Magnetic tuning film bulk acoustic resonator and preparation method and application thereof

Abstract

This invention discloses a magnetically tuned thin-film bulk acoustic resonator (FBAR), its fabrication method, and its applications. The FBAR comprises a first electrode, a piezoelectric material layer, and a second electrode stacked sequentially. The second electrode comprises at least one alternating layer of a first material layer and at least one layer of a second material layer, wherein the at least one first material layer is a magnetostrictive thin film, and the magnetostrictive thin film and the piezoelectric material layer cooperate to form a magnetoelectric heterojunction. This invention provides a magnetically tuned thin-film bulk acoustic resonator that uses a magnetically stretched composite thin film as the upper electrode. Utilizing the magnetoelectric effect of the magnetic and piezoelectric materials, the resonant frequency of the FBAR can be adjusted in the low-frequency, mid-frequency, and even high-frequency range under the influence of a magnetic field.

Description

Technical Field

[0001] This invention relates in particular to a magnetically tuned thin-film bulk acoustic resonator, its fabrication method, and its application, belonging to the field of communication technology. Background Technology

[0002] With the rapid development of 5G technology, there is a strong demand for small-size, high-frequency, wide-bandwidth, high-performance, and low-power radio frequency (RF) filters. Currently, industry and academia have explored filtering technologies such as surface acoustic wave (SAW), bulk acoustic wave (BAW), and thin-film bulk acoustic resonator (FBAR) filters to better meet the practical needs of 5G mobile communication. Thin-film bulk acoustic resonator filters (FBARs) possess excellent and reliable filtering performance, small size, low power consumption, and ease of integration, and are considered the best solution for RF filters in current communication terminals.

[0003] Thin-film bulk acoustic filters have a small tuning range and are typical narrowband devices. If a single thin-film bulk acoustic filter can be used to freely switch between multiple communication frequency bands with adjustable operating bandwidth to meet the requirements of broadband signal processing, it would be of great value for making full use of precious spectrum resources and simplifying wireless communication systems.

[0004] The frequency tuning techniques for FBARs mainly focus on three aspects: tuning during fabrication, tuning after fabrication, and tuning during use. During FBAR fabrication, chemical mechanical polishing (CMP) is often used to improve the uniformity of the thin film, and adding a temperature compensation layer reduces temperature-induced frequency drift, thus improving device stability. However, these two frequency tuning techniques have limited flexibility. After fabrication, the resonant frequency can be tuned through thin film or mass deposition, but this process is cumbersome and difficult to implement. Both pre- and post-fabrication frequency tuning techniques suffer from a limited tuning range and are suitable only for devices requiring specific high-precision resonant frequencies.

[0005] Existing tuning schemes for FBARs generally rely on changes in external conditions such as electric fields, temperature, and magnetic fields to reversibly adjust the resonant frequency within a certain range. However, existing technologies still suffer from drawbacks such as a small adjustment range, complex device structure and fabrication processes, and stringent material preparation conditions that hinder widespread application. One approach is to replace the top electrode of the FBAR with a magnetic material. The magnetoelectric heterojunction formed by the magnetic material and piezoelectric material exhibits a strong magnetoelectric effect. Current experiments have demonstrated that the resonant frequency of the FBAR can vary over a considerable range under the influence of an external magnetic field, with theoretical justification. Currently, the magnetic materials used in experiments are mainly FeGa or FeCo alone. While this has achieved some success, it still suffers from drawbacks such as a large driving magnetic field and high hysteresis and eddy current losses at high frequencies, resulting in insignificant changes in the FBAR's resonant frequency with the magnetic field at high frequencies. Although FeGaB, a single material, has significantly improved hysteresis and eddy current losses at high frequencies compared to FeGa and FeCo, and its Young's modulus changes more significantly under the influence of a magnetic field, single materials still struggle to meet the frequency adjustment requirements of modern high-frequency communication systems. Summary of the Invention

[0006] The main objective of this invention is to provide a magnetically tuned thin-film bulk acoustic resonator, its fabrication method, and its application, in order to overcome the shortcomings of the prior art.

[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0008] This invention provides a magnetically tuned thin-film bulk acoustic resonator, comprising a first electrode, a piezoelectric material layer, and a second electrode stacked sequentially; characterized in that: the second electrode comprises at least one first material layer and at least one second material layer stacked alternately, wherein the at least one first material layer is a magnetostrictive thin film, and the magnetostrictive thin film and the piezoelectric material layer cooperate to form a magnetoelectric heterojunction.

[0009] Furthermore, the second material layer includes any one or more combinations of a soft magnetic film, an acoustic matching layer, and a magnetostrictive film, but is not limited thereto.

[0010] Furthermore, the magnetostrictive thin film can be made of FeGa, FeGaB, FeCo, etc., the acoustic matching layer can be made of Al2O3 and SiO2, etc., and the soft magnetic thin film can be made of NiFe, etc.

[0011] In some more specific implementations, the bottom layer of the second electrode is a first material layer and the top layer is a second material layer, or the bottom and top layers of the second electrode are both first material layers, and the second material layer is located between the bottom and top layers. It can be understood that the second electrode can be a sandwich structure in which the bottom and top layers are both first material layers and the middle layer contains a second material layer.

[0012] Furthermore, the bottom layer of the second electrode is grown on a piezoelectric layer.

[0013] In some more specific implementations, the bottom layer of the second electrode is a magnetostrictive thin film, and the top layer can be one of a soft magnetic thin film, an acoustic matching layer, and a magnetostrictive thin film.

