Volume acoustic apparatus and method for producing a volume acoustic apparatus

Abstract

The invention relates to a volume acoustic apparatus, comprising a resonator device. The resonator device comprises a first piezoelectric element (1), a second piezoelectric element (2), and a high-f-Q structure (3). The volume acoustic apparatus further comprises a first electrode device (7a) and a second electrode device (8a), wherein the first electrode device and the second electrode device are located on a first side and / or a second side, respectively, of the resonator device. A material of the high-f-Q structure comprises a high-f-Q material, in particular having an f-Q value of more than 1013 at a frequency of greater than or equal to 3 GHz.

Description

[0001] Description

[0002] title

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

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

[0005] State of the art

[0006] In high-frequency technology, bulk acoustic wave (BAW) components are used as resonators in filters and oscillators. The operating frequency of the components is primarily determined by the thickness of a piezoelectric layer and the speed of sound in the piezoelectric material. To achieve higher operating frequencies, the layer thickness must be reduced. Tolerances are therefore becoming increasingly important.

[0007] With a smaller layer thickness, the capacitance of the BAW component increases. To maintain the wave impedance, the component area must therefore be reduced at the same time. However, acoustic energy is lost at the edge of the component. As the component is reduced in size, edge losses increase quadratically with the operating frequency. The technology of BAW components therefore reaches its limits at approximately 10 GHz. Higher frequencies in the range above 10 GHz require thinner resonator layers, which, for example, leads to higher demands regarding layer thickness accuracy. However, as the layer thickness of the piezoelectric layer(s) decreases, their crystalline quality decreases. The quality factor of a resonator decreases, and with it, the performance parameters of filters, such as insertion losses or slope, suffer.

[0008] There are also FBAR (film bulk acoustic resonator) components whose resonance frequency can be influenced by lateral excitation using interdigital electrodes.

[0009] US 11,258,423 B2 discloses a lateral volume acoustic FBAR component whose resonance frequency can be influenced by lateral excitation using interdigital electrodes.

[0010] Lateral bulk acoustic FBAR devices offer additional design parameters for the interdigital electrodes, allowing the resonator's resonance frequencies to be lithographically defined. Furthermore, lateral BAW resonators can excite not only longitudinal thickness extension modes but also transverse lateral extension modes. This allows for simultaneously exciting combined modes, resulting in an increased electromechanical coupling coefficient.

[0011] However, lateral BAW components also suffer from a degradation of the Q factor (quality factor) at high frequencies due to the poorer material quality of thinner layers.

[0012] Disclosure of the invention

[0013] The invention provides a volume acoustic device and a method for producing a volume acoustic device having the features of the independent patent claims.

[0014] Preferred embodiments are the subject of the respective subclaims.

[0015] According to a first aspect, the invention accordingly relates to a volume acoustic device with a resonator device. The resonator device comprises a first piezoelectric element, at least one second piezoelectric element, and a high-fQ structure. The volume acoustic device further comprises a first electrode device and a second electrode device, wherein the first electrode device and the second electrode device are each arranged on a first side and / or second side of the resonator device. The high-fQ structure is arranged between the first piezoelectric element and the second piezoelectric element and / or on a side opposite the electrode device. A material of the high-fQ structure comprises a high-fQ material, in particular with a value of fQ of more than 10 13 at a frequency greater than or equal to 3 GHz.

[0016] According to a second aspect, the invention relates to a method for producing a volume acoustic device. A resonator device is formed, comprising a first piezoelectric element, at least one second piezoelectric element, and a high-fQ structure. Furthermore, a first electrode device and a second electrode device are formed, wherein the first electrode device and the second electrode device are each arranged on a first side and / or second side of the resonator device. The high-fQ structure is arranged between the first piezoelectric element and the second piezoelectric element and / or on a side opposite the electrode device. A material of the high-fQ structure comprises a high-fQ material, in particular with an fQ value of more than 10 13 at a frequency greater than or equal to 3 GHz.

