Suspension of electrode structures using dielectric materials.

Abstract

An apparatus for suspending an electrode structure using a dielectric is disclosed. In an exemplary embodiment, the apparatus includes a surface acoustic wave filter having a piezoelectric layer and an electrode structure. The electrode structure has a first surface facing the piezoelectric layer and separated from the piezoelectric layer by a distance. The surface acoustic wave filter also includes a dielectric disposed on at least one other surface of the electrode structure and configured to extend beyond a plane defined by the first surface of the electrode structure toward the piezoelectric layer to define a cavity between at least a portion of the first surface of the electrode structure and the piezoelectric layer.

Description

[Technical field]

[0001] The present disclosure relates generally to wireless transceivers and other components that employ filters, and more specifically to surface-acoustic-wave (SAW) filters having a dielectric that suspends at least a portion of an electrode structure away from a piezoelectric layer. [Background technology]

[0002] Electronic devices communicate information using radio-frequency (RF) signals. These radio-frequency signals allow users to talk to friends, download information, share pictures, remotely control home devices, and receive global positioning information. To transmit 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) jammers or noise with frequencies outside the frequency band. However, it may be difficult to design filters that provide filtering for radio-frequency applications, including those that utilize frequencies above 2 gigahertz (GHz). Summary of the Invention [Means for solving the problem]

[0003] An apparatus is disclosed that implements a technique for suspending an electrode structure using a dielectric. In an exemplary implementation, a surface acoustic wave filter includes a dielectric, an electrode structure, and a piezoelectric layer. The dielectric partially encapsulates the electrode structure and suspends at least a portion of the electrode structure "above" or away from the piezoelectric layer. Due to the suspension, a cavity exists between the fingers of the electrode structure and the piezoelectric layer. In this way, the fingers are physically decoupled from the piezoelectric layer and do not create a mass load on the piezoelectric layer. This physical decoupling provides additional design flexibility and freedom in determining the thickness and material of the fingers, since the target conductivity can be easily optimized without the constraint of mitigating acoustic attenuation, elastic losses in the electrode structure, nonlinearity, and / or acoustic migration.

[0004] In one exemplary embodiment, an apparatus for filtering is disclosed. The apparatus includes a surface acoustic wave filter having a piezoelectric layer and an electrode structure. The electrode structure has a first surface facing the piezoelectric layer and separated from the piezoelectric layer by a distance. The surface acoustic wave filter also includes a dielectric disposed on at least one other surface of the electrode structure and configured to extend beyond a plane defined by the first surface of the electrode structure toward the piezoelectric layer to define a cavity between at least a portion of the first surface of the electrode structure and the piezoelectric layer by a distance.

[0005] In one exemplary aspect, an apparatus for filtering is disclosed. The apparatus includes a surface acoustic wave filter configured to generate a filtered signal from a radio frequency signal. The surface acoustic wave filter includes means for converting the radio frequency signal into an acoustic wave and converting the propagated acoustic wave into a filtered signal. The surface acoustic wave filter also includes means for propagating the acoustic wave across a plane to generate the propagated acoustic wave. The surface acoustic wave filter further includes means for suspending at least a portion of the means for converting away from the plane.

[0006] In an exemplary embodiment, a method for manufacturing a surface acoustic wave filter is disclosed. The method includes providing a piezoelectric layer. The method also includes providing an electrode structure having a first surface facing the piezoelectric layer and separated from the piezoelectric layer by a distance. The method further includes providing a dielectric material suspending at least a portion of the first surface of the electrode structure a distance from the piezoelectric layer.

[0007] In an exemplary embodiment, a surface acoustic wave filter is disclosed. The surface acoustic wave filter includes a piezoelectric layer having a plane. The surface acoustic wave filter also includes an electrode structure having fingers. The fingers have a first surface facing the plane of the piezoelectric layer and a second surface facing at least partially away from the piezoelectric layer. The surface acoustic wave filter also includes a dielectric configured to separate the fingers of the electrode structure from the plane of the piezoelectric layer. The dielectric includes a cap disposed over the second surface of the finger. The dielectric also includes a spacer disposed between the piezoelectric layer and the cap with a gap present between the fingers. [Brief description of the drawings]

[0008] [Figure 1] 1 illustrates an exemplary operating environment for suspending an electrode structure using a dielectric. [Diagram 2] 1 illustrates an exemplary wireless transceiver that includes at least one surface acoustic wave filter having a dielectric suspending an electrode structure. [Diagram 3] 1 illustrates an exemplary component of a surface acoustic wave filter having a dielectric suspending an electrode structure. [Figure 4] 1 illustrates a first exemplary implementation of a thin film surface acoustic wave filter having a dielectric suspending an electrode structure. [Diagram 5] 1 illustrates a second exemplary implementation of a thin film surface acoustic wave filter having a dielectric suspending an electrode structure. [Figure 6] 1 illustrates a third exemplary implementation of a thin film surface acoustic wave filter having a dielectric suspending an electrode structure. [Figure 7]1 illustrates a fourth exemplary implementation of a thin film surface acoustic wave filter having a dielectric suspending an electrode structure. [Figure 8] 13 illustrates a fifth exemplary implementation of a thin film surface acoustic wave filter having a dielectric suspending an electrode structure. [Figure 9] FIG. 2 is a flow diagram illustrating an exemplary process for manufacturing a surface acoustic wave filter having a dielectric suspending electrode structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] To transmit 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) jammers or noises with frequencies outside the frequency band. Electroelastic devices (e.g., "elastic filters") may be used to filter high frequency signals in many applications, such as those involving frequencies greater than 100 megahertz (MHz). An elastic filter is tuned to pass certain frequencies (e.g., frequencies within its passband) and attenuate other frequencies (e.g., frequencies outside its passband). By using a piezoelectric material as a vibration medium, an elastic filter works by converting an electric signal wave propagating along a conductor into an elastic wave (e.g., an elastic signal wave) formed across the piezoelectric material. The elastic wave is then converted back into a filtered electric signal. An elastic filter may include an electrode structure that transforms or converts between electric and elastic waves.

[0010] Elastic waves propagate through piezoelectric materials at velocities that are significantly smaller than the propagation velocity of electrical waves. In general, the magnitude of the wave propagation velocity is proportional to the size of the wavelength of the wave. As a result, after conversion of the electrical signal wave to an elastic signal wave, the wavelength of the elastic signal wave is significantly smaller than the wavelength of the electrical signal wave. The resulting smaller wavelength of the elastic signal wave allows filtering to be performed using smaller filter devices. This allows elastic filters to be used in space-constrained devices, including portable electronic devices such as mobile phones.

[0011] Some elastic filters have electrode structures in direct physical contact with the piezoelectric material or separated by a thin dielectric layer, such as a dielectric layer having a thickness of less than 20 nanometers. This direct or indirect physical contact can produce undesirable side effects such as elastic losses, nonlinearities, and / or acoustic migration in the electrode structure. In some cases, acoustic migration can degrade the elastic properties of the filter and / or short out the fingers of the electrode structure over time.

[0012] In addition, due to direct or indirect physical contact, the fingers of the electrode structure generate mass loading on the piezoelectric material. This mass loading can attenuate the acoustic wave, which can impair filter performance and further complicate the design of the elastic filter. Consider the trade-off that occurs between electrical conductivity and acoustic wave attenuation. For example, by increasing the thickness of the fingers, the electrical conductivity can be increased. However, increasing the thickness of the fingers also increases the mass loading, which can further attenuate the acoustic wave and degrade the performance of the elastic filter. As a result, the electrical conductivity of the elastic filter is at least partially constrained to ensure proper generation and propagation of the acoustic wave.