[0014] Furthermore, the number of the first material layer and the second material layer in the second electrode are equal, or the first material layer has one more layer than the second material layer; understandably, assuming the first material layer is A, the second material layer is B, and the number of layers or the ratio is n, then the structure of the second electrode is: (A / B). n Or (A / B) n In structure A, the bottom layer of the second electrode must be a magnetostrictive thin film, and the top layer can be any one of a soft magnetic thin film, an acoustic matching layer, and a magnetostrictive thin film; where A / B represents a thin film structure in which the first material layer and the second material layer are deposited alternately, and the volume ratio of the two materials varies from 1:1 to 5:1; if it is (A / B) n If structure A is used, then A must be the same magnetostrictive material, that is, the bottom layer and the top layer of the second electrode are both the first material layer, and both are magnetostrictive thin films.

[0015] Furthermore, the ratio of the total volume of all first material layers to the total volume of all second material layers in the second electrode is 1:1 to 5:1.

[0016] In some more specific implementations, the first electrode, the piezoelectric material layer, and the second electrode are stacked sequentially on the cavity structure.

[0017] Furthermore, the first electrode, the piezoelectric material layer, and the second electrode are sequentially stacked on the substrate, and the cavity structure is formed within the substrate.

[0018] Furthermore, the cavity structure is formed on the first surface of the substrate, and the first electrode, the piezoelectric material layer, and the second electrode are sequentially stacked on the first surface of the substrate; or, the cavity structure is formed on the second surface of the substrate, and the first electrode, the piezoelectric material layer, and the second electrode are sequentially stacked on the first surface of the substrate, with the first surface and the second surface facing away from each other.

[0019] Furthermore, the first electrode, the piezoelectric material layer, and the second electrode are sequentially stacked on the substrate, wherein at least a local area of ​​the second electrode is recessed in a direction away from the substrate to form a cavity structure.

[0020] This invention also provides a method for fabricating the magnetically tuned thin-film bulk acoustic resonator, including the steps of fabricating a first electrode, a piezoelectric material layer, a second electrode, and a cavity structure; characterized in that the step of fabricating the second electrode includes: alternately stacking at least one first material layer and at least one second material layer on the piezoelectric material layer, wherein at least one of the first material layers is formed of a magnetostrictive thin film, and the magnetostrictive thin film and the piezoelectric material layer cooperate to form a magnetoelectric heterojunction.

[0021] Furthermore, the step of fabricating the second electrode also includes: first forming a first material layer on the piezoelectric material layer as the bottom layer of the second electrode, and then growing the remaining structural layers of the second electrode.

[0022] This invention also provides a bulk acoustic wave filter, which includes the magnetically tuned thin-film bulk acoustic wave resonator.

[0023] This invention also provides a communication device, including a radio frequency filter, wherein the radio frequency filter includes the magnetically tuned thin-film bulk acoustic resonator.

[0024] Compared with the prior art, the advantages of the present invention include:

[0025] 1) This invention provides a magnetically tuned thin-film bulk acoustic resonator, which uses a magnetically stretchable composite film as the upper electrode and utilizes the magnetoelectric effect of magnetic and piezoelectric materials to achieve adjustment of the resonant frequency of the FBAR in the low-frequency, mid-frequency and even high-frequency range under the action of a magnetic field.

[0026] 2) By employing FeGa, FeCo, or FeGaB multilayer composite films, this invention enables the magnetically stretchable composite film to possess excellent soft magnetic properties, large magnetostriction, large piezoelectric coefficient, low hysteresis loss and eddy current loss at high frequencies, and further enables the resonant frequency of FBAR to be tuned in the high-frequency band through the magnetoelectric coupling mechanism generated by the "product effect" of piezoelectric and magnetostrictive materials. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a magnetically tuned thin-film bulk acoustic resonator with a concave air gap provided in Embodiment 1 of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of a magnetically tuned thin-film bulk acoustic resonator with an upwardly convex cavity structure provided in Embodiment 2 of the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of a magnetically tuned silicon-etched bulk acoustic resonator provided in Embodiment 3 of the present invention. Detailed Implementation

[0030] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0031] The inventors of this invention discovered that using a single-layer magnetostrictive material has problems such as large eddy current losses at high frequencies, poor soft magnetic properties, or sacrificing the material's own saturation magnetostriction coefficient, which further limits the resonant frequency adjustment range of the resonator under magnetic field drive. To solve this problem, the present invention provides a magnetically tuned thin-film bulk acoustic resonator that uses a multilayer composite magnetostrictive thin film to improve this problem.

[0032] In order to achieve wide-range frequency adjustment of FBAR in the low-frequency, mid-frequency and even high-frequency regions, the upper electrode (i.e. the aforementioned second electrode, the same below) of the FBAR device provided in this embodiment of the invention is mainly composed of a magnetostrictive thin film. Based on the magnetostrictive properties and ΔE effect of the magnetostrictive thin film itself, as well as the magnetoelectric coupling mechanism generated by the "product effect" of piezoelectric material and magnetostrictive material, the resonant frequency of the FBAR device is achieved, and the purpose of dynamic adjustment within a certain range is realized through the magnetic field.

[0033] This invention provides a magnetically tuned thin-film bulk acoustic resonator (FBAR) that uses a magnetostrictive composite thin film as the upper electrode and forms a magnetoelectric heterojunction with a piezoelectric material layer. The resonant frequency of the FBAR device exhibiting a thickness-extension vibration mode is theoretically proven to be determined by the equivalent Young's modulus of the magnetoelectric heterojunction. When the magnetostrictive thin film is subjected to an external magnetic field, its Young's modulus changes accordingly, and the equivalent Young's modulus of the magnetoelectric heterojunction also changes accordingly, thereby enabling the resonant frequency of the FBAR device to change accordingly with the change of the magnetic field.

