Surface Acoustic Wave Components Research Articles

Vertical Surface Phononic Mach-Zehnder Interferometer

In this work, we propose and explore a double-stage phononic crystal (PnC) consisting of a top suspended $\mathrm{ZnO}$ layer, an array of sandwiched $\mathrm{Si}$ pillars, and a bottom $\mathrm{ZnO}$ layer on a $\mathrm{Si}$ substrate. The proposed double-stage PnC exhibits interesting behavior of routing the incident surface acoustic waves (SAWs) based on polarization and frequency, so that it can be considered as an efficient building block for alternative multistage SAW components. Here, we design the double-stage PnC to behave as an efficient vertical SAW splitter in a Mach-Zehnder interferometer, using the excitation of appropriate surface-coupled modes through the periodic locally resonating pillars. Benefiting from the acoustoelectric effect in $\mathrm{ZnO}$, the exposed top $\mathrm{ZnO}$ layer serves as the sensing branch, and the bottom $\mathrm{ZnO}$ layer serves as the reference branch in the presented vertical Mach-Zehnder interferometer. The vertical configuration of the proposed design allows exposure of the top $\mathrm{ZnO}$ layer to external stimulations, such as exposure to ultraviolet illumination or a hydrogen environment, while protecting the underlying parts from being exposed. This structural aspect simplifies the experimental implementation of our design in comparison with the conventional planar Mach-Zehnder interferometers by avoiding the necessity of in-plane focusing of external stimulation on the sensing branch. Our optimized Mach-Zehnder interferometer shows an output transmission signal of \ensuremath{-}8 dB and a high extinction ratio of 23 dB at 8.6 GHz when the conductivity of the top $\mathrm{ZnO}$ layer is increased from about 1 S/m to 100 S/m via external stimulation. Here, we propose a highly sensitive miniature vertical surface acoustic Mach-Zehnder interferometer, which may open up alternative horizons for future multistage SAW components.

Thermal Modulation of Gigahertz Surface Acoustic Waves on Lithium Niobate

Surface acoustic wave (SAW) devices have wide range of applications in microwave signal processing. Microwave SAW components benefit from higher quality factors and much smaller crosstalk when compared to their electromagnetic counterparts. Efficient routing and modulation of SAWs are essential for building large-scale and versatile acoustic-wave circuits. Here, we demonstrate integrated thermo-acoustic modulators using two SAW platforms: bulk lithium niobate and thin-film lithium niobate on sapphire. In both approaches, the gigahertz-frequency SAWs are routed by integrated acoustic waveguides while on-chip microheaters are used to locally change the temperature and thus control the phase of SAW. Using this approach, we achieved phase changes of over 720 degrees with the responsibility of 2.6 deg/mW for bulk lithium niobate and 0.52 deg/mW for lithium niobate on sapphire. Furthermore, we demonstrated amplitude modulation of SAWs using acoustic Mach Zehnder interferometers. Our thermo-acoustic modulators can enable reconfigurable acoustic signal processing for next generation wireless communications and microwave systems.

Single-mode and ultra-broadband gigahertz surface acoustic waveguides on AlN-on-SiC substrates

This paper proposes a class of high-performance surface acoustic wave (SAW) waveguides based on AlN-on-SiC substrates. Under the existing crystal growth and processing technology, these SAW waveguides offer excellent performance in single mode, low loss, ultra-broadband, operating at gigahertz frequencies. Quasi-Rayleigh SAWs can be excited by traditional interdigital transducers and guided freely with excellent efficiency. Based on these SAW waveguides, we further demonstrate SAW splitters and ring cavities with ultra-high qualities up to 107. These SAW components complement future integrated phononic circuits for high-frequency and compact acoustic manipulating, signal processing, sensing, computing, etc.

Tunable multidispersive bands of inductive origin in piezoelectric phononic plates

A variety of multidispersive, localized, or extended in frequency, bands, induced by inductance-based external electric circuits in piezoelectric phononic plates, is studied both theoretically and experimentally in this work. Their origin, tightly related to an equivalent LC-circuit behavior, is analyzed in detail and their interaction with the Lamb-like guided modes of the plate is also discussed. These bands, easily tuned by the choice of the parameters of the external electric circuitry, lead to a non-destructive, real-time control of the dispersion characteristics of these structures. Our device and analysis can find application in the improvement of surface acoustic wave components by offering additional degrees of freedom.

