Bulk acoustic wave (BAW) device with oppositely polarized piezoelectric layer for higher order resonance and method of manufacture

Abstract

A bulk acoustic wave (BAW) device includes a layer stack (102) including a first electrode (104A) and a second electrode (104B), a first piezoelectric layer (106A) between the electrodes, and a second piezoelectric layer (106B) between the first piezoelectric layer and the second electrode. The polarization (P2) of the crystal structure of the second piezoelectric layer is opposite the polarization (P1) of the crystal structure of the first piezoelectric layer to achieve a higher order resonant frequency in the BAW device by reducing only the layers in the stack of thin layers. In some examples, the BAW device is a two-terminal device and does not include a metal layer configured as a third electrode. In some examples, the BAW device includes at least one intermediate layer (120, 122, 124) between the first and second piezoelectric layers, and the total combined thickness of the at least one intermediate layer is less than 4% of the total thickness of the layer stack.

Description

Technical Field

[0001] Generally speaking, the technology of the present disclosure relates to microacoustic devices and, more particularly, to bulk acoustic wave (BAW) resonators for use in higher frequency BAW filters. Background Art

[0002] Wireless devices, such as cellular phones, communicate by sending and receiving wireless signals over the air. For example, cellular phones send and receive wireless signals in limited radio frequency ranges, and these ranges vary depending on geographic regions (e.g., countries) of the world. Therefore, wireless devices such as cellular phones need to include filters for passing frequencies of radio frequency (RF) signals in certain ranges while blocking other ranges throughout the world.

[0003] Microacoustic filters use surface acoustic wave (SAW) resonators or bulk acoustic wave (BAW) resonators to filter the frequencies sent and received by wireless devices. Microacoustic filters convert input RF signals into acoustic waves, filter the acoustic waves, and convert the filtered acoustic waves into output RF signals. The input RF signal is provided to electrodes separated by layers of piezoelectric material, which expands and contracts in response to the input RF signal to generate acoustic waves. The frequency of the acoustic wave resonating in the layer stack of the BAW device is inversely proportional to the combined thickness of the electrode and the piezoelectric layer. As cellular technology evolves from 5G to 6G and 7G, the operating frequency will exceed 10GHz. Therefore, the frequency filtered by the microacoustic resonator will increase, and, using traditional BAW devices, the electrodes and piezoelectric layers will have to continue to become thinner. However, as the layers become thinner, ohmic losses and power density increase, breakdown voltage decreases, and manufacturability becomes more challenging. Therefore, in order to achieve 6G and 7G operating frequencies, BAW devices are needed that can operate at such frequencies without significantly thinning the electrode and piezoelectric layers of the layer stack. Summary of the invention

[0004] Various aspects of the disclosure herein include a bulk acoustic wave (BAW) device having oppositely polarized piezoelectric layers for higher order resonances. A method of manufacturing a BAW device having oppositely polarized piezoelectric layers is also disclosed. In an exemplary aspect, a layer stack of an exemplary BAW device includes a first layer of piezoelectric material ("first piezoelectric layer") and a second layer of piezoelectric material adjacent to the first piezoelectric layer ("second piezoelectric layer"). The second piezoelectric layer has a crystal structure with a polarization opposite to the polarization of the crystal structure of the first piezoelectric layer. In an exemplary aspect, the oppositely polarized crystal structures in the first piezoelectric layer and the second piezoelectric layer enable resonance in a higher order mode, thereby operating at a higher frequency without thinning the layers in the layer stack.

[0005] In some examples, the BAW device is a two-terminal device. In this regard, the BAW device has a first electrode adjacent to the first piezoelectric layer and a second electrode adjacent to the second piezoelectric layer. In one example, the first electrode and the second electrode are adjacent to the outer surfaces of the corresponding first and second piezoelectric layers. The first electrode and the second electrode are configured to be coupled to the first terminal and the second terminal. Applying a voltage difference between the first terminal and the second terminal generates an electric field in the layer stack of the BAW device, which causes opposite responses (e.g., expansion and contraction) in the first piezoelectric layer and the second piezoelectric layer, eliminating the first-order resonance and achieving the second-order resonance. In another exemplary aspect, the layer stack of the BAW device does not include a third electrode configured to be coupled to the third terminal between the first piezoelectric layer and the second piezoelectric layer. In this example, the layer stack of the BAW device is used as a single resonant cavity between the first electrode and the second electrode, rather than as two resonant cavities, and the two resonant cavities will be operated using the third electrode.

[0006] In other examples, the layer stack of the BAW device includes one or more intermediate layers arranged between a first piezoelectric layer and a second piezoelectric layer. The one or more intermediate layers may include at least one amorphous layer to reduce the transfer of crystal structure information from the first piezoelectric layer during the formation of the second piezoelectric layer, thereby enabling the formation of a crystal structure having a polarization opposite to that of the first piezoelectric layer in the second piezoelectric layer. For example, the distance between the first piezoelectric layer and the second piezoelectric layer is less than four percent (4%) of the thickness of the layer stack. In this way, the addition of one or more intermediate layers enables the formation of an opposite crystal structure of the second piezoelectric layer while minimizing the increase in the thickness of the layer stack to avoid a decrease in the resonant frequency.

[0007] In this regard, in one aspect, a two-terminal BAW device is disclosed. The two-terminal BAW device includes a layer stack, the layer stack including a first electrode configured to be coupled to a first terminal and a second electrode configured to be coupled to a second terminal. The layer stack also includes a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer including a first crystal structure having a first polarization, and a second piezoelectric layer between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a second crystal structure having a second polarization opposite to the first polarization.

[0008] In another aspect, a BAW device comprising a layer stack is disclosed. The layer stack comprises a first electrode, a second electrode, and a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer comprising a first crystal structure having a first polarization. The layer stack also comprises a second piezoelectric layer between the first piezoelectric layer and the second electrode, the second piezoelectric layer comprising a second crystal structure having a second polarization opposite to the first polarization. The layer stack also comprises: at least one intermediate layer between the first piezoelectric layer and the second piezoelectric layer, wherein a distance between the first piezoelectric layer and the second piezoelectric layer is less than four percent (4%) of a total thickness of the layer stack.

[0009] In another aspect, a two-terminal BAW device is disclosed. The two-terminal BAW device includes a layer stack. The layer stack includes a first unit for receiving a first voltage, a second unit for receiving a second voltage, and a first crystal unit having a first polarization and arranged between the first unit for receiving the first voltage and the second unit for receiving the second voltage. The layer stack also includes a second crystal unit, the second crystal unit having a second polarization opposite to the first polarization and arranged between the first crystal unit and the second unit for receiving the second voltage. The difference between the first voltage and the second voltage excites an acoustic wave in the first crystal unit and the second crystal unit.

[0010] In another aspect, a BAW device is disclosed. The BAW device includes a layer stack. The layer stack includes a first unit for receiving a first voltage, a second unit for receiving a second voltage, and a first crystal unit having a first polarization and arranged between the first unit for receiving the first voltage and the second unit for receiving the second voltage. The layer stack includes a second crystal unit having a second polarization opposite to the first polarization and arranged between the first crystal unit and the second unit for receiving the second voltage, and at least one intermediate unit between the first crystal unit and the second crystal unit. The distance between the first crystal unit and the second crystal unit is less than four percent (4%) of the total thickness of the layer stack.