[0013] Some techniques can mitigate undesirable side effects (such as elastic loss, nonlinearity, or acoustic migration) by optimizing the metal layers of the electrode structure. However, the trade-off between electrical conductivity and acoustic attenuation can still constrain the design of the elastic filter.

[0014] To address this challenge, a technique is described for suspending the electrode structure using a dielectric. In an exemplary implementation, a surface acoustic wave filter includes a dielectric, an electrode structure, and a piezoelectric layer. The dielectric partially encapsulates the electrode structure and suspends at least a portion of the electrode structure "above" or away from the piezoelectric layer. The suspension results in a cavity between the fingers of the electrode structure and the piezoelectric layer. In this manner, the fingers are physically decoupled from the piezoelectric layer and do not create a mass load on the piezoelectric layer. This physical decoupling provides additional design flexibility and freedom in determining the thickness and material of the fingers, since the target conductivity can be easily optimized without the constraint of mitigating acoustic attenuation, acoustic losses in the electrode structure, nonlinearity, and / or acoustic migration. These techniques can be used with and provide advantages over acoustic filters that support frequencies above 2 GHz, as well as other acoustic filters that support frequencies below 2 GHz.

[0015] 1 illustrates an exemplary environment 100 for suspending an electrode structure using a dielectric. 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 shown as a smartphone. However, the computing device 102 may 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 wireless device, or the like.

[0016] The base station 104 communicates with the computing device 102 via a wireless link 106, which may be implemented as any suitable type of wireless link. Although illustrated as a tower of a cellular network, the 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-to-peer device, a mesh network node, etc. Thus, the computing device 102 may communicate with the base station 104 or other devices via a wireless connection.

[0017] The wireless link 106 may include a downlink of data or control information communicated from the base station 104 to the computing device 102, an uplink of other data or control information communicated from the computing device 102 to the base station 104, or both a downlink and an uplink. The wireless link 106 may be implemented using any suitable communications protocol or standard, such as IEEE 802.11 (e.g., Wi-Fi®), IEEE 802.15 (e.g., Bluetooth®), IEEE 802.16 (e.g., WiMAX®), etc., such as 2nd-generation (2G), 3rd-generation (3G), 4th-generation (4G), or 5th-generation (5G) cellular. In some implementations, the wireless link 106 may provide power wirelessly, and the base station 104 or the computing device 102 may include a power source.

[0018] As shown, the computing device 102 includes an application processor 108 and a computer-readable storage medium (CRM 110). The application processor 108 may include any type of processor, such as a multi-core processor, that executes processor-executable code stored by the CRM 110. The 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., disks), etc. In the context of the present disclosure, the CRM 110 is implemented to store instructions 112, data 114, and other information of the computing device 102, and therefore does not include a transitory propagating signal or carrier wave.

[0019] Computing device 102 may also include input / output ports 116 (I / O ports 116) and a display 118. I / O ports 116 allow for data exchange or interaction with other devices, networks, or users. 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 touch screens, and the like. Display 118 presents graphics of computing device 102, such as user interfaces associated with an operating system, programs, or applications. Alternatively or additionally, display 118 may be implemented as a display port or virtual interface through which graphical content of computing device 102 is presented.

[0020] The wireless transceiver 120 of the computing device 102 provides connectivity to respective networks 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 exemplary environment 100, the wireless transceiver 120 enables the computing device 102 to communicate with the base station 104 and the network connected to the base station 104. However, the wireless transceiver 120 may also enable the computing device 102 to communicate "directly" with other devices or networks.

[0021] The wireless transceiver 120 includes circuitry and logic for transmitting 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 the communication signals (e.g., for generating or processing the signals). The wireless transceiver 120 may also include logic for performing in-phase / quadrature (I / Q) operations, such as combining, encoding, modulating, decoding, demodulating, 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 realized using multiple or different sections to implement respective transmit and receive operations (e.g., separate transmit and receive chains). In general, the wireless transceiver 120 processes data and / or signals associated with communicating data of the computing device 102 via the antenna 122.

[0022] In the example shown in FIG. 1, the wireless transceiver 120 includes at least one surface acoustic wave filter 124. In some implementations, the wireless transceiver 120 includes multiple surface acoustic wave filters 124, which may be formed from surface acoustic wave resonators arranged in series, in parallel, in a ladder structure, in a lattice structure, or some combination thereof. The surface acoustic wave filter 124 may be a thin-film surface acoustic wave filter 126 (TFSAW filter 126) or another type of surface acoustic wave filter not shown, such as a high-quality temperature-compensated surface acoustic wave filter (HQ-TC SAW filter). In general, the surface acoustic wave filter 124 has a sufficient electromechanical coupling coefficient (k 2 ) (e.g., having an electromechanical coupling coefficient greater than a design threshold).

[0023] The surface acoustic wave filter 124 includes at least one electrode structure 128 and a dielectric 130 (e.g., a dielectric material or at least one dielectric layer). The dielectric 130 partially encapsulates the electrode structure 128 and suspends at least a portion of the electrode structure 128 above the piezoelectric layer of the surface acoustic wave filter 124. In particular, the dielectric 130 allows a cavity to be formed between the fingers of the electrode structure 128 and the piezoelectric layer. This cavity allows the fingers of the electrode structure 128 to be physically decoupled from the piezoelectric layer. In other words, the dielectric 130 maintains a separation between the fingers of the electrode structure 128 and the piezoelectric layer.

[0024] By suspending the fingers of the electrode structure 128, the electromechanical coupling coefficient of the surface acoustic wave filter 124 can be reduced. However, the distance between the electrode structure 128 and the piezoelectric layer (e.g., the height of the cavity) can be determined to allow a target electromechanical coupling coefficient to be realized. By suspending the fingers, some negative side effects associated with direct or indirect physical contact can be avoided. These negative side effects can include elastic losses, nonlinearity, and / or acoustic migration in the electrode structure 128. Furthermore, the conductivity of the electrode structure is no longer constrained by acoustic attenuation. The surface acoustic wave filter 124 is further described with respect to FIG. 2.

[0025] 2 illustrates an exemplary wireless transceiver 120. In the illustrated configuration, the wireless transceiver 120 includes a transmitter 202 and a receiver 204 coupled to a first antenna 122-1 and a second antenna 122-2, respectively. In other implementations, the transmitter 202 and the receiver 204 may be connected to the same antenna via 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 surface acoustic wave filter 124-1. The receiver 204 includes at least one second surface acoustic wave 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 (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 the application processor 108 (of FIG. 1) or another processor (e.g., a modem) associated with the wireless transceiver 120.

[0026] In some implementations, the wireless transceiver 120 is implemented using multiple circuits (e.g., multiple integrated circuits), such as a transceiver circuit 236 and a radio-frequency front-end (RFFE) circuit 238. Thus, the components forming the transmitter 202 and the receiver 204 are distributed across these circuits. As shown in FIG. 2, the transceiver circuit 236 includes a digital-to-analog converter 206 of the transmitter 202, a mixer 208-1 of the transmitter 202, a mixer 208-2 of the receiver 204, and an analog-to-digital converter 214 of the receiver 204. In other implementations, the digital-to-analog converter 206 and the analog-to-digital converter 214 may be implemented on another separate circuit, including the application processor 108 or a modem. The high frequency front-end circuit 238 includes an amplifier 210 in the transmitter 202 , a surface acoustic wave filter 124 - 1 in the transmitter 202 , a surface acoustic wave filter 124 - 2 in the receiver 204 , and an amplifier 212 in the receiver 204 .

