Bulk acoustic component and method for producing a bulk acoustic component

Abstract

The invention relates to a bulk acoustic component (10) comprising a first electrode contact (120) and a second electrode contact (122); a piezoelement having at least one first piezoelectric layer (101), as a semiconductor, with a first doping and / or at least one second piezoelectric layer (102), as a semiconductor, with a second doping, the piezoelectric layers being situated between the first electrode contact (120) and the second electrode contact (122) and stacked in a stack assembly or forming the first electrode contact (120) and / or the second electrode contact (122); and a voltage source which is connected to the first electrode contact (120) and to the second electrode contact (122) and to which a DC or AC voltage can be applied in such a way that the thickness of a space charge zone (RL-1, RL-2) in the first piezoelectric layer (101) and / or in the second piezoelectric layer (102) can be regulated. The bulk acoustic component (10) further comprises a substrate (SB) and an acoustic reflector element (RE), the acoustic reflector element (RE) being provided in or on the substrate (SB), and the stack assembly being provided on the substrate (SB) and / or on the reflector element (RE).

Description

[0001] Description

[0002] title

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

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

[0005] State of the art

[0006] Volume acoustic devices can be used as resonators in filters and oscillators, with their operating frequencies determined by the thickness of the piezoelectric layer and the speed of sound within the piezoelectric material. To achieve higher operating frequencies, the layer thickness can be reduced, although tolerances play a crucial role. However, a reduced layer thickness can increase the device's capacitance. If the electromagnetic wave impedance is to be maintained, it may be necessary to simultaneously reduce the device area. However, this can lead to acoustic energy loss at the device's edges, meaning that edge losses can increase quadratically with the operating frequency as the device size decreases. Therefore, it may be desirable to improve the suitability of volume acoustic devices (BAW) for frequencies above 10 GHz.

[0007] An alternative to reducing the layer thickness is the excitation of higher-order modes, which is collectively referred to as Overtoned Bulk Acoustic Resonator (OBAR). However, this concept is susceptible to the oscillation of additional modes and is inefficient in its excitation (low piezoelectric coupling).

[0008] Furthermore, it can be difficult to deposit high-quality piezoelectric layers with low thickness, as there is typically a high defect density at the interface with the underlying material, which heals itself as the layer grows, i.e., as the layer thickness increases.

[0009] Furthermore, thick layers with alternating material polarization can be used, a significant advantage of which is that an exciting electric field can directly excite an overtone, since the exciting force also changes direction with the changing material polarization. Manufacturing such layers of alternating polarization is challenging. Since the aforementioned concept aims to utilize the highest possible frequency resonance, the electrode thickness plays 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. The electrode also degrades the quality factor of the resonator. One possibility is to detach the electrodes from the piezoelectric material and capacitively couple them to the resonator via a gap.

[0010] US 2018 / 085787 A1 describes a volume acoustic component.

[0011] Disclosure of the invention

[0012] The present invention provides a volume acoustic component according to claim 1 and a method for manufacturing a volume acoustic component according to claim 12.

[0013] Preferred further training courses are the subject of the subclaims.

[0014] Advantages of the Invention: The underlying idea of ​​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 achieved, and a simple technological implementation is possible.

[0015] The aforementioned volume-acoustic component enables an alternative technology pathway for unlocking higher frequency ranges.

[0016] According to the invention, the volume acoustic component comprises a first electrode contact and a second electrode contact; a piezoelectric element with at least one first piezoelectric layer as a semiconductor with at least one first doping and / or at least one second piezoelectric layer as a semiconductor with a second doping, which are arranged between the first electrode contact and the second electrode contact and are stacked in a stacking arrangement or form the first electrode contact and / or the second electrode contact themselves;and a voltage source which is connected to the first electrode contact and to the second electrode contact and to which a DC or AC voltage can be applied, such that the thickness of a space charge region in the first piezoelectric layer and / or in the second piezoelectric layer is controllable, wherein the volume acoustic device 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.

