Thickness Shear Mode Resonators Research Articles

Charge transport and acoustic loss in lithium niobate-lithium tantalate solid solutions at temperatures up to 900 °C

Polar oxides, in particular solid solutions of lithium niobate and lithium tantalate (LNT, LiNb1-xTaxO3) are a variable model system to study fundamental materials properties due to miscibility of the edge compounds lithium niobate (LN, LiNbO3) and lithium tantalate (LT, LiTaO3) as well as tunable domain structures. Further new applications in the field of high-temperature actuators are aimed as LNT crystals potentially combine the advantages of the edge compounds with respect to high thermal stability and high piezoelectric coefficients. Beside LN and LT, LNT crystals of two compositions (LiNb0.88Ta0.12O3 and LiNb0.5Ta0.5O3) were grown by the Czochralski technique. Electrical conductivity, lithium diffusion and acoustic loss of LNT at high temperatures were investigated and correlated. Two techniques, namely impedance spectroscopy and resonant piezoelectric spectroscopy (RPS) are applied in this investigation. The electrical conductivity of investigated samples increases linearly in an Arrhenius presentation up to ∼605 °C. After a transition range of 605–620 °C, the conductivity increases linearly again for LT, but the slope is decreased by about 0.15 eV. This indicates that the conductivity below and above the Curie temperature is governed by a slightly different process. In contrast, LN shows a gradually increasing slope in the Arrhenius representation above the transition temperature range mentioned above. Here, a single activation energy cannot be assigned. The increase can be explained by the limited thermal stability of LN at elevated temperatures. Further, the acoustic loss in LNT thickness-shear mode resonators operated at about 2 and 10 MHz is determined by RPS and found to strongly increase above about 450 °C. In addition, the acoustic loss is modelled using independent materials data including electrical conductivity as determined here, and found to be in excellent agreement with the RPS data for the 10 MHz resonator. Based on the modelling, the loss above 450 °C is governed by conductivity-induced piezoelectric/carrier relaxation which can be attributed to lithium migration.

Temperature characteristics of a thickness shear mode quartz crystal resonator bonded to a support substrate

Thickness shear mode (TSM) resonators consisting of metal films and quartz plates are widely used for sensor applications such as film thickness monitoring, force sensors, and odor sensors. However, the current sensor geometry prevents further improvements in its sensitivity and stability. Thinning the plate is necessary for high sensitivity, and advanced fabrication technologies are required for their commercialization. The solution is to use a support substrate to increase the mechanical strength, which can guide the transmittance of the electric field. Herein, we report a TSM resonator bonded to a support substrate. An AT-cut quartz resonator with a floating electrode on the top side was bonded to the support substrate. Two excitation electrodes were placed under the substrate. The support substrates evaluated in this study included borosilicate glass, Z-cut quartz crystals, and AT-cut quartz crystal plates. The quartz crystal resonator (QCR) bonded to the AT-cut quartz crystal plate and positioned at 90° to the crystallographic x-axis shows an excellent temperature coefficient of frequency of −60 ± 14 ppb/°C for a temperature range 11–40 °C. The proposed method reduces temperature sensitivity to 1/4 or less compared to that without a substrate. Furthermore, the resonator could be used as a quartz crystal microbalance. The proposed method may inspire further high-frequency QCR-based biochemical chips or various sensor applications with TSM resonators.

High-temperature behavior of housed piezoelectric resonators based on CTGS

Abstract. A temperature sensor based on piezoelectric single crystals allowing stable operation in harsh environments such as extreme temperatures and highly reducing or oxidizing atmospheres is presented. The temperature dependence of the mechanical stiffness of thickness shear mode resonators is used to determine temperature changes. The sensor is based on catangasite (Ca3TaGa3Si2O14 – CTGS), a member of a langasite crystal family. CTGS exhibits an ordered crystal structure and low acoustic losses, even at 1000 ∘C. The resonance frequency and quality factor of unhoused and of housed CTGS resonators are measured up to about 1030 ∘C. A temperature coefficient of the resonance frequency of about 200 Hz K−1 for a 5 MHz device is found and enables determination of temperature changes as small as 0.04 K. Housed CTGS resonators do not show any significant change in the resonance behavior during a 30 d, long-term test at 711 ∘C.

Modeling and Electrode Design Optimizations of Plano-Plano Langasite Crystal Resonator.