[0027] 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-upconversion transmit signal 220 to the first mixer 208-1. The pre-upconversion transmit signal 220 may be a baseband signal or an intermediate frequency signal. The first mixer 208-1 upconverts the pre-upconversion transmit signal 220 using a local oscillator (LO) signal 222 provided by the local oscillator 216. The first mixer 208-1 generates an upconverted signal, called a pre-filter transmit signal 224. The pre-filter transmit signal 224 may be a radio frequency signal and may 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 surface acoustic wave filter 124-1.

[0028] The first surface acoustic wave filter 124-1 filters the amplified pre-filtered transmit signal 224 to generate a filtered transmit signal 226. As part of the filtering process, the first surface acoustic wave filter 124-1 attenuates noise or unwanted frequencies in the pre-filtered 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.

[0029] During reception, the antenna 122-2 receives a radio frequency receive signal 228 and passes the radio frequency receive signal 228 to the receiver 204. The second surface acoustic wave filter 124-2 receives the received radio frequency receive signal 228, which is represented by a prefilter receive signal 230. The second surface acoustic wave filter 124-2 filters out any noise or unwanted frequencies in the prefilter receive signal 230 to generate a filtered receive signal 232.

[0030] The amplifier 212 of the receiver 204 amplifies the filtered receive signal 232 and passes the amplified filtered receive signal 232 to a second mixer 208-2. The second mixer 208-2 downconverts the amplified filtered receive signal 232 using the local oscillator signal 222 to generate a downconverted receive signal 234. The analog-to-digital converter 214 converts the downconverted receive signal 234 to a digital signal that may be processed by the application processor 108 or another processor (e.g., a modem) associated with the wireless transceiver 120.

[0031] 2 illustrates one exemplary configuration of the wireless transceiver 120. Other configurations of the wireless transceiver 120 may support multiple frequency bands and share the antenna 122 across multiple transceivers. Those skilled in the art can appreciate various other configurations in which the surface acoustic wave filter 124 may be included. For example, the surface acoustic wave filter 124 may be integrated into a duplexer or diplexer of the wireless transceiver 120. Exemplary implementations of the surface acoustic wave filter 124-1 or 124-2 are further described with respect to FIGS. 3-8.

[0032] 3 shows exemplary components of a surface acoustic wave filter 124. In the illustrated configuration, the surface acoustic wave filter 124 includes an electrode structure 128, a dielectric 130 (e.g., a dielectric material), at least one piezoelectric layer 302, and at least one substrate layer 304. The electrode structure 128 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, optionally, one or more adhesion layers. By way of example, the metal layers may be comprised of aluminum (Al), copper (Cu), silver (Ag), gold (Au), tungsten (W), or some combination or doped version thereof. The adhesion layers may be comprised of chromium (Cr), titanium (Ti), molybdenum (Mo), or some combination thereof.

[0033] The electrode structure 128 may include one or more interdigital transducers 306. The interdigital transducers 306 convert electrical signals into acoustic waves and convert acoustic waves into filtered electrical signals. The interdigital transducers 306 include at least two comb structures 308-1 and 308-2. Each comb structure 308-1 and 308-2 includes a bus bar 310 (e.g., a conductive segment or rail) and a number of fingers 312 (e.g., electrode fingers). In some examples, the thickness of the fingers 312 may be about 100 to 1500 nanometers. An exemplary interdigital transducer 306 is further described with respect to FIG. 4. Although not explicitly shown, the electrode structure 128 may also include two or more reflectors. In an exemplary implementation, the interdigital transducer 306 is disposed between two reflectors, which reflect the acoustic waves back toward the interdigital transducer 306.

[0034] The dielectric 130 includes at least one cap 314 and a number of spacers 316. The cap 314 refers to a portion of the dielectric 130 that may be disposed on the electrode structure 128. In this case, the cap 314 is disposed over at least a portion of the length of the finger 312. In an exemplary implementation, the cap 314 is disposed over a majority of the length of the finger 312. Optionally, the cap 314 may also be disposed over the bus bar 310, the reflector, or other portions of the chip. The thickness of the cap 314 may be about 100 nanometers or more (e.g., about 200, 500, 1,000, or 2000 nanometers).

[0035] Generally, the cap 314 adheres to the electrode structure 128 and serves as a base or framework for suspending the electrode structure 128. In some embodiments, the cap 314 may also serve as the main layer of a hermetic package. An additional dielectric layer may be disposed over the cap 314 to provide protection against moisture.

[0036] The spacer 316 is disposed between a portion of the piezoelectric layer 302 and the cap 314 through a gap in the electrode structure 128 (e.g., a gap between the fingers 312). In some cases, the spacer 316 is also disposed between the bus bar 310 and the piezoelectric layer 302. Additionally or alternatively, the spacer 316 may be disposed between the reflector and the piezoelectric layer 302. In this manner, the spacer 316 supports the bus bar 310 and / or the reflector and provides access holes and feeder lines for etching, which will be described in more detail with respect to FIG. 9. In general, the spacer 316 may have a thickness greater than the thickness of the fingers 312. The spacer 316 provides structural support for elevating the cap 314 above the piezoelectric layer 302. By elevating the cap 314, the spacer 316 suspends at least a portion of the electrode structure 128 (e.g., at least a portion of the fingers 312) away from the piezoelectric layer 302. In other words, the spacer 316 has a size sufficient to physically separate a portion of the electrode structure 128 from the piezoelectric layer 302 .

[0037] A cavity 318 (or gap) is formed between the suspended electrode structure 128 and the piezoelectric layer 302. The cavity 318 may contain a gas, such as air. In some implementations, the height of the cavity 318 is about 1-50 nanometers. For example, the height of the cavity 318 may be about 10, 30, or 50 nanometers. In general, the term "about" may mean that any of the heights may be within + / - 10% of a particular value or less (e.g., within + / - 5%, + / - 3%, or + / - 2% of a particular value).

[0038] The height of the cavity 318 is determined to allow a target electromechanical coupling coefficient to be achieved while realizing the benefits associated with suspending the electrode structure 128. For example, the height of the cavity 318 may be about 10 nanometers to achieve an electromechanical coupling coefficient of about 7%. By increasing the height of the cavity 318, the electromechanical coupling coefficient can be decreased. Also, by decreasing the height of the cavity 318, the electromechanical coupling coefficient can be increased.

[0039] The spacers 316 provide stability and support to prevent the cavity 318 from collapsing. The spacers 316 also reflect surface acoustic waves. In some implementations, the spacers 316 are placed at nodes of standing surface acoustic waves to minimize attenuation.

[0040] The dielectric 130 may be formed using a variety of different types of dielectric materials, such as silicon dioxide (SiO2), carbon doped oxide film (SiCOH), nitride, aluminum oxide (Al2O3), polymer (e.g., benzocyclobutene (BCB) or polyimide), titanium dioxide (TiO2), hafnium dioxide (HfO2), yttrium oxide (Y2O3), zirconium dioxide (ZrO2), or some combination or doped version thereof. In some implementations, the dielectric is composed of multiple layers. The multiple layers may be formed using the same material or different materials. Also, the cap 314 and the spacer 316 may be implemented using the same material or different materials.

