Patent Application
20220116014
Certain aspects of the present disclosure relate generally to electronic components and, more particularly, to surface acoustic wave (SAW) devices implemented with high-permittivity dielectric elements.
Electronic devices include traditional computing devices such as desktop computers, notebook computers, tablet computers, smartphones, wearable devices like a smartwatch, internet servers, and so forth. These various electronic devices provide information, entertainment, social interaction, security, safety, productivity, transportation, manufacturing, and other services to human users. These various electronic devices depend on wireless communications for many of their functions. Wireless communication systems and devices are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems, (e.g., a Long Term Evolution (LTE) system, or a New Radio (NR) system).
Wireless communication transceivers used in these electronic devices generally include multiple radio frequency (RF) filters for filtering a signal for a particular frequency or range of frequencies. Electroacoustic devices (e.g., “acoustic filters”) are used for filtering high-frequency (e.g., generally greater than 100 MHz) signals in many applications. Using a piezoelectric, material as a vibrating medium, acoustic resonators operate by transforming an electrical signal wave that is propagating along an electrical conductor into an acoustic wave that is propagating via the piezoelectric material. The acoustic wave propagates at a velocity having a magnitude that is significantly less than that of the propagation velocity of the electromagnetic wave. Generally, the magnitude of the propagation velocity of a wave is proportional to a size of a wavelength of the wave. Consequently, after conversion of an electrical signal into an acoustic signal, 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 enables filtering to be performed using a smaller filter device. This permits acoustic resonators to be used in electronic devices having size constraints, such as the electronic devices enumerated above (e.g., particularly including portable electronic devices such as cellular phones).
Today, surface acoustic wave (SAW) or bulk acoustic wave (BAW) components may be used in wireless communication devices, such as for implementing RF filters. In SAW technology, the acoustic wave propagates laterally on a surface of a piezoelectric substrate, with the movement of the piezoelectric generated by metal interdigitated transducers (IDTs) on the surface. The wavelength of the acoustic wave may be defined by the pitch (e.g., the width of the metal finger and gap) of the IDT. In BAW technology, the acoustic wave propagates vertically through a three-dimensional structure, with an electric field applied through electrodes above and below a piezoelectric material. The wavelength, in this case, is defined by the thickness of the piezoelectric material.
In one type of SAW device, a surface acoustic wave is generated by an input IDT and detected by an output IDT. In another type of SAW device, the acoustic energy may be confined using reflectors on either side of the IDT. A planar resonant cavity created between two mirrors consisting of reflecting metal strips can also be used to trap the acoustic energy.
As the number of frequency bands used in wireless communications increases and as the desired frequency band of filters widen, the performance of acoustic filters increases in importance to reduce losses and increase overall performance of electronic devices. Acoustic filters with improved performance, particularly filters with reduced intermodulation distortion, are therefore sought after.
The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description,” one will understand how the features of this disclosure provide advantages that include implementation of high-permittivity dielectric materials in surface acoustic wave (SAW) technology to, for example, reduce intermodulation distortion (IMD).
Certain aspects of the present disclosure provide a SAW device. The SAW device generally includes a piezoelectric substrate, an interdigital transducer (IDT) disposed above the piezoelectric substrate, and a plurality of first regions of dielectric material. The IDT includes a first electrode having a first plurality of fingers and a second electrode having a second plurality of fingers interdigitated with the first plurality of fingers of the first electrode. The plurality of first regions is disposed above the piezoelectric substrate and between the first and second pluralities of fingers of the IDT, and the dielectric material has a relative permittivity greater than 3.9.
Certain aspects of the present disclosure provide a wireless device. The wireless device generally includes a radio frequency (RF) circuit and a SAW filter coupled to the RF circuit. The SAW filter generally includes a piezoelectric substrate, an interdigital transducer (IDT) disposed above the piezoelectric substrate, and a plurality of regions of dielectric material. The IDT includes a first electrode having a first plurality of fingers and a second electrode having a second plurality of fingers interdigitated with the first plurality of fingers of the first electrode. The plurality of regions is disposed above the piezoelectric substrate and between the first and second pluralities of fingers of the IDT, and the dielectric material has a relative permittivity greater than 3.9.
Certain aspects of the present disclosure generally relate to a method for fabricating a SAW device. The method generally includes forming an IDT above a piezoelectric substrate, the IDT comprising a first electrode having a first plurality of fingers and a second electrode having a second plurality of fingers interdigitated with the first plurality of fingers of the first electrode. The method further includes forming a plurality of regions of dielectric material above the piezoelectric substrate and between the first and second pluralities of fingers of the IDT, the dielectric material of the plurality of regions having a relative permittivity greater than 3.9.
