Acoustic device comprising acoustic mirror coordinated optimized for longal and shear

Abstract

An acoustic device includes a piezoelectric layer between a first bottom electrode and a second top electrode, and an acoustic mirror optimized for reflecting longitudinal waves and shear waves at a target operating frequency. The acoustic mirror includes a lower acoustic impedance layer and at least one higher acoustic impedance layer. In one example, the layers of the acoustic mirror alternate between a lower impedance and a higher impedance, with a first lower acoustic impedance layer adjacent the bottom electrode and a first higher acoustic impedance layer having a greater thickness than a second higher acoustic impedance layer. In another example, the acoustic mirror has a higher acoustic impedance layer having a thickness corresponding to at least half of a wavelength of the target operating frequency in the higher acoustic impedance layer. An acoustic device having an acoustic mirror optimized for both longitudinal and shear waves reduces energy loss to improve efficiency.

Description

BACKGROUND

[0001] I. TECHNICAL FIELD

[0002] The technology of this disclosure relates generally to microacoustic devices, and more particularly to acoustic resonators for high frequency filters.

[0003] II. BACKGROUND

[0004] Wireless devices, such as cellular telephones, communicate by transmitting and receiving electromagnetic waves in the air. Cellular telephones, for example, are wireless devices that are only allowed to operate within limited ranges of radio frequencies, and these ranges vary according to the geographic region (e.g., country) of the world. Thus, cellular telephones throughout the world have filters for limiting the frequency signals that are transmitted and received. The frequency of the wireless signals is limited by radio frequency filters that are implemented by acoustic resonators, which are microacoustic devices that are small enough to fit into handheld devices. Acoustic resonators include surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, and Lamé mode resonators. Acoustic resonators include electrodes on piezoelectric materials to convert electromagnetic waves to acoustic waves, filter the acoustic waves, and convert the filtered waves back to electromagnetic waves. Some energy is lost in the acoustic waves within the piezoelectric materials, and additional energy loss is caused by acoustic waves escaping the piezoelectric devices. Battery-powered handheld wireless devices that employ acoustic devices have strict energy efficiency requirements. Thus, manufacturers of such acoustic devices are continually striving to improve energy efficiency. In this regard, it is desirable to minimize the acoustic losses in the acoustic devices used in radio frequency filters. SUMMARY

[0005] Disclosed aspects in the detailed description include an acoustic device that includes an acoustic mirror that is cooperatively optimized for longitudinal and shear wave reflection. Related methods of manufacturing acoustic devices with cooperatively optimized acoustic mirrors are also disclosed. Acoustic waves propagating through a piezoelectric material in an acoustic device include longitudinal and shear waves. Acoustic mirrors used to reflect acoustic waves can be designed to primarily reflect longitudinal waves and not shear waves, which have a different frequency than longitudinal waves, resulting in significant energy loss. In this regard, an example acoustic device is provided that includes a piezoelectric layer between a first bottom electrode and a second top electrode, and an acoustic mirror that includes at least one higher impedance layer that is cooperatively optimized for reflecting longitudinal and shear waves corresponding to a target operating frequency. The acoustic mirror includes a lower acoustic impedance layer (lower impedance layer) and at least one higher acoustic impedance layer (higher impedance layer). In one example, the layers of the acoustic mirror alternate between a lower impedance and a higher impedance, with a second higher impedance layer having a greater thickness than a first higher impedance layer. In another example, the acoustic mirror has a single higher impedance layer that has a thickness corresponding to at least half of a wavelength of the target operating frequency in the higher impedance layer. Acoustic devices with acoustic mirrors that are cooperatively optimized for both longitudinal and shear waves reduce energy loss to improve efficiency.

[0006] In a first example aspect, an acoustic device is disclosed. The acoustic device includes a first electrode, a piezoelectric layer disposed on a first side of the first electrode, and a second electrode disposed on the piezoelectric layer. The acoustic device further includes an acoustic mirror disposed on a second side of the first electrode opposite the piezoelectric layer. The acoustic mirror includes a first higher impedance layer having a first thickness, and a second higher impedance layer having a second thickness, where the second thickness is greater than the first thickness. The acoustic mirror further includes a first lower impedance layer between the first higher impedance layer and the second higher impedance layer, and a second lower impedance layer between the second higher impedance layer and the first electrode.

[0007] In another example aspect, a method of manufacturing an acoustic device is disclosed. The method includes forming an acoustic mirror. Forming the acoustic mirror includes forming a first higher impedance layer having a first thickness, and forming a first lower impedance layer on the first higher impedance layer. Forming the acoustic mirror further includes forming a second higher impedance layer having a second thickness on the first lower impedance layer, where the second thickness is greater than the first thickness, and forming a second lower impedance layer on the second higher impedance layer. Forming the acoustic device further includes forming a first electrode on the acoustic mirror, forming a piezoelectric layer on the first electrode, and forming a second electrode on the piezoelectric layer.

[0008] In another example aspect, an acoustic device is disclosed. The acoustic device includes a first electrode, a piezoelectric layer disposed on a first side of the first electrode, a second electrode disposed on the piezoelectric layer, and an acoustic mirror. The acoustic mirror is disposed on a second side of the first electrode opposite the piezoelectric layer. The acoustic mirror includes a first higher impedance layer including a higher impedance material having a first thickness corresponding to more than half a wavelength of a target frequency in the higher impedance material. The acoustic mirror also includes a first lower impedance layer including a lower impedance material having a second thickness corresponding to less than half a wavelength of the target frequency in the lower impedance material, the first lower impedance layer disposed between the first higher impedance layer and the first electrode. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a cross-sectional side view of an example acoustic device in which the acoustic mirror includes higher impedance layers having different thicknesses to optimize reflection of longitudinal and shear waves at a target frequency;

[0010] Figure 2 is a detailed cross-sectional view of an example layer stack that can be in an acoustic device in Figure 1 , in which the layer stack includes a second higher impedance layer that is thicker than a first higher impedance layer to synergistically optimize for reflection of longitudinal and shear waves;

[0011] Figure 3 is a flowchart illustrating a method of manufacturing an acoustic device that includes higher impedance layers having different thicknesses to synergistically optimize for reflection of longitudinal and shear waves, the acoustic device including but not limited to Figure 1 , and Figure 2 acoustic devices in

[0012] Figure 4 is another example of an acoustic device in which the thickness of a higher impedance layer in the acoustic mirror is synergistically optimized for reflection of both longitudinal and shear waves at a target frequency;

[0013] Figure 5 is a block diagram of an example wireless communication device that includes an integrated circuit (IC) that can include an acoustic device that includes at least one higher impedance layer having a thickness that is synergistically optimized for reflection of longitudinal and shear waves, the acoustic device including but not limited to Figure 1 , Figure 2 , and Figure 4 acoustic devices in Figure 3 , and can be manufactured according to an example manufacturing process in

[0014] Figure 6is a block diagram of an example processor-based system that can include an acoustic device that includes at least one higher impedance layer having a thickness that is co-optimized for reflection of longitudinal and shear waves, including but not limited to the acoustic device in Figure 1 , Figure 2 and Figure 4 , and can be manufactured according to the example manufacturing process in Figure 3 . DETAILED DESCRIPTION

[0015] Reference now is made to the drawings, where the number of example aspects of this disclosure is described. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.

