Showing papers on "Interdigital transducer published in 2013"

Magnetoelectric thin film composites with interdigital electrodes

Abstract: Magnetoelectric (ME) thin film composites on silicon cantilevers are fabricated using Pb(Zr0.52Ti0.45)O3 (PZT) films with interdigital transducer electrodes on the top side and FeCoSiB amorphous magnetostrictive thin films on the backside. These composites without any direct interface between the piezoelectric and magnetostrictive phase are superior to conventional plate capacitor-type thin film ME composites. A limit of detection of 2.6 pT/Hz1/2 at the mechanical resonance is determined which corresponds to an improvement of a factor of approximately 2.8 compared to the best plate type sensor using AlN as the piezoelectric phase and even a factor of approximately 4 for a PZT plate capacitor.

Low propagation loss in a one-port SAW resonator fabricated on single-crystal diamond for super-high-frequency applications

Abstract: Diamond has the highest known SAW phase velocity, sufficient for applications in the gigahertz range. However, although numerous studies have demonstrated SAW devices on polycrystalline diamond thin films, all have had much larger propagation loss than single-crystal materials such as LiNbO3. Hence, in this study, we fabricated and characterized one-port SAW resonators on single-crystal diamond substrates synthesized using a high-pressure and high-temperature method to identify and minimize sources of propagation loss. A series of one-port resonators were fabricated with the interdigital transducer/ AlN/diamond structure and their characteristics were measured. The device with the best performance exhibited a resonance frequency f of 5.3 GHz, and the equivalent circuit model gave a quality factor Q of 5509. Thus, a large fQ product of approximately 2.9 × 1013 was obtained, and the propagation loss was found to be only 0.006 dB/wavelength. These excellent properties are attributed mainly to the reduction of scattering loss in a substrate using a single-crystal diamond, which originated from the grain boundary of diamond and the surface roughness of the AlN thin film and the diamond substrate. These results show that single-crystal diamond SAW resonators have great potential for use in low-noise super-high-frequency oscillators.

Lamb wave transducers made of piezoelectric macro‐fiber composite

Abstract: During recent years, an intensive research activity concerning the application of Lamb waves (LWs) for SHM has been observed. LWs may be generated and sensed using different types of transducers, and their selection is essential for the SHM system's performance. Results of the investigation of three types of transducers based on macro-fiber composite (MFC) are presented in this paper; two types of commercially available MFC actuators are compared with a novel type of custom-designed interdigital transducer also based on the MFC substrate. After a short presentation of the piezoelectric transducer designed for SHM applications, details concerning the proposed interdigital transducer design are provided. Beampatterns of the investigated transducers are first compared using numerical FEM simulations, and next, the numerically obtained beampatterns are verified experimentally using laser vibrometry. In the final part of this paper, advantages and disadvantages of the investigated transducers are discussed. Copyright © 2012 John Wiley & Sons, Ltd.

High k t 2 ×Q, multi-frequency lithium niobate resonators

Abstract: This paper presents design and vacuum measurements of lithium niobate (LN) contour-mode resonators (CMR). By carefully positioning the interdigital transducer (IDT), we achieved CMRs with kt2×Q of 7%*2150=148 (IDT @ node) or resonators with very high kt2 of 12.3% and spur-attenuated response (IDT @ anti-node). In addition, we demonstrated resonators with frequencies ranging from 400MHz to 800MHz on a single chip.

Packageless AlN/ZnO/Si Structure for SAW Devices Applications

Abstract: The possibility to perform a packageless structure for acoustic wave sensors applications based on AlN/interdigital transducer/ZnO/Si structure was investigated. The effect of thicknesses of AlN and ZnO thin films on structure performance was simulated by 2-D finite element method. Theoretical predictions were confirmed by in-situ measurements of frequency, insertion loss, and thickness during deposition of AlN layer on ZnO/Si.

CMOS-compatible ruggedized high-temperature Lamb wave pressure sensor.

