Micro-acoustic filter having layer arrangement comprising cavity

Abstract

An apparatus for implementing a microacoustic filter having a cavity stack is disclosed. In an example aspect, the apparatus includes a microacoustic filter having an electrode structure (310), a cavity stack (126), a buffer layer (128), and a piezoelectric layer (130). The cavity stack includes a conductive layer (312), a base layer (316), and at least two pillars (314) extending through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity (318) between the base layer and the conductive layer. A buffer layer (128) is disposed between the electrode (310) structure and the conductive layer (312) of the cavity stack. The piezoelectric layer (130) is disposed between the buffer layer (128) and the electrode structure (310).

Description

Technical Field

[0001] The present disclosure relates generally to wireless transceivers and other components employing filters, and more particularly to microacoustic filters implemented using cavity stacks. Background Art

[0002] Electronic devices use radio frequency (RF) signals to communicate information. These RF signals enable users to talk with friends, download information, share pictures, remotely control home devices, and receive global positioning information. In order to send or receive RF signals within a given frequency band, electronic devices may use filters to pass signals within the band and suppress (e.g., attenuate) interference or noise with frequencies outside the band. However, designing filters that provide filtering for RF applications, including those utilizing frequencies below 2.6 gigahertz (GHz), can be challenging. Summary of the invention

[0003] A device is disclosed that uses a piezoelectric material that excites a plate mode to implement a microacoustic filter with a cavity stack. In an example implementation, the microacoustic filter includes a piezoelectric layer (e.g., formed using aluminum scandium nitride), a cavity stack, and a buffer layer disposed between the cavity stack and the piezoelectric layer. The piezoelectric material has a crystal orientation that enables the excitation of a plate mode (e.g., a Lamé mode) having an orientation orthogonal to a surface of the piezoelectric layer (e.g., having an orientation along a vertical axis). The top layer of the cavity stack and the buffer layer enable the piezoelectric layer (such as aluminum scandium nitride) to be epitaxially grown. This enables the piezoelectric layer (such as aluminum scandium nitride) to be deposited directly onto the buffer layer and the cavity stack without the need to use a layer removal process or a transfer process. This manufacturing process enables the microacoustic filter to have a competitive price point compared to surface acoustic wave filters using other piezoelectric materials (such as lithium niobate or lithium tantalate piezoelectric materials and bulk wafer materials, the wafer size of which includes 150 mm or larger). Compared to some surface acoustic wave filters, the microacoustic filter can also have a higher electromechanical coupling coefficient and quality factor. This improved performance can be due at least in part to the inherent confinement of the cavity present in the cavity stack to the acoustic wave.

[0004] In an example aspect, a device for filtering is disclosed. The device includes a microacoustic filter having an electrode structure, a cavity stack, a buffer layer, and a piezoelectric layer. The cavity stack includes a conductive layer, a substrate layer, and at least two pillars, the at least two pillars extending through a plane defined by a surface of the substrate layer and extending toward the conductive layer to form a cavity between the substrate layer and the conductive layer. The buffer layer is disposed between the electrode structure and the conductive layer of the cavity stack. The piezoelectric layer is disposed between the buffer layer and the electrode structure.

[0005] In an example aspect, a device for filtering is disclosed. The device includes a microacoustic filter configured to generate a filter signal from a radio frequency signal. The microacoustic filter includes components for converting the radio frequency signal into an acoustic wave and converting the formed acoustic wave into a filter signal. The microacoustic filter also includes components for using a piezoelectric layer to excite a plate mode to generate a formed acoustic wave. The microacoustic filter additionally includes components for enabling epitaxial growth of the piezoelectric layer. The microacoustic filter also includes components for confining the energy of the plate mode within the components for exciting the plate mode and the components for enabling epitaxial growth.

[0006] In an example aspect, a method for manufacturing a microacoustic filter is disclosed. The method includes providing a cavity stack including a conductive layer, a substrate layer, and at least two pillars, the at least two pillars extending through a plane defined by a surface of the substrate layer and extending toward the conductive layer to form a cavity between the substrate layer and the conductive layer. The method also includes using epitaxy to dispose a buffer layer on the surface of the conductive layer. The method also includes disposing a piezoelectric layer on the surface of the buffer layer.

[0007] In an example aspect, a piezoelectric device is disclosed. The piezoelectric device includes an electrode structure, a buffer layer, and a piezoelectric layer. The buffer layer is configured to enable epitaxial growth of aluminum scandium nitride (AlScN). The piezoelectric layer is disposed between the buffer layer and the electrode structure. The piezoelectric layer includes aluminum scandium nitride (AlScN) having a crystal axis orientation that is substantially orthogonal to a flat surface of the piezoelectric layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 An example operating environment for a microacoustic filter having a cavity stack is illustrated.

[0009] Figure 2 An example wireless transceiver including at least one microacoustic filter having a cavity stack is illustrated.

[0010] Figure 3 An example assembly of a microacoustic filter having a cavity stack is illustrated.

[0011] Figure 4 Example implementations of microacoustic filters having cavity stacks are illustrated.

[0012] Figure 5 Example compensation layers for a microacoustic filter with a cavity stack are illustrated.

[0013] Figure 6 is a flow chart illustrating an example process for fabricating a microacoustic filter having a cavity stack. DETAILED DESCRIPTION

[0014] To send or receive radio frequency signals within a given frequency band, electronic devices may use filters to pass signals within the frequency band and suppress (e.g., attenuate) interference or noise with frequencies outside the frequency band. Electroacoustic devices (e.g., "acoustic filters") may be used to filter high-frequency signals (such as those with frequencies greater than 100 megahertz (MHz)) in many applications. Acoustic filters are tuned to pass certain frequencies (e.g., frequencies within their passband) and attenuate other frequencies (e.g., frequencies outside their passband). Using piezoelectric materials, acoustic filters operate by transforming an electrical signal wave applied to an electrical conductor into an acoustic wave (e.g., an acoustic signal wave) formed across the piezoelectric material. The acoustic wave is then converted back into an electrical filter signal. Acoustic filters may include electrode structures that transform or convert between electromagnetic waves and acoustic waves.

[0015] Acoustic waves are characterized by a velocity that has a magnitude much smaller than the velocity of electromagnetic waves. Generally speaking, the magnitude of the propagation velocity of a wave is proportional to the wavelength of the wave. Therefore, after converting the electrical signal wave into an acoustic signal wave, the wavelength of the acoustic signal wave is significantly smaller than the wavelength of the electrical signal wave. The resulting smaller wavelength of the acoustic signal wave enables the use of smaller filter devices to perform filtering. This permits the use of acoustic filters in space-constrained devices, including portable electronic devices such as cellular phones.

[0016] However, designing an acoustic filter that supports frequencies between about 500 megahertz (MHz) and 2.6 gigahertz (GHz) and is cost-competitive can be challenging. Some surface acoustic wave filters can support these frequencies and have a relatively low price point; however, the electromechanical coupling coefficient and / or quality factor of these filters may not be sufficient for some applications. Many surface acoustic wave filters rely on lithium niobate (LiNbO 3 ) or lithium tantalate (LiTaO 3 ) piezoelectric materials, which can be purchased as single crystals with a variety of possible different crystal orientations. However, as wafer sizes increase to 150 millimeters (mm) or larger, these piezoelectric materials can become significantly more expensive or unavailable.