[0016] Aspects disclosed in the DETAILED DESCRIPTION include an acoustic wave device that includes an acoustic mirror co-optimized for longitudinal and shear wave reflection. Related methods of manufacturing the acoustic mirror are also disclosed. Acoustic waves propagating through a piezoelectric material in an acoustic device include longitudinal and shear waves. An acoustic mirror for reflecting acoustic waves can be designed to primarily reflect longitudinal waves rather than shear waves, which have a different frequency than longitudinal waves, resulting in significant energy loss. In this regard, an example acoustic device 100 is provided as shown in Figure 1 , which includes a piezoelectric layer 114 between a first bottom electrode 118 and a second top electrode 110A, and an acoustic mirror 102 that includes at least one higher impedance layer 104A co-optimized for reflection of longitudinal and shear waves corresponding to a target operating frequency. The acoustic mirror 102 includes lower acoustic impedance layers (lower impedance layers) 122, 124, 126 and at least one higher acoustic impedance layer (higher impedance layer) 104A. In one example, the layers of the acoustic mirror 102 alternate between lower and higher impedance, with the second higher impedance layer 104A having a greater thickness than the first higher impedance layer 106A. In another example, the acoustic mirror 102 has a single higher impedance layer having a thickness corresponding to at least half the wavelength of the target frequency in the higher impedance layer. The acoustic device 100 having the acoustic mirror 102 co-optimized for both longitudinal and shear waves reduces energy loss to improve efficiency.

[0017] Figure 1is a cross-sectional side view of the acoustic device 100, where the acoustic mirror 102 includes a first higher impedance layer 106A and a second higher impedance layer 104A in the first resonator 108A, respectively, and a third higher impedance layer 106B and a fourth higher impedance layer 104B in the second resonator 108B, respectively. The second higher impedance layer 104A and the fourth higher impedance layer 104B have thicknesses that are co-optimized for reflecting longitudinal and shear waves at a target frequency. In other words, the thicknesses of the second higher impedance layer 104A and the fourth higher impedance layer 104B are related to the wavelengths of the longitudinal and shear waves at the respective target resonant frequencies of the first resonator 108A and the second resonator 108B, which can have different resonant frequencies.

[0018] The acoustic device 100 also includes a second top electrode 110A and a third top electrode 110B for receiving respective signals that generate acoustic waves in different regions 112A and 112B of the piezoelectric layer 114. The regions 112A and 112B of the piezoelectric layer 114 correspond to the resonators 108A, 108B. The resonators 108A, 108B also employ corresponding regions 116A, 116B of a first bottom electrode 118 that provides a common reference voltage for the resonators 108A, 108B. The top electrodes 110A, 110B, the piezoelectric layer 114, and the bottom electrode 118 extend in a plane in the X-axis and Y-axis directions. The top electrodes 110A and 110B and the bottom electrode 118 can include, but are not limited to, any one or more of molybdenum (Mo), platinum (Pt), ruthenium (Ru), osmium (Os), iridium (Ir), aluminum (Al), and copper (Cu), as well as alloys and / or combinations thereof.

[0019] The signals applied to the first top electrode 110A and the second top electrode 110B primarily generate longitudinal waves (e.g., waves in a direction orthogonal to the piezoelectric layer 114 or in the Z-axis direction) in the piezoelectric layer 114. However, shear waves (e.g., traveling in the X-axis and / or Y-axis directions) can also be generated directly or by converting longitudinal waves at edges and surface layers through which the longitudinal waves propagate. The piezoelectric layer 114 can include, but is not limited to, any one of aluminum nitride (AIN), aluminum scandium nitride (AlScN), aluminum yttrium nitride (AlYN), zinc oxide (ZnO), lithium tantalate (LiTa03), and lithium niobate (LiNb03).

[0020] The piezoelectric layer 114 is disposed on a first side S1 (e.g., an upper side in the Z-axis direction) of the bottom electrode 118, and the acoustic mirror 102 is disposed on a second side S2 (e.g., a lower side in the Z-axis direction) of the bottom electrode 118 opposite the piezoelectric layer 114. The acoustic mirror 102 is provided to reflect energy of the waves generated in the piezoelectric layer 114 to reduce or prevent energy loss of the acoustic device 100 through the substrate 120.

[0021] The layers in the acoustic mirror 102 alternate between one of the lower impedance layers 122, 124, and 126 in the first resonator 108A and one of the higher impedance layers 106A and 104A in the second resonator 108B and one of the higher impedance layers 106B and 104B. The acoustic mirror 102 includes a bottom lower impedance layer 122 adjacent to the substrate 120. In order from the substrate 120 in the resonator 108A toward the bottom electrode 118, the acoustic mirror 102 next includes a first higher impedance layer 106A. A first lower impedance layer 124 is between the first higher impedance layer 106A and a second higher impedance layer 104A, and a second lower impedance layer 126 is between the second higher impedance layer 104A and the bottom electrode 118. The lower impedance layers 122, 124, and 126 are layers of a lower acoustic impedance material 128 (lower impedance material) including, but not limited to, one or more of silicon dioxide (SiO2), silicon oxycarbide (SiOC), silicon oxycarbonitride (SiOCN), and silicon oxyfluoride (SiOF). The higher impedance layers 104A and 106A are layers of a higher acoustic impedance material 130 (higher impedance material) including, but not limited to, one or more of tungsten (W), Mo, Os, Ir, and Pt, having a higher or greater acoustic impedance than the lower acoustic impedance material 128. The materials identified here are merely non-limiting examples.

[0022] A conventional acoustic mirror design can include two mirror pairs, each mirror pair including a lower impedance layer and a higher impedance layer, where the thickness of each layer corresponds to one quarter (1 / 4) of the wavelength (Lambda) (λ).