Abstract: This paper describes the development of a novel ruggedized high-temperature pressure sensor operating in lateral field exited (LFE) Lamb wave mode. The comb-like structure electrodes on top of aluminum nitride (AlN) were used to generate the wave. A membrane was fabricated on SOI wafer with a 10 µm thick device layer. The sensor chip was mounted on a pressure test package and pressure was applied to the backside of the membrane, with a range of 20–100 psi. The temperature coefficient of frequency (TCF) was experimentally measured in the temperature range of −50 °C to 300 °C. By using the modified Butterworth–van Dyke model, coupling coefficients and quality factor were extracted. Temperature-dependent Young's modulus of composite structure was determined using resonance frequency and sensor interdigital transducer (IDT) wavelength which is mainly dominated by an AlN layer. Absolute sensor phase noise was measured at resonance to estimate the sensor pressure and temperature sensitivity. This paper demonstrates an AlN-based pressure sensor which can operate in harsh environment such as oil and gas exploration, automobile and aeronautic applications.

High-Q capacitive-piezoelectric AlN Lamb wave resonators

Abstract: The use of capacitive-piezoelectric transducers, formed by separating a piezoelectric structure from its electrodes by sub-micron gaps, has raised the measured quality factor of aluminum nitride (AlN) Lamb wave resonators (LWR) from the ~1,000 of typical square-edged conventional devices (with contacting electrodes) to over 5,000 at 940 MHz, posting the highest reported Q for non-overmoded pure AlN resonators using d31 (e31) transduction at this frequency range. The Q · f product achieved here is significantly higher than that of a previous 1.2-GHz capacitive-piezoelectric contour-mode ring, mainly due to the use of Lamb wave modes that allow better support isolation to prevent energy loss to the substrate. In addition, the use of interdigital transducer (IDT) electrodes successfully decouples the resonance frequency from overall device dimensions, offering a CAD-definable design parameter for fine-frequency control. The effective coupling coefficient of keff2 = 0.3% achieved by this device is lower than the 1.6% typically observed for conventional AlN Lamb wave resonators, but still sufficient to avoid pass-band distortion in the 0.1% bandwidth filters needed for next-generation RF channel-selecting communication front-ends.

Thin films and techniques for SAW sensor operation above 1000°C

Abstract: High temperature (300°C to 1400°C) wireless sensors have applications in energy exploration and generation, harsh environment industrial processing, and aerospace engineering. Existing technology developed at the University of Maine allows the fabrication of surface acoustic wave (SAW) langasite (LGS) sensors with Pt-Rh/ZrO2 electrodes that can deliver long-term stable operation up to 850°C. Since LGS remains piezoelectric up to its melting point of ~1400°C, it is desirable to extend the current SAW sensor temperature range of operation. In addition, it is desirable to diminish the SAW interdigital transducer (IDT) electrode dimensions to increase the wireless frequency of operation towards the GHz range. In this work, new thin film electrode materials have been investigated to allow the operation of SAW one-port resonators up to 1000°C and beyond. In particular, alternative Pt/Al2O3 and Pt-Rh/HfO2 thin film electrode compositions are presented, which yield operation of SAW resonator sensors up to 1100°C. In addition to a previously used capping layer, an interfacial layer has been added between the LGS and the electrodes to delay any interdiffusion between the materials and extend the temperature and/or time of sensor performance. Finally, it is also reported in this work that exposure of untreated SAW device electrodes with 120 nm thick and 2μm wide Pt-Rh/ZrO2 co-deposited IDT fingers to temperatures above 850°C can create long platinum-rich nano-whiskers. These structures short-circuit the SAW interdigital (IDT) fingers, rendering the device unusable. The short-circuit problem was solved by the use of multilayered electrode structures and the used of the capping layer.

