Piezoelectric transducers with different polarization directions

Abstract

A transducer device (600) is described, comprising a substrate (194) having an opening (516) and a cantilever device (522A) having a first end on the substrate and a second end suspended over the opening (516). In at least one example, the cantilever device (522A) includes a first piezoelectric layer (180a) having a first surface and a first polarization direction. The cantilever device (522A) further includes a second piezoelectric layer (182a) having a second surface opposite to the first surface and a second polarization direction different from the first polarization direction. The cantilever device (522A) further includes a first electrode (160a) on the first surface and a second electrode (164a) on the second surface.

Description

[Background technology]

[0001] A transducer can convert between mechanical energy (e.g., vibration) and electrical energy. A transducer may take the form of a cantilever containing a flap (e.g., a piezoelectric flap) suspended over an opening. The flap vibrates in response to a stimulus (e.g., sound wave, weight), generating an electrical signal representing that stimulus. This electrical signal can then be further processed to extract information. For example, if the stimulus is a sound wave, the electrical signal is processed to produce an audio signal. In another example, if the stimulus is velocity, the electrical signal can make a measurement of acceleration.

[0002] Various examples will be better understood from the detailed description and accompanying drawings provided below. However, this disclosure should not be considered as being limited to these specific examples, and this disclosure is for illustrative and understanding purposes only. [Brief explanation of the drawing]

[0003] [Figure 1] This is a schematic diagram illustrating a system comprising a transducer having two electrodes and two piezoelectric layers having different polarization directions, following at least one example.

[0004] [Figure 2A] This is a schematic diagram illustrating a cross-section of the transducer shown in Figure 1, following at least one example.

[0005] [Figure 2B] This is a graph of the electric field between the electrodes of the transducer in Figure 1, following at least one example.

[0006] [Figure 2C] This is a graph of the voltage between the electrodes of the transducer in Figure 1, following at least one example.

[0007] [Figure 3A]This is a graph of the transverse distortion in the x-direction of the transducer, following several examples. [Figure 3B] This is a graph of the electric field along the z-direction of the transducer, following several examples. [Figure 3C] This is a graph of the voltage difference between the electrodes of a transducer, following several examples.

[0008] [Figure 4] This is a schematic diagram illustrating an acoustic system that includes an acoustic device and a microphone, including the transducer shown in Figure 2A, following at least one example.

[0009] [Figure 5] This is a schematic diagram illustrating a cross-sectional view of an acoustic device, following at least one example.

[0010] [Figure 6] This is a schematic diagram illustrating a cross-sectional view of a microphone, following at least one example.

[0011] [Figure 7] This is a schematic diagram illustrating a cross-sectional view of a transducer comprising two electrodes and two piezoelectric layers formed on different wafers, following at least one example.

[0012] [Figure 8A] This is a schematic diagram illustrating a transducer configured as an accelerometer, following at least one example.

[0013] [Figure 8B] This is a schematic diagram illustrating a transducer configured as a sensor, following at least one example.

[0014] [Figure 9] This is a flowchart illustrating a method for forming a transducer, following at least one example.

[0015] [Figure 10] A flowchart of a method for forming a transducer comprising two wafers according to at least one example.

[0016] [Figure 11] A flowchart of a method for forming a transducer comprising a piezoelectric layer fabricated by different processes according to at least one example. SUMMARY OF THE INVENTION

[0017] In at least one example, an apparatus is described that includes a substrate having an aperture, and a cantilever device having a first end on the substrate and a second end suspended over the aperture. The cantilever includes a first piezoelectric layer having a first surface and a first polarization direction. In at least one example, the cantilever further includes a second piezoelectric layer having a second surface opposite the first surface and a second polarization direction different from the first polarization direction. The cantilever further includes a first electrode on the first surface and a second electrode on the second surface. In at least one example, the first polarization direction has a first component along an axis orthogonal to the first surface, the second polarization direction has a second component along this axis, and the first component and the second component have the same magnitude and opposite directions.

[0018] In at least one example, a method is described that includes forming a substrate having an aperture and forming a cantilever device having a first end on the substrate and a second end suspended over the aperture. The method of forming the cantilever device includes forming a first piezoelectric layer having a first polarization direction and a first surface. In at least one example, forming the cantilever device includes forming a second piezoelectric layer having a second polarization direction different from the first polarization direction and a second surface opposite the first surface. The method of forming the cantilever device includes forming a first electrode on the first surface and forming a second electrode on the second surface.

[0019] In at least one example, forming a first electrode and a first piezoelectric layer includes forming the first electrode and the first piezoelectric layer on a first wafer including a substrate, wherein the first piezoelectric layer has a third surface opposite to the first surface. In at least one example, forming a second electrode and a second piezoelectric layer includes forming a second electrode and a second piezoelectric layer on a second wafer, wherein the second piezoelectric layer has a fourth surface opposite to the second surface. A method for forming a cantilever device includes bonding the third surface to the fourth surface. A method for forming a cantilever device further includes removing the second wafer from the second piezoelectric layer and the second electrode, and etching the substrate to form an opening.

[0020] In at least one example, an apparatus is described comprising a substrate having an opening and a cantilever device having a first end on the substrate and a second end suspended over the opening. The cantilever device includes a first piezoelectric layer having a first surface and a first polarization direction. In at least one example, the cantilever device includes a second piezoelectric layer having a second surface opposite to the first surface and a second polarization direction different from the first polarization direction. The cantilever device further includes a first electrode on the first surface and a second electrode on the second surface. In at least one example, the first polarization direction has a first component along an axis perpendicular to the first surface, and the second polarization direction has a second component along this axis, and the first and second components are of the same size and opposite directions. [Modes for carrying out the invention]

[0021] A transducer can convert between mechanical energy (e.g., vibration) and electrical energy. A transducer may take the form of a cantilever including a flap (e.g., a piezoelectric flap) suspended over an opening. The piezoelectric flap may be a piezoelectric bimorph flap including three electrodes and two piezoelectric layers between the electrodes. For example, a piezoelectric bimorph flap may include a top electrode above the upper piezoelectric layer, a bottom electrode between the upper and lower piezoelectric layers (the lower piezoelectric layer between the upper and lower piezoelectric layers), and a bottom electrode below the lower piezoelectric layer. When the piezoelectric bimorph flap bends upward or downward due to a stimulus, if the bimorph flap is symmetrical, equal and opposite strains occur across the entire upper and lower piezoelectric layers, and the resulting strains may have odd symmetry around a neutral axis. The neutral axis may be parallel to the surface of the piezoelectric bimorph flap and perpendicular to the direction of the force. The neutral axis can be the line where the stress is zero in the material of the piezoelectric bimorph flap. This occurs because the stress / strain reverses direction between the top and bottom, from compression to tension (or vice versa, depending on the bending direction). If the piezoelectric bimorph flap has a symmetrical structure (e.g., symmetrical in the material), the neutral axis can be precisely at the center. If there is asymmetry, the neutral axis may shift upward or downward.

[0022] If the upper and lower piezoelectric materials are of the same material, the piezoelectric layers may have the same polarization direction (or the same intrinsic polarization direction). Strain can generate an upper electric field in the upper piezoelectric material and a lower electric field in the lower piezoelectric material. These electric fields have odd symmetry around the neutral axis of the piezoelectric bimorph flap (e.g., opposite polarity but equal magnitude), and the net electric fields between the top and bottom electrodes cancel each other out. Therefore, an intermediate electrode can be provided at the interface between the upper and lower piezoelectric layers to measure the upper and lower electric fields separately and to measure the strain generated by the stimulus.