[0023] In the acoustic device 100, the acoustic mirror 102 is cooperatively optimized for reflecting longitudinal acoustic waves and shear acoustic waves by optimizing a first thickness T106A of the first higher impedance layer 106A, a second thickness T104A of the second higher impedance layer 104A, and third and fourth thicknesses T124 and T126 of the lower impedance layers 124 and 126, respectively, as a function of the wavelength of the acoustic waves propagating through the acoustic mirror 102. The longitudinal waves are generated in the piezoelectric layer 114 at or about a target frequency, which is the frequency at which the acoustic device 100 is intended to operate. In some examples, the acoustic device 100 has a target frequency F 100 (e.g., 11 GHz to 15 GHz). The longitudinal waves have a longitudinal wavelength λ LL that depends on the acoustic impedance of the material through which the acoustic waves propagate. The acoustic impedance determines the speed of the acoustic waves. Thus, the longitudinal wavelength λ LL depends on the frequency and material properties. For example, the generated shear waves can have a frequency that is about half the frequency of the longitudinal waves, so the shear wavelength λ SL can be about twice the length of the longitudinal wavelength (i.e., half the frequency).

[0024] In some examples, the co-optimized acoustic reflector 102 includes thicknesses T126 and T124 that are less than half (<1 / 2) of the longitudinal wavelength λ LL . Alternatively, in some examples, the thicknesses T126 and T124 are each less than half (<1 / 2) of the shear wavelength λ SL . The thicknesses T126 and T124 can be different from each other or the same as each other. In some examples, the lower impedance layers 126 and 124 are each a quarter (1 / 4) or about 1 / 4 of the longitudinal wavelength λ LL in the lower acoustic impedance material 128 at the target frequency F L . In other words, in some examples, the lower impedance layers have thicknesses T126 and T124 of λ 100 / 4.

[0025] The first higher impedance layer 106A in the acoustic reflector 102 has a first thickness T106A that can be less than half of the longitudinal wavelength λ LH (<λ LH / 2) in the higher acoustic impedance material 130 at the target frequency F 100 . In some examples, the first thickness T106A can be less than half of the shear wavelength λ SH (<λ SH / 2) in the higher acoustic impedance material 130 at the target frequency F 100 . In some examples, the thickness T106A of the first higher impedance layer 106A is a quarter (1 / 4) of the longitudinal wavelength λ LH (λ LH / 4) in the higher acoustic impedance material 130 at the target frequency F 100 . In some examples, the thickness T106A of the first higher impedance layer 106A is within a range of twenty percent (20%) of a quarter of the wavelength λ LH in the higher acoustic impedance material 130 at the target frequency F 100 . In some examples, the thickness T106A of the first higher impedance layer 106A is a quarter (1 / 4) of the shear wavelength λ SH (λ SH / 4) in the higher acoustic impedance material 130 at the target frequency F 100 . In some examples, the thickness T106A of the first higher impedance layer 106A is a quarter (1 / 4) of the longitudinal wavelength λ SH in the higher acoustic impedance material 130 at the target frequency F 100 . In some examples, the thickness T106A of the first higher impedance layer 106A is within a range of twenty percent (20%) of a quarter of the shear wavelength λ SH in the higher acoustic impedance material 130 at the target frequency F LH .

[0026] In comparison to the conventional acoustic reflector described above, the second higher impedance layer 104A has a second thickness T104A that is greater than a first thickness T106A of the first higher impedance layer 106A. In particular, the second thickness T104A can be greater than half of the longitudinal wavelength λ LH (> λ LH / 2), while the thickness T106A of the first higher impedance layer 106A is less than half of the wavelength λ LH (< λ LH / 2). In some examples, the second thickness T104A is at least twice (2x) the first thickness T106A. In some examples, the second thickness T104A is at least three times (3x) the first thickness T106A. In some examples, the second thickness T104A of the second higher impedance layer 104A is three-quarters (3 / 4) of the wavelength λ 100 (3 λ LH / 4) in the higher acoustic impedance material 130 at the target frequency F LH In some examples, the second thickness T104A of the second higher impedance layer 104A is within 20% (less or more) of three-quarters (3 / 4) of the wavelength λ LH (3 λ LH / 4). In other words, the second thickness T104A can be within a range of (0.8) x (3 λ LH / 4) to (1.2) x (3 λ LH / 4). The second higher impedance layer 104A including a thickness T104A within the range disclosed above provides a synergistic optimization of the reflection characteristics of the longitudinal and shear waves generated in the region 112A of the piezoelectric layer 114.

[0027] Alternatively, the second thickness T104A can be greater than half of the shear wavelength λ SH (> λ LH / 2), while the thickness T106A of the first higher impedance layer 106A is less than half of the shear wavelength λ SH (< λ SH / 2). In some examples, the second thickness T104A of the second higher impedance layer 104A is three-quarters (3 / 4) of the wavelength λ 100 (3 λ SH / 4) in the higher acoustic impedance material 130 at the target frequency F SH In some examples, the second thickness T104A of the second higher impedance layer 104A is within 20% (less or more) of three-quarters (3 / 4) of the shear wavelength λ SH (3 λ SH / 4). In other words, the second thickness T104A can be within a range of (0.8) x (3 λ SH / 4) to (1.2) x (3 λ SHwithin the range disclosed above.

[0028] The second higher impedance layer 104A, including a thickness T104A within the range disclosed above, provides a synergistic optimization of the reflection properties of the longitudinal and shear waves generated in the region 112A of the piezoelectric layer 114. In the resonator 108B, the acoustic mirror 102 includes a stack 134 of lower and higher impedance layers corresponding to the layers of the acoustic mirror 102 in the resonator 108A. In particular, the thicknesses of the layers in the stack 134 in the resonator 108B can be the same as the thicknesses of the layers in the acoustic mirror 102 of the resonator 108A discussed above.

[0029] In the resonator 108A, a first top electrode 110A is disposed on the piezoelectric layer 114 opposite the region 116A of the bottom electrode 118, and a second top electrode 110B is disposed on the piezoelectric layer 114 opposite the region 116B of the bottom electrode 118. In the acoustic mirror 102 opposite the region 116B of the bottom electrode 118, the acoustic device 100 includes a third higher impedance layer 106B and a fourth higher impedance layer 104B. The fourth higher impedance layer 104B is disposed between the first lower impedance layer 124 and the second lower impedance layer 126. The third higher impedance layer 106B has a fifth thickness T106B, which can be within the range of the thickness T106A of the first higher impedance layer 106A, but can be different from the thickness T106A. The fourth higher impedance layer 104B has a sixth thickness T104B, which can be within the range of the thickness T104A of the second higher impedance layer 104A, but can be different from the thickness T104A. In any case, the sixth thickness T104B of the fourth higher impedance layer 104B is greater than the fifth thickness T106B of the third higher impedance layer 106B.