[0017] The invention enables the avoidance or reduction of inefficient excitation of higher modes. Furthermore, it enables the avoidance or reduction of the reduction in resonant frequency caused by the mass loading of the electrode onto the resonator. Additionally, it enables the avoidance or reduction of technologically challenging layers with alternating polarization or very thin piezoelectric layers. Finally, a simplified technological implementation can be achieved by growing the structures instead of bonding two different material layers and by simply tuning the resonant frequency via a DC voltage.

[0018] It is also possible for there to be only one piezoelectric semiconductor layer. This layer can then form n-type and p-type regions through doping, which can lead to the space charge region between the regions (within the same layer). However, different piezoelectric semiconductors with two or more layers can also be used, which can then contain different dopings within themselves, or only one specific doping, or no doping at all, or an intrinsic zone (different doping), or a combination of these cases.

[0019] All the aforementioned features, advantages and properties relating to multiple piezoelectric layers can also apply to the version with only one piezoelectric layer.

[0020] According to the invention, higher operating frequencies above, for example, 10 GHz can be achieved for volume acoustic components, such as resonators.

[0021] The volume acoustic component according to the invention can, at least according to one embodiment, represent an acoustic high-frequency resonator made of a piezoelectric semiconductor (AlN, GaN, AlGaN, etc.), which can be embodied by the piezoelectric element, and for frequencies >10 GHz with electrical excitation. The one or more layers of the piezoelectric element can be so heavily doped that a space charge region can form, for example, adjacent to a transition to an adjacent semiconductor or metal layer or other doping of the same layer. This can be the case, for example, between a heavily n- and p-doped region, or between a metal and an n- or p-doped region, which forms a Schottky resonator.

[0022] This can represent a contact. In this space charge region, unlike in the rest of the semiconductor, there are no free charge carriers, so the entire applied voltage can drop across precisely this space charge region. In a piezoelectric semiconductor, this can lead to mechanical expansion being excited exclusively in the space charge region by the inverse piezoelectric effect, for example, by an electric field.

[0023] In the event that the thickness of the space charge region is approximately half an acoustic wavelength, a resonator can be achieved whose

[0024] The resonant frequency is determined by the thickness of the space charge region and not by the piezoelectric layer thickness (m). It should be noted that the layer thickness should be very thin for high frequencies and is difficult to produce in this way. In the case of a Schottky contact design, the metal layer can be included in the total thickness of the piezoelectric element and should be one or a multiple of half the wavelength for the aforementioned effect. A highly doped region of the semiconductor outside the space charge region (e.g., in the first and / or second piezoelectric layer) can act as an electrode, provided the appropriate doping results in sufficiently high conductivity.

[0025] If the dimensions of the layer(s) in the overall layer / stack create a harmonic corresponding to more than half an acoustic wavelength, the piezoelectric coupling can be higher than in the case of a conventional OBAR. This is due to the fact that in an OBAR, the applied voltage drops across the entire layer, resulting in a weaker exciting electric field.

[0026] Higher operating frequencies can therefore be achieved for volume acoustic resonators, which is possible through a simple technological implementation. Furthermore, tuning can be accomplished via a DC voltage, and nonlinear effects for frequency mixing can be utilized by modulating the space charge region thickness with an AC voltage. The aforementioned design also allows for simple electrode structuring. According to a preferred embodiment of the volume acoustic component, it constitutes an acoustic resonator.

[0027] According to a preferred embodiment of the volume acoustic component, the acoustic reflector element is an air cavity in the substrate or is arranged as an acoustic Bragg reflector on the substrate and / or in the stack arrangement.

[0028] According to a preferred embodiment of the volume acoustic component, the piezoelectric element comprises at least one metal layer which is in contact with the first piezoelectric layer or the second piezoelectric layer, wherein the space charge region is formed in the first piezoelectric layer or in the second piezoelectric layer and adjacent to the metal layer by a doping difference to the metal layer.

[0029] According to a preferred embodiment of the volume acoustic component, the thickness of the piezoelectric element corresponds to a multiple of half a wavelength of an operating frequency of the volume acoustic component.

[0030] According to a preferred embodiment of the volume acoustic component, a thickness of the piezoelectric element greater than half a wavelength of an operating frequency of the volume acoustic component and a harmonic of the operating frequency corresponds to.

