Acoustic resonator device operating in higher order mode

Abstract

The present technology relates to an acoustic resonator device operating in a higher order mode. More specifically, embodiments of the present technology provide an acoustic resonator device that includes a piezoelectric layer disposed between a first electrode and a second electrode. The total thickness of the first electrode, the second electrode, and the third electrode allows the device to operate according to a second (or higher order) thickness extension mode. Other embodiments are also present.

Description

Technical Field The present technology relates to acoustic resonator devices. Background Art Acoustic resonators have a wide range of implementations and applications. One implementation of an acoustic resonator is a film bulk acoustic resonator. Bulk acoustic wave resonators (BAW) and their various configurations, such as film bulk acoustic resonators (FBARs), solid mounted resonators (SMRs), and reverse stacked FBARs (RSBARs), provide a wide range of applications in communication systems, especially in filters for radio frequency (RF) signal processing. The continued scaling of technology and the emergence of 5G and beyond communication networks have created a need for compact, efficient, and high-performance filtering solutions. In existing approaches, FBAR devices include a piezoelectric layer sandwiched between two electrodes and are typically designed to operate at a specific resonant frequency, which is determined by the physical dimensions and material properties of the resonator. The resonator is used to allow signals at the resonant frequency to pass or reject the signal, thereby providing filtering functionality. Unfortunately, for the reasons provided below, existing acoustic resonators are insufficient. New and improved acoustic resonator devices are needed. Summary of the invention In one aspect, the present disclosure relates to an acoustic resonator device comprising: a first electrode characterized by a first thickness, the first electrode comprising a first metal; a second electrode characterized by a second thickness, the second electrode comprising a second metal; and a first piezoelectric layer disposed between the first electrode and the second electrode, the first piezoelectric layer characterized by a third thickness; wherein: the total thickness including the first thickness, the second thickness and the third thickness is associated with two or more stress half-waves; and the acoustic resonator device is characterized by an operating frequency of at least 5 GHz. On the other hand, the present disclosure relates to an acoustic resonator device, comprising: a first electrode characterized by a first thickness, the first electrode comprising a first metal; a second electrode characterized by a second thickness, the second electrode comprising a second metal; and a first piezoelectric layer disposed between the first electrode and the second electrode, the first piezoelectric layer characterized by a third thickness; wherein: the total thickness includes the first thickness; the second thickness and the third thickness are associated with two or more stress half-waves; and the acoustic resonator device operates in a second or higher thickness extension mode. On the other hand, the present disclosure relates to an acoustic resonator device, comprising: a first electrode characterized by a first thickness, the first electrode comprising a first metal; a second electrode characterized by a second thickness, the second electrode comprising a second metal; a third electrode characterized by a third thickness, the third electrode comprising a third metal; a first piezoelectric layer disposed between the first electrode and the second electrode, the first piezoelectric layer characterized by a fourth thickness; and a second piezoelectric layer disposed between the second electrode and the third electrode, the second piezoelectric layer characterized by a fifth thickness; wherein the acoustic resonator device operates in a third or higher thickness extension mode. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified diagram illustrating a resonator operating in a first thickness extensional mode. Figure 2A is a simplified diagram illustrating a resonator 200 operating in a third thickness extensional mode in accordance with an embodiment of the present technology. Figure 2B is a diagram illustrating the operation of the resonator 200 . Figure 3A is a simplified diagram illustrating a resonator 300 operating in a third thickness extensional mode in accordance with an embodiment of the present technology. Figure 3B is a diagram illustrating the operation of the resonator 300 . Figure 4 is a simplified diagram illustrating a resonator 400 including two piezoelectric layers in accordance with an embodiment of the present technology. Figure 5A is a simplified diagram illustrating a resonator 500 including two piezoelectric layers and a double layer electrode in accordance with an embodiment of the present technology. Figure 5B is a diagram illustrating the operation of the resonator 500 . Figure 6 is a simplified diagram illustrating a resonator 600 including two piezoelectric layers separated by electrodes in accordance with an embodiment of the present technology. Figure 7 is a simplified diagram illustrating a resonator 700 including two piezoelectric layers separated by a layer of electrode material in accordance with an embodiment of the present technology. DETAILED DESCRIPTION The present technology relates to acoustic resonators. More specifically, embodiments of the present technology provide an acoustic resonator device that includes a piezoelectric layer disposed between a first electrode and a second electrode. The thickness of the first electrode and the second electrode allow the device to operate according to a second (or higher order) thickness extension mode. Other embodiments exist. In the context of resonator design, electrodes play a crucial role in determining resonator performance and characteristics. For example, resonant frequency, mode bandwidth, electrical losses, and device size are important characteristics. As an example, the bandwidth of a mode can be defined by the interval between its parallel and series resonant frequencies, represented by the formula bw=fp-fs. Various existing FBAR designs provide resonators