Layered Surface Acoustic Wave Research Articles

Spurious Mitigation of Layered Surface Acoustic Wave Resonators With Double-Busbar Configuration Using 42°YX-Lithium Tantalate Thin Plate

This article investigates a spurious resonance appearing near the antiresonance when the double-busbar configuration is applied to layered surface acoustic wave (SAW) resonators using 42 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> YX-LiTaO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_3$</tex-math> </inline-formula> thin plates, and possible mitigation methods are studied both theoretically and experimentally. First, the origin of the spurious resonance is revealed, and the influence of structural parameters is studied using the periodic 3-D finite-element method (FEM) powered by the hierarchical cascading technique (HCT). Then, possible methods are discussed for spurious mitigation. Finally, experimental data are provided for validation of the present analysis.

Surface Acoustic Wave Characteristics with a Layered Structure of IDT/θ° YX-LiTaO3/SiO2/AlN/diamond

A new layered surface acoustic wave (SAW) structure was proposed by Murata Co., Ltd recently. It was reported that such structure could achieve an incredible high performance including a higher quality factor Q and electromechanical coupling coefficient K2. For deeply understanding propagating characteristics and optimizing the performance of the SAWs in such structure, a layered structure of IDT/θ° YX-LiTaO3/SiO2/AlN/Diamond with different structural parameters were theoretically investigated by FEM method. The calculated admittance shows that four eigenmodes simultaneously exist in such layered structure including the main mode SH SAW. And compared with the Traditional SAW structure, the main mode could achieve a higher value of K2 with sacrificing its velocity a little. Different metal layers (Au, Al, and Cu) were examined as the electrode material. With Au employed, the K2 of the main mode is a little larger resulting from better suppression of the spurious modes. The optimum thickness of electrode and piezoelectric layer are 0.2 and 0.02λ, respectively. In this case, the K2 for the SH SAW achieves its maximum value of 12.20% with a large phase velocity of 3608 m/s. Furthermore, the pure SH SAW can be obtained with the Y-cut Euler angle θ from 0° to 60°, where its K2 has a wide range of 8.70 to 13.69%. Consequently, the work provides a theoretical guide for designing SAW devices of different bandwidth and operation frequency with such structure.

A Miniature Layered SAW Contact Stress Sensor for Operation in Cramped Metallic Slits

Based on passive and wireless surface acoustic wave (SAW) sensing technology, a sensor terminal was designed to measure the contact stress in a cramped metallic slit with less than 0.5 mm in width. A layered structure of force-sensitive element with 0.5 mm in total thickness was put forward to package SAW resonator. Thin films with elasticity and flexibility were adopted to transfer load effectively between rigid surfaces. A flexible transmission line with double-stub structure and a patch microstrip antenna were used to realize the wireless interrogation to the sensor. The force-sensitive element model was built and simulated with FEA software (COMSOL Multiphysics). The sensor prototype exhibited significant linear and repeatable frequency shifts for the loads in the range of 0–4 MPa. The linearity error was ±3% of full-scale output (FSO), and the accuracy was ±1.25% FSO. The usage of elastic films in force-sensitive element caused hysteresis in output, but the hysteresis error was controlled in an acceptable range of ±3.8% FSO.

SAW propagation characteristics of TeO3/3C-SiC/LiNbO3 layered structure

Surface acoustic wave (SAW) devices based on Lithium Niobate (LiNbO3) single crystal are advantageous because of its high SAW phase velocity, electromechanical coupling coefficient and cost effectiveness. In the present work a new multi-layered TeO3/3C-SiC/128° Y-X LiNbO3 SAW device has been proposed. SAW propagation properties such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of the TeO3/SiC/128° Y-X LiNbO3 multi layered structure is examined using theoretical calculations. It is found that the integration of 0.09λ thick 3C-SiC over layer on 128° Y-X LiNbO3 increases its electromechanical coupling coefficient from 5.3% to 9.77% and SAW velocity from 3800 ms−1 to 4394 ms−1. The SiC/128° Y-X LiNbO3 bilayer SAW structure exhibits a high positive TCD value. A temperature stable layered SAW device could be obtained with introduction of 0.007λ TeO3 over layer on SiC/128° Y-X LiNbO3 bilayer structure without sacrificing the efficiency of the device. The proposed TeO3/3C-SiC/128° Y-X LiNbO3 multi-layered SAW structure is found to be cost effective, efficient, temperature stable and suitable for high frequency application in harsh environment.