[0030] The acoustic device 100 can include any of a bulk acoustic wave (BAW) resonator and a solidly mounted resonator (SMR). The acoustic mirror 102 can include a Bragg mirror, and in the case of a BAW resonator, the acoustic mirror 102 can include a stack of layers having a thickness within a range of 0.1 to 1.0 micrometers. Figure 1 In an alternative to the BAW resonator shown, the following can be employed in an acoustic device including a Lamé mode resonator and a surface acoustic wave (SAW) device (not shown).

[0031] Figure 2 is a detailed cross-sectional view of a layer stack 200 in the acoustic device 100 in Figure 1 is a detailed cross-sectional view of a layer stack 200 in the acoustic device 100 in Figure 1The layers of the layer stack 200 are formed in order from the substrate 206 (of silicon (Si)) to the second top electrode 208. The layer stack 200 includes a bottom lower impedance layer 210 of the acoustic reflector 212. The bottom lower impedance layer 210 can be a layer of amorphous SiO2or other lower acoustic impedance material as described above.

[0032] A seed layer 214 is formed on the bottom lower impedance layer 210 to provide a crystal lattice structure for growing the first higher impedance layer 204 (e.g., W). In one example, the first higher impedance layer 204 can be formed by sputtering W onto the seed layer 214. The seed layer 214 can also be referred to as an adhesion layer because it also improves adhesion of the first higher impedance layer 204 to the bottom lower impedance layer 210. For example, the seed layer 214 can be titanium (Ti) or aluminum nitride (AIN). In cases where the lower impedance layer has good adhesion to the first higher impedance layer, a first lower impedance layer 216 can be formed directly on the first higher impedance layer 204. As an example, SiO2has good adhesion when formed on W. Another seed layer (e.g., an adhesion layer of Ti or AIN) 218 is formed on the first lower impedance layer 216 before the second higher impedance layer 202 is formed on the first lower impedance layer 216. A second lower impedance layer 220 is formed on the second higher impedance layer 202. Next, a first bottom electrode 222 of a metal (e.g., molybdenum (Mo)), a piezoelectric layer 224 (e.g., aluminum nitride (AIN) or aluminum scandium nitride (AlScN)), and a top electrode 208 are formed in order in the Z-axis direction. The second top electrode 208 is also a metal electrode, which can be the same or different material as the first bottom electrode 222.

[0033] Although Figure 2 Although not shown in FIG. 2, the layer stack 200 can include additional layers. For example, in examples where the top electrode 208 is a different material than the bottom electrode 222, a buffer layer can be needed between the top electrode 208 and the piezoelectric layer 224. Additionally, a buffer layer can be included on the bottom electrode 222 prior to forming the piezoelectric material 224 (e.g., to improve lattice matching). Additionally, the layer stack 200 can also include a passivation layer that protects the top electrode 208 and can also be used for frequency tuning of the acoustic device 100. However, it should be understood that the buffer layer, passivation layer, and seed layers (214 and 218) are significantly thinner than the acoustically active layers and, thus, do not significantly affect the resonant frequency of the layer stack 200 in the acoustic device 100.

[0034] A fabrication process can be employed to fabricate an acoustic device including an acoustic reflector including at least one higher impedance layer having a thickness that is cooperatively optimized for reflecting both longitudinal and shear waves generated in a piezoelectric layer, including but not limited to Figure 1 The acoustic device 100 in FIG. 2. In this regard,Figure 3 is a flowchart illustrating an example manufacturing process 300 of manufacturing an acoustic device 100 including at least one higher impedance layer having a thickness that is cooperatively optimized for reflecting both longitudinal and shear waves generated in a piezoelectric layer, including but not limited to Figure 1 acoustic device 100 in FIG. 1. The manufacturing process 300 is discussed with respect to Figure 1 acoustic device 100 in FIG. 1, but note that the manufacturing process 300 is not limited to manufacturing Figure 1 the acoustic device in FIG. 1.

[0035] In this regard, example steps of manufacturing the acoustic device 100 include forming the acoustic reflector 102 (block 302), including forming a first higher impedance layer 106A having a first thickness T106 (block 304) and forming a first lower impedance layer 124 on the first higher impedance layer 106A (block 306). Forming the acoustic reflector 102 also includes forming a second higher impedance layer 104A having a second thickness T104 on the first lower impedance layer 124, where the second thickness T104 is greater than the first thickness T106 (block 308). Forming the acoustic reflector 102 also includes forming a second lower impedance layer 126 on the second higher impedance layer 104A (block 310). Forming the acoustic device 100 also includes forming a bottom electrode 118 on the acoustic reflector 102 (block 312) and forming a piezoelectric layer 114 on the bottom electrode 118 (block 314). Forming the acoustic device 100 also includes forming a first top electrode 110A on the piezoelectric layer 114 (block 316). Other manufacturing processes can also be employed to manufacture the acoustic device 100 including an acoustic reflector including at least one higher impedance layer having a thickness that is cooperatively optimized for reflecting both longitudinal and shear waves generated in a piezoelectric layer.

[0036] Figure 1 The acoustic device 100 in FIG. 1 is a first example of an acoustic device including at least one higher impedance layer having a thickness that is cooperatively optimized for reflecting both longitudinal and shear waves generated in a piezoelectric layer. Figure 4 is a cross-sectional side view of an acoustic device 400 in which a thickness T402 of a higher impedance layer 402 in an acoustic reflector 404 is optimized for reflecting both longitudinal and shear waves at a target frequency F 400 in FIG. 1. The acoustic device 400 responds to receiving signals IN1 and IN2 at a second top electrode 406A and a third top electrode 406B in a manner similar to Figure 1The acoustic device 100 operates in a manner that causes the expansion and contraction of the piezoelectric layer 408 between the top electrodes 406A, 406B and the first bottom electrode 410. The thickness T408A of the piezoelectric layer 408 between the second top electrode 406A and the first bottom electrode 410 may be equal to or greater than the thickness T408B of the piezoelectric layer 408 between the top electrode 406B and the bottom electrode 410. In this example, the acoustic reflector 404 may include only one mirror pair 414 for reasons including reducing process steps, thereby reducing manufacturing costs, and / or improving heat dissipation through conduction to the substrate 412, since the low-impedance acoustic impedance material 420 (e.g., SiO2) is a poor thermal conductor.