[0017] In order to provide certain cost and performance improvements, the technology for implementing a microacoustic filter with a cavity stack uses a piezoelectric material configured to excite a plate mode. In an example implementation, the microacoustic filter includes a piezoelectric layer formed (for example, using scandium aluminum nitride), a cavity stack, and a buffer layer disposed between the cavity stack and the piezoelectric layer. The piezoelectric material has a crystal orientation that enables the excitation of a plate mode (for example, a Lamé mode) having an orientation orthogonal to a surface of the piezoelectric layer (for example, having an orientation along a vertical axis). The cavity stack includes a conductive layer, a substrate layer, and at least two posts that suspend the conductive layer "above" the substrate layer to form a cavity.

[0018] Conductive layers and buffer layers enable epitaxial growth of piezoelectric materials, such as, for example, scandium aluminum nitride. This enables the piezoelectric material to be deposited directly onto the buffer layer and cavity stack without the use of a layer removal process or a transfer process. This manufacturing process enables microacoustic filters to have a competitive price point compared to surface acoustic wave filters using lithium niobate or lithium tantalate piezoelectric materials and bulk wafer materials having wafer sizes of 150 mm or larger.

[0019] Compared to some surface acoustic wave filters, microacoustic filters can have higher electromechanical coupling coefficients and quality factors. This improved performance can be due at least in part to the inherent confinement of acoustic waves by the cavities present in the cavity stack. These techniques can be used with and provide benefits to microacoustic filters that support frequencies above 500 MHz, as well as other microacoustic filters that support frequencies equal to or below 2.6 GHz.

[0020] Figure 1 An example environment 100 for a microacoustic filter with a cavity stack is illustrated. In the environment 100, a computing device 102 communicates with a base station 104 via a wireless communication link 106 (wireless link 106). In this example, the computing device 102 is depicted as a smart phone. However, the computing device 102 can be implemented as any suitable computing or electronic device, such as a modem, a cellular base station, a broadband router, an access point, a cellular phone, a gaming device, a navigation device, a media device, a laptop computer, a desktop computer, a tablet computer, a wearable computer, a server, a network attached storage (NAS) device, a smart appliance or other Internet of Things (IoT) device, a medical device, a vehicle-based communication system, a radar, a radio device, and the like.

[0021] Base station 104 communicates with computing device 102 via wireless link 106, which may be implemented as any suitable type of wireless link. Although depicted as a cellular network tower, base station 104 may represent or be implemented as another device, such as a satellite, a server device, a terrestrial television broadcast tower, an access point, a peer device, a mesh network node, etc. Thus, computing device 102 may communicate with base station 104 or another device via a wireless connection.

[0022] Wireless link 106 may include a downlink of data or control information communicated from base station 104 to computing device 102, an uplink of other data or control information communicated from computing device 102 to base station 104, or both. Wireless link 106 may be implemented using any suitable communication protocol or standard, such as second generation (2G), third generation (3G), fourth generation (4G), or fifth generation (5G) cellular; IEEE 802.11 (e.g., ); IEEE 802.15 (e.g., ); IEEE 802.16 (e.g., ); etc. In some implementations, the wireless link 106 can provide power wirelessly, and the base station 104 or the computing device 102 can include a power source.

[0023] As shown, computing device 102 includes an application processor 108 and a computer-readable storage medium 110 (CRM 110). Application processor 108 may include any type of processor, such as a multi-core processor, that executes processor executable code stored by CRM 110. CRM 110 may include any suitable type of data storage medium, such as volatile memory (e.g., random access memory (RAM)), non-volatile memory (e.g., flash memory), optical media, magnetic media (e.g., disk), etc. In the context of the present disclosure, CRM 110 is implemented to store instructions 112, data 114, and other information for computing device 102, and therefore does not include transient propagating signals or carrier waves.

[0024] The computing device 102 may also include input / output ports 116 (I / O ports 116) and a display 118. The I / O ports 116 enable data exchange or interaction with other devices, networks, or users. The I / O ports 116 may include serial ports (e.g., universal serial bus (USB) ports), parallel ports, audio ports, infrared (IR) ports, user interface ports such as a touch screen, and the like. The display 118 presents graphics of the computing device 102, such as a user interface associated with an operating system, program, or application. Alternatively or additionally, the display 118 may be implemented as a display port or a virtual interface through which the graphical content of the computing device 102 is presented.

[0025] The wireless transceiver 120 of the computing device 102 provides connectivity to a corresponding network and other electronic devices connected thereto. The wireless transceiver 120 may facilitate communication over any suitable type of wireless network, such as a wireless local area network (WLAN), a peer-to-peer (P2P) network, a mesh network, a cellular network, an ultra-wideband (UWB) network, a wireless wide area network (WWAN), and / or a wireless personal area network (WPAN). In the context of the example environment 100, the wireless transceiver 120 enables the computing device 102 to communicate with the base station 104 and the network connected thereto. However, the wireless transceiver 120 may also enable the computing device 102 to communicate "directly" with other devices or networks.

[0026] The wireless transceiver 120 includes circuits and logic components for sending and receiving communication signals via the antenna 122. The components of the wireless transceiver 120 may include amplifiers, switches, mixers, analog-to-digital converters, filters, etc. for conditioning communication signals (e.g., for generating or processing signals). The wireless transceiver 120 may also include logic components that perform in-phase / quadrature (I / Q) operations such as synthesis, encoding, modulation, decoding, demodulation, etc. In some cases, the components of the wireless transceiver 120 are implemented as separate transmitter and receiver entities. Additionally or alternatively, the wireless transceiver 120 may be implemented using multiple or different parts to implement corresponding transmission and reception operations (e.g., separate transmission chains and reception chains). In general, the wireless transceiver 120 processes data and / or signals associated with data communicated to the computing device 102 via the antenna 122.

[0027] exist Figure 1 In the example shown, the wireless transceiver 120 includes at least one microacoustic filter 124 (e.g., an acoustic filter, a plate mode acoustic wave filter, a cavity plate mode microacoustic filter, or a membrane filter). In some specific implementations, the wireless transceiver 120 includes a plurality of microacoustic filters 124, which may be formed by microacoustic resonators arranged in series, in parallel, in a ladder structure, in a grid structure, or some combination thereof. Although the microacoustic filter 124 can be any type of microacoustic filter, the technology for implementing the microacoustic filter using a specific cavity stack is particularly cost-competitive for wafer sizes of approximately 150 mm, 200 mm, or 300 mm. In general, the term "approximately" can mean that any wafer size can be within + / -10% or less of the specified value (e.g., within + / -5%, + / -3%, or + / -2% of the specified value).