[0023] Forming an intermediate electrode between the lower and upper piezoelectric layers presents challenges. For example, the crystal quality / crystallinity of the piezoelectric layer may be best when grown on silicon, and the crystal quality of the upper piezoelectric layer may be compromised after depositing the intermediate electrode on the lower piezoelectric layer and then depositing the material for forming the upper piezoelectric layer. The intermediate electrode can introduce a mass load, which can lower the resonant frequency of the transducer. Furthermore, the intermediate electrode can increase manufacturing costs due to the additional masking required to pattern vias for connecting to the intermediate electrode through the upper and lower piezoelectric layers.

[0024] This specification discloses a transducer comprising two piezoelectric layers having different polarization directions (or different inherent polarization directions) and two electrodes. The two electrodes include a top electrode on the top of a first surface of a first piezoelectric layer (e.g., an upper piezoelectric layer) and a bottom electrode on a second surface of a second piezoelectric layer (e.g., a lower piezoelectric layer). In one example, the electrode-free surfaces of the first and second piezoelectric layers face each other. There may be no intermediate material between these surfaces. In at least one example, there may be a bonding material between these surfaces. The transducer may be in the form of a cantilever, with a first end of the cantilever resting on a substrate having an opening, and a second end of the cantilever suspended above the opening. The cantilever may be a beam, a diaphragm, a set of cantilever beams having a non-uniform cross-section, a partial film, a film having a slit, and the like. The cantilever may be configured as a piezoelectric microphone, piezoelectric speaker, piezoelectric micromachine ultrasonic transducer, piezoelectric accelerometer, or voice accelerometer.

[0025] In at least one example, the polarization directions of the first and second piezoelectric layers are such that the first component of the first polarization direction of the first piezoelectric layer is opposite to the second component of the second polarization direction of the second piezoelectric layer, and both the first and second components are perpendicular to the neutral axis. The neutral axis may be an axis parallel to the surface of the piezoelectric bimorph flap and perpendicular to the direction of force. In at least one example, different polarization directions are achieved by crystal growth. In at least one example, different polarization directions are achieved by inverting and joining two films of piezoelectric layers having the same polarization direction, so that the resulting piezoelectric layer has opposite polarization directions.

[0026] The examples described herein may offer various advantages. For example, the fabrication process for forming the transducer device is simplified by eliminating the intermediate electrode between the top and bottom electrodes. By not forming an intermediate electrode between the piezoelectric layers, at least two fabrication masks can be eliminated. For example, by using two piezoelectric layers having inherently opposite polarizations (or polarizations) and two electrodes (e.g., a top electrode and a bottom electrode), interconnection routing, via formation, and trench formation for connecting to the intermediate electrode are avoided. By using two piezoelectric layers having inherently opposite polarizations, strain-field coupling is observed throughout the entire volume of the transducer device. In one example, the coupling coefficient k of the transducer devices of various examples is described. 2 The coupling coefficient k of a three-electrode-based bimorph piezoelectric structure and a two-electrode-based unimorph structure. 2 It is greater than. Other technical effects will become apparent from the various examples described herein. Here, in the drawings, the same reference number or other reference designations are used to indicate the same or similar features (by function and / or structure).

[0027] Figure 1 is a schematic diagram illustrating a system 100 comprising a transducer having two electrodes and two piezoelectric layers having different polarization directions, according to at least one example. The system 100 includes a cantilever device 101 and a processing circuit 102. The cantilever device 101 includes a semiconductor structure 114 (e.g., fixed constraint) and a bimorph piezoelectric cantilever 122, partly located on the semiconductor structure 114. In at least one example, the bimorph piezoelectric cantilever 122 includes a first electrode 160a (e.g., top electrode), a second electrode 164a (e.g., bottom electrode), a first piezoelectric layer 180a, and a second piezoelectric layer 182a. The first electrode 160a is located on a first surface (e.g., top surface) of the first piezoelectric layer 180a. The second electrode 164a is located on a second surface (e.g., bottom surface) of the second piezoelectric layer 182a. In at least one example, the first electrode 160a and the second electrode 164a extend along the x-direction for a length of less than half the respective length (length along the x-direction) of the first piezoelectric layer 180a and the second piezoelectric layer 182a.

[0028] The first piezoelectric layer 180a is adjacent to the second piezoelectric layer 182a, and no electrodes are present between them. In at least one example, the first piezoelectric layer 180a is in direct contact with the second piezoelectric layer 182a. In at least one example, the first piezoelectric layer 180a is bonded to the second piezoelectric layer 182a via a bonding material. The first piezoelectric layer 180a and the second piezoelectric layer 182a are made of the same material or different materials. In at least one example, the first piezoelectric layer 180a and the second piezoelectric layer 182a are manufactured or deposited using different manufacturing processes. The first piezoelectric layer 180a and the second piezoelectric layer 182a may have the same thickness or different thicknesses (e.g., thickness along the z-direction).

[0029] The first piezoelectric layer 180a has a first polarization direction. The second piezoelectric layer 182a has a second polarization direction. These different polarization directions may be due to different intrinsic polarization directions between the first piezoelectric layer 180a and the second piezoelectric layer 182a. In at least one example, the second polarization direction has a second component that is different (e.g., opposite) to the first component of the first polarization direction. In at least one example, the first and second components have the same size and opposite directions. In at least one example, the first and second components are aligned along axes perpendicular to the first surface (and neutral axis). In at least one example, the first piezoelectric layer 180a has a different crystallinity or crystallinity than the second piezoelectric layer 182a. For example, the first piezoelectric layer 180a has a first degree of crystallinity or crystallization, which is an inverted mirror image of the second degree of crystallinity or crystallization of the second piezoelectric layer 182a.

[0030] The fabrication process for forming the bimorph piezoelectric cantilever 122 is simplified by the absence of an intermediate electrode between the first electrode 160a (e.g., the top electrode) and the second electrode 164a (e.g., the bottom electrode). By not forming an intermediate electrode between the first piezoelectric layer 180a and the second piezoelectric layer 182a, it is achieved to eliminate at least two fabrication masks. For example, by using the first piezoelectric layer 180a and the second piezoelectric layer 182a having inherently opposite polarization (or polarization), interconnection routing and the formation of vias and trenches for connecting to an intermediate electrode are avoided.

[0031] In at least one example, the first electrode 160a is coupled to the processing circuit 102 by terminal 170a, and the second electrode 164a is coupled to the processing circuit 102 by terminal 171a. The processing circuit 102 includes (or is part of) an integrated circuit that includes logic and / or circuits for converting analog voltages generated on the first electrode 160a and the second electrode 164a into processed signals (e.g., audio signals, sensor outputs, etc.). The processing circuit 102 can actuate the bimorph piezoelectric cantilever 122 by applying voltages to the first electrode 160a and the second electrode 164a. In at least one example, the processing circuit 102 includes logic for setting the states of the first electrode 160a, the second electrode 164a, the first piezoelectric layer 180a, and the second piezoelectric layer 182a. For example, the processing circuit 102 may clamp or fix the edges of the first electrode 160a, the second electrode 164a, the first piezoelectric layer 180a, and the second piezoelectric layer 182a to the semiconductor structure 114. In at least one example, the processing circuit 102 is an application-specific integrated circuit (ASIC). In at least one example, the processing circuit 102 includes one or more physical processor devices that execute instructions stored in non-temporary memory to perform the processing and control functions described herein.

[0032] The semiconductor structure 114 includes an oxide layer 193 and a substrate 194. In at least one example, the oxide layer 193 may be omitted, and the substrate 194 may be directly bonded to the second electrode 164a and / or the second piezoelectric layer 182a. In at least one example, the substrate 194 does not extend completely along the length of the bimorph piezoelectric cantilever 122, leaving an opening through which a portion of the bimorph piezoelectric cantilever 122 is suspended. This opening allows the bimorph piezoelectric cantilever 122 to bend or vibrate based on stimuli that may be supplied to the bimorph piezoelectric cantilever 122 through the opening or through terminals 170a and 171a.