[0037] The higher impedance layer 402 in mirror pair 414 includes a corresponding Figure 1 The second higher impedance layer 104A has a second thickness T104A and a fifth thickness T402. Specifically, the thickness T402 of the higher impedance layer 402 is greater than the wavelength λ of the sound wave in the higher impedance layer 402 at the target operating frequency of the acoustic device 400. H Half of (>λ) H / 2). Wavelength λ in high-impedance layer 402 at a specific frequency H The acoustic impedance depends on the higher acoustic impedance material 416 (e.g., W) that forms the high impedance layer 402. In some examples, the thickness T402 at wavelength λ H Three-quarters (3 / 4xλ) H Within twenty percent (i.e., + / - 20%) of the wavelength λ. In some examples, the thickness T402 is within λ. H Three-quarters of it.

[0038] The mirror pair 414 also includes a low impedance layer 418 of a low acoustic impedance material 420 (e.g., SiO2) and has a thickness T418 that is less than the target operating frequency F. 400 The wavelength λ of the sound wave in the lower acoustic impedance material 420 L Half of the impedance layer 418. A lower impedance layer 418 is disposed between the higher impedance layer 402 and the bottom electrode 410. In some examples, the thickness T418 of the lower impedance layer 418 is equal to the wavelength λ. L 20% of a quarter or within a quarter of the wavelength. In other words, the lower impedance layer 418 can have λ L / 4 thickness or λ L Thickness between 4 / 4 (80% and 120%).

[0039] The combination of thicknesses T418 and T402 is synergistically optimized for reflecting both longitudinal and shear waves generated in the piezoelectric layer 408.

[0040] The acoustic device 400 also includes a bottom lower impedance layer 422 having a thickness T422, which can be greater than the range of thicknesses T418 described above, as there is significantly less energy remaining in the acoustic waves in the bottom lower impedance layer 422 than in the acoustic waves in the lower impedance layer 418.

[0041] The acoustic devices 100 and 400 according to aspects disclosed herein can be provided in or integrated into any processor-based device. Examples, without limitation, include a set top box, an entertainment unit, a navigation device, a communications device, a fixed location data unit, a mobile location data unit, a global positioning system (GPS) device, a mobile phone, a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a tablet, a phablet, a server, a computer, a portable computer, a mobile computing device, a wearable computer (e.g., a smart watch, a health or fitness tracker, eyewear, etc.), a desktop computer, a personal digital assistant (PDA), a monitor, a computer monitor, a television, a tuner, a radio, a satellite radio, a music player, a digital music player, a portable music player, a digital video player, a video player, a digital video disc (DVD) player, a portable digital video player, an automobile, a transportation component, avionics systems, a drone, and a multicopter.

[0042] In this regard, Figure 5 An example wireless communication device 500 including radio frequency (RF) components formed from one or more ICs 502 is illustrated, where any of the ICs 502 can include an acoustic device including at least one higher impedance layer having a thickness that is cooperatively optimized for reflection of longitudinal and shear waves, including but not limited to Figure 1 , Figure 2 and Figure 4 acoustic devices disclosed herein, in accordance with any of the aspects disclosed herein. As an example, the wireless communication device 500 can include or be provided in any of the devices described above. As shown in Figure 5 the wireless communication device 500 includes a transceiver 504 and a data processor 506. The data processor 506 can include a memory for storing data and program codes. The transceiver 504 includes a transmitter 508 and a receiver 510 that support bi-directional communication. In general, the wireless communication device 500 can include any number of transmitters 508 and / or receivers 510 for any number of communication systems and frequency bands. All or a portion of the transceiver 504 can be implemented on one or more analog ICs, RF ICs (RFICs), mixed-signal ICs, etc.

[0043] The transmitter 508 or receiver 510 can be implemented with a super-heterodyne architecture or a direct-conversion architecture. In a super-heterodyne architecture, a signal is frequency converted between RF and baseband in multiple stages, e.g., from RF to an intermediate frequency (IF) in one stage, and then from IF to baseband in another stage. In a direct-conversion architecture, a signal is frequency converted between RF and baseband in one stage. Super-heterodyne and direct-conversion architectures can use different circuit blocks and / or have different requirements. In Figure 5 In the wireless communication device 500 of FIG. 5, the transmitter 508 and receiver 510 are implemented with a direct-conversion architecture.

[0044] In the transmit path, the data processor 506 processes data to be transmitted and provides I and Q analog output signals to the transmitter 508. In the exemplary wireless communication device 500, the data processor 506 includes digital-to-analog converters (DACs) 512(1), 512(2) to convert digital signals generated by the data processor 506 into I and Q analog output signals (e.g., I and Q output currents) for further processing.

[0045] Within the transmitter 508, lowpass filters 514(1), 514(2) filter the I and Q analog output signals, respectively, to remove undesired signals caused by the prior digital-to-analog conversion. Amplifiers (AMPs) 516(1), 516(2) amplify the signals from the lowpass filters 514(1), 514(2), respectively, and provide I and Q baseband signals. An upconverter 518 upconverts the I and Q baseband signals with I and Q transmit (TX) local oscillator (LO) signals from a TX LO signal generator 522 through mixers 520(1), 520(2) to provide an upconverted signal 524. A filter 526 filters the upconverted signal 524 to remove undesired signals caused by the signal upconversion and noise in the receive frequency band. A power amplifier (PA) 528 amplifies the upconverted signal 524 from the filter 526 to obtain a desired output power level and provide a transmit RF signal. The transmit RF signal is routed through a duplexer or switch 530 and transmitted via an antenna 532.

[0046] In the receive path, the antenna 532 receives signals transmitted by base stations and provides a received RF signal that is routed through the duplexer or switch 530 and provided to a low noise amplifier (LNA) 534. The duplexer or switch 530 is designed to operate with a particular receive (RX) to TX duplexer frequency separation, such that RX signals are isolated from TX signals. The received RF signal is amplified by the LNA 534 and filtered by a filter 536 to obtain a desired RF input signal. Down-conversion mixers 538(1), 538(2) mix the output of the filter 536 with I and Q RX LO signals (i.e., LO I and LO Q) from an RX LO signal generator 540 to generate I and Q baseband signals. The I and Q baseband signals are amplified by AMPs 542(1), 542(2) and further filtered by low pass filters 544(1), 544(2) to obtain I and Q analog input signals that are provided to the data processor 506. In this example, the data processor 506 includes analog-to-digital converters (ADCs) 546(1), 546(2) to convert the analog input signals to digital signals to be further processed by the data processor 506.

