Bulk acoustic wave device and method for manufacturing bulk acoustic wave device

Abstract

The invention relates to a bulk acoustic wave device comprising a resonator arrangement. The resonator arrangement comprises a first piezoelectric element (1), a second piezoelectric element (2) and a high fQ structure (3). The bulk acoustic wave device further comprises a first electrode arrangement (7a) and a second electrode arrangement (8a), the first electrode arrangement and the second electrode arrangement being arranged on a first side and / or a second side, respectively, of the resonator arrangement. The material of the high fQ structure comprises a high fQ material having a fQ value greater than 1013, especially at frequencies greater than or equal to 3 GHz.

Description

Technical Field

[0001] This invention relates to a bulk acoustic wave device and a method for manufacturing the bulk acoustic wave device. Background Technology

[0002] In the field of high-frequency technology, bulk acoustic wave (BAW) components are used as resonators in filters and oscillators. The operating frequency of these components is mainly determined by the thickness of the piezoelectric layer and the velocity of sound in the piezoelectric material. To achieve higher operating efficiency, the layer thickness must be reduced. Therefore, tolerances become increasingly important.

[0003] As the layer thickness decreases, the capacitance of BAW components increases. To maintain a constant wave impedance, the component area must also be reduced. However, acoustic energy loss occurs at the component edges. As component size shrinks, edge losses increase with the square of the operating frequency. Therefore, BAW component technology approaches its application limit at approximately 10 GHz. Higher frequencies above 10 GHz require even smaller resonator layer thicknesses, leading to, for example, higher requirements for layer thickness precision. However, as the thickness of the piezoelectric layer or individual piezoelectric layers decreases, its crystal quality deteriorates. The resonator's quality factor decreases, resulting in worse filter performance parameters, such as increased insertion loss or deteriorated edge steepness.

[0004] In addition, there are film bulk acoustic resonators (FBAR) whose resonant frequency can be adjusted by lateral excitation using interdigital electrodes.

[0005] A transverse bulk acoustic wave (FBAR) element is known from US 11,258,423 B2, the resonant frequency of which can be adjusted by transverse excitation using interdigitated electrodes.

[0006] For lateral bulk acoustic wave (FBAR) devices, additional design parameters can be used for the interdigitated electrodes, which can be used to determine the resonant frequency of the resonator through photolithography. Furthermore, lateral BAW resonators can excite not only longitudinal thickness scaling modes but also additional lateral thickness scaling modes. This allows for the simultaneous excitation of combined modes, resulting in a higher electromechanical coupling coefficient.

[0007] However, due to the poor quality of the thinner material, the transverse BAW element also suffers from Q-factor (quality factor) degradation at high frequencies. Summary of the Invention

[0008] The present invention provides a bulk acoustic wave device having the features described in the independent claims and a method for manufacturing the bulk acoustic wave device.

[0009] The preferred embodiments are the subject of each dependent claim.

[0010] Therefore, according to a first aspect, the present invention relates to a bulk acoustic wave device having a resonator facility. The resonator facility includes a first piezoelectric element, at least one second piezoelectric element, and a high fQ structure. The bulk acoustic wave device further includes a first electrode facility and a second electrode facility, wherein the first electrode facility and the second electrode facility are respectively arranged on a first side and / or a second side of the resonator facility. The high fQ structure is arranged between the first piezoelectric element and the second piezoelectric element and / or on a side opposite to one of the electrode facilities. The material of the high fQ structure includes a high fQ material, which has a fQ greater than 10 at frequencies greater than or equal to 3 GHz. 13 The fQ value.

[0011] According to a second aspect, the present invention relates to a method for manufacturing a bulk acoustic wave device. A resonator facility is constructed, comprising a first piezoelectric element, at least one second piezoelectric element, and a high fQ structure. A first electrode facility and a second electrode facility are also constructed, wherein the first electrode facility and the second electrode facility are respectively arranged on a first side and / or a second side of the resonator facility. The high fQ structure is arranged between the first piezoelectric element and the second piezoelectric element and / or on a side opposite to one of the electrode facilities. The material of the high fQ structure comprises a high fQ material, and the facility material, in particular, has a fQ greater than 10 at frequencies greater than or equal to 3 GHz. 13 The fQ value.

