Enhanced Coupling Coefficient in Dual-Mode ZnO/SiC Surface Acoustic Wave Devices with Partially Etched Piezoelectric Layer

Surface acoustic wave (SAW) devices based on multi-layer structures have been widely used in filters and sensors. The electromechanical coupling factor (K2), which reflects energy-conversion efficiency, directly determines the bandwidth of the filter and the sensitivity of sensor. In this work, a new configuration of dual-mode (quasi-Rayleigh and quasi-Sezawa) SAW devices on a ZnO/SiC layered structure exhibiting significantly enhanced K2 was studied using the finite element method (FEM), which features in the partial etching of the piezoelectric film between the adjacent interdigitated electrodes (IDTs). The influences of piezoelectric film thickness, etching ratio, top electrodes, bottom electrodes, and the metallization ratio on the K2 were systematically investigated. The optimum K2 for the quasi-Rayleigh mode and quasi-Sezawa mode can exceed 12% and 8%, respectively, which increases by nearly 12 times and 2 times that of the conventional ZnO/SiC structure. Such significantly promoted K2 is of great benefit for better comprehensive performance of SAW devices. More specifically, a quasi-Rayleigh mode with relatively low acoustic velocity (Vp) can be applied into the miniaturization of SAW devices, while a quasi-Sezawa mode exhibiting a Vp value higher than 5000 m/s is suitable for fabricating SAW devices requiring high frequency and large bandwidth. This novel structure has proposed a viable route for fabricating SAW devices with excellent overall performance.

In-Situ Process and Simulation of High-Performance Piezoelectric-on-Silicon Substrate for SAW Sensor

This paper studied the manufacturing process of Piezoelectric-on-Silicon (POS) substrate which integrates 128° Y–X Lithium niobate thin film and silicon wafer using Smart-Cut technology. The blistering and exfoliation processes of the He as-implanted LN crystal under different annealing temperatures are observed by the in-situ method. Unlike the conventional polishing process, the stripping mechanism of the Lithium niobate thin film is changed by controlling annealing temperature, which can improve the surface morphology of the peeling lithium niobate thin film. We prepared the 128° Y–X POS substrate with high single-crystal Lithium niobate thin film and surface roughness of 3.91 nm through Benzocyclobutene bonding. After simulating the surface acoustic wave (SAW) characteristics of the POS substrate, the results demonstrate that the Benzocyclobutene layer not only performs as a bonding layer but also can couple more vibrations into the LN thin film. The electromechanical coupling coefficient of the POS substrate is up to 7.59% in the Rayleigh mode when hLN/λ is 0.3 and hBCB/λ is 0.1. Therefore, as a high-performance substrate material, the POS substrate has proved to be an efficient method to miniaturize and integrate the SAW sensor.

A single Rayleigh mode may exist with multiple values of phase-velocity at one frequency

SUMMARY Other than commonly assumed in seismology, the phase velocity of Rayleigh waves is not necessarily a single-valued function of frequency. In fact, a single Rayleigh mode can exist with three different values of phase velocity at one frequency. We demonstrate this for the first higher mode on a realistic shallow seismic structure of a homogeneous layer of unconsolidated sediments on top of a half-space of solid rock (LOH). In the case of LOH a significant contrast to the half-space is required to produce the phenomenon. In a simpler structure of a homogeneous layer with fixed (rigid) bottom (LFB) the phenomenon exists for values of Poisson’s ratio between 0.19 and 0.5 and is most pronounced for P-wave velocity being three times S-wave velocity (Poisson’s ratio of 0.4375). A pavement-like structure (PAV) of two layers on top of a half-space produces the multivaluedness for the fundamental mode. Programs for the computation of synthetic dispersion curves are prone to trouble in such cases. Many of them use mode-follower algorithms which loose track of the dispersion curve and miss the multivalued section. We show results for well established programs. Their inability to properly handle these cases might be one reason why the phenomenon of multivaluedness went unnoticed in seismological Rayleigh wave research for so long. For the very same reason methods of dispersion analysis must fail if they imply wave number kl(ω) for the lth Rayleigh mode to be a single-valued function of frequency ω. This applies in particular to deconvolution methods like phase-matched filters. We demonstrate that a slant-stack analysis fails in the multivalued section, while a Fourier–Bessel transformation captures the complete Rayleigh-wave signal. Waves of finite bandwidth in the multivalued section propagate with positive group-velocity and negative phase-velocity. Their eigenfunctions appear conventional and contain no conspicuous feature.