[0047] In Figure 5 In the wireless communication device 500, the TX LO signal generator 522 generates I and Q TX LO signals for frequency up-conversion, and the RX LO signal generator 540 generates I and Q RX LO signals for frequency down-conversion. Each LO signal is a periodic signal having a particular base frequency. A TX phase-locked loop (PLL) circuit 548 receives timing information from the data processor 506 and generates control signals for adjusting the frequency and / or phase of the TX LO signals from the TX LO signal generator 522. Similarly, an RX PLL circuit 550 receives timing information from the data processor 506 and generates control signals for adjusting the frequency and / or phase of the RX LO signals from the RX LO signal generator 540.

[0048] Figure 6 An example of a processor-based system 600 is illustrated that can employ an acoustic device including at least one higher impedance layer having a thickness that is co-optimized for reflection of longitudinal and shear waves, including but not limited to Figure 1 、 Figure 2 and Figure 4acoustic device in a computing device, and in accordance with aspects disclosed herein. In this example, the processor-based system 600 includes one or more central processing units (CPUs) 602, which can also be referred to as CPU or processor cores, each including one or more processors 604. The CPUs 602 can have cache memory 606 coupled to the processors 604 for rapid access to temporarily stored data. The CPUs 602 are coupled to a system bus 608 and can be interconnected to primary and secondary devices included in the processor-based system 600. As is well known, the CPUs 602 communicate with these other devices by exchanging address, control, and data information over the system bus 608. For example, the CPUs 602 can communicate bus transaction requests to the memory controller 610 as an example of a secondary device. Although not illustrated in Figure 6 multiple system buses 608 can be provided; with each system bus 608 constituting a different fabric.

[0049] Other primary and secondary devices can be connected to the system bus 608. As Figure 6 illustrated, these devices can include, by way of example, a memory system 612 (which includes the memory controller 610 and one or more memory arrays 614), one or more input devices 616, one or more output devices 618, one or more network interface devices 620, and one or more display controllers 622. The input devices 616 can include any type of input device, including but not limited to input keys, switches, voice processors, and the like. The output devices 618 can include any type of output device, including but not limited to audio, video, other visual indicators, and the like. The network interface devices 620 can be any devices configured to allow exchange of data to and from a network 624. The network 624 can be any type of network, including but not limited to a wired or wireless network, a private or public network, a local area network (LAN), a wireless local area network (WLAN), a wide area network (WAN), a BLUETOOTH® network, and the Internet. The network interface devices 620 can be configured to support any type of communications protocol desired. TM

[0050] The CPUs 602 can also be configured to access the display controllers 622 over the system bus 608 to control the information sent to one or more displays 626. The display controllers 622 communicate information intended for display to the displays 626 via one or more video processors 628, which process the information intended for display into a format suitable for the displays 626. The displays 626 can include any type of display, including but not limited to a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, or a light emitting diode (LED) display, among others. ​

[0051] Those skilled in the art will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithms described in connection with the aspects disclosed herein can be implemented as electronic hardware, instructions stored in memory or in another computer-readable medium, and / or combinations of both. The memory disclosed herein can be of any type and size and can be configured to store data desired in any type of format. To clearly illustrate this interchangeability, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. How such functionality is implemented depends upon the particular application, design choices, and / or design constraints imposed on the overall system. Skilled artisans can implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0052] The various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein can be implemented or performed with a processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0053] The aspects disclosed herein can be embodied in hardware and in instructions stored in hardware, and can reside, for example, in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer readable medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an ASIC. The ASIC can reside in a remote station. In the alternative, the processor and the storage medium can reside as discrete components in a remote station, a base station, or a server.

[0054] It is also noted that the operational steps described in any of the example aspects herein are described to provide examples and discussion. The operations described can be performed in numerous different sequences other than the illustrated sequences. Furthermore, operations described in a single operational step can actually be performed in a number of different steps. Additionally, one or more operational steps discussed in the example aspects can be combined. It is understood that all the different modifications can be made to the operational steps illustrated in the flowcharts. It is also understood that the operational steps illustrated in the flowcharts can be implemented by a variety of different techniques and that the different techniques can be used for some of the operational steps illustrated in the flowcharts. For example, data, instructions, commands, information, signals, bits, symbols, and chips that can be referenced throughout the above description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0055] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other variations. Thus, the disclosure is not intended to be limited to the examples described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0056] Various implementation examples are described in the following numbered clauses:

[0057] 1. An acoustic device, the acoustic device comprising:

[0058] a first electrode;

[0059] a piezoelectric layer disposed on a first side of the first electrode;

[0060] a second electrode disposed on the piezoelectric layer; and

[0061] an acoustic mirror disposed on a second side of the first electrode opposite the piezoelectric layer, the acoustic mirror comprising:

[0062] a first higher impedance layer having a first thickness;

[0063] a second higher impedance layer having a second thickness, wherein the second thickness is greater than the first thickness;

[0064] a first lower impedance layer between the first higher impedance layer and the second higher impedance layer; and

[0065] a second lower impedance layer between the second higher impedance layer and the first electrode.

[0066] 2. The acoustic device of clause 1, wherein the second thickness of the second higher-impedance layer is at least twice the first thickness of the first higher-impedance layer.

[0067] 3. The acoustic device of clause 1, wherein the second thickness of the second higher-impedance layer is at least three times the first thickness of the first higher-impedance layer.

[0068] 4. The acoustic device of any of clauses 1-3, wherein:

[0069] the first and second lower-impedance layers each include a lower-impedance material; and

[0070] the first and second higher-impedance layers each include a higher-impedance material having a greater acoustic impedance than the lower-impedance material.

[0071] 5. The acoustic device of clause 4, wherein:

[0072] the first lower-impedance layer has a third thickness corresponding to less than half a wavelength of a target frequency in the lower-impedance material;

[0073] the second lower-impedance layer has a fourth thickness corresponding to less than half the wavelength of the target frequency in the lower-impedance material;

[0074] the first thickness corresponds to less than half a wavelength of the target frequency in the higher-impedance material; and

[0075] the second thickness corresponds to more than half the wavelength of the target frequency in the higher-impedance material.

[0076] 6. The acoustic device of clause 4, wherein:

[0077] the first lower-impedance layer has a third thickness corresponding to one quarter of a wavelength of a target frequency in the lower-impedance material;

[0078] the second lower-impedance layer has a fourth thickness corresponding to one quarter of a wavelength of the target frequency in the lower-impedance material;

[0079] the first thickness corresponds to one quarter of a wavelength of the target frequency in the higher-impedance material; and

[0080] the second thickness corresponds to three quarters of the wavelength of the target frequency in the higher-impedance material.