[0017] Advantages of the invention

[0018] The volume acoustic device is suitable for use in high frequency ranges with a high k t 2 -Q-product, where k t denotes the electromechanical coupling coefficient and Q denotes the quality factor. The high value for k t 2 -Q-product corresponds to a high slope and a low insertion loss, which is particularly advantageous for filters

[0019] Material-related acoustic losses are reduced by shifting part of the acoustic energy into a high-f Q material, where f is the frequency of an coupled electromagnetic wave. By using a high-f Q material, the material's inherent damping is reduced, thereby increasing the Q factor.

[0020] According to a further development of the volume acoustic device, the high-FQ structure consists exclusively of a high-fQ material. Alternatively, the high-FQ structure consists of several high-fQ materials, for example, several layers of different high-fQ materials.

[0021] According to a further development of the volume acoustic device, the material of the high-fQ structure comprises at least one of silicon carbide, silicon nitride, silicon and diamond. These are high-fQ materials.

[0022] According to a further development of the volume-acoustic device, a material of the first piezoelectric element essentially corresponds to a material of the second piezoelectric element. The material can, in particular, comprise aluminum nitride, an alloy with scandium, zinc oxide, lithium tantalate, or lithium niobate.

[0023] According to a further development of the volume acoustic device, the first piezoelectric element and the second piezoelectric element each have at least one piezoelectric layer, with the polarization directions of the piezoelectric layers being aligned parallel or antiparallel to each other. The parallel or antiparallel polarity can be achieved, for example, by adding alloying agents to the material of the first piezoelectric element and / or the second piezoelectric element.

[0024] The polarization directions of the first piezoelectric element and the second piezoelectric element can be selected depending on the arrangement and the potentials of the first electrode device and the second electrode device such that a target resonance mode is formed.

[0025] In a vertical fundamental mode, for example, a mode with at least one antinode in each of the first piezoelectric element, the second piezoelectric element and the high-fQ structure can form as the target resonance mode.

[0026] According to a further development of the volume acoustic device, an acoustic layer thickness of the piezoelectric layers corresponds to half an acoustic wavelength of a given resonance mode.

[0027] According to a further development of the volume acoustic device, an acoustic layer thickness of the high-fQ structure corresponds to an integer multiple of half an acoustic wavelength of a given resonance mode.

[0028] According to a further development of the volume acoustic device, the first electrode device and the second electrode device form an interdigital electrode pair.

[0029] According to a further development of the volume acoustic device, the high-fQ structure is designed as a layer stack

[0030] According to a further development of the volume acoustic device, the resonator device is arranged on a substrate, wherein a cavity is formed between the resonator device and the substrate. An acoustic impedance jump occurs at the cavity.

[0031] According to a further development, the volume acoustic device comprises a substrate, wherein a Bragg reflector is alternatively arranged between the resonator device and the substrate. As a result, the acoustic energy is reflected.

[0032] According to a further development of the volume acoustic device, a material of the first electrode device and / or the second electrode device comprises at least one of aluminum, titanium, and copper. These materials have a low mass density. This is advantageous because, depending on the target resonance mode, the electrode mass resonates, and additional moving mass shifts the resonance frequency to lower frequencies. According to a further development of the volume acoustic device, additional piezoelectric layers are provided, which serve to specifically excite higher modes and keep the electromechanical coupling coefficient as high as possible.

[0033] According to a further development, the volume acoustic device is a resonator, an oscillator (particularly for use in the radar range) or a filter (particularly for use in the high-frequency range).

[0034] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawing.

[0035] Short description of the drawings

[0036] They show:

[0037] Figure 1 is a cross-sectional view of a volume acoustic device according to an embodiment of the invention;

[0038] Figure 2 is a cross-sectional view of a volume acoustic device according to a further embodiment of the invention;

[0039] Figure 3 is a cross-sectional view of a volume acoustic device according to a further embodiment of the invention;

[0040] Figure 4 is a cross-sectional view of a volume acoustic device according to a further embodiment of the invention; and

[0041] Figure 5 is a flowchart of a method for manufacturing a volume acoustic device according to an embodiment of the invention.

[0042] In all figures, identical or functionally equivalent elements and devices are provided with the same reference numerals. The numbering of process steps serves the purpose of clarity and is generally not intended to imply a specific chronological order. In particular, several process steps can be performed simultaneously.