About the evaluation of the results of the microseismic sounding method in their geological interpretation

Работа посвящена анализу результатов двумерного численного решения прямой задачи рассеяния фундаментальной моды Рэлея на двух скоростных неоднородностях, расположенных друг под другом. Данная модель позволила проанализировать некоторые случаи использования метода микросейсмического зондирования (ММЗ) в условиях сложно построенных сред. С использованием численной модели, построенной из первых принципов в прямом моделировании получены оценки вертикальной разрешающей способности метода микросейсмического зондирования. Рассмотрены случаи ряда конкретных геометрических размеров и ряда упругих параметров включений, со значениями, близкими к встречающимся в природных условиях. Выработаны и сформулированы простые практические приемы, с помощью которых можно оценивать вертикальное разрешение объектов при интерпретации разрезов микросейсмического зондирования по экспериментально полученным разрезам. Оценка вертикальной разрешающей способности ММЗ на синтетических данных состоит в том, что, если расстояние между центрами двух малых по сравнению с глубиной залегания неоднородностей, расположенных друг над другом, составляет 36 41 (или более) от длины фундаментальной моды волны Рэлея, равной R Нcenter/ 0,4, где Нcenter глубина середины между центрами неоднородностей, то изображения этих неоднородностей будут разрешены в поле случайных волн Рэлея. То есть, для разрешимости по ММЗ расстояние по вертикали между центрами малых неоднородностей должно составлять Нcenter или более. Выработанные приемы использованы для оценки разрешения горизонтально залегающих слоев в разрезах, полученных в ходе изучения зоны сочленения Таманского полуострова и Крыма при геологической интерпретации результатов микросейсмических исследований. The paper is devoted to the analysis of the results of a twodimensional numerical solution of the direct scattering problem of the fundamental Rayleigh mode on two velocity inhomogeneities located one under another. This model made it possible to analyze some cases of using the method of microseismicsounding (MMS) in conditions of complex structured media.Using the numerical model built from first principles in direct modeling, we obtained estimates of the vertical resolution of the microseismic sounding method. The cases of a number of specific geometrical dimensions and a number of elastic parameters of inclusions with values close to those encountered in natural conditions are considered.Simple practical methods have been developed and formulated, with the help of which one can estimate the vertical resolution of objects when interpreting microseismic sounding sections obtainedexperimentally.Estimation of the vertical resolution of the MMS on synthetic data is that, if the distance between the centers of two small inhomogeneities, one above the other, compared to the depth, is 36 41 (or more) of the fundamental mode of the Rayleigh wave, equal to R Hcenter/ 0.4, where Hcenter is the midpoint depth between the centers of inhomogeneities, then the images of these inhomogeneities will be resolved in the field of random Rayleigh waves. That is, to ensure the resolution of the MMS, the vertical distance between the centers of small discontinuities should be Hcenter or more. The techniques developed were used to assess the resolution of horizontallylying layers in the sections obtained during the study of the junction zone of the Taman Peninsula and the Crimea in the course of geological interpretation of microseismic research results.

Theoretical Derivation and Simulation of the Equation of Evaporation Line in Water Evaporation

The Rayleigh fractionation model is first deduced by the principle of dynamic reaction, which indicates that Rayleigh fractionation can be explained by dynamic characteristics of isotopic molecules in the reaction process. Subsequently, the analytic expression of evaporation line is deduced under equilibrium condition in the open systems of Rayleigh mode, which shows that it is an exponential form. The simulation results show that the slope of the evaporation line under equilibrium condition changes with the temperature that the higher the temperature is, the smaller the slope is and thus the higher the degree of enrichment is. This research can provide reference basis for better understanding the dynamic characteristics of isotopic molecules in evaporation process.

Design and Fabrication of Nanoscale IDTs Using Electron Beam Technology for High-Frequency SAW Devices

High-frequency Rayleigh-mode surface acoustic wave (SAW) devices were fabricated for 4G mobile telecommunications. The RF magnetron sputtering method was adopted to grow piezoelectric aluminum nitride (AlN) thin films on the Si3N4/Si substrates. The influence of sputtering parameters on the crystalline characteristics of AlN thin films was investigated. The interdigital transducer electrodes (IDTs) of aluminum (Al) were then fabricated onto the AlN surfaces by using the electron beam (e-beam) direct write lithography method to form the Al/AlN/Si3N4/Si structured SAW devices. The Al electrodes were adopted owing to its low resistivity, low cost, and low density of the material. For 4G applications in mobile telecommunications, the line widths of 937 nm, 750 nm, 562 nm, and 375 nm of IDTs were designed. Preferred orientation and crystalline properties of AlN thin films were determined by X-ray diffraction using a Siemens XRD-8 with CuKαradiation. Additionally, the cross-sectional images of AlN thin films were obtained by scanning electron microscope. Finally, the frequency responses of high-frequency SAW devices were measured using the E5071C network analyzer. The center frequencies of the high-frequency Rayleigh-mode SAW devices of 1.36 GHz, 1.81 GHz, 2.37 GHz, and 3.74 GHz are obtained. This study demonstrates that the proposed processing method significantly contributes to high-frequency SAW devices for wireless communications.