Manufacturing method of high-frequency bulk acoustic wave resonator

Abstract

The invention provides a manufacturing method of a high-frequency bulk acoustic wave resonator, and the method comprises the steps: forming a piezoelectric layer on a first substrate, the piezoelectric layer comprises a first thin film layer and a second thin film layer which are alternately stacked, and at least one of the first thin film layer and the second thin film layer is a ferroelectric thin film layer; forming a first electrode and a dielectric layer on the piezoelectric layer; forming an opening for exposing a part of the first electrode in the dielectric layer; bonding the dielectric layer to the second substrate, and removing the first substrate; forming a second electrode on one side, far away from the second substrate, of the piezoelectric layer; wherein the polarities of the adjacent first thin film layer and second thin film layer are opposite to each other, so that a first-order resonance mode is inhibited, and an N-order resonance mode is excited. The polarities of the adjacent first thin film layer and second thin film layer are opposite, a high-order resonance mode is excited under the condition of maintaining a relatively thick piezoelectric layer, and the resonant frequency of the resonator is remarkably improved; in addition, an electrode material layer does not need to be inserted between the first film layer and the second film layer, the manufacturing method is simple, and the device performance is high.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology and relates to a method for fabricating a high-frequency bulk acoustic resonator. Background Technology

[0002] Currently, wireless data transmission requires radio frequency (RF) filters with operating frequencies of 5 GHz or higher. The filters used in 5G communication are mainly bulk acoustic wave (BAW) filters and surface acoustic wave (SAW) filters. BAW devices have extremely high Q values ​​(above 4000), operate in frequency bands from 100 MHz to 20 GHz, and offer advantages such as high operating frequency, low insertion loss, high frequency selectivity, high power capacity, and strong electrostatic discharge (ESD) immunity, making them the best solution for future RF front-ends.

[0003] With increasing application demands, microwave acoustics not only needs to extend its operating frequency range to the Ku, Ka bands, and even millimeter-wave (mm-Wave) bands, but also needs to meet ultra-wideband requirements. In traditional single-layer piezoelectric thin-film resonators, since the resonant frequency of the bulk acoustic resonator is positively correlated with the ratio of longitudinal sound velocity to film thickness, this means that the thickness of the piezoelectric film used in filters at higher frequency bands such as 5G will be even smaller. For example, the piezoelectric film thickness for operating frequencies above 10GHz must be less than 100nm, which would severely degrade the quality of the piezoelectric film crystal and cause a sharp decrease in the resonator's power handling capability, electromechanical coupling coefficient, and Q value.

[0004] Therefore, how to provide a method for fabricating a high-frequency bulk acoustic resonator that can increase the resonant frequency of the resonator while maintaining the thickness of the piezoelectric layer and thus improve the device performance has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for manufacturing a high-frequency bulk acoustic resonator, which solves the problem of performance degradation of the bulk acoustic resonator when the resonant frequency is increased in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a method for manufacturing a high-frequency bulk acoustic resonator, comprising the following steps:

[0007] A first substrate is provided, and a piezoelectric layer is formed on the first substrate. The piezoelectric layer includes alternating stacked first and second thin film layers, wherein at least one of the first and second thin film layers is a ferroelectric thin film layer.

[0008] A first electrode is formed on the side of the piezoelectric layer away from the first substrate, and a dielectric layer is formed on the side of the piezoelectric layer away from the first substrate, the dielectric layer covering the first electrode;

[0009] An opening is formed in the dielectric layer, the opening exposing a portion of the first electrode;

[0010] A second substrate is provided, the dielectric layer is bonded to the second substrate, and the first substrate is removed;

[0011] A second electrode is formed on the side of the piezoelectric layer away from the second substrate;

[0012] A first electrode pad and a second electrode pad are formed on the side of the piezoelectric layer away from the second substrate. The first electrode pad penetrates the piezoelectric layer and is electrically connected to the first electrode, and the second electrode pad is electrically connected to the second electrode.