[0031] According to a preferred embodiment of the volume acoustic component, the first electrode contact is represented by the first piezoelectric layer or by the metal layer and / or the second electrode contact is represented by the second piezoelectric layer or by the metal layer.

[0032] According to a preferred embodiment of the volume acoustic component, a DC voltage and / or an AC voltage is applied to the piezoelectric element, with which the thickness of the space charge region can be modulated. According to a preferred embodiment of the volume acoustic component, the piezoelectric element comprises at least one intrinsic region which is in contact with or formed within the first piezoelectric layer or the second piezoelectric layer.

[0033] According to a preferred embodiment of the volume acoustic component, it is a MEMS component and represents an acoustic filter.

[0034] 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.

[0035] 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 other applications, and can relate to or represent MEMS sensors.

[0036] According to the invention, the method for manufacturing a volume acoustic component involves providing a substrate and arranging a first electrode contact and a second electrode contact and / or a piezoelectric element between them, with at least one first piezoelectric layer having at least one first doping and / or a second piezoelectric layer having a second doping, which are arranged between the first electrode contact and the second electrode contact and stacked in a stacking arrangement or form the first electrode contact and / or the second electrode contact themselves; providing a voltage source which is connected to the first electrode contact and to the second electrode contact and to which a DC or AC voltage can be applied, such that the thickness of a space charge region in the first piezoelectric layer and / or in the second piezoelectric layer is controllable;and the provision of an acoustic reflector element, wherein the acoustic reflector element is arranged in or on the substrate and the stacking arrangement is arranged on the substrate and / or on the reflector element. For fabrication, in particular, an epitaxial and single-crystal growth, for example of GaN or AIGaN layers, can be implemented, which can be realized on various types of substrates, for example on GaN, sapphire, Si and SiC, wherein at least in the case of Si and SiC, one or more intermediate layers may be necessary for lattice matching.

[0037] Doping can be introduced, for example, by ion implantation, diffusion, or, particularly advantageous due to the high homogeneity achieved, directly during the (epitaxial) growth of the GaN layer. Suitable dopants include Si, Ge, Ti, Zr, Nb, or S for n-doped regions and, for example, Mg, Ca, Zn, Mn, or Be for p-doped regions. By introducing the dopants during layer growth, a dopant gradient can be introduced into the layer, either in the growth direction or the layer thickness direction. It can be advantageous to dope the region where the space charge region will later form with a concentration that results in the desired space charge region thickness. Below or outside this region, a significantly higher concentration can be chosen to increase conductivity and reduce series resistance and thus losses.

[0038] In the case of an applied alternating voltage, the material properties inside and outside the space charge region can differ, which can lead to different acoustic wavelengths inside and outside the space charge region. Therefore, it may be necessary to optimize the layer thicknesses accordingly. BAW resonators according to the invention can be characterized in that their mechanical excitation by the piezoelectric effect can take place exclusively in the space charge region.

[0039] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings. Brief description of the drawings

[0040] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing.

[0041] They show:

[0042] Fig. 1 shows a schematic sectional view of a piezoelectric element for a volume acoustic component according to an embodiment of the present invention;

[0043] Fig. 2 shows a schematic sectional view of a piezoelectric element for a volume acoustic component according to a further embodiment of the present invention;

[0044] Fig. 3 shows a profile of the thickness of the space charge region with the doping concentration;

[0045] Fig. 4 shows a schematic sectional view of a piezoelectric element for a volume acoustic component according to a further embodiment of the present invention;

[0046] Fig. 5a shows a schematic sectional view of a volume acoustic component according to an embodiment of the present invention;

[0047] Fig. 5b shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0048] Fig. 6 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0049] Fig. 7 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0050] Fig. 8 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0051] Fig. 9 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0052] Fig. 10 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0053] Fig. 11 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0054] Fig. 12 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0055] Fig. 13 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0056] Fig. 14 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention;

[0057] Fig. 15 shows a schematic representation of the suppression of the resonant frequency by a DC voltage; and

[0058] Fig. 16 shows a block diagram of process steps of the method for manufacturing a volume acoustic component according to an embodiment of the present invention.

