electric field, the piezoelectric coupling is no longer proportional to the area balance of the aforementioned product, but rather to the area amount.

[0067] The arrows indicate the electric field strength. An active resonator zone is indicated by the dashed box. The lateral dimension of the resonator zone is very large relative to the layer thickness. Likewise, the length between the resonator zone and the electrical contacts can be very small. Fig. 2 shows a schematic sectional view of a volume acoustic component according to another embodiment of the present invention.

[0068] The design of Fig. 2 is similar to that of Fig. 1, since it also has a cavity in the dielectric below the lower (first) electrode contact 120 as a reflector element RE. However, the design of Fig. 2 differs from the design of Fig.1 that the first electrode contact 120 and the second electrode contact 122 themselves can be designed not as an electrode plate or independently formed contact but as an electrode layer with an electrode material that can itself be doped or undoped in order to be able to have a two-dimensional electron gas at the boundary layer G1e between the first electrode contact 120 and the first piezoelectric layer 101 due to the existing doping jump and likewise to be able to have a two-dimensional electron gas at the boundary layer G3e between the second electrode contact 122 and the third piezoelectric layer 103 (or further piezoelectric layer in the case of several such layers) due to the existing doping jump. With the contact pads K for the electrode contacts 122 and 120 (approximately according to Fig.1) or with electrode pads EK provided specifically for the electrode layers 120 or 122, preferably at a lateral edge of the electrode layer (120 and / or 122, shown only for layer 122 in Fig. 2). A voltage signal can be applied to these pads according to the embodiments of the invention (for example, according to Fig. 1).

[0069] In other words, the difference from Fig. 1 lies solely in the electrode contacts 120 and 122. In the embodiment of Fig. 2, these are also implemented with layers of the two-dimensional electron gas. Furthermore, an intermediate variant between the first and second embodiments may also be possible, i.e., such that only one of the two electrodes 120 or 122 can be replaced by a layer of a two-dimensional electron gas. Fig. 3 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention.

[0070] The design of Fig. 3 advantageously corresponds to that of Fig. 1 with the difference that instead of the cavity in a dielectric, an acoustic Bragg reflector can be arranged as a reflector element RE below the stack arrangement and on the substrate SB.

[0071] Fig. 4 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention.

[0072] The design of Fig. 4 advantageously corresponds to that of Fig. 2 with the difference that instead of the cavity in a dielectric, an acoustic Bragg reflector can be arranged as a reflector element RE below the stack arrangement and on the substrate SB.

[0073] In general, it should be noted that SMR structures can be advantageous in applications where high signal power needs to be processed, such as in base stations and in the transmit path, due to better thermal coupling to the substrate. FBAR structures, on the other hand, can usually exhibit lower insertion losses, which can be advantageous for larger bandwidths and the receive path.

[0074] If metallic reflector layers are used in an SMR architecture, they can serve directly as the resonator's electrodes. In FBAR resonators, the thickness of the electrodes can also be matched to the wavelength of the pass frequency.

[0075] The material systems mentioned can be deposited on silicon wafers using methods such as sputtering, molecular beam epitaxy (MBE), or metal organic vapor deposition (MOCVD). This is also possible in (almost) single-crystal form using a suitable substructure or intermediate layers. One example is the growth of single-crystal AlGaN on Si using an AlN buffer, which allows the entire resonator to be constructed in single-crystal form. This achieves very low material damping and thus minimizes losses. Furthermore, the two material partners can be grown epitaxially onto one another, which can ensure high piezoelectric quality even with thin individual layers (e.g., for high frequencies), since the crystal lattice structure is retained over a large area even when the material is changed at the interface.

[0076] By connecting a number of such resonators in suitable circuits to form so-called ladder and / or grid configurations, filter components can be realized that are permeable to defined frequency ranges and may be necessary for any frequency band in mobile communications. These filters may be necessary to prevent signal interference between transmit and receive channels, both in the RF front ends of mobile devices and in base stations.

[0077] The volume acoustic (resonator) component according to the invention can also be used as a high-precision timing oscillator, in filter components for frequencies in the GHz range or as a gravimetric resonance sensor.