[0011] In another exemplary aspect, a method of manufacturing a two-terminal BAW device is disclosed. The method includes forming a layer stack, the layer stack including a first electrode configured to be coupled to a first terminal and a second electrode configured to be coupled to a second terminal. The layer stack also includes a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer including a piezoelectric material having a first crystal structure with a first polarization; and a second piezoelectric layer between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a piezoelectric material having a second crystal structure, the second crystal structure having a second polarization opposite to the first polarization. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1is a cross-sectional view of an exemplary bulk acoustic wave (BAW) device in a fixed mounted resonator (SMR) example, wherein the layer stack includes a first piezoelectric layer and a second piezoelectric layer having opposite crystal polarizations for higher order operation;

[0013] Figure 2 It is used to manufacture Figure 1 A high-level flow chart of a method for a BAW device in FIG.

[0014] Figure 3A-3H Is manufacturing Figure 1 A detailed flow chart of an exemplary method for a BAW device in Figure 4A-4H The stage in

[0015] Figure 4A-4H yes Figure 1 Schematic diagram of a cross-section of a BAW device during the manufacturing stage;

[0016] Figure 5 is a cross-sectional view of a BAW device including an exemplary layer stack in an example of a film bulk acoustic wave resonator (FBAR), wherein the layer stack includes a first piezoelectric layer and a second piezoelectric layer having opposite crystal polarizations;

[0017] Figure 6 Yes, it can include Figure 1 A block diagram of an exemplary wireless communication device including a BAW device; and

[0018] Figure 7 Yes, it can include Figure 1 Block diagram of an exemplary processor-based system with BAW devices. DETAILED DESCRIPTION

[0019] With reference now to the accompanying drawings, several exemplary aspects of the present disclosure are 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.

[0020] Various aspects of the disclosure herein include a bulk acoustic wave (BAW) device having oppositely polarized piezoelectric layers for higher order resonances. A method of manufacturing a BAW device having oppositely polarized piezoelectric layers is also disclosed. In an exemplary aspect, a layer stack of an exemplary BAW device includes a first layer of piezoelectric material ("first piezoelectric layer") and a second layer of piezoelectric material adjacent to the first piezoelectric layer ("second piezoelectric layer"). The second piezoelectric layer has a crystal structure with a polarization opposite to the polarization of the crystal structure of the first piezoelectric layer. In an exemplary aspect, the oppositely polarized crystal structures in the first piezoelectric layer and the second piezoelectric layer enable resonance in a higher order mode, thereby operating at a higher frequency without thinning the layers in the layer stack.

[0021] In some examples, the BAW device is a two-terminal device. In this regard, the BAW device has a first electrode adjacent to the first piezoelectric layer and a second electrode adjacent to the second piezoelectric layer. In one example, the first electrode and the second electrode are adjacent to the outer surfaces of the corresponding first and second piezoelectric layers. The first electrode and the second electrode are configured to be coupled to the first terminal and the second terminal. Applying a voltage difference between the first terminal and the second terminal generates an electric field in the layer stack of the BAW device, which causes opposite responses (e.g., expansion and contraction) in the first piezoelectric layer and the second piezoelectric layer, eliminating the first-order resonance and achieving the second-order resonance. In another exemplary aspect, the layer stack of the BAW device does not include a third electrode configured to be coupled to the third terminal between the first piezoelectric layer and the second piezoelectric layer. In this example, the layer stack of the BAW device is used as a single resonant cavity between the first electrode and the second electrode, rather than as two resonant cavities, and the two resonant cavities will be operated using the third electrode.

[0022] In other examples, the layer stack of the BAW device includes one or more intermediate layers arranged between a first piezoelectric layer and a second piezoelectric layer. The one or more intermediate layers may include at least one amorphous layer to reduce the transfer of crystal structure information from the first piezoelectric layer during the formation of the second piezoelectric layer, thereby enabling the formation of a crystal structure having a polarization opposite to that of the first piezoelectric layer in the second piezoelectric layer. For example, the distance between the first piezoelectric layer and the second piezoelectric layer is less than four percent (4%) of the thickness of the layer stack. In this way, the addition of one or more intermediate layers enables the formation of an opposite crystal structure of the second piezoelectric layer while minimizing the increase in the thickness of the layer stack to avoid a decrease in the resonant frequency.

[0023] As used herein, the term “BAW device” includes a BAW resonator and a BAW filter employing the BAW resonator. Figure 1 The exemplary BAW resonator 100 (“BAW device 100”) shown includes a layer stack 102 configured to resonate in a high-order mode in response to a radio frequency (RF) input signal that provides an oscillating voltage V between a first electrode 104A and a second electrode 104B of the layer stack 102. IN . Oscillation voltage V IN A changing electric field E100 is generated in the layer stack 102. The layer stack 102 includes a first piezoelectric layer 106A and a second piezoelectric layer 106B, which are layers of piezoelectric material that expand and contract in response to the electric field E100. The first piezoelectric layer 106A is between the first electrode 104A and the second electrode 104B, and the second piezoelectric layer 106B is between the first piezoelectric layer 106A and the second electrode 104B. Therefore, the electric field E100 between the first and second electrodes 104A and 104B is applied to both the first and second piezoelectric layers 106A and 106B, causing them to respond to the oscillating voltage VIN The molten metal 200 expands and contracts, thereby generating sound waves in the layer stack 102 .

[0024] The first electrode 104A and the second electrode 104B are provided with a voltage V IN The first electrode 104A and the second electrode 104B are on the outer surfaces 108A and 108B of the piezoelectric layers 106A and 106B, respectively. The first electrode 104A and the second electrode 104B are configured to be coupled to a first terminal (not shown) and a second terminal (not shown), respectively, to receive a voltage V IN . In some examples, the first electrode 104A and the second electrode 104B can be a first terminal and a second terminal. The first electrode 104A and the second electrode 104B have sufficient thickness to minimize ohmic losses, avoid high power density, and maintain a high Q value in the BAW device 100. The metal layer configured as an electrode in the BAW resonator has a thickness of at least 15 nanometers (nm). For example, the thickness of the first electrode 104A can be in the range of 50-150nm, and more specifically about 100nm, and the thickness of the first piezoelectric layer 106A is in the range of 200-300nm, and more specifically about 255nm. The first and second electrodes 104A and 104B having greater thickness also improve heat dissipation from the first and second piezoelectric layers 106A and 106B. A metal layer configured as an electrode in a BAW device is also configured to couple to a terminal, wherein the metal layer includes lateral regions configured to couple to thicker metal regions, input / output (I / O) pads, vertical interconnect through-holes (vias), or a trace coupled to another component.

[0025] Some conventional BAW filters having multiple piezoelectric layers include a third (middle) electrode between the piezoelectric layers to control the piezoelectric layers individually, or work together with electrodes on the outer surfaces (e.g., corresponding to outer surfaces 108A and 108B) to cooperatively control the oscillation of the entire layer stack. However, the layer stack 102 in the BAW device 100 does not include a metal layer configured to couple to the electrode and the third terminal because the BAW device 100 is a two-terminal BAW device. In other words, the voltage V applied to the first electrode 104A and the second electrode 104B is IN It is the only RF signal applied for controlling the BAW device 100 , and there is no third electrode in the BAW device 100 through which another electrical signal is received.