[0028] The micro-acoustic filter 124 includes at least one cavity stack 126, at least one buffer layer 128, at least one piezoelectric layer 130, and at least one metal layer 132. In some embodiments, the piezoelectric layer 130 is formed using scandium aluminum nitride 134. The crystal orientation of the piezoelectric layer 130 is provided so as to be able to excite a main wave mode having an orientation orthogonal to the flat surface of the piezoelectric layer 130. Example main wave modes include plate modes 136 (e.g., Lamé plate modes). The plate mode 136 excites an acoustic wave that causes different horizontal portions (e.g., left and right portions) of the piezoelectric layer 130 to move in opposite directions along the vertical axis. The plate mode 136 is a quasi-steady-state mode.

[0029] The cavity stack 126 and the buffer layer 128 enable or promote epitaxial growth of the piezoelectric layer 130. Specifically, when aluminum scandium nitride 134 (or a similar material) is used, the distance between atoms within the membrane layer (or "top" layer) of the cavity stack 126 and atoms within the buffer layer 128 has a relationship that promotes epitaxial growth of the aluminum scandium nitride 134. Generally speaking, the buffer layer 128 represents a crystalline seed layer for epitaxy to enable deposition of a crystalline layer of aluminum scandium nitride 134.

[0030] In some implementations, the cavity stack 126 represents a silicon-on-insulator (SOI) wafer. The cavity stack 126 suspends the buffer layer 128 and the piezoelectric layer 130 to provide isolation or confinement for the plate mode 136. The cavity stack 126 also provides a conductive back side to improve the electric field coupling between the electrode fingers of the metal layer 132. The electric field coupling via the conductive back side of the cavity stack 126 and the crystal orientation of the piezoelectric layer 130 enables the plate mode 136 to be excited. The suspension aspect and the resistivity (e.g., conductivity) aspect of the cavity stack 126 enable the microacoustic filter 124 to achieve a specific electromechanical coupling coefficient and / or quality factor.

[0031] The metal layer 132 includes an electrode structure (eg, Figure 3 The electrode structure 302) can be disposed on the piezoelectric layer 130. By using the technology of scandium aluminum nitride 134, the microacoustic filter 124 can be designed to support frequencies between about 500 MHz and 2.6 GHz, including frequencies at about 1.5 GHz and 2.5 GHz. Although higher frequencies are also possible. Generally speaking, the term "about" can mean that any frequency can be within + / -10% or less of the specified value (for example, within + / -5%, + / -3% or + / -2% of the specified value). About Figure 2 The microacoustic filter 124 is further described.

[0032] Figure 2An example wireless transceiver 120 is illustrated. In the depicted configuration, the wireless transceiver 120 includes a transmitter 202 and a receiver 204, which are coupled to a first antenna 122-1 and a second antenna 122-2, respectively. In other specific implementations, the transmitter 202 and the receiver 204 can be connected to the same antenna through a duplexer (not shown). The transmitter 202 is shown to include at least one digital-to-analog converter 206 (DAC 206), at least one first mixer 208-1, at least one amplifier 210 (e.g., a power amplifier), and at least one first micro-acoustic filter 124-1. The receiver 204 includes at least one second micro-acoustic filter 124-2, at least one amplifier 212 (e.g., a low noise amplifier), at least one second mixer 208-2, and at least one analog-to-digital converter 214 (ADC 214). The first mixer 208-1 and the second mixer 208-2 are coupled to a local oscillator 216. Although not explicitly shown, the digital-to-analog converter 206 of the transmitter 202 and the analog-to-digital converter 214 of the receiver 204 may be coupled to ( Figure 1 ) application processor 108 or another processor associated with the wireless transceiver 120 (e.g., a modem).

[0033] In some implementations, wireless transceiver 120 is implemented using multiple circuits (e.g., multiple integrated circuits) such as transceiver circuit 236 and radio frequency front end (RFFE) circuit 238. Thus, the components that form transmitter 202 and receiver 204 are distributed across these circuits. Figure 2 As shown, the transceiver circuit 236 includes the digital-to-analog converter 206 of the transmitter 202, the mixer 208-1 of the transmitter 202, the mixer 208-2 of the receiver 204, and the analog-to-digital converter 214 of the receiver 204. In other specific implementations, the digital-to-analog converter 206 and the analog-to-digital converter 214 can be implemented on another separate circuit including the application processor 108 or the modem. The RF front-end circuit 238 includes the amplifier 210 of the transmitter 202, the micro-acoustic filter 124-1 of the transmitter 202, the micro-acoustic filter 124-2 of the receiver 204, and the amplifier 212 of the receiver 204.

[0034] During transmission, the transmitter 202 generates a radio frequency transmit signal 218 that is transmitted using the antenna 122-1. To generate the radio frequency transmit signal 218, the digital-to-analog converter 206 provides a pre-up-converted transmit signal 220 to the first mixer 208-1. The pre-up-converted transmit signal 220 may be a baseband signal or an intermediate frequency signal. The first mixer 208-1 uses a local oscillator (LO) signal 222 provided by the local oscillator 216 to up-convert the pre-up-converted transmit signal 220. The first mixer 208-1 generates an up-converted signal, which is referred to as a pre-filter transmit signal 224. The pre-filter transmit signal 224 may be a radio frequency signal and include some noise or unwanted frequencies, such as harmonic frequencies. The amplifier 210 amplifies the pre-filter transmit signal 224 and passes the amplified pre-filter transmit signal 224 to the first micro-acoustic filter 124-1.

[0035] The first micro-acoustic filter 124-1 filters the amplified pre-filter transmit signal 224 to generate a filtered transmit signal 226. As part of the filtering process, the first micro-acoustic filter 124-1 attenuates noise or unwanted frequencies within the pre-filter transmit signal 224. The transmitter 202 provides the filtered transmit signal 226 to the antenna 122-1 for transmission. The transmitted filtered transmit signal 226 is represented by the radio frequency transmit signal 218.

[0036] During reception, antenna 122-2 receives RF receive signal 228 and passes RF receive signal 228 to receiver 204. Second micro-acoustic filter 124-2 accepts received RF receive signal 228, which is represented by pre-filter receive signal 230. Second micro-acoustic filter 124-2 filters any noise or unwanted frequencies within pre-filter receive signal 230 to generate filtered receive signal 232.

[0037] The amplifier 212 of the receiver 204 amplifies the filtered received signal 232 and passes the amplified filtered received signal 232 to the second mixer 208-2. The second mixer 208-2 downconverts the amplified filtered received signal 232 using the local oscillator signal 222 to generate a downconverted received signal 234. The analog-to-digital converter 214 converts the downconverted received signal 234 into a digital signal that can be processed by the application processor 108 or another processor associated with the wireless transceiver 120 (e.g., a modem).

[0038] Figure 2One example configuration of the wireless transceiver 120 is illustrated. Other configurations of the wireless transceiver 120 may support multiple frequency bands and share the antenna 122 across multiple transceivers. A person of ordinary skill in the art may appreciate various other configurations that may include the micro-acoustic filter 124. For example, the micro-acoustic filter 124 may be integrated into a duplexer or a diplexer of the wireless transceiver 120. Figures 3 to 5 An example implementation of the microacoustic filter 124 - 1 or 124 - 2 is further described.