[0078] Fig. 5 shows a block diagram of method steps of the method for producing a volume acoustic component according to an embodiment of the present invention.

[0079] In the method for producing a volume acoustic component, a substrate is provided S1 and a first electrode contact and a second electrode contact are arranged S2; wherein a piezoelectric element having at least a first piezoelectric layer and a second piezoelectric layer and a third piezoelectric layer is arranged between the first electrode contact and the second electrode contact in a stack arrangement;wherein a doping difference is present between the first piezoelectric layer and the second piezoelectric layer and / or between the second piezoelectric layer and the third piezoelectric layer, such that a two-dimensional electron gas can be formed at an interface between the first piezoelectric layer and the second piezoelectric layer and / or a two-dimensional electron gas can be formed between the second piezoelectric layer and the third piezoelectric layer;and the first piezoelectric layer is electrically contacted via the first electrode contact and the second piezoelectric layer is electrically contacted at the interface to the first piezoelectric layer via a first electrical contact and the third piezoelectric layer is electrically contacted at the interface to the second piezoelectric layer via a second electrical contact and the third piezoelectric layer is electrically contacted at an upper side of the stack arrangement with the second electrode contact;and a voltage source which is connected to the first electrode contact and to the second electrode contact as well as to the first electrical contact and the second electrical contact, and to which an alternating voltage is applied such that the first electrode contact and the second electrical contact are connected to an identical polarity of the alternating voltage and the second electrode contact and the first electrical contact are connected to a different identical polarity of the alternating voltage, wherein the volume acoustic component further comprises a substrate and an acoustic reflector element, wherein the acoustic reflector element is arranged in or on the substrate and the stack arrangement is arranged on the substrate and / or on the reflector element;

[0080] Although the present invention has been fully described above using preferred embodiments, it is not limited thereto but can be modified in many ways.

Claims

Claims 1. Volume acoustic component (10) comprising, - a first electrode contact (120) and a second electrode contact (122); - a piezoelectric element (100) with a predetermined number n of piezoelectric layers (101, 102, ...), where n is greater than or equal to 2, which are arranged between the first electrode contact (120) and the second electrode contact (122) and stacked in a stack arrangement; wherein a doping difference is present between two adjacent piezoelectric layers such that a two-dimensional electron gas can be formed at an interface between the respective adjacent piezoelectric layers; and a first piezoelectric layer (101) of the piezoelectric layers (101, 102, ...) is electrically contacted via the first electrode contact (120) and at least one i-th electrical contact (ELi) for i from an interval [1; n-1] is present, with which the two-dimensional electron gas is electrically contacted at the i-th interface between the i-th and (i+1)-th piezoelectric layer and the n-th piezoelectric layer at an upper side of the stack arrangement with the second electrode contact. (122) is electrically contacted; and - a voltage source (SP) which is connected to the first electrode contact (120) and to the second electrode contact (122) as well as to the i-th electrical contact (ELi), and to which an alternating voltage can be applied, such that when n is an even number, the first electrode contact (120) and the second electrode contact (122) are of the same polarity and, when n is an odd number, the first electrode contact (120) and the second electrode contact (122) are of opposite polarity and the i-th electrical contact (ELi) is of opposite polarity to the (i-1)-th and / or to the (i+1)-th electrical contact or the i-th electrical contact (ELi) is of opposite polarity to the first electrode contact (120) when i=1 and to the second electrode contact (122) when i= n-1, wherein the volume-acoustic component (10) further comprises a substrate (SB) and an acoustic reflector element (RE), wherein the acoustic reflector element (RE) is arranged in or on the substrate (SB) and the stack arrangement is arranged on the substrate (SB) and / or on the reflector element (RE).

2. Volume acoustic component (10) according to claim 1, which represents an acoustic resonator.

3. Volume acoustic component (10) according to claim 1 or 2, wherein the acoustic reflector element (RE) is an air cavity in the substrate (SB) and / or in a dielectric (DI) or is arranged as an acoustic Bragg reflector on the substrate (SB) and / or in the stack arrangement.