[0033] Figure 2A is a schematic diagram illustrating a cross-section 200 of the transducer of Figure 1, according to at least one example. The cross-section 200 illustrates the surfaces of the first piezoelectric layer 180a and the second piezoelectric layer 182a. These surfaces include a first surface 205a (e.g., top surface) and an opposite second surface 206a (e.g., bottom surface) of the first piezoelectric layer 180a, a third surface 205b (e.g., top surface) and an opposite fourth surface 206b (e.g., bottom surface) of the second piezoelectric layer 182a. The first electrode 160a is on the first surface 205a, and the bottom electrode 164a is on the fourth surface 206b. Here, there is an interface surface 283 between the second surface 206a of the first piezoelectric layer 180a and the third surface 205b of the second piezoelectric layer 182a. In at least one example, the interface surface 283 indicates that the second surface 206a is in direct contact with or attached to the third surface 205b. In at least one example, the interface surface 283 indicates that the second surface 206a is indirectly in contact with or attached to the third surface 205b. For example, a bonding material may be present between the second surface 206a and the third surface 205b.

[0034] In at least one example, the first piezoelectric layer 180a and the second piezoelectric layer 184a contain aluminum nitride (AlN). In at least one example, the thickness of the first piezoelectric layer 180a containing AlN of a certain thickness is configured to increase / maximize the signal-to-noise ratio (SNR) and sensitivity. For example, to maximize the SNR and sensitivity, the thickness of the AlN is substantially in the range of 200 nm to 500 nm. As described herein, the first component in the first polarization direction of the first piezoelectric layer 180a is opposite to the second component in the second polarization direction of the second piezoelectric layer 182a. Section 200 illustrates the AlN compound in the first piezoelectric layer 180a and the second piezoelectric layer 182a, where nitrogen atoms 210 and aluminum atoms 212 are shown in the first piezoelectric layer 180a, and nitrogen atoms 211 and aluminum atoms 213 are shown in the second piezoelectric layer 182a. In this example, the first polarization direction 281 extends along the -z direction from the aluminum atom 212 of the first AlN compound to the nitrogen atom 210 of the second AlN compound in the first piezoelectric layer 180a. The second polarization direction 282 extends along the z direction from the aluminum atom 213 of the AlN compound to the nitrogen atom 211 of the second AlN compound in the second piezoelectric layer 182a, and the second polarization direction 282 is opposite to the first polarization direction 281. In at least one example, the polarization directions can be any direction in the first piezoelectric layer 180a and the second piezoelectric layer 182a, as long as they have at least one opposite component (for example, a component of the polarization direction in the first piezoelectric layer 180a is opposite to a component of the polarization direction in the second piezoelectric layer 182a). For example, as shown in Figure 2A, the first piezoelectric layer 180a may have a polarization direction 283 having a component 283a parallel to the surface 206a / 205b and a component 283b perpendicular to the surface 206a / 205b. The second piezoelectric layer 182a may have a polarization direction 285 having a component 285a parallel to the surface 206a / 205b and a component 285b perpendicular to the surface 206a / 205b. The components 283b and 285b may have opposite directions but may have the same size.In at least one example, the polarization directions of the first piezoelectric layer 180a and the second piezoelectric layer 182a are orthogonal, and the polarization direction of one layer is opposite to that of the other layer.

[0035] Figure 2B is a graph 220 of the electric field E over the thickness of the first piezoelectric layer 180a and the thickness of the second piezoelectric layer 182a between the first electrode 160a and the second electrode 164a in Figures 1 and 2A, following at least one example. TIFF2026522372000002.tif312 decreases from position z0 (e.g., at the second electrode 164a) to position z1 (e.g., at surface 206a / 205b or interface surface 283), and increases from position z1 to position z2 (e.g., at the first electrode 160a). This electric field has the same polarity throughout (e.g., pointing in the negative z direction) due to the opposing polarization directions of the components in the first piezoelectric layer 180a and the second piezoelectric layer 182a.

[0036] Figure 2C is a graph 230 of the voltage between the electrodes of the transducer in Figure 1, following at least one example. Integrating the electric field E in Figure 2B yields the voltage between the second electrode 164a and the first electrode 160a. This voltage is expressed as follows: TIFF2026522372000003.tif422

[0037] In at least one example, due to the opposing polarization directions of the components in the first piezoelectric layer 180a and the second piezoelectric layer 182a, the voltage V between the second electrode 164a and the first electrode 160a is not zero.

[0038] The piezoelectric layer corresponds to the electromechanical coupling coefficient k 2 This has a function that represents the proportion of energy that the piezoelectric material can convert / transduce between the electrical domain and the mechanical domain. A phenomenological model derived from the thermodynamic potential mathematically describes the piezoelectric properties. For a piezoelectric layer under isothermal and adiabatic conditions (e.g., the first piezoelectric layer 180a), neglecting higher-order effects, the elastic Gibbs function can be described as follows: TIFF2026522372000004.tif13148 Here, g is the piezoelectric voltage coefficient, s is the elastic compliance, and β is the inverse permittivity. The independent variables in this equation are stress T and electrical displacement D. The superscripts of these constants indicate the independent variables that are kept constant when defining the constants, and the subscripts define a tensor that takes into account the anisotropy of the material.

[0039] The linear equation for piezoelectricity with respect to this potential is determined from the derivative of the Gibbs function G1 and is as follows: TIFF2026522372000005.tif3097 Here, S is the strain and E is the electric field. The elements of the tensor are reduced to a 6x6 matrix, where 1, 2, and 3 specify the elements of normal stress and strain, and 4, 5, and 6 specify the elements of shear stress and strain. The thermodynamic potential can be used to express the piezoelectric linear equation as follows: TIFF2026522372000006.tif9085 Here, d, e, g, and h are piezoelectric constants, s and c are elastic compliance and stiffness, respectively, and ε and β are permittivity and inverse permittivity, respectively.

[0040] The relationship between these equations can be expressed in matrix form as follows: TIFF2026522372000007.tif2346

[0041] This matrix is ​​a generalized expression of the following equation. TIFF2026522372000008.tif827

[0042] Many elements of the matrix in equation (13) are either zero or not independent due to the crystal symmetry, and therefore the number of independence constants decreases. The matrix in equation (13) has two independent free dielectric constants. TIFF2026522372000009.tif938, three independent piezoelectric constants (d 33 d 31 d 15 ), and five independent elastic constants under short-circuit boundary conditions It has TIFF2026522372000010.tif11166. The reduced matrix represents the relationship between the material constants and the variables S, T, E, and D.

[0043] In at least one example, the coefficient d 31 is the piezoelectric coupling coefficient that represents how much stress is coupled to the electric displacement and vice versa. The sign and magnitude depend on the material polarization. In at least one example, the piezoelectric coupling coefficient d for the first piezoelectric layer 180a 31 has the same magnitude as the piezoelectric coupling coefficient d of the second piezoelectric layer 182a 31 but opposite polarities.

