Acoustic wave device for asymmetric band, method for manufacturing same, charging when compression, tworking or tworking, and similar compression, tworking

Abstract

The present disclosure relates to an acoustic wave device for asymmetric frequency bands and a manufacturing process for making an acoustic wave device. The disclosed acoustic wave device includes at least one first electrode (102: 152), at least one second electrode (104: 152), a first piezoelectric layer (114) having a recess (116), and a second piezoelectric layer (118) completely covering the recess. Herein, the at least one first electrode is formed over the first piezoelectric layer, and the at least one second electrode is formed over the second piezoelectric layer and confined within the recess. The second piezoelectric layer does not cover a portion of the first piezoelectric layer that is vertically below the at least one first electrode. The first piezoelectric layer and the second piezoelectric layer are formed of different piezoelectric materials.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of provisional patent application serial number 63 / 401,433 filed on August 26, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to an acoustic wave device for asymmetric frequency bands and a manufacturing process for making the acoustic wave device. Background Art

[0004] Acoustic wave devices are widely used in modern electronics. For the most part, an acoustic wave device includes a piezoelectric layer in contact with one or more electrodes. Materials suitable for the piezoelectric layer acquire an electrical charge when compressed, twisted, or distorted, and similarly, compress, twist, or distort when an electrical charge is applied to the material. Therefore, when an alternating electrical signal is applied to the one or more electrodes in contact with the piezoelectric layer, a corresponding mechanical signal (i.e., oscillation or vibration) is transduced therein. Based on the characteristics of the one or more electrodes on the piezoelectric layer, the properties of the materials used in the piezoelectric layer, and other factors such as the shape of the acoustic wave device and other structures disposed on the device, the mechanical signal transduced in the piezoelectric layer exhibits a frequency dependence on the alternating electrical signal. Acoustic wave devices exploit this frequency dependence to provide one or more functions.

[0005] Exemplary acoustic wave devices include surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators, which are increasingly used to form filters for transmission and reception of radio frequency (RF) signals for communications. Due to the stringent requirements placed on filters for modern RF communication systems, it is desirable that acoustic wave devices for these applications provide high quality factors and wide bandwidths (i.e., high electromechanical coupling coefficients) and be small in size.

[0006] In conventional acoustic wave device designs, each device die includes only one piezoelectric layer formed of a single piezoelectric material. One piezoelectric material can only have a relatively high electromechanical coupling coefficient and a relatively low quality factor, or a relatively high quality factor and a relatively low electromechanical coupling coefficient. Conventional device dies compromise between the electromechanical coupling coefficient and the quality factor. Therefore, filters formed from these conventional device dies will produce either a relatively wide bandwidth (i.e., a relatively high electromechanical coupling coefficient) with a reduced skirt steepness (i.e., a relatively low quality factor) or a relatively steep skirt (i.e., a high quality factor) with a reduced bandwidth (i.e., a relatively low electromechanical coupling coefficient).

[0007] However, in many applications, the frequency band of one filter is asymmetric. For example, the B3 transmit band (1710-1785 MHz) requires a high steepness on the upper band edge due to the close receive path to its right, while the lower band edge can be extended without a strict rejection specification. In another example, the B41F band (2496-2690 MHz) requires a high steepness on the lower band edge due to the WiFi channel, while the upper band edge has no strict rejection specification.

[0008] In view of the above, there is an ongoing need to improve acoustic wave device designs to achieve the desired characteristics of both quality factor and electromechanical coupling coefficient for asymmetric frequency band applications. Additionally, there is a need to keep the final product size competitive. Summary of the invention

[0009] The present disclosure relates to an acoustic wave device for an asymmetric frequency band and a manufacturing process for making an acoustic wave device. The disclosed acoustic wave device includes at least one first electrode, at least one second electrode, a first piezoelectric layer having a first recess, and a second piezoelectric layer completely covering the first recess. In this article, at least one first electrode is formed above the first piezoelectric layer, and at least one second electrode is formed above the second piezoelectric layer and confined within the first recess. The second piezoelectric layer does not cover the portion of the first piezoelectric layer vertically below the at least one first electrode. The first piezoelectric layer and the second piezoelectric layer are formed of different piezoelectric materials.

[0010] In one embodiment of the acoustic wave device, the first recess has a tapered sidewall such that a width of the first recess decreases from an upper portion to a lower portion of the first recess, wherein an angle formed between the tapered sidewall and a horizontal plane is between 20 and 55 degrees.

[0011] In one embodiment of the acoustic wave device, the first recess does not extend completely through the first piezoelectric layer. The first piezoelectric layer comprises a first piezoelectric section directly below the first recess such that the second piezoelectric layer is formed over the first piezoelectric section. The first piezoelectric section has a thickness between 0 μm and 0.2 μm.

[0012] In one embodiment of the acoustic wave device, the first piezoelectric layer and the second piezoelectric layer have different quality factors and different electromechanical coupling coefficients.

[0013] In one embodiment of the acoustic wave device, each of the first piezoelectric layer and the second piezoelectric layer is formed of one of aluminum nitride (AlN), indium-doped aluminum nitride (ScAlN), magnesium hydrofluoride aluminum nitride (MgHfAlN), aluminum magnesium zirconium nitride (MgZrAlN) and aluminum magnesium titanium nitride (MgTiAlN).

[0014] In one embodiment of the acoustic wave device, the first piezoelectric layer is formed of AlN, and the second piezoelectric layer is formed of one of ScAlN, MgHfAlN, MgZrAlN, and MgTiAlN.

[0015] According to one embodiment, the acoustic wave device further includes a bottom electrode structure having a first bottom electrode and a second bottom electrode. In this article, at least one first electrode includes a first top electrode, and at least one second electrode includes a second top electrode. The second piezoelectric layer extends above the top surface of the first piezoelectric layer. The bottom electrode structure is formed below the first piezoelectric layer. The first bottom electrode is vertically below the first top electrode, and the second bottom electrode is vertically below the second top electrode. The first resonator is at least composed of the first bottom electrode, the first top electrode, and the portion of the first piezoelectric layer vertically located between the first bottom electrode and the first top electrode. The second resonator is at least composed of the second bottom electrode, the second top electrode, and the second piezoelectric layer.

[0016] According to one embodiment, the acoustic wave device further includes a reflective structure having a first reflector and a second reflector. In this article, each of the first reflector and the second reflector has alternating high acoustic impedance sections and low acoustic impedance sections. The first reflector is vertically below the first bottom electrode, and the first resonator further includes the first reflector. The second reflector is vertically below the second bottom electrode, and the second resonator further includes the second reflector.

[0017] In one embodiment of the acoustic wave device, the first piezoelectric layer is formed of lithium tantalate (LT), lithium niobate, or quartz, and the second piezoelectric layer is formed of one of AlN, ScAlN, MgHfAlN, MgZrAlN, and MgTiAlN.

[0018] In one embodiment of the acoustic wave device, at least one first electrode includes two or more first interdigital transducer (IDT) electrodes, and at least one second electrode includes two or more second IDT electrodes. In this article, the first IDT electrode is formed above the first piezoelectric layer, and the second IDT electrode is formed above the second piezoelectric layer and confined within the second piezoelectric layer. The first resonator is composed of at least the first IDT electrode and the portion of the first piezoelectric layer vertically below the first IDT electrode, and the second resonator is composed of at least the second IDT electrode and the second piezoelectric layer below the second IDT electrode. The top surface of the first piezoelectric layer and the top surface of the second piezoelectric layer are coplanar.