Enhancement of effective electromechanical coupling factor by mass loading in layered surface acoustic wave device structures

This paper describes a drastic enhancement of the effective coupling factor by mass loading in layered surface acoustic wave (SAW) device structures such as the ScAlN film/Si substrate structure. This phenomenon occurs when the piezoelectric layer exhibits a high acoustic wave velocity. The mass loading decreases the SAW velocity and causes SAW energy confinement close to the top surface where an interdigital transducer is placed. It is shown that this phenomenon is obvious even when an amorphous SiO2 film is deposited on the top surface for temperature compensation. This enhancement was also found in various combinations of electrode, piezoelectric layer, and/or substrate materials. The existence of this phenomenon was verified experimentally using the ScAlN film/Si substrate structure.

Surface acoustic wave devices on AlN/3C–SiC/Si multilayer structures

Surface acoustic wave (SAW) propagation characteristics in a multilayer structure including a piezoelectric aluminum nitride (AlN) thin film and an epitaxial cubic silicon carbide (3C–SiC) layer on a silicon (Si) substrate are investigated by theoretical calculation in this work. Alternating current (ac) reactive magnetron sputtering was used to deposit highly c-axis-oriented AlN thin films, showing the full width at half maximum (FWHM) of the rocking curve of 1.36° on epitaxial 3C–SiC layers on Si substrates. In addition, conventional two-port SAW devices were fabricated on the AlN/3C–SiC/Si multilayer structure and SAW propagation properties in the multilayer structure were experimentally investigated. The surface wave in the AlN/3C–SiC/Si multilayer structure exhibits a phase velocity of 5528 m s−1 and an electromechanical coupling coefficient of 0.42%. The results demonstrate the potential of AlN thin films grown on epitaxial 3C–SiC layers to create layered SAW devices with higher phase velocities and larger electromechanical coupling coefficients than SAW devices on an AlN/Si multilayer structure. Moreover, the FWHM values of rocking curves of the AlN thin film and 3C–SiC layer remained constant after annealing for 500 h at 540 °C in air atmosphere. Accordingly, the layered SAW devices based on AlN thin films and 3C–SiC layers are applicable to timing and sensing applications in harsh environments.

Layered Surface Acoustic Wave Hydrogen Sensor with Nanoporous Polyaniline as the Active Layer

In recent years, a small but critically informed literature has emerged which points to the link between opportunities to engage in generative acts and desistance from crime. This paper outlines the nature and limits of generative moments (conceived as the philosophy or practice of caring in non-violent and durable ways for self, other and future) with regard to the incarceration of a group of young males interviewed since 2003. Specifically, it poses the question of who or what it has been possible for these young men to care about within and beyond custody and highlights some of the factors which undermine generative concerns and actions. In concluding, the paper offers several ideas for enhancing generative opportunities within custodial environments.

UV detection based on a ZnO∕LiNbO3 layered surface acoustic wave oscillator circuit

This study elucidates the combination of an oscillator circuit with a high-frequency amplifier, a matching network, and a layered surface acoustic wave device for detecting ultraviolet (UV) light. The oscillator circuit shows an excellent performance with the resonance frequency of 109.34MHz and phase noise of −107.137dB at 100kHz. The frequency shift that is caused by the interaction between the acoustic wave and carriers upon excitation by UV light in the ZnO thin film is discussed. The frequency variation of the oscillator steadily increases with the intensity of the UV light. An extreme frequency shift of 63.75kHz was observed as the UV light intensity reached 1250μW∕cm2.

Layered Surface Acoustic Wave Hydrogen Sensor Based on Polyethylaniline Nanofibers

Here we report on a layered Surface Acoustic Wave (SAW) gas sensor featuring polyethylaniline nanofibers as the active layer. A rapidly-mixed reaction was employed to synthesize polyethylaniline nanofibers. The product was deposited on a microfabricated ZnO/36° YX LiTaO3 SAW transducer. Scanning Electron Microscopy (SEM) and Ultraviolet-visible spectroscopy (UV-vis) were utilized to characterize the nanomaterials. The novel sensor was tested towards different concentrations of hydrogen at room temperature. It was observed that the sensor maintained a stable baseline with good repeatability. Hence, the sensor is expected to be potentially attractive for industrial applications.

Highly sensitive ultraviolet detector using a ZnO/Si layered SAW oscillator

This study elucidates a highly sensitive ultraviolet light detector using the combination of an oscillator circuit with a high-frequency amplifier, a matching network and a layered surface acoustic wave (SAW) device. In this structure, a ZnO thin film is simultaneously used as an active layer for UV detection and a piezoelectric layer for exciting a high-order surface acoustic wave. The microstructure and crystallization of ZnO films were investigated using the scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SAW oscillator shows a good performance with output power of − 1.14 dBm and phase noise of −94.7 dBc at 100 kHz. Firstly, the frequency shifts of the oscillator exhibit rapid increase with the intensity of the UV light. Then the increased shifts decayed at certain UV intensity due to the saturated photogenerated carriers. An extreme frequency shift of 1017 kHz was obtained as the UV intensity reached 551 μW/cm 2. The maximum sensitivity of 8.12 ppm/(μW/cm 2) can be obtained in this detector.