[0012] The bulk acoustic wave device is suitable for use in applications with high k t 2 ∙ In the high-frequency range of the Q product, where k t Let k represent the electromechanical coupling coefficient, and Q represent the quality factor. t 2 • The Q product value corresponds to high edge steepness and low insertion loss, which is particularly advantageous for filters.

[0013] By transferring a portion of the acoustic energy to a high-fQ material, the material-induced acoustic loss can be reduced, where f represents the frequency of the coupled electromagnetic wave. Using a high-fQ material reduces the material's own damping, thereby increasing the Q factor.

[0014] According to one extension of the aforementioned bulk acoustic wave device, the high-fQ structure is composed of only one type of high-fQ material. Alternatively, the high-fQ structure is composed of multiple high-fQ materials, for example, multiple layers of different high-fQ materials.

[0015] According to one extension of the bulk acoustic wave device, the material of the high fQ structure includes at least one selected from silicon carbide, silicon nitride, silicon, and diamond. High fQ materials are discussed herein.

[0016] According to one extension of the bulk acoustic wave device, the material of the first piezoelectric element is substantially equivalent to the material of the second piezoelectric element. This material may in particular include aluminum nitride, scandium-containing alloys, zinc oxide, lithium tantalate, or lithium niobate.

[0017] According to one extension of the bulk acoustic wave device, the first piezoelectric element and the second piezoelectric element each have at least one piezoelectric layer, wherein the polarization directions of the piezoelectric layers are oriented parallel to or antiparallel to each other. This parallel or antiparallel polarity can be achieved, for example, by adding alloying elements to the materials of the first and / or second piezoelectric elements.

[0018] The polarization directions of the first and second piezoelectric elements can be selected based on the arrangement and potential of the first and second electrode facilities to form the target resonant mode.

[0019] For example, in the vertical fundamental mode, modes with at least one oscillating ventral zone in the first piezoelectric element, the second piezoelectric element, and the high fQ structure can be constructed as the target resonant modes.

[0020] According to one extension of the bulk acoustic wave device, the acoustic layer thickness of the piezoelectric layer is equivalent to half the acoustic wavelength of a pre-given resonant mode.

[0021] According to one extension of the bulk acoustic device, the acoustic layer thickness of the high fQ structure is equivalent to an integer multiple of half the acoustic wavelength of a pre-given resonant mode.

[0022] According to one extension of the bulk acoustic wave device, the first electrode facility and the second electrode facility constitute an interdigital electrode pair.

[0023] According to one extension of the bulk acoustic wave device, the high fQ structure is constructed as a stack.

[0024] According to one extension of the bulk acoustic wave device, a resonator facility is arranged on a substrate, wherein a cavity is formed between the resonator facility and the substrate. An acoustic impedance jump occurs at the cavity.

[0025] According to one extended embodiment, the bulk acoustic wave device includes a substrate, wherein a Bragg reflector is alternately arranged between the resonator facility and the substrate. This allows acoustic energy to be reflected.

[0026] According to one extension of the bulk acoustic wave device, the first electrode arrangement and / or the second electrode arrangement are made of at least one of aluminum, titanium, and copper. These materials have low mass density. This is advantageous because, depending on the target resonant mode, the electrode mass vibrates, and the additional mass that moves with it shifts the resonant frequency to a lower frequency.

[0027] According to an extension of the bulk acoustic wave device, an additional piezoelectric layer is provided, which is used to selectively excite higher-order modes and keep the electromechanical coupling coefficient as large as possible.

[0028] According to one extension, the bulk acoustic device is a resonator, an oscillator (especially for use in the radar field), or a filter (especially for use in the high-frequency field).

[0029] Other advantages, features and details of the present invention will become apparent from the following description, in which different embodiments are described in detail with reference to the accompanying drawings. Attached Figure Description

[0030] Figure 1 A cross-sectional view of a bulk acoustic wave device according to an embodiment of the present invention is shown; Figure 2 A cross-sectional view of a bulk acoustic wave device according to another embodiment of the present invention is shown; Figure 3 A cross-sectional view of a bulk acoustic wave device according to another embodiment of the present invention is shown; Figure 4 A cross-sectional view of a bulk acoustic wave device according to another embodiment of the present invention is shown; and Figure 5 A flowchart illustrating a method for manufacturing a bulk acoustic device according to an embodiment of the present invention is shown.