[0039] Figure 3 Example components of a microacoustic filter 124 are illustrated. In the depicted configuration, the microacoustic filter 124 includes an electrode structure 302, a piezoelectric layer 130, a buffer layer 128, and a cavity stack 126. The electrode structure 302 includes a conductive material (such as a metal) and may include one or more layers. The one or more layers may include one or more metal layers and may optionally include one or more adhesion layers. As an example, the metal layer may be composed of aluminum (Al), copper (Cu), silver (Ag), gold (Au), tungsten (W), or some combination or doping thereof. The adhesion layer may be composed of chromium (Cr), titanium (Ti), molybdenum (Mo), or some combination thereof.

[0040] The electrode structure 302 may include one or more interdigital transducers 304. The interdigital transducers 304 convert electrical signals into acoustic waves and convert acoustic waves into filtered electrical signals. The interdigital transducers 304 include at least two comb structures 306-1 and 306-2. Each comb structure 306-1 and 306-2 includes a busbar 308 (e.g., a conductive segment or conductive rail) and a plurality of fingers 310 (e.g., electrode fingers). Figure 4 An example interdigital transducer 304 is further described. Although not explicitly shown, the electrode structure 302 may also include two or more reflectors. In an example implementation, the interdigital transducer 304 is arranged between two reflectors.

[0041] The piezoelectric layer 130 has a crystalline (or crystal) structure defined by an ordered arrangement of particles (e.g., atoms, ions, or molecules). The crystalline structure of the piezoelectric layer 130 is selected so that the piezoelectric layer 130 excites a plate mode 136. In some implementations, scandium aluminum nitride 134 may be used. Some implementations of scandium aluminum nitride 134 have a ratio of approximately 70 aluminum atoms and 30 scandium atoms per 100 nitrogen atoms. Adding scandium atoms to the aluminum-nitrogen lattice softens the aluminum-nitrogen lattice structure, which can increase its piezoelectric coupling and the bandwidth of the microacoustic filter 124. The crystal axis orientation of the piezoelectric layer 130 is approximately orthogonal to the plane of the piezoelectric layer 130.

[0042] The buffer layer 128 can be implemented using a variety of different materials. For example, the buffer layer 128 can include at least one of the following types of materials: aluminum (Al), aluminum nitride (AlN), gallium (Ga), gallium nitride (GaN), hafnium (Hf), hafnium nitride (HfN), molybdenum (Mo), molybdenum nitride (MoN), niobium (Nb), niobium nitride (NbN), silicon carbide (SiC), scandium (Sc), scandium nitride (ScN), titanium (Ti), titanium nitride (TiN), zinc (Zn), zinc oxide (ZnO), zirconium (Zr) or zirconium nitride (ZrN), or a combination thereof. In some specific implementations, the buffer layer 128 can be implemented using a metal layer.

[0043] The cavity stack 126 includes at least one conductive layer 312, at least two pillars 314, and at least one base layer 316. The conductive layer 312 serves as a film layer of the cavity stack 126 and has a resistivity of less than about 0.1 ohm centimeters (Ω·cm) (e.g., a conductivity greater than about 10 Siemens / cm (S / cm)). Generally speaking, the resistivity of the conductive layer 312 is such that the conductivity through the conductive layer 312 between the two fingers 310 is approximately the same magnitude as the conductivity along the interdigital transducer 304.

[0044] To achieve epitaxial growth of the piezoelectric layer 130, the conductive layer 312 may be formed using a single crystalline material rather than an amorphous material. In an exemplary implementation, the conductive layer 312 includes doped silicon (Si). The doped silicon may have a relative humidity greater than about 10 18 The doping concentration of atoms / cm3 is set to achieve the target resistivity. Generally, the thickness of the conductive layer 312 is sufficient to support suspending the buffer layer 128, the piezoelectric layer 130 and the electrode structure 302 "above" the base layer 316. According to the Miller index, the conductive layer 312 can be represented as Si (1 1 1).

[0045] The pillar 314 is disposed between the conductive layer 312 and the base layer 316. The pillar 314 may be made of a dielectric material such as silicon dioxide (SiO 2 )). Generally speaking, posts 314 provide structural support to elevate conductive layer 312 "above" base layer 316. By elevating conductive layer 312, posts 314 suspend at least a portion of piezoelectric layer 130, buffer layer 128, and conductive layer 312 away from base layer 316. Posts 314 are positioned at different points along an axis orthogonal to the longitudinal axis of fingers 310 of electrode structure 302. In some aspects, the material of posts 314 can be selected (e.g., such as SiO 2 In the case of ) to provide temperature compensation effect.

[0046] The post 314 defines a cavity 318 (or gap) between the conductive layer 312 and the base layer 316. The cavity 318 may contain a gas, such as air. The post 314 provides stability and support to prevent the cavity 318 from collapsing. In some embodiments, the fingers 310 of the interdigital transducer 304 are positioned between the posts 314 along an axis orthogonal to the longitudinal axis of the fingers 310. Any reflector may also be positioned between the posts 314 along the axis. In this sense, the cavity 318 may be considered to be "below" the fingers 310 and / or the reflectors. Generally speaking, it may be advantageous to position the cavity 318 below a portion of the electrode structure 302 because the acoustic waves (or plate waves) are confined in the piezoelectric layer 130, the buffer layer 128, and the conductive layer 312.

[0047] In order to achieve a resonant frequency between about 500 MHz and 2.5 GHz, the piezoelectric layer 130 and the conductive layer 312 may each have a thickness between about 0.5 micrometers and 5 micrometers (μm). In addition, the spacing of the interdigital transducer 304 may be between about 500 nanometers (nm) and 5 μm. In some specific implementations, the thickness of the piezoelectric layer 130 and the thickness of the conductive layer 312 are approximately equal. For example, the thickness of the piezoelectric layer 130 and the thickness of the conductive layer 312 may both be approximately equal to 1000 nm to achieve a first micro-acoustic filter 124 with a resonant frequency of about 1.5 GHz. As another example, the thickness of the piezoelectric layer 130 and the thickness of the conductive layer 312 may both be approximately equal to 600 nm to achieve a second micro-acoustic filter 124 with a resonant frequency of about 2.6 GHz. In general, the term "about" may mean that any thickness may be within + / -10% or less of a specified value (e.g., within + / -5%, + / -3%, or + / -2% of a specified value). The thickness of the buffer layer 128 may be smaller than the thickness of the piezoelectric layer 130 .

[0048] The design of the microacoustic filter 124 can achieve an electromechanical coupling coefficient (k) greater than 10% (eg, 10.5%, 11%, 12%, or 15%). 2 ). Generally speaking, the term "about" can mean that any electromechanical coupling coefficient can be within + / -10% or less of the specified value (e.g., within + / -5%, + / -3%, or + / -2% of the specified value). One way to define the electromechanical coupling coefficient is further shown in Equation 1 below:

[0049]

[0050] where f s is the resonant frequency, and f pThe microacoustic filter 124 may also be designed to achieve an absolute value of a temperature coefficient of frequency (TCF) of about 40 parts per million per Kelvin (ppm / K) or less (eg, a temperature coefficient of frequency of about -40 ppm / K or greater).