[0059] In the figures, identical reference symbols denote identical or functionally equivalent elements.

[0060] Fig. 1 shows a schematic sectional view of a piezoelectric element for a volume acoustic component according to an embodiment of the present invention.

[0061] The piezoelectric element 100 can comprise at least a first piezoelectric layer 101 as a semiconductor with a first doping (e.g., in an n-type semiconductor) and a second piezoelectric layer 102 (e.g., in a p-type semiconductor) as a semiconductor with a second doping, which can themselves form the first electrode contact 120 and the second electrode contact 122. The doping can create a space charge region RL in the first piezoelectric layer 101 and an adjacent space charge region in the second piezoelectric layer 102, whereby both adjacent space charge regions can be counted as a single total space charge region RL.

[0062] On the other hand, the piezoelectric element 100 can also have only the first piezoelectric layer 101 as a semiconductor, which can then itself have a first doping (e.g., n-contact) and a further doping (e.g., p-contact) within the layer itself. This allows the space charge region to form within this single layer. The remaining examples from Figures 2 to 14 can also be realized with only one piezoelectric layer, which can have correspondingly doped sub-regions.

[0063] The Piezoelectric Element 100 can thus represent a pn junction in a piezoelectric semiconductor. In the n-type region, electrons are introduced by donor atoms. These electrons do not form covalent bonds with neighboring atoms and are therefore available for charge transport. Conversely, holes can be introduced by acceptor atoms in the p-type region, which can then be filled by electrons. The space charge region forms at the pn junction because electrons diffuse from the n-type region into the p-type region. The donor and acceptor atoms remain behind and are then ionized (electrons to maintain charge neutrality may have diffused away). This is accompanied by an electric field that can develop due to the presence of the donor and acceptor atoms. Consequently, the free charge carriers (drift current) move in this field against the direction of diffusion. The size (thickness) of the space charge region is reached when the drift and diffusion currents balance each other.

[0064] Fig. 2 shows a schematic sectional view of a piezoelectric element for a volume acoustic component according to a further embodiment of the present invention.

[0065] The representation in Fig. 2 is similar to that in Fig. 1, except that the piezoelectric element in Fig. 2 comprises a metal layer MS instead of the second piezoelectric layer. This metal layer is in contact with the first piezoelectric layer 101, and the space charge region RL forms in the first piezoelectric layer 101 and adjacent to the metal layer MS, forming a Schottky contact. In this case, the free charge carriers may diffuse into the metal MS because the energy level of the conduction band electrons / valence band holes in the n- / p-type semiconductor of the first piezoelectric layer 101 is higher / lower than in the metal MS.The thickness of the space charge region RL can be approximately determined (in the static case the piezoelectric space charge is neglected) by the electron charge, the permittivity, the acceptor concentration, the donor concentration, the diffusion voltage and the externally applied voltage, where q is the electron charge, E is the permittivity, NA is the acceptor concentration, ND is the donor concentration, pD is the diffusion voltage and U is the externally applied voltage.

[0066] If a voltage U=UDC+UACs\n (o>t) is applied, then if <pD-UDC»UAC die Raumladungszonendicke als Konstant angesehen werden. Genauer wird diese dann durch die Fremdatomkonzentration (ND und NÄ) und durch den Gleichspannungsanteil UDC bestimmt. Es kann wegen der Diffusionsspannung im piezoelektrischen Halbleiter in der Raumladungszone, auch eine statische Auslenkung ausgebildet werden. Durch die hohe Linearität der mechanischen Größen lässt sich die statische und zeitabhängige Auslenkung als lineare Superposition ansehen. Fig. 3 zeigt ein Profil der Dicke der Raumladungszone mit der Dotierkonzentration.

[0067] The diagram on the left shows the exemplary space charge region thickness RL-D plotted against the donor concentration (logarithmic x-axis scale) in the GaN semiconductor-metal contact (Schottky contact). Three different voltages for UDC are shown for this case, demonstrating that space charge region thicknesses of less than 50 nm are possible.