[0031] In all the accompanying drawings, identical or functionally equivalent elements and devices are given the same reference numerals. The numbering of method steps is intended for clarity and generally does not indicate a specific chronological order. In particular, multiple method steps may be performed simultaneously. Detailed Implementation

[0032] Figure 1 A cross-sectional view of the bulk acoustic wave device 100 is shown. The bulk acoustic wave device 100 includes a resonator facility 5. The resonator facility 5 includes a first piezoelectric element 1, a second piezoelectric element 2, and a high fQ structure 3 disposed between the first piezoelectric element 1 and the second piezoelectric element 2.

[0033] The first piezoelectric element 1 and the second piezoelectric element 2 are each composed of layers of piezoelectric material. The material of the first piezoelectric element 1 can be substantially equivalent to the material of the second piezoelectric element 2. The polarization direction 10 of the first piezoelectric element 1 is parallel to the polarization direction 11 of the second piezoelectric element 2.

[0034] The acoustic layer thicknesses of piezoelectric elements 1 and 2 are respectively equivalent to half the acoustic wavelength of a pre-defined resonant mode.

[0035] The high fQ structure 3 can be constructed as a multi-layered stack and is at least partially, preferably entirely, composed of a high fQ material. This can be understood as the material having an fQ greater than 10 at frequencies greater than or equal to 3 GHz. 13 The value is . Exemplary materials are silicon carbide, silicon nitride, silicon, and diamond.

[0036] The acoustic layer thickness of the high fQ structure 3 is equivalent to an odd multiple of half the acoustic wavelength of the pre-given resonant mode.

[0037] The bulk acoustic wave device 100 includes a substrate 12, on which a layer 4 is disposed, and a second piezoelectric element 2 is constructed on the layer.

[0038] In layer 4, a cavity 6 is formed between the resonator facility 5 and the substrate 12.

[0039] In addition, the bulk acoustic wave device 100 includes a first electrode facility 7a and a second electrode facility 8a, wherein the first electrode facility 7a and the second electrode facility 8a are respectively arranged on a first side of the resonator facility 5 away from the substrate 12.

[0040] The first electrode facility 7a and the second electrode facility 8a constitute an interdigitated electrode pair. At the interface facing the cavity 6, electromagnetic waves coupled into the resonator facility 5 via the first electrode facility 7a are reflected.

[0041] The materials of the first electrode facility 7a and / or the second electrode facility 8a may include at least one of aluminum, titanium and copper.

[0042] The acoustic isolation trench 18 limits the resonator laterally and prevents acoustic energy loss.

[0043] A high-frequency signal is fed into the bulk acoustic wave device 100 at the first electrode facility 7a. The electromagnetic wave is converted into an acoustic wave by the first piezoelectric element 1 at the first electrode facility 7a, and then converted back into an electromagnetic wave at the second electrode facility 8a. At a given electromagnetic wave frequency or acoustic wave frequency, the acoustic wave wavelength λ... a The sound velocity c of the corresponding layer material s The following conclusions can be drawn: λ a = c s / f. If the layer thickness d of acoustic resonator facility 5 p This is equivalent to more than half the acoustic wavelength of the converted electromagnetic wave, i.e. d p = (n+½)∙λ a Where n = 0, 1, …, the incident signal is transmitted; otherwise, it is reflected. Therefore, resonator facility 5 is equivalent to a bulk acoustic resonator.

[0044] In another embodiment, the polarization directions of the first piezoelectric element 1 and the second piezoelectric element 2 are oriented antiparallel. In this case, the acoustic layer thickness of the high fQ structure 3 is equivalent to an even multiple of the entire acoustic wavelength of the pre-given resonant mode.

[0045] Figure 2 A cross-sectional view of another bulk acoustic wave device 200 is shown. (Compared to...) Figure 1 Unlike the bulk acoustic wave device 100 shown, the high fQ structure 3 is arranged on the substrate-facing side of the second piezoelectric element 2. Furthermore, the polarization directions 10 and 11 are antiparallel.

[0046] Figure 3 A cross-sectional view of another bulk acoustic wave device 300 is shown. (Compared to...) Figure 1 Unlike the bulk acoustic wave device 100 shown, the first electrode facility 7b and the second electrode facility 8b are arranged on both the side of the resonator facility 5 facing the substrate 12 and the side facing away from the substrate 12, and are interconnected through their respective vias 16 and 17. This achieves particularly efficient excitation.