that utilize relatively thin electrodes operating in a first thickness extension mode, which facilitates certain operating characteristics. However, this approach has limitations in managing stress waves within the electrodes and can affect conductivity and bandwidth, as well as other performance metrics. As technology moves toward higher frequencies and miniaturization, managing electrode characteristics, especially thickness, becomes a challenging task, requiring a careful balance between electrical and mechanical properties. The resonant frequency of an FBAR is - roughly speaking - inversely proportional to the total thickness of the resonator stack. To achieve higher operating frequencies, it involves reducing the layer thickness. For example, the thinness of the electrodes is also important to ensure that they do not significantly affect the overall thickness and therefore the resonant frequency. However, thinner electrodes, while facilitating high frequency operation, are susceptible to reduced conductivity. In addition, for high frequency operation (e.g., 5 GHz and above), it becomes a challenge to manufacture electrodes that are thin enough to achieve high frequencies. Ensuring high yields in the high frequency FBAR manufacturing process while maintaining the necessary performance parameters can be economically and technically challenging. It should be appreciated that embodiments of the present technology provide acoustic resonator devices that operate at high frequencies (e.g., in excess of 5 GHz) without significantly reducing electrode thickness (e.g., electrodes no thinner than 100 nm). For example, depending on the implementation, different electrode thicknesses and compositions (e.g., aluminum and tungsten) may be used, which allow for different acoustic impedances and mechanical properties, thereby providing a platform for tuning the device for optimal bandwidth (e.g., fp-fs), electrical performance, and resonant characteristics, potentially improving the efficiency and performance of the device across a variety of applications. Where the total thickness allows for multiple stress maxima disposed within the FBAR stack, the device may exhibit improved acoustic and electrical performance during operation. This may enhance the usability of the device, especially in high frequency applications. Frequency filters utilizing FBAR resonators to operate at high frequencies (e.g., 12 GHz) are provided according to various embodiments of the prior art. These filters can function in the range of 3 to 20 GHz and potentially higher. In some prior art approaches, the resonators are operated in the TE1 mode and scaled down in layer thickness to achieve the desired 12 GHz frequency. These resonators are engineered to operate with a single acoustic stress maximum localized within the piezoelectric layer. The stress gradually decreases to zero toward both the lower and upper surfaces, see Figure 1 The operating frequency is defined by matching one stress half-wave between the lower and upper surfaces along the z-axis. This operating mode is called the first thickness extension mode TE1 or fundamental mode. It should be appreciated that embodiments according to the present technology allow the thickness of one or optionally both electrode layers to operate with an additional stress half-wave within the respective electrode layer. For example, a configuration with one or more thick electrodes introduces additional stress zeros disposed within the stack, thereby allowing operation at high frequencies while using relatively thick (compared to resonators operating in TE1 mode) electrodes. This thus results in improved conductivity and structural strength. For example, an exemplary implementation involving thickening one electrode enables a film bulk acoustic resonator (FBAR) to operate in TE2 mode, while thickening both electrodes allows the FBAR to operate in TE3 and / or higher order modes. According to various embodiments, an FBAR operating in TE3 mode is configured to resonate at a predefined operating frequency by incorporating two additional stress zeros within its layer stack. The operating frequency is determined by allowing three stress half-waves along its z-axis. This operating mode is designated as the third thickness extended mode or TE3. By matching three rather than a single half-wave between the upper and lower surfaces, the resonator design is free to configure an FBAR stack with approximately three times the thickness - maintaining the same operating frequency. Subsequently, two supplementary stress peaks are strategically placed within the thickened electrode layer, thereby ensuring significantly enhanced conductivity (see Figure 2A , see page 6 for detailed instructions). The following description is presented to enable one of ordinary skill in the art to make and use the invention and incorporate it into the context of a particular application. Various modifications and various uses in different applications will be readily apparent to one of ordinary skill in the art, and the general principles defined herein may be applied to a wide range of embodiments. Therefore, the present technology is not intended to be limited to the embodiments presented, but should be accorded the widest scope consistent with the principles and novel features disclosed herein. In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the present technology. However, it will be apparent to those skilled in the art that the present technology may be practiced without being limited to these specific details. In other examples, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring the present technology. The reader should pay attention to all papers and documents that are filed at the same time as this specification and are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. Unless otherwise expressly stated, all features disclosed in this specification (including any attached claims, abstracts and drawings) can be replaced by alternative features for the same, equivalent or similar purposes. Therefore, unless otherwise expressly stated, each feature disclosed is only an example of a series of general equivalent or similar features. Furthermore, any element in the claims that does not explicitly recite “means” for performing a specified function or “step” for performing a specific function should not be construed as a “means” or “step” clause