Parallel Resonance Frequency Research Articles

Electro-acoustic hysteresis behaviour of PZT thin film bulk acoustic resonators

Thin film bulk acoustic resonators (FBARs) based on Pb(Zr x Ti (1− x) )O 3 (PZT) with varying compositions, ranging from x=0.25 to 0.6, were fabricated to investigate hysteresis-like dependencies of the resonance frequency and electro-mechanical coupling constant on bias voltage. The resonators, formed by a simple sandwich structure consisting of bottom electrode, PZT thin film and top electrode, arranged on a planar acoustic mirror, were designed to give a resonance frequency of about 2 GHz. PZT thin films were deposited in a planar multi target sputtering system using three metallic targets in a reactive Ar/O 2 mixture. For low Zr-content, where PZT is grown in the tetragonal phase, the parallel resonance frequencies are strongly dependent on the applied electric field, while the series resonance frequency is practically unaffected. This behaviour is completely different for rhombohedral PZT at higher Zr-content. Here the series resonance frequency becomes strongly field dependent, which can be attributed to 109°/71° domain switching. As a potential application based on the observed strong field dependence of the acoustic properties, a bandwidth-tuneable or programmable RF filter based on PZT FBARs is proposed.

Suitability of PZT ceramics for mass sensors versus widespread used quartz crystals

Two piezoelectric materials, quartz and ceramic (PZT), were evaluated as mass sensors. Quartz crystals (polished and unpolished) and one ceramic (Nb–Mn–PZT) were used to detect and quantify fructose in aqueous solutions and s-butylamine in vapour. The frequencies at minimum impedance (fn), maximum impedance (fm), series resonance frequency (fs) and parallel resonance frequency (fp) were monitored. Sensitivities of the devices to the chemical compounds are compared and related to the observed changes of the electrical parameters of the equivalent circuit. Roughness of the surface of the discs (ceramic and quartz crystals) and electrodes were measured and their influence in the observed frequency responses discussed.

Contribution to the electromechanical and nonlinear properties of GaPO4 crystals.

In the last decade, much attention has been given to piezoelectric crystals with large electromechanical coupling coefficient. The quartz homeotypes berlinite and gallium orthophosphate (GaPO4), along with the calcium gallo-germanates such as langasite are representative of these crystals. The coupling coefficient k26 associated with thickness-shear mode resonators is two times greater than that of quartz, increasing the spacing between the series and parallel resonance frequencies of resonators suitable for the frequency range from 1 to 100 MHz. This is important for some types of crystal oscillators and monolithic filters. The large electromechanical coupling coefficient also increases the difference between the temperature dependencies of the fundamental resonance frequency and its harmonics. In this paper, measured resonance frequency-temperature characteristics of the fundamental and third harmonics of selected rotated Y-cut GaPO4 resonators vibrating in the thickness-shear mode are presented. Further attention is given to the measurement of some nonlinear properties of rotated Y-cut GaPO4 resonators. Knowledge of such nonlinear interactions is important for the analysis of intermodulation phenomena in resonators, and for the application of GaPO4 resonators in crystal oscillators, filters and other electronic devices.

Deposition of ZnO thin films by magnetron sputtering for a film bulk acoustic resonator

To fabricate lateral-field excitation (LFE)-mode solid mounted resonator (SMR)-type film bulk acoustic resonators (FBARs), piezoelectric ZnO layers were deposited in an RF magnetron sputtering system. Control of the crystallinity, microstructure and electric properties of the piezoelectric layers was essential for fabricating high-quality LFE-mode SMR-type FBARs. In the appropriate deposition condition for FBAR devices, ZnO thin films with highly c-axis-preferred orientation (XRD rocking curve, σ=2.17°), high resistivity of 10 6 Ω cm and surface roughness of 10.6 Å were deposited. Optimal substrate rotation was especially important for improvement of the c-axis-preferred orientation of ZnO films. Plasma properties such as the electron temperature, plasma density and saturated ion current were also analyzed for optimal ZnO deposition conditions using a Langmuir double-probe system. The resonator, for which the active piezoelectric area was 200×200 μm 2, consisted of 1.25-μm-thick ZnO film and a 110-nm Au electrode. Its series and parallel resonance frequencies appeared at 1.68 and 1.71 GHz, respectively, and the quality factor was 201.4±7.4.

Resonant spectrum method to characterize piezoelectric films in composite resonators.

In this paper, we present a direct method to characterize a piezoelectric film that is sandwiched with two electrodes and deposited on a substrate to form a four-layer thickness extension mode composite resonator (also known as over-moded resonator). Based on the parallel and series resonant frequency spectra of a composite resonator, the electromechanical coupling factor, the density and the elastic constant of the piezoelectric film can be evaluated directly. Experimental results on samples consisting of ZnO films on fused quartz substrates with different thickness are presented. They show good agreement with theoretical prediction. The mechanical effect of the electrode on the method is investigated, and numerical simulation shows that the effect of the electrodes can be properly corrected by the modified formulae presented in this paper. The effect of mechanical loss in piezoelectric film and in substrate on this method also has been investigated. It is proven that the method is insensitive to the losses.