[0034] The resonant frequency of a magnetically tuned thin-film bulk acoustic resonator provided in this invention can change with the magnetic field, thereby enabling the passband center frequency of the bulk acoustic filter to switch within the range of 0 to 100 MHz. It can also be dynamically modulated by the magnetic field according to the required application and operating conditions, thereby greatly reducing the number of RF front-end filters used for frequency band switching in modern communication systems, as well as reducing the complexity of the equipment and lowering the cost of mobile phones.

[0035] The specific principle is as follows: The resonant frequency f0 of the bulk acoustic resonator is determined by the equivalent Young's modulus of the magnetoelectric heterojunction, as shown in Equation 1):

[0036]

[0037] In the formula, T0 represents the thickness of the bulk acoustic resonator, and equation E eq and ρ eq The equivalent Young's modulus and equivalent density of the resonator can be expressed as E, respectively. eq =∑E i vi and ρ eq =∑ρ i vi is used to calculate, where E i It is Young's modulus, V i It is the volume ratio of each layer of the magnetoelectric heterojunction in the device (i.e., the volume ratio of each layer of material in the magnetoelectric heterojunction composed of piezoelectric material and the second electrode); therefore, as a magnetic field is applied to the bulk acoustic resonator, the mechanical resonant frequency will drift due to the change of Young's modulus of the magnetostrictive film with the magnetic field (ΔE effect), thus making the bulk acoustic resonator magnetically tunable.

[0038] Currently, the most outstanding magnetic thin films in terms of magnetostriction performance include FeGa, FeGaB, and FeCo. FeGa films have large magnetostriction performance and relatively good soft magnetic properties, but their high magnetostriction and large spin lattice coupling also lead to high hysteresis and a large Gilbert damping coefficient, making it difficult for a single FeGa film to achieve high magnetoelastic coupling. Although FeGaB films have excellent soft magnetic properties and a large piezomagnetic coefficient, the doping with boron reduces their saturation magnetostriction and magnetization performance.

[0039] In this embodiment of the invention, a magnetostrictive composite film is formed by combining FeGa, FeCo, or FeGaB magnetostrictive films with other functional films as the top electrode. This results in the top electrode having good soft magnetic properties, large magnetostriction, large piezomagnetic coefficient, and reduced hysteresis loss and eddy current loss at high frequencies. Through the magnetoelectric coupling mechanism generated by the "product effect" of piezoelectric and magnetostrictive materials, the resonant frequency of the FBAR can be tuned in the high-frequency band.

[0040] The following will further explain the technical solution, its implementation process and principle in conjunction with the accompanying drawings and specific implementation examples. Unless otherwise specified, the thin film fabrication process and photolithography used in the embodiments of the present invention are known to those skilled in the art.

[0041] The structures of the three magnetostrictive thin-film-based magnetically tuned bulk acoustic resonators provided in the embodiments of the present invention are as follows: Figure 1 , Figure 2 and Figure 3 As shown, where, Figure 1 It is a cavity-type (convex) device. Figure 2For cavity-type (recessed) devices and Figure 3 Bulk silicon etched devices.

[0042] Please see Figure 3 Taking a bulk silicon etched FBAR as an example, a magnetically tunable bulk silicon etched FBAR includes a high-resistivity Si substrate, a buffer layer, a lower electrode (i.e., the aforementioned first electrode, the same below) and a piezoelectric material layer sequentially on the upper surface of the high-resistivity Si substrate. An upper electrode is provided on the piezoelectric material layer and forms a magnetoelectric heterojunction with the piezoelectric material layer. The upper electrode includes at least one A material layer (i.e., the aforementioned first material layer, the same below) and a B material layer (i.e., the aforementioned second material layer, the same below). The A material layer must be a magnetostrictive layer, and the B material layer is any one of a soft magnetic film, an acoustic matching layer and a magnetostrictive film.

[0043] Specifically, the substrate is a high-resistivity silicon substrate. Choosing high-resistivity silicon as the substrate can reduce the occurrence of many parasitic effects and can be integrated with CMOS processes, thereby reducing costs. The buffer layer can be an AlN layer, and the lower electrode is a metal electrode, the material of which can be any one of Mo, Pt, Al, W and Ru.

[0044] Specifically, the optional materials for the piezoelectric material layer include binary piezoelectric single crystals (which can be formed by metal-organic chemical vapor deposition) or polycrystalline thin films AlN, ZnO (which can be formed by magnetron sputtering), ternary or multi-element piezoelectric polycrystalline thin films AlScN, AlErN, BaSrTiO3, ternary piezoelectric single crystal thin films (which can be formed by grinding and thinning or smart exfoliation) LiNbO3, and LiTaO3.

[0045] In some more specific implementations, the number of material A layers and material B layers in the upper electrode can be the same and they can be arranged alternately. For example, the upper electrode can be composed of multiple magnetostrictive films and multiple soft magnetic films; multiple magnetostrictive films and multiple acoustic matching layers; or it can be composed of multiple or multiple layers of magnetostrictive films, specifically in the following ways:

[0046] 1) In the magnetostrictive thin film, material A is a magnetostrictive thin film of FeGa, FeGaB, or FeCo with a certain thickness, and material B is an acoustic matching layer of Al2O3 and SiO2 with a certain thickness. For example, the upper electrode can be a multilayer magnetostrictive composite thin film of [FeGaB(45nm) / Al2O3(5nm)]×10 or FeGa(450nm) / Al2O3(50nm). Compared with a magnetostrictive thin film of the same thickness, the magnetostrictive composite thin film containing the acoustic matching layer can not only achieve acoustic matching, but also increase the resistance of a single magnetostrictive thin film, making the high-frequency soft magnetic characteristics of the composite thin film better, and effectively reducing eddy current loss and Gilbert damping (Note: Taking a total film thickness of 500nm as an example, there are two specific structures: [A(45nm) / Al2O3(5nm)]×10 and A(45nm) / Al2O3(50nm), where A is one of the magnetostrictive thin films such as FeGa, FeGaB, or FeCo).