[0081] 7. The acoustic device of any one of Clauses 1-6, further comprising:

[0082] a second electrode disposed on the piezoelectric layer over a first region of the first electrode;

[0083] a third electrode disposed on the piezoelectric layer over a second region of the first electrode; and in the acoustic reflector adjacent to the second region of the first electrode:

[0084] a third higher impedance layer having a fifth thickness; and

[0085] a fourth higher impedance layer having a sixth thickness between the first lower impedance layer and the second lower impedance layer,

[0086] wherein the sixth thickness is greater than the fifth thickness.

[0087] 8. The acoustic device of Clause 7, further comprising:

[0088] a substrate; and

[0089] a bottom lower impedance layer between the substrate and the first higher impedance layer and between the substrate and the third higher impedance layer.

[0090] 9. The acoustic device of any one of Clauses 1-8, further comprising:

[0091] a first adhesion layer between the first lower impedance layer and the first higher impedance layer; and

[0092] a buffer layer between the first electrode and the piezoelectric layer.

[0093] 10. The acoustic device of Clause 8, wherein:

[0094] the first lower impedance layer, the second lower impedance layer, and the bottom lower impedance layer each comprise silicon dioxide (Si02);

[0095] the first higher impedance layer and the second higher impedance layer each comprise tungsten (W);

[0096] the second electrode and the first electrode comprise molybdenum (Mo); and

[0097] the piezoelectric layer comprises aluminum nitride (AIN).

[0098] 11. The acoustic device of any one of clauses 1-10, the integrated circuit being integrated into a device selected from the group consisting of: a set top box; an entertainment unit; a navigation device; a communications device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smart phone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computer; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player; a portable digital video player; an automobile; a transportation component; avionics systems; a drone; and a multicopter.

[0099] 12. A method of manufacturing an acoustic device, the method comprising:

[0100] forming an acoustic reflector, comprising:

[0101] forming a first higher impedance layer having a first thickness;

[0102] forming a first lower impedance layer on the first higher impedance layer;

[0103] forming a second higher impedance layer having a second thickness on the first lower impedance layer; and

[0104] forming a second lower impedance layer on the second higher impedance layer;

[0105] forming a first electrode on the acoustic reflector;

[0106] forming a piezoelectric layer on the first electrode; and

[0107] forming a second electrode on the piezoelectric layer,

[0108] wherein the second thickness is greater than the first thickness.

[0109] 13. The method of clause 12, wherein:

[0110] forming the first lower impedance layer comprises forming the first lower impedance layer of a lower impedance material; and

[0111] forming the second lower impedance layer comprises forming the second lower impedance layer of the lower impedance material,

[0112] wherein the first higher impedance layer and the second higher impedance layer each comprise a higher impedance material having a greater acoustic impedance than the lower impedance material.

[0113] 14. The method of clause 13, wherein:

[0114] the first thickness corresponds to less than half of a wavelength of a target frequency in the higher impedance material; and

[0115] the second thickness corresponds to more than half of the wavelength of the target frequency in the higher impedance material.

[0116] 15. The method of clause 13, wherein:

[0117] the first thickness corresponds to one quarter of a wavelength of a target frequency in the higher impedance material; and

[0118] the second thickness corresponds to three quarters of the wavelength of the target frequency in the higher impedance material.

[0119] 16. An acoustic device, comprising:

[0120] a first electrode;

[0121] a piezoelectric layer disposed on a first side of the first electrode;

[0122] a second electrode disposed on the piezoelectric layer; and

[0123] an acoustic reflector disposed on a second side of the first electrode opposite the piezoelectric layer, the acoustic reflector comprising:

[0124] a first higher impedance layer comprising a higher impedance material having a first thickness, the first thickness corresponding to more than half of a wavelength at a target frequency in the higher impedance material; and

[0125] a first lower impedance layer comprising a lower impedance material having a second thickness, the second thickness corresponding to less than half of a wavelength of the target frequency in the lower impedance material, the first lower impedance layer disposed between the first higher impedance layer and the first electrode.

[0126] 17. The acoustic device of clause 16, further comprising:

[0127] a substrate; and

[0128] a second lower impedance layer comprising the lower impedance material having a third thickness, the second lower impedance layer between the first higher impedance layer and the substrate.

[0129] 18. The acoustic device of clause 17, further comprising:

[0130] a second higher impedance layer between the second lower impedance layer and the substrate and comprising the higher impedance material having a fourth thickness, the fourth thickness being less than half of the wavelength of the target frequency in the higher impedance material; and

[0131] a third lower impedance layer comprising the lower impedance material having a fifth thickness, the third lower impedance layer being between the second higher impedance layer and the substrate.

[0132] 19. The acoustic device of any one of clauses 16-18, wherein:

[0133] the first thickness corresponds to three quarters of the wavelength of the target frequency in the higher impedance material;

[0134] the second thickness corresponds to one quarter of the wavelength of the target frequency in the lower impedance material.

[0135] 20. The acoustic device of clause 17 or clause 18, wherein:

[0136] the first and second lower impedance layers comprise silicon dioxide (Si02);

[0137] the first higher impedance layer comprises tungsten (W);

[0138] the second electrode and the first electrode comprise molybdenum (Mo); and

[0139] the piezoelectric layer comprises aluminum nitride (AIN).

[0140] 21. The acoustic device of clause 18, wherein the first thickness of the first higher impedance layer is at least twice the fourth thickness of the second higher impedance layer.

[0141] 22. The acoustic device of clause 18, wherein the first thickness of the first higher impedance layer is at least three times the fourth thickness of the second higher impedance layer.

Claims

1. An acoustic device, the acoustic device comprising: First electrode; A piezoelectric layer is disposed on a first side of the first electrode; The second electrode is disposed on the piezoelectric layer; and An acoustic reflector is disposed on the second side of the first electrode opposite to the piezoelectric layer, and the acoustic reflector comprises: A first higher impedance layer, the first higher impedance layer having a first thickness; A second higher impedance layer, the second higher impedance layer having a second thickness, wherein the second thickness is greater than the first thickness; A first lower impedance layer, wherein the first lower impedance layer is located between the first higher impedance layer and the second higher impedance layer; and A second lower impedance layer is located between the second higher impedance layer and the first electrode.

2. The acoustic device of claim 1, wherein the second thickness of the second higher impedance layer is at least twice the first thickness of the first higher impedance layer.