[0051] The base layer 316 includes one or more sub-layers that provide support for the microacoustic filter 124. In one example implementation, the base layer 316 is formed using silicon (Si). The base layer 316 may represent a wafer.

[0052] In some implementations, the microacoustic filter 124 includes at least one compensation layer 320, such as Figure 5 The compensation layer 320 may provide temperature compensation so that the microacoustic filter 124 can achieve a target frequency temperature coefficient based on the thickness of the piezoelectric layer 130. In an example implementation, the compensation layer 320 is made of silicon dioxide (SiO 2 ) can be implemented. Other example implementations can use other types of materials, such as doped silicon dioxide, silicon nitride (SiN), silicon oxynitride (SiON), or fluorine-doped silicon oxide (SiOF). In some applications, the microacoustic filter 124 may not include, for example, the compensation layer 320 to reduce the cost of the microacoustic filter 124.

[0053] In some aspects, the microacoustic filter 124 can be considered a resonator. Sometimes, the microacoustic filter 124 can be connected to other resonators associated with a layer stack different from the microacoustic filter 124. In other aspects, the microacoustic filter 124 can be implemented as multiple interconnected resonators using the same layers (e.g., buffer layer 128, piezoelectric layer 130, and / or conductive layer 312). Figure 4 The microacoustic filter 124 is further described.

[0054] Figure 4 An example implementation of a microacoustic filter 124 having a cavity stack 126 is illustrated. Figure 4 A three-dimensional perspective view 400-1 of the microacoustic filter 124 is shown at the top of Figure 4 A two-dimensional cross-sectional view 400 - 2 of the microacoustic filter 124 is shown at the bottom of FIG. The microacoustic filter 124 includes an electrode structure 302 , a piezoelectric layer 130 , a buffer layer 128 , and a cavity stack 126 . The electrode structure 302 may include one or more interdigital transducers 304 .

[0055] In the depicted configuration shown in the two-dimensional cross-sectional view 400-2, the buffer layer 128 is disposed between the piezoelectric layer 130 and the cavity stack 126. The piezoelectric layer 130 is disposed between the electrode structure 302 and the buffer layer 128. The conductive layer 312 of the cavity stack 126 is disposed between the buffer layer 128 and the pillars 314. The pillars 314 are disposed between the base layer 316 and the conductive layer 312. Specifically, the pillars 314 extend through a plane defined by a surface of the base layer 316 and toward the conductive layer 312 to form a cavity 318 between the base layer 316 and the conductive layer 312.

[0056] In the three-dimensional perspective view 400-1, the IDT 304 is shown as having two comb structures 306-1 and 306-2, wherein the fingers 310 extend toward each other from the two busbars 308. The fingers 310 are arranged in an interlocking manner between the two busbars 308 of the IDT 304 (e.g., arranged in an interdigitated manner). In other words, the fingers 310 connected to the first busbar 308 extend toward the second busbar 308, but are not connected to the second busbar 308. Similarly, the fingers 310 connected to the second busbar 308 extend toward the first busbar 308, but are not connected to the first busbar 308.

[0057] In the direction along the busbar 308, there is an overlap region that includes a central region where a portion of one finger 310 overlaps a portion of an adjacent finger 310. This central region including the overlap may be referred to as an orifice, track, or active region, where an electric field is generated between the fingers 310 to cause an acoustic wave 412 to form in at least this region of the piezoelectric layer 130.

[0058] The physical periodicity of the fingers 310 is referred to as the spacing 404 of the interdigital transducer 304. The spacing 404 can be indicated in various ways. For example, in some aspects, the spacing 404 can correspond to the magnitude of the distance between adjacent fingers 310 of the interdigital transducer 304 in the central region. For example, the distance can be defined as the distance between the center points of each finger in the fingers 310. When the fingers 310 have a uniform width, the distance can usually be measured between the right (or left) edge of one finger 310 and the right (or left) edge of the adjacent finger 310. In some aspects, the average value of the distance between adjacent fingers 310 of the interdigital transducer 304 can be used for the spacing 404. The frequency is at least partially determined by the characteristics of the micro-acoustic filter 124.

[0059] In the three-dimensional perspective view 400-1, the micro-acoustic filter 124 is defined by a first (X) axis 406, a second (Y) axis 408, and a third (Z) axis 410. The first axis 406 and the second axis 408 are parallel to the planar surface of the piezoelectric layer 130, and the second axis 408 is perpendicular to the first axis 406. The third axis 410 is orthogonal (e.g., perpendicular) to the planar surface of the piezoelectric layer 130. The busbars 308 of the interdigital transducer 304 are oriented parallel to the first axis 406. The fingers 310 of the interdigital transducer 304 are oriented parallel to the second axis 408. The fingers 310 generate an electric field in a direction substantially parallel to the first axis 406. The electric field can generate a quasi-steady-state acoustic wave 412, which is trapped within the piezoelectric layer 130, the buffer layer 128, and the conductive layer 312 and exists between adjacent fingers 310 of the electrode structure 302.

[0060] like Figure 4 As shown, each of the posts 314 can extend in a continuous manner across the second (Y) axis 408. Other specific implementations can implement each post 314 in a segmented manner across the second (Y) axis 408. In other words, each post 314 can be implemented using multiple posts that are arranged at similar points on the first (X) axis 406 along the second (Y) axis 408. In general, the posts 314 are positioned so that the width of the cavity 318 along the first (X) axis 406 can be approximately equal to or greater than the distance between the first finger and the last finger 310 of the interdigital transducer 304.

[0061] During operation, the microacoustic filter 124 receives RF signals such as Figure 2 , or the pre-filter transmit signal 224 or the pre-filter receive signal 230 shown in . The electrode structure 302 excites the acoustic wave 412 in the piezoelectric layer 130 using the inverse piezoelectric effect. For example, the interdigital transducers 304 in the electrode structure 302 generate an alternating electric field based on the received radio frequency signal. The piezoelectric layer 130 enables the acoustic wave 412 to be formed in response to the alternating electric field generated by the interdigital transducers 304. In other words, the piezoelectric layer 130 at least partially enables the acoustic wave 412 to be formed in response to the electrical stimulation performed by one or more interdigital transducers 304.

[0062] The acoustic wave 412 is formed within the piezoelectric layer 130, the buffer layer 128, and the conductive layer 312, and interacts with the interdigital transducer 304. The formed acoustic wave 412 can be a standing wave. In some implementations, two reflectors within the electrode structure 302 cause the acoustic wave 412 to be formed as a standing wave across a portion of the first (X) axis 406.

[0063] Using the piezoelectric effect, the electrode structure 302 generates a filtered RF signal based on the formed acoustic wave 412. Specifically, due to the mechanical stress generated by the formation of the acoustic wave 412, the piezoelectric layer 130 generates an alternating electric field. The alternating electric field induces an alternating current in another interdigital transducer or the interdigital transducer 304. The alternating current forms a filtered RF signal provided at the output of the microacoustic filter 124. The filtered RF signal may include Figure 2 The filtered transmit signal 226 or the filtered receive signal 232 .