[0044] Figures 3A, 3B, and 3C are graphs 300, 320, and 330 respectively showing, according to some examples, the lateral strain in the x - direction of the transducer, the electric field along the z - direction of the transducer, and the voltage difference between the electrodes of the transducer. Graph 300 shows the lateral strain in the x - direction of the bimorph piezoelectric cantilever 122. In at least one example, the lateral strain in the x - direction shows odd symmetry about the neutral axis of the bimorph piezoelectric cantilever 122. The bimorph piezoelectric cantilever 122 has opposite polarities in the first piezoelectric layer 180a (e.g., the top layer) and the second piezoelectric layer 182a (e.g., the bottom layer). Graph 320 shows the electric field along the x - direction of the bimorph piezoelectric cantilever 122. In at least one example, this electric field has even symmetry about the neutral axis of the bimorph piezoelectric cantilever 122. In at least one example, since the first piezoelectric layer 180a (e.g., the top layer) and the second piezoelectric layer 182a (e.g., the bottom layer) have structurally opposite material polarizations, the electric field has the same sign along the z - direction. Graph 330 illustrates the voltage between the first electrode 160a and the second electrode 164a. In at least one example, due to the even symmetry of the electric field, a voltage difference occurs between the first electrode 160a and the second electrode 164a. In at least one example, the voltage can be sensed using the first electrode 160a and the second electrode 164a when there is no intermediate electrode.

[0045] Figure 4 is a schematic diagram illustrating an acoustic system 400 including the transducer of Figure 2A, according to at least one example. In at least one example, the acoustic system 400 includes a microphone 401, a processing circuit 102, and a device 403. In at least one example, the microphone 401 and the processing circuit 102 together form an audio system 404. The microphone 401 includes a micro-electromechanical system (MEMS) or nano-electromechanical system (NEMS) that converts incident sound waves into mechanical energy. The microphone 401 outputs an analog electrical signal at the microphone output to the audio input of the processing circuit 102.

[0046] In at least one example, the microphone 401 includes a plurality of cantilever flaps, each cantilever having similar characteristics and functions to the bimorph piezoelectric cantilever 122. The plurality of cantilever flaps can be arranged in any configuration (e.g., a rectangular array, a circular array, etc.). In at least one example, the plurality of cantilever flaps vibrate in response to external sound waves, generating an electrical signal representing the sound waves. In at least one example, the outputs from the plurality of cantilever flaps of the microphone 401 are coupled to a microphone output. The microphone output is coupled to the audio input of the processing circuit 102 in Figure 1. In at least one example, the audio output is coupled to device 403, providing device 403 with a processed audio output (e.g., a digital signal representing the audio perceived by microphone 401). In at least one example, device 403 is any suitable client using the audio output from audio system 404. Examples of device 403 include smart devices, smartphones, tablets, electric vehicles, wearable devices, computers, etc.

[0047] The processing circuit 102 includes (or is part of) an integrated circuit that includes logic and / or circuits for converting an audio input in the analog or acoustic domain (e.g., an analog signal) to an audio output in the digital or electrical domain (e.g., a digital signal). In at least one example, the processing circuit 102 includes a power management circuit that turns off the microphone 401 (e.g., by cutting off the power or gate the power supply) when it detects a low-power (or sleep) mode or a programmable or predetermined inactive period (e.g., a period when no sound is detected by the microphone 401). In some examples, the audio device 104 includes a speaker with a cantilever flap in addition to the microphone 401. In at least one example, the bimorph piezoelectric cantilever 122 of the microphone 401 is configured as a speaker. In some other examples, the system (e.g., a stress sensor, accelerometer, energy harvester, etc.) may include a piezoelectric transducer having a cantilever flap as in some examples.

[0048] Figure 5 is a schematic diagram illustrating a cross-sectional view of an acoustic device 500 according to at least one example. In at least one example, the acoustic device 500 includes a microphone 401 on a substrate 590. The microphone 401 includes a piezoelectric cantilever system 510, openings 516 and 519, and a slit or opening 518 on a semiconductor structure 114. The piezoelectric cantilever system 510 includes piezoelectric flaps 522A and 522B. The acoustic device 500 further includes a processing circuit 102 (e.g., an integrated circuit) encapsulated in epoxy 554 and bond wires 552 electrically coupled between the processing circuit 102 and the microphone 401. In at least one example, the acoustic device 500 further includes a case or package 596 enclosing the processing circuit 102, the piezoelectric cantilever system 510 (of the microphone 401), and the rear volume space 592.

[0049] In at least one example, the acoustic device 500 is configured as a microphone. In at least one example, the acoustic device 500 is configured as a speaker. In at least one example, the acoustic device 500 is a packaged device comprising a piezoelectric cantilever system 510 and an integrated circuit 102 on a substrate 590. The substrate 590 may be a package substrate or a printed circuit board (PCB), etc. The substrate 590 comprises silicon oxide (SiO2) or any other suitable material.

[0050] In at least one example, the piezoelectric cantilever system 510 includes piezoelectric flaps 522A and 522B. In at least one example, the films of each piezoelectric flap 522A and 522B have one end coupled to a semiconductor structure 114 having an opening 516, and the other end of each flap can move up and down as a cantilever or flap over the opening 516. Each piezoelectric flap 522A and 522B includes two piezoelectric layers, the two piezoelectric layers are in contact with each other, and each has electrodes on the top and bottom surfaces of the two piezoelectric layers. In at least one example, the polarization directions in the two piezoelectric layers are orthogonal, and the polarization direction in one layer is opposite to the polarization direction in the other layer. This eliminates the need for an intermediate electrode between the two piezoelectric layers for each piezoelectric flap 522A and 522B.

[0051] In at least one example, a slit or opening 518 separates the piezoelectric flaps 522A and 522B. In at least one example, the slit or opening 518 allows each flap to move independently of the others in a certain operation. In at least one example, a processing circuit 102 individually controls each piezoelectric flap of the piezoelectric cantilever system 510. In at least one example, the processing circuit 102 operates each piezoelectric flap 522A and 522B as a sensor (e.g., as part of a microphone for detecting sound waves and converting them into electrical signals) or as an actuator (e.g., as a speaker for generating sound waves, or to move the flaps in another way). The piezoelectric cantilever system 510 is a MEMS or NEMS in which the flaps are each fabricated to micrometer or nanometer dimensions.

[0052] In at least one example, an interconnect (e.g., bond wire 551) connects the processing circuit 102 to the piezoelectric cantilever system 510 in a communicative manner. In at least one example, epoxy 554 encases the processing circuit 102. In at least one example, the piezoelectric cantilever system 510 and the processing circuit 102 are located on separate dies. In at least one example, the piezoelectric cantilever system 510 and the processing circuit 102 are located on the same die.

[0053] In at least one example, the substrate 590 also includes an opening 519 that communicates with the opening 516 and exposes the piezoelectric flaps 522A and 522B to the outside of the acoustic device 500. The openings 516 and 519 define a front volume space (or audio port). When the processing circuit 102 operates the piezoelectric flaps 522A and 522B as part of a microphone, the piezoelectric flaps 522A and 522B detect sound waves propagating from outside the acoustic device 500 through the front volume space defined by the opening 516 and generate an electrical signal in response to the detection of sound waves. In at least one example, the processing circuit 102 extracts various characteristics of the piezoelectric flaps 522A and 522B (e.g., frequency response, resonant frequency, etc.) from the electrical signal.

[0054] In at least one example, a case or package 596 is mounted on a substrate 590. The case or package 596 encloses the piezoelectric cantilever system 510, the integrated circuit 102, the bond wires 551, and the epoxy 554. The case or package 596 is made of any suitable material such as metal or plastic and isolates the piezoelectric cantilever system 510 and the processing circuit 102 from noise and mechanical stress. The case or package 596 defines a rear volumetric space 592 from which the piezoelectric flaps 522A and 522B of the piezoelectric cantilever system 510 can move (e.g., vibrate). In at least one example, air fills the rear volumetric space 592.