Inkjet Printed All-Polymer Flexural Plate Wave Sensors

Abstract: We discuss the fabrication and performance of an all-polymer, flexural plate wave gravimetric sensor using flexible, piezoelectric Polyvinylidene fluoride as the substrate and an inkjet-printed interdigital transducer (IDT) employing conductive poly(3, 4-ethylenedioxythiophene) poly(styrenesulfonate) to excite Lamb waves within the film. Lamb waves are measured both electronically, using a second IDT, and mapped directly using a scanning laser Doppler vibrometer. Pulsed wave excitation is utilized to isolate the weak acoustic signal from the electromagnetic crosstalk, enabling the measurement of relative changes in the resonant frequency, Δf/f0, in response to added mass, Δm, to the sensing area. A gravimetric mass sensitivity equivalent to Δf/(f0Δm)=-153 cm2/g is measured by mass loading the sensor with printed polymer layers. It is found that the low stiffness of the substrate contributes significantly to the response of the sensor, yielding a measured overall sensitivity of Δf/(f0Δm)=-83 cm2/g.

Longitudinal-Type Leaky Surface Acoustic Wave on LiNbO3with High-Velocity Thin Film

Abstract: The loss reduction of a longitudinal-type leaky surface acoustic wave (LLSAW) by loading with a dielectric thin film with a higher velocity than the substrate is proposed. An aluminum nitride (AlN) thin film was adopted as a high-velocity thin film, and the propagation properties of an LLSAW on an X36°Y-LiNbO3 (LN) substrate were investigated. First, the elastic constants c11 and c44 of an amorphous AlN (a-AlN) thin film deposited by RF magnetron sputtering were determined from the measured phase velocities of two SAW modes with mutually perpendicular particle motion, and they were 78 and 96% of those of a single-crystal AlN thin film. Next, from the theoretical calculation for the LLSAW on X36°Y-LN using the determined constants, it was found that the LLSAW attenuation can be reduced to zero by loading with an a-AlN thin film. Then, the propagation properties of the LLSAW on X36°Y-LN were measured by using an interdigital transducer pair. It was found that the losses due to bulk wave radiation can be reduced by loading with an a-AlN thin film.

An integrated passive impedance-loaded SAW sensor

Abstract: An integrated passive impedance-loaded SAW H2S sensor working at room temperature has been presented in this paper. The sensor consists of a SAW transponder with delay line structure and a resistive H2S sensor as an impedance-loaded sensor. The SAW delay line was fabricated on a 128° LiNbO3 substrate and its center frequency is 233 MHz. The resistive sensor composed of the nano-crystalline SnO2 film and aluminum electrodes was also fabricated on the same substrate. The gas sensing properties of the resistive H2S sensor have been tested separately. In order to maximize the sensitivity of the whole sensor, the resistance of the impedance-loaded sensor was adjusted to match the output impedance of the SAW interdigital transducer (IDT) by changing the resistivity of the Sb-doped SnO2 nano-crystalline films and optimizing the electrode structure. The variation in the return loss magnitude was increased to 2.51 dB. Finally, the impedance-loaded SAW sensor was configured and measured wirelessly for various H2S concentrations at room temperature. The measurement results show that the proposed H2S sensor not only has good repeatability and high sensitivity but also is capable of passive wireless detection at room temperature.

Correspondence - Acoustic waves in a structure containing two piezoelectric plates separated by an air (vacuum) gap

Abstract: This paper presents experimental results for the characteristics of acoustic waves propagating in a structure containing two parallel piezoelectric plates (I and II) separated by an air gap. Plate I, made of Y-X lithium niobate, contained two interdigital transducers that excited and received an acoustic wave with shear-horizontal polarization. Piezoelectric plate II, made of lithium niobate, was placed above and between the transducers, separated by a fixed gap. For its certain orientation, the amplitude-frequency characteristic showed sharply defined resonant attenuation peaks, which were situated at an equidistant separation from each other. The depth of the peaks was observed to decrease with a wider gap between the plates. It has been stated that these peaks are associated with the resonant reflections of a slot acoustic wave across the width of plate II. Experimentally determined phase velocities and electromechanical coupling coefficient for the slot wave in the structure under study are in a good agreement with theoretical values for various crystallographic orientations of plate II. A comparison between the experimental and theoretical results has allowed us to state two conditions for the slot wave to exist. The structures described may be employed for noncontact excitation of acoustic waves in the plates and for the development of various liquid, gas, and temperature sensors.