[0013] The adjacent first and second thin film layers have opposite polarities to suppress the first-order resonant mode and excite the Nth-order resonant mode, where N is an integer greater than 1.

[0014] Optionally, after forming the first electrode pad and the second electrode pad, a voltage or voltage pulse is applied between the first electrode and the second electrode to control the polarity direction of the ferroelectric thin film layer, so that the polarities of adjacent first thin film layers and second thin film layers are opposite.

[0015] Optionally, the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer, wherein the first piezoelectric layer includes at least one of alternately stacked first thin film layers and second thin film layers, and the second piezoelectric layer includes at least one of alternately stacked first thin film layers and second thin film layers, and the step of forming the piezoelectric layer includes:

[0016] The first piezoelectric layer is formed on the first substrate;

[0017] The first electrode is formed on the side of the first piezoelectric layer away from the first substrate;

[0018] The first electrode, the dielectric layer, and the opening are formed on the side of the first piezoelectric layer away from the first substrate;

[0019] The dielectric layer is bonded to the second substrate, and the first substrate is removed;

[0020] The second piezoelectric layer is formed on the side of the first piezoelectric layer away from the second substrate.

[0021] Optionally, after removing the first substrate, the method further includes a step of thinning the side of the first piezoelectric layer away from the second substrate.

[0022] Optionally, the piezoelectric layer comprises alternating stacked piezoelectric thin film layers / ferroelectric thin film layers.

[0023] Optionally, the piezoelectric layer comprises alternating stacked ferroelectric thin film layers / ferroelectric thin film layers.

[0024] Optionally, the material of the ferroelectric thin film layer includes Sc. x Al 1-x One or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3.

[0025] Optionally, the thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

[0026] Optionally, the material of the first electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf; the material of the second electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf.

[0027] Optionally, the method for forming the piezoelectric layer includes one or more of physical vapor deposition, chemical vapor deposition, and spin coating.

[0028] As described above, in the fabrication method of the high-frequency bulk acoustic wave resonator of the present invention, the polarities of adjacent first and second thin film layers are opposite, breaking the inverse relationship between the resonant frequency and the piezoelectric layer thickness of the traditional bulk acoustic wave resonator. While maintaining a thicker piezoelectric layer, the higher-order resonant modes of the resonator are excited, significantly improving the resonant frequency of the bulk acoustic wave resonator. In addition, the adjacent first and second thin film layers are in direct contact, eliminating the need to insert an electrode material layer between the first and second thin film layers. The fabrication method is simple and the device performance is high. Attached Figure Description

[0029] Figure 1 The diagram shows the process flow chart of the fabrication method of the high-frequency bulk acoustic resonator in an embodiment of the present invention.

[0030] Figure 2 The diagram shows a first substrate provided in an embodiment of the present invention, on which a first piezoelectric layer is formed.

[0031] Figure 3 The diagram shown is a schematic diagram of the formation of the first electrode in an embodiment of the present invention.

[0032] Figure 4 The diagram shown is a schematic diagram of the formation of the dielectric layer in an embodiment of the present invention.

[0033] Figure 5 The diagram shown is a schematic diagram of the planarized dielectric layer in an embodiment of the present invention.

[0034] Figure 6 The diagram shown illustrates the formation of an opening in an embodiment of the present invention.

[0035] Figure 7 The diagram shown is a schematic of a second substrate provided in an embodiment of the present invention, to which a dielectric layer is bonded.

[0036] Figure 8 The diagram shown is a schematic of removing the first substrate in an embodiment of the present invention.

[0037] Figure 9 The diagram shown is a schematic representation of the thinned and exposed first piezoelectric layer in an embodiment of the present invention.

[0038] Figure 10 The diagram shown is a schematic diagram of the formation of the second piezoelectric layer in an embodiment of the present invention.

[0039] Figure 11 The diagram shown is a schematic diagram of the formation of the second electrode in an embodiment of the present invention.