Determination of ZnO temperature coefficients using thin film bulk acoustic wave resonators

Thin film bulk acoustic wave (BAW) resonators have been the subject of research in RF microelectronics for some time. Much of the interest lay in utilizing the resonators to design filters for wireless applications. Some of the major advantages BAW devices present over other filter technologies in use today include size reduction and the possibility of on-chip integration. As the technology matures, the necessity to more fully characterize the performance of the devices and to develop more accurate models describing their behavior is apparent. In this investigation, the effects that temperature variations have on 1.8-2.0 GHz zinc oxide (ZnO)-based solidly mounted BAW resonators (SMRs) are studied. The average temperature coefficients of the series and parallel resonant frequencies of the fabricated devices are found to be -31.5 ppm/degrees C and -35.3 ppm/degrees C, respectively. The slight decrease in separation between the two resonant frequencies with temperature implies there is slightly less effective coupling with increased temperature. No definite trend is found describing the behavior of the quality factor (Q) of the resonator with temperature variations. With little temperature coefficient data for thin film ZnO available in the literature, the importance of an accurate model is evident. The resonator device performance is simulated using Ballato's electronic circuit model for acoustic devices on a SPICE-based platform. By virtue of the comparison between the predicted and measured device response, various material parameters are extracted.

CAD model analysis of the air‐gap type TFBAR

AbstractA CAD model for an air‐gap‐type TFBAR is presented. Aluminum nitride is used as the piezoelectric material with platinum electrodes. To verify the model, simulated and measured results are compared for various top electrode thicknesses, and the agreement is within 0.5% for the parallel resonance frequency. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 384–385, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10469

Electrode modification and the response of the acoustic shear wave device operating in liquids

The effect of electrode polarity, geometry, and stray capacitance on the performance of the thickness-shear mode acoustic wave sensor operating in electrolytes and solutions of biomolecules has been studied. In contrast to the well-known mass-based response of the device operating in the gas phase, the response in a liquid is governed by several factors including acoustoelectric and fringing field effects, which are known to be active at the edges of the electrodes. In order to investigate and utilize these effects, we modified the electrode geometry to increase the edge length, which, in turn, raises the sensitivity of the device. These changes which constituted either complete coverage of the back of the device with electrode material, or the removal of disks and lines from the electrode surface, resulted in a two to three times enhancement of sensor response. Such modifications that extend device sensitivity beyond the electrode area to the quartz region of the sensing structure also provide a better surface for the immobilization of various probes. We verified the enhancing ability of the modified electrodes for the case of adsorption of the protein avidin and neutravidin, followed by their affinity reactions with biotinylated biomolecules. It was found that the active electrode in contact with electrolyte exhibits a sensitivity of about twice that of the grounded electrode. The existence of stray capacitance around the cell was confirmed by shielding the cell assembly with a bath of concentrated KCl solution. This shielding effect was measured to be about 25-60 Hz in series resonant frequency and -1000 Hz in parallel resonant frequency.

AlN-based film bulk acoustic resonator devices with W/SiO2 multilayers reflector for rf bandpass filter application

In this article, a reactively sputtered aluminum nitride (AlN) piezoelectric film and its application for a film bulk acoustic resonator (FBAR) device are presented. The FBAR is composed of an AlN film sandwiched between top aluminum (Al) and bottom gold (Au) electrodes and an acoustic reflector block of SiO2/W stacked multilayers. Both the top and bottom electrodes are connected by a transmission line. The insertion loss (S21) and return loss (S11) were 6.1 and 37.19 dB, respectively. Using the empirical definition technique, the series resonance frequency (fs) and parallel resonance frequency (fp) were found to be 1.976 and 2.005 GHz, respectively. Based on these findings, the effective electromechanical coupling coefficient (Keff2) and the quality factor (Q) were also obtained as 3.53% and 4261, respectively.

Evaluation of electromechanical coupling factor for a piezoelectric quartz crystal in liquid phase

Based on the Butterworth–Van Dyke (BVD) equivalent circuit model for a quartz crystal, the general equations upon the series resonant-frequency f s, and parallel resonant-frequency f p, were obtained by solving the quadratic equation of frequency at susceptance B=0. Consequently, the electromechanical coupling factor ( K) in liquid was first evaluated by using f s and f p. In sucrose solutions, it was seen that K 2 decreases as ( ρη) 1/2 increases, where ρ and η were the density and viscosity of the solution, respectively. It was also interesting to find that K 2 linearly correlates with ( ρη) 1/2 of the media. The regression equation was K 2=−1.216×10 −6( ρη) 1/2+5.204×10 −6, correlation coefficient r 2=0.9954. Regardless of unknown reason for this linear relationship, it was evident that the values of K 2 showed apparent difference when a quartz crystal worked in different media.