Electrothermal Modeling of Surface Acoustic Wave Resonators and Filters.

In this article, an electrothermal modeling approach of surface acoustic wave (SAW) resonators and filters is presented. The starting point for the model is a preliminary design that has to be assessed for thermal aspects. Due to the high geometrical complexity of SAW components, simplifications are elaborated and qualified on resonator and filter levels to prepare the design for thermal simulation. A thermal model is created and simulated in a finite-element method environment. The simulated behavior is exported as a thermal impedance and implemented in a circuit model of a SAW filter. The layout's electromagnetic behavior is taken into account. Electrothermal models of the SAW resonators and the bus bars are developed. The interface to the thermal impedance is achieved by the use of electrothermal ports. The dynamic effect of the frequency shift is included. Verification is done by a comparison of the temperature increase of a resonator in a filter test structure to a corresponding simulation model. The filter is excited by a radio frequency large signal, and the temperature is detected by the use of a resistive temperature sensor. A simulation that shows the impact of mutual heating between the resonators in a filter environment is performed.

Enhancing RF Bulk Acoustic Wave Devices: Multiphysical Modeling and Performance

The rapid proliferation of smartphones, tablets, and intelligent wearables is proof of the global success of high-performance RF acoustic devices based on bulk acoustic wave (BAW) and surface acoustic wave (SAW) technologies. Advanced wireless communication standards, such as 4G/LTE and the upcoming 5G, make the implementation of new RF features (power handling, wider bandwidth, and reconfigurability) mandatory in modern end-user equipment for mobile communications. This leads to an increasing demand for SAW and BAW components due to their compatibility with higher frequencies. In the year 2020, shipments of RF filters will exceed 68 billion (Figure 1), of which about 40 billion will be high-performance filters, such as film bulk acoustic resonators (FBARs), high quality factor (Q) BAW components, temperature-compensated (TC) SAW components, and thin-film SAW components [1]-[3].

High-gain leaky surface acoustic wave amplifier in epitaxial InGaAs on lithium niobate heterostructure

Active surface acoustic wave components have the potential to transform RF front ends by consolidating functionalities that currently occur across multiple chip technologies, leading to reduced insertion loss from converting back and forth between acoustic and electronic domains in addition to improved size and power efficiency. This letter demonstrates a significant advance in these active devices with a compact, high-gain, and low-power leaky surface acoustic wave amplifier based on the acoustoelectric effect. Devices use an acoustically thin semi-insulating InGaAs surface film on a YX lithium niobate substrate to achieve exceptionally high acoustoelectric interaction strength via an epitaxial In0.53Ga0.47As(P)/InP quaternary layer structure and wafer-scale bonding. We demonstrate 1.9 dB of gain per acoustic wavelength and power consumption of 90 mW for 30 dB of electronic gain. Despite the strong intrinsic leaky propagation loss, 5 dB of terminal gain is obtained for a semiconductor that is only 338 μm long due to state-of-the-art heterogenous integration and an improved material platform.

Microwave Acoustic Wave Devices: Recent Advances on Architectures, Modeling, Materials, and Packaging

This paper reviews applications of acoustic wave devices in mobile communication. After a general and historical introduction to bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices, a review is given on the architectures where acoustic wave devices are applied driving the requirements on the SAW and BAW components. Following this, we discuss the progress in technology important materials. Next, an overview on the modeling and characterization of SAW and BAW at high power levels is given. Finally an overview of packaging technologies and an outlook to future developments is provided. Finally, an outlook to future developments is provided.