[0064] It should be understood that although Figure 4 A certain number of fingers are illustrated in the example, but the actual number of fingers and the length and width of the fingers and busbars may be different in actual implementations. Such parameters depend on the specific application and the desired filter characteristics. In addition, the microacoustic filter 124 may include a plurality of interconnected electrode structures 302, each of which includes a plurality of interdigital transducers 304 to achieve a desired passband (e.g., a plurality of interconnected resonators or interdigital transducers 304 connected in series or in parallel to form a desired filter transfer function).

[0065] Although not explicitly shown, the electrode structure 302 may also include two or more reflectors. In an example implementation, the interdigital transducer 304 is arranged between two reflectors (not shown). Each reflector within the electrode structure 302 may have a grating structure with two busbars and conductive fingers connected to the two busbars. In some implementations, the spacing of the reflectors may be similar or the same as the spacing 404 of the interdigital transducers 304. Some implementations of the microacoustic filter 124 may include one or more compensation layers 320, such as with respect to Figure 5 as further described.

[0066] Figure 5 An example compensation layer 320 of a microacoustic filter 124 is illustrated. In the depicted configuration, the microacoustic filter 124 includes a first compensation layer 320-1, a second compensation layer 320-2, and / or a third compensation layer 320-3. The first compensation layer 320-1 is disposed across the fingers 310 of the electrode structure 302. Because the surface of the first compensation layer 320-1 is exposed within the layer stack of the microacoustic filter 124, the thickness of the first compensation layer 320-1 can be trimmed relatively easily to achieve a desired frequency temperature coefficient.

[0067] The second compensation layer 320-2 is disposed between the electrode structure 302 and the piezoelectric layer 130. The thickness of the second compensation layer 320-2 may be designed to enable the microacoustic filter 124 to achieve a target electromechanical coupling coefficient for some applications.

[0068] The third compensation layer 320-3 is disposed between the conductive layer 312 and the cavity 318. The length of the third compensation layer 320-3 across the first (X) axis 408 may extend between the pillars 314, such as Figure 5 Alternatively, the length of the third compensation layer 320-3 along the first (X) axis 408 may be less than the distance between the pillars 314. Figure 5 The microacoustic filter 124 is shown as including three compensation layers 320, but other implementations of the microacoustic filter 124 may include only the first compensation layer 320-1, only the second compensation layer 320-2, only the third compensation layer 320-3, or some combination thereof.

[0069] Figure 6 6 is a flow chart illustrating an example process 600 for manufacturing a microacoustic filter 124 having a cavity stack 126. The process 600 is described in the form of a set of blocks 602-606 that specify operations that may be performed. However, the operations are not necessarily limited to Figure 6 600 or described herein, as these operations may be performed in an alternative order or in a fully or partially overlapping manner. Moreover, more, fewer, and / or different operations may be performed to perform process 600 or alternative processes. The operations represented by the illustrated blocks of process 600 may be performed to manufacture (e.g., Figures 1 to 3 More specifically, the operations of process 600 may be performed at least in part to manufacture (eg, Figure 4 and Figure 5 ) piezoelectric layer 130 of the microacoustic filter 124.

[0070] At 602, a cavity stack is provided that includes a conductive layer, a base layer, and at least two pillars extending through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity between the base layer and the conductive layer. For example, the manufacturing process provides a cavity stack 126, such as Figure 3 or Figure 4 As shown. Cavity stack 126 includes a conductive layer 312, which can be formed using a single crystal material (e.g., a non-amorphous material) and has a resistivity of less than about 0.1 Ω·cm (e.g., a conductivity greater than about 10 S / cm). Conductive layer 312 represents a film layer of cavity stack 126. Cavity stack 126 also includes a base layer 316 and pillars 314. Base layer 316 can be formed using silicon, and pillars 314 can be formed using silicon dioxide.

[0071] Posts 314 suspend conductive layer 312 “above” base layer 316 to form cavity 318. Specifically, posts 314 extend through a plane defined by a surface of base layer 316 and toward conductive layer 312 to form cavity 318 therebetween.

[0072] At 604, a buffer layer is disposed on the surface of the conductive layer. For example, the manufacturing process disposes the buffer layer 128 on the surface of the conductive layer 312, such as Figure 4 and Figure 5 The buffer layer 128 can be implemented using a variety of different materials. Generally speaking, the buffer layer 128 enables the material forming the piezoelectric layer 130 to grow epitaxially.

[0073] At 606, the piezoelectric layer 130 is disposed on the surface of the buffer layer using epitaxy. For example, the manufacturing process uses epitaxy to dispose the piezoelectric layer 130 on the surface of the buffer layer 128. In some implementations, the piezoelectric layer 130 is formed using aluminum scandium nitride 134. The piezoelectric layer 130 can have a crystalline structure that excites a primary wave mode (e.g., a plate mode 136) having an orientation along the third (Z) axis 410. By using epitaxy and materials such as aluminum scandium nitride 134, the cost of manufacturing the microacoustic filter 124 can be lower than other types of filters that rely on a layer removal process or a transfer process and utilize piezoelectric materials (such as lithium niobate or lithium tantalate). Although in Figure 6 Although not explicitly shown, the manufacturing process may also include depositing the electrode structure 302 on the piezoelectric layer 130 .

[0074] There are various processes for making the microacoustic filter 124. In one process, the cavity stack 126 is commercially available and the buffer layer 128 and the piezoelectric layer 130 are disposed on the cavity stack 126 using a sputtering process. In another process, the cavity stack 126 is made using a Bosch process to form the cavity 318. Some processes may include depositing a passivation layer and / or depositing one or more compensation layers 320.

[0075] Although the techniques for implementing the microacoustic filter 124 are described with respect to aluminum scandium nitride 134 as the piezoelectric layer 130, other specific implementations are possible. For example, these techniques can be applied to fabricating other microacoustic filters 124 using aluminum nitride (AlN) as the piezoelectric layer 130. Aluminum nitride can have the same or similar crystal axis orientation as the aluminum scandium nitride 134.

[0076] Some aspects are described below.

[0077] Aspect 1: A device, comprising:

[0078] A micro-acoustic filter, the micro-acoustic filter comprising:

[0079] Electrode structure;

[0080] A cavity stack, the cavity stack comprising:

[0081] Conductive layer;

[0082] basal layer; and

[0083] at least two posts extending through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity between the base layer and the conductive layer;

[0084] a buffer layer disposed between the electrode structure and the conductive layer of the cavity stack; and

[0085] A piezoelectric layer is disposed between the buffer layer and the electrode structure.

[0086] Aspect 2: The device according to aspect 1, wherein the microacoustic filter is configured to excite a plate mode in the piezoelectric layer.

[0087] Aspect 3: The device of aspect 1 or 2, wherein the piezoelectric layer comprises aluminum scandium nitride (AlScN).

[0088] Aspect 4: The device of any preceding aspect, wherein the conductive layer has a resistivity of less than about 0.1 ohm-cm.

[0089] Aspect 5: The device of any preceding aspect, wherein the conductive layer comprises doped silicon (Si).

[0090] Aspect 6: The device according to aspect 5, wherein the doped silicon (Si) has a carbon content greater than about 10 18 atoms / cm3 doping concentration.