Utilization of phononic-crystal reflective gratings in a layered surface acoustic wave device

In this paper, a design that combines two-port surface acoustic wave (SAW) devices and phononic crystals (PCs) acting as reflected gratings is demonstrated. Finite-difference time-domain method is used to analyze SAWs encountering the PC and optimize the design. A layered ZnO/Si SAW device and a square lattice PC composing of cylindrical holes on silicon were fabricated. With the PC of 15-layer cylinders, experimental insertion loss shows a 7 dB improvement at 212 MHz at central frequency. In addition, the size of gratings is reduced significantly as compared to the traditional gratings with hundreds of metal strips.

Layered SAW gas sensor based on CSA synthesized polyaniline nanofiber on AlN on 64° YX LiNbO 3 for H 2 sensing

A 64° YX LiNbO 3 surface acoustic wave (SAW) transducer was fabricated and then aluminium nitride (AlN) layer was deposited on the active area of the device as acoustic wave guiding layer. Structural studies revealed that the deposited AlN thin films have strong preferential c-axis orientation. Morphological analysis showed that the AlN layer is compact with grain dimensions of less than 80 nm. Polyaniline nanofibers were polymerized from the reactions in which an oxidant was rapidly mixed with the aniline monomer in an acidic environment. The polymer was synthesized in camphor sulfonic acid (CSA) to obtain 50 nm average diameter polyaniline nanofibers. These nanofibers were deposited on the layered SAW device and were tested towards hydrogen (H 2) gas while operating at room temperature. The device demonstrated a large and reproducible response to different concentrations of the H 2 gas making it an ideal candidate for H 2 sensing at room temperature.

Design of dispersive layered SAW filters with CMOS low noise amplifier

Up to now, RF front‐end surface acoustic wave (SAW) filters for mobile communication are mainly fabricated on LiNbO3 and LiTaO3 substrates. A monolithic integration of these filters on Si substrates is highly desirable, but Si is non piezoelectric. One alternative is the deposition of a piezoelectric film on the semiconductor substrate. CMOS technology is very attractive for integrating the radio frequency modules in a single chip. This paper presents the analysis and realisation of a SAW passband filter on silicon substrate based on a piezoelectric ZnO thin film working near 1 GHz , integrated with a CMOS low‐noise amplifier. We propose a modified coupling of modes (COM) approach for a layered ZnO/Si surface acoustic wave filter. The COM parameters in this formulation are the Rayleigh wave velocity, the electromechanical coupling coefficient, the complex reflection coefficient, the transduction coefficient and the inter‐digital capacitance C. This is a dispersive SAW layered filter some parameters of which become frequency dependent due to the phase velocity dispersion. We present the theoretical and experimental results of the filter integrated with a CMOS low noise amplifier.

Very high frequency SAW devices based on nanocrystalline diamond and aluminum nitride layered structure achieved using e-beam lithography

Very high frequency surface acoustic wave (SAW) devices based on the AlN/diamond layered structure are fabricated by direct writing using e-beam lithography on the nucleation side of nanocrystalline diamond (NCD) films deposited by microwave plasma assisted chemical vapor deposition process. The NCD nucleation side is characterized from the point of view of microstructure, morphology and surface topography. Surface roughness as low as 6 nm is reached, which enhances the deposition of AlN film on this flat surface. The interdigital transducers IDTs made in aluminum with lateral resolution down to 600 nm are successfully patterned on the AlN/NCD layered structure with an adapted technological process. Experimental results show that the Rayleigh wave and the higher mode are generated. A high frequency around 4 GHz (mode 1) is obtained for the considered layered structure SAW device, exhibiting a phase velocity of 9200 m/s taking into account the wavelength of 2.4 μm. This value agrees well with calculated values determined from dispersion curves of phase velocity.

Improved Frequency Responses of Saw Filters with Interdigitated Interdigital Transducers on ZnO/Diamond/Si Layered Structure

AbstractThere are many investigations on surface acoustic wave (SAW) filters with interdigitated interdigital transducers (IIDT) in the last two decades; however, the same is not true for the case of IIDT SAW filters fabricated on layered piezoelectric substrates. Therefore, the aim of this study is to explore the characteristics of the IIDT structures on layered piezoelectric media and further, to improve the frequency response of layered IIDT SAW filters with the unique dispersive properties of a layered piezoelectric structure. A method based on the effective permittivity approach, the coupling of modes (COM) model, and the H-matrix is utilized to analyze the characteristics of IIDT on the ZnO/Diamond/Si layered structure. In this study, it is shown that by optimizing the ratio of input to output IDT pairs, the side-lobe level of frequency responses on the ZnO/Diamond/Si layered structure could be suppressed, similar to that on the half-space substrate. In addition, it is also proved that the notched pass-band could be flattened out by designing the center frequency on the local maximum of the electromechanical coupling coefficient dispersion curve.