Design of mode selective actuators for Lamb wave excitation in composite plates

Abstract: Structural Health Monitoring based on Lamb waves, a type of ultrasonic guided waves, is a promising method for in-service inspection of composite structures. In this study, mode selective actuators are developed to excite a particular Lamb wave mode in quasi-isotropic CFRP (carbon fibre-reinforced polymer) plates. Different manufacturing technologies based on monolithic piezoceramics and piezocomposites are described. The actuators are based on interdigital transducer design in order to control the frequency as well as the wavelength of the desired mode within the excitation. To determine the wavelength of the desired Lamb wave mode, experimental dispersion diagrams of the CFRP plates are measured using air-coupled ultrasonic scanning technique. The dispersion diagrams show the A0 and S0 mode in a frequency range of 25–400 kHz. A mode selective actuator is designed to amplify the A0 mode and to attenuate the S0 mode at 40 kHz. Within experimental tests the actuator and circular piezoceramic sensors are applied on a CFRP plate in order to determine the mode selectivity. These tests are accompanied by 2D finite element simulations. On the basis of simulations and experimental test the influence of different parameters such as number and width of electrode segments, excitation signals and apodization is investigated. The results show that a mode selectivity of the A0 mode in CFRP plates can be achieved by the designed actuator.

Numerical simulation of surface acoustic wave actuated cell sorting

Abstract: We consider the mathematical modeling and numerical simulation of high throughput sorting of two different types of biological cells (type I and type II) by a biomedical micro-electro-mechanical system (BioMEMS) whose operating behavior relies on surface acoustic wave (SAW) manipulated fluid flow in a microchannel. The BioMEMS consists of a separation channel with three inflow channels for injection of the carrier fluid and the cells, two outflow channels for separation, and an interdigital transducer (IDT) close to the lateral wall of the separation channel for generation of the SAWs. The cells can be distinguished by fluorescence. The inflow velocities are tuned so that without SAW actuation a cell of type I leaves the device through a designated outflow channel. However, if a cell of type II is detected, the IDT is switched on and the SAWs modify the fluid flow so that the cell leaves the separation channel through the other outflow boundary. The motion of a cell in the carrier fluid is modeled by the Finite Element Immersed Boundary method (FE-IB). Numerical results are presented that illustrate the feasibility of the surface acoustic wave actuated cell sorting approach.

Vibration sensor based on surface acoustic wave radio frequency identification technology and application for vibration sensor

Abstract: The invention relates to a vibration sensor based on a surface acoustic wave radio frequency identification technology and application for the vibration sensor The vibration sensor can be used for identifying the identity of a measured object in a radio frequency manner, and can also be used for monitoring whether the vibration acceleration of the measured object exceeds a set threshold value or not and then recording the vibration acceleration of the measured object; a surface acoustic wave device comprises an antenna, a piezoelectric substrate, an interdigital transducer, reflecting gratings and an elastic element; radixes in the reflecting gratings are used for coding radio frequency tags; the 1-3 reflecting gratings are connected with the elastic element, and then a normally open loop is formed; when the vibration acceleration induced by the vibration sensor exceeds the set threshold value, the reflecting gratings, the elastic element and matched networks jointly form a closed loop; and features of echo signals reflected back to a reader are changed, so that the vibration sensor can alarm after the vibration acceleration in a superthreshold is recorded Compared with the prior art, the vibration sensor has the characteristics that a measuring method is simple, multidimensional and multi-range measurement can be realized, the vibration sensor is wide in application, and the like

Capacitively coupled IDT for high temperature SAW devices

Abstract: Harsh environment surface acoustic wave (SAW) sensors are being researched and developed jointly by the University of Maine (UMaine) and Environetix Technologies Corp. for wireless and wired sensor applications, such as those found in gas turbines and power plant combustors. One goal of this work is to extend the operational temperature range of SAW sensors above 1000°C, potentially up to near the melting point of piezoelectric langasite crystals at 1400°C. To achieve stable performance at 1000°C and above, UMaine has developed nanocomposite thin film electrode materials, such as PtRh/HfO2, and protecting capping layers, such as SiAlON and Al2O3. However, these protective top layers, which aid in extending the life of the electrodes, are electrical insulators that prevent direct bonding to the electrodes. The UMaine team also found evidence of accelerated thin-film degradation close to the SAW interdigital transducer (IDT) bond pad welds at these extreme temperatures. This paper introduces a high temperature capacitive approach to electrically couple to the IDT, thus allowing electrical access to the SAW device. The capacitive coupling approach also avoids premature failure of the nanocomposite film caused by interdiffusion between the bond wires and the SAW IDT bond pads. The technique has been successfully implemented and SAW device operation at 1000°C has been achieved.