Starter/generator employing resonant-converter-fed induction machine. I. Analysis

A new procedure to start a jet engine (JE) and to generate power by means of a single induction machine (IM) directly coupled to the turbine is presented. The JE is brought to an initial speed by the motoring operation of the IM. Later, the IM is taken into generating mode and the turbine is applied to its excitation. The turbine catches up and starts to drive the induction generator (IG). The generated power is converted to a three-phase, 400 Hz voltage-regulated bus via a double stage power conversion utilizing a 20 kHz parallel resonant high frequency AC link and pulse density modulated converter technology. Independent of the engine speed, a constant amplitude and constant frequency three-phase voltage-regulated AC bus is formed and maintained by the proper control of the power converters. The feasibility of operation of such a system has been demonstrated in software where the JE turbine is modeled and replaced by a DC machine. An introduction, background, operation principles of the overall system, and the related software simulations are presented and discussed.

Starter/generator employing resonant-converter-fed induction machine. II. Hardware prototype

The feasibility of operation of a new procedure to start a jet engine (JE) and to generate power by means of a single induction machine (IM) directly coupled to the turbine has been shown by means of a hardware prototype. An introduction, background, operation principle of this type of a system and software simulation portion was presented in Part I. Both in software simulation and in the experimental phase of the studies the JE is replaced by a DC machine. The DC machine is brought to an initial speed by the motoring operation of the IM. Later, the IM is taken into generating mode and the DC machine is into motoring mode of operation. This mode would correspond to the turbine catch-up initiation phase and initiate driving phase of the induction generator in the actual world. The generated power is then converted to a three-phase, 400 Hz (in software), 60 Hz (in hardware), 115 V voltage-regulated bus via a double stage power conversion utilizing a 20 kHz parallel resonant high frequency AC link and pulse density modulated converter technology. Independent of the coupled machine speed, a constant amplitude and constant frequency three-phase voltage-regulated AC bus is formed and maintained by the proper control of the power converters.

Response of a thickness-shear mode quartz crystal resonator upon hydrogel formation

The response of an AT-cut quartz crystal piezoelectric resonator operating in the thickness shear mode (TSM) during polymer gel formation has been examined by acoustic network analysis. The series and parallel resonant frequencies as well as the amplitude and phase of the impedance of the TSM resonator were monitored in real-time when a layer of polyacrylamide gel was formed on one side of the sensor. Various concentrations of radical initiator and crosslinking agents were used to control the rates of polymerization and crosslinking during the hydrogel formation. The increase in the magnitude of the minimum impedance and the decrease in the maximum phase angle were observed as a result of the damping of both the magnitude-frequency and phase-frequency curves, caused by the transformation of the contacting medium from a viscous liquid to a viscoelastic hydrogel. Significant difference was observed between the responses of series and parallel resonant frequencies. The series resonant frequency increases while the parallel resonant frequency decreases during gel formation, and the magnitude of change in the parallel frequency is several times that in the series frequency. Small variations in the gelforming solutions such as the depletion of buffer and addition of double-stranded DNA cause distinct changes in the response profiles of the quartz resonator.

Evaluation of the material parameters of piezoelectric materials by various methods

The elastic, dielectric and piezoelectric constants of four piezoelectric materials, including polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, PZT/epoxy 1-3 composite, and lead metaniobate ceramic, have been evaluated from the impedance data using five different methods. A method described in ANSI/IEEE Std. 176-1987, though based on formulae derived for loss-less materials, is found to be applicable to materials with moderate loss. However, for high-loss materials such as polyvinylidene fluoride, the electromechanical coupling constant (/spl kappa//sub t/) obtained by the method of Std. 176 is substantially higher than the actual value. Calculations based on a piezoelectric resonance analysis program (PRAP) combine the best features of two earlier methods. In addition to the impedance at the parallel resonance frequency, impedances at two other frequencies are required for calculation. The PRAP method gives quite accurate material parameters regardless of the magnitude of the loss, but the parameters (including /spl kappa//sub t/) vary by as much as 15% depending on the choice of data. In the nonlinear regression method described in the present work, all the impedance data points around the resonance are least-squares fitted to the theoretical expression for the impedance. Besides the advantage of requiring no arbitrary choice of data, the nonlinear regression method can readily take account of the frequency dependence of the dielectric constant.

Determination of the piezoelectric electromechanical coupling constant k13 using a frequency ratio method

An alternative method to determine the electromechanical coupling constant k13 for the length-thickness piezoelectric resonator is presented. Data relating the electromechanical coupling constant k13 to the parallel resonance frequency ratios are tabulated. A third order polynomial was found to represent the relationship accurately for k13 = 0.01 to 0.6. The coefficients of the polynomial and typical errors in the fit are reported.