as specified in 35 USC 112, paragraph 6. In particular, the use of “the step of” or “the action of” in the claims herein is not intended to invoke the provisions of 35 USC 112, paragraph 6. When an element is referred to herein as being "connected" or "coupled" to another element, it is understood that the element may be directly connected to the other element or have an intervening element present between the elements. Conversely, when an element is referred to as being "directly connected" or "directly coupled" to another element, it is understood that there are no intervening elements in the "direct" connection between the elements. However, the presence of a direct connection does not exclude other connections in which intervening elements may be present. When an element is referred to herein as being "disposed" in some manner relative to another element (e.g., disposed on, disposed between, disposed below, disposed adjacent to, or disposed in some other relative manner), it is understood that the element may be disposed directly relative to the other element (e.g., disposed directly on the other element) or have intervening elements present between the elements. Conversely, when an element is referred to as being "directly disposed" relative to another element, it is understood that in the "direct" instance there are no intervening elements. However, the presence of a direct disposition does not exclude other instances in which intervening elements may be present. Similarly, when an element is referred to herein as being "joined" to another element, it is understood that the element may be directly joined to the other element (without any intervening elements) or have an intervening element present between the joined elements. Conversely, when an element is referred to as being "directly joined" to another element, it is understood that there are no intervening elements in the "direct" joining between the elements. However, the presence of direct joining does not exclude other forms of joining in which intervening elements may be present. Likewise, when an element is referred to herein as a "layer," it is understood that the layer may be a single layer or may include multiple layers. For example, a conductive layer may include multiple different conductive materials or multiple layers of different conductive materials, and a dielectric layer may include multiple dielectric materials or multiple layers of dielectric materials. When a layer is described as being coupled or connected to another layer, it is understood that the coupled or connected layer may include intervening elements that exist between the coupled or connected layers. Conversely, when a layer is referred to as being "directly" connected or coupled to another layer, it is understood that there are no intervening elements between the layers. However, the presence of a directly coupled or connected layer does not exclude other connections in which intervening elements may exist. In addition, the terms left, right, front, back, top, bottom, forward, backward, clockwise and counterclockwise are used only for explanation purposes and are not limited to any fixed direction or orientation. Instead, they are only used to indicate the relative position and / or direction between the various parts of an object and / or component. In addition, for ease of description, the methods and processes described herein may be described in a particular order. However, it should be understood that unless the context indicates otherwise, the intermediary processes may occur before and / or after any portion of the described processes, and that various other procedures may be reordered, added, and / or omitted according to various embodiments. Unless otherwise indicated, all numbers used herein to indicate quantities, dimensions, and the like are to be understood as being modified in all instances by the term "about". In this application, unless otherwise specifically indicated, the use of the singular includes the plural, and the use of the terms "and" and "or" means "and / or" unless otherwise indicated. In addition, the use of the terms "comprise" and "have", as well as other forms such as "includes", "included", "has", "have", and "had" are to be considered non-exclusive. In addition, terms such as "element" or "component" encompass both elements and components comprising one unit and elements and components comprising more than one unit, unless otherwise specifically indicated. As used herein, the phrase "at least one of..." preceding a series of items separated by the terms "and" or "or" modifies the entire list, rather than each member of the list (i.e., each item). The phrase "at least one of..." does not require selection of at least one of each item listed; rather, the phrase allows for a meaning that includes at least one of any one item and / or at least one of any combination of items. For example, the phrase "at least one of A, B, and C" or "at least one of A, B, or C" each refers to only A, only B, or only C; and / or any combination of A, B, and C. In examples where selection of "at least one of each of A, B, and C," or alternatively, "at least one of A, at least one of B, and at least one of C," is intended, it is explicitly described as such. Figure 1is a simplified diagram illustrating a resonator operating in a first thickness extensional mode. To achieve operation at a target frequency (e.g., 12 GHz), the layer thicknesses of the resonator are scaled down. A resonator 100 designed to operate with a single acoustic stress maximum localized within the piezoelectric layer comprises a top electrode 101, a piezoelectric layer 102, and a bottom electrode 103. Here, the stress decays monotonically to zero toward both the lower and upper surfaces of the device, with one stress half-wave matching along the z-axis between these surfaces, defining its operating frequency. This operating mode is referred to as the fundamental thickness extensional mode (i.e., TE1), and involves a single stress wave 104 extending through the entire thickness of the resonator 100 encompassing electrodes 101 and 103 and the piezoelectric layer 102. The wavelength of the stress wave 104 determines the operating frequency of the resonator. Achieving high frequencies, such as 12 GHz, requires extremely thin layer stacks and, critically, very thin electrodes characterized by poor electrical conductivity. Figure 2A 2 is a simplified diagram illustrating a resonator 200 operating in a third thickness extension mode according to an embodiment of the present technology. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art will recognize many variations, alternatives, and modifications. The resonator 200 is configured to operate in a third thickness extension mode (TE3) characterized by three different acoustic stress maxima. Within its structure, the resonator 200 includes a top electrode 201, a piezoelectric layer 202, and a bottom electrode 203. The acoustic stress maxima are strategically located: maximum 210 is located within the top electrode 201, maximum 211 is located within the piezoelectric layer 202, and maximum 212 is located within the bottom electrode 203. Thickening one or both electrode layers allows additional stress half-waves to reside within the electrode layers. For example, additional stress zeros are introduced within the stack through increased thickness, and high frequencies can be achieved with significantly thicker electrodes, thereby achieving significantly enhanced conductivity. For example, when only one of the two electrodes is thickened, the resonator operates in the second thickness extension (TE2) mode; if both are thickened electrodes, it operates in the third thickness extension (TE3) mode. For example, the electrode layers are configured to be thick enough to accommodate additional stress field maxima therein. In various embodiments, the design of the stack is optimized to ensure the necessary bandwidth under the new operating mode - TE2 when one electrode is thickened, and TE3 when two electrodes are thickened, and the subsequent discussion focuses primarily on the latter case. An acoustic resonator designed to operate in the TE3 mode resonates at a defined operating frequency by incorporating two additional stress zeros within the stack. It determines its operating frequency by accommodating three stress half-waves (synonymous with the TE3 motion mode) along its z-axis. The ability to match three rather than one half-waves between the upper and lower surfaces allows the stack to be designed to be approximately three times thicker while maintaining the same operating frequency. As shown, two additional stress maxima are located within the electrode layer. These three stress waves, identified by their respective maxima 210, 211, and 212, facilitate operation of the resonator at high frequencies (e.g., 12 GHz). The material for electrodes 201 and 203 is selected based on their acoustic impedance for the desired performance, thereby customizing them for a particular application. In an embodiment, electrodes 201 and 203 include molybdenum, and other metallic materials may also be used. For example, layer 202 includes a piezoelectric material that generates an electrical charge in response to applied mechanical stress. For example, layer 202 may include aluminum nitride (AlN), aluminum scandium nitride (ASN), which is a type of piezoelectric material that includes a solid solution of scandium nitride (ScN). For example, the chemical formula of ASN is Al 1-x Sc x N, where x represents the proportion of scandium. Other piezoelectric materials may also be used, which may be used in high frequency applications, such as signal filtering where energy conversion efficiency is important. Piezoelectric materials may also include zinc oxide, lead zirconate, barium strontium titanate, lithium niobate, lithium tantalate, and / or other materials. In addition, electrode thickness is important in resonator design. Although thin electrodes may present problems such as reduced conductivity and compromised mechanical rigidity, resonator 200 addresses this problem by providing electrodes 201 and 203 with a substantial thickness of approximately 3000 angstroms. In contrast, piezoelectric layer 202 may have a thickness of approximately 1000 angstroms. It should be appreciated that other thicknesses are possible. Figure 2B is a diagram illustrating the operation of the resonator 200. Figure 2B As shown in FIG. 4 , the operation of the resonator 200 in the TE3 mode is at about 12 GHz, with both a large frequency response and a bandwidth (eg, a bandwidth of about 250 to 500 MHz). Figure 3A 300 is a simplified diagram illustrating a resonator 300 operating in a third thickness extension mode according to an embodiment of the present technology. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art will recognize many variations, alternatives, and modifications. Resonator 300 includes a top double layer electrode, a bottom double layer electrode, and a piezoelectric layer 303 disposed between the top double layer electrode and the bottom double layer electrode. The top double layer electrode includes a metal layer 301 and a metal layer 302. For example, metal layer 301 includes an aluminum material, and metal layer 302 includes a tungsten material. It should be understood that other materials are also possible. For example, different metal layers—as part of the double layer electrodes—are characterized by different acoustic impedances and electrical conductivities. For example, tungsten layers (e.g., layers 302 and 304) act as acoustic mirror layers, which reduce stress fields in the highly conductive Al layer. For example, metal layers 302 and 304 (e.g., acting as acoustic mirror layers) can be much thinner (e.g., about 360 angstroms) than metal layers 301 and 305 (e.g., aluminum layers having a thickness of about 2500 angstroms), while the piezoelectric layer is characterized by a thickness of about 800 angstroms. Other thicknesses are possible depending on the metal layer materials and their properties. For example, when resonator 300 operates in the third thickness extensional mode (i.e., TE3), three stress waves such as Figure 3A The general positioning is shown in FIG. 3 ; stress wave 310 is positioned in layer 301 ; stress wave 311 is positioned in layers 302 , 303 , and 304 ; stress wave 312 is positioned in layer 305 . Figure 3B is a diagram illustrating the operation of the resonator 300. Figure 3B , the operation of the resonator 300 in the TE3 mode is at about 12 GHz, with both a large frequency response and a bandwidth (eg, a bandwidth of about 1150 MHz). Figure 4 0045 is a simplified diagram illustrating a resonator 400 including two piezoelectric layers according to an embodiment of the present technology. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art will recognize many variations, alternatives, and modifications. Resonator 400 includes two layers of piezoelectric material (i.e., 402 and 403) disposed between electrode 401 and electrode 404. The two piezoelectric layers have opposite c-axis orientations, as explained below in paragraph 0045. In an embodiment, electrodes 401 and 404 include molybdenum, and other metallic materials may also be used. Figure 5A 5 is a simplified diagram illustrating a resonator 500 including two piezoelectric layers and a double layer electrode according to an embodiment of the present technology. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art will recognize many variations, alternatives, and modifications. Resonator 500 includes a top double layer electrode including layer 501 and layer 502. Resonator 500 also includes a bottom double layer electrode including layer 505 and layer 506. Piezoelectric layers 503 and 504 are disposed between the top double layer electrode and the bottom double layer electrode. As an example, layer 501 includes an aluminum material, and layer 502 includes a tungsten material. Similarly, layer 506 includes an aluminum material, and layer 505 includes a tungsten material. As explained above, the aluminum and tungsten electrode layers are configured to be different thicknesses based on their acoustic and electrical properties. For example, aluminum electrode layers (eg, layers 501 and 506) are characterized by a thickness of approximately 2500 angstroms, and tungsten electrode layers (eg, layers 502 and 505) are characterized by a thickness of approximately 480 angstroms. In various embodiments, piezoelectric layers 503 and 504 include the same piezoelectric material (e.g., ASN material), but are configured in different directions. For example, layer 503 is configured to have a c-axis direction opposite to the c-axis direction of layer 504. For example, the term "c-axis" refers to a specific directional axis in the growth of a thin piezoelectric film, which is related to electrical and mechanical response. When a piezoelectric film is gradually formed on a bottom electrode designated as an electrical ground and reference growth surface, the c-axis can be oriented positively or negatively relative to this reference surface. A positive c-axis orientation means that it points upward from the reference, aligned with a positive applied electric field toward the top electrode. On the other hand, a negative c-axis orientation means that it points downward to the reference surface. Therefore, when a positive voltage is applied to a film with a positive c-axis, it compresses (CP type, "positive compression"). If a negative voltage is applied to a film with a negative c-axis, it also compresses (CN type, "negative compression"). For example, according to various embodiments of the present invention, layer 504 is configured for positive compression and layer 503 is configured for negative compression. Since piezoelectric materials are anisotropic and have different properties at different axes, when two piezoelectric material layers with different orientations are stacked as shown in FIG5, the configuration can produce a parallel connection that increases the impedance of the resonator. For example, layers 503 and 504 are each configured to be approximately 1800 angstroms thick. In various embodiments, resonator 500 is configured to operate in a fourth thickness extended (TE4) mode. Figure 5B is a graph illustrating the operation of resonator 500. Depending on the implementation, resonator 500 can operate in TE2 mode at about 7 GHz or in TE4 mode at about 12 GHz. When operating in TE4 mode at 12 GHz, resonator 500 is characterized by a large bandwidth of about 1.4 GHz (compared to about 67 MHz in TE2 mode). In addition, resonator 500 is characterized by a low sheet resistance of about 0.196 ohms squared in both TE2 and TE4 modes. Figure 66 is a simplified diagram illustrating a resonator 600 including two piezoelectric layers separated by electrodes in accordance with an embodiment of the present technology. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art will recognize many variations, alternatives, and modifications. Resonator 600 includes a top double layer electrode including layer 601 and layer 602. Resonator 600 also includes a bottom double layer electrode including layer 606 and layer 607. Piezoelectric layers 603 and 605 are disposed between the top double layer electrode and the bottom double layer electrode. Electrode layer 604 is disposed between piezoelectric layers 603 and 605. As an example, layer 601 includes an aluminum material, and layer 602 includes a tungsten material. Similarly, layer 607 includes an aluminum material, and layer 606 includes a tungsten material. In accordance with an embodiment of the present technology, electrode layer 604 disposed between two piezoelectric layers (characterized by different orientations) may include a tungsten material. As explained above, the aluminum and tungsten electrode layers are configured to be different thicknesses based on their acoustic and electrical properties. As Figure 6 , the aluminum electrode layer is thicker than the tungsten electrode layer for the reasons provided above. It should be understood that other electrode layers may also be used, which are configured to have thicknesses based on their electrical and acoustic properties. In various embodiments, piezoelectric layers 603 and 605 include the same piezoelectric material (e.g., ASN material). Depending on the embodiment, piezoelectric layers 603 and 605 can be configured in the same orientation or in different orientations. In an embodiment, layer 603 is configured to have a c-axis direction opposite to the c-axis direction of layer 605. In various embodiments, as explained above, piezoelectric layers 603 and 605 include ASN materials configured in different crystal orientations. For example, for a particular application, using electrode layer 604 disposed between piezoelectric layers 603 and 605, a high-order thickness extension (TE) may be achieved as required for the desired frequency and bandwidth. n For example, as shown, the electrode layer 604 is thinner than the piezoelectric layers 603 and 605, but it should be understood that the electrode layer 604 can be thicker depending on the materials used and the implementation.