[0026] The first and second piezoelectric layers 106A and 106B can be designed to operate in a similar but complementary manner to achieve higher order resonances in the layer stack 102. To this end, the first piezoelectric layer 106A and the second piezoelectric layer 106B can be formed of the same piezoelectric material 110 (e.g., aluminum scandium nitride (AlScN), specifically AlSc30N, or other piezoelectric materials can be used in addition or alternatively). In another aspect, the thickness T of the first piezoelectric layer 106A is 106A The thickness T of the second piezoelectric layer 106B may be 106B Alternatively, the thickness T of the second piezoelectric layer 106B is 106B The thickness T of the first piezoelectric layer 106A may be 106A The thickness T is in the range of 90% to 110%, so that the first and second piezoelectric layers 106A and 106B have resonant frequency ranges that are similar or overlap with each other. 106A and T 106B is the thickness T of the layer stack 102 102 The thickness T of the layer stack 102 is measured in the corresponding direction. 102 The thickness T of the first and second piezoelectric layers 106A and 106B is 106A and T 106B , the thickness T of the first electrode 104A 104A and the thickness T of the second electrode 104B 104B .

[0027] Although the first and second piezoelectric layers 106A and 106B may be formed of the same piezoelectric material 110 and may have the same or similar thickness T 106A and T 106B , but the second piezoelectric layer 106B has a crystal polarization P2 in a direction opposite to the crystal polarization P1 of the first piezoelectric layer 106A. Specifically, the piezoelectric material 110 of the first and second piezoelectric layers 106A and 106B is formed (e.g., grown) in a lattice structure in which atoms are oriented in a particular direction, which is called polarization. As explained in more detail below, making the polarizations P1 and P2 of the first and second piezoelectric layers 106A and 106B opposite to each other includes growing the piezoelectric material 110 of the second piezoelectric layer 106B on the first piezoelectric layer 106A.

[0028] The opposite polarization of the first and second piezoelectric layers 106A and 106B causes them to have equal responses to the electric field E100, but in opposite directions. In a device having two piezoelectric layers (106A and 106B) that expand and contract independently, the fundamental (first order) mode of operation is not well supported. However, the response of the two piezoelectric layers (106A and 106B) that are equal in size due to the same thickness is compatible with resonance in higher order modes at twice the fundamental resonant frequency. BAW devices typically have a wavelength of twice the length of the acoustic cavity of the layer stack 102 at a frequency that resonates in the fundamental mode. In higher order modes, such as the second harmonic where the resonant frequency is doubled, the resonant frequency wavelength is the same or approximately the same as the acoustic cavity length. The acoustic cavity length of the layer stack 102 in the BAW device 100 is based on the acoustic velocity of the metal forming the first electrode 104A and the second electrode 104B, the piezoelectric material 110 forming the first piezoelectric layer 106A and the second piezoelectric layer 106B, and the respective thicknesses of the layers of the layer stack 102 (e.g., T 104A , T 104B , T 106A and T 106B The acoustic cavity length can also be described based on the corresponding acoustic impedance of each layer of the layer stack 102.

[0029] The expansion and contraction of the first and second piezoelectric layers 106A and 106B in (approximately) equal and opposite manners causes them to cancel each other out. Achieving this behavior may include forming the second piezoelectric layer 106B to have the same crystal structure of the same piezoelectric material 110 grown under the same conditions to the same thickness but with opposite polarization relative to the first piezoelectric layer 106A. However, it may also be possible to achieve this behavior by forming the second piezoelectric layer 106B of a different piezoelectric material 110, which may have a different thickness but still have opposite polarization to achieve the desired equal but opposite response to the electric field. In such an example, the piezoelectric material 110 and thickness may be selected based on the speed of sound, which affects the length of the acoustic cavity.

[0030] Figure 1 The BAW device 100 in FIG. 1 is an example in which a layer stack 102 is employed in a fixed mounted resonator (SMR). In this regard, the layer stack 102 is coupled to or mounted on an acoustic mirror 112 (e.g., a Bragg mirror), which is further coupled to a target substrate 114. The acoustic mirror 112 includes a high acoustic impedance layer 116, such as tungsten (W), within an amorphous layer 118, the amorphous layer having a lower acoustic impedance than the acoustic impedance layer 116. For example, the amorphous layer 118 can be silicon dioxide (SiO2). The target substrate 114 can be any suitable material, such as glass or silicon.

[0031] Figure 1 The layer stack 102 in may also include one or more intermediate layers 120, 122, and 124 between the first piezoelectric layer 106A and the second piezoelectric layer 106B. Alternatively, a BAW device as disclosed herein may have no intermediate layers.

[0032] If you will refer to Figure 4A-4H As described in the manufacturing stages 400A-400H in the embodiment of the present invention, one or more intermediate layers 120, 122 and 124 are residual layers for manufacturing a second piezoelectric layer 106B having a desired polarization on the first piezoelectric layer 106A. In order to manufacture the layer stack 102 so that the second piezoelectric layer 106B has a crystal polarization P2 opposite to the polarization P1 of the first piezoelectric layer 106A, the first piezoelectric layer 106A is first grown on the target substrate 114 under specific conditions according to the method 300. Subsequently, the conditions used to grow the first piezoelectric layer 106A can be reproduced for growing the second piezoelectric layer 106B on the first piezoelectric layer 106A.

[0033] When a lattice structure (crystal) is grown on an existing crystal, information about the crystal structure is transferred from the existing crystal to the growing crystal. For example, if the growing crystal has a different geometry than the existing crystal (e.g., a larger or smaller lattice constant), the growing crystal may have irregularities that weaken the structure and affect the electrical properties. The existing crystal may also affect the geometry of the growing crystal, at least initially. As the growing crystal thickens, the lattice structure may become more regular, but irregularities may extend from the boundaries to the existing crystal. When the goal is to grow a crystal with a small thickness on an existing crystal, a method is used to avoid the transfer of crystal information from the existing crystal to the growing crystal. In this regard, in an exemplary aspect, on a first substrate ( Figure 1After growing the first piezoelectric layer 106A on the inner surface 109A of the first piezoelectric layer 106A (not shown) and growing the first electrode 104A on the outer surface 108A, the first substrate is removed from the inner surface 109A of the first piezoelectric layer 106A, and the second piezoelectric layer 106B is grown on the inner surface 109A of the first piezoelectric layer 106A. One or more intermediate layers 120, 122, 124 may be used to avoid the transfer of crystal information from the first piezoelectric layer 106A and to reconstruct the conditions when the first piezoelectric layer 106A was grown. The intermediate layer 120 may be an amorphous layer, such as titanium nitride (TiN) formed on the first piezoelectric layer 106A, to act as a buffer from the lattice structure of the crystal forming the first piezoelectric layer 106A. An intermediate layer 122 may be further used on the intermediate layer 120 to more tightly produce an amorphous layer on which the first piezoelectric layer 106A is grown, as described below. For example, the intermediate layer 122 may be an amorphous SiO2 layer. The intermediate layer 124 is a seed layer provided on the intermediate layer 122 to establish a specific crystal orientation (and polarization) of the second piezoelectric layer 106B. By growing the second piezoelectric layer 106B on the first piezoelectric layer 106A in this manner, the polarization of the crystals of the second piezoelectric layer 106B can be opposite to the polarization of the crystals of the first piezoelectric layer 106A.