[0019] In one embodiment of the acoustic wave device, at least one first electrode includes a plurality of first top electrodes, at least one second electrode includes a plurality of second top electrodes, and the first piezoelectric layer further includes a second recess. In this article, the second piezoelectric layer continuously covers both the first recess and the second recess without covering any portion of the first piezoelectric layer vertically below each of the plurality of first top electrodes. The plurality of first top electrodes are formed above the first piezoelectric layer, and the plurality of second top electrodes are formed above the second piezoelectric layer. Two of the plurality of second top electrodes are confined within the first recess and the second recess, respectively.

[0020] According to one embodiment, a method for manufacturing an acoustic wave device starts with providing an acoustic wave device precursor with a complete first piezoelectric layer. A first piezoelectric layer having a recess is then formed by removing a portion of the complete first piezoelectric layer, the recess extending from the top surface of the complete first piezoelectric layer toward the bottom surface of the complete first piezoelectric layer. Next, a common second piezoelectric layer covering the entire first piezoelectric layer is deposited so that the common second piezoelectric layer contacts the entire top surface of the first piezoelectric layer and the exposed surface within the recess. After depositing the common second piezoelectric layer, the common second piezoelectric layer is patterned to provide a second piezoelectric layer. In this article, the second piezoelectric layer completely covers the recess without covering the entire first piezoelectric layer. The second piezoelectric layer is formed of a piezoelectric material different from the first piezoelectric layer. Then, at least one first electrode is formed above the first piezoelectric layer, and at least one second electrode is formed above the second piezoelectric layer and confined within the recess. At least one first electrode does not overlap with the second piezoelectric layer.

[0021] In one embodiment of the method for manufacturing an acoustic wave device, forming the recess includes forming a starting recess from a top surface of the complete first piezoelectric layer toward a bottom surface of the complete first piezoelectric layer without extending completely through the complete first piezoelectric layer. In this context, a piezoelectric segment of the complete first piezoelectric layer remains directly below the starting recess. Next, the remaining piezoelectric segment is thinned to provide the recess with a thinned piezoelectric segment directly below the recess.

[0022] In one embodiment of the method for manufacturing an acoustic wave device, the starting recess is formed by one of a piezoelectric milling process, a dry etching process, and a wet etching process. The remaining piezoelectric segment is thinned by a trimming process. The top surface of the thinned piezoelectric segment has a roughness of less than 1 nm, and the thinned piezoelectric segment has a thickness between 0 μm and 0.2 μm.

[0023] In one embodiment of the method for manufacturing an acoustic wave device, the recess has a tapered sidewall such that a width of the recess decreases from an upper portion to a lower portion of the recess. An angle formed between the tapered sidewall and a horizontal plane is between 20 and 55 degrees.

[0024] In one embodiment of the method for manufacturing an acoustic wave device, the common second piezoelectric layer is patterned by one of a piezoelectric milling process, a dry etching process, and a wet etching process.

[0025] In one embodiment of the method for manufacturing an acoustic wave device, the first piezoelectric layer and the second piezoelectric layer have different quality factors and different electromechanical coupling coefficients.

[0026] In one embodiment of the method for manufacturing an acoustic wave device, each of the first piezoelectric layer and the second piezoelectric layer is formed of one of AlN, ScAlN, MgHfAlN, MgZrAlN, and MgTiAlN.

[0027] In one embodiment of the method for manufacturing an acoustic wave device, the first piezoelectric layer is formed of AlN, and the second piezoelectric layer is formed of one of the group consisting of ScAlN, MgHfAlN, MgZrAlN, and MgTiAlN.

[0028] On the other hand, any of the aforementioned aspects, and / or various individual aspects and features as described herein, may be combined individually or together to obtain additional advantages. Unless otherwise indicated herein, any of the various features and elements disclosed herein may be combined with one or more other disclosed features and elements.

[0029] Those skilled in the art will appreciate the scope of the present disclosure and become aware of additional aspects thereof after reading the following detailed description of the preferred embodiments and the associated drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0031] Figure 1 An exemplary acoustic wave device according to some embodiments of the present disclosure is shown.

[0032] Figure 2A-2B An alternative acoustic wave device according to some embodiments of the present disclosure is shown.

[0033] Figure 3 Insertion loss comparisons between alternative acoustic wave devices and conventional acoustic wave devices are shown.

[0034] Figure 4 Another alternative acoustic wave device according to some embodiments of the present disclosure is shown.

[0035] Figure 5A-11 Shown is a method for implementing Figure 1 An exemplary fabrication process for an acoustic wave device is shown.

[0036] It should be understood that for the sake of clarity of illustration, Figure 1-11 May not be drawn to scale. DETAILED DESCRIPTION

[0037] The embodiments set forth below represent information necessary to enable those skilled in the art to practice the embodiments and to illustrate the best mode for practicing the embodiments. After reading the following description with reference to the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and will appreciate the applications of these concepts not specifically set forth herein. It should be understood that these concepts and applications are within the scope of the present disclosure and the appended claims.

[0038] It will be appreciated that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish different elements. For example, without departing from the scope of the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes any and all combinations of one or more items in the associated listed items.

[0039] It should be understood that when an element such as a layer, a region or a substrate is referred to as being "on another element" or "extending onto another element", it may be directly on another element or directly extending onto another element, or there may also be an intermediate element. On the contrary, when an element is referred to as being "directly on another element" or "extending directly onto another element", there is no intermediate element. Similarly, it should be understood that when an element such as a layer, a region or a substrate is referred to as being "above another element" or "extending above another element", it may be directly above another element or directly extending above another element, or there may also be an intermediate element. On the contrary, when an element is referred to as being "directly above another element" or "extending directly above another element", there is no intermediate element. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to another element, or there may be an intermediate element. On the contrary, when an element is referred to as being "directly connected" or "directly coupled" to another element, there is no intermediate element.

[0040] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe one element, layer or region's relationship to another element, layer or region as illustrated in the figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0041] The terms used herein are only used for the purpose of describing specific embodiments and are not intended to limit the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an", and "said" are also intended to include the plural forms. It should also be understood that when used herein, the terms "comprises", "comprising", "includes", and / or "including" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0042] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. It will be further understood that, unless expressly defined herein, the terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art, and will not be interpreted in an idealized or overly formal sense.

[0043] Embodiments are described herein with reference to schematic illustrations of embodiments of the present disclosure. In this way, the actual sizes of layers and elements may be different, and it is expected that they will be different from the illustrated shapes due to, for example, manufacturing techniques and / or tolerances. For example, a zone shown or described as a square or rectangle may have a circular or curved feature, and a zone shown as a straight line may have some irregularities. Therefore, the zone shown in the figure is schematic, and its shape is not intended to illustrate the precise shape of the zone of the device, and is not intended to limit the scope of the present disclosure. In addition, for illustrative purposes, the size of a structure or zone may be enlarged relative to other structures or zones, and therefore a structure or zone is provided to illustrate the general structure of this theme, and may be drawn to scale or may not be drawn to scale. Common elements between the accompanying drawings may be shown in this article with common element numbers, and may not be repeatedly described subsequently.