SAW array sensor

Abstract: A surface acoustic wave (SAW) array sensor having an input interdigital transducer (IDT); first and second output IDTs that are disposed at both sides of the input IDT, respectively; a first delay line between the input IDT and the first output IDT; and a second delay line between the input IDT and the second output IDT, wherein the first and second delay lines have different lengths; and related devices.

Surface acoustic wave filter

Abstract: The utility model discloses a surface acoustic wave filter The surface acoustic wave filter comprises a plurality of surface acoustic wave resonators, wherein each surface acoustic wave resonator comprises an interdigital transducer and a reflecting grating; the surface acoustic wave resonators are partially high-impedance surface acoustic wave resonators leastways; two interdigital transducers of the high-impedance surface acoustic wave resonators are arranged side by side, and share two reflecting gratings; an output bus bar of the first interdigital transducer is electrically connected with an input bus bar of the second interdigital transducer; the input bus bar of the first interdigital transducer and the output bus bar of the second interdigital transducer are arranged at a same end; and the two reflecting gratings are arranged on the outer sides of the two interdigital transducers According to the surface acoustic wave filter disclosed by the utility model, under a same impedance, the high-impedance surface acoustic wave resonators have more digital logarithms or less apertures, and current on each transducer bar is weakened, so that power bearing capacity of the surface acoustic wave filter is greatly improved under a precondition of not changing the electric performance of the surface acoustic wave filter

Acoustic surface wave resonator

Abstract: The invention provides an acoustic surface wave resonator which comprises a piezoelectric substrate, an interdigital transducer, two reflecting grates and two sound absorbing parts. The piezoelectric substrate is made from ST cutting type quartz. The interdigital transducer is etched on the piezoelectric substrate and can send 433.92MHz center frequency, wherein the periodic section length M is 7.2mum, the interdigital width a is 1.9mum, an interdigital spacing b is 1.7mum, finger logarithm N is 100, sound bore diameter W is 720mum, and the aluminum strip thickness of interdigital fingers H is 200nm. The two reflecting grates are respectively etched on two sides of the interdigital transducer, the number Nref of reflecting grate fingers on each side is 200, and a distance S between the reflecting grates on two sides and the interdigital transducer is 9.0mum. The sound absorbing parts are respectively arranged on one side of each reflecting grate away from the interdigital transducer. The acoustic surface wave resonator has high quality factor Q and frequency stability, is not prone to environmental influence and has the advantages of being small in volume, light in weight and the like.

Radio frequency identification system based on SAW technology

Abstract: The invention discloses a radio frequency identification system based on an SAW technology. The radio frequency identification system based on the SAW technology comprises an acoustic surface wave tag and a matched reader. The acoustic surface wave tag is formed by a substrate, an interdigital transducer and a reflection electrode, wherein the interdigital transducer and the reflection electrode are arranged on the substrate. The reader comprises a control processing module, a transmitting module, a receiving module, a circulator, a transmit-receive antenna and a phase-locked loop frequency synthesizer, wherein the transmitting module and the receiving module are respectively connected to the control processing module, the circulator is simultaneously connected to the transmitting module and the receiving module, the transmit-receive antenna is connected to the circulator, and the phase-locked loop frequency synthesizer provides local oscillator signals to the transmitting module and the receiving module.