[0001] Figure 7700 is a simplified diagram illustrating a resonator 700 including two piezoelectric layers separated by a layer of electrode material according to an embodiment of the present technology. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art will recognize many variations, alternatives, and modifications. Resonator 700 includes a top double-layer electrode including layer 701 and layer 702. Resonator 700 also includes a bottom double-layer electrode including layer 708 and layer 709. Piezoelectric layers 703 and 707 are disposed between the top double-layer electrode and the bottom double-layer electrode. Piezoelectric layers 703 and 707 are separated by three electrode layers 704, 705, and 706. For example, layers 702, 704, 706, and 708 interfacing with piezoelectric layers 703 and 707 include tungsten materials. As an example, in the top electrode, layer 701 includes an aluminum material, and layer 702 includes a tungsten material. Similarly, in the bottom electrode, layer 709 includes an aluminum material, and layer 708 includes a tungsten material. According to an embodiment of the present technology, the electrode layers 704, 705, and 706 disposed between the two piezoelectric layers include a tungsten material (layer 704), an aluminum material (layer 705), and a tungsten material (layer 706), respectively. As explained above, the aluminum and tungsten electrode layers are configured to have different thicknesses based on their acoustic and electrical properties. For the reasons provided above, the aluminum electrode layer is thicker than the tungsten electrode layer. It should be understood that other electrode layers may also be used, which are configured to have thicknesses based on their electrical and acoustic properties.