Layered SAW gas sensor with single-walled carbon nanotube-based nanocomposite coating

A Surface acoustic wave (SAW) sensor using a ZnO guiding layer on 36° Y-cut X-propagation LiTaO 3 piezoelectric substrate has been designed and fabricated. Single-walled carbon nanotube (SWCNT)-based nanocomposite coatings have been deposited using the Langmuir–Blodgett technique. The sensor was tested towards H 2 , NH 3 , NO 2 gases, in the range of 0.030–1%, 30–1000 ppm, 1–10 ppm, respectively. The output signal was the phase of the SAW device, which was monitored using a network analyzer. The developed sensor has a high sensitivity, good repeatability and low detection limit at sub-ppm levels, at room temperature. The experimental results obtained are compared to a theoretical model and the SAW gas sensing mechanisms are discussed with the acoustoelectric effect that appears to be dominant in the SAW response.

A layered surface acoustic wave gas sensor based on apolyaniline/In2O3 nanofibre composite

A polyaniline/In2O3 nanofibre composite based layered surface acoustic wave (SAW) sensorhas been developed and investigated for different gases. Chemicaloxidative polymerization of aniline in the presence of finely dividedIn2O3 was employed to synthesize a polyanilinenanofibre/In2O3 nanoparticle composite. The nanocomposite was deposited onto a layeredZnO/64° YX LiNbO3 SAW transducer. The novel sensor was exposed toH2,NO2 and CO gases. Fast response and recovery times with good repeatability were observed atroom temperature.

The Preparation of Piezoelectric ZnO Films by RF Magnetron Sputtering for Layered Surface Acoustic Wave Device Applications

Crystalline structures, intrinsic stress, and surface roughness of piezoelectric ZnO films deposited on sapphire substrates by rf magnetron sputtering and sequential post-annealing treatments were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements. The rf power used and O2/(Ar+O2) gas ratio greatly affected the crystallinity and surface roughness of the ZnO film. A c-axis preferred orientation with superior surface roughness was achieved at a specific rf power and O2/(Ar+O2) gas flow ratio. In addition, the original intrinsic stress was also markedly released (stress=0.325 ×1010 dyn/cm2) and a uniform surface (Ra=2.42 nm) was produced by a post-annealing treatment at a temperature of 400 °C under oxygen ambient. An acoustic wave at the center frequency of 240 MHz (hZnO/λ=0.1) was obtained from the ZnO/sapphire-layered surface acoustic wave (SAW) device using this optimized ZnO film.

Layered WO3/ZnO/36° LiTaO3 SAW gas sensor sensitive towards ethanol vapour and humidity

Ethanol sensing in dry and humid air by layered surface acoustic wave (SAW) devices is presented. The transducing platform is based on 36° YX LiTaO3 layered SAW device, utilising a 1.2μm zinc oxide (ZnO) intermediate layer and 150nm tungsten trioxide (WO3) sensing layer. Sheet conductivity calculations show that maximum sensitivity is achieved for ZnO layer thickness between 1 and 1.5μm. Sensor performance was analyzed in terms of response magnitude as a function of operational temperature and different relative humidity (RH). Frequency shifts of 119, 90 and 86kHz towards 500ppm of ethanol in synthetic air were observed for 0, 25 and 50% RH, respectively. All RH levels were measured at 20°C. At an operating temperature of 300°C, the largest response towards 500ppm of ethanol was observed. Response magnitude was found to decrease with increasing RH and decreasing operating temperature. Furthermore, the effect of elevated temperatures on the sensors surface morphology is characterised by AFM and SEM techniques. It is suggested that the morphological modifications, due to elevated temperatures play an important role in the sensing behaviour of the WO3 films.

A novel weighted method for layered SAW filters using slanted finger interdigital transducers

In this paper, we propose a novel weighted method to improve the inclined pass-band problem that is intrinsic to surface acoustic wave (SAW) filters with slanted finger interdigital transducers (SFITs). By the dispersive characteristics of SAW in layered piezoelectric substrates, the present method could make the inclined pass-band flatter or the bandwidth wider. We derived a coupling-of-modes model for the calculation of the frequency responses of layered SAW devices with SFITs and calculated the dispersive characteristics of an AlN/silicon layered piezoelectric substrate, such as the phase velocity and the electromechanical coupling coefficient. Then we utilized the dispersive electromechanical coupling coefficient to flatten the inclined pass-band and the dispersive phase velocity to widen the bandwidth. Two designed examples of wide-band layered SAW filters using SFITs on AlN/silicon substrates are presented to prove the validity of the proposed method: one is designed to flatten the inclination of the pass-band; the other, to widen the bandwidth. Results show that the dispersions of layered piezoelectric media are favourable for improving the performance of SFIT-based SAW filters.