Electro-mechanical transducer element, liquid droplet ejecting head, image forming apparatus, and electro-mechanical transducer element manufacturing method

Abstract: An electro-mechanical transducer element is disclosed. The electro-mechanical transducer element includes a first electrode formed on a substrate; an electro-mechanical transducer film formed on at least a part of the first electrode; and a second electrode formed on at least a part of the electro-mechanical transducer film. In at least one cross section of the electro-mechanical transducer film, a film thickness distribution shape is convex to the second electrode side.

One-port SAW resonators fabricated on single-crystal diamond

Abstract: Diamond has the highest known surface acoustic wave (SAW) phase velocity, sufficient for applications in the gigahertz range. In addition, diamond can be synthesized from methane gas by chemical vapor deposition (CVD) and is also free from rare earth and rare metal materials. Although numerous studies have demonstrated SAW devices on polycrystalline diamond thin films, all of these devices have a much larger propagation loss than single-crystal materials such as LiNbO3, LiTaO3, and quartz. Hence, we fabricated and characterized one-port SAW resonators on single-crystal diamond substrates synthesized using a high-pressure high-temperature method and microwave plasma CVD to identify and minimize sources of propagation loss. A series of one-port resonators were fabricated with an interdigital transducer (IDT)/AlN/diamond structure, and their characteristics were measured. The best performing device using a type-Ib (100) diamond single crystal exhibited a resonance frequency f of 5.2 GHz, and the equivalent circuit model gave a quality factor Q of 8346. Thus, a large fQ product of 4.4 × 1013 was obtained, and the propagation loss was found to be only 0.004 dB/wavelength. These excellent properties are attributed to the large group velocity, lack of grain boundaries in the single-crystal diamond, smooth surface of the AlN thin film and diamond substrate, and inclusion of energy-trapping gratings in the IDT. These results show that single-crystal diamond SAW resonators have great potential for use in low-noise super-high-frequency oscillators as sustainable SAW devices.

Temperature-Compensated and High-Q Piezoelectric Aluminum Nitride Lamb Wave Resonators for Timing and Frequency Control Applications