[0091] Aspect 7: The apparatus of any preceding aspect, wherein the conductive layer and the buffer layer are collectively configured to enable epitaxial growth of the piezoelectric layer.

[0092] Aspect 8: The device of any preceding aspect, wherein the conductive layer comprises a single crystalline material.

[0093] Aspect 9: The device according to aspect 8, wherein the single crystal material comprises silicon having a Miller index of (1 1 1).

[0094] Aspect 10: The device of any preceding aspect, wherein the buffer layer comprises at least one of the following materials:

[0095] Aluminum (Al) or aluminum nitride (AlN);

[0096] Gallium (Ga) or gallium nitride (GaN);

[0097] Hafnium (Hf) or hafnium nitride (HfN);

[0098] Molybdenum (Mo) or molybdenum nitride (MoN);

[0099] Niobium (Nb) or niobium nitride (NbN);

[0100] Silicon carbide (SiC);

[0101] Scandium (Sc) or scandium nitride (ScN);

[0102] Titanium (Ti) or titanium nitride (TiN);

[0103] Zinc (Zi) or zinc oxide (ZnO); or

[0104] Zirconium (Zr) or zirconium nitride (ZrN).

[0105] Aspect 11: The apparatus according to any preceding aspect, wherein:

[0106] The electrode structure includes a plurality of fingers arranged across a plane having a first axis perpendicular to the plurality of fingers and a second axis parallel to the plurality of fingers; and

[0107] The plurality of fingers are positioned between the at least two posts along the first axis.

[0108] Aspect 12: The device according to any preceding aspect, wherein the microacoustic filter comprises at least one of the following:

[0109] a first compensation layer, the first compensation layer being disposed on the electrode structure;

[0110] a second compensation layer, the second compensation layer being arranged between the electrode structure and the piezoelectric layer; or

[0111] A third compensation layer is disposed between the conductive layer and the cavity.

[0112] Aspect 13: The device according to aspect 12, wherein the first compensation layer, the second compensation layer or the third compensation layer comprises silicon dioxide (SiO 2 ) or doped silicon dioxide.

[0113] Aspect 14: The apparatus according to any preceding aspect, wherein:

[0114] The microacoustic filter includes a plurality of cascaded resonators; and

[0115] A resonator in the plurality of cascaded resonators includes the cavity stack, the piezoelectric layer, and the buffer layer.

[0116] Aspect 15: The apparatus according to any of the preceding aspects, further comprising:

[0117] A wireless transceiver coupled to at least one antenna, the wireless transceiver including the microacoustic filter and configured to use the microacoustic filter to filter wireless signals communicated via the at least one antenna.

[0118] Aspect 16: The apparatus of any preceding aspect, wherein the microacoustic filter is configured to have a resonant frequency between approximately 500 megahertz and 2.6 gigahertz.

[0119] Aspect 17: The apparatus according to Aspect 16, wherein:

[0120] The conductive layer has a thickness between about 0.5 micrometers and 5 micrometers; and

[0121] The piezoelectric layer has a thickness between about 0.5 micrometers and 5 micrometers;

[0122] Aspect 18: The device of aspect 17, wherein the thickness of the conductive layer and the thickness of the piezoelectric layer are substantially equal.

[0123] Aspect 19: The device of aspect 17, wherein a thickness of the buffer layer is less than the thickness of the piezoelectric layer.

[0124] Aspect 20: A device, comprising:

[0125] A micro-acoustic filter, the micro-acoustic filter being configured to generate a filtered signal from a radio frequency signal, the micro-acoustic filter comprising:

[0126] means for converting the radio frequency signal into an acoustic wave and converting the resulting acoustic wave into the filtered signal;

[0127] means for exciting a plate mode using a piezoelectric layer to produce said formed acoustic wave;

[0128] means for enabling epitaxial growth of the piezoelectric layer; and

[0129] Means for confining energy of the plate mode within the means for exciting the plate mode and within the means for enabling epitaxial growth.

[0130] Aspect 21: The apparatus according to Aspect 20, wherein:

[0131] The microacoustic filter comprises a substrate layer; and

[0132] The means for limiting the energy of the plate mode comprises means for suspending the means for enabling epitaxial growth away from the base layer.

[0133] Aspect 22: A method for manufacturing a microacoustic filter, the method comprising:

[0134] providing a cavity stack including a conductive layer, a base layer, and at least two pillars extending through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity between the base layer and the conductive layer;

[0135] disposing a buffer layer on the surface of the conductive layer; and

[0136] A piezoelectric layer is disposed on the surface of the buffer layer using epitaxy.

[0137] Aspect 23: The method of aspect 22, wherein the conductive layer comprises a single crystalline material.

[0138] Aspect 24: The method according to aspect 22 or 23, wherein the conductive layer comprises a doping concentration greater than about 10 18 atoms / cubic centimeter of doped silicon (Si).

[0139] Aspect 25: The method according to any one of aspects 22 to 24, wherein the buffer layer comprises at least one of the following materials:

[0140] Aluminum (Al) or aluminum nitride (AlN);

[0141] Gallium (Ga) or gallium nitride (GaN);

[0142] Hafnium (Hf) or hafnium nitride (HfN);

[0143] Molybdenum (Mo) or molybdenum nitride (MoN);

[0144] Niobium (Nb) or niobium nitride (NbN);

[0145] Silicon carbide (SiC);

[0146] Scandium (Sc) or scandium nitride (ScN);

[0147] Titanium (Ti) or titanium nitride (TiN);

[0148] Zinc (Zi) or zinc oxide (ZnO); or

[0149] Zirconium (Zr) or zirconium nitride (ZrN).

[0150] Aspect 26: A piezoelectric device, comprising:

[0151] Electrode structure;

[0152] A buffer layer configured to enable epitaxial growth of aluminum scandium nitride (AlScN)

[0153] growth; and

[0154] A piezoelectric layer is disposed between the buffer layer and the electrode structure, the piezoelectric layer comprising the aluminum scandium nitride (AlScN) having a crystal axis orientation substantially orthogonal to a planar surface of the piezoelectric layer.

[0155] Aspect 27: The piezoelectric device of aspect 26, wherein the piezoelectric layer is configured to excite a plate mode.

[0156] Aspect 28: The piezoelectric device according to Aspect 26 or 27, further comprising:

[0157] Cavity stacking,

[0158] The buffer layer is arranged between the cavity stack and the piezoelectric layer.

[0159] Aspect 29: The piezoelectric device according to Aspect 28, wherein the cavity stack comprises:

[0160] Conductive layer;

[0161] basal layer; and

[0162] At least two posts extend through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity between the base layer and the conductive layer.

[0163] Aspect 30: The piezoelectric device according to Aspect 29, wherein:

[0164] The conductive layer comprises doped silicon (Si);

[0165] The base layer comprises silicon (Si); and

[0166] The at least two columns comprise silicon dioxide (SiO 2 ).