[0040] Figure 12 The diagram shown is a schematic diagram of the formation of a contact through hole in an embodiment of the present invention.

[0041] Figure 13 The diagram shown illustrates the formation of the first electrode pad and the second electrode pad in an embodiment of the present invention.

[0042] Component designation explanation

[0043] 1 First substrate

[0044] 2A First thin film layer

[0045] 2A Second thin film layer

[0046] 3 First Electrode

[0047] 4. Dielectric layer

[0048] 5 Openings

[0049] 6 Second substrate

[0050] 7 Second electrode

[0051] 8 Contact Through Holes

[0052] 9 First electrode pad

[0053] 10 Second electrode pad

[0054] Steps S1 to S6 Detailed Implementation

[0055] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0056] Please see Figures 1 to 13 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0057] This embodiment provides a method for fabricating a high-frequency bulk acoustic resonator. Please refer to [link to relevant documentation]. Figure 1 The method for manufacturing the high-frequency bulk acoustic resonator includes the following steps:

[0058] S1: Provide a first substrate, and form a piezoelectric layer on the first substrate, the piezoelectric layer comprising alternating stacked first thin film layers and second thin film layers, at least one of the first thin film layers and the second thin film layer being a ferroelectric thin film layer;

[0059] S2: A first electrode is formed on the side of the piezoelectric layer away from the first substrate, and a dielectric layer is formed on the side of the piezoelectric layer away from the first substrate, the dielectric layer covering the first electrode;

[0060] S3: An opening is formed in the dielectric layer, the opening exposing a portion of the first electrode;

[0061] S4: Provide a second substrate, bond the dielectric layer to the second substrate, and remove the first substrate;

[0062] S5: A second electrode is formed on the side of the piezoelectric layer away from the second substrate;

[0063] S6: A first electrode pad and a second electrode pad are formed on the side of the piezoelectric layer away from the second substrate. The first electrode pad penetrates the piezoelectric layer and is electrically connected to the first electrode, and the second electrode pad is electrically connected to the second electrode.

[0064] The fabrication method of the high-frequency bulk acoustic resonator of this embodiment will be described in detail below with reference to the specific accompanying drawings.

[0065] First, please refer to Figure 2Step S1: Provide a first substrate 1 and form a piezoelectric layer on the first substrate 1. The piezoelectric layer includes alternatingly stacked first thin film layer 2A and second thin film layer 2B, and at least one of the first thin film layer 2A and the second thin film layer 2B is a ferroelectric thin film layer.

[0066] As an example, the material of the first substrate 1 includes, but is not limited to, single-crystal silicon, silicon carbide, germanium, sapphire, or gallium nitride.

[0067] As an example, at least one of the first thin film layer 2A and the second thin film layer 2B is a ferroelectric thin film layer, which can be an alternating stack of piezoelectric thin film layers / ferroelectric thin film layers, or an alternating stack of ferroelectric thin film layers / ferroelectric thin film layers.

[0068] As an example, the piezoelectric thin film layer refers to a thin film layer with piezoelectric properties, and the ferroelectric thin film layer refers to a thin film layer that has both piezoelectric and ferroelectric properties.

[0069] As an example, when the piezoelectric layer employs alternating stacked piezoelectric thin film layers / ferroelectric thin film layers, the material of the piezoelectric thin film layer includes AlN, Al x Ga 1-x N(0 < x < 1), Al 1-x Sc x The ferroelectric thin film layer is made of one or more of the following materials: N (0 < x < 1), LiNbO3, ZnO, PZT, PbTiO3, and Ga2O3, and the material of the ferroelectric thin film layer includes Sc. x Al 1-x One or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3.

[0070] As an example, when the piezoelectric layer employs alternating stacks of ferroelectric thin film layers, the material of the ferroelectric thin film layers includes Sc. x Al 1-x One or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3.