Certain aspects of the present disclosure are directed to a SAW device. The SAW device generally includes a piezoelectric substrate, a dielectric layer disposed above the piezoelectric substrate, and an IDT disposed above the dielectric layer. The dielectric layer primarily comprises a different material than the piezoelectric substrate. The IDT is generally composed of a first electrode having a first plurality of fingers and a second electrode having a second plurality of fingers interdigitated with the first plurality of fingers of the first electrode.
Certain aspects of the present disclosure are directed to a plurality of resonators forming a filter circuit. In this case, the SAW device described herein may be a resonator in the plurality of resonators.
To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the appended drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation.
Certain aspects of the present disclosure generally relate to a surface acoustic wave (SAW) device with a dielectric material having a relatively high permittivity (e.g., a relative permittivity (εr)>3.9, and in some cases, εr>9.3) disposed between the fingers of an interdigital transducer (IDT). The high-permittivity dielectric regions may reduce leakage current between the fingers of the IDT, thereby reducing intermodulation distortion (IMD) and improving linearity for the SAW device.
The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary implementations and is not intended to represent the only implementations in which the invention may be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary implementations. The detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary implementations. In some instances, some devices are shown in block diagram form. Drawing elements that are common among the following figures may be identified using the same reference numerals.
The electroacoustic device 100 includes an electrode structure 104, that may be referred to as an interdigital transducer (IDT), on the surface of a piezoelectric material 102. The electrode structure 104 generally includes first and second comb-shaped electrode structures (conductive and generally metallic) with electrode fingers extending from two busbars towards each other arranged in an interlocking manner in between the two busbars (e.g., arranged in an interdigitated manner). An electrical signal excited in the electrode structure 104 (e.g., applying an AC voltage) is transformed into an acoustic wave 106 that propagates in a particular direction via the piezoelectric material 102. The acoustic wave 106 is transformed back into an electrical signal and provided as an output. In many applications, the piezoelectric material 102 has a particular crystal orientation such that when the electrode structure 104 is arranged relative to the crystal orientation of the piezoelectric material 102, the acoustic wave mainly propagates in a direction perpendicular to the direction of the fingers (e.g., parallel to the busbars).
Between the busbars, there is an overlap region including a central region where a portion of one finger overlaps with a portion of an adjacent finger as illustrated by the central region 225. This central region 225 including the overlap may be referred to as the aperture, track, or active region where electric fields are produced between the fingers 226 to cause an acoustic wave to propagate in this region of the piezoelectric material 102. The periodicity of the fingers 226 is referred to as the pitch of the IDT. The pitch may be indicated in various ways. For example, in certain aspects, the pitch may correspond to a magnitude of a distance between fingers in the central region 225. This distance may be defined, for example, as the distance between center points of each of the fingers (and may be generally measured between a right (or left) edge of one finger and the right (or left) edge of an adjacent finger when the fingers have uniform width). In certain aspects, an average of distances between adjacent fingers may be used for the pitch. The frequency at which the piezoelectric material vibrates is a main resonance frequency of the electrode structure 204a. This frequency is determined at least in part by the pitch of the IDT 205 and other properties of the electroacoustic device 100.
The IDT 205 is arranged between two reflectors 228 which reflect the acoustic wave back towards the IDT 205 for the conversion of the acoustic wave into an electrical signal via the IDT 205 in the configuration shown and to prevent losses (e.g., confine and prevent escaping acoustic waves). Each reflector 228 has two busbars and a grating structure of conductive fingers that each connect to both busbars. The pitch of the reflector may be similar to or the same as the pitch of the IDT 205 to reflect acoustic waves in the resonant frequency range. But many configurations are possible.
When converted back to an electrical signal, the converted electrical signal may be provided as an output, such as to one of the first terminal 220 or the second terminal 230, while the other terminal may function as an input.
A variety of electrode structures are possible.
It should be appreciated that while a certain number of fingers 226 are illustrated, the number of actual fingers and length(s) and width(s) of the fingers 226 and busbars may be different in an actual implementation. Such parameters depend on the particular application and desired filter characteristics. In addition, a SAW filter may include multiple interconnected electrode structures each including multiple IDTs to achieve a desired passband (e.g., multiple interconnected resonators or IDTs to form a desired filter transfer function).
Electroacoustic devices such as SAW resonators are being designed to cover more frequency ranges (e.g., 500 MHz to 6 GHz), to have higher bandwidths (e.g., up to 20%), and to have improved efficiency and performance. In general, SAW resonators are subject to nonlinearities that give rise to intermodulation distortion (IMD). For example, slight conductivity through the air or dielectric between the IDT electrodes can cause arcing and can worsen the nonlinearity, power durability, and compression of the device. Cascading the acoustic track can reduce certain amounts of intermodulation distortion, but this technique occupies increased space to implement and leads to larger SAW devices.