Adhesive Wafer Bonding Applied for Fabrication of True-Chip-Size Packages for SAW Devices

Surface Acoustic Wave (SAW) filters are key components for mobile communication. In SAW devices mechanical waves propagate on the surface of a piezoelectric bulk material such as LiNbO3 or LiTaO3. SAW components require advanced cavity packaging solutions in order to enable the mechanical wave propagation on the substrate material. Size reduction of SAW filters allows further miniaturization of mobile phones and an extension of their functionality. The mobile communication industry, therefore, demands advanced cavity package technologies to be developed for SAW components. These packages have to offer high performance, high reliability, and low cost while maintaining a form factor as small as possible. To address these requirements EPCOS has developed a Die Sized SAW Package (DSSP), a true chip-size wafer level package for SAW filters. This paper discusses the manufacturing process of wafer-level-packages for SAW-devices with a special focus on the adhesive wafer bonding technology.

Low-Temperature Bumpless Bonding for Surface Acoustic Wave Components

A low-temperature bonding process for surface acoustic wave (SAW) components was developed in ambient air by the surface activated bonding (SAB) method. In this method, the assembly was achieved using not Au bumps but Au bumpless structures directly. The required bonding pressure was optimized. To compare this method with conventional thermocompression bonding and thermosonic bonding methods, die shear and electrical tests were performed to determine the mechanical and electrical properties, respectively. Under optimized parameters, the bonding feasibility of miniaturized SAW components was confirmed at 25–100 °C in ambient air with the proper signal output and a high bonding strength. Scanning electron microscopy and energy dispersive X-ray spectrometry observations showed that no intermetallic compound formed around the bond interfaces.

Numerical study of the spectral 3-D Green's function singularities for piezoelectric SAW components

This article deals with the numerical study of the singularities appearing in the spectral 3-D Green's function associated with the piezoelectric surface acoustic wave components (so-called SAW components). These electrical units are currently used today in several devices produced by the telecommunications industry (radio, TV, radar, and digital telecommunication systems). The need to improve their performance has motivated engineers and researchers to use mathematical modeling intensively, in particular the integral equations technique here used, which requires the computing of the associated Green's function and the study of its properties.

Performance Evaluation of Saw Devices by Simulation

Surface acoustic wave (SAW) devices have been used since the early 1990s as critical components in many radio frequency (RF) transmitters and receivers due to their small size, efficient operation, and excellent performance characteristics. In today’s wireless applications, the number of passive SAW components used is on the increase. SAW devices are being used in mobile phones and wireless devices as RF resonator filters, intermediate frequency filters, and local oscillators. In addition, SAW devices have recently been defined and used for sensing various measurands, including gases, liquids, ice, and mechanical vibrations. Because SAW devices are so widely used, it is desirable to evaluate the device prior to fabrication, especially in cases where the devices’ material and dimensions have a major influence on the performance of the overall system. In this article the authors present the frequency response simulation of SAW devices using MATLAB™. Both equivalent circuit and transmission matrices model have been simulated for three different types of SAW devices: a delay line, a one-port resonator, and a two-port resonator. The results obtained are presented along with the design parameters and models used in the simulations.

Perspectives of SAW Based Processor Implementation for Mobile Communications

The new approaches to the development of the mobile telecommunication systems' wireless interface based on the use of surface acoustic waves (SAW) are considered in the paper. The completed analysis has shown, that the proposed new architecture of the wireless interface with code-time division multiple access (CTDMA), based on SAW components, is potentially capable of approaching the UMTS/IMT2000 requirements for mobile telecommunication systems of 3-rd generation. The appropriate application in the system of 3rd generation of the CTDMA wireless interface, taking into account the features of SAW components and the possibility of an integration with the standards of the GSM-900/DCS-1800 system, can provide effective cellular telecommunications with the flexible adaptation to possible operating conditions.

SAW spectral characteristics of the YZ-LiNbO3-thin-lead-film layered structure

An acousto-optical study of the effect of a lead film on propagation of high-power surface acoustic waves (SAW) along the Z direction on the Y cut of LiNbO3 is reported. The presence of the metal film has been found to stimulate spatial oscillations of SAW components and suppress the onset of nonlinearity. If the film is more narrow than the SAW aperture, one observes considerable inflow of acoustic energy from the free surface to the film region. A study of the film-induced sound-velocity dispersion revealed it to have a linear pattern. An analysis of the results within the present theoretical models of soliton development showed that a soliton-like monopulse can form only if a very thin (∼150 A) lead film is present.