[0071] As an example, in this embodiment, the piezoelectric layer is composed of alternately stacked piezoelectric thin film layers / ferroelectric thin film layers, wherein the first thin film layer 2A is a piezoelectric thin film layer and the second thin film layer 2B is a ferroelectric thin film layer; specifically, in this embodiment, the first thin film layer 2A is a single-crystal AlN layer and the second thin film layer 2B is a Sc layer. 0.3 Al 0.7 N layers.

[0072] As an example, the methods for forming the first thin film layer 2A and the second thin film layer 2B include one or more of physical vapor deposition, chemical vapor deposition, or spin coating. Preferably, in this embodiment, the first thin film layer 2A and the second thin film layer 2B are formed using MOCVD, MBE, ALD, or PLD.

[0073] Next, please refer to Figures 3 to 4 Step S2: A first electrode 3 is formed on the side of the piezoelectric layer away from the first substrate 1, and a dielectric layer 4 is formed on the side of the piezoelectric layer away from the first substrate 1, the dielectric layer 4 covering the first electrode 3.

[0074] As an example, such as Figure 3 As shown, after forming the first electrode material layer and patterning it, the first electrode 3 is obtained. The material of the first electrode 3 includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf. The thickness of the first electrode 3 does not exceed 0.3 μm. Specifically, in this embodiment, the first electrode 3 adopts a Mo metal layer.

[0075] As an example, such as Figure 4 As shown, a dielectric layer 4 is formed covering the first electrode 3. Since the dielectric layer 4 is relatively thick and has an uneven surface, please refer to [reference needed]. Figure 5 It also includes a step of planarizing the surface of the dielectric layer 4, for example, by using chemical mechanical polishing (CMP) to planarize the surface of the dielectric layer 4.

[0076] As an example, the material of the dielectric layer 4 includes, but is not limited to, silicon dioxide, silicon nitride, aluminum oxide, etc., and is preferably silicon dioxide.

[0077] Next, please refer to Figure 6 Step S3: An opening 5 is formed in the dielectric layer 4, and the opening 5 exposes a portion of the first electrode 3.

[0078] As an example, the opening 5 is formed by etching or other suitable methods, wherein the opening 5 exposes a portion of the first electrode 3, and another portion of the first electrode 3 is covered by the dielectric layer 4.

[0079] Next, please refer to Figures 7 to 8 Step S4: Provide a second substrate 6, bond the dielectric layer 4 to the second substrate 6, and remove the first substrate 1.

[0080] As an example, the material of the second substrate 6 includes, but is not limited to, single-crystal silicon, silicon carbide, germanium, sapphire or gallium nitride, etc., and the structure forming the opening 5 is inverted so that the dielectric layer 4 and the second substrate 6 are bonded together.

[0081] As an example, the second substrate 6 and the opening 5 together form a cavity, which serves as an acoustic mirror structure to confine sound waves within the piezoelectric layer, preventing sound waves from leaking to the second substrate 6, thereby reducing energy loss, improving the performance of the resonator, and helping to achieve a high Q value and low insertion loss.

[0082] As an example, the methods for removing the first substrate 1 include, but are not limited to, one or more of ion implantation stripping, mechanical polishing, polishing, wet etching, and dry etching.

[0083] As an example, after removing the first substrate 1, the bottom surface of the first thin film layer 2A is exposed. During the removal of the first substrate 1, the quality of the bottom surface of the first thin film layer 2A is damaged to some extent. Please refer to [link / reference needed]. Figure 9 It also includes a step of thinning the bottom surface of the first thin film layer 2A to remove the first thin film layer 2A of poor quality. The method of thinning the first thin film layer 2A includes etching, polishing or other suitable methods.