[0047] 2) In the upper electrode, material A is a magnetostrictive thin film of FeGa, FeCo, etc. (excluding FeGaB) with a certain thickness, and material B is a soft magnetic thin film of NiFe with a certain thickness; for example, the upper electrode can be [FeGa / NiFe]. n Thin film or [FeGa / NiFe] n The addition of a NiFe soft magnetic film to the FeGa thin film enhances the piezomagnetic coefficient of the upper electrode due to the exchange coupling between the soft magnetic film and the magnetostrictive film, resulting in a [FeGa / NiFe] [combination]. n The thin film simultaneously possesses the high permeability and low coercivity of NiFe and the high saturation magnetostriction and saturation magnetization of FeGa, thereby reducing the FMR linewidth of single-phase FeGa at the same thickness. Furthermore, hysteresis and eddy current losses at high frequencies are also significantly reduced, making it highly suitable for strain-mediated ME heterojunctions. It is worth noting that [FeGa / NiFe]... n The total thickness of the film, the thickness of each layer of the FeGa and NiFe films, and the volume ratio between FeGa and NiFe can be changed according to actual needs.

[0048] Example 1

[0049] Please see Figure 1 A magnetically tuned thin-film bulk acoustic resonator with a concave air gap includes a high-resistivity Si substrate and, sequentially stacked on the upper surface of the high-resistivity Si substrate, an AlN buffer layer, a Mo electrode, an AlN piezoelectric material layer, and a [FeGa / NiFe] layer. n The thin film, namely [FeGa / NiFe] n A thin film is stacked on the AlN piezoelectric material layer and serves as the upper electrode, and the [FeGa / NiFe]...n The thin film is bonded to the AlN piezoelectric material layer to form a magnetoelectric heterojunction; and the upper surface of the high-resistivity Si substrate is further provided with at least one groove, and the upper surface of the high-resistivity Si substrate and the inner wall of the groove are further covered with a SiO2 passivation layer.

[0050] In this embodiment, the fabrication process of a magnetically tuned thin-film bulk acoustic resonator with a concave air gap includes:

[0051] 1) Cleaning the high-resistivity silicon substrate: sequentially ultrasonically treat with acetone for 5 min, ultrasonically treat with isopropanol for 5 min, and treat with deionized water for 2 min, wherein the deionized water is repeatedly cleaned 5 times.

[0052] 2) A groove cavity structure with a depth of 2.5 μm is formed on the upper surface of a high-resistivity silicon substrate using reactive ion etching (RIE);

[0053] 3) A 200nm SiO2 cavity passivation layer is formed on the upper surface, cavity bottom and four walls of the high-resistivity silicon substrate by plasma-enhanced chemical vapor deposition (PECVD) at 350℃ to prevent subsequent processes from having an adverse effect on the high-resistivity silicon substrate.

[0054] 4) A layer of amorphous silicon is deposited in the cavity as a sacrificial layer using PECVD. The thickness of the sacrificial layer should be greater than the thickness of the cavity to ensure sufficient grinding thickness during CMP.

[0055] 5) Perform chemical mechanical polishing (CMP) on the upper surface of the high-resistivity silicon substrate, retain the SiO2 cavity passivation layer originally deposited on the upper surface of the high-resistivity silicon substrate, and remove the amorphous Si above the edge of the SiO2 cavity passivation layer and the upper surface of the cavity, so that the upper surface of the sacrificial amorphous Si is at the same level as the upper surface of the SiO2 cavity passivation layer on the substrate outside the cavity, leaving only the amorphous Si in the cavity as the sacrificial layer, and then clean it;

[0056] 6) A thin (50 nm) AlN buffer layer, a Mo metal lower electrode of a certain thickness (200 nm), a (1 μm) AlN piezoelectric material layer, and a [FeGa / NiFe] layer are sequentially deposited on the upper surface of a high-resistivity silicon substrate using methods such as magnetron sputtering. n film;

[0057] 7) [FeGa / NiFe] was etched using an ion beam etching (IBE) machine. 16 Upper electrode pattern;

[0058] 8) The pattern of piezoelectric material AlN was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP180). The etching gas was Cl2:BCl3:Ar = 32sccm:8sccm:5sccm, where Cl2 and BCl3 react with AlN and Ar is used for physical bombardment.

[0059] 9) The Mo pattern on the lower electrode was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP380), with the etching gas being SF6 at 80 sccm and an etching rate of approximately 4.7 nm / s.

[0060] 10) A 400 nm SiO2 isolation layer was grown by PECVD (350 °C), and the isolation layer pattern was etched by reactive ion etching (RIE);

[0061] 11) Using the liff-off process, Ti / Au 30nm / 200nm top electrodes are evaporated with an Ei-5z electron beam, then stripped and patterned.

[0062] 12) A release window is obtained by dry etching around the cavity. HF solution is injected from the release window to remove the SiO2 isolation layer and form a cavity.