[0043] Description of the embodiments

[0044] Figure 1 shows a cross-sectional view of a volume acoustic device 100. The volume acoustic device 100 comprises a resonator device 5. The resonator device 5 comprises a first piezoelectric element 1, a second piezoelectric element 2, and a high-FQ structure 3 arranged between the first piezoelectric element 1 and the second piezoelectric element 2.

[0045] The first piezoelectric element 1 and the second piezoelectric element 2 are each layers of a piezoelectric material. A material of the first piezoelectric element 1 can essentially correspond to a material of the second piezoelectric element 2. A polarization direction 10 of the first piezoelectric element 1 is parallel to the polarization direction 11 of the second piezoelectric element 2.

[0046] An acoustic layer thickness of the piezoelectric elements 1, 2 corresponds to half an acoustic wavelength of a given resonance mode.

[0047] The high-FQ structure 3 can be formed as a multilayer stack and consists at least partially, preferably completely, of a high-FQ material. This can be understood as meaning that the material has a FQ value of more than 10 13at a frequency greater than or equal to 3 GHz. Examples of materials are silicon carbide, silicon nitride, silicon and diamond

[0048] An acoustic layer thickness of the high-FQ structure 3 corresponds to an odd multiple of half an acoustic wavelength of the given resonance mode. The volume acoustic device 100 comprises a substrate 12, wherein a layer 4 is arranged on the substrate, on which, in turn, the second piezoelectric element 2 is formed.

[0049] In the layer 4, a cavity 6 is formed between the resonator device 5 and the substrate 12.

[0050] Furthermore, the volume acoustic device 100 comprises a first electrode device 7a and a second electrode device 8a, wherein the first electrode device 7a and the second electrode device 8a are each arranged on a first side of the resonator device 5 facing away from the substrate 12.

[0051] The first electrode device 7a and the second electrode device 8a form an interdigital electrode pair. At the interface with the cavity 6, a reflection of an electromagnetic wave coupled into the resonator device 5 by means of the first electrode device 7a occurs.

[0052] A material of the first electrode device 7a and / or the second electrode device 8a may comprise at least one of aluminum, titanium and copper.

[0053] Acoustic isolation trenches 18 limit the resonator laterally and prevent acoustic energy losses.

[0054] A high-frequency signal is fed into the volume acoustic device 100 at the first electrode device 7a. The electromagnetic wave is converted at the first electrode device 7a by the first piezoelectric element 1 into an acoustic wave and at the second electrode device 8a back into an electromagnetic wave. For a given electromagnetic or acoustic frequency, the acoustic wavelength Z results. a about the speed of sound c s of the respective layer material as follows: a = Cs / f. If the layer thickness d p the acoustic resonator device 5 corresponds to a multiple of half an acoustic wavelength of the converted electromagnetic wave, ie d p = (n+%)-X a for n = 0, 1, the incoming signal is transmitted and otherwise reflected. The resonator device 5 therefore corresponds to a volume acoustic resonator.

[0055] In a further embodiment, the polarizations of the first piezoelectric element 1 and the second piezoelectric element 2 are aligned antiparallel. An acoustic layer thickness of the high-fQ structure 3 then corresponds to an even multiple of a whole acoustic wavelength of the predetermined resonance mode.

[0056] Figure 2 shows a cross-sectional view of another volume acoustic device 200. In contrast to the volume acoustic device 100 shown in Figure 1, the high-FQ structure 3 is arranged on the substrate-facing side of the second piezoelectric element 2. Furthermore, the polarization directions 10, 11 are antiparallel.

[0057] Figure 3 shows a cross-sectional view of another volume acoustic device 300. In contrast to the volume acoustic device 100 shown in Figure 1, the first electrode device 7b and the second electrode device 8b are arranged both on the side of the resonator device 5 facing the substrate 12 and on the side facing away from the substrate 12 and are connected to one another via respective vias 16, 17. This results in particularly efficient excitation.

[0058] The polarization directions 10, 11 of the first piezoelectric element 1 and the second piezoelectric element 2 are aligned parallel, with the first electrode device 7b and the second electrode device 8b being arranged symmetrically on the two sides of the resonator device 5 in the region of the cavity 6. Figure 4 shows a cross-sectional view of another volume-acoustic device 400. In contrast to the volume-acoustic device 300 shown in Figure 3, the polarization directions 10, 11 of the first piezoelectric element 1 and the second piezoelectric element 2 are aligned antiparallel, with the first electrode device 7b and the second electrode device 8b being arranged antisymmetrically on the two sides of the resonator device 5 in the region of the cavity 6.