Notably, the relative permittivity (εr) of the piezoelectric substrate influences the intermodulation (nonlinearity) characteristic of a SAW filter. Nonlinear Mason equivalent circuit models have been used to simulate the effects that substrate permittivity can have on the nonlinearity of SAW filters. Furthermore, the relative permittivity of the material separating the electrodes that form IDTs on a SAW device likewise influences the nonlinearity behavior of the device. By adjusting the relative permittivity of certain dielectric structures in a SAW device, intermodulation distortion of the device can be reduced.
A material 302 may be disposed above and between the fingers 304a-d of the IDT. The material 302 may be air, for example, when the electroacoustic device 300 is a standard SAW device. Alternatively, the material 302 may be a dielectric material such as silicon dioxide (SiO2) if the electroacoustic device 300 is a temperature-compensated surface acoustic wave (TCSAW) device. The material 302 may have a low relative permittivity (e.g., εr=1 for air and εr=3.9 for SiO2).
The electroacoustic device 300 (e.g., that may be configured as or be a part of a SAW resonator) is similar to the electroacoustic device 100 of
As shown in
Intermodulation improvement has been observed in devices that include a thin dielectric layer, such as dielectric layer 308, composed of a dielectric material that has a high relative permittivity. Accordingly, in certain aspects of the present disclosure, the dielectric layer 308 comprises aluminum oxide (Al2O3), also referred to as alumina, having a relative permittivity range of 9.3-11.5. In certain other aspects, the dielectric layer 308 may comprise any dielectric material that has a relative permittivity greater than 3.9.
According to certain aspects of the present disclosure, the electroacoustic device 300 may be implemented in a filter or duplexer of a radio frequency (RF) circuit for use in a wireless communications device. Such a wireless communications device is described in further detail in the description of
As explained above, it may be desirable in some applications to have a continuous thin layer of high-permittivity dielectric deposited above the piezoelectric substrate. In other applications, depositing structured, high-permittivity dielectric regions between the electrodes of an IDT may offer lower intermodulation distortion in SAW devices. The structured, high-permittivity dielectric regions may be discontinuous, thereby increasing the thickness of the dielectric region while reducing any impact on the electromechanical coupling between the IDT electrodes and the piezoelectric substrate.
The dielectric regions 408 may serve as a high-permittivity dielectric region between the electrode fingers 304a-d to increase permittivity and reduce leakage current between the electrodes. As a result, intermodulation distortion in the electroacoustic device 400 may be reduced. The dielectric regions 408 may have a height 414, which may be selected based on several factors including, but not limited to, the SAW frequency, the distance 416 between electrode fingers 304a-d (or the pitch as described above), the quality factor (Q), the coupling, and/or the height 310 of the electrode fingers 304a-d. For certain aspects, the dielectric regions 408 may have uniform height, whereas in other aspects, the dielectric regions may have two or more different heights.
Table 1 provides a non-exhaustive list of materials that may be suitable to use for the dielectric regions 408. Table 1 also includes the relative permittivity for each of the listed materials.
According to certain aspects of the present disclosure, the height 414 of at least one of the plurality of dielectric regions 408 may be less than 50% of the height 310 of the first and second pluralities of fingers of the IDT. In certain aspects, the height 414 of at least one of the plurality of dielectric regions 408 may be at least 5% of the height 310 of at least one of the first or the second pluralities of fingers 304a-d of the IDT. For example, the height 414 of the plurality of dielectric regions 408 may be at least 5 nm for a finger height of 100 nm.
According to certain aspects of the present disclosure, the electroacoustic device 400 may further include one or more additional regions of dielectric material or air. For example, the one or more additional regions may be the material 302 described above with respect to
According to certain aspects of the present disclosure, the electroacoustic device 400 may be implemented in a filter or duplexer of a RF circuit for use in a wireless communications device. Such a wireless communications device is described in further detail in the description of
According to certain aspects of the present disclosure, the electroacoustic device 400 may further include a second layer that is provided on (or at least above) the piezoelectric substrate 306. For example, as illustrated in the electroacoustic device 430 of
According to certain aspects, the dielectric regions 408 may be implemented in a thin-film SAW device, where the first and second pluralities of fingers 304a-d of the IDT and the dielectric regions 408 are disposed above a thin-film piezoelectric layer, as compared to the piezoelectric substrate 306. The thin-film piezoelectric layer may be disposed above a substrate, which may comprise a temperature compensation layer (e.g., composed of SiO2), at least one charge trapping layer, and at least one substrate layer.