[0063] Example 2

[0064] Please see Figure 2 A magnetically tuned thin-film bulk acoustic resonator with a convex cavity structure includes a Si(100) substrate and, sequentially stacked on the upper surface of the Si(100) substrate, an AlN buffer layer, a Mo electrode, an AlN piezoelectric material layer, and a [FeGa / NiFe] layer. n The thin film, namely [FeGa / NiFe] n A thin film is stacked on the AlN piezoelectric material layer and serves as the upper electrode, and the [FeGa / NiFe]... n The thin film is bonded to the AlN piezoelectric material layer to form a magnetoelectric heterojunction; and the AlN buffer layer has at least one groove on the side surface near the Si substrate.

[0065] In this embodiment, the fabrication process of a magnetically tuned thin-film bulk acoustic resonator with a convex cavity structure includes:

[0066] 1) Cleaning the high-resistivity silicon substrate: sequentially ultrasonically treat with acetone for 5 min, ultrasonically treat with isopropanol for 5 min, and treat with deionized water for 2 min, wherein the deionized water is repeatedly cleaned 5 times.

[0067] 2) A layer of metallic germanium is deposited on the upper surface of a high-resistivity silicon substrate as a sacrificial layer;

[0068] 3) A thin (50 nm) AlN buffer layer, a certain thickness (200 nm) Mo metal layer for the lower electrode, a (1 μm) AlN piezoelectric material layer, and a 480 nm [FeGa / NiFe] layer are sequentially deposited on the surface of a high-resistivity silicon substrate using magnetron sputtering. 16 film;

[0069] 4) [FeGa / NiFe] was etched using an ion beam etching (IBE) machine. 16 Upper electrode pattern;

[0070] 5) The pattern of piezoelectric material AlN was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP180). The etching gas was Cl2:BCl3:Ar = 32sccm:8sccm:5sccm, where Cl2 and BCl3 react with AlN and Ar is used for physical bombardment.

[0071] 6) The Mo pattern on the lower electrode was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP380), with the etching gas being SF6 at 80 sccm and an etching rate of approximately 4.7 nm / s.

[0072] 7) A 400 nm SiO2 isolation layer was grown by PECVD (350 °C), and the isolation layer pattern was etched by reactive ion etching (RIE);

[0073] 8) Using a liff-off process, Ti / Au 30nm / 200nm top electrodes are evaporated with an Ei-5z electron beam, then stripped and patterned.

[0074] 9) By using dry etching or other methods, a release window is obtained around the cavity, and H2O2 solution is injected from the release window to remove the SiO2 isolation layer and form a cavity.

[0075] Example 3

[0076] Please see Figure 3 A magnetically tunable silicon-etched bulk acoustic resonator includes a high-resistivity Si(100) substrate and, sequentially stacked on the surface of the high-resistivity Si(100) substrate, an AlN buffer layer, a Mo electrode, an AlN piezoelectric material layer, and a [FeGa / NiFe] layer. n The thin film, namely [FeGa / NiFe] nA thin film is stacked on the AlN piezoelectric material layer and serves as the upper electrode, and the [FeGa / NiFe]... n The thin film is bonded to the AlN piezoelectric material layer to form a magnetoelectric heterojunction; and a through hole is also provided in the Si substrate along the thickness direction.

[0077] Specifically, [FeGa / NiFe] n The thin film, from bottom to top, has a structure of FeGa / NiFe / FeGa / NiFe...FeGa / NiFe. When [FeGa / NiFe]... n Once the total thickness of the thin film is fixed, a suitable combination of thin films can be selected based on actual needs, considering both the number of layers and the FeGa:NiFe volume ratio.

[0078] For example, [FeGa / NiFe] n The total thickness of the thin film is 480 nm. When n = 1, [FeGa / NiFe] n The composition of the thin film is: (240nm FeGa / 240nm NiFe); when n=8, [FeGa / NiFe] n The thin film composition is: (30nm FeGa / 30nm NiFe)8; when n=16, [FeGa / NiFe] n The thin film composition is: (15nm FeGa / 15nm NiFe) 16 When n = 30, [FeGa / NiFe] n The thin film composition is: (8nm FeGa / 8nm NiFe) 30 .

[0079] It should be noted that, theoretically, as the number of layers increases, [FeGa / NiFe] n The film's performance initially improves (i.e., it possesses both the high magnetostrictive properties of FeGa and the good soft magnetic properties of NiFe) and then deteriorates. The specific number of layers depends on the actual growth process conditions (as the number of layers increases [FeGa / NiFe]). n The selection should be based on factors such as the stress between each thin film layer, which can severely hinder the subsequent fabrication of devices and easily lead to device failure, and the actual application requirements.

[0080] In this embodiment, the fabrication process of a magnetically tuned silicon-etched bulk acoustic resonator includes:

[0081] 1) Cleaning the high-resistivity silicon substrate: sequentially ultrasonically treat with acetone for 5 min, ultrasonically treat with isopropanol for 5 min, and treat with deionized water for 2 min, wherein the deionized water is repeatedly cleaned 5 times.

[0082] 2) A thin (50 nm) AlN buffer layer, a certain thickness (200 nm) Mo metal layer for the lower electrode, a (1 μm) AlN piezoelectric material layer, and a 480 nm [FeGa / NiFe] layer were sequentially deposited on the surface of a high-resistivity silicon substrate using magnetron sputtering. 16 film;

[0083] 3) [FeGa / NiFe] was etched using an ion beam etching (IBE) machine. 16 Upper electrode pattern;

[0084] 4) The piezoelectric material AlN pattern was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP180). The etching gas was Cl2:BCl3:Ar = 32sccm:8sccm:5sccm, where Cl2 and BCl3 react with AlN and Ar is used for physical bombardment.