[0084] For example, please refer to Figure 10 After thinning the bottom surface of the first thin film layer 2A, the second thin film layer 2B is formed on the side of the first thin film layer 2A away from the second substrate 6. That is, in this application, the piezoelectric layer is formed in two steps. The piezoelectric layer can be regarded as being composed of a first piezoelectric layer and a second piezoelectric layer. First, a first piezoelectric layer is formed on the first substrate 1. Then, the first electrode 3, the dielectric layer 4, and the opening 5 are formed on the first piezoelectric layer. Then, it is bonded to the second substrate 6 and the first substrate 1 is removed. Finally, a second piezoelectric layer is formed on the side of the first piezoelectric layer away from the second substrate 6, thus completing the fabrication of the piezoelectric layer.

[0085] As an example, in this embodiment, the piezoelectric layer consists of a three-layer structure: a second thin film layer 2B, a first thin film layer 2A, and a second thin film layer 2B. The first thin film layer 2A is a single-crystal material layer, and the second thin film layers 2B on both sides of the first thin film layer 2A are deposited based on the first thin film layer 2A as a substrate. This results in a piezoelectric layer with better overall quality. In other examples, the number of piezoelectric layers is not limited to a three-layer structure; the number of layers can be set according to requirements and is not limited to this embodiment.

[0086] It should be noted that, in another example, the required number of piezoelectric layers can also be formed on the first substrate 1. Removing the first substrate 1 does not require forming a piezoelectric layer, and this also falls within the scope of protection of the present invention.

[0087] As an example, the thickness of the first thin film layer 2A is not less than 0.01 μm, the thickness of the second thin film layer 2B is not less than 0.01 μm, and the total thickness of the piezoelectric layer does not exceed 2 μm.

[0088] Next, please refer to Figure 11 Step S5: A second electrode 7 is formed on the side of the piezoelectric layer away from the second substrate 6.

[0089] As an example, a second electrode material layer is formed and patterned on the side of the piezoelectric layer away from the second substrate 6 to obtain the second electrode 7. The material of the second electrode 7 includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf. Specifically, in this embodiment, the second electrode 7 adopts a Mo metal layer.

[0090] Next, please refer to Figures 12 to 13 Step S6 is executed: a first electrode pad 9 and a second electrode pad 10 are formed on the side of the piezoelectric layer away from the second substrate 6. The first electrode pad 9 penetrates the piezoelectric layer and is electrically connected to the first electrode 3. The second electrode pad 10 is electrically connected to the second electrode 7.

[0091] As an example, such as Figure 12 As shown, before forming the first electrode pad 9 and the second electrode pad 10, a contact via 8 penetrating the piezoelectric layer is formed in the piezoelectric layer. The projection of the contact via 8 onto the second substrate 6 does not overlap with the projection of the opening 5 onto the second substrate 6.

[0092] As an example, such as Figure 13 As shown, the first electrode pad 9 extends into the contact through hole 8 and is electrically connected to the first electrode 3. The first electrode pad 9 and the second electrode pad 10 are used to lead out the first electrode 3 and the second electrode 7.

[0093] As an example, the projection of the contact via 8 onto the second substrate 6 does not overlap with the projection of the opening 5 onto the second substrate 6. That is, the contact via 8 is located on the periphery of the opening 5, which can avoid introducing acoustic obstructions in the resonant region, prevent noise and energy loss, and avoid noise near the resonant peak.

[0094] As an example, after forming the first electrode pad 9 and the second electrode pad 10, a voltage or voltage pulse is applied between the first electrode 3 and the second electrode 7 to control the polarity direction of the ferroelectric thin film layer, so that the polarities of adjacent first thin film layers 2A and second thin film layers 2B are opposite (polarization directions are opposite).

[0095] As an example, the ferroelectricity of the ferroelectric thin film layer causes spontaneous polarization inside. The polarization state can be changed by applying an external voltage between the first electrode 3 and the second electrode 7, and the polarization state can be maintained after the external voltage is removed, thereby achieving opposite polarity control between adjacent first thin film layers 2A and second thin film layers 2B.