[0068] The thickness of the space charge region can only be determined by the dopant concentration, the diffusion voltage and the applied voltage, these parameters of which can easily be kept constant via a resonator and also via a wafer.

[0069] The image on the right shows that a higher doping concentration can lead to a sharper separation between the zone with and without free charge carriers, as indicated by the steep drop in the curves. This drop represents the normalized (to the maximum concentration) concentration of free charge carriers. The area where the curve drops to zero is the space charge region (no free charge carriers). For example, a Schottky junction is located at x = 500 nm, and a standard ohmic junction at x = 0 nm. Furthermore, the image shows that the space charge region d becomes thinner with increasing doping concentration; the higher the doping concentration, the smaller d becomes.

[0070] Fig. 4 shows a schematic sectional view of a piezoelectric element for a volume acoustic component according to a further embodiment of the present invention.

[0071] Figure 4 is similar to Figure 1 and Figure 2, except that the piezoelectric element 100 can comprise at least one intrinsic region 200, which may be formed adjacent to the first piezoelectric layer 101. In the case of Figure 4, this intrinsic region 200 can be located between the first piezoelectric layer 101 and the metal layer MS, with a space charge region RL forming in the first piezoelectric layer 101 towards the intrinsic region 200.

[0072] If the space charge region RL becomes thinner due to the doping concentration, such an intrinsic region can be utilized. The thickness without free charge carriers, i.e., the thickness in which mechanical excitation occurs, is then determined by the thickness d of the space charge region RL and the thickness di of the intrinsic region. This can increase the voltage required for current flow. Linear behavior can be achieved even at lower reverse voltages. In the passive case (UDC = 0 V), the AC voltage can have higher amplitudes. The intrinsic region can correspond to a region of the first or second (or subsequent) piezoelectric or semiconductor layer that may have no or very little base doping compared to the rest of the layer.

[0073] A high applied negative DC voltage can result in high linearity and a thick space charge region. If a passive approach (i.e., UDC=0V) is used, the diffusion voltage can be very high. <pD»UAC). Eine hohe Dotier- bzw. Akzeptorkonzentration kann eine scharfe und dünne Raumladungszone und hohe Leitfähigkeit außerhalb dieser bewirken.

[0074] Fig. 5a shows a schematic sectional view of a volume acoustic component according to an embodiment of the present invention.

[0075] The sectional view shows a schematic section through the layers of the volumetric acoustic element 10.

[0076] The volume acoustic component 10 comprises a first electrode contact 120, which can correspond to the first piezo layer 101 (approximately n-type) and a second electrode contact 122, which can correspond to a metal layer MA, and these can form a piezo element 100.

[0077] Furthermore, an ohmic contact EK can be applied laterally to and from the stack of the first piezo layer 101, making contact with it. The space charge region RL can form in the first piezo layer 101 and adjacent to the metal layer MS. The first piezo layer 101 can be arranged on a substrate SB, and between these two, the first piezo layer 101 can extend across a cavity as an (acoustic) reflector element RE on lateral residual areas of a sacrificial layer SL made of approximately SiO2.

[0078] The invention can be advantageously used for volume acoustic resonator components such as resonators / oscillators, RF filters, or other components, and relates to MEMS components for RF systems in mobile communications (filters) or radar (oscillators).

[0079] The space charge region RL can be realized by a Schottky contact with the metal layer MS, which can form the upper electrode 122. The metal thickness and the doped semiconductor thickness (space charge region RL and free charge carrier zone) together form the resonator and should, in total, correspond to half a wavelength of the effective acoustic wave. The metal layer MS and the free charge carrier layer can be as thin as possible, since the acoustic wave is only excited in the space charge region RL, and thus the ratio between space charge thickness and half a wavelength decisively determines the excitation (qualitative plot of the mechanical displacement to the right of the stack in Fig. 5a). However, the aforementioned layers should not be too thin, as this would impair the electrical conductivity.