[0041] In some implementations, the surface acoustic wave filter 124 includes an additional dielectric layer, such as one or more of the dielectric layers shown in Figure 6. This dielectric layer may act as an etch stop or barrier layer during the manufacturing process. Additionally or alternatively, the dielectric layer acts as a seal or protective layer from external elements.

[0042] In an exemplary implementation, the piezoelectric layer 302 can be implemented using a variety of different materials that exhibit piezoelectric properties (e.g., can convert mechanical energy to electrical energy or electrical energy to mechanical energy). Exemplary types of materials include lithium niobate (LiNbO3), lithium tantalate (LiTaO3), quartz, aluminum nitride (AlN), aluminum scandium nitride (AlScN), or some combination thereof. In general, the material forming the piezoelectric layer 302 has a crystalline structure. The crystalline structure is defined by an ordered arrangement of particles (e.g., atoms, ions, or molecules). In some aspects, the material and crystalline structure of the piezoelectric layer 302 are selected such that the piezoelectric layer has a shear mode, a Rayleigh mode, or a longitudinal mode.

[0043] The substrate layer 304 includes one or more sublayers that may support passivation, temperature compensation, power handling, mode suppression, etc. By way of example, the substrate layer 304 may include at least one compensation layer 320, at least one charge trapping layer 322, at least one support layer 324, or some combination thereof. These sublayers may be considered part of the substrate layer 304 or separate layers in their own right.

[0044] The compensation layer 320 may provide temperature compensation to enable the surface acoustic wave filter 124 to achieve a target frequency temperature coefficient based on the thickness of the piezoelectric layer 302. In some implementations, the thickness of the compensation layer 320 may be adjusted to provide mode suppression (e.g., suppress spurious plate modes). In an exemplary implementation, the compensation layer 320 may be implemented using at least one silicon dioxide (SiO2) layer, at least one doped silicon dioxide layer, at least one silicon nitride layer, at least one silicon oxynitride layer, or some combination thereof. In some applications, the substrate layer 304 may not include the compensation layer 320, for example, to reduce the cost of the surface acoustic wave filter 124.

[0045] The charge trapping layer 322 may trap induced charges at the interface between the compensation layer and the support layer, for example to suppress nonlinear substrate effects. The charge trapping layer 322 may include at least one polysilicon (poly-Si) layer (e.g., a polycrystalline silicon layer or a multicrystalline silicon layer), at least one amorphous silicon layer, at least one silicon nitride (SiN) layer, at least one silicon oxynitride (SiON) layer, at least one aluminum nitride (AlN) layer, diamond-like carbon (DLC), diamond, or some combination thereof.

[0046] The support layer 324 may allow acoustic waves to form across the surface of the piezoelectric layer 302 and reduce the amount of energy leaking into the substrate layer 304. In some implementations, the support layer 324 may also function as the compensation layer 320. In general, the support layer 324 is composed of a material that is non-conductive and provides insulation. For example, the support layer 324 may be formed using a silicon (Si) material (e.g., a doped high resistivity silicon material), a sapphire material (e.g., aluminum oxide (Al2O3)), a silicon carbide (SiC) material, a fused silica material, quartz, glass, diamond, or some combination thereof. In some implementations, the support layer 324 has a relatively similar thermal expansion coefficient (TEC) as the piezoelectric layer 302. The support layer 324 may also have a specific crystal orientation to support suppression or damping of spurious modes.

[0047] In some aspects, the surface acoustic wave filter 124 can be considered a resonator. In some cases, the surface acoustic wave filter 124 can be connected to other resonators associated with a different layer stack than the surface acoustic wave filter 124. In other aspects, the surface acoustic wave filter 124 can be implemented as multiple interconnected resonators using the same layers (e.g., the piezoelectric layer 302 and / or the substrate layer 304). The electrode structure 128 and the dielectric 130 are further described with respect to FIG. 4.

[0048] 4 illustrates an exemplary implementation of a thin-film surface acoustic wave filter 126 having a dielectric 130 suspending an electrode structure 128. A three-dimensional perspective view 400-1 of the thin-film surface acoustic wave filter 126 is shown at the top of FIG 4, and a two-dimensional cross-sectional view 400-2 of the thin-film surface acoustic wave filter 126 is shown at the bottom of FIG 4.

[0049] The thin-film surface acoustic wave filter 126 includes an electrode structure 128, a dielectric 130, a piezoelectric layer 302, and at least one substrate layer 304. The electrode structure 128 may include one or more interdigital transducers 306. In the illustrated configuration shown in the two-dimensional cross-section 400-2, the piezoelectric layer 302 is disposed between the dielectric 130 and the substrate layer 304. The dielectric 130 encapsulates (e.g., surrounds, physically contacts, or is at least adjacent to) at least one other surface of the fingers 312 that faces at least partially away from the piezoelectric layer 302. The cap 314 and spacer 316 of the dielectric 130 are further described with respect to FIG. 5. In some implementations, the dielectric 130 is disposed across the busbar 310 of the electrode structure 128, as shown in FIG. 4.

[0050] The dielectric 130 forms a cavity 318 between the fingers 312 and the piezoelectric layer 302. In some cases, the cavity 318 can be considered a collection of multiple cavities that do not intersect. In other cases, the cavity 318 can be considered a single cavity with intersecting branches. In some cases, the width of the cavity 318 can be approximately equal to the width of the fingers 312. In general, the term "about" can mean that any of the widths can be within + / - 10% of a particular value or less (e.g., within + / - 5%, + / - 3%, or + / - 2% of a particular value). In other implementations, the width of the cavity 318 can be greater than the width of the fingers 312, as will be further described with respect to FIG. 5. In some aspects, the dielectric 130 does not form a cavity between the bus bar 310 and the piezoelectric layer 302. Some package structures can have an outer layer formed by the dielectric 130. Other package structures can have an outer layer that is different from the dielectric 130. In some cases, the dielectric 130 and the outer layer are separated by a distance and a separate cavity exists between the dielectric 130 and the outer layer of the package.

[0051] In the three-dimensional perspective view 400-1, the interdigital transducer 306 is shown having two comb structures 308-1 and 308-2 with fingers 312 extending from two bus bars 310 towards each other. The fingers 312 are interlockingly arranged (e.g., interdigitally arranged) between the two bus bars 310 of the interdigital transducer 306. In other words, the fingers 312 connected to a first bus bar 310 extend towards, but do not connect to, the second bus bar 310. Similarly, the fingers 312 connected to the second bus bar 310 extend towards, but do not connect to, the first bus bar 310.

[0052] In a direction along the busbar 310, there is an overlap region, including a central region, where a portion of one finger 312 overlaps with a portion of an adjacent finger 312. This central region, including the overlap, may be referred to as an aperture, track, or active region, where an electric field is generated between the fingers 312 to form an acoustic wave 402 in at least this region of the piezoelectric layer 302.

[0053] The physical periodicity of the fingers 312 is referred to as the pitch 404 of the interdigital transducer 306. The pitch 404 may be indicated in various ways. For example, in certain aspects, the pitch 404 may correspond to the magnitude of the distance between adjacent fingers 312 of the interdigital transducer 306 in the central region. This distance may be defined, for example, as the distance between the center points of each of the fingers 312. When the fingers 312 have a uniform width, the distance may generally be measured between the right (or left) edge of one finger 312 and the right (or left) edge of an adjacent finger 312. In certain aspects, the average of the distances between adjacent fingers 312 of the interdigital transducer 306 may be used for the pitch 404. The frequency at which the piezoelectric layer 302 vibrates is the primary resonant frequency of the electrode structure 128. The frequency is determined, at least in part, by the pitch 404 of the interdigital transducer 306 and other characteristics of the thin film surface acoustic wave filter 126.