The operations 500 may begin, at block 502, with the fabrication facility forming an IDT above a piezoelectric substrate. The formed IDT may include a first electrode having a first plurality of fingers and a second electrode having a second plurality of fingers interdigitated with the first plurality of fingers of the first electrode.
Referring to block 504, a plurality of dielectric regions is formed above the piezoelectric substrate and between the first and second pluralities of fingers of the IDT. The formed plurality of dielectric regions may have a relative permittivity greater than 3.9. For example, at least one of the plurality of dielectric regions may comprise aluminum oxide (Al2O3), hafnium dioxide (HfO2), hafnium silicon oxide (HfSiO2), zirconium dioxide (ZrO2), or tantalum pentoxide (Ta2O5). According to certain aspects of the present disclosure, forming the plurality of dielectric regions at block 504 may involve performing atomic layer deposition (ALD) to deposit the plurality of dielectric regions above the piezoelectric substrate and between the first and second pluralities of fingers of the IDT.
The antenna 722 may be used for both wirelessly transmitting and receiving data. The transceiver circuit 700 includes a receive path through the one or more filters 720 to be provided to a low noise amplifier (LNA) 724 and a further filter 726 and then downconverted from the receive frequency to a baseband frequency through one or more mixer circuits 728 before the signal is further processed (e.g., provided to an analog-to-digital converter (ADC) and then demodulated or otherwise processed in the digital domain). There may be separate filters for the receive circuit (e.g., may have a separate antenna or have separate receive filters) that may be implemented using the filter circuit 600 of
The base station 804 communicates with the electronic device 802 via the wireless link 806, which may be implemented as any suitable type of wireless link. Although depicted as a base station tower of a cellular radio network, the base station 804 may represent or be implemented as another device, such as a satellite, terrestrial broadcast tower, access point, peer-to-peer device, mesh network node, fiber optic line, another electronic device generally as described above, and so forth. Hence, the electronic device 802 may communicate with the base station 804 or another device via a wired connection, a wireless connection, or a combination thereof. The wireless link 806 can include a downlink of data or control information communicated from the base station 804 to the electronic device 802 and an uplink of other data or control information communicated from the electronic device 802 to the base station 804. The wireless link 806 may be implemented using any suitable communication protocol or standard, such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE), 3GPP NR 5G, IEEE 802.11, IEEE 802.16, Bluetooth™, and so forth.
The electronic device 802 includes a processor 880 and a memory 882. The memory 882 may be or form a portion of a computer-readable storage medium. The processor 880 may include any type of processor, such as an application processor or a multi-core processor, that is configured to execute processor-executable instructions (e.g., code) stored by the memory 882. The memory 882 may include any suitable type of data storage media, such as volatile memory (e.g., random access memory (RAM)), non-volatile memory (e.g., flash memory), optical media, magnetic media (e.g., disk or tape), and so forth. In the context of this disclosure, the memory 882 is implemented to store instructions 884, data 886, and other information of the electronic device 802, and thus when configured as or part of a computer-readable storage medium, the memory 882 does not include transitory propagating signals or carrier waves.
The electronic device 802 may also include input/output ports 890. The I/O ports 890 enable data exchanges or interaction with other devices, networks, or users or between components of the device.
The electronic device 802 may further include a signal processor (SP) 892 (e.g., such as a digital signal processor (DSP)). The signal processor 892 may function similar to the processor and may be capable of executing instructions and/or processing information in conjunction with the memory 882.
For communication purposes, the electronic device 802 also includes a modem 894, a wireless transceiver 896, and an antenna (not shown). The wireless transceiver 896 provides connectivity to respective networks and other electronic devices connected therewith using radio-frequency (RF) wireless signals and may include the transceiver circuit 700 of
The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application-specific integrated circuit (ASIC), or processor.
By way of example, an element, or any portion of an element, or any combination of elements described herein may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoCs), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.
Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.
As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database, or another data structure), ascertaining, and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, “determining” may include resolving, selecting, choosing, establishing, and the like.
Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage, or mode of operation. The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B and object B touches object C, then objects A and C may still be considered coupled to one another—even if objects A and C do not directly physically touch each other. For instance, a first object may be coupled to a second object even though the first object is never directly physically in contact with the second object. The terms “circuit” and “circuitry” are used broadly and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuit.
The apparatus and methods described in the detailed description are illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented using hardware, for example.
One or more of the components, steps, features, and/or functions illustrated herein may be rearranged and/or combined into a single component, step, feature, or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from features disclosed herein. The apparatus, devices, and/or components illustrated herein may be configured to perform one or more of the methods, features, or steps described herein.
It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover at least: a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c). All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatus described above without departing from the scope of the claims.