[0080] To fabricate such a structure, an n-doped GaN layer can be grown, for example, with Si doping, on a sacrificial substrate. The layer can then be transferred to a Si wafer with a structured passivation layer, such as SiO2. The GaN layer can then be structured, for example, by plasma etching, e.g., using chlorine chemistry with a stop in the GaN layer. The etch depth must be at least equal to the thickness of the space charge region RL to isolate the space charge region laterally from the electrical contact EK. The contact point for the ohmic contact EK can be recessed, or only an insulating trench can be created between the space charge region and the contact zone EK. The insulating trench or recess does not necessarily have to be as deep as shown in the figures.Figure 5a shows that the etching depth does not necessarily correlate with the extent of the space charge region, as etching can be performed to varying depths. Furthermore, a metallization for the ohmic contact (EK) and, if necessary, a different metallization for the Schottky contact (e.g., the MS layer) can be applied and structured. Typical metals for an ohmic contact on n-doped GaN include Ti, Al, and Ti / Al. The local dopant concentration beneath the ohmic contact can be further increased by local ion implantation for lower contact resistance. Schottky contacts on n-doped GaN are typically achieved using Pt, Ni, or Ni / Au.

[0081] Alternatively, an n-doped GaN layer can be grown on Si using intermediate layers, e.g., AIN and AIGaN. Here too, the GaN layer can be structured, e.g., by plasma etching, e.g., using chlorine chemistry with a stop within the GaN layer, and a metallization (EK) can be applied and structured for the ohmic contact, and possibly another metallization for the Schottky contact.

[0082] In this alternative, the interlayers beneath the resonator can also be removed, for example by etching the Si wafer with a stop at the interlayers and then selectively removing them. In this case, the passivation between the Si substrate and the GaN layer can be, for example, an AIN layer.

[0083] Other components of the remaining embodiments can also be manufactured analogously.

[0084] Fig. 5b shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention.

[0085] The volume acoustic component 10 of Fig. 5b corresponds to that of Fig. 5a, wherein the side regions of the passivation layer SL and the cavity as a reflector element can be replaced by a stack of layers of an acoustic Bragg reflector, which can be located below the first piezoelectric layer 101 (first electrode 120) and on the substrate SB. Such a surface mount resonator-SMR arrangement can also be used in each of the following examples.

[0086] Fig. 6 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention.

[0087] The volume acoustic component from Fig. 6 is similar to the component from Fig. 5a, except that instead of the metal layer MS on the top surface, a second piezoelectric layer 102 is arranged, which can be connected via a side contact EK and can itself serve as the upper electrode 122. In this example, the first piezoelectric layer 101 (which also takes on the role of the lower electrode 120) can be an n-type and the second piezoelectric layer a p-type. This allows a space charge region RL to form in both piezoelectric layers 101 and 102. The electrode function can be achieved with high doping concentrations.

[0088] Fig. 7 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention.

[0089] To avoid an excessively thin space charge region due to high doping concentrations, an intrinsic region 200 can be inserted into the stack. This embodiment is shown in Fig. 7 for the example according to Fig. 5a, where a Schottky contact with the metal layer MS as the upper electrode 122 is shown, and for the corresponding embodiment to Fig. 6, an intrinsic region 200 according to Fig. 8 is inserted between the first piezo layer 101 and the second piezo layer 102, wherein the space charge region RL (also comprising the intrinsic region 200) extends into the first piezo layer 101 in region RL-1 and into the second piezo layer 102 in region RL-2.

[0090] Fig. 9 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention. The resonators of Figures 1 to 8 can reach their limits at very high frequencies because the thickness of the electrodes (regardless of whether they are metallic or implemented as doped semiconductors) can become so thin that technological implementation becomes difficult, and the excitation region (space charge region) can become too small due to the electrode thickness. Furthermore, the entire stack can become so thin that it is difficult or impossible to implement technologically. To remedy this, any harmonic of the layer stack can be used, which can be the case for a Schottky contact in the embodiment shown in Fig. 9. The structure of the volume acoustic component can then be similar to that of Fig.5a, with the difference that a thicker first piezo layer 101 is used, which can correspond to the thickness of a harmonic. Fig. 10 shows this analogously for a pn junction of the setup according to Fig. 6, where the first piezo layer 101 and the second piezo layer 102 can be correspondingly thicker for the harmonics. Fig. 9 and Fig. 10 show this thickness by way of example for a third harmonic.