Polymer-coated quartz crystal resonators for multi-information sensing

A study of polyphosphazene-coated QCRs gas sensors using both mass and electrical loadings has been performed. In addition to the device series resonance frequency, the parallel resonant frequency was measured in an attempt to characterise the changes in the dielectric properties of the coating during the detection process. The result is a sensor with an additional parameter to improve selectivity.

Polymer-coated QCR sensors for the detection of organic solvents in water

Poly(ethyl acrylate) (PEA), poly(epichlorohydrin) (PECH) and a silicon-based copolymer of trimethoxypropylsilane/octadecyltrimethoxysilane (TMPS/ODTMS) were used as sensitive materials for the detection of organic solvent molecules in water. Quartz crystal resonators (QCR) with modified electrode configurations are used to monitor the changes in mass and in electrical properties by measuring the shifts in series resonance frequency ( f s), parallel resonance frequency ( f p), and frequency of maximum admittance ( f m), respectively. The result is a multi-information chemical sensor. The sensor signals are completely reversible at room temperature with the response and recovery time in the order of minutes under our measurement conditions. The sensitivities obtained from the measurements of f m for all organic solvents investigated are generally larger than those obtained from f s and f p. It is also found that there is no correlation between the measured sensitivities of the series resonance frequency and the boiling point temperatures of the organic solvents investigated in the liquid phase under our experimental conditions, as is generally obtained in the gas phase.

QCM Operation in Liquids: An Explanation of Measured Variations in Frequency and Q Factor with Liquid Conductivity

Recently, several reports have shown that when one side of a quartz crystal microbalance (QCM) is exposed to a liquid, the parallel (but not the series) resonant frequency is influenced by the conductivity and dielectric constant of the liquid. The effect is still controversial and constitutes a serious complication in many applications of the QCM in liquid environments. One suggestion has been that acoustically induced surface charges couple to charged species in the conducting liquid. To explore this effect, we have measured the parallel and the series mode resonance frequencies, and the corresponding Q factors, for a QCM with one side facing a liquid. These four quantities have all been measured versus liquid conductivity, using a recently developed experimental setup. It allows the simultaneous measurement of the resonant frequency and the Q factor of an oscillating quartz crystal, intermittently disconnected from the driving circuit. Based on these results, a simple model together with an equivalent circuit for a quartz crystal exposed to a liquid is presented. The analysis shows that it is not necessary to infer the existence of surface charges (or other microscopic phenomena such as electrical double layers) to account for the influence of the liquid's electrical properties on the resonant frequency. Our results show that the contacting conductive liquid, in effect, enlarges the electrode area on the liquid side and thereby changes the parallel resonant frequency. By proper design of the QCM measurement, perturbing effects due to the liquid's electrical properties can be circumvented.

Interfacial Hybridization of RNA Homopolymers Studied by Liquid Phase Acoustic Network Analysis

Hybridization of RNA homopolymers has been employed to verify the possibility of developing a biosensor for nucleic acid based on the thickness-shear mode (TSM) acoustic wave device. The results clearly show that RNA homopolymers can be successfully immobilized onto a PdO electrode surface by chemisorption and that sequence-specific hybridization can be detected. The characterization of TSM sensors upon hybridization of immobilized nucleic acid is achieved through the network analysis of impedance measurements. Multidimensional chemical information regarding nucleic acid hybridization at the interface through correlation with such parameters as the series and parallel resonant frequencies, frequencies at the maximum and minimum impedance, and equivalent circuit elements was obtained. The effect of temperature on RNA homopolymer hybridization has also been examined. The results show that the series resonant frequency increases when single strand Poly C hybridizes to complementary Poly G from solution at lo...

Analysis of electrical equivalent circuit of quartz crystal resonator loaded with viscous conductive liquids

An electrical equivalent circuit of quartz crystal resonator (QCR), with modified electrodes, loaded with a viscous conductive liquid is proposed. The electrode in contact with the liquid is modified so as to create an unmetallized crystal surface in contact with the liquid and thus to introduce an acoustoelectric interaction at the crystal | liquid interface. The admittance—impedance characteristics of the equivalent circuit of the loaded QCR are analyzed to obtain expressions for the changes in the series and parallel resonant frequencies in terms of the liquid viscosity η L, density ϱ L, dielectric constant ϵ L, and conductivity σ, as well as the quartz parameters and electrode area geometry. Using a network analyzer, the S parameters of the equivalent circuit of various conductive liquid-loaded QCRs are measured and analyzed. It is shown that in addition to being a well-known detector of mechanical properties of liquids, a QCR, when properly designed, can be used to monitor the electrical properties of dilute ionic solutions.