[0059] Depending on the selected potential configuration, lateral and / or vertical field configurations result in the resonator device 5, which allow the excitation of combined acoustic vertical and lateral modes.

[0060] Figure 5 shows a flow chart of a method for manufacturing a volume acoustic device, in particular one of the volume acoustic devices 100 to 400 described above.

[0061] In a first method step S1, a resonator device 5 is formed, comprising a first piezoelectric element 1, a second piezoelectric element 2, and a high-FQ structure 3 arranged between the first piezoelectric element 1 and the second piezoelectric element 2.

[0062] In a second method step S2, a first electrode device 7a-7c and a second electrode device 8a-8c are formed, wherein the first electrode device 7a-7c and the second electrode device 8a-8c are each arranged on a first side and / or second side of the resonator device 5. A material of the high-FQ structure comprises a high-fQ material, in particular with a value of fQ of more than 10 13 at a frequency greater than or equal to 3 GHz.

Claims

Claims 1. A volume acoustic device (100; 200; 300; 400), comprising a resonator device (5) comprising a first piezoelectric element (1), at least one second piezoelectric element (2), and a high-fQ structure (3); and a first electrode device (7a-7c) and a second electrode device (8a-8c), wherein the first electrode device (7a-7c) and the second electrode device (8) are each arranged on a first side and / or second side of the resonator device (5); wherein the high-fQ structure is arranged between the first piezoelectric element (1) and the second piezoelectric element (2) and / or on a side opposite the electrode device (7a, 8a), and; wherein a material of the high-fQ structure (3) comprises a high-fQ material, in particular with a value of fQ of more than 10 13 at a frequency greater than or equal to 3 GHz.

2. Volume acoustic device (100; 200; 300; 400) according to claim 1, wherein the material of the high-fQ structure (3) comprises at least one of silicon carbide, silicon nitride, silicon and diamond 3. Volume acoustic device (100; 200; 300; 400) according to claim 1 or 2, wherein a material of the first piezoelectric element (1) substantially corresponds to a material of the second piezoelectric element (2).

4. Volume acoustic device (100; 200; 300; 400) according to one of the preceding claims, wherein the first piezoelectric element (1) and the second piezoelectric element (2) each have at least one piezoelectric layer, wherein polarization directions (10, 11) of the piezoelectric layers are parallel or antiparallel to one another are aligned.

5. Volume acoustic device (100; 200; 300; 400) according to claim 4, wherein an acoustic layer thickness of the piezoelectric layers corresponds in each case to half an acoustic wavelength of a predetermined resonance mode.

6. Volume acoustic device (100; 200; 300; 400) according to one of the preceding claims, wherein an acoustic layer thickness of the high-fQ structure (3) corresponds to an integer multiple of half an acoustic wavelength of a given resonance mode 7. Volume acoustic device (100; 200; 300; 400) according to one of the preceding claims, wherein the high-fQ structure (3) is formed as a layer stack.

8. Volume acoustic device (100; 200; 300; 400) according to one of the preceding claims, wherein the resonator device (5) is arranged on a substrate (12), wherein a cavity (6) is formed between the resonator device (5) and the substrate (12).

9. Volume acoustic device (100; 200; 300; 400) according to one of the preceding claims, comprising a substrate (12), wherein a Bragg reflector (13) is arranged between the resonator device (5) and the substrate (12) 10. A method for producing a volume acoustic device (100; 200; 300; 400), comprising the steps: Forming (S1) a resonator device (5) comprising a first piezoelectric element (1), a second piezoelectric element (2), and a high-fQ structure (3); and Forming (S2) a first electrode device (7a-7c) and a second electrode device (8a-8c), wherein the first electrode device (7a- 7c) and the second electrode device (8a-8c) are each arranged on a first side and / or second side of the resonator device (5); wherein a material of the high-fQ structure (3) comprises a high-fQ material, in particular with a value of fQ of more than 10 13at a frequency greater than or equal to 3 GHz.

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