[0091] The major advantage over a conventional OBAR is that the modal electromechanical coupling can improve for higher modes, one reason being that the entire voltage drop is limited to the space charge region and not the entire stack. Therefore, the electric field cannot oppose the deflection.

[0092] In simplified terms for a 1D layer stack (in the z-direction), the modal electromechanical coupling can be calculated by an integral over the layer thickness l from n, the mode number (n=1 is the fundamental mode and n=2 the first harmonic), e33, the piezoelectric coupling constant, Sn, the strain amplitude, and Ez, the electric field (via sin(nnz / l)). If an alternating voltage V is applied to both the OBAR and the resonator, the electric field is approximately Ez,0BAR = V / l in the first case and Ez,RLZ = V / d = nV / l in the latter. The coupling of the OBAR is always zero for even n and remains constant for odd n. In contrast, the coupling of the resonator according to the invention can improve with increasing n.

[0093] Fig. 11 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention.

[0094] As shown in Figures 11 and 12, an intrinsic region 200 can also be used when applying the harmonics, with Figure 11 showing this for a Schottky contact and for the embodiment according to Figure 5a (only according to Figure 11 with a thicker first piezo layer 101) and Figure 12 showing this for a pn junction, correspondingly for the embodiment of Figure 8. It can be seen that the space charge regions RL-1 and RL-2 in the piezo layers 101 and 102 are thinner than for the fundamental mode.

[0095] Fig. 13 shows a schematic sectional view of a volume acoustic component according to a further embodiment of the present invention.

[0096] At high frequencies, the space charge region can become very thin, and consequently the junction capacitance can increase, resulting in a low impedance level. This can be reduced or avoided by also implementing a Schottky contact to the piezoelectric semiconductor 101 in the Schottky version of the resonator shown in Fig. 9. In other words, a metal layer MS can also be connected to the first piezoelectric layer 101, with the lower metal layer MS then being laterally contacted by an ohmic contact EK. In this way, a lower space charge region RL can form in the lower region of the first piezoelectric layer 101, and an upper space charge region RL-2 can form in the upper region of the first piezoelectric layer 101. Fig. 14 shows that in the case of a pn contact from Fig.10 Even any number of pn junctions can be implemented, with several space charge regions forming between them. Fig. 15 shows a schematic representation of suppressing the resonant frequency by a DC voltage.

[0097] Figure 15 (left) shows the strain at resonance in a piezoelectric semiconductor (oriented along the z-axis) when no DC voltage is applied. The 5th harmonic is present. The hatched areas (positive direction as shown in the left image) are the regions where space charge regions are present. This means that these are also the regions where piezoelectric coupling occurs (where the electric field is non-zero). For a DC voltage of zero volts, the regions are of equal size. The coupling is the integral of the product of the constant electric field and the strain. Since both wave crests are positive, the coupling is also positive. In the case shown in the right image, where a non-zero DC voltage is applied such that one space charge region just disappears (begins to conduct) and the other becomes twice as large, the coupling becomes zero.The reason for this is that the aforementioned integral becomes zero (the area balance becomes zero, since the positive areas equal the negative side of the hatched areas). This means, however, that no resonance can be excited, so the resonator is "switched off".

[0098] In both cases of Fig. 13 and Fl. 14, the applied DC voltage should be zero, otherwise the space charge regions may become of different thicknesses and thus no longer be suitable for exciting individual resonances.

[0099] This fact can also be advantageously used to switch off the resonator, since a DC voltage UDC=Uoff can make the coupling zero, as shown in Fig. 15.

[0100] It is possible that the coupling will not improve, since in these cases the applied voltage can be distributed equally across all space charge regions.

[0101] The presented resonators can also be used as frequency-generating components (e.g., as mixers). In this case, not only a DC voltage and the desired AC voltage are applied, but also an additional AC voltage (local oscillator LO).