[0044] Figure 1 An exemplary acoustic wave device 100 according to some embodiments of the present disclosure is shown. For illustrative purposes, the acoustic wave device 100 includes a first resonator 102 and a second resonator 104, each of which is a bulk acoustic wave (BAW) solid-state mounted resonator (SMR). In different applications, the acoustic wave device 100 may include more resonators, and each resonator may be another type of resonator, such as a film bulk acoustic wave resonator (FBAR), a common surface acoustic wave (SAW) resonator, a temperature compensated (TC) SAW resonator, a guided SAW resonator, a hybrid of a SAW / BAW resonator (e.g., an XBAW resonator), etc. It should be noted that the first resonator 102 and the second resonator 104 have different piezoelectric materials.

[0045] In detail, the acoustic wave device 100 includes a reflective structure 110, a bottom electrode structure 112 above the reflective structure 110, a first piezoelectric layer 114 having a recess 116 above the bottom electrode structure 112, a second piezoelectric layer 118 completely covering the recess 116 and extending above the top surface of the first piezoelectric layer 114, and a first top electrode structure 112.

[0046] electrode 120 and a second top electrode 122. The first piezoelectric layer 114 and the second piezoelectric layer 118 are formed of different piezoelectric materials.

[0047] In one embodiment, the reflective structure 110 includes a low acoustic impedance region 124, a plurality of high acoustic impedance sections 126 embedded in the low acoustic impedance region 124, and a dielectric layer 128. For the purpose of this description, there are four high acoustic impedance sections 126: a first upper high acoustic impedance section 126-1U, a first lower high acoustic impedance section 126-1L, a second upper high acoustic impedance section 126-2U, and a second lower high acoustic impedance section 126-2L. In different applications, there may be fewer or more high acoustic impedance sections 126 embedded in the low acoustic impedance region 124.

[0048] Herein, the first lower high acoustic impedance section 126-1L and the second lower high acoustic impedance section 126-2L are located above the bottom portion 124-B of the low acoustic impedance zone 124. The first upper high acoustic impedance section 126-1U is vertically above the first lower high acoustic impedance section 126-1L and is separated from the first lower high acoustic impedance section 126-1L by the middle portion 124-M of the low acoustic impedance zone 124. Similarly, the second upper high acoustic impedance section 126-2U is vertically above the second lower high acoustic impedance section 126-2L and is also separated from the second lower high acoustic impedance section 126-2L by the middle portion 124-M of the low acoustic impedance zone 124. In one embodiment, the top surface of the first upper high acoustic impedance section 126-1U, the top surface of the second upper high acoustic impedance section 126-2U, and the top surface of the low acoustic impedance zone 124 are coplanar.

[0049] The dielectric layer 128 is formed over the low acoustic impedance region 124 and the high acoustic impedance segment 126 embedded in the low acoustic impedance region 124. In one embodiment, the dielectric layer 128 contacts the top surface of the first upper high acoustic impedance segment 126-1U, the top surface of the second upper high acoustic impedance segment 126-2U, and the top surface of the low acoustic impedance region 124.

[0050] The first upper high acoustic impedance section 126-1U, the first lower high acoustic impedance section 126-1L, the section of the bottom portion 124-B of the low acoustic impedance zone 124 directly below the first lower high acoustic impedance section 126-1L, the section of the middle portion 124-M of the low acoustic impedance zone 124 vertically located between the first upper high acoustic impedance section 126-1U and the first lower high acoustic impedance section 126-1L, and the section of the dielectric layer 128 directly above the first upper high acoustic impedance section 126-1U constitute a first reflector 130-1. The second upper high acoustic impedance section 126-2U, the second lower high acoustic impedance section 126-2L, another section of the bottom portion 124-B of the low acoustic impedance zone 124 directly below the second lower high acoustic impedance section 126-2L, another section of the middle portion 124-M of the low acoustic impedance zone 124 vertically located between the second upper high acoustic impedance section 126-2U and the second lower high acoustic impedance section 126-2L, and another section of the dielectric layer 128 directly above the second upper high acoustic impedance section 126-2U constitute the second reflector 130-2. The low acoustic impedance zone 124 has a lower acoustic impedance, a lower density, and a lower hardness than the high acoustic impedance section 126, and can be formed of silicon oxide (SiO2) or aluminum (Al). Each high acoustic impedance section 126 is formed of a high acoustic impedance material such as tungsten (W), molybdenum (Mo), or platinum (Pt). The dielectric layer 128 may be formed of SiO 2 . In some applications, such as FBAR applications, the reflective structure 110 is omitted in the acoustic wave device 100 .

[0051] The bottom electrode structure 112 is formed above the dielectric layer 128 of the reflective structure 110 and includes a first bottom electrode 136, a second bottom electrode 138, and a planarization oxide 140. The first bottom electrode 136 is vertically above the first reflector 130-1, and the second bottom electrode 138 is vertically above the second reflector 130-2. The planarization oxide 140 surrounds the first bottom electrode 136 and the second bottom electrode 138, and can electrically separate the first bottom electrode 136 and the second bottom electrode 138. Each bottom electrode 136 / 138 may include two bottom electrode layers 142 and 144. The second bottom electrode layer 144 is above the dielectric layer 128 and may be formed of aluminum copper (AlCu), while the first bottom electrode layer 142 is above the second bottom electrode layer 144 and may be formed of W, Mo, or Pt.

[0052] A first piezoelectric layer 114 having a recess 116 is formed above the bottom electrode structure 112. The recess 116 has a tapered sidewall such that the width of the recess 116 decreases from an upper portion to a lower portion of the recess 116. An angle α formed between the tapered sidewall and a horizontal plane (e.g., parallel to the bottom surface of the first piezoelectric layer 114) is between 20 degrees and 55 degrees. In one embodiment, the recess 116 extends from the top surface of the first piezoelectric layer 114 toward the bottom surface of the first piezoelectric layer 114 without extending completely through the first piezoelectric layer 114. A thin piezoelectric section 114-F of the first piezoelectric layer 114 is directly below the recess 116. In one embodiment, the recess 116 may extend completely through the first piezoelectric layer 114 from the top surface of the first piezoelectric layer 114 to the bottom surface of the first piezoelectric layer 114 (not shown). The recess 116 is vertically above the second bottom electrode 138.

[0053] The second piezoelectric layer 118 completely covers the recess 116 (i.e., covers the bottom surface and sidewalls of the recess 116) and extends over the top surface of the first piezoelectric layer 114, so that the second piezoelectric layer 118 is also vertically above the second bottom electrode 138. The second piezoelectric layer 118 does not cover the portion of the first piezoelectric layer 114 that is vertically above the first bottom electrode 136. The first piezoelectric layer 114 and the second piezoelectric layer 118 are formed of two different piezoelectric materials, each of which is one of the following: aluminum nitride (AlN), scandium-doped aluminum nitride (ScAlN), magnesium hydrofluoride aluminum nitride (MgHfAlN), magnesium zirconium aluminum nitride (MgZrAlN), and magnesium titanium aluminum nitride (MgTiAlN). In a non-limiting example, the first piezoelectric layer 114 can be formed of AlN, which has a relatively high quality factor, and the second piezoelectric layer 118 can be formed of ScAlN, whose electromechanical coupling coefficient (k2e) depends on the percentage of Sc (i.e., the higher the percentage of Sc, the higher the electromechanical coupling coefficient of ScAlN). Instead of ScAlN, the second piezoelectric layer 118 can be formed of MgHfAlN, MgZrAlN, or MgTiAlN. The first piezoelectric layer 114 has a thickness between 0.3 μm and 1.4 μm, and the second piezoelectric layer 118 has a thickness between 0.2 μm and 1 μm. When the recess 116 does not extend completely through the first piezoelectric layer 114, the thin piezoelectric segment 114-F has a thin thickness between 0 μm and 0.2 μm or between 20 nm and 40 nm. The thin piezoelectric segment 114-F is vertically between the second piezoelectric layer 118 and the second bottom electrode 138. When the recess 116 extends completely through the first piezoelectric layer 114 , the thin piezoelectric segment 114 -F is omitted, and the second piezoelectric layer 118 is in contact with the second bottom electrode 138 (not shown).