[0085] 5) The Mo pattern on the lower electrode was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP380), with the etching gas being SF6 at 80 sccm and an etching rate of approximately 4.7 nm / s.

[0086] 6) A 400 nm SiO2 isolation layer was grown by PECVD (350 °C), and the isolation layer pattern was etched by reactive ion etching (RIE);

[0087] 7) Using a liff-off process, Ti / Au 30nm / 200nm top electrodes are evaporated with an Ei-5z electron beam, then stripped and patterned.

[0088] 8) High-resistivity silicon thinning and polishing (thinning from 695μm to 100μm), and using the back-overlay etching technology of double-sided lithography machine MA6 to form a shape corresponding to the upper electrode resonant region. Finally, the window is released through deep silicon etching process to form an air interface in the lower electrode region.

[0089] Example 4

[0090] A magnetically tuned silicon-etched bulk acoustic resonator includes a high-resistivity Si(100) substrate and an AlN buffer layer, a Mo electrode, an AlN piezoelectric material layer, and (FeGa / NiFe) layers sequentially stacked on the upper surface of the high-resistivity Si(100) substrate. n FeGa thin film, the [FeGa / NiFe] n A magnetostrictive thin film is stacked on the AlN piezoelectric material layer and serves as the upper electrode.

[0091] Specifically, (FeGa / NiFe) n In a FeGa thin film, FeGa and NiFe thin films are alternately arranged, with the bottom and top layers both being FeGa films. When the total thickness of the magnetostrictive film is fixed and the FeGa:NiFe (volume ratio) remains constant, the number of layers n is adjusted according to actual needs; for example, (FeGa / NiFe). n When the total thickness of the FeGa film is 100 nm and the volume ratio of FeGa to NiFe is 1:1, the number of FeGa and NiFe films is shown in Table 1.

[0092] Table 1 shows the structural parameters of the magnetostrictive thin film.

[0093]

[0094] When (FeGa / NiFe) n With the total thickness and number of layers n of the FeGa film fixed, the volume ratio of the FeGa film to the NiFe film can be changed, for example, (FeGa / NiFe). n The total thickness of the FeGa film is 100 nm, and the volume ratios of the FeGa film and the NiFe film when the number of layers n = 3 are shown in Table 2.

[0095] Table 2 shows the structural parameters of the magnetostrictive thin film.

[0096]

[0097] Example 5

[0098] A magnetically tuned silicon-etched bulk acoustic resonator includes a high-resistivity Si(100) substrate and an AlN buffer layer, a Mo lower electrode, an AlN piezoelectric material layer, and (FeGa / Al2O3) sequentially stacked on the upper surface of the high-resistivity Si(100) substrate. n Or (FeGaB / Al2O3) n The thin film, namely (FeGa / Al2O3) n Or (FeGaB / Al2O3) n The thin film is stacked on the AlN piezoelectric material layer and serves as the upper electrode.

[0099] Specifically, after the thickness of the FeGa film is determined, the number of layers n is determined according to the actual application requirements. The thickness of Al2O3 can be selected from 5nm, which has been verified to be a suitable value. For example, (FeGa / Al2O3). n The total thickness of the film is 500 nm, and n is determined to be 10 layers. Therefore, (FeGa / Al2O3) nThe thin film has the following configuration: (45nm FeGa / 5nm Al2O3) 10 Or it could be (41nm FeGa / 5nm Al2O3) 10 / 41nmFeGa.

[0100] In this embodiment, the fabrication process of a magnetically tuned silicon-etched bulk acoustic resonator includes:

[0101] 1) Cleaning the high-resistivity silicon substrate: sequentially ultrasonically treat with acetone for 5 min, ultrasonically treat with isopropanol for 5 min, and treat with deionized water for 2 min, wherein the deionized water is repeatedly cleaned 5 times.

[0102] 2) A thin (50nm) AlN buffer layer, a certain thickness (200nm) Mo metal layer for the lower electrode, a (1μm) AlN piezoelectric material layer, and a 500nm (45nm FeGa / 5nm Al2O3) layer are sequentially deposited on the surface of a high-resistivity silicon substrate by magnetron sputtering. 10 film;

[0103] 3) (45nm FeGa / 5nm Al2O3) was etched using an ion beam etching (IBE) machine. 10 Upper electrode pattern;

[0104] 4) The piezoelectric material AlN pattern was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP180). The etching gas was Cl2:BCl3:Ar = 32sccm:8sccm:5sccm, where Cl2 and BCl3 react with AlN and Ar is used for physical bombardment.

[0105] 5) The Mo pattern on the lower electrode was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP380), with the etching gas being SF6 at 80 sccm and an etching rate of approximately 4.7 nm / s.

[0106] 6) A 400 nm SiO2 isolation layer was grown by PECVD (350 °C), and the isolation layer pattern was etched by reactive ion etching (RIE);

[0107] 7) Using a liff-off process, Ti / Au 30nm / 200nm top electrodes are evaporated with an Ei-5z electron beam, then stripped and patterned.

[0108] 8) High-resistivity silicon thinning and polishing (thinning from 695μm to 100μm), and using the back-overlay etching technology of double-sided lithography machine MA6 to form a shape corresponding to the upper electrode resonant region. Finally, the window is released through deep silicon etching process to form an air interface in the lower electrode region.