[0034] As disclosed herein, a two-terminal BAW device 100 includes a layer stack 102 including a first voltage V IN+ The first unit and the second unit for receiving the second voltage V IN- The second unit. Signal voltage V IN is the first voltage V IN+ and the second voltage V IN- The layer stack 102 includes a first polarization P1 and is arranged to receive a first voltage V IN+ The first unit and the second unit for receiving the second voltage V IN- The layer stack 102 also includes a first crystal unit having a second polarization P2 opposite to the first polarization P1 and arranged for receiving a first voltage V IN+ The first unit and the second unit for receiving the second voltage V IN- The second crystal unit between the second unit. The first voltage V IN+ and the second voltage V IN- The difference between the first and second crystal units excites acoustic waves.

[0035] In some examples, the BAW device 100 includes a layer stack 102 including a first voltage V IN+ The first unit and the second unit for receiving the second voltage V IN- The second unit. Signal voltage V IN is the first voltage V IN+ and the second voltage VIN- The BAW device 100 includes a first polarization P1 and is arranged to receive a first voltage V IN+ The first unit and the second unit for receiving the second voltage V IN- The layer stack 102 also includes a first crystal unit having a second polarization P2 opposite to the first polarization P1 and arranged for receiving a first voltage V IN+ The first unit and the second unit for receiving the second voltage V IN- The second crystal unit between the second unit. The first voltage V IN+ and the second voltage V IN- The difference between the first and second crystal units excites acoustic waves in the first and second crystal units. The stacked layer 102 also includes at least one intermediate unit between the first and second crystal units. The distance between the first and second crystal units is less than the total thickness T of the stacked layer 102. 102 Four percent (4%) of

[0036] Figure 2 It is used to manufacture Figure 1 A high-level flow chart of a method 200 for a BAW device 100 in FIG. 1 . The method 200 includes forming a layer stack 102 (block 202), including: forming a first electrode 104A configured to be coupled to a first terminal (block 204), forming a second electrode 104B configured to be coupled to a second terminal (block 206), and forming a first piezoelectric layer 106A between the first electrode 104A and the second electrode 104B, the first piezoelectric layer 106A including a piezoelectric material 110 having a first crystal structure with a first polarization P1 (block 208). Forming the layer stack 102 also includes: forming a second piezoelectric layer 106B between the first piezoelectric layer 106A and the second electrode 104B, the second piezoelectric layer 106B including a second crystal structure with a second polarization P2 opposite to the first polarization P1 (block 210). Optionally, in Figure 1 In the case where the BAW device 100 in EMBODIMENT 1 comprises an SMR BAW device, the method 200 further includes forming an acoustic mirror 112 on the first electrode 104A (block 212 ), and coupling the target substrate 114 to the acoustic mirror 112 (block 214 ).

[0037] Figure 3A-3H is a flow chart of method 300, further detailing the method for manufacturing Figure 1 A method 200 is provided for use in a BAW device 100. Figure 4A-4H is a cross-sectional view of the BAW device 100 at manufacturing stages 400A- 400H corresponding to the method 300 . Figure 4A-4H The feature numbers of the BAW device 100 shown in FIG. Figure 1 Same as in. Figure 4A-4HDimensions (eg, thickness) of layers shown in the drawings may not be drawn to scale and, for ease of illustration, may be shown herein as larger or smaller than actual sizes relative to other features.

[0038] exist Figure 3A In the method 300, forming the first piezoelectric layer 106A of the BAW device includes: forming a first seed layer 404 on a sacrificial substrate 402 (block 302), such as Figure 4A As shown. The sacrificial substrate 402 can be an amorphous source substrate, such as glass, silicon, or another suitable material that can be selected for easier grinding and / or crystal structure neutrality. The first seed layer 404 can be formed by a material 406 that causes the desired crystal structure orientation (e.g., polarization) of the piezoelectric material 110 in the first piezoelectric layer 106A. Growing the first seed layer 404 to at least about ten (10) nm thick can ensure that the inner surface 109A of the first seed layer 404 has established a uniform crystal orientation. The first seed layer 404 can be selected to have large main grains, which produce self-oriented growth. For example, for the piezoelectric material 110, the material 406 of the first seed layer 404 can be aluminum nitride (AlN). For example, the process for forming the seed layer 404 can include sputtering, pulsed laser deposition (PLD) and / or metal organic chemical vapor deposition (MOCVD).

[0039] although Figure 4A 4, but before forming the first seed layer 404 on (e.g., directly on) the other amorphous layer 410, another amorphous layer 410, which may be another amorphous material, such as SiO2, may be formed on (e.g., directly on) the sacrificial substrate 402. As further explained below, adding the other amorphous layer 410 simplifies the removal of the sacrificial substrate 402 without damaging the first piezoelectric layer 106A. Adding the other amorphous layer 410 also isolates the first seed layer 404 from any crystalline structural information that may be transferred from the sacrificial substrate 402.

[0040] For example, the phrases "directly on" and "in direct contact with" as used herein with reference to two layers indicate that there are no intervening layers or other materials between the two layers.

[0041] exist Figure 3B In the process, forming the first piezoelectric layer 106A further includes forming a piezoelectric material 110 on the sacrificial substrate 402 (block 304), which may also include forming a piezoelectric material 110 on the first seed layer 404 (block 306), such as Figure 4B The piezoelectric material 110 can be grown directly on the first seed layer 404 to a thickness T in an epitaxial process. 106AGrowing the piezoelectric material 110 on the first seed layer 404 produces a crystal structure with a specific polarization, which is based on the crystal orientation information of the first seed layer 404 transferred to the piezoelectric material 110. For example, the crystals of the first piezoelectric layer 106A may have a polarization P1 in the Y-axis direction (e.g., perpendicular to the first seed layer 404). Figure 4B As shown, the Y-axis direction in this figure is orthogonal to the first piezoelectric layer 106A.

[0042] Figure 3C The forming of the first electrode 104A includes forming a metal layer configured as an electrode on the outer surface 108A of the first piezoelectric layer 106A (block 308), such as Figure 4C As shown in the manufacturing stage 400C. As described above, the first electrode 104A has a high conductivity and a thickness T 104A A layer of conductive metal (e.g., Mo) with a thickness T 104A is the thickness T of the first piezoelectric layer 106A 106A In the case of an SMR BAW device, forming the BAW device 100 also includes the additional optional steps of forming an acoustic mirror 112 on the first electrode 104A (block 310) and coupling a target substrate 114 to the acoustic mirror 112 (block 312). Coupling the target substrate 114 to the acoustic mirror 112 may include bonding the target substrate 114 to the acoustic mirror 112.

[0043] Figure 3D An optional step (block 314) is included to flip the BAW device 100 for top-side processing, such as Figure 4D The manufacturing stage 400D is shown in FIG. Figure 4D , flipping of the BAW device 100 illustrates the transfer of processing from the sacrificial substrate 402 to the target substrate 114 to allow for top-side processing. In some examples, flipping the BAW device 100 at the manufacturing stage 400D may not be necessary to perform processing as disclosed herein.

[0044] Figure 3E The formation of the second piezoelectric layer 106B includes removing the sacrificial substrate 402 and the first seed layer 404 from the first piezoelectric layer 106A (block 316), as shown in FIG. Figure 4E The manufacturing stage 400E is shown in the above Figure 4A In the example discussed, in which another amorphous layer 410 (e.g., SiO2) is formed on the sacrificial substrate 402 before the first seed layer 404 is formed on the sacrificial substrate 402, the additional amorphous layer 410 is also removed. The sacrificial substrate 402, the first seed layer 404, and the optional additional amorphous layer 410 can be removed from the first piezoelectric layer 106A by one or more of grinding, spin etching, and other suitable processes to expose the inner surface 109A of the first piezoelectric layer 106A.