[0054] The first top electrode 120 is formed above the first piezoelectric layer 114 and vertically above the first bottom electrode 136. The second top electrode 122 is formed above the second piezoelectric layer 118, confined within the recess 116, and vertically above the second bottom electrode 138. Each top electrode 120 / 122 may include a spacer ring 146 formed around the periphery of the top electrode 120 / 122, a first top electrode layer 148 formed above the first piezoelectric layer 114 / second piezoelectric layer 118 and extending above the spacer ring 146, an electrode seed layer 150 formed above the first top electrode layer 148, and a second top electrode layer 152 formed above the electrode seed layer 150. Generally, the top electrode 120 / 122 may be divided into a central region 153 and a boundary (BO) region 154, the BO region surrounding the central region 153 and at the periphery of the top electrode 120 / 122. In one embodiment, the BO region 154 may have a double-step configuration with an inner step S1 and an outer step S2. U.S. Patent Application Publication No. 20200228089 describes apparatus and methods for forming components such as top electrodes 120 / 122 having a dual-step configuration.

[0055] In this article, the spacer ring 146 can be formed of a dielectric material, such as silicon dioxide, silicon nitride, aluminum nitride or a combination thereof. The first top electrode layer 148 can be formed of W, Mo, Pt or other conductive materials with high acoustic impedance properties. The electrode seed layer 150 can be formed of titanium tungsten (TiW) or titanium (Ti). The second top electrode layer 152 can be formed of AlCu or other highly conductive materials.

[0056] Herein, the first resonator 102 (e.g., BAW SMR) is composed of a first reflector 130-1, a first bottom electrode 136, a first top electrode 120, and a portion of the first piezoelectric layer 114 vertically located between the first bottom electrode 136 and the first top electrode 120. The second resonator 104 (e.g., BAW SMR) is composed of a second reflector 130-2, a second bottom electrode 138, a second top electrode 122, and a second piezoelectric layer 118. When the recess 116 does not extend completely through the first piezoelectric layer 114, the second resonator 104 further includes a thin piezoelectric section 114-F. Since the thickness of the thin piezoelectric section 114-F (compared to the thickness of the second piezoelectric layer 118) is relatively thin, the second resonator 104 is substantially based on the quality factor and electromechanical coupling coefficient of the second piezoelectric layer 118. In different applications, such as FBAR applications, the first resonator 102 does not include the first reflector 130-1, and is composed of the first bottom electrode 136, the first top electrode 120, and a portion of the first piezoelectric layer 114 vertically located between the first bottom electrode 136 and the first top electrode 120. The second resonator 104 does not include the second reflector 130-2, and is composed of the second bottom electrode 138, the second top electrode 122, and the second piezoelectric layer 118.

[0057] It should be noted that the acoustic wave device 100 having the first resonator 102 and the second resonator 104 is formed on one acoustic wave wafer through the same manufacturing process (details are described below). Compared with a conventional acoustic wave device (formed on one acoustic wave wafer) including only one piezoelectric material, the acoustic wave device 100 includes at least two piezoelectric materials and can achieve desired frequency band characteristics, such as a desired bandwidth at one band edge and a desired skirt steepness at another band edge.

[0058] In addition, the acoustic wave device 100 may further include a passivation layer 160 to protect the acoustic wave device 100 from the external environment. The passivation layer 160 covers the first top electrode 120, the second top electrode 122, the portion of the first piezoelectric layer 114 exposed by the first top electrode 120 and the second piezoelectric layer 118, and the portion of the second piezoelectric layer 118 exposed by the second top electrode 122. The passivation layer 160 may be formed of silicon nitride (SiN), SiO2, or silicon oxynitride (SiON) with a thickness of about 1000 Å. and between.

[0059] exist Figure 1 In FIG. 1 , the acoustic wave device 100 is shown as including two resonators having two different piezoelectric materials. In different applications, one acoustic wave device may include more resonators having different piezoelectric materials. Figure 2A-2B An alternative acoustic wave device 200 is shown that includes a plurality of resonators according to some embodiments of the present disclosure. Figure 2A A top view of an alternative acoustic wave device 200 is shown, and Figure 2B A cross-sectional view of an alternative acoustic wave device 200 along dashed line CC' is shown. For purposes of this description, the alternative acoustic wave device 200 includes five A-type resonators 202, seven B-type resonators 204, and seven device through-holes 206. Each A-type resonator 202 has a Figure 1 The first resonator 102 shown in FIG. 1 is similar in configuration to that shown in FIG. 1 , and each B-type resonator 204 has a configuration similar to that of the first resonator 102 shown in FIG. Figure 1 In various applications, the alternative acoustic wave device 200 may include fewer or more A-type resonators 202 and fewer or more B-type resonators 204. In addition, each resonator 202 / 204 in the alternative acoustic wave device 200 may be a FBAR, a common SAW resonator, a TC SAW resonator, a guided SAW resonator, a hybrid of a SAW / BAW resonator (e.g., an XBAW resonator), etc.

[0060] like Figure 2B As shown in , an alternative acoustic wave device 200 includes a reflective structure 210, a bottom electrode structure 212 above the reflective structure 210, a first piezoelectric layer 214 having a plurality of recesses 216 above the bottom electrode structure 212, a second piezoelectric layer 218 completely covering each recess 216 and extending above the top surface of the first piezoelectric layer 214, and a plurality of top electrodes 220. The first piezoelectric layer 214 and the second piezoelectric layer 218 are formed of different piezoelectric materials.

[0061] The reflective structure 210 includes a plurality of reflectors 230, each of which belongs to a corresponding resonator 202 / 204. Each reflector 230 may have the same configuration as the first reflector 130-1 or the second reflector 130-2, such as Figure 1 In some applications, such as FBAR applications, the reflective structure 210 is omitted in the alternative acoustic wave device 200. Therefore, each resonator 202 / 204 does not include a reflector 230.

[0062] The bottom electrode structure 212 is located above the reflective structure 210 and includes a plurality of bottom electrodes 236, each of which belongs to a corresponding resonator 202 / 204. Each bottom electrode 236 has the same configuration as the first bottom electrode 136 or the second bottom electrode 138, such as Figure 1In one embodiment, the bottom electrode structure 212 further includes bottom electrode connectors 239 for connecting the bottom electrodes 236 of different resonators 202 / 204 (for example, the bottom electrode 236 of the first A-type resonator 202-1, the bottom electrode 236 of the second A-type resonator 202-2, and the bottom electrode 236 of the first B-type resonator 204-1 are connected together through some bottom electrode connectors 239, and the bottom electrode 236 of the third A-type resonator 202-3 and the bottom electrode 236 of the second B-type resonator 204-2 are connected together through one bottom electrode connector 239). Each bottom electrode 236 and each bottom electrode connector 239 are formed by the same electrode layer.