[0054] In the three-dimensional perspective view 400-1, the thin-film surface acoustic wave filter 126 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 plane of the piezoelectric layer 302, and the second axis 408 is perpendicular to the first axis 406. The third axis 410 is perpendicular (e.g., vertical) to the plane of the piezoelectric layer 302. The bus bars 310 of the interdigital transducer 306 are oriented to be parallel to the first axis 406. The fingers 312 of the interdigital transducer 306 are oriented to be parallel to the second axis 408. The orientation of the piezoelectric layer 302 also causes the acoustic waves 402 to form primarily in the direction of the first axis 406. Thus, an acoustic wave 402 is formed in a direction substantially perpendicular to the direction of the fingers 312 of the interdigital transducer 306 .

[0055] In operation, the surface acoustic wave filter 124 (e.g., the thin film surface acoustic wave filter 126 of FIG. 4 or another type of surface acoustic wave filter) receives a radio frequency signal, such as the pre-filtered transmit signal 224 or the pre-filtered receive signal 230 shown in FIG. 2. The electrode structure 128 excites an acoustic wave 402 on the piezoelectric layer 302 using the inverse piezoelectric effect. For example, the interdigital transducer 306 in the electrode structure 128 generates an alternating electric field based on the received radio frequency signal. The piezoelectric layer 302 allows the formation of the acoustic wave 402 in response to the alternating electric field generated by the interdigital transducer 306. In other words, the piezoelectric layer 302 causes the formation of the acoustic wave 402, at least in part, in response to electrical stimulation by one or more interdigital transducers 306.

[0056] The acoustic wave 402 propagates across the piezoelectric layer 302 and interacts with the interdigital transducer 306 or another interdigital transducer in the electrode structure 128 (not shown in FIG. 4). The propagating acoustic wave 402 can be a standing wave. In some implementations, two reflectors in the electrode structure 128 cause the acoustic wave 402 to form as a standing wave across a portion of the piezoelectric layer 302. In other implementations, the acoustic wave 402 propagates across the piezoelectric layer 302 from the interdigital transducer 306 to another interdigital transducer (not shown).

[0057] Using the piezoelectric effect, the electrode structure 128 generates a filtered radio frequency signal based on the propagated surface acoustic wave 402. In particular, the piezoelectric layer 302 generates an alternating electric field due to mechanical stress generated by the propagation of the acoustic wave 402. The alternating electric field induces an alternating current in the other interdigital transducer or the interdigital transducer 306. This alternating current forms a filtered radio frequency signal provided at the output of the surface acoustic wave filter 124. The filtered radio frequency signal may include the filtered transmit signal 226 or the filtered receive signal 232 of FIG. 2.

[0058] Although a particular number of fingers is shown in FIG. 4, it should be understood that the actual number of fingers, as well as the length and width of the fingers and busbars, may vary in an actual implementation. Such parameters depend on the particular application and the desired filter characteristics. In addition, the thin film surface acoustic wave filter 126 or another type of surface acoustic wave filter may include multiple interconnected electrode structures (e.g., multiple interconnected resonators or interdigital transducers 306 connected in series or parallel to form a desired filter transfer function), each including multiple interdigital transducers 306 to achieve a desired passband.

[0059] Although not explicitly shown, the electrode structure 128 may also include two or more reflectors. In an exemplary implementation, the interdigital transducer 306 is disposed between two reflectors (not shown), which reflect the acoustic waves 402 back toward the interdigital transducer 306. Each reflector in the electrode structure 128 may have two bus bars and a lattice structure of conductive fingers, each connected to both bus bars. In some implementations, the pitch of the reflectors may be similar or the same as the pitch 404 of the interdigital transducer 306 to reflect the acoustic waves 402 within the resonant frequency range. Features of the dielectric 130 are further described with respect to FIG. 5.

[0060] 5 shows another exemplary implementation of a thin-film surface acoustic wave filter 126 having a dielectric 130 that suspends an electrode structure 128. In the illustrated configuration, the finger 312 of the electrode structure 128 is shown to have four surfaces 502-1, 502-2, 502-3, and 502-4. The surfaces 502-1 and 502-2 may be substantially parallel to each other. Also, the surfaces 502-3 and 502-4 may be substantially parallel to each other and perpendicular to the surfaces 502-1 and 502-2. The surface 502-1 faces the piezoelectric layer 302 and is close to the piezoelectric layer 302. The surface 502-1 is separated from the piezoelectric layer 302 by a distance. This distance may correspond to the height of the cavity 318. The surface 502-2 faces the surface 502-1 and faces at least partially away from the piezoelectric layer 302. In some embodiments, the third (Z) filter axis 410 is substantially perpendicular to the surfaces 502-1 and 502-2. The surfaces 502-3 and 502-4 are adjacent to the surfaces 502-1 and 502-2. The first (X) axis 406 can be substantially perpendicular to the surfaces 502-3 and 502-4.

[0061] As shown in FIG. 5, the dielectric 130 encapsulates or surrounds at least a portion of the surfaces 502-2 to 502-4 of the fingers 312. The dielectric 130 extends beyond the plane defined by the first surface 502-1 of the electrode structure 128 toward the piezoelectric layer 302 to define a cavity 318. A dashed line is shown in FIG. 5 to distinguish between the cap 314 and the spacer 316 of the dielectric 130. In this case, the cap 314 represents a portion of the dielectric 130 disposed on the surface 502-2 of the finger 312 and / or disposed on the spacer 316. The spacer 316 represents a portion of the dielectric 130 disposed between the surfaces 502-3 and 502-4 of adjacent fingers 312. In general, the spacer 316 includes a portion of the dielectric 130 that extends beyond the first surface 502-1 toward the piezoelectric layer 302. In some implementations, the spacer 316 abuts the piezoelectric layer 302 .

[0062] Although not explicitly shown, the electrode structure 128 may also have two other surfaces that are substantially perpendicular to the second (Y) axis 408. The dielectric 130 may optionally encapsulate or surround at least a portion of these surfaces.

[0063] Along the second (Y) axis 408, the spacer 316 may be implemented as one continuous piece. Alternatively, the spacer 316 may be implemented using multiple pieces that are physically separated from one another along the second (Y) axis 408. In some implementations, the length of the spacer 316 along the second (Y) axis 408 may be approximately equal to the length of the adjacent cavity 318. In other implementations, the length of the spacer 316 along the second (Y) axis 408 is less than the length of the adjacent cavity 318, but is greater than half the length of the adjacent cavity 318. In still other implementations, the length of the spacer 316 is greater than the length of the adjacent cavity 318.

[0064] The cap 314 may be implemented as one continuous piece along the first (X) axis 406 and / or the second (Y) axis 408. Alternatively, the cap 314 may be implemented using multiple pieces that are physically separated from one another along the first (X) axis 406 and / or the second (Y) axis 408. Generally, the cap 314 is disposed on the spacer 316. In some cases, the cap 314 is also disposed over at least a portion of the electrode structure 128, such as over at least a portion of the fingers 312, at least a portion of the busbar 310, and / or at least a portion of the reflector.

[0065] The thin film surface acoustic wave filter 126 of FIG. 5 is similar to the thin film surface acoustic wave filter 126 of FIG. 4, except that the width of the cavity 318 is larger than the width of the fingers 312. In other words, the width of the cavity 318 extends beyond the width of the fingers 312. As an example, the width of the cavity 318 may be about 1%, 5%, or 10% larger than the width of the fingers 312. In general, the width of the cavity 318 is constrained by the target width of the spacer 316 to provide structural support for suspending the electrode structure 128. The thin film surface acoustic wave filter 126 may also include an additional dielectric layer, as further described with respect to FIG. 6.