[0096] In another example, when both the first thin film layer 2A and the second thin film layer 2B are ferroelectric thin film layers, the polarization reversal voltage between different ferroelectric thin films varies due to factors such as deposition conditions, material type, and doping concentration. When an external voltage is applied between the first electrode 3 and the second electrode 7, the polarization state of one of the adjacent first thin film layer 2A and the second thin film layer 2B remains unchanged, while the polarization state of the other layer is reversed, thereby achieving opposite polarity control between the adjacent first thin film layer 2A and the second thin film layer 2B.

[0097] It should be noted that in other examples, the first thin film layer 2A and the second thin film layer 2B formed by deposition are material layers with opposite polarities, and it is not necessary to apply an external voltage between the first electrode 3 and the second electrode 7 to adjust the polarity of the ferroelectric thin film layer. Although the formation of piezoelectric layers with opposite polarities by deposition process has high requirements for deposition conditions, material type, doping concentration, etc., it still falls within the scope of protection of this invention.

[0098] Specifically, when the polarization directions of the first thin film layer 2A and the second thin film layer 2B are opposite, there is a 180° phase difference in the piezoelectric response to the electrical signal. The inverse piezoelectric effect causes one of the adjacent first thin film layer 2A and second thin film layer 2B to be subjected to compressive stress and the other to be subjected to tensile stress, which suppresses the first-order asymmetric thickness expansion mode and excites the corresponding higher-order thickness expansion mode.

[0099] As an example, in this embodiment, the piezoelectric layer consists of a three-layer structure, suppressing the first-order asymmetric thickness extension mode and exciting the third-order thickness extension mode, enabling the resonator to operate at frequencies above 24 GHz. In another example, the piezoelectric layer consists of a three-layer structure; by adjusting the thicknesses of the first electrode 3, the piezoelectric layer, and the second electrode 7, the third-order thickness extension mode can be suppressed, while a fourth-order overtone thickness mode can be excited. When the total number of layers of the first thin film layer 2A and the second thin film layer 2B is N, and the polarities of adjacent first thin film layers 2A and second thin film layers 2B are opposite, an Nth-order thickness extension mode or an N+1th-order overtone thickness mode can be excited, improving the operating frequency band.

[0100] As an example, using a thicker piezoelectric layer to achieve ultra-high frequencies in the resonator results in a piezoelectric layer with high crystal quality and low defect density, leading to higher Q values, lower losses, and higher power capacity in the device, making it more suitable for low-power mobile communications and wireless communication applications requiring low interference. Furthermore, to ensure the manufacturing yield of the resonator, the thickness uniformity of the piezoelectric layer needs to be better than 0.5%, and a thicker piezoelectric layer can significantly improve manufacturing yield and stability. In addition, it is not necessary to reduce the thickness of the piezoelectric layer to achieve frequency increases in the resonator, making it particularly suitable for new high-frequency bands in 5G, high-frequency satellite communications, 5G millimeter-wave bands, and 6G ultra-high-frequency bands.

[0101] As an example, in traditional bulk acoustic resonators made of single-layer piezoelectric materials, the electromechanical coupling coefficient of the excited high-frequency modes is inversely proportional to the order of the higher-order modes. Therefore, the electromechanical coupling coefficient of the resonator is very small at higher orders, and the corresponding filter bandwidth is very small, which is difficult to meet the needs of practical communication applications. In this invention, the electromechanical coupling coefficient of the higher-order modes of the device is independent of the order, and it can maintain a high electromechanical coupling coefficient and a large bandwidth at high frequencies, making it very suitable for high-frequency and high-bandwidth application scenarios.

[0102] As an example, in existing technologies, when high-frequency modes are excited using piezoelectric and ferroelectric thin film layers with opposite polarities, an electrode material layer needs to be inserted between the piezoelectric and ferroelectric thin film layers. Polarity reversal is achieved by applying a very high bias voltage to the electrode material layer. However, inserting an electrode material layer severely affects the crystal quality of the piezoelectric and ferroelectric thin film layers, deteriorating the device's out-of-band rejection and in-band loss characteristics, while also posing significant challenges to cost, controllability, and integration. In this application, the first thin film layer 2A and the second thin film layer 2B are in direct contact, eliminating the need to insert an electrode material layer between them. This results in a simpler device structure and higher device performance.