[0063] The first piezoelectric layer 214 formed above the bottom electrode structure 212 includes a plurality of recesses 216. Each recess 216 has a tapered sidewall such that the width of one recess 216 decreases from an upper portion to a lower portion of the recess 216. An angle α formed between the tapered sidewall and a horizontal plane (e.g., parallel to the bottom surface of the first piezoelectric layer 214) is between 20 degrees and 55 degrees. In one embodiment, each recess 216 extends from the top surface of the first piezoelectric layer 214 toward the bottom surface of the first piezoelectric layer 214 without extending completely through the first piezoelectric layer 214. A thin piezoelectric section 214-F of the first piezoelectric layer 214 is directly below the corresponding recess 216. In one embodiment, each recess 216 may extend completely through the first piezoelectric layer 214 from the top surface of the first piezoelectric layer 214 to the bottom surface of the first piezoelectric layer 214 (not shown). Each recess 216 is vertically above the corresponding reflector 230.

[0064] The second piezoelectric layer 218 completely covers each recess 216 (e.g., the bottom surface and sidewalls of each recess 216) and extends above the top surface of the first piezoelectric layer 214. In one embodiment, the second piezoelectric layer 218 may extend continuously across adjacent recesses 216 (e.g., the first B-type resonator 204-1 and the second B-type resonator 204-2 are adjacent to each other). Herein, each of the first B-type resonator 204-1 and the second B-type resonator 204-2 includes a portion of the second piezoelectric layer 218 vertically above the corresponding reflector 230. In one embodiment, the second piezoelectric layer 218 may include multiple separate portions to cover different recesses 216 (not shown, for example, some B-type resonators 204 are not adjacent to each other). Regardless of the continuity of the second piezoelectric layer 218, the second piezoelectric layer 218 does not cover the portion of the first piezoelectric layer 214 vertically above the reflector 230 of the first A-type resonator 202.

[0065] The first piezoelectric layer 214 and the second piezoelectric layer 218 are formed of different piezoelectric materials. In one embodiment, the first piezoelectric layer 214 can be formed of AlN, and the second piezoelectric layer 218 can be formed of ScAlN (the percentage of Sc can vary for different applications), MgHfAlN, MgZrAlN or MgTiAlN. The first piezoelectric layer 214 has a thickness between 0.3 μm and 1.4 μm, and the second piezoelectric layer 218 has a thickness between 0.2 μm and 1 μm. When each recess 216 does not extend completely through the first piezoelectric layer 214, each thin piezoelectric segment 214-F has a thickness between 0 μm and 0.2 μm, or between 20 nm and 40 nm, and is vertically between the second piezoelectric layer 218 and the corresponding bottom electrode 236. When each recess 116 extends completely through the first piezoelectric layer 214 , the thin piezoelectric segment 214 -F is omitted, and the second piezoelectric layer 218 is in contact with the corresponding bottom electrode 236 (not shown).

[0066] Each top electrode 220 belongs to a corresponding resonator 202 / 204 and has the same configuration as the first top electrode 120 or the second top electrode 122. In one embodiment, the alternative acoustic wave device 200 further includes a top electrode connector 241 for connecting the top electrodes 220 of different resonators 202 / 204 (for example, the top electrode 220 of the second A-type resonator 202-2, the top electrode 220 of the first B-type resonator 204-1, and the top electrode 220 of the second B-type resonator 204-2 are connected together through the top electrode connector 241). Each top electrode 220 and each top electrode connector 241 are formed of the same electrode layer.

[0067] In addition, the device through-holes 206 of the alternative acoustic wave device 200 are formed in the first piezoelectric layer 214. Each device through-hole 206 is electrically connected to an adjacent resonator having a bottom electrode lead 243 or a top electrode lead 245. Figure 2B , the bottom electrode 236 of the first A-type resonator 202-1 is connected to the first device via 206-1 through one bottom electrode lead 243, and the top electrode 220 of the third A-type resonator 202-3 is connected to the second device via 206-2 through one top electrode lead 245. Herein, the bottom electrode lead 243 is formed of the same electrode layer as the bottom electrode 236, and the top electrode lead 245 is formed of the same electrode layer as the top electrode 220.

[0068] In addition, the alternative acoustic wave device 200 may further include a passivation layer 260 formed over each top electrode 220, a portion of the first piezoelectric layer 214 (exposed by the top electrode 220, the top electrode connector 241, the top electrode lead 245, and the second piezoelectric layer 218), and a portion of the second piezoelectric layer 118 (exposed by the top electrode 220, the top electrode connector 241, and the top electrode lead 245), without covering each device through hole 206. The passivation layer 260 may be formed of SiN, SiO2, or SiON, with a thickness of about 1000 Å. and between.

[0069] It should be noted that the alternative acoustic wave device 200 including a plurality of A-type resonators 202 and B-type resonators 204 is formed on the same wafer and is capable of achieving a filtering function. The A-type resonators 202 and the B-type resonators 204 are manufactured within the same process. Compared to a conventional acoustic wave device (formed on the same wafer) including only one piezoelectric material, the alternative acoustic wave device 200 includes at least two piezoelectric materials and can achieve desired frequency band characteristics, such as a desired bandwidth at one band edge and a desired skirt steepness at another band edge.

[0070] Figure 3 The insertion loss (S) between the alternative acoustic wave device 200 and some conventional acoustic wave devices having a piezoelectric material is shown. 21 )Compare. Figure 3, three dashed curves represent three conventional acoustic wave devices, each of which includes one piezoelectric material (e.g., an AlN type acoustic wave device, an ScAlN type acoustic wave device with a relatively low Sc percentage, and an ScAlN type acoustic wave device with a relatively high Sc percentage), and one solid curve represents an alternative acoustic wave device 200 having two piezoelectric materials (e.g., AlN and ScAlN with relatively high Sc percentages). The first conventional acoustic wave device having the piezoelectric material AlN has the steepest band skirts with the narrowest bandwidth at both band edges, the second conventional acoustic wave device having the low Sc piezoelectric material ScAlN has the medium steep band skirts with the medium bandwidth at both band edges, and the third conventional acoustic wave device having the high Sc piezoelectric material ScAlN has the least steep band skirts with the widest bandwidth at both band edges. On the other hand, the alternative acoustic wave device 200 is able to achieve the steepest band skirt on the lower band edge (as the first conventional acoustic wave device using the piezoelectric material AlN), and achieve the widest bandwidth on the upper band edge (as the third conventional acoustic wave device using the high Sc piezoelectric material ScAlN). Therefore, one acoustic wave device (e.g., the alternative acoustic wave device 200) including two piezoelectric materials can meet the desired characteristics of both the quality factor (i.e., the band skirt steepness) and the electromechanical coupling coefficient (i.e., the bandwidth) for asymmetric band applications. In other words, one acoustic wave device including two piezoelectric materials can achieve the desired band skirt steepness on one band edge while achieving the desired bandwidth on the other band edge.