[0047] The polarization directions 10 and 11 of the first piezoelectric element 1 and the second piezoelectric element 2 are parallel, wherein the first electrode facility 7b and the second electrode facility 8b are symmetrically arranged on both sides of the resonator facility 5 within the region of the cavity 6.

[0048] Figure 4 A cross-sectional view of another bulk acoustic wave device 400 is shown. (Compared to...) Figure 3 Unlike the bulk acoustic wave device 300 shown, the polarization directions 10 and 11 of the first piezoelectric element 1 and the second piezoelectric element 2 are oriented antiparallel, and the first electrode facility 7b and the second electrode facility 8b are arranged antisymmetrically on both sides of the resonator facility 5 within the region of the cavity 6.

[0049] Depending on the selected potential configuration, transverse and / or vertical field configurations are generated in resonator facility 5, which allow for acoustic vertical and transverse modes of excitation combination.

[0050] Figure 5 A flowchart is shown for a method of manufacturing a bulk acoustic wave device, particularly one of the aforementioned bulk acoustic wave devices 100 to 400.

[0051] In the first method step S1, a resonator facility 5 is constructed, which includes a first piezoelectric element 1, a second piezoelectric element 2, and a high fQ structure 3 disposed between the first piezoelectric element 1 and the second piezoelectric element 2.

[0052] In the second method step S2, first electrode facilities 7a-7c and second electrode facilities 8a-8c are constructed, wherein the first electrode facilities 7a-7c and the second electrode facilities 8a-8c are respectively arranged on the first side and / or the second side of the resonator facility 5. The material of the high fQ structure includes a high fQ material, which has a value greater than 10 at frequencies greater than or equal to 3 GHz. 13 The fQ value.

Claims

1. A bulk acoustic wave device (100; 200; 300; 400), comprising: Resonator facility (5), the resonator facility including a first piezoelectric element (1), at least one second piezoelectric element (2) and a high fQ structure (3); and The first electrode facility (7a-7c) and the second electrode facility (8a-8c), wherein, The first electrode facility (7a-7c) and the second electrode facility (8) are respectively arranged on the first side and / or the second side of the resonator facility (5); The high fQ structure is arranged between the first piezoelectric element (1) and the second piezoelectric element (2) and / or on the side opposite to the electrode facilities (7a, 8a); and The high fQ structure (3) is made of a high fQ material, which has a fQ greater than 10 at frequencies greater than or equal to 3 GHz. 13 The fQ value.

2. The bulk acoustic wave device (100; 200; 300; 400) according to claim 1, wherein, The material of the high fQ structure (3) includes at least one of silicon carbide, silicon nitride, silicon, and diamond.

3. The bulk acoustic wave device (100; 200; 300; 400) according to claim 1 or 2, wherein, The material of the first piezoelectric element (1) is substantially equivalent to the material of the second piezoelectric element (2).

4. The bulk acoustic wave device (100; 200; 300; 400) according to any 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 the polarization directions (10, 11) of the piezoelectric layers are oriented parallel to each other or antiparallel to each other.

5. The bulk acoustic wave device (100; 200; 300; 400) according to claim 4, wherein, The acoustic layer thickness of the piezoelectric layer is equivalent to half the acoustic wavelength of the pre-given resonant mode.

6. The bulk acoustic wave device (100; 200; 300; 400) according to any one of the preceding claims, wherein, The acoustic layer thickness of the high fQ structure (3) is equivalent to an integer multiple of half the acoustic wavelength of a pre-given resonant mode.

7. The bulk acoustic wave device (100; 200; 300; 400) according to any one of the preceding claims, wherein, The high fQ structure (3) is constructed as a stack.

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

9. The bulk acoustic wave device (100; 200; 300; 400) according to any one of the preceding claims, having a substrate (12), wherein, A Bragg reflector (13) is arranged between the resonator facility (5) and the substrate (12).

10. A method for manufacturing a bulk acoustic wave device (100; 200; 300; 400), comprising the following steps: Construct (S1) a resonator facility (5), which includes a first piezoelectric element (1), a second piezoelectric element (2) and a high fQ structure (3); And constructing (S2) a first electrode facility (7a-7c) and a second electrode facility (8a-8c), wherein, The first electrode facility (7a-7c) and the second electrode facility (8a-8c) are respectively arranged on the first side and / or the second side of the resonator facility (5); The high fQ structure (3) is made of a high fQ material, which has a fQ greater than 10 at frequencies greater than or equal to 3 GHz. 13 The fQ value.

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