3. The acoustic device of claim 1, wherein the second thickness of the second higher impedance layer is at least three times the first thickness of the first higher impedance layer.

4. The acoustic device according to claim 1, wherein: The first low-resistivity layer and the second low-resistivity layer each comprise a low-resistivity material; and The first higher impedance layer and the second higher impedance layer each contain a higher impedance material having a greater acoustic impedance than the lower impedance material.

5. The acoustic device according to claim 4, wherein: The first lower impedance layer has a third thickness, which corresponds to half the wavelength of the target frequency in the lower impedance material; The second lower impedance layer has a fourth thickness, the fourth thickness corresponding to half the wavelength of the target frequency in the lower impedance material; The first thickness corresponds to half the wavelength of the target frequency, which is less than that in the higher impedance material; and The second thickness corresponds to half the wavelength of the target frequency in the higher impedance material.

6. The acoustic device according to claim 4, wherein: The first lower impedance layer has a third thickness, which corresponds to one-quarter of the wavelength of the target frequency in the lower impedance material; The second lower impedance layer has a fourth thickness, which corresponds to one-quarter of the wavelength of the target frequency in the lower impedance material; The first thickness corresponds to one-quarter of the wavelength of the target frequency in the higher impedance material; and The second thickness corresponds to three-quarters of the wavelength of the target frequency in the higher impedance material.

7. The acoustic device according to claim 1, further comprising: The second electrode is disposed on the piezoelectric layer above the first region of the first electrode; A third electrode is disposed on the piezoelectric layer above the second region of the first electrode; as well as In the acoustic reflector adjacent to the second region of the first electrode: A third higher impedance layer, the third higher impedance layer having a fifth thickness; and A fourth higher impedance layer, wherein the fourth higher impedance layer has a sixth thickness between the first lower impedance layer and the second lower impedance layer, The sixth thickness is greater than the fifth thickness.

8. The acoustic device according to claim 7, further comprising: substrate; and A lower impedance layer is provided at the bottom, which is located between the substrate and the first higher impedance layer, and between the substrate and the third higher impedance layer.

9. The acoustic device according to claim 1, further comprising: A first adhesive layer is located between the first lower impedance layer and the first higher impedance layer; and A buffer layer is provided between the first electrode and the piezoelectric layer.

10. The acoustic device according to claim 8, wherein: The first lower impedance layer, the second lower impedance layer, and the bottom lower impedance layer each contain silicon dioxide (SiO2); The first higher impedance layer and the second higher impedance layer each contain tungsten (W); The second electrode and the first electrode both contain molybdenum (Mo); and The piezoelectric layer contains aluminum nitride (AlN).

11. The acoustic device of claim 1, wherein the acoustic device is integrated into a device selected from the group consisting of: set-top boxes; entertainment units; navigation devices; communication devices; fixed location data units; mobile location data units; global positioning system (GPS) devices; mobile phones; cellular phones; smartphones; session initiation protocol (SIP) phones; tablet computers; tablet phones; servers; computers; portable computers; mobile computing devices; wearable computing devices; desktop computers; personal digital assistants (PDAs); monitors; computer monitors; televisions; tuners; radios; satellite radios; music players; digital music players; portable music players; digital video players; video players; digital video disc (DVD) players; portable digital video players; automobiles; vehicle components; avionics systems; unmanned aerial vehicles; and multi-rotor aircraft.

12. A method for manufacturing an acoustic device, the method comprising: Forming an acoustic reflector includes: A first high-resistivity layer with a first thickness is formed; A first lower impedance layer is formed on the first higher impedance layer; A second higher impedance layer having a second thickness is formed on the first lower impedance layer; and A second lower impedance layer is formed on the second higher impedance layer; A first electrode is formed on the acoustic reflector; A piezoelectric layer is formed on the first electrode; and A second electrode is formed on the piezoelectric layer. The second thickness is greater than the first thickness.

13. The method according to claim 12, wherein: Forming the first lower impedance layer includes forming the first lower impedance layer of a lower impedance material; and Forming the second lower impedance layer includes forming the second lower impedance layer of the lower impedance material. The first higher impedance layer and the second higher impedance layer each contain a higher impedance material having a greater acoustic impedance than the lower impedance material.

14. The method of claim 13, wherein: The first thickness corresponds to a wavelength less than half the target frequency in the higher impedance material; and The second thickness corresponds to half the wavelength of the target frequency in the higher impedance material.

15. The method according to claim 13, wherein: The first thickness corresponds to one-quarter of the wavelength of the target frequency in the higher impedance material; and The second thickness corresponds to three-quarters of the wavelength of the target frequency in the higher impedance material.

16. An acoustic device, the acoustic device comprising: First electrode; A piezoelectric layer is disposed on a first side of the first electrode; The second electrode is disposed on the piezoelectric layer; and An acoustic reflector is disposed on the second side of the first electrode opposite to the piezoelectric layer, and the acoustic reflector comprises: A first higher impedance layer, comprising a higher impedance material having a first thickness corresponding to a wavelength greater than half the wavelength at a target frequency in the higher impedance material. and A first lower impedance layer comprising a lower impedance material having a second thickness corresponding to half the wavelength of the target frequency in the lower impedance material, the first lower impedance layer being disposed between the first higher impedance layer and the first electrode.

17. The acoustic device according to claim 16, further comprising: substrate; and A second lower impedance layer, comprising the lower impedance material having a third thickness, is located between the first higher impedance layer and the substrate.

18. The acoustic device according to claim 17, further comprising: A second higher impedance layer is located between the second lower impedance layer and the substrate, and includes the higher impedance material having a fourth thickness less than half the wavelength of the target frequency in the higher impedance material. and A third lower impedance layer, comprising the lower impedance material having a fifth thickness, is located between the second higher impedance layer and the substrate.

19. The acoustic device according to claim 16, wherein: The first thickness corresponds to three-quarters of the wavelength of the target frequency in the higher acoustic impedance material; The second thickness corresponds to one-quarter of the wavelength of the target frequency in the lower impedance material.

20. The acoustic device according to claim 17, wherein: The first lower impedance layer and the second lower impedance layer comprise silicon dioxide (SiO2); The first higher impedance layer contains tungsten (W); The second electrode and the first electrode both contain molybdenum (Mo); and The piezoelectric layer contains aluminum nitride (AlN).

21. The acoustic device of claim 18, wherein the first thickness of the first higher impedance layer is at least twice the fourth thickness of the second higher impedance layer.

22. The acoustic device of claim 18, wherein the first thickness of the first higher impedance layer is at least three times the fourth thickness of the second higher impedance layer.

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