[0071] An acoustic wave device having two piezoelectric materials may include Figure 1 , 2A and two or more BAW resonators shown in 2B. In various applications, one acoustic wave device having two piezoelectric materials may include two or more SAW resonators. Figure 4 Another alternative acoustic wave device 300 having a SAW resonator is shown. For the purposes of this description, the alternative acoustic wave device 300 includes two SAW resonators 302 and 304, each of which is a guided SAW resonator. In different applications, the acoustic wave device 100 includes more SAW resonators, and each resonator can be a common SAW resonator or a TCSAW resonator.

[0072] In detail, the alternative acoustic wave device 300 includes a substrate 306, a reflective structure 310 above the substrate 306, a first piezoelectric layer 314 having a recess 316 above the reflective structure 310, a second piezoelectric layer 318 completely filling the recess 316, two or more first interdigital transducer (IDT) electrodes 320 having a plurality of first electrode fingers 320-F (e.g., one first IDT electrode 320-1 having two first electrode fingers as an input electrode, and another first IDT electrode 320-2 having three first electrode fingers as an output electrode), and two or more second IDT electrodes 322 having a plurality of second electrode fingers 322-F (e.g., one second IDT electrode 322-1 having two second electrode fingers as an input electrode, and another second IDT electrode 322-2 having three second electrode fingers as an output electrode). The first piezoelectric layer 314 and the second piezoelectric layer 318 are formed of different piezoelectric materials.

[0073] The substrate 306 may have a thickness between 50 μm and 750 μm, and may be formed of various materials including glass, sapphire, quartz, silicon (Si), or gallium arsenide (GaAs), among others, with Si being a common option. The reflective structure 310 includes a low acoustic impedance region 324, a plurality of high acoustic impedance segments 326, and a plurality of functional segments 327. The high acoustic impedance segments 326 and the functional segments 327 are embedded in the low acoustic impedance region 324. For the purpose of this description, there are two high acoustic impedance segments 326 (e.g., a first high acoustic impedance segment 326-1 and a second high acoustic impedance segment 326-2) and two functional segments 327 (e.g., a first functional segment 327-1 and a second functional segment 327-2). In different applications, there may be more high acoustic impedance segments 326 and / or more functional segments 327 embedded in the low acoustic impedance region 324. Herein, the first high acoustic impedance section 326-1 and the second high acoustic impedance section 326-2 are embedded at the bottom portion of the low acoustic impedance zone 324 and contact the substrate 306. The first functional section 327-1 is vertically above the first high acoustic impedance section 326-1 and is separated from the first high acoustic impedance section 326-1 by the middle portion 324-M of the low acoustic impedance zone 324. Similarly, the second functional section 327-2 is vertically above the second high acoustic impedance section 326-2 and is also separated from the second high acoustic impedance section 326-2 by the middle portion 324-M of the low acoustic impedance zone 324. In one embodiment, the top surface of the first functional section 327-1, the top surface of the second functional section 327-2, and the top surface of the low acoustic impedance zone 324 are coplanar.

[0074] The first high acoustic impedance section 326-1, the first functional section 327-1, and the section of the middle part 324-M of the low acoustic impedance zone 324 vertically located between the first high acoustic impedance section 326-1 and the first functional section 327-1 constitute the first reflector 330-1. The second high acoustic impedance section 326-2, the second functional section 327-2, and another section of the middle part 324-M of the low acoustic impedance zone 324 vertically located between the second high acoustic impedance section 326-2 and the second functional section 327-2 constitute the second reflector 330-2. The low acoustic impedance zone 324 has a lower acoustic impedance, a lower density, and a lower hardness than the high acoustic impedance section 326, and can be formed of SiO2 or Al. The high acoustic impedance section 326 is formed of a high acoustic impedance material, such as W, Mo, or Pt. In addition, the functional region 327 may be formed of one or more dielectric materials such as oxide and nitride or one or more metal materials such as Pt, W, and ruthenium (Ru).

[0075] A first piezoelectric layer 314 having a recess 316 is formed above the reflective structure 310. The recess 316 has a tapered sidewall so that the width of the recess 316 decreases from an upper portion to a lower portion of the recess 316. An angle α formed between the tapered sidewall and a horizontal plane (e.g., parallel to the bottom surface of the first piezoelectric layer 314) is between 20 degrees and 55 degrees. In one embodiment, the recess 316 extends from the top surface of the first piezoelectric layer 314 toward the bottom surface of the first piezoelectric layer 314 without extending completely through the first piezoelectric layer 314. A thin piezoelectric section 314-F of the first piezoelectric layer 314 is directly below the recess 316. In one embodiment, the recess 316 may extend completely through the first piezoelectric layer 314 from the top surface of the first piezoelectric layer 314 to the bottom surface of the first piezoelectric layer 314 (not shown). The recess 316 is vertically above the second reflector 330-2.

[0076] The second piezoelectric layer 318 completely fills the recess 316 so that the second piezoelectric layer 318 is also vertically above the second reflector 330-2. In one embodiment, the top surface of the second piezoelectric layer 318 and the top surface of the first piezoelectric layer 314 are coplanar. The first piezoelectric layer 314 and the second piezoelectric layer 318 are formed by two different piezoelectric materials, each of which is one of lithium tantalate (LT), lithium niobate, quartz, AlN, ScAlN, MgHfAlN, MgZrAlN and MgTiAlN. In a non-limiting example, the first piezoelectric layer 314 can be formed by LT, and the second piezoelectric layer 118 can be formed by AIN or ScAlN. In addition, the first piezoelectric layer 314 has a thickness between 0.3μm and 1.4μm, and the second piezoelectric layer 318 has a thickness between 0.2μm and 1μm. When the recess 316 does not extend completely through the first piezoelectric layer 314, the thin piezoelectric segment 314-F has a thickness between 0 μm and 0.2 μm or between 20 nm and 40 nm, and is vertically located between the second piezoelectric layer 318 and the second reflector 330-2. When the recess 316 extends completely through the first piezoelectric layer 314, the thin piezoelectric segment 314-F is omitted, and the second piezoelectric layer 318 contacts the second reflector 330-2 (not shown).

[0077] It should be noted that in some applications, such as common SAW resonator applications or TC SAW resonator applications, the reflective structure 310 is omitted in the alternative acoustic wave device 300. Therefore, the first piezoelectric layer 314 is in contact with the substrate 306. If the recess 316 extends completely through the first piezoelectric layer 314, the second piezoelectric layer 318 is also in contact with the substrate 306.

[0078] The first IDT electrode 320 is formed over the first piezoelectric layer 314, and the second IDT electrode 322 is formed over and confined within the second piezoelectric layer 318. Each IDT electrode 320 / 322 may be formed of aluminum or the like.

[0079] The first SAW resonator 302 is composed of a first reflector 330-1, a first IDT electrode 320, and a portion of the first piezoelectric layer 314 vertically below the first IDT electrode 320. The second SAW resonator 304 is composed of a second reflector 330-2, a second IDT electrode 322, and a second piezoelectric layer 318. When the recess 316 does not extend completely through the first piezoelectric layer 314, the second SAW resonator 304 further includes a thin piezoelectric section 314-F. Since the thickness of the thin piezoelectric section 314-F (compared to the thickness of the second piezoelectric layer 318) is relatively thin, the second resonator 304 is substantially based on the quality factor and electromechanical coupling coefficient of the second piezoelectric layer 318.