[0002] In various embodiments, piezoelectric layers 703 and 707 include the same piezoelectric material (e.g., ASN material). Depending on the embodiment, piezoelectric layers 703 and 707 can be configured in the same orientation or in different orientations. In an embodiment, layer 703 is configured to have a c-axis direction opposite to the c-axis direction of layer 707. In various embodiments, as explained above, piezoelectric layers 703 and 707 include ASN materials configured in different crystal orientations. For example, for a particular application, using electrode layers 704, 705, and 706 disposed between piezoelectric layers 703 and 707, high-order thickness extension (TE) can be achieved as required for the desired frequency and bandwidth. n , n>1, for example, TE2, TE3, TE4, etc.) mode. While the above is a complete description of specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present technology, which is defined by the appended claims.

Claims

1. An acoustic resonator device, comprising: a first electrode characterized by a first thickness, the first electrode comprising a first metal; a second electrode characterized by a second thickness, the second electrode comprising a second metal; and a first piezoelectric layer disposed between the first electrode and the second electrode, the first piezoelectric layer being characterized by a third thickness; in: A total thickness including the first thickness, the second thickness, and the third thickness is associated with two or more stress half-waves; and The acoustic resonator device is characterized by an operating frequency of at least 5 GHz. 2 . The acoustic resonator device of claim 1 , wherein the first thickness is different from the second thickness.

3. The acoustic resonator device of claim 1, wherein the first thickness is greater than the second thickness, and the first thickness is associated with a first stress half-wave.

4. The acoustic resonator device of claim 1, wherein the total thickness is associated with three stress half-waves. 5 . The acoustic resonator device of claim 1 , wherein the acoustic resonator device operates in a second thickness extensional mode or a third thickness extensional mode.

6. The acoustic resonator device of claim 1, wherein: The first electrode further includes a third metal, and a distance between the first metal and the first piezoelectric layer is greater than a distance between the third metal and the first piezoelectric layer.

7. The acoustic resonator device of claim 6, wherein the first metal is characterized by a first acoustic impedance, the third metal is characterized by a second acoustic impedance, and the second acoustic impedance is greater than the first acoustic impedance.

8. The acoustic resonator device of claim 6, wherein the first metal is characterized by a greater thickness than the third metal.

9. The acoustic resonator device of claim 1 , further comprising a second piezoelectric layer disposed between the first electrode and the first piezoelectric layer, the first piezoelectric layer and the second piezoelectric layer being characterized by different orientations; Wherein the total thickness is associated with three or more stress half-waves.

10. An acoustic resonator device comprising: a first electrode characterized by a first thickness, the first electrode comprising a first metal; a second electrode characterized by a second thickness, the second electrode comprising a second metal; and a first piezoelectric layer disposed between the first electrode and the second electrode, the first piezoelectric layer being characterized by a third thickness; in: The total thickness includes the first thickness; The second thickness and the third thickness are associated with two or more stress half-waves; and The acoustic resonator device operates in a second or higher thickness extensional mode.

11. The acoustic resonator device of claim 10, wherein the second thickness extensional mode is characterized by an operating frequency of at least 6 GHz.

12. The acoustic resonator device of claim 10, wherein the second electrode further comprises a third metal. 13 . The acoustic resonator device of claim 10 , further comprising a third electrode and a second piezoelectric layer, the second piezoelectric layer being disposed between the third electrode and the first electrode.

14. An acoustic resonator device comprising: a first electrode characterized by a first thickness, the first electrode comprising a first metal; a second electrode characterized by a second thickness, the second electrode comprising a second metal; a third electrode characterized by a third thickness, the third electrode comprising a third metal; a first piezoelectric layer disposed between the first electrode and the second electrode, the first piezoelectric layer being characterized by a fourth thickness; and a second piezoelectric layer disposed between the second electrode and the third electrode, the second piezoelectric layer being characterized by a fifth thickness; wherein the acoustic resonator device operates in a third or higher thickness extensional mode.

15. The acoustic resonator device of claim 14, wherein the first metal is characterized by a first acoustic impedance and the second metal is characterized by a second acoustic impedance, and the second acoustic impedance is greater than the first acoustic impedance.

16. The acoustic resonator device of claim 14, wherein the first piezoelectric layer comprises an aluminum compound.

17. The acoustic resonator device of claim 14, wherein the first thickness is different from the second thickness.

18. The acoustic resonator device of claim 14, wherein the first thickness is greater than the second thickness, and the first thickness is associated with a first stress half-wave.

19. The acoustic resonator device of claim 14, wherein the first piezoelectric layer is characterized by a different orientation than the second piezoelectric layer.

20. The acoustic resonator device of claim 14, wherein the first thickness matches the third thickness.

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