[0045] Figure 3F It is shown that forming the second piezoelectric layer 106B also includes forming one or more intermediate layers 120, 122, 124, such as Figure 4F In some examples, if the second piezoelectric layer 106B has a polarization P2 opposite to the polarization P1 of the first piezoelectric layer 106A (see Figure 4G ) can be grown directly on the first piezoelectric layer 106A, and one or all of the intermediate layers 120, 122, 124 may not be required. Figure 3F In Figure 4F As shown, forming the second piezoelectric layer 106B includes: forming a second seed layer 124 (intermediate layer 124) on the inner surface 109A of the first piezoelectric layer 106A (box 318). As previously described, the second seed layer 124 provides orientation for the crystal structure of the second piezoelectric layer 106B. However, in some examples, forming the second seed layer 124 directly on the inner surface 109A of the first piezoelectric layer 106A may allow some crystal structure information to be transmitted from the piezoelectric material 110 in the first piezoelectric layer 106A to the second seed layer 124, and then to the piezoelectric material 110 of the second piezoelectric layer 106B. Such crystal structure information may interfere with the formation of a second piezoelectric layer 106B having a polarization P2 that is opposite to the polarization P1 of the first piezoelectric layer 106A (e.g., in direction).

[0046] Therefore, at least to reduce or avoid the transmission of such crystal structure information, in some examples, forming the second piezoelectric layer 106B further includes: forming a first amorphous layer 120 (intermediate layer 120) in direct contact with the inner surface 109A of the first piezoelectric layer 106A (block 318) and forming a second seed layer 124 (block 320) on the first amorphous layer 120. Forming the second seed layer 124 on the first amorphous layer 120 may include: forming the second seed layer 124 directly on the first amorphous layer 120.

[0047] However, in some examples, it may be desirable to further isolate the second seed layer 124 from the first piezoelectric layer 106A to further reduce or avoid the transmission of crystal structure information from the first piezoelectric layer 106A to the second piezoelectric layer 106B, and to more clearly replicate the conditions of the piezoelectric material 110 that formed the first piezoelectric layer 106A. Therefore, in the above example, in which the additional amorphous layer 410 is formed on the sacrificial substrate 402 before forming the first seed layer 404, the intermediate layer 122 is a second amorphous layer included on the first amorphous layer 120 before forming the second seed layer 124. Therefore, the formation Figure 3FThe second piezoelectric layer 106B in the embodiment may also include: forming a second amorphous layer 122 in direct contact with the first amorphous layer 120 and forming a second seed layer 124 in direct contact with the second amorphous layer 122 (box 322). In addition, in some examples, forming the first amorphous layer 120, the second amorphous layer 122, and the second seed layer 124 also includes: forming the first amorphous layer 120, the second amorphous layer 122, and the second seed layer 124 to have a total combined thickness of less than four percent (4%) of the total thickness of the layer stack 102.

[0048] exist Figure 3G In Figure 4G As shown in manufacturing stage 400G in FIG. 4 , forming the second piezoelectric layer 106B includes: forming a piezoelectric material 110 (324) on the inner surface 109A of the first piezoelectric layer 106A, which further includes: forming the piezoelectric material 110 directly on the second seed layer 124 (box 326). The piezoelectric material 110 of the second piezoelectric layer 106B grows on the second seed layer 124 with a polarization P2 opposite to the polarization P1 of the first piezoelectric layer 106A. The conditions used to grow the piezoelectric material 110 of the first piezoelectric layer 106A on the first seed layer 404 are replicated for growing the piezoelectric material 110 of the second piezoelectric layer 106B on the second seed layer 124. In this way, the crystal structures of the first piezoelectric layer 106A and the second piezoelectric layer 106B are made as similar as possible. The second piezoelectric layer 106B is grown on the inner surface 109A of the first piezoelectric layer 106A, which is the back side of the first piezoelectric layer 106A and is exposed by flipping during the layer transfer of the first piezoelectric layer 106A from the first substrate to the target substrate 114. Growing the piezoelectric material 110 of the second piezoelectric layer 106B on the inner surface 109A (i.e., the back side) of the first piezoelectric layer 106A causes the piezoelectric material 110 of the second piezoelectric layer 106B to grow with a polarization opposite to that of the first piezoelectric layer 106A, which means that the polarizations P1 and P2 of the first piezoelectric layer 106A and the second piezoelectric layer 106B are opposite to each other. Therefore, the crystal structures of the first piezoelectric layer 106A and the second piezoelectric layer 106B will have almost the same but opposite reactions to the applied electric field.

[0049] exist Figure 3H In the method 300, the method 300 includes: forming the second electrode 104B on the second piezoelectric layer 106B (block 328), which further includes: forming a second metal layer configured as an electrode on the second piezoelectric layer 106B (block 330). The second electrode 104B and the first electrode 104A are metal layers configured as electrodes that are further configured to be coupled to a terminal. Forming the layer stack 102 according to the method 300 does not include: forming a metal layer configured as an electrode between the first piezoelectric layer 106A and the second piezoelectric layer 106B.

[0050] Figure 5is a cross section of a BAW device 500, which is Figure 1 The layer stack 502 corresponding to the layer stack 102 is implemented as an example of a thin film bulk acoustic wave resonator (FBAR). The BAW device 500 includes a substrate 504, which can be formed to define an air cavity 506 between the first electrode 104A and the substrate 504. Alternatively, a frame 508 can be arranged between the substrate 504 and the first electrode 104A to form the air cavity 506. In this example, a membrane 510 can be arranged between the first electrode 104A and the substrate 504, and specifically between the first electrode 104A and the air cavity 506. The layer stack 502 of the BAW device 500 is the same as the layer stack 102 described in detail above.

[0051] According to aspects disclosed herein, a two-terminal BAW device having a second piezoelectric layer polarized opposite to the polarization of the first piezoelectric layer can be provided in or integrated into any processor-based device. Examples include, but are not limited to, 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, smart phones, session initiation protocol (SIP) phones, tablets, phablets, servers, computers, portable computers, mobile computing devices, wearable computing devices (e.g., smart watches, health or fitness trackers, glasses, etc.), desktop computers, personal digital assistants (PDAs), monitors, computer monitors, televisions, tuners, radio units, satellite radio units, music players, digital music players, portable music players, digital video disc (DVD) players, portable digital video players, automobiles, vehicle components, avionics systems, drones, and multirotors.

[0052] Figure 6 An exemplary wireless communication device 600 is shown that includes radio frequency (RF) components formed from one or more integrated circuits (ICs) 602 and may include, for example, Figure 1 and Figure 5 As shown in the exemplary two-terminal BAW device according to any aspect disclosed herein, the two-terminal BAW device has a polarization of the second piezoelectric layer opposite to the polarization of the first piezoelectric layer. As an example, the wireless communication device 600 may include or be provided in any of the above-mentioned devices. Figure 6As shown, the wireless communication device 600 includes a transceiver 604 and a data processor 606. The data processor 606 may include a memory for storing data and program codes. The transceiver 604 includes a transmitter 608 and a receiver 610 that support two-way communication. In general, the wireless communication device 600 may include any number of transmitters 608 and / or receivers 610 for any number of communication systems and frequency bands. All or part of the transceiver 604 may be implemented on one or more analog ICs, RFICs, mixed signal ICs, etc.