Transient grating measurements of picosecond acoustic pulses in metal films

A transient grating technique is used to detect picosecond acoustic pulses in supported metal films. Crossed femtosecond laser pulses generate acoustic responses with longitudinal components propagating normal to the film plane and surface acoustic wave components propagating in the film plane. Surface “ripple” associated with both components is detected through the diffraction of a probe beam. The measurements yield enhanced information content for characterization of film thickness and mechanical properties.

Surface acoustic wave technology and applications

Since the advent of the interdigital transduction for efficient transducer of surface acoustic waves (SAW), SAW devices have provided a key technology for communication and signal processing systems. In order to obtain the required electrical terminal characteristics, a diverse number of SAW components have evolved. Some of these components include bidirectional and unidirectional transducers, couplers, beam compressors, waveguides, and reflectors. The various SAW components are monolithically integrated, using processors similar to those for integrated circuits, on a piezoelectric substrate to produce dispersive filters, linear phase filters, resonators, convolvers, and correlators. These devices are manufactured for a wide variety of applications which include TV‐IF, cable TV, VCRs, fiber optic repeaters, radar, spread spectrum receivers, cellular radio, sensors, and a variety of communication receiver applications. The technological innovations and operation of the primary SAW components will be discussed. The presentation will focus on component implementations, their operation, and their most significant parameters. A review of some of the key developments of SAW technology and their applications will also be presented.

Modeling, simulation, and design of SAW grating filters

A systematic procedure for modeling, simulating, and designing SAW (surface acoustic wave) grating filters, taking losses into account, is described. Grating structures and IDTs (interdigital transducers) coupling to SAWs are defined by cascadable transmission-matrix building blocks. Driving point and transfer characteristics (immittances) of complex architectures consisting of gratings, transducers, and coupling networks are obtained by chain-multiplying building-block matrices. This modular approach to resonator filter analysis and design combines the elements of lossy filter synthesis with the transmission-matrix description of SAW components. A multipole filter design procedure based on a lumped-element-model approximation of one-pole two-port resonator building blocks is given and the range of validity of this model examined. The software for simulating the performance of SAW grating devices based on this matrix approach is described, and its performance, when linked to the design procedure to form a CAD/CAA (computer-aided design and analysis) multiple-filter design package, is illustrated with a resonator filter design example.

Surface-acoustic-wave devices for communications

Surface-wave components have demonstrated performance capabilities in the VHF/UHF range which are available with no other filtering technique. The major advantages of the filters are their small size, high reliability, low cost, high Q, good reproducibility, temperature stability, wide dynamic range, and linear phase response, as well as special characteristics relevant to specific applications. Surface-acousticwave (SAW) devices are used for bandpass filtering [1], matched filtering for radar pulse compression [2], [3] or spread-spectrum signal processing [4], delay lines [5], and frequency control elements [3], [6]. Within the context of communication systems' applications, this paper reviews the state of the art for SAW components from high-performance fixed-tuned devices to tunable or programmable filters. Major technological advances discussed include unidirectional SAW filters [7] which eliminate bidirectionality loss and simultaneously suppress in-band spurious responses to achieve an insertion loss below 1 dB with a 0.04-dB peak-to-peak ripple. A novel surface-wave sub-system [8] which offers revolutionary signal processing functions through transform processing is also described.

Microsound Components, Circuits, and Applications

Surface acoustic wave components have been realized which perform the functions of transduction, amplification, and coupling. Applications are suggested which make use of these components. Exploratory work in connection with surface acoustic waveguides suggests the feasibility of acoustic analogs of conventional microwave transmission line (microsound) components on the surface of crystal and substrates. These microsound transmission lines, hybrids, and directional couplers interconnect microsound transducers, amplifiers, isolators, and phase shifters to form microsound circuits capable of autocorrelation, Fourier transformation, and cross correlation functions. Compatible component configurations are proposed and evaluated which perform these basic functions. The anticipated difficulties with their realization are discussed and the current status of critical problems including the epitaxial growth of thin films and submicron etching procedures will be given. Several circuits capable of performing correlation functions are given.