[0055] In at least one example, the slit or opening 518 allows air to flow between the rear volumetric space 592 and the front volumetric space (defined by the opening 516) to equalize the air pressure on both sides of the piezoelectric flaps 522A and 522B. In at least one example, the slit or opening 518 allows air to flow between the rear volumetric space 592 and the front volumetric space (defined by the opening 516) to prevent stress that could otherwise damage or reduce the sensitivity of the piezoelectric flaps 522A and 522B when they are operating as microphones. In at least one example, the slit or opening 518 is narrow enough to prevent sound waves from reaching the rear volumetric space 592 and to set a lower cutoff frequency for the microphones.

[0056] As described herein, the fabrication process for forming the acoustic device 500 is simplified by removing the intermediate electrode between the top and bottom electrodes on the piezoelectric layers of the piezoelectric flaps 522A and 522B. By not forming an intermediate electrode between the piezoelectric layers of the piezoelectric flaps 522A and 522B, at least two fabrication masks are eliminated. For example, by using two piezoelectric layers with inherently opposite polarizations and two electrodes (e.g., a top electrode and a bottom electrode) in each piezoelectric flap 522A and 522B, interconnection routing, via formation, and trench formation for connecting to the intermediate electrode are avoided. In at least one example, strain-field coupling is observed throughout the entire volume of the piezoelectric flaps 522A and 522B.

[0057] Figure 6 is a schematic diagram illustrating a cross-sectional view of a microphone 600 according to at least one example. In at least one example, the microphone 600 includes a piezoelectric cantilever system 610 including piezoelectric bimorph flaps 522A and 522B. In at least one example, a slit or opening 518 separates the piezoelectric bimorph flaps 522A and 522B. Each piezoelectric flap is a piezoelectric bimorph flap having a multilayer structure. The bimorph flap 522A has a first electrode 160a and a second electrode 164a, with a first piezoelectric layer 180a between the first electrode 160a and the second piezoelectric layer 182a. The second piezoelectric layer 182a is located between the second electrode 164a and the first piezoelectric layer 180a. The bimorph flap 522B has a third electrode 660b (e.g., a top electrode) and a fourth electrode 664b (e.g., a bottom electrode), with a third piezoelectric layer 680b between the top electrode 660b and the fourth piezoelectric layer 682b. The fourth piezoelectric layer 682b is located between the second electrode 664b and the third piezoelectric layer 680b. The illustrated portion of the piezoelectric cantilever system 610 shows two piezoelectric bimorph flaps 522A and 522B, but the piezoelectric cantilever system 610 may include any suitable number of piezoelectric bimorph flaps. In at least one instance, the piezoelectric bimorph flaps 522A and 522B may be in a cantilever system described in U.S. Patent Application No. 18 / 240,668, entitled “Piezoelectric Audio Device,” filed August 31, 2023; U.S. Patent Application No. 18 / 495,675, entitled “Wake-up Mechanism for Audio System,” filed October 26, 2023; and U.S. Patent Application No. 18 / 522,145, entitled “Piezoelectric Transducer Having Tapered Cantilever,” filed November 28, 2023, which are incorporated in their entirety by reference. [Patent Document 1] U.S. Patent Application No. 18 / 240,668 [Patent Document 2] U.S. Patent Application No. 18 / 495,675 [Patent Document 3] U.S. Patent Application No. 18 / 522,145

[0058] In at least one example, the first electrode 160a and the second electrode 164a are coupled to terminals 170a and 171a, respectively. In at least one example, the top electrode 660b and the bottom electrode 664b are coupled to terminals 670b and 671b, respectively. In at least one example, electrodes 160a, 164a, 660b, and 660b include one or more layers of any suitable conductive material. Electrodes 160a, 164a, 660b, and 660b, as well as piezoelectric layers 180a, 182a, 680b, and 682b, include materials compatible with CMOS processing. In at least one example, electrodes 160a, 164a, 660b, and 664b include molybdenum (Mo or "moly"). In at least one example, the piezoelectric layers 180a, 182a, 680b, and 682b contain aluminum nitride ("AlN").

[0059] The piezoelectric layers 180a and 182a of the piezoelectric flap 522A are in contact with each other or bonded to each other via a bonding material. The polarization directions of the piezoelectric layers 180a and 182a of the piezoelectric flap 522A are orthogonal, and the polarization direction of piezoelectric layer 180a is opposite to that of piezoelectric layer 182a. This eliminates the need for an intermediate electrode between the two piezoelectric layers 180a and 182a for the piezoelectric flap 522A. In at least one example, the piezoelectric layers 680b and 682b of the piezoelectric flap 522B are in contact with each other or bonded to each other via a bonding material. In at least one example, the polarization directions of the piezoelectric layers 680b and 682b of the piezoelectric flap 522B are orthogonal, and the polarization direction of piezoelectric layer 680b is opposite to that of piezoelectric layer 682b. This allows for the removal of the intermediate electrode between the two piezoelectric layers 680a and 682b for the piezoelectric flap 522B. As described herein, the fabrication process for forming the microphone 600 is simplified by removing the intermediate electrode between the first electrode 160a and the second electrode 182a on the piezoelectric layer of the piezoelectric flap 522A. Similarly, the intermediate electrode is removed between the third electrode 660b and the fourth electrode 664b on the piezoelectric layer of the piezoelectric flap 522B.

[0060] In at least one example, terminals 170a, 171a, 670b, and 671b may include any suitable electrical connector for transferring current. In at least one example, terminals 170a and 171a electrically couple the piezoelectric bimorph flap 522A to a first receiver (Rx) circuit (not shown). In at least one example, terminals 670b and 671b electrically couple the piezoelectric bimorph flap 622B to a second Rx circuit (not shown). The first and second Rx circuits provide the electrical signals sensed from terminals 170a, 171a, 670b, and 671b to a processing circuit 102 for processing. In at least one example, the first and second Rx circuits are part of the processing circuit 102. In at least one example, terminals 170a and 171a electrically couple the piezoelectric bimorph flap 522A to a first transmitter (Tx) circuit (not shown). In at least one example, terminals 670b and 671b electrically couple the piezoelectric bimorph flap 622B to a second Tx circuit (not shown). In at least one example, the microphone 600 is configured as a speaker. In one such example, the first and second Tx circuits provide electrical signals to terminals 170a, 171a, 670b, and 671b via the processing circuit 102 to activate or bend one or more piezoelectric bimorph flaps 522A or 622B to produce sound. In at least one example, the first and second Tx circuits are part of the processing circuit 102.

[0061] Figure 7 is a schematic diagram illustrating a cross-sectional view of a transducer 700 comprising two electrodes and two piezoelectric layers formed on different wafers or substrates, according to at least one example. In at least one example, the piezoelectric layers 180a and 182a are bonded to each other by forming each piezoelectric layer on a separate wafer or substrate. In at least one example, the first piezoelectric layer 180a is grown on a first substrate or wafer 715, and the second piezoelectric layer 182b is grown on a second substrate or wafer 730. In at least one example, the respective electrodes are formed on the top surface of each piezoelectric layer. After the first piezoelectric layer 180a is grown on the first substrate or wafer 715 and the second piezoelectric layer 182a is grown on the second substrate or wafer 730, part or all of the substrate is etched, one of the piezoelectric layers is inverted, and bonded to the surface of the other piezoelectric layer opposite to its electrode.

[0062] In at least one example, a bottom electrode 164a is formed on the top of the surface of a second piezoelectric layer 182a grown on a second substrate or wafer 730, and then the second substrate is etched. Subsequently, the surface of the second piezoelectric layer 182a opposite to the bottom electrode 164a is bonded to the surface of a first piezoelectric layer 180a grown on a first substrate or wafer 715. In at least one example, the same piezoelectric material is used for the first piezoelectric layer 180a and the second piezoelectric layer 182a, and their polarization directions are the same. By reversing one of the piezoelectric layers before bonding the surfaces of the piezoelectric layers opposite to each electrode, the polarization direction of one piezoelectric layer becomes opposite to that of the other piezoelectric layer.