Abstract: Author(s): Lin, Chih-Ming | Advisor(s): Pisano, Albert P. | Abstract: The explosive development of wireless and mobile communication systems has lead to rapid technology innovation in component performance, complementary metal-oxide semiconductor (CMOS) compatible fabrication techniques, and system improvement to satisfy requirements for faster signal processing, cost efficiency, chip miniaturization, and low power consumption. The demands for the high-performance communication systems whose fundamentals are precise timing and frequency control have driven the current research interests to develop advanced reference oscillators and radio frequency (RF) bandpass filters. In turn a promising microelectromechanical systems (MEMS) resonator technology is required to achieve the ultimate goal. That is, micromechanical vibrating resonators with high quality factor (Q) and good frequency-temperature stability at high series resonance frequency (fs) are the required fundamental components for a high-performance wireless communication system.Recently, Lamb wave mode propagating in piezoelectric thin plates has attracted great attention for designs of the electroacoustic resonators since it combines the advantages of bulk acoustic wave (BAW) and surface acoustic wave (SAW): high phase velocity and multiple frequency excitation by an interdigital transducer (IDT). More specifically, the Lamb wave resonator (LWR) based on an aluminum nitride (AlN) thin film has attracted many attentions because it can offer the high resonance frequency, small temperature-induced frequency drift, low motional resistance, and CMOS compatibility. The lowest-order symmetric (S0) Lamb wave mode propagation in the AlN thin plate is particularly preferred because it exhibits a phase velocity close to 10,000 m/s, a low dispersive phase velocity characteristic, and a moderate electromechanical coupling coefficient. However, the uncompensated AlN LWR shows a first-order temperature coefficient of frequency (TCF) of approximately -25 ppm/C. This level of the temperature stability is unsuitable for any timing application. In addition, the Q of the AlN LWR is degraded to several hundred while the IDT finger width is downscaled to a nanometer scale to raise the resonance frequency up to a few GHz.This dissertation presents comprehensive analytical and experimental results on a new class of temperature-compensated and high-Q piezoelectric AlN LWRs. The temperature compensation of the AlN LWR using the S0 Lamb wave mode is achieved by adding a layer of silicon dioxide (SiO2) with an appropriate thickness ratio to the AlN thin film, and the AlN/SiO2 LWRs can achieve a low first-order TCF at room temperature. Based on the multilayer plate composed of a 1-um-thick AlN film and a 0.83-um-thick SiO2 layer, a temperature-compensated LWR operating at a series resonance frequency of 711 MHz exhibits a zero first-order TCF and a small second-order TCF of -21.5 ppb/C^2 at its turnover temperature, 18.05 C. The temperature dependence of fractional frequency variation is less than 250 parts per million (ppm) over a wide temperature range from -55 to 125 C. In addition to the temperature compensation at room temperature, the thermal compensation of the AlN LWRs is experimentally demonstrated at high temperatures. By varying the normalized AlN and SiO2 thicknesses to the wavelength, the turnover temperature can be designed at high temperatures and the AlN LWRs are temperature-compensated at 214, 430, and 542 C, respectively. The temperature-compensated AlN/SiO2 LWRs are promising for a lot of applications including thermally stable oscillators, bandpass filters, and sensors at room temperature as well as high temperatures.The influences of the bottom electrode upon the characteristics of the LWRs utilizing the S0 Lamb wave mode in the AlN thin plate are theoretically and experimentally studied. Employment of a floating bottom electrode for the LWR reduces the static capacitance in the AlN membrane and accordingly enhances the effective coupling coefficient. The floating bottom electrode simultaneously offers a large coupling coefficient and a simple fabrication process than the grounded bottom electrode but the transduction efficiency is not sacrificed. In contrast to those with the bottom electrode, an AlN LWR with no bottom electrode shows a high Q of around 3,000 since it gets rid of the electrical loss in the metal-to-resonator interface. In addition, it exhibits better power handling capacity than those with the bottom electrode since less thermal nonlinearity induced by the self-heating exists in the resonators.In order to boost the Q, a new class of the AlN LWRs using suspended convex edges is introduced in this dissertation for the first time. The suspended convex edges can efficiently reflect the Lamb waves back towards the transducer as well as confine the mechanical energy in the resonant body. Accordingly the mechanical energy dissipation through the support tethers is significantly minimized and the Q can be markedly enhanced. More specifically, the measured frequency response of a 491.8-MHz LWR with suspended biconvex edges yields a Q of 3,280 which represents a 2.6x enhancement in Q over a 517.9-MHz LWR based on the same AlN thin plate but with the suspended flat edges. The suspended convex edges can efficiently confine mechanical energy in the LWR and reduce the energy dissipation through the support tethers without increasing the motional impedance of the resonator. In addition, the radius of curvature of the suspended convex edges and the AlN thickness normalized to the wavelength can be further optimized to simultaneously obtain high Q, low motional impedance, and large effective coupling coefficient.To further enhance the Q of the LWR, a composite plate including an AlN thin film and an epitaxial cubic silicon carbide (3C-SiC) layer is introduced to enable high-Q and high-frequency micromechanical resonators utilizing high-order Lamb wave modes. The use of the epitaxial 3C-SiC layer is attractive as SiC crystals have been theoretically proven to have an exceptionally large fs and Q product due to its low acoustic loss characteristic at microwave frequencies. In addition, AlN and 3C-SiC have well-matched mechanical and electrical properties, making them a suitable material stack for the electroacoustic resonators. The epitaxial 3C-SiC layer not only provides the micromechanical resonators with a low acoustic loss layer to boost their Q but also enhances the electromechanical coupling coefficients of some high-order Lamb waves in the AlN/3C-SiC composite plate. A micromachined electroacoustic resonator utilizing the third quasi-symmetric (QS3) Lamb wave mode in the AlN/3C-SiC composite plate exhibits a Q of 5,510 at 2.92 GHz, resulting in the highest fs and Q product, 1.61x10^13 Hz, among suspended piezoelectric thin film resonators to date.