[0066] 6 illustrates yet another exemplary implementation of a thin-film surface acoustic wave filter 126 having a dielectric 130 suspending an electrode structure 128. In the illustrated configuration, the thin-film surface acoustic wave filter 126 includes dielectric layers 602-1, 602-2, and 602-3. In other implementations, the thin-film surface acoustic wave filter 126 includes a subset of the dielectric layers 602-1, 602-2, and / or 602-3, or additional dielectric layers not shown. In some cases, the dielectric layers 602-1 through 602-3 act as etch stop layers or barrier layers during fabrication of the thin-film surface acoustic wave filter 126.

[0067] The dielectric layer 602-1 is disposed between the dielectric 130 and the piezoelectric layer 302, between the dielectric 130 and the cavity 318, and between the dielectric 130 and the surfaces 502-2 to 502-4 of the fingers 312. In an exemplary implementation, the dielectric layer 602-1 may have a thickness of about 1 to 100 nanometers. The dielectric layer 602-2 is disposed on the surface 502-1 of the fingers 312. Thus, the dielectric layer 602-2 is between the fingers 312 and the cavity 318. The dielectric layer 602-3 is disposed on the surface of the piezoelectric layer 302. Thus, the dielectric layer 602-3 is between the piezoelectric layer 302 and the dielectric 130, and between the piezoelectric layer 302 and the cavity 318. The thicknesses of the dielectric layers 602-2 and 602-3 may be about 1 to 5 nanometers.

[0068] Although described with respect to the thin-film surface acoustic wave filter 126, the technique for suspending the electrode structure 128 using the dielectric 130 may also be applied to other types of surface acoustic wave filters. For example, the compensation layer 320 of the high-quality temperature-compensated surface acoustic wave filter may function as the dielectric 130 and suspend the electrode structure 128 of the high-quality temperature-compensated surface acoustic wave filter. In this manner, the compensation layer 320 may provide temperature compensation to enable the high-quality temperature-compensated surface acoustic wave filter to achieve a target frequency temperature coefficient while suspending the electrode structure 128. As an example, the compensation layer 320 may be implemented using at least one silicon dioxide layer.

[0069] Those skilled in the art can appreciate various other configurations in which the dielectric 130 may suspend the electrode structure 128. For example, some implementations may have one or more gaps between the fingers 312 that do not include the spacer 316. In this case, the cap 314 may extend down along a portion of the surface 502-3 or 502-4 of the finger 312 along which the spacer 316 is not present. The spacer 316 may also be a continuous piece or multiple pieces that extend along the second (Y) axis 408. The length of the spacer 316 along the second (Y) axis 408 may be determined to provide sufficient structural support to suspend the electrode structure 128. The height and width of the cavity 318 may also be determined to achieve a target electromechanical coupling coefficient and avoid negative side effects of a physical coupling between the electrode structure 128 and the piezoelectric layer 302.

[0070] As another example, other implementations may not include the cap 314, or the cap 314 may be disposed over a portion of the finger 312. Consider the case where the cap 314 is disposed over the spacer 316 and extends over a portion of the width of the finger 312 along the first (X) axis 406. In this manner, the caps 314 associated with adjacent spacers 316 are physically separated. In another case, the cap 314 extends over a portion of the length of the finger 312 along the second (Y) axis 408. Also, the cap 314 may include a continuous piece or multiple pieces that extend along the first (X) axis 406 and / or the second (Y) axis 408.

[0071] 7 shows another exemplary implementation of a thin-film surface acoustic wave filter 126 having a dielectric 130 suspending an electrode structure 128. The thin-film surface acoustic wave filter 126 of FIG. 7 is similar to the thin-film surface acoustic wave filter 126 of FIG. 5, except that the fingers 312 of FIG. 7 have a triangular shape instead of a rectangular shape. In the illustrated configuration, the fingers 312 of the electrode structure 128 are shown to have three surfaces 502-1, 502-2, and 502-3. The surface 502-1 faces the piezoelectric layer 302 and is adjacent to the piezoelectric layer 302. The surfaces 502-2 and 502-3 face at least partially away from the piezoelectric layer 302.

[0072] As shown in Figure 7, the dielectric 130 encapsulates or surrounds the surfaces 502-2 and 502-3 of the fingers 312. A dashed line is shown in Figure 7 to distinguish between the cap 314 and the spacer 316 of the dielectric 130. In this case, the cap 314 represents a portion of the dielectric 130 that is disposed on the spacer 316. The spacer 316 represents a portion of the dielectric 130 that is disposed between the surfaces 502-2 and 502-3 of adjacent fingers 312.

[0073] FIG. 8 illustrates yet another exemplary implementation of a thin-film surface acoustic wave filter 126 having a dielectric 130 suspending an electrode structure 128. The thin-film surface acoustic wave filter 126 of FIG. 8 is similar to the thin-film surface acoustic wave filter 126 of FIG. 5 and FIG. 7, except that the fingers 312 of FIG. 8 have a rounded shape instead of a rectangular or triangular shape. In the illustrated configuration, the fingers 312 of the electrode structure 128 are shown to have two surfaces 502-1 and 502-2. The surface 502-1 faces the piezoelectric layer 302 and is adjacent to the piezoelectric layer 302. The surface 502-2 faces at least partially away from the piezoelectric layer 302.

[0074] As shown in Figure 8, the dielectric 130 encapsulates or surrounds the surface 502-2 of the finger 312. A dashed line is shown in Figure 8 to distinguish between the cap 314 and the spacer 316 of the dielectric 130. In this case, the cap 314 represents a portion of the dielectric 130 that is disposed on the surface 502-2 of the finger 312 and on the spacer 316. The spacer 316 represents a portion of the dielectric 130 that is disposed between the surfaces 502-2 of adjacent fingers 312.

[0075] Although not explicitly shown in Figures 5, 7, and 8, other implementations of the thin film surface acoustic wave filter 126 may have the dielectric 130 disposed at least partially on one or more of the surfaces 502-2 to 502-4. In some cases, the spacers 316 of the dielectric 130 are sufficient to suspend the electrode structure 128. Thus, the dielectric 130 may be implemented, optionally, without the cap 314. In other words, some implementations of the dielectric 130 may include the spacers 316 and may not include the cap 314.

[0076] Although the techniques for suspending the electrode structure 128 using the dielectric 130 have been described with respect to the thin film surface acoustic wave filter 126 of Figures 4-8, these techniques may also be applied to other types of surface acoustic wave filters 124. For example, these techniques may be applied to a surface acoustic wave filter 124 that includes an electrode structure 128, a dielectric 130, and a piezoelectric layer 302, but does not include a substrate layer 304. In other words, these techniques may be applied to a surface acoustic wave filter 124 that has a substrate layer 304 formed using the same piezoelectric material as the piezoelectric layer 302.

[0077] FIG. 9 is a flow diagram illustrating an example process 900 for fabricating a surface acoustic wave filter 124 having a dielectric suspending an electrode structure. The process 900 is described in the form of a set of blocks 902-906 that specify operations that may be performed. However, the operations are not necessarily limited to the order shown in FIG. 9 or described herein, as the operations may be performed in alternative orders or in a fully or partially overlapping manner. Also, more, fewer, and / or different operations may be performed to perform the process 900 or alternative processes. The operations represented by the illustrated blocks of the process 900 may be performed to fabricate a surface acoustic wave filter 124 (e.g., of FIGS. 1-3). More specifically, the operations of the process 900 may be performed, at least in part, to suspend at least a portion of the electrode structure 128 using a dielectric 130 (e.g., of FIGS. 4-8).