[0063] Figure 8A is a schematic diagram illustrating a transducer configured as an accelerometer 800 according to at least one example. The accelerometer 800 includes a bimorph piezoelectric cantilever 122 fixed on a semiconductor structure 114 and suspended over an opening. In at least one example, the bimorph piezoelectric cantilever 122 is enclosed within an enclosure 802. The accelerometer also includes a mass 810, the mass 810 (e.g., a metal layer) coupled to the bimorph piezoelectric cantilever 122. When the accelerometer moves, the mass 810 exerts a force on the bimorph piezoelectric cantilever 122. The stress on the bimorph piezoelectric cantilever 122 generates an electric field between a first electrode 160a and a second electrode 164a. The electric field E is sensed by a voltage measuring circuit 812 as a voltage between the first electrode 160a and the second electrode 164a. This voltage represents the acceleration (or velocity) of the accelerometer 800.

[0064] Figure 8B is a schematic diagram illustrating a transducer configured as a sensor 820 according to at least one example. In at least one example, the bimorph piezoelectric cantilever 122 is used to sense the presence or absence of a device or material. In at least one example, the bimorph piezoelectric cantilever 122 is enclosed within an enclosure 802 and a sensor film 821. The sensor film 821 is mechanically coupled to or directly attached to the top electrode 160a or the first piezoelectric layer 180a. The sensor film 821 can transmit a force 826 to the bimorph piezoelectric cantilever 122. The force 826 generates stress in the piezoelectric layer of the bimorph piezoelectric cantilever 122, causing it to bend. The bending of the first and second piezoelectric layers 180a and 182a generates an electric field between the first electrode 160a and the second electrode 164a. The electric field E is sensed by the voltage measuring circuit 812 as a voltage between the first electrode 160a and the second electrode 164a. This voltage represents the sensed force 826.

[0065] Figure 9 is a flowchart 900 of a method for forming a transducer, following at least one example. While the various blocks in flowchart 900 are illustrated in a specific order, the order can be changed. For example, some blocks may be performed before others, and some blocks may be performed simultaneously. The methods for forming cantilevers in the various examples herein may involve manufacturing processes, tools, and software for performing these various blocks.

[0066] In block 901, a substrate (e.g., a semiconductor structure 114) is formed and etched to obtain an opening (e.g., an opening 516). In block 902, a bimorph piezoelectric cantilever 122 is formed on the substrate such that a first end of the bimorph piezoelectric cantilever 122 is on the substrate and a second end of the bimorph piezoelectric cantilever 122 is suspended over the opening. This opening allows the bimorph piezoelectric cantilever 122 to vibrate in response to a stimulus. Blocks 903 to 906 describe the formation of the bimorph piezoelectric cantilever 122.

[0067] In block 903, a bimorph piezoelectric cantilever 122 is formed by forming or growing a first piezoelectric layer 180a having a first polarization direction. The formation of the bimorph piezoelectric cantilever 122 further includes forming or growing a second piezoelectric layer 182a having a second polarization direction different from the first polarization direction. In at least one example, the second polarization direction has a second component that is different (e.g., opposite) to the first component of the first polarization direction. In at least one example, the first and second components have the same size and opposite directions. In at least one example, the first and second components are aligned along an axis perpendicular to the first surface (and neutral axis). In at least one example, the first piezoelectric layer 180a has a different crystallinity or crystallization than the second piezoelectric layer 182a. For example, the first piezoelectric layer 180a has a first degree of crystallinity or crystallization, which is an inverted mirror image of the second degree of crystallinity or crystallization of the second piezoelectric layer 182a. In block 905, the first electrode 160a is formed on the first surface 205a of the first piezoelectric layer 180a. In block 906, the second electrode 164a is formed on a second surface (for example, a fourth surface 206b) opposite to the first surface 205a.

[0068] Various blocks may be carried out in different orders. For example, after the substrate or semiconductor structure 114 is formed, a second electrode 164a is fabricated on the substrate (block 906). Then, a second piezoelectric layer 182a is grown on the second electrode 164a (block 904). On the top surface of the second piezoelectric layer 182a, a first piezoelectric layer 180a is grown, and the first piezoelectric layer 180a has a polarization direction in which its components are opposite to those of the second piezoelectric layer 182a (block 903). Subsequently, a first electrode 160a is formed on the top surface of the first piezoelectric layer 180a (block 905).

[0069] Figure 10 is a flowchart 1000 of a method for forming a transducer comprising two wafers, following at least one example. While the various blocks in flowchart 1000 are shown in a specific order, the order can be changed. For example, some blocks may be performed before others, while others may be performed simultaneously. The methods for forming cantilevers in the various examples herein may involve fabrication processes, tools, and software for performing these various blocks.

[0070] In at least one example, blocks 903-906 may be replaced by blocks 1001-1005. In block 1001, a first electrode 160a and a first piezoelectric layer 180a are formed on a first substrate or wafer 715. In block 1002, a second electrode 162a and a second piezoelectric layer 182a are formed on a second substrate or wafer 730. In block 1003, a third surface of the first piezoelectric layer 180a, opposite to the first surface 205a, is bonded to a fourth surface of the second piezoelectric layer 182a, opposite to the surface on which the second electrode 164a is formed. The bonding process includes etching or removing the second substrate or wafer 730, thereby exposing the fourth surface of the second piezoelectric layer 182a, as shown in block 1004. In at least one example, a bonding material is deposited on the fourth surface of the second piezoelectric layer 182a and / or the third surface of the first piezoelectric layer 180a. In at least one example, instead of a bonding material, the fourth surface of the second piezoelectric layer 182a and the third surface of the first piezoelectric layer 180a are bonded under certain temperature and pressure.

[0071] The process of forming the cantilever involves inverting the second piezoelectric layer 182a and associated electrodes 164a before etching the second substrate or wafer 730. By inverting the second piezoelectric layer 182a, at least one component of the polarization direction of the second piezoelectric layer 182a is opposite to the component of the polarization direction of the first piezoelectric layer 180a. In block 1005, the first substrate or wafer 715 is etched to form an opening such that a portion of the second piezoelectric layer 182a is suspended over the opening.

[0072] Figure 11 is a flowchart 1100 of a method for forming a transducer having a piezoelectric layer fabricated using various different processes, following at least one example. While the various blocks in flowchart 1100 are shown in a specific order, the order can be changed. For example, some blocks may be performed before others, and some blocks may be performed simultaneously. The methods for forming cantilevers in the various examples herein may involve fabrication processes, tools, and software for performing these various blocks.

[0073] In at least one example, blocks 903-906 may be replaced by blocks 1001-1004. In block 1101, a bottom electrode 164a is formed on a substrate or semiconductor structure 114. In block 1102, a first piezoelectric material (e.g., a second piezoelectric layer 182a) is deposited or grown on the bottom electrode 164a using a first fabrication process (e.g., metal-organic chemical vapor deposition (MOCVD)). In block 1103, a second piezoelectric material (e.g., a first piezoelectric layer 180a) is deposited or grown on the first piezoelectric material using a second fabrication process (e.g., a chemical vapor deposition process). By using two different processing methods for growing the first and second piezoelectric materials, at least one component of the polarization direction of the first piezoelectric material is opposite to that of at least one component of the polarization direction of the second piezoelectric material (e.g., they are equal in size but opposite in direction or sign). In block 1104, the first electrode 160a (for example, the top electrode) is formed on the second piezoelectric material.