[0167] Unless the context dictates otherwise, the use of the word "or" herein may be considered an "inclusive or" or use of a term that permits inclusion or application of one or more items linked by the word "or" (e.g., the phrase "A or B" may be interpreted as permitting only "A," only "B," or both "A" and "B"). As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items (including a single member). As an example, "at least one of a, b, or c" is intended to encompass: a, b, c, ab, ac, bc, and abc, as well as any combination with multiple identical elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other ordering of a, b, and c). In addition, the items represented in the drawings and the terms discussed herein may indicate one or more items or terms, and thus the singular or plural forms of those items and terms may be referred to interchangeably in this written description. Finally, although the subject matter has been described in language specific to structural features or methodological operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or operations described above, including not necessarily limited to the organization in which the features are arranged or the order in which the operations are performed.

Claims

1. A device, the device include: A micro-acoustic filter, the micro-acoustic filter comprising: Electrode structure; A cavity stack, the cavity stack comprising: Conductive layer; basal layer; and at least two posts extending through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity between the base layer and the conductive layer; a buffer layer disposed between the electrode structure and the conductive layer of the cavity stack; and A piezoelectric layer is disposed between the buffer layer and the electrode structure. 2 . The device of claim 1 , wherein the microacoustic filter is configured to excite a plate mode in the piezoelectric layer.

3. The device of claim 1, wherein the piezoelectric layer comprises aluminum scandium nitride (AlScN).

4. The device of claim 1, wherein the conductive layer has a resistivity of less than about 0.1 ohm-cm. The device of claim 1 , wherein the conductive layer comprises doped silicon (Si).

6. The device of claim 5, wherein the doped silicon (Si) has a 18 atoms / cm3 doping concentration. 7 . The device of claim 1 , wherein the conductive layer and the buffer layer are collectively configured to enable epitaxial growth of the piezoelectric layer. The device of claim 1 , wherein the conductive layer comprises a single crystalline material.

9. The device of claim 8, wherein the single crystal material comprises silicon having a Miller index of (11 1).

10. The device of claim 1, wherein the buffer layer comprises at least one of the following materials: Aluminum (Al) or aluminum nitride (AlN); Gallium (Ga) or gallium nitride (GaN); Hafnium (Hf) or hafnium nitride (HfN); Molybdenum (Mo) or molybdenum nitride (MoN); Niobium (Nb) or niobium nitride (NbN); Silicon carbide (SiC); Scandium (Sc) or scandium nitride (ScN); Titanium (Ti) or titanium nitride (TiN); Zinc (Zi) or zinc oxide (ZnO); or Zirconium (Zr) or zirconium nitride (ZrN).

11. The device according to claim 1, in: The electrode structure includes a plurality of fingers arranged across a plane having a first axis perpendicular to the plurality of fingers and a second axis parallel to the plurality of fingers; and The plurality of fingers are positioned between the at least two posts along the first axis.

12. The device of claim 1, wherein the microacoustic filter comprises at least one of: a first compensation layer, the first compensation layer being disposed on the electrode structure; a second compensation layer, the second compensation layer being arranged between the electrode structure and the piezoelectric layer; or A third compensation layer is disposed between the conductive layer and the cavity.

13. The device according to claim 12, wherein the first compensation layer, the second compensation layer or the third compensation layer comprises silicon dioxide (SiO 2 ) or doped silicon dioxide.

14. The device according to claim 1, in: The microacoustic filter includes a plurality of cascaded resonators; and A resonator in the plurality of cascaded resonators includes the cavity stack, the piezoelectric layer, and the buffer layer.

15. The device according to claim 1, further comprising: include: A wireless transceiver coupled to at least one antenna, the wireless transceiver including the microacoustic filter and configured to use the microacoustic filter to filter wireless signals communicated via the at least one antenna.

16. The apparatus of claim 1, wherein the microacoustic filter is configured to have a resonant frequency between approximately 500 megahertz and 2.6 gigahertz.

17. The device according to claim 16, in: The conductive layer has a thickness between about 0.5 micrometers and 5 micrometers; and The piezoelectric layer has a thickness between approximately 0.5 microns and 5 microns.

18. The device of claim 17, wherein the thickness of the conductive layer and the thickness of the piezoelectric layer are approximately equal.

19. The device of claim 17, wherein a thickness of the buffer layer is less than the thickness of the piezoelectric layer.

20. A device, the device include: A micro-acoustic filter, the micro-acoustic filter being configured to generate a filtered signal from a radio frequency signal, the micro-acoustic filter comprising: means for converting the radio frequency signal into an acoustic wave and converting the resulting acoustic wave into the filtered signal; means for exciting a plate mode using a piezoelectric layer to produce said formed acoustic wave; means for enabling epitaxial growth of the piezoelectric layer; and Means for confining energy of the plate mode within the means for exciting the plate mode and within the means for enabling epitaxial growth.

21. The device according to claim 20, in: The microacoustic filter comprises a substrate layer; and The means for limiting the energy of the plate mode comprises means for suspending the means for enabling epitaxial growth away from the base layer.

22. A method for manufacturing a micro-acoustic filter, the method include: providing a cavity stack including a conductive layer, a base layer, and at least two pillars extending through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity between the base layer and the conductive layer; Disposing a buffer layer on the surface of the conductive layer; as well as A piezoelectric layer is disposed on the surface of the buffer layer using epitaxy.

23. The method of claim 22, wherein the conductive layer comprises a single crystalline material.

24. The method of claim 22, wherein the conductive layer comprises a doping concentration greater than about 10 18 atoms / cubic centimeter of doped silicon (Si).

25. The method of claim 22, wherein the buffer layer comprises at least one of the following materials: Aluminum (Al) or aluminum nitride (AlN); Gallium (Ga) or gallium nitride (GaN); Hafnium (Hf) or hafnium nitride (HfN); Molybdenum (Mo) or molybdenum nitride (MoN); Niobium (Nb) or niobium nitride (NbN); Silicon carbide (SiC); Scandium (Sc) or scandium nitride (ScN); Titanium (Ti) or titanium nitride (TiN); Zinc (Zi) or zinc oxide (ZnO); or Zirconium (Zr) or zirconium nitride (ZrN).

26. A piezoelectric device, the piezoelectric device include: Electrode structure; a buffer layer configured to enable epitaxial growth of aluminum scandium nitride (AlScN); and A piezoelectric layer is disposed between the buffer layer and the electrode structure, the piezoelectric layer comprising the aluminum scandium nitride (AlScN) having a crystal axis orientation substantially orthogonal to a planar surface of the piezoelectric layer.

27. The piezoelectric device of claim 26, wherein the piezoelectric layer is configured to excite a plate mode.

28. The piezoelectric device according to claim 26, wherein the piezoelectric device further comprises: include: Cavity stacking, The buffer layer is arranged between the cavity stack and the piezoelectric layer.

29. The piezoelectric device of claim 28, wherein the cavity stack include: Conductive layer; Basal layer; and At least two posts extend through a plane defined by a surface of the base layer and toward the conductive layer to form a cavity between the base layer and the conductive layer.

30. The piezoelectric device according to claim 29, in: The conductive layer comprises doped silicon (Si); The base layer comprises silicon (Si); and The at least two columns comprise silicon dioxide (SiO 2 ).

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