[0103] In summary, in the fabrication method of the high-frequency bulk acoustic wave resonator of the present invention, the adjacent first and second thin film layers have opposite polarities, breaking the inverse relationship between the resonant frequency and the piezoelectric layer thickness of the traditional bulk acoustic wave resonator. This significantly improves the resonant frequency of the bulk acoustic wave resonator by maintaining a relatively thick piezoelectric layer while exciting higher-order resonant modes. Furthermore, the adjacent first and second thin film layers are in direct contact, eliminating the need to insert an electrode material layer between them, simplifying the fabrication method and resulting in high device performance. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0104] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for fabricating a high-frequency bulk acoustic resonator, characterized in that, Includes the following steps: A first substrate is provided, and a piezoelectric layer is formed on the first substrate. The piezoelectric layer includes alternating stacked first and second thin film layers, wherein at least one of the first and second thin film layers is a ferroelectric thin film layer. A first electrode is formed on the side of the piezoelectric layer away from the first substrate, and a dielectric layer is formed on the side of the piezoelectric layer away from the first substrate, the dielectric layer covering the first electrode; An opening is formed in the dielectric layer, the opening exposing a portion of the first electrode; A second substrate is provided, the dielectric layer is bonded to the second substrate, and the first substrate is removed; A second electrode is formed on the side of the piezoelectric layer away from the second substrate; A first electrode pad and a second electrode pad are formed on the side of the piezoelectric layer away from the second substrate. The first electrode pad penetrates the piezoelectric layer and is electrically connected to the first electrode, and the second electrode pad is electrically connected to the second electrode. The adjacent first and second thin film layers have opposite polarities to suppress the first-order resonant mode and excite the Nth-order resonant mode, where N is an integer greater than 1.

2. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that: After forming the first electrode pad and the second electrode pad, the method further includes applying a voltage or voltage pulse between the first electrode and the second electrode to control the polarity direction of the ferroelectric thin film layer, so that the polarities of adjacent first thin film layers and second thin film layers are opposite.

3. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that, The piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer. The first piezoelectric layer includes at least one of alternately stacked first thin film layers and second thin film layers. The second piezoelectric layer includes at least one of alternately stacked first thin film layers and second thin film layers. The step of forming the piezoelectric layer includes: The first piezoelectric layer is formed on the first substrate; The first electrode is formed on the side of the first piezoelectric layer away from the first substrate; The first electrode, the dielectric layer, and the opening are formed on the side of the first piezoelectric layer away from the first substrate; The dielectric layer is bonded to the second substrate, and the first substrate is removed; The second piezoelectric layer is formed on the side of the first piezoelectric layer away from the second substrate.

4. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 3, characterized in that: After removing the first substrate, the method further includes a step of thinning the side of the first piezoelectric layer away from the second substrate.

5. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that: The piezoelectric layer comprises alternating stacked piezoelectric thin film layers / ferroelectric thin film layers.

6. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that: The piezoelectric layer comprises alternating stacked ferroelectric thin film layers / ferroelectric thin film layers.

7. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that: The ferroelectric thin film layer is made of Sc. x Al 1-x One or more of N (0.2≤x≤0.5), BST, PZT, and PbTiO3.

8. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that: The thickness of the first thin film layer is not less than 0.01 μm, and the thickness of the second thin film layer is not less than 0.01 μm.

9. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that: The material of the first electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf; the material of the second electrode includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf.

10. The method for manufacturing a high-frequency bulk acoustic resonator according to claim 1, characterized in that: The methods for forming the piezoelectric layer include one or more of physical vapor deposition, chemical vapor deposition, and spin coating.

Images