[0080] It should be noted that if the first SAW resonator 302 and the second SAW resonator 304 are common SAW resonators or TC SAW resonators, the first resonator 302 does not include the first reflector 330-1, and is composed of the first IDT electrode 320 and the portion of the first piezoelectric layer 314 vertically below the first IDT electrode 320. The second resonator 304 does not include the second reflector 330-2, and is composed of the second IDT electrode 322 and the second piezoelectric layer 118 vertically below the second IDT electrode 322. Regardless of whether the reflector 330 is present, the alternative acoustic wave device 300 having the first SAW resonator 302 and the second SAW resonator 304 is formed on one acoustic wave wafer by the same manufacturing process.

[0081] Figure 5A-11 Provides a way to implement Figure 1 . Although the exemplary steps are shown in sequence, the exemplary steps are not necessarily dependent on the order. Some steps can be completed in a different order than presented. In addition, the process within the scope of the present disclosure may include more than Figure 5A-11 Fewer or more steps as shown in .

[0082] Initially, the acoustic wave device precursor 400 is

[0083] Figure 5A and 5B As shown in . Figure 5A , the acoustic wave device precursor 400 includes a reflective structure 110, a bottom electrode structure 112 above the reflective structure 110, and a complete first piezoelectric layer 114IN above the bottom electrode structure 112. The complete first piezoelectric layer 114IN may be formed of AlN having a thickness between 0.3 μm and 1.4 μm. The complete first piezoelectric layer 114IN has a flat surface without any concave portion. For some applications, the acoustic wave device precursor 400 may further include a mask layer 402 formed above the complete first piezoelectric layer 114IN and a resist pattern 404 having an opening 406 formed above the mask layer 402, such as Figure 5B . Herein, the mask layer 402 may be formed of W, and the resist pattern 404 may be formed of a photoresist material. The opening 406 is vertically above the second bottom electrode 138 of the bottom electrode structure 112, and may have a width wider than the second bottom electrode 138. In some applications, such as FBAR applications, the reflective structure 110 is omitted in the acoustic wave device precursor 400.

[0084] Next, a starting recess 116S is formed, which extends from the top surface of the complete first piezoelectric layer 114IN toward the bottom surface of the complete first piezoelectric layer 114IN to provide an intermediate first piezoelectric layer 114IT, such as Fig. 6AAs shown in . The starting recess 116S has a tapered sidewall so that the width of the starting recess 116S decreases from the upper portion to the lower portion of the starting recess 116S. The angle α formed between the tapered sidewall and a horizontal plane (e.g., parallel to the bottom surface of the intermediate first piezoelectric layer 114IT) at the starting recess 116S point is between 20 degrees and 55 degrees. In this article, the starting recess 116S does not extend completely through the intermediate first piezoelectric layer 114IT. The piezoelectric segment 114-FS remains directly below the starting recess 116S. In one embodiment, the starting recess 116S can be formed by a piezoelectric milling process, which can be precisely controlled to form the tapered sidewall. In another embodiment, the starting recess 116S can be formed by a dry etching process. Due to the non-uniformity of the piezoelectric milling process or the non-uniformity of the dry etching process, the remaining piezoelectric segment 114-FS may require a thickness of at least 75nm (e.g., between 75nm and 0.25μm).

[0085] Alternatively, if the acoustic wave device precursor 400 includes a mask layer 402 and a resist pattern 404 having an opening 406, in addition to forming the starting recess 116S, a portion of the mask layer 402 is removed to provide a mask pattern 402P, such as Figure 6B . The mask pattern 402P has an opening that is the same size as the opening 406 of the resist pattern 404. The top portion (e.g., the widest portion) of the starting recess 116S also has the same size as the opening 406 of the resist pattern 404. Herein, the mask pattern 402P and the starting recess 116S can be formed by the same wet etching process. Due to the non-uniformity of the wet etching process, the remaining piezoelectric segment 114-FS needs to have a thickness of at least 75 nm (e.g., between 75 nm and 0.25 μm).

[0086] Figure 7 A planarization trimming step is shown to provide a recess 116 within the first piezoelectric layer 114. The remaining piezoelectric segment 114-FS is thinned to a thin piezoelectric segment 114-F, having a thickness between 0 μm and 0.2 μm or between 20 nm and 40 nm. The thin piezoelectric segment 114-F acts as a seed layer for the deposition of the piezoelectric layer. Therefore, the thin piezoelectric segment 114-F has high uniformity requirements, which directly affects the electromechanical coupling coefficient of the deposited piezoelectric material (details described below). In this article, the high uniformity requirements indicate that the top surface of the thin piezoelectric segment 114-F has a roughness of less than 1 nm. The recess 116 maintains the tapered sidewalls with the same angle α between 20 degrees and 55 degrees as the starting recess 116S. The remaining piezoelectric segment 114-FS is thinned to a thin piezoelectric segment 114-F by the trimming process. In addition, if the mask pattern 402P and the resist pattern 404 are above the middle first piezoelectric layer 114IT (eg Figure 6B), the mask pattern 402P and the resist pattern 404 (not shown) may be removed before or after the planarization trimming step.

[0087] After forming the recess 116 in the first piezoelectric layer 114, a common second piezoelectric layer 118C is deposited to cover the entire first piezoelectric layer 114. Figure 8 As shown in . The common second piezoelectric layer 118C is in contact with the entire top surface of the first piezoelectric layer 114 and the exposed surface within the recess 116. Since the angle α is relatively small, the deposition of the common second piezoelectric layer 118C will face a smaller risk of cracking. The thin piezoelectric section 114-F is a seed layer for depositing the common second piezoelectric layer 118C within the recess 116. The uniformity of the thin piezoelectric section 114-F will affect the electromechanical coupling coefficient of the common second piezoelectric layer 118C (in particular, the electromechanical coupling coefficient of the portion of the common second piezoelectric layer 118C vertically above the thin piezoelectric section 114-F). The common second piezoelectric layer 118C can be formed of ScAIN, MgHfAIN, MgZrAIN or MgTiAIN with a thickness between 0.2μm and 1μm.

[0088] like Fig. 9 , the common second piezoelectric layer 118C is then patterned to provide the second piezoelectric layer 118. The second piezoelectric layer 118 completely covers the recess 116 and extends over the top surface of the first piezoelectric layer 114, without covering the portion of the first piezoelectric layer 114 that is vertically above the first bottom electrode 136. Therefore, the second piezoelectric layer 118 is vertically above the second bottom electrode 138 within the bottom electrode structure 112. The common second piezoelectric layer 118C is patterned by a piezoelectric milling process or an etching process.

[0089] Next, a first top electrode 120 is formed over the first piezoelectric layer 114 and vertically over the first bottom electrode 136 to complete the first resonator 102, and a second top electrode 122 is formed over the second piezoelectric layer 118, confined within the recess 116, and vertically over the second bottom electrode 138 to complete the second resonator 104, as shown in FIG. Fig.10 Finally, a passivation layer 160 is formed to complete the acoustic wave device 100. The passivation layer 160 covers the first top electrode 120, the second top electrode 122, the portion of the first piezoelectric layer 114 exposed by the first top electrode 120 and the second piezoelectric layer 118, and the portion of the second piezoelectric layer 118 exposed by the second top electrode 122.

[0090] It is contemplated that any of the aforementioned aspects, and / or the various individual aspects and features described herein, may be combined to obtain additional advantages. Unless otherwise indicated herein, any of the various embodiments disclosed herein may be combined with one or more other disclosed embodiments.