[0109] Example 6

[0110] A magnetically tuned silicon-etched bulk acoustic resonator includes a Si substrate and an AlN buffer layer, a Mo electrode, an AlN piezoelectric material layer, and a FeGa / Al2O3 or (FeGa / NiFe)n / Al2O3 thin film sequentially stacked on the upper surface of the Si substrate. The FeGa / Al2O3 or (FeGa / NiFe)n / Al2O3 thin film is stacked on the AlN piezoelectric material layer and serves as the upper electrode.

[0111] For example, the upper electrode can be a 450nm FeGa / 50nm Al2O3 thin film, which is the simplest combination of FeGa and Al2O3. That is, a certain thickness of FeGa thin film is deposited first, followed by a certain thickness of Al2O3 thin film. The specific thickness of FeGa and Al2O3 is determined by the actual requirements.

[0112] It should be noted that FeGa in the above embodiments can be replaced with FeGa or various combinations of FeGa / NiFe mentioned above.

[0113] In this embodiment, the fabrication process of a magnetically tuned silicon-etched bulk acoustic resonator includes:

[0114] 1) Cleaning the high-resistivity silicon substrate: sequentially ultrasonically treat with acetone for 5 min, ultrasonically treat with isopropanol for 5 min, and treat with deionized water for 2 min, wherein the deionized water is repeatedly cleaned 5 times.

[0115] 2) A thin (50nm) AlN buffer layer, a certain thickness (200nm) Mo metal layer for the lower electrode, a (1μm) AlN piezoelectric material layer, and a 450nm FeGa / 50nm Al2O3 thin film were sequentially deposited on the surface of a high-resistivity silicon substrate by magnetron sputtering.

[0116] 3) The 450nm FeGa / 50nm Al2O3 upper electrode pattern was etched using an ion beam etching (IBE) machine;

[0117] 4) The piezoelectric material AlN pattern was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP180). The etching gas was Cl2:BCl3:Ar = 32sccm:8sccm:5sccm, where Cl2 and BCl3 react with AlN and Ar is used for physical bombardment.

[0118] 5) The Mo pattern on the lower electrode was etched using an inductively coupled plasma (ICP) etching machine (Oxford ICP380), with the etching gas being SF6 at 80 sccm and an etching rate of approximately 4.7 nm / s.

[0119] 6) A 400 nm SiO2 isolation layer was grown by PECVD (350 °C), and the isolation layer pattern was etched by reactive ion etching (RIE);

[0120] 7) Using a liff-off process, Ti / Au 30nm / 200nm top electrodes are evaporated with an Ei-5z electron beam, then stripped and patterned.

[0121] 8) High-resistivity silicon thinning and polishing (thinning from 695μm to 100μm), and using the back-overlay etching technology of double-sided lithography machine MA6 to form a shape corresponding to the upper electrode resonant region. Finally, the window is released through deep silicon etching process to form an air interface in the lower electrode region.

[0122] Comparative Example 1

[0123] A magnetically tuned thin-film bulk acoustic resonator with a concave air gap is disclosed. Its structure and fabrication process are basically the same as in Example 1, except that: Comparative Example 1 uses a FeGa thin film as the upper electrode, and this FeGa thin film is different from the [FeGa / NiFe] film in Example 1. n The magnetostrictive films have the same thickness.

[0124] Comparative Example 2

[0125] A magnetically tuned thin-film bulk acoustic resonator with a convex cavity structure is disclosed. Its structure and fabrication process are basically the same as in Example 2, except that Example 2 uses a FeGa thin film as the upper electrode, and this FeGa thin film is different from the [FeGa / NiFe] film in Example 2. n The magnetostrictive films have the same thickness.

[0126] Comparative Example 3

[0127] A magnetically tunable silicon-etched bulk acoustic resonator has a structure and fabrication process basically the same as that of Example 3, except that: Comparative Example 3 uses a FeGa thin film as the top electrode, and this FeGa thin film is different from the [FeGa / NiFe] in Example 3. n The magnetostrictive films have the same thickness.

[0128] Through comparative testing of the devices in Examples 1-6 and Comparative Examples 1-3, the inventors of this case found that using a single FeGa thin film of the same thickness is superior to using [FeGa / NiFe]. n Compared to magnetostrictive films, the related magnetic properties, such as eddy current loss, coercivity, FMR linewidth, and piezomagnetic coefficient at high frequencies, deteriorate. Specifically, this manifests as higher eddy current loss, higher coercivity, higher FMR, and lower piezomagnetic coefficient. As a result, the magnetoelectric coupling performance between FeGa films and piezoelectric materials deteriorates. Under the same magnetic field, the change in the device's resonant frequency will decrease, or in other words, the response to the magnetic field will weaken.

[0129] The devices in Comparative Examples 1-3 differ slightly in structure, but their core purpose is to confine sound waves within a piezoelectric resonator using three different air gap structures (FBAR, or Thin Film Bulk Acoustic Resonator, whose core structure is a sandwich piezoelectric resonator composed of electrodes / piezoelectric layers / electrodes, operating in a vibration mode along the thickness direction. An RF voltage is applied between the upper and lower electrodes, utilizing the piezoelectricity of the material to convert the electrical signal into sound waves. According to transmission line theory, to confine the sound waves within the piezoelectric resonator, the acoustic impedance of the upper and lower electrodes must be zero or infinite, causing the sound waves to form standing waves between the two interfaces, resulting in resonance. Air has an acoustic impedance approximately of zero, making it a good reflective medium. The upper electrode of the device is exposed to air, forming a good acoustic reflection interface at the top. Therefore, an air interface is introduced on the lower surface through micromachining, resulting in the three structures described in this paper). However, these three structures do not affect the change of the device's resonant frequency under a magnetic field. This invention provides a magnetically tuned thin-film bulk acoustic resonator (FBAR) using a magnetically stretchable composite film as the upper electrode. Utilizing the magnetoelectric effect of the magnetic and piezoelectric materials, the resonant frequency of the FBAR can be adjusted in the low-frequency, mid-frequency, and even high-frequency range under the influence of a magnetic field. Furthermore, by employing FeGa, FeCo, or FeGaB multilayer composite films, this invention enables the magnetically stretchable composite film to possess excellent soft magnetic properties, large magnetostriction, a large piezoelectric coefficient, and low hysteresis and eddy current losses at high frequencies. Moreover, through the magnetoelectric coupling mechanism generated by the "product effect" between the piezoelectric and magnetostrictive materials, the resonant frequency of the FBAR can be tuned in the high-frequency range.