[0074] The following are additional examples provided in view of the implementation described above. Here, one or more features of an example may be combined, alone or in combination, with one or more features of one or more other examples to form further examples that are also included within the scope of this disclosure. In this way, one implementation may be combined with one or more other implementations without changing the scope of the disclosure.

[0075] Example 1 is an apparatus comprising a substrate having an opening and a cantilever device having a first end on the substrate and a second end suspended over the opening. The cantilever device comprises a first piezoelectric layer having a first surface and a first polarization direction, a second piezoelectric layer having a second surface opposite to the first surface and a second polarization direction different from the first polarization direction, a first electrode on the first surface, and a second electrode on the second surface.

[0076] Example 2 is an apparatus according to any example of this specification, in particular Example 1, wherein the first polarization direction has a first component along an axis perpendicular to the first surface, and the second polarization direction has a second component along this axis, and the first and second components are of the same size and opposite directions.

[0077] Example 3 is an apparatus according to any example of this specification, in particular Example 1, wherein the first polarization direction has a first component along a first axis, and the first axis is perpendicular to a second axis between a first end and a second end.

[0078] Example 4 is an apparatus according to any example of this specification, in particular Example 1, wherein the first polarization direction is associated with the first piezoelectric coupling coefficient, the second polarization direction is associated with the second piezoelectric coupling coefficient, and the second and first piezoelectric coupling coefficients have the same magnitude.

[0079] Example 5 is an apparatus according to any example of this specification, in particular Example 1, wherein the first piezoelectric layer is in contact with the second piezoelectric layer.

[0080] Example 6 is any example of this specification, in particular an apparatus according to Example 1, wherein the cantilever device further includes a bonding layer between the first piezoelectric layer and the second piezoelectric layer.

[0081] Example 7 is an apparatus according to any example of this specification, in particular Example 1, wherein the first piezoelectric layer and the second piezoelectric layer have the same thickness.

[0082] Example 8 is an apparatus according to any example of this specification, in particular Example 1, wherein the first piezoelectric layer and the second piezoelectric layer have opposite crystal orientations.

[0083] Example 9 is any example of this specification, in particular an apparatus according to Example 1, wherein the first piezoelectric layer and the second piezoelectric layer contain the same piezoelectric material.

[0084] Example 10 is any example of this specification, in particular an apparatus according to Example 1, wherein the first piezoelectric layer and the second piezoelectric layer comprise different piezoelectric materials.

[0085] Example 11 is any example of this specification, in particular an apparatus according to Example 1, wherein the first electrode and the second electrode extend along no more than half the length of the first piezoelectric layer and the second piezoelectric layer, respectively.

[0086] Example 12 is any example of this specification, in particular an apparatus according to Example 1, in which the cantilever device is configured as one of a piezoelectric microphone, a piezoelectric speaker, a piezoelectric micromachine ultrasonic transducer, a piezoelectric accelerometer, or a voice accelerometer.

[0087] Example 13 is an apparatus comprising a substrate having an opening and a cantilever device having a first end on the substrate and a second end suspended over the opening. The cantilever device comprises a first piezoelectric layer having a first surface and a first polarization direction, a second piezoelectric layer having a second surface opposite to the first surface and a second polarization direction different from the first polarization direction, a first electrode on the first surface, and a second electrode on the second surface.

[0088] Example 14 is an apparatus according to any example of this specification, in particular Example 13, wherein the first polarization direction has a first component along an axis perpendicular to the first surface, and the second polarization direction has a second component along this axis, and the first and second components are of the same size and opposite directions.

[0089] Example 15 is an apparatus according to any example of this specification, in particular Example 13, wherein the first polarization direction corresponds to a first crystal orientation of the first piezoelectric layer, and the second polarization direction corresponds to a second crystal orientation of the second piezoelectric layer, the second crystal orientation being different from the first crystal orientation.

[0090] Example 16 is an apparatus according to any example of this specification, in particular Example 13, wherein the first polarization direction corresponds to a first coupling coefficient of the first piezoelectric layer, and the second polarization direction corresponds to a second coupling coefficient of the second piezoelectric layer, the second coupling coefficient having the opposite polarity to the first coupling coefficient.

[0091] Example 17 is any example of this specification, in particular an apparatus according to Example 13, wherein the first piezoelectric layer and the second piezoelectric layer contain the same piezoelectric material, or the first piezoelectric layer and the second piezoelectric layer contain different piezoelectric materials.

[0092] Example 18 is an apparatus according to any example herein, in particular Example 13, comprising a case, an integrated circuit, and a device coupled to the integrated circuit, wherein the integrated circuit and the device are covered by the case, and the device includes a substrate and a cantilever device.

[0093] Example 19 is any example of this specification, in particular an apparatus according to Example 18, in which the integrated circuit is configured to operate the device as one of a piezoelectric microphone, a piezoelectric speaker, a piezoelectric micromachine ultrasonic transducer, a piezoelectric accelerometer, or a voice accelerometer.

[0094] Example 20 is a method comprising forming a substrate having an opening and forming a cantilever device having a first end on the substrate and a second end suspended over the opening. Forming the cantilever device comprises forming a first piezoelectric layer having a first polarization direction and a first surface, forming a second piezoelectric layer having a second polarization direction different from the first polarization direction and a second surface opposite to the first surface, forming a first electrode on the first surface and forming a second electrode on the second surface.

[0095] Example 21 is a method according to any example of this specification, in particular Example 20, wherein forming a first electrode and a first piezoelectric layer comprises forming the first electrode and the first piezoelectric layer on a first wafer including a substrate, the first piezoelectric layer having a third surface opposite to the first surface. Forming a second electrode and a second piezoelectric layer comprises forming a second electrode and a second piezoelectric layer on a second wafer, the second piezoelectric layer having a fourth surface opposite to the second surface. Forming a cantilever device comprises bonding the third surface to the fourth surface, removing the second wafer from the second piezoelectric layer and the second electrode, and etching the substrate to form an opening.

[0096] Example 22 is an example of any of the foregoing, in particular a method according to Example 20, in which forming a second piezoelectric layer includes forming a second piezoelectric layer on a first piezoelectric layer.

[0097] Beyond what is described herein, various modifications can be made to disclose implementations and such implementations without departing from the scope of this disclosure. Accordingly, the illustrations of implementations herein should be construed as examples and not limit the scope of this disclosure.

[0098] In this description, the term “to connect” may include connections, communications, or signaling paths that enable a functional relationship consistent with this description. For example, if device A generates a signal to control device B in order to perform a certain action, then (a) in the first example, device A is connected to device B by a direct connection, or (b) in the second example, if the intervening component C does not alter the functional relationship between device A and device B, device A is connected to device B via the intervening component C, so that device B is controlled by device A by the control signal generated by device A.

[0099] Furthermore, in this document, the phrase "based on ~" means "based on ~ at least partially." Therefore, if X is based on Y, X can be a function of Y and any number of other factors.

[0100] A device “configured” to perform a certain task or function may be configured at the time of manufacture (e.g., by programming and / or wiring) to perform such a function, and / or may be configurable (or reconfigurable) by the user after manufacture to perform such a function and / or other additional or alternative functions. Such configuration may be via the device’s firmware and / or software programming, via the construction and / or layout of the device’s hardware components and interconnections, or a combination thereof.

[0101] As used herein, the terms “terminal,” “node,” “interconnection,” “pin,” and “lead” are interchangeable. Unless otherwise specified, these terms are generally used to mean the interconnection or termination of device elements, circuit elements, integrated circuits, devices, or other electronic or semiconductor components.