[0102] U=UDC+ULOs\n (a>LOt)+U AC sin (a>t)

[0103] This modulates the space charge thickness (ULO is sufficiently large) depending on the angular frequency c LO and leads to strong nonlinearities, which in turn generate usable intermodulation products (e.g. rr LO).

[0104] Fig. 16 shows a block diagram of process steps of the method for manufacturing a volume acoustic component according to an embodiment of the present invention.

[0105] The method for manufacturing a volume acoustic component involves providing S1 a substrate and arranging a first electrode contact and a second electrode contact and / or a piezoelectric element between them (with at least a first piezoelectric layer) and / or a second piezoelectric layer, which are arranged between the first electrode contact and the second electrode contact and stacked in a stack arrangement or form the first electrode contact and / or the second electrode contact themselves; providing S2 a voltage source, which is connected to the first electrode contact and to the second electrode contact and to which a DC or AC voltage can be applied, such that the thickness of a space charge region in the first piezoelectric layer and / or in the second piezoelectric layer is controllable;and a provision S3 of an acoustic reflector element, wherein the acoustic reflector element is arranged in or on the substrate and the stacking arrangement is arranged on the substrate and / or on the reflector element.;

[0106] Although the present invention has been fully described above with reference to 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 at least one first piezoelectric layer (101) as a semiconductor with at least one first doping and / or at least one second piezoelectric layer (102) as a semiconductor with a second doping, which are arranged between the first electrode contact (120) and the second electrode contact (122) and are stacked in a stacking arrangement or form the first electrode contact (120) and / or the second electrode contact (122) themselves; and - a voltage source (SP) which is connected to the first electrode contact (120) and to the second electrode contact (122) and to which a direct or alternating voltage can be applied, such that the thickness of a space charge region (RL) in the first piezoelectric layer (101) and / or in the second piezoelectric layer (102) is controllable, 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) 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, wherein the piezoelectric element (100) comprises at least one metal layer (MS) which is in contact with the first piezoelectric layer (101) or with the second piezoelectric layer (102) and wherein the space charge region (RL) is located in the first piezoelectric layer (101) or in the second piezoelectric layer (102) and adjacent to the metal layer (MS) is formed by a doping difference to the metal layer.

5. Volume acoustic component (10) according to one of claims 1 to 4, wherein a thickness of the piezoelectric element (100) corresponds to a multiple of half a wavelength of an operating frequency of the volume acoustic component (10).

6. Volume acoustic component (10) according to one of claims 1 to 4, wherein a thickness of the piezoelectric element (100) corresponds to more than half a wavelength of an operating frequency of the volume acoustic component (10) and a harmonic of the operating frequency.

7. Volume acoustic component (10) according to one of claims 1 to 6, in which the first electrode contact (120) is represented by the first piezoelectric layer (101) or by the metal layer and / or the second electrode contact (122) is represented by the second piezoelectric layer (102) or by the metal layer.

8. Volume acoustic component (10) according to one of claims 1 to 7, in which a DC voltage and / or an AC voltage is applied to the piezoelectric element (100) with which the thickness of the space charge region (RL) can be modulated.

9. Volume acoustic component (10) according to one of claims 1 to 8, wherein the piezoelectric element (100) comprises at least one intrinsic region (200) which is adjacent to or formed in the first piezoelectric layer (101) or the second piezoelectric layer (102).

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. Method for manufacturing 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) and / or a piezoelectric element (100) in between with at least one first piezoelectric layer (101) with at least one first doping and / or a second piezoelectric layer (102) with a second doping, which are arranged between the first electrode contact (120) and the second electrode contact (122) and are stacked in a stacking arrangement or form the first electrode contact (120) and / or the second electrode contact (122) themselves; - Providing (S2) a voltage source (SP) which is connected to the first electrode contact (120) and to the second electrode contact (122) and to which a DC or AC voltage can be applied, such that the thickness of a space charge region (RL) in the first piezoelectric layer (101) and / or in the second piezoelectric layer (102) is controllable; - Providing (S3) an acoustic reflector element (RE), wherein the acoustic reflector element (RE) is arranged in or on the substrate (SB) and the stacking arrangement is arranged on the substrate (SB) and / or on the reflector element (RE).

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