[0091] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered to be within the scope of the concepts disclosed herein and the claims below.

Claims

1. An acoustic wave device comprising: at least one first electrode; at least one second electrode; A first piezoelectric layer having a first concave portion; as well as A second piezoelectric layer completely covering the first recess, wherein: The at least one first electrode is formed over the first piezoelectric layer, and the at least one second electrode is formed over the second piezoelectric layer and confined within the first recess; the second piezoelectric layer does not cover a portion of the first piezoelectric layer vertically below the at least one first electrode; and The first piezoelectric layer and the second piezoelectric layer are formed of different piezoelectric materials.

2. The acoustic wave device of claim 1, wherein the first recess has a tapered sidewall such that a width of the first recess decreases from an upper portion to a lower portion of the first recess, wherein an angle formed between the tapered sidewall and a horizontal plane is between 20 degrees and 55 degrees.

3. The acoustic wave device of claim 1, wherein: The first recess does not extend completely through the first piezoelectric layer; The first piezoelectric layer includes a first piezoelectric segment directly below the first recess, such that the second piezoelectric layer is formed above the first piezoelectric segment; and The first piezoelectric section has a thickness between 0 μm and 0.2 μm. 4 . The acoustic wave device according to claim 1 , wherein the first piezoelectric layer and the second piezoelectric layer have different quality factors and different electromechanical coupling coefficients.

5. The acoustic wave device according to claim 4, wherein each of the first piezoelectric layer and the second piezoelectric layer is formed of one of the group consisting of aluminum nitride (AlN), indium-doped aluminum nitride (ScAlN), magnesium hydrofluoride aluminum nitride (MgHfAlN), aluminum magnesium zirconium nitride (MgZrAlN) and aluminum magnesium titanium nitride (MgTiAlN).

6. The acoustic wave device of claim 5, wherein: The first piezoelectric layer is formed of AIN; and The second piezoelectric layer is formed of one of the group consisting of ScAlN, MgHfAlN, MgZrAlN and MgTiAlN.

7. The acoustic wave device of claim 5, further comprising a bottom electrode structure having a first bottom electrode and a second bottom electrode, wherein: The at least one first electrode comprises a first top electrode, and the at least one second electrode comprises a second top electrode; The second piezoelectric layer extends above a top surface of the first piezoelectric layer; The bottom electrode structure is formed below the first piezoelectric layer; The first bottom electrode is vertically below the first top electrode, and the second bottom electrode is vertically below the second top electrode; a first resonator constituted by at least the first bottom electrode, the first top electrode and a portion of the first piezoelectric layer vertically located between the first bottom electrode and the first top electrode; and The second resonator is constituted by at least the second bottom electrode, the second top electrode and the second piezoelectric layer.

8. The acoustic wave device of claim 7, further comprising a reflective structure having a first reflector and a second reflector, wherein: Each of the first reflector and the second reflector has alternating high acoustic impedance sections and low acoustic impedance sections; the first reflector is vertically below the first bottom electrode, and the first resonator further comprises the first reflector; and The second reflector is vertically below the second bottom electrode, and the second resonator further comprises the second reflector.

9. The acoustic wave device of claim 4, wherein: The first piezoelectric layer is formed of lithium tantalate (LT), lithium niobate or quartz; and The second piezoelectric layer is formed of one selected from the group consisting of AlN, ScAlN, MgHfAlN, MgZrAlN and MgTiAlN.

10. The acoustic wave device of claim 9, wherein: The at least one first electrode comprises two or more first interdigital transducer (IDT) electrodes, and the at least one second electrode comprises two or more second IDT electrodes; The first IDT electrode is formed above the first piezoelectric layer, and the second IDT electrode is formed above the second piezoelectric layer and confined within the second piezoelectric layer; A first resonator is constituted by at least the first IDT electrode and a portion of the first piezoelectric layer vertically below the first IDT electrode; and The second resonator is constituted by at least the second IDT electrode and the second piezoelectric layer below the second IDT electrode. 11 . The acoustic wave device of claim 10 , wherein a top surface of the first piezoelectric layer and a top surface of the second piezoelectric layer are coplanar.

12. The acoustic wave device of claim 1, wherein: The at least one first electrode comprises a plurality of first top electrodes, and the at least one second electrode comprises a plurality of second top electrodes; The first piezoelectric layer further comprises a second concave portion; the second piezoelectric layer continuously covers both the first recess and the second recess without covering any portion of the first piezoelectric layer vertically below each of the plurality of first top electrodes; and The plurality of first top electrodes are formed over the first piezoelectric layer, and the plurality of second top electrodes are formed over the second piezoelectric layer, wherein two of the plurality of second top electrodes are confined within the first recess and the second recess, respectively.

13. A method comprising: Providing an acoustic wave device precursor, the acoustic wave device precursor comprising a complete first piezoelectric layer; forming a first piezoelectric layer having a recess by removing a portion of the complete first piezoelectric layer, wherein the recess extends from a top surface of the complete first piezoelectric layer toward a bottom surface of the complete first piezoelectric layer; Depositing a common second piezoelectric layer to cover the entire first piezoelectric layer, such that the common second piezoelectric layer is in contact with the entire top surface of the first piezoelectric layer and the exposed surface within the recess; Patterning the common second piezoelectric layer to provide a second piezoelectric layer, wherein: The second piezoelectric layer completely covers the recess but does not cover the entire first piezoelectric layer; and The first piezoelectric layer and the second piezoelectric layer are formed of different piezoelectric materials; as well as • forming at least one first electrode over the first piezoelectric layer, and forming at least one second electrode over the second piezoelectric layer and confined within the recess, wherein the at least one first electrode does not overlap the second piezoelectric layer.

14. The method of claim 13, wherein forming the recess comprises: forming a starting recess from the top surface of the complete first piezoelectric layer toward the bottom surface of the complete first piezoelectric layer without extending completely through the complete first piezoelectric layer, wherein a piezoelectric segment of the complete first piezoelectric layer remains directly below the starting recess; as well as • Thinning the remaining piezoelectric section to provide the recess with a thinned piezoelectric section directly beneath the recess.

15. The method according to claim 14, wherein: The starting recess is formed by one of a piezoelectric milling process, a dry etching process and a wet etching process; The remaining piezoelectric segment is thinned by a trimming process; The top surface of the thinned piezoelectric segment has a roughness of less than 1 nm; and • The thinned piezoelectric segment has a thickness between 0 and 0.2 μm.

16. The method of claim 13, wherein the recess has a tapered sidewall such that a width of the recess decreases from an upper portion to a lower portion of the recess, wherein an angle formed between the tapered sidewall and a horizontal plane is between 20 and 55 degrees. 17 . The method of claim 13 , wherein the common second piezoelectric layer is patterned by one of a piezoelectric milling process, a dry etching process, and a wet etching process.

18. The method of claim 13, wherein the first piezoelectric layer and the second piezoelectric layer have different quality factors and different electromechanical coupling coefficients. 19 . The method of claim 18 , wherein each of the first piezoelectric layer and the second piezoelectric layer is formed of one of the group consisting of AlN, ScAlN, MgHfAlN, MgZrAlN, and MgTiAlN.

20. The method of claim 19, wherein: The first piezoelectric layer is formed of AIN; and The second piezoelectric layer is formed of one of the group consisting of ScAlN, MgHfAlN, MgZrAlN and MgTiAlN.

Images