[0078] At 902, a piezoelectric layer is provided. For example, a manufacturing process provides the piezoelectric layer 302, as shown in Figures 4-8. The piezoelectric layer 302 may be implemented using materials such as lithium niobate, lithium tantalate, quartz, aluminum nitride, scandium aluminum nitride, or some combination thereof. In some aspects, the structure of the piezoelectric layer 302 is tailored to enable the piezoelectric layer 302 to have or support a shear mode, a Rayleigh mode, or a longitudinal mode.

[0079] At 904, an electrode structure is provided having a first surface facing the piezoelectric layer and separated from the piezoelectric layer by a distance. For example, the manufacturing process provides an electrode structure 128, as shown in Figures 4-8. The electrode structure 128 includes a first surface 502-1 facing the piezoelectric layer 302, as shown in Figures 5, 7, and 8. The first surface 502-1 is separated from the piezoelectric layer 302 by a distance. An exemplary distance may be about 1-50 nanometers. The electrode structure 128 may also have at least one other surface, such as any of the surfaces 502-2, 502-3, and / or 502-4 shown in Figures 5, 7, or 8. The electrode structure 128 may be formed using a conductive material, such as a metal.

[0080] At 906, a dielectric is provided that suspends at least a portion of the first surface of the electrode structure a distance away from the piezoelectric layer. For example, the manufacturing process provides a dielectric 130 that suspends at least a portion of the first surface 502-1 of the electrode structure 128 a distance away from the piezoelectric layer 302, as shown in Figures 4-8. The portion of the electrode structure 128 may refer to the finger 312. In particular, the dielectric 130 extends beyond the first surface 502-1 of the finger 312 toward the piezoelectric layer 302 to define a cavity 318. The cavity 318 may have a width similar to or greater than the finger 312 of the electrode structure 128. Also, the cavity 318 may have a length similar to or less than the finger 312 of the electrode structure 128. In some cases, the dielectric 130 abuts the piezoelectric layer 302. Optionally, the manufacturing process may also provide one or more of the dielectric layers 602-1 to 602-3 of FIG.

[0081] An etching process may be used to suspend the electrode structure 128 using the dielectric 130. In this case, the fabrication process provides a sacrificial structure, such as an amorphous silicon (a-Si) layer, on the piezoelectric layer 302. For example, the sacrificial structure may be provided after the step described in 902 and before the step described in 904. The sacrificial structure defines the volume and location of the cavity 318 and is removed later in the fabrication process. Optionally, the fabrication process provides a dielectric layer 602-2 to provide a protective layer for the electrode structure 128 during removal of the sacrificial layer. After providing the dielectric 130 in 906, the fabrication process etches through the cap 314 and / or the spacer 316 to access the sacrificial structure. The manufacturing process removes the sacrificial structure using a chemical such as xenon difluoride (XeF2) to create a volume for the cavity 318 between the surface 502-1 of a portion of the electrode structure 128 (e.g., finger 312) and the piezoelectric layer 302.

[0082] Wafer bonding may also be used to suspend the electrode structure 128 using the dielectric 130. In this case, the manufacturing process provides the piezoelectric layer 302 on a first wafer as described at 902. The manufacturing process also provides the electrode structure 128 and the dielectric 130 on a second wafer as described at 904 and 906. The manufacturing process bonds the first wafer to the second wafer to form a cavity 318 between the surface 502-1 of the portion of the electrode structure 128 and the piezoelectric layer 302.

[0083] Several aspects are described below.

[0084] Aspect 1: 1. A surface acoustic wave filter comprising: A piezoelectric layer; an electrode structure having a first surface facing the piezoelectric layer and spaced a distance from the piezoelectric layer; and a dielectric disposed on at least one other surface of the electrode structure and configured to extend beyond a plane defined by the first surface of the electrode structure toward the piezoelectric layer to define a cavity between the first surface of the electrode structure and the piezoelectric layer.

[0085] Example 2: The apparatus of Example 1, wherein the dielectric is configured to suspend at least a portion of the electrode structure a distance from the piezoelectric layer.

[0086] Embodiment 3: A device according to embodiment 1 or 2, wherein a dielectric is attached to at least one other surface of the electrode structure.

[0087] Embodiment 4: A device according to any of embodiments 1 to 3, wherein a portion of the dielectric extends beyond the plane through different gaps in the electrode structure.

[0088] Aspect 5: the electrode structure includes a plurality of gaps; The device of any one of aspects 1 to 4, wherein at least a portion of the dielectric material is present in the plurality of gaps and in contact with the piezoelectric layer.

[0089] Embodiment 6: The device of any of embodiments 1-5, wherein the cavity is at least partially filled with a gas.

[0090] Embodiment 7: The apparatus of embodiment 6, wherein the gas comprises air.

[0091] Aspect 8: The electrode structure is a first comb structure including a first busbar and a first set of fingers extending from the first busbar; a second comb structure including a second busbar and a second set of fingers extending from the second busbar; The apparatus of any one of embodiments 1-7, wherein a cavity is present between the piezoelectric layer and the fingers of the first set of fingers and the second set of fingers.

[0092] Aspect 9: at least one other surface of the electrode structure includes a second surface facing at least partially away from the piezoelectric layer; The dielectric is a cap disposed over a second surface of the finger; 9. The apparatus of embodiment 8, comprising: a spacer disposed between the piezoelectric layer and the cap with gaps between the fingers.

[0093] Example 10: The device of example 9, wherein the cap and the spacer comprise the same dielectric material.

[0094] Example 11: The device of example 9 or 10, wherein the cap has a thickness of about 100 nanometers to 2000 nanometers.

[0095] Embodiment 12: The apparatus of any of embodiments 8-11, wherein the cavity extends along the length of the finger.

[0096] Embodiment 13: An apparatus according to any of embodiments 8-12, wherein the width of the cavity is greater than the width of each of the fingers.

[0097] Aspect 14: The dielectric material is A layer of silicon dioxide, A nitride layer, A layer of aluminum oxide, A layer of polymer, A layer of titanium dioxide, A layer of hafnium dioxide, a layer of yttrium oxide, or A layer of zirconium dioxide.

[0098] Embodiment 15: A device according to any one of embodiments 1 to 14, wherein the height of the cavity is between about 1 nanometer and 50 nanometers.

[0099] Aspect 16: The piezoelectric layer is Shear mode, Rayleigh mode, or 16. The apparatus of any of aspects 1-15, configured to excite one of the following longitudinal modes:

[0100] Aspect 17: A surface acoustic wave filter comprising: a first dielectric layer disposed between the dielectric and the electrode structure, between the dielectric and the piezoelectric layer, and between the dielectric and the cavity; a second dielectric layer disposed between the first surface of the electrode structure and the cavity; or The device of any one of aspects 1 to 16, further comprising at least one of a third dielectric layer disposed between the piezoelectric layer and the cavity, and a third dielectric layer disposed between the piezoelectric layer and the dielectric.

[0101] Aspect 18: the surface acoustic wave filter includes a first dielectric layer; 18. The device of embodiment 17, wherein the first dielectric layer has a thickness between about 1 nanometer and 100 nanometers.