4. Volume acoustic component (10) according to one of claims 1 to 3, in which the first piezoelectric layer (101) comprises a first doping or no doping and an adjacent second piezoelectric layer (102) comprises a second doping and a third piezoelectric layer (103) adjacent to the second piezoelectric layer comprises a third doping or no doping, wherein the first doping differs from the second doping and / or the second doping differs from the third doping in such a way that in each case the boundary layer can be formed from a two-dimensional electron gas at the interface between the first piezoelectric layer (101) and the second piezoelectric layer (102) and / or at the interface between the second piezoelectric layer (102) and the third piezoelectric layer (103).

5. Volume acoustic component (10) according to one of claims 1 to 4, wherein a lateral trench is formed in the stack arrangement up to the first piezoelectric layer (101) and delimits the stack arrangement from a lateral side.

6. Volume acoustic component (10) according to one of claims 1 to 5, wherein the i-th electrical contact (E Li) extends as a through-contact through the stack arrangement.

7. Volume acoustic component (10) according to one of claims 1 to 6, wherein the first electrode contact (120) and / or the second electrode contact (122) comprises an electrode layer or an electrical contact material with an electrode doping.

8. Volume acoustic component (10) according to claim 7, wherein the first electrode contact (120) and / or the second electrode contact (122) form the electrical Contact material with the electrode doping and the electrode doping differs from the respective doping of the adjacent piezoelectric layer in such a way that a boundary layer made of a two-dimensional electron gas can be formed at an interface between the first piezoelectric layer (101) and the adjacent electrode contact and / or at an interface between the n-th piezoelectric layer (103) and the adjacent electrode contact (122).

9. Volume acoustic component (10) according to claim 8, wherein the voltage source (SP) is connectable to the two-dimensional electron gas at the interface between the first piezoelectric layer (101) and the adjacent electrode contact and / or to the interface between the n-th piezoelectric layer (103) and the adjacent electrode contact (122).

10. Volume acoustic component (10) according to one of claims 1 to 9, which is a MEMS component and represents an acoustic filter.

11. Volume acoustic component (10) according to one of claims 1 to 10, which is designed for operation as a resonator at an acoustic frequency of greater than or equal to 10 GHz.

12. A method for producing a volume acoustic component (10), comprising the steps: - Providing (S1) a substrate (130) and arranging (S2) a first electrode contact (120) and a second electrode contact (122); wherein a piezoelement (100) with a predetermined number n of piezoelectric layers (101, 102, ...), where n is greater than or equal to 2, is arranged between the first electrode contact (120) and the second electrode contact (122) and is stacked in a stack arrangement; wherein a doping difference is present between two mutually adjacent piezoelectric layers such that a two-dimensional electron gas can be formed at an interface between the respective adjacent piezoelectric layers; and a first piezoelectric layer (101) of the piezoelectric layers (101, 102, ...) is electrically contacted via the first electrode contact (120) and at least one i-th electrical contact (ELi) is provided for i from an interval [1; n-1], with which the two-dimensional electron gas is electrically contacted at the i-th interface between the i-th and (i+1)-th piezoelectric layer and the n-th piezoelectric layer is electrically contacted at an upper side of the stack arrangement with the second electrode contact (122); and a voltage source (SP) is provided which is connected to the first electrode contact (120) and to the second electrode contact (122) as well as to the i-th electrical contact (ELi), and to which an alternating voltage can be applied, such that when n is an even number, the first electrode contact (120) and the second electrode contact (122) are polarized in the same way and when n is an odd number, the first electrode contact (120) and the second electrode contact (122) are polarized in opposite directions and the i-th electrical contact (ELi) is polarized in opposite directions to the (i-1)-th and / or the (i+1)-th electrical contact or the i-th electrical contact (ELi) is polarized in opposite directions to the first electrode contact (120),when i=1 and opposite polarity to the second electrode contact (122) when i=n-1, wherein the volume acoustic component (10) further comprises a substrate (SB) and an acoustic reflector element (RE), wherein the acoustic reflector element (RE) is arranged in or on the substrate (SB) and the stack arrangement is arranged on the substrate (SB) and / or on the reflector element (RE).

Images