Analysis of Rayleigh wave radiations from leaky SAW resonators

Abstract: The Rayleigh wave radiations from leaky surface acoustic wave (SAW) resonators on around 42° Y-cut LiTaO3 substrates are known as one of acoustic loss mechanisms. This paper analyzes and characterizes the Rayleigh wave radiations and develops the analytical model for the radiations. First, the finite element method (FEM) analyses and optical probe measurements reveal that the scattering of leaky SAW at the gap between interdigital transducer (IDT) and dummy electrodes generates the Rayleigh wave radiations. Based on the result, the simple and fast analytical model using the point sources is developed to simulate the Rayleigh wave radiations. The model precisely simulates the measurement patterns of radiations about 1,000 times faster than the FEM.

Qualitative and quantitative analysis of surface-acoustic-wave-based ultraviolet photodetectors

Abstract: Surface-acoustic-wave (SAW) based ultraviolet (UV) photodetectors with multiple optical sensing areas is presented by depositing patterned ZnO films on a LiNbO3 substrate. Two different types of electrodes, uniform interdigital transducer (IDT) and slanted finger interdigital transducer (SFIT), are designed and fabricated to analyze the performances of SAW array UV photodetectors. By tuning ultraviolet wavelengths, qualitative characteristics of SAW UV photodetectors are observed through the measurements of SAW attenuation. Quantitative analyses of the photodetectors are presented by varying light intensities. Moreover, dynamic responses of SAW array UV photodetectors under the illumination of different optical wavelengths are also demonstrated. Ultraviolet light of 350 nm with power densities of 8.46 and 18.34 μW/cm2 is detectable from a UV photodetector with uniform IDT and SFIT, respectively. This study not only indicates that a SAW-based UV sensor is a potential candidate of array UV photodetectors but also provides a comprehensive analysis of SAW UV photodetectors.

Stable lithium niobate waveguide devices, and methods of making and using same

Abstract: Embodiments of the present invention provide stable lithium niobate waveguide devices, and methods of making and using the same. A lithium niobate-based waveguide device may include a Z-cut lithium niobate substrate having upper and lower surfaces, an optical waveguide embedded within the lithium niobate substrate, a signal electrode disposed on the upper surface of lithium niobate substrate and parallel to the optical waveguide, guard electrodes disposed on the upper surface of the lithium niobate substrate and flanking but spaced apart from the signal electrode, and a conductive layer on the lower surface of the lithium niobate substrate, wherein the conductive layer serves as a common ground reference for the signal and guard electrodes.

Experimental Study of Fine Frequency Selection Techniques for Piezoelectric Aluminum Nitride Lamb Wave Resonators

Abstract: Experimental Study of Fine Frequency Selection Techniques for Piezoelectric Aluminum Nitride Lamb Wave Resonators by Ting-Ta Yen Master of Science, Plan II in Electrical Engineering and Computer Sciences University of California, Berkeley Professor Albert P. Pisano, Chair Strong demand for high-Q resonators and filters in mobile wireless communication systems has initiated various research on radio frequency microelectromechanical systems (RF MEMS). Several CMOS-compatible RF MEMS resonator technologies, either electrostatic or piezoelectric, can provide multi-frequency operation on a single substrate and have the potential to realize a channel-select RF front-end architecture. However, utilizing a narrowband filter bank in such an architecture as the key component for frequency selection leads to a major challenge: fine frequency control. Depending upon the standard, it may entail the simultaneous fabrication of tens to hundreds of filters with 0.05 to 0.1% bandwidth, and spacing. Aluminum nitride (AlN) Lamb wave resonators (LWRs) utilize piezoelectric transduction to ensure low motional resistance. The resonance frequency of a LWR is defined by interdigital transducer (IDT) pitch and is thus decoupled from the overall device dimensions. This fine frequency selection technique is enabled by adjusting the so-called AlN "overhang" dimension allowing control of relative frequency of Lamb wave resonators in an array to 0.1%. Experimental results suggest the center frequency of LWRs can be linearly adjusted by up to 5% with no significant effect on other resonator parameters including Q, Rm, C0, and kt . Closely and evenly spaced AlN Lamb wave resonators, without post-process trimming, demonstrate the potential to realize a pure mechanical, high performance, yet low power RF front-end system. Albert P. Pisano Date