[0102] Aspect 19: the surface acoustic wave filter includes a second dielectric layer or a third dielectric layer; 19. The device of embodiment 17 or 18, wherein the second dielectric layer or the third dielectric layer has a thickness of about 1 to 5 nanometers.

[0103] Aspect 20: A surface acoustic wave filter includes a plurality of cascaded resonators; 20. The device of any one of aspects 1-19, wherein one resonator of the plurality of cascaded resonators includes a piezoelectric layer and a dielectric layer.

[0104] Aspect 21: 21. The apparatus of any of aspects 1-20, further comprising a wireless transceiver coupled to the at least one antenna, the wireless transceiver including a surface acoustic wave filter and configured to filter wireless signals communicated via the at least one antenna using the surface acoustic wave filter.

[0105] Example 22: The device of any one of Examples 1 to 21, wherein the surface acoustic wave filter includes a thin-film surface acoustic wave filter.

[0106] Aspect 23: 1. A surface acoustic wave filter configured to generate a filtered signal from a radio frequency signal, comprising: means for converting radio frequency signals into elastic waves and converting the propagated elastic waves into a filtered signal; means for propagating an elastic wave across a plane to generate a propagated elastic wave; and means for suspending at least a portion of the means for transducing out of a plane.

[0107] Example 24: The apparatus of Example 23, wherein the suspending means includes a means for reflecting elastic waves.

[0108] A method for manufacturing a surface acoustic wave filter, comprising the steps of: Providing a piezoelectric layer; providing an electrode structure having a first surface facing the piezoelectric layer and spaced a distance from the piezoelectric layer; providing a dielectric body suspending at least a portion of a first surface of the electrode structure a distance from the piezoelectric layer.

[0109] Aspect 26: providing a sacrificial layer on a surface of the piezoelectric layer, the sacrificial layer being between the piezoelectric layer and a portion of the first surface of the electrode structure; Etching through the dielectric to the sacrificial layer; 26. The method of embodiment 25, further comprising removing the sacrificial layer to form a cavity between a portion of the first surface of the electrode structure and the piezoelectric layer.

[0110] Aspect 27: Providing the piezoelectric layer includes providing a piezoelectric layer on a first wafer; providing an electrode structure and providing a dielectric includes providing an electrode structure and a dielectric on a second wafer; The method is 26. The method of embodiment 25, further comprising bonding the first wafer to a second wafer to form a cavity between a portion of the first surface of the electrode structure and the piezoelectric layer.

[0111] Aspect 28: A surface acoustic wave filter, comprising: A piezoelectric layer having a flat surface; an electrode structure including fingers, the fingers having a first surface facing the plane of the piezoelectric layer and a second surface facing at least partially away from the piezoelectric layer; a dielectric configured to separate the fingers of the electrode structure from the plane of the piezoelectric layer; a cap disposed over a second surface of the finger; a spacer disposed between the piezoelectric layer and the cap across the gap between the fingers; and a dielectric.

[0112] Aspect 29: A surface acoustic wave filter as described in aspect 28, wherein the dielectric spacer is configured to extend beyond a plane defined by the first surfaces of the fingers toward the plane of the piezoelectric layer to define a cavity between the first surfaces of the fingers and the plane of the piezoelectric layer.

[0113] Aspect 30: A surface acoustic wave filter as described in aspect 29, wherein the cavity extends along the length of the finger and extends beyond the width of the finger.

[0114] Aspect 31: A surface acoustic wave filter as described in aspect 29 or 30, wherein the surface acoustic wave filter includes a dielectric layer arranged between the dielectric and the fingers, between the dielectric and the piezoelectric layer, and between the dielectric and the cavity.

[0115] Example 32: A surface acoustic wave filter according to any one of Examples 29 to 31, wherein the surface acoustic wave filter includes a dielectric layer disposed between the fingers and the cavities.

[0116] Embodiment 33: A surface acoustic wave filter according to any one of embodiments 29 to 32, wherein the surface acoustic wave filter includes a dielectric layer arranged between the piezoelectric layer and the cavity and between the piezoelectric layer and the dielectric.

[0117] Example 34: A surface acoustic wave filter according to any one of Examples 28 to 33, wherein the cap and the spacer comprise different dielectric materials.

[0118] Aspect 35: a surface acoustic wave filter configured to generate standing surface acoustic waves across a plane of the piezoelectric layer; The surface acoustic wave filter according to any one of embodiments 28 to 34, wherein the spacer is disposed at a node of a standing surface acoustic wave.

[0119] Unless the context dictates otherwise, use of the word "or" herein may be considered as use of "inclusive or" or as a term permitting the inclusion or application of one or more items associated 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 single members. By way of example, "at least one of a, b, or c" is intended to include a, b, c, ab, ac, bc, and abc, as well as any combination having multiple identical elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or a, b, and c in any other order). Additionally, items depicted in the accompanying drawings and terms discussed herein may refer to one or more items or terms, and thus references may be made interchangeably to the singular or plural forms of the items and terms herein. Finally, although subject matter has been described in language specific to structural features or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the particular features or acts described above, including but not necessarily limited to the organization in which features are arranged or the order in which acts are performed. [Explanation of symbols]

[0120] 124 Surface Acoustic Wave Filter 126 Thin-Film Surface Acoustic Wave Filters 128 Electrode structure 130 Dielectric 302 Piezoelectric layer 310 First bus bar, second bus bar 312 Finger 314 Cap 316 Spacer 318 Cavity 602-1, 602-2, 602-3 Dielectric layers

Claims

1. A surface acoustic wave filter, comprising: a piezoelectric layer having a flat surface; an electrode structure including fingers, the fingers having first surfaces facing the plane of the piezoelectric layer and second surfaces facing at least partially away from the piezoelectric layer; a dielectric configured to separate the fingers of the electrode structure from the plane of the piezoelectric layer; a cap disposed over the second surface of the finger; a dielectric including a spacer disposed between the piezoelectric layer and the cap across the gap between the fingers.

2. 2. The surface acoustic wave filter of claim 1, wherein the dielectric spacers are configured to extend beyond a plane defined by the first surfaces of the fingers toward the plane of the piezoelectric layer to define cavities between the first surfaces of the fingers and the plane of the piezoelectric layer.

3. 3. The surface acoustic wave filter of claim 2, wherein the cavity extends along the length of the finger and extends across the width of the finger.

4. 3. The surface acoustic wave filter of claim 2, wherein the surface acoustic wave filter includes a dielectric layer disposed between the dielectric and the fingers, between the dielectric and the piezoelectric layer, and between the dielectric and the cavity.

5. 3. The surface acoustic wave filter of claim 2, wherein the surface acoustic wave filter includes a dielectric layer disposed between the fingers and the cavities.

6. 3. The surface acoustic wave filter of claim 2, wherein the surface acoustic wave filter includes a dielectric layer disposed between the piezoelectric layer and the cavity and between the piezoelectric layer and the dielectric.

7. The surface acoustic wave filter of claim 1 , wherein the cap and the spacer comprise different dielectric materials.

8. the surface acoustic wave filter is configured to generate standing surface acoustic waves across the plane of the piezoelectric layer; 2. The surface acoustic wave filter of claim 1, wherein the spacer is disposed at a node of the standing surface acoustic wave.

9. A surface acoustic wave filter as described in claim 1, wherein the cap and the spacer comprise the same dielectric material.

10. The surface acoustic wave filter of claim 1, wherein the cap has a thickness of approximately 100 nanometers to 2000 nanometers.

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