[0130] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A magnetically-tuned film bulk acoustic resonator comprising a first electrode, a piezoelectric material layer, and a second electrode stacked in sequence; characterized in that: The second electrode comprises at least one first material layer and at least one second material layer which are alternately stacked, a ratio of a total volume of all the first material layers to a total volume of all the second material layers in the second electrode is 1:1-5:1, the first material layer is a magnetostrictive film, the second material layer comprises a combination of any one or more of a soft magnetic film, an acoustic matching layer and a magnetostrictive film, the second electrode cooperates with the piezoelectric material layer to form a magnetoelectric heterojunction, and a material of the magnetostrictive film is FeGa, FeCo or FeGaB; A resonance frequency f0 of the magnetically tunable film bulk acoustic resonator is determined by an equivalent Young's modulus of the magnetoelectric heterojunction, and the resonance frequency f0 of the magnetically tunable film bulk acoustic resonator satisfies: wherein T0 represents a thickness of the magnetically tunable film bulk acoustic resonator, E eq and The bottom layer of the second electrode is the first material layer, and the top layer of the second electrode is the second material layer, or the bottom layer and the top layer of the second electrode are the first material layers, and the second material layer is located between the bottom layer and the top layer. eq is an equivalent Young's modulus and an equivalent density of the magnetically tunable film bulk acoustic resonator, and wherein, E i is an equivalent Young's modulus of the magnetoelectric heterostructure, V i is a volume ratio of each layer of the magnetoelectric heterostructure in the device.

2. The magnetically-tuned film bulk acoustic resonator of claim 1, wherein: The bottom layer of the second electrode is formed by growing on the piezoelectric layer.

3. The magnetically tunable film bulk acoustic resonator of claim 1, wherein: The number of the first material layers is equal to that of the second material layers in the second electrode, or the number of the first material layers is one more than that of the second material layers.

4. The magnetically-tuned film bulk acoustic resonator of claim 1, wherein: The first electrode, the piezoelectric material layer and the second electrode are sequentially stacked on the cavity structure.

5. The magnetically tunable film bulk acoustic resonator of claim 1, wherein: The first electrode, the piezoelectric material layer and the second electrode are sequentially stacked on the substrate, and the cavity structure is formed in the substrate.

6. The magnetically-tuned film bulk acoustic resonator of claim 5, wherein: The cavity structure is formed on a first surface of the substrate, and the first electrode, the piezoelectric material layer and the second electrode are sequentially stacked on the first surface of the substrate; or the cavity structure is formed on a second surface of the substrate, and the first electrode, the piezoelectric material layer and the second electrode are sequentially stacked on the first surface of the substrate, the first surface being opposite to the second surface.

7. The magnetically-tuned film bulk acoustic resonator of claim 6, wherein: The first electrode, the piezoelectric material layer and the second electrode are sequentially stacked on the substrate, and at least a partial region of the second electrode is concave to form the cavity structure in a direction away from the substrate.

8. The magnetically tunable film bulk acoustic resonator of claim 5, wherein: The step of manufacturing the second electrode comprises: alternately stacking at least one first material layer and at least one second material layer on the piezoelectric material layer, a ratio of a total volume of all the first material layers to a total volume of all the second material layers is 1:1-5:1, the first material layer is formed by a magnetostrictive film, the second material layer comprises a combination of any one or more of a soft magnetic film, an acoustic matching layer and a magnetostrictive film, the second electrode cooperates with the piezoelectric material layer to form a magnetoelectric heterojunction, and a material of the magnetostrictive film is FeGa, FeCo or FeGaB; 9. The method of claim 1-8, comprising the steps of fabricating a first electrode, a piezoelectric material layer, a second electrode, and a cavity structure; wherein, A resonance frequency f0 of the magnetically tunable film bulk acoustic resonator is determined by an equivalent Young's modulus of the magnetoelectric heterojunction, and the resonance frequency f0 of the magnetically tunable film bulk acoustic resonator satisfies: The step of manufacturing the second electrode further comprises: growing the first material layer as a bottom layer of the second electrode, and then growing the remaining structure layers of the second electrode on the bottom layer. wherein T0 represents the thickness of the magnetically tunable film bulk acoustic resonator ，E eq and The magnetically tunable film bulk acoustic resonator comprises any one of claims 1-8. eq Eeffis the equivalent Young's modulus and and wherein E i Eeffis the equivalent Young's modulus of the magnetoelectric heterostructure, V i is the volume ratio of each layer of the magnetoelectric heterostructure in the device.

10. The method of claim 9, wherein, The radio frequency filter comprises any one of claims 1-8.

11. A bulk acoustic wave filter characterized by ​ 12. A communications device comprising a radio frequency filter, characterised in that: ​

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