[0053] The transmitter 608 or the receiver 610 may be implemented using 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, for example, 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 may use different circuit blocks and / or have different requirements. Figure 6 In the wireless communication device 600 in FIG. 1 , the transmitter 608 and the receiver 610 are implemented using a direct conversion architecture.

[0054] In the transmit path, the data processor 606 processes data to be transmitted and provides I and Q analog output signals to a transmitter 608. In the exemplary wireless communication device 600, the data processor 606 includes digital-to-analog converters (DACs) 612(1), 612(2) for converting digital signals generated by the data processor 606 into I and Q analog output signals, such as I and Q output currents, for further processing.

[0055] Within the transmitter 608, low pass filters 614(1), 614(2) filter the I and Q analog output signals, respectively, to remove undesired signals caused by the previous digital-to-analog conversion. Amplifiers (AMPs) 616(1), 616(2) amplify the signals from the low pass filters 614(1), 614(2), respectively. An up converter 618 up-converts the I and Q baseband signals with I and Q TX local oscillator (LO) signals from a transmit (TX) local oscillator (LO) signal generator 622 via mixers 620(1), 620(2) to provide an up-converted signal 624. A filter 626 filters the up-converted signal 624 to remove undesired signals caused by the up-conversion and noise in the receive frequency band. A power amplifier (PA) 628 amplifies the up-converted signal 624 from the filter 626 to obtain a desired output power level and provides a transmit RF signal. The transmit RF signal is routed through a duplexer or switch 630 and sent via an antenna 632. Either of the low pass filters 614(1) and 614(2) or the filter 626 may be a BAW filter package 603.

[0056] In the receive path, antenna 632 receives signals transmitted by a base station and provides a received RF signal, which is routed through a duplexer or switch 630 and provided to a low noise amplifier (LNA) 634. The duplexer or switch 630 is designed to operate with a specific receive (RX) to TX duplexer frequency separation so that the RX signal is isolated from the TX signal. The received RF signal is amplified by LNA 634 and filtered by filter 636 to obtain the desired RF input signal. Down-conversion mixers 638 (1), 638 (2) mix the output of filter 636 with the I and Q RX LO signals (i.e., LO_I and LO_Q) from RX LO signal generator 640 to generate I and Q baseband signals. The I and Q baseband signals are amplified by AMPs 642 (1), 642 (2) and further filtered by low pass filters 644 (1), 644 (2) to obtain I and Q analog input signals that can be provided to data processor 606. Any of the filter 636 and the low pass filters 644(1), 644(2) may be a BAW filter package 603. In this example, the data processor 606 includes analog-to-digital converters (ADCs) 646(1), 646(2) for converting analog input signals into digital signals for further processing by the data processor 606.

[0057] exist Figure 6In the wireless communication device 600 of FIG. 6 , the TX LO signal generator 622 generates I and Q TX LO signals for up-conversion, and the RX LO signal generator 640 generates I or Q RX LO signals for down-conversion. Each LO signal is a periodic signal with a specific base frequency. The TX phase-locked loop (PLL) circuit 648 receives timing information from the data processor 606 and generates a control signal for adjusting the frequency and / or phase of the TX LO signal from the TX LO signal generator 622. Similarly, the RX PLL circuit 650 receives timing information from the data processor 606 and generates a control signal for adjusting the frequency and / or phase of the RX LO signal from the RX LO signal generator 640.

[0058] Figure 7 An example of a processor-based system 700 is shown, including a Figure 1 and Figure 5 Circuitry of an exemplary two-terminal BAW device as shown and in accordance with any aspect disclosed herein, the two-terminal BAW device having a polarization of a second piezoelectric layer opposite to the polarization of a first piezoelectric layer. In this example, a processor-based system 700 includes one or more central processor units (CPUs) 702, which may also be referred to as CPUs or processor cores, each core including one or more processors 704. The CPU 702 may have a cache memory 706 coupled to the processor 704 for quickly accessing temporarily stored data. The CPU 702 is coupled to a system bus 708 and may mutually couple master devices and slave devices included in the processor-based system 700. As is well known, the CPU 702 communicates with these other devices by exchanging address, control, and data information on the system bus 708. For example, as an example of a slave device, the CPU 702 may transmit a bus transaction request to a memory controller 710. Although Figure 7 Although not shown, multiple system buses 708 may be provided, each system bus 708 forming a different structure.

[0059] Other master devices and slave devices may be connected to the system bus 708. Figure 7As shown, as an example, these devices may include a memory system 712, which includes a memory controller 710 and one or more memory arrays 714, one or more input devices 716, one or more output devices 718, one or more network interface devices 720, and one or more display controllers 722. Input device 716 may include any type of input device, including but not limited to input keys, switches, voice processors, etc. Output device 718 may include any kind of output device, including but not limited to audio, video, other visual indicators, etc. Network interface device 720 can be any device configured to allow data to be exchanged with network 724. Network 724 can be any type of network, including but not limited to wired or wireless networks, private or public networks, local area networks (LANs), wireless local area networks (WLANs), wide area networks (WANs), Bluetooth TM Networks and the Internet. Network interface device 720 may be configured to support any type of communication protocol desired.

[0060] The CPU 702 may also be configured to access a display controller 722 via the system bus 708 to control information sent to one or more displays 726. The display controller 722 sends information to the display 726 for display via one or more video processors 728, which processes the information to be displayed into a format suitable for the display 726. The display 726 may 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.

[0061] It will be further understood by those skilled in the art that the various illustrative logic blocks, modules, circuits and algorithms described in conjunction with the various aspects disclosed herein can be implemented as electronic hardware, instructions stored in a memory or another computer-readable medium and executed by a processor or other processing device, or a combination of the two. As an example, the master device and slave device described herein can be adopted in any circuit, hardware component, IC or IC chip. The memory disclosed herein can be a memory of any type and size, and can be configured to store any type of information required. In order to clearly illustrate this interchangeability, the functions of various illustrative components, blocks, modules, circuits and steps are generally described above. How to realize such functions depends on specific applications, design choices and / or design constraints imposed on the entire system. The technician can realize the described functionality in a changing manner for each specific application, but such realization decisions should not be interpreted as causing departure from the scope of the present disclosure.

[0062] The various illustrative logic blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented or performed using 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. The processor may be a microprocessor, but in an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0063] Aspects disclosed herein may be embodied in hardware and instructions stored in hardware, and may reside in, for example, random access memory (RAM), flash memory, read-only memory (ROM), electrically programmable ROM (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, removable disks, CD-ROMs, or any other form of computer-readable medium known in the art. An exemplary storage medium is coupled to a processor so that the processor can read information from the storage medium and write information to the storage medium. In an alternative, the storage medium may be an integral part of the processor. The processor and storage medium may reside in an ASIC. The ASIC may reside in a remote station. Alternatively, the processor and storage medium may reside in a remote station, a base station, or a server as discrete components.

[0064] It should also be noted that the operational steps described in any exemplary aspects of this article are described to provide examples and discussions. The described operations can be performed in many different sequences in addition to the sequence shown. In addition, the operations described in a single operational step can actually be performed in several different steps. In addition, one or more operational steps discussed in the exemplary aspects can be combined. It should be understood that the operational steps shown in the flow chart can be modified in many different ways, which is obvious to those skilled in the art. It will also be understood by those skilled in the art that information and signals can be represented using various technologies and methods. For example, the data, instructions, commands, information, signals, bits, symbols, and chips mentioned throughout the above description can be represented by voltage, current, electromagnetic waves, magnetic fields or particles, light fields or particles, or any combination thereof.