[0102] A circuit or device described herein as including certain components may instead be adapted to be combined with such components to form the described circuit or device. For example, a structure described as including one or more semiconductor elements (such as transistors), one or more passive elements (such as resistors, capacitors, and / or inductors), and / or one or more sources (such as voltage and / or current sources) may instead include only the semiconductor elements within a single physical device (e.g., a semiconductor die and / or integrated circuit (IC) package), which may be adapted, either during or after manufacturing, for example, by an end user and / or a third party, to be combined with at least some of the passive elements and / or sources to form the described structure.

[0103] While this specification describes the use of specific transistors, other transistors (or equivalent devices) may be used instead with little or no modification to the rest of the circuit. For example, field-effect transistors ("FETs") (such as n-channel FETs (NFETs) or p-channel FETs (PFETs)), bipolar junction transistors (BJTs, e.g., NPN transistors or PNP transistors), insulated-gate bipolar transistors (IGBTs), and / or junction field-effect transistors (JFETs) may be used instead of or in combination with the devices described herein. Transistors may be depletion-mode devices, drain-extension devices, enhancement-mode devices, natural transistors, or other types of device structure transistors. Such devices may also be mounted in or on silicon substrates (Si), silicon carbide substrates (SiC), gallium nitride substrates (GaN), or gallium arsenide substrates (GaAs).

[0104] The circuits described herein are reconfigurable to include additional or different components, thereby providing functionality at least partially similar to that available before the component substitution. Components indicated as resistors generally represent any one or more elements that, unless otherwise specified, are connected in series and / or parallel to provide the impedance amount represented by the indicated resistors. For example, a resistor or capacitor indicated and described herein as a single component may instead be multiple resistors or capacitors, each connected in parallel between the same nodes. For example, a resistor or capacitor indicated and described herein as a single component may instead be multiple resistors or capacitors, each connected in series between the same two nodes as a single resistor or capacitor.

[0105] Some elements of the examples described may be included in an integrated circuit, while others may be outside of it, but in other examples, additional or fewer features may be incorporated into the integrated circuit. Also, some or all of the features illustrated as being outside of an integrated circuit may be included in an integrated circuit, and / or some of the features illustrated as being inside an integrated circuit may be incorporated outside of it. As used herein, the term “integrated circuit” means one or more circuits that are (1) incorporated in / on a semiconductor substrate, (2) incorporated in a single semiconductor package, (3) incorporated in the same module, and / or (4) incorporated in / on the same printed circuit board.

[0106] In the above description, the term "grounding" includes chassis grounding, earth grounding, floating grounding, virtual grounding, digital grounding, common grounding, and / or any other form of grounding connection applicable to or appropriate to the teachings herein. Unless otherwise stated herein, "about," "approximately," or "substantially" preceding a parameter means within ±10 percent of that parameter, and if the parameter is zero, it means within a reasonable range near zero.

Claims

1. It is a device, A substrate having an opening, A cantilever device having a first end on the substrate and a second end suspended above the opening, Includes, The aforementioned cantilever device A first piezoelectric layer having a first surface and a first polarization direction, A second piezoelectric layer having a second surface opposite to the first surface and having a second polarization direction different from the first polarization direction, The first electrode on the first surface, The second electrode on the second surface, including, Device.

2. The apparatus according to claim 1, wherein the first polarization direction has a first component along an axis perpendicular to the first surface, the second polarization direction has a second component along the axis, and the first component and the second component are of the same size and in opposite directions.

3. The apparatus according to claim 1, wherein the first polarization direction has a first component along a first axis, and the first axis is perpendicular to a second axis between the first end and the second end.

4. The apparatus according to claim 1, wherein the first piezoelectric layer has a first piezoelectric coupling coefficient, the second piezoelectric layer has a second piezoelectric coupling coefficient, and the second piezoelectric coupling coefficient and the first piezoelectric coupling coefficient have the same magnitude and opposite polarity.

5. The apparatus according to claim 1, wherein the first piezoelectric layer is in contact with the second piezoelectric layer.

6. The apparatus according to claim 1, wherein the cantilever device further includes a bonding layer between the first piezoelectric layer and the second piezoelectric layer.

7. The apparatus according to claim 1, wherein the first piezoelectric layer and the second piezoelectric layer have the same thickness.

8. The apparatus according to claim 1, wherein the first piezoelectric layer and the second piezoelectric layer have opposite crystal orientations.

9. The apparatus according to claim 1, wherein the first piezoelectric layer and the second piezoelectric layer contain the same piezoelectric material.

10. The apparatus according to claim 1, wherein the first piezoelectric layer and the second piezoelectric layer include different piezoelectric materials.

11. The apparatus according to claim 1, wherein the first electrode and the second electrode extend along half or less of the respective lengths of the first piezoelectric layer and the second piezoelectric layer.

12. The apparatus according to claim 1, wherein the cantilever device is configured as one of a piezoelectric microphone, a piezoelectric speaker, a piezoelectric micromachine ultrasonic transducer, a piezoelectric accelerometer, or a voice accelerometer.

13. It is a device, A substrate having an opening, A cantilever device having a first end on the substrate and a second end suspended above the opening, Includes, The aforementioned cantilever device A first piezoelectric layer having a first surface and a first intrinsic polarization direction, A second piezoelectric layer having a second surface opposite to the first surface and having a second inherent polarization direction different from the first inherent polarization direction, The first electrode on the first surface, The second electrode on the second surface, including, Device.

14. The apparatus according to claim 13, wherein the first inherent polarization direction has a first component along an axis perpendicular to the first surface, the second inherent polarization direction has a second component along the axis, and the first component and the second component have the same size and opposite directions.

15. The apparatus according to claim 13, wherein the first inherent polarization direction corresponds to a first crystal orientation of the first piezoelectric layer, the second inherent polarization direction corresponds to a second crystal orientation of the second piezoelectric layer, and the second crystal orientation is different from the first crystal orientation.

16. The apparatus according to claim 13, wherein the first piezoelectric layer has a first piezoelectric coupling coefficient, the second piezoelectric layer has a second piezoelectric coupling coefficient, and the first and second coupling coefficients have the same magnitude and opposite directions.

17. The apparatus according to claim 13, wherein the first piezoelectric layer and the second piezoelectric layer contain the same piezoelectric material.

18. The apparatus according to claim 13, The case and Integrated circuits and The device coupled to the aforementioned integrated circuit, Includes, The integrated circuit and the device are covered by the case, and the device includes the substrate and the cantilever device. Device.

19. The apparatus according to claim 18, wherein the integrated circuit is configured to operate the device as one of a piezoelectric microphone, a piezoelectric speaker, a piezoelectric micromachine ultrasonic transducer, a piezoelectric accelerometer, or a voice accelerometer.

20. It is a method, Forming a substrate having an opening, To form a cantilever device having a first end on the substrate and a second end suspended above the opening, Includes, Forming the aforementioned cantilever device To form a first piezoelectric layer having a first polarization direction and a first surface, A second piezoelectric layer is formed having a second polarization direction different from the first polarization direction and a second surface opposite to the first surface. Forming a first electrode on the first surface, Forming a second electrode on the second surface, Methods that include...

21. The method according to claim 20, Forming the first electrode and forming the first piezoelectric layer includes forming the first electrode and the first piezoelectric layer on a first wafer including the substrate, wherein the first piezoelectric layer has a third surface opposite to the first surface. The formation of the second electrode and the second piezoelectric layer includes forming the second electrode and the second piezoelectric layer on a second wafer, wherein the second piezoelectric layer has a fourth surface opposite to the second surface. Forming the aforementioned cantilever device The third surface is joined to the fourth surface, Removing the second wafer from the second piezoelectric layer and the second electrode, Etching the substrate in order to form the aforementioned opening, Methods that include...

22. A method according to claim 20, wherein forming the second piezoelectric layer includes forming the second piezoelectric layer on the first piezoelectric layer.

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