[0065] The foregoing description of the present disclosure is provided to enable those skilled in the art to implement or use the present disclosure. Various modifications to the present disclosure will be apparent to those skilled in the art, and the general principles defined herein may also be applied to other variations. Therefore, the present disclosure is not intended to be limited to the examples and designs described herein, but is given the widest scope consistent with the principles and novel features disclosed herein.

[0066] Example implementations are described in the following numbered clauses: 1. A two-terminal bulk acoustic wave (BAW) device, comprising: A layer stack, the layer stack comprising: a first electrode configured to be coupled to a first terminal; a second electrode configured to be coupled to a second terminal; a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer comprising a first crystal structure having a first polarization; and A second piezoelectric layer is between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a second crystal structure having a second polarization opposite to the first polarization. 2. A two-terminal BAW device according to clause 1, wherein: Between the first piezoelectric layer and the second piezoelectric layer, the layer stack does not include a metal layer configured as an electrode. 3. A two-terminal BAW device according to clause 1 or clause 2, wherein: The first piezoelectric layer and the second piezoelectric layer include the same piezoelectric material. 4. A two-terminal BAW device according to any one of clauses 1 to 3, wherein the layer stack further comprises: at least one intermediate layer between the first piezoelectric layer and the second piezoelectric layer. 5. The two-terminal BAW device of clause 4, wherein the at least one intermediate layer comprises an amorphous layer comprising an amorphous material. 6. A two-terminal BAW device according to clause 5, wherein the amorphous material comprises titanium nitride (TiN). 7. A two-terminal BAW device according to clause 5, wherein the amorphous material comprises silicon dioxide (SiO2). 8. A two-terminal BAW device according to any of clauses 4 to 7, wherein the at least one intermediate layer comprises a seed layer configured to determine the second polarization of the second piezoelectric layer. 9. A two-terminal BAW device according to clause 8, wherein: The second piezoelectric layer includes aluminum scandium nitride (AlScN); and The seed layer includes aluminum nitride (AlN). 10. A two-terminal BAW device according to any one of clauses 1 to 9, wherein: The first electrode is in direct contact with the first piezoelectric layer; and The second electrode is in direct contact with the second piezoelectric layer. 11. A two-terminal BAW device according to any one of clauses 1 to 10, wherein: The first piezoelectric layer comprises a first thickness; and The second piezoelectric layer includes a second thickness in a range from 90% to 110% of the first thickness. 12. A two-terminal BAW device according to any one of clauses 1 to 11, further comprising: an acoustic mirror coupled to the first electrode. 13. A two-terminal BAW device according to any one of clauses 1 to 11, further comprising: substrate; an air cavity between the first electrode and the substrate; and A membrane is between the air cavity and the first electrode. 14. A two-terminal BAW device as described in any one of clauses 1 to 13, integrated into a device selected from the group consisting of: a set-top box; an entertainment unit; a navigation device; a communication device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smartphone; a Session Initiation Protocol (SIP) phone; a tablet computer; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television set; a tuner; a radio unit; a satellite radio unit; 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 vehicle component; an avionics system; an unmanned aerial vehicle; and a multirotor aircraft. 15. A BAW device, comprising: A layer stack, the layer stack comprising: a first electrode; a second electrode; a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer comprising a first crystal structure having a first polarization; a second piezoelectric layer between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a second crystal structure having a second polarization opposite to the first polarization; and at least one intermediate layer between the first piezoelectric layer and the second piezoelectric layer, Therein, a distance between the first piezoelectric layer and the second piezoelectric layer is less than four percent (4%) of a total thickness of the layer stack. 16. A BAW device according to clause 15, wherein: The first piezoelectric layer and the second piezoelectric layer include the same piezoelectric material. 17. A BAW device according to clause 15 or clause 16, wherein a distance between the first piezoelectric layer and the second piezoelectric layer is equal to a thickness of the at least one intermediate layer. 18. A BAW device according to any one of clauses 15 to 17, wherein the at least one intermediate layer comprises a titanium nitride (TiN) layer. 19. A BAW device according to any one of clauses 15 to 18, wherein the at least one intermediate layer comprises a silicon dioxide (SiO2) layer. 20. A BAW device according to any one of clauses 15 to 19, wherein the at least one intermediate layer comprises a seed layer configured to determine the second polarization of the second piezoelectric layer. 21. A BAW device according to clause 20, wherein: The second piezoelectric layer includes aluminum scandium nitride (AlScN); and The seed layer includes aluminum nitride (AlN). 22. The BAW device of any one of clauses 15 to 21, further comprising: an acoustic mirror coupled to the first electrode. 23. A BAW device according to any one of clauses 15 to 21, further comprising: substrate; an air cavity between the first electrode and the substrate; and A membrane is between the air cavity and the first electrode. 24. A method for manufacturing a two-terminal BAW device, the method comprising: Formation stack, including: forming a first electrode configured to be coupled to a first terminal; forming a second electrode configured to be coupled to the second terminal; forming a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer including a first crystal structure having a first polarization; and A second piezoelectric layer is formed between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a second crystal structure having a second polarization opposite to the first polarization. 25. A method according to clause 24, wherein: Forming the first piezoelectric layer includes: forming a piezoelectric material on a sacrificial substrate; Forming the first electrode includes: forming a first metal layer configured as an electrode on an outer surface of the first piezoelectric layer; Forming the second piezoelectric layer includes: removing the sacrificial substrate from the first piezoelectric layer and forming the piezoelectric material on an inner surface of the first piezoelectric layer; and Forming the second electrode includes forming a second metal layer configured as an electrode on the second piezoelectric layer. 26. The method of clause 25, wherein forming the first piezoelectric layer further comprises: forming a first seed layer on the sacrificial substrate; and The piezoelectric material is formed on the first seed layer. 27. The method according to clause 25 or clause 26, wherein forming the second piezoelectric layer further comprises: forming a second seed layer on the inner surface of the first piezoelectric layer; and The piezoelectric material is formed on the second seed layer. 28. The method according to clause 27, further comprising: forming a first amorphous layer in direct contact with the inner surface of the first piezoelectric layer; and The second seed layer is formed on the first amorphous layer. 29. The method according to clause 28, further comprising: forming a second amorphous layer in direct contact with the first amorphous layer; and The second seed layer is formed in direct contact with the second amorphous layer. 30. A method according to clause 29, wherein: Forming the first amorphous layer, the second amorphous layer, and the second seed layer further includes forming the first amorphous layer, the second amorphous layer, and the second seed layer to a total combined thickness of less than four percent (4%) of a total thickness of the layer stack. 31. A method according to any one of clauses 24 to 30, wherein: Forming the layer stack does not include forming a metal layer configured as an electrode between the first piezoelectric layer and the second piezoelectric layer. 32. A method according to any one of clauses 24 to 31, further comprising: forming an acoustic mirror on the first electrode; and A target substrate is formed on the acoustic mirror. 33. A method according to any one of clauses 24 to 31, further comprising: forming a film on the first electrode; forming a substrate on the first electrode; and An air cavity is formed between the first electrode and the substrate. 34. A two-terminal bulk acoustic wave (BAW) device comprising: A layer stack, the layer stack comprising: a first unit for receiving a first voltage; a second unit for receiving a second voltage; a first crystal unit having a first polarization and arranged between the first unit for receiving the first voltage and the second unit for receiving the second voltage; and a second crystal unit having a second polarization opposite to the first polarization and arranged between the first crystal unit and the second unit for receiving the second voltage, The difference between the first voltage and the second voltage excites acoustic waves in the first crystal unit and the second crystal unit. 35. A BAW device, comprising: A layer stack, the layer stack comprising: a first unit for receiving a first voltage; a second unit for receiving a second voltage; a first crystal unit having a first polarization and arranged between the first unit for receiving the first voltage and the second unit for receiving the second voltage; a second crystal unit having a second polarization opposite to the first polarization and arranged between the first crystal unit and the second unit for receiving the second voltage; and at least one intermediate unit between the first crystal unit and the second crystal unit, Wherein a distance between the first crystal unit and the second crystal unit is less than four percent (4%) of a total thickness of the layer stack.

Claims

1. A two-terminal bulk acoustic wave (BAW) device, comprising: A layer stack, the layer stack comprising: a first electrode configured to be coupled to a first terminal; a second electrode configured to be coupled to a second terminal; a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer comprising a first crystal structure having a first polarization; and A second piezoelectric layer is between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a second crystal structure having a second polarization opposite to the first polarization.

2. The two-terminal BAW device according to claim 1, wherein: Between the first piezoelectric layer and the second piezoelectric layer, the layer stack does not include a metal layer configured as an electrode.

3. The two-terminal BAW device according to claim 1, wherein: The first piezoelectric layer and the second piezoelectric layer include the same piezoelectric material.

4. The two-terminal BAW device according to claim 1, wherein: The layer stack further comprises at least one intermediate layer between the first piezoelectric layer and the second piezoelectric layer.

5. The two-terminal BAW device according to claim 4, wherein: The at least one intermediate layer includes an amorphous layer including an amorphous material.

6. The two-terminal BAW device according to claim 5, wherein: The amorphous material includes titanium nitride (TiN).

7. The two-terminal BAW device according to claim 5, wherein: The amorphous material includes silicon dioxide (SiO2).

8. The two-terminal BAW device according to claim 4, wherein: The at least one intermediate layer comprises a seed layer configured to determine the second polarization of the second piezoelectric layer.

9. The two-terminal BAW device of claim 8, wherein: The second piezoelectric layer includes aluminum scandium nitride (AlScN); and The seed layer includes aluminum nitride (AlN).

10. The two-terminal BAW device of claim 1, wherein: The first electrode is in direct contact with the first piezoelectric layer; and The second electrode is in direct contact with the second piezoelectric layer.

11. The two-terminal BAW device of claim 1 , wherein: The first piezoelectric layer comprises a first thickness; and The second piezoelectric layer includes a second thickness in a range from 90% to 110% of the first thickness.

12. The two-terminal BAW device of claim 1, further comprising an acoustic mirror coupled to the first electrode.

13. The two-terminal BAW device of claim 1 , further comprising: substrate; an air cavity between the first electrode and the substrate; as well as A membrane is between the air cavity and the first electrode.

14. The two-terminal BAW device of claim 1 , incorporated into a device selected from the group consisting of: a set-top box; an entertainment unit; a navigation device; a communication 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 computer; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television set; a tuner; a radio unit; a satellite radio unit; 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 vehicle component; an avionics system; an unmanned aerial vehicle; and a multirotor aircraft.

15. A BAW device, comprising: A layer stack, the layer stack comprising: a first electrode; a second electrode; a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer comprising a first crystal structure having a first polarization; a second piezoelectric layer between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a second crystal structure having a second polarization opposite to the first polarization; and at least one intermediate layer between the first piezoelectric layer and the second piezoelectric layer, Therein, a distance between the first piezoelectric layer and the second piezoelectric layer is less than four percent (4%) of a total thickness of the layer stack.

16. The BAW device according to claim 15, wherein: The first piezoelectric layer and the second piezoelectric layer include the same piezoelectric material.

17. The BAW device according to claim 15, wherein: A distance between the first piezoelectric layer and the second piezoelectric layer is equal to a thickness of the at least one intermediate layer.

18. The BAW device according to claim 15, wherein: The at least one intermediate layer includes a titanium nitride (TiN) layer.

19. The BAW device according to claim 15, wherein: The at least one intermediate layer includes a silicon dioxide (SiO2) layer.

20. The BAW device according to claim 15, wherein: The at least one intermediate layer comprises a seed layer configured to determine the second polarization of the second piezoelectric layer.

21. The BAW device according to claim 20, wherein: The second piezoelectric layer includes aluminum scandium nitride (AlScN); and The seed layer includes aluminum nitride (AlN).

22. The BAW device of claim 15, further comprising an acoustic mirror coupled to the first electrode.

23. The BAW device according to claim 15, further comprising: substrate; an air cavity between the first electrode and the substrate; as well as A membrane is between the air cavity and the first electrode.

24. A method of manufacturing a two-terminal BAW device, the method comprising: Formation stack, including: forming a first electrode configured to be coupled to a first terminal; forming a second electrode configured to be coupled to the second terminal; forming a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer including a first crystal structure having a first polarization; and A second piezoelectric layer is formed between the first piezoelectric layer and the second electrode, the second piezoelectric layer including a second crystal structure having a second polarization opposite to the first polarization.

25. The method of claim 24, wherein: Forming the first piezoelectric layer includes: forming a piezoelectric material on a sacrificial substrate; Forming the first electrode includes: forming a first metal layer configured as an electrode on an outer surface of the first piezoelectric layer; Forming the second piezoelectric layer includes: removing the sacrificial substrate from the first piezoelectric layer and forming the piezoelectric material on an inner surface of the first piezoelectric layer; and Forming the second electrode includes forming a second metal layer configured as an electrode on the second piezoelectric layer.

26. The method according to claim 25, wherein: Forming the first piezoelectric layer further includes: forming a first seed layer on the sacrificial substrate; and The piezoelectric material is formed on the first seed layer.

27. The method according to claim 25, wherein: Forming the second piezoelectric layer further includes: forming a second seed layer on the inner surface of the first piezoelectric layer; and The piezoelectric material is formed on the second seed layer.

28. The method according to claim 27, further comprising: forming a first amorphous layer in direct contact with the inner surface of the first piezoelectric layer; as well as The second seed layer is formed on the first amorphous layer.

29. The method according to claim 28, further comprising: forming a second amorphous layer in direct contact with the first amorphous layer; as well as The second seed layer is formed in direct contact with the second amorphous layer.

30. The method of claim 29, wherein: Forming the first amorphous layer, the second amorphous layer, and the second seed layer further includes forming the first amorphous layer, the second amorphous layer, and the second seed layer to a total combined thickness of less than four percent (4%) of a total thickness of the layer stack.

31. The method of claim 24, wherein: Forming the layer stack does not include forming a metal layer configured as an electrode between the first piezoelectric layer and the second piezoelectric layer.

32. The method of claim 24, further comprising: forming an acoustic mirror on the first electrode; as well as A target substrate is formed on the acoustic mirror.

33. The method of claim 24, further comprising: forming a film on the first electrode; forming a substrate on the first electrode; as well as An air cavity is formed between the first electrode and the substrate.

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