The 3-D finite-element model (FEM) of a Y-cut plano-plano langasite crystal thickness shear mode (TSM) resonator is presented, and Mindlin's theory is used to investigate the optimal electrode shapes and sizes for langasite crystal resonator. Circular and elliptical electrodes of various arc lengths are studied to identify the most optimal electrode design configuration in order to achieve TSM vibration free from any anharmonic modes. Simulation results show that resonators with elliptical electrodes have noticeably better suppression of spurious modes compared to that of circular electrodes. Moreover, spurious mode suppression is accomplished for multiple electrode sizes for the same shape, which greatly differs from Mindlin's theory. Hence, three optimized designs are shortlisted and their mass loading sensitivities are investigated. Circular and elliptical electrodes of the same area show similar responses to added mass, indicating that elliptical electrodes have no apparent advantage over circular electrode in mass sensing applications.

Design and Development of Microscale Thickness Shear Mode (TSM) Resonators for Sensing Neuronal Adhesion.

The overall goal of this study is to develop thickness shear mode (TSM) resonators for the real-time, label-free, non-destructive sensing of biological adhesion events in small populations (hundreds) of neurons, in a cell culture medium and subsequently in vivo in the future. Such measurements will enable the discovery of the role of biomechanical events in neuronal function and dysfunction. Conventional TSM resonators have been used for chemical sensing and biosensing applications in media, with hundreds of thousands of cells in culture. However, the sensitivity and spatial resolution of conventional TSM devices need to be further enhanced for sensing smaller cell populations or molecules of interest. In this report, we focus on key challenges such as eliminating inharmonics in solution and maximizing Q-factor while simultaneously miniaturizing the active sensing (electrode) area to make them suitable for small populations of cells. We used theoretical expressions for sensitivity and electrode area of TSM sensors operating in liquid. As a validation of the above design effort, we fabricated prototype TSM sensors with resonant frequencies of 42, 47, 75, and 90 MHz and characterized their performance in liquid using electrode diameters of 150, 200, 400, 800, and 1,200 μm and electrode thicknesses of 33 and 230 nm. We validated a candidate TSM resonator with the highest sensitivity and Q-factor for real-time monitoring of the adhesion of cortical neurons. We reduced the size of the sensing area to 150–400 μm for TSM devices, improving the spatial resolution by monitoring few 100–1,000s of neurons. Finally, we modified the electrode surface with single-walled carbon nanotubes (SWCNT) to further enhance adhesion and sensitivity of the TSM sensor to adhering neurons (Marx, 2003).

Multi-parameter sensing using thickness shear mode (TSM) resonators – a feasibility analysis

Abstract. Multi-parameter sensing is examined for thickness shear mode (TSM) resonators that are in mechanical contact with thin films and half-spaces on both sides. An expression for the frequency-dependent electrical admittance of such a system is derived which delivers insight into the set of material and geometry parameters accessible by measurement. Further analysis addresses to the problem of accuracy of extracted parameters at a given uncertainty of experiment. Crucial quantities are the sensitivities of measurement quantities with respect to the searched parameters determined as the first derivatives by using tentative material and geometry parameters. These sensitivities form a Jacobian matrix which is used for the exemplary study of a system consisting of a TSM resonator of AT-cut quartz coated by a copper layer and a glycerol half-space on top. Resonant and anti-resonant frequencies and bandwidths up to the 16th overtone are evaluated in order to extract the full set of six material–geometry parameters of this system as accurately as possible. One further outcome is that the number of employed measurement values can be extremely reduced when making use of the knowledge of the Jacobian matrix calculated before.

Experimental Studies in Micromachined AT-Cut Quartz-Based Differential Vacuum Gauges

In this paper, a micromachined differential pressure sensor based on force frequency effect in AT-cut quartz bulk acoustic wave resonators for vacuum measurements is presented. The frequency shift arising from the stresses generated in the quartz due to force application is known as the force frequency effect. Pressure is sensed by monitoring the shifts in the thickness shear mode resonance frequency of AT-cut quartz resonator due to the application of differential pressure across the micromachined quartz diaphragm. The sensors exhibit a large dynamic range of 1 mTorr–100 Torr with a resolution of ~1 mTorr (in the medium vacuum regime). A parametric study has also been carried out to study the effect of resonator thickness and diameter on sensitivity. It was found that the sensor’s response to pressure is extremely sensitive to mechanical boundary conditions, which results in performance characteristics such as dependence on the direction of the applied pressure and unexpected scaling with the diaphragm radius.

Characterizing the Spatially Dependent Sensitivity of Resonant Mass Sensors Using Inkjet Deposition

Micro- and millimeter-scale resonant mass sensors have received widespread attention due to their robust and sensitive performance in a wide range of detection applications. A key performance metric for such systems is the sensitivity of the resonant frequency of a device to changes in mass, which needs to be calibrated. This calibration is complicated by the fact that the position of the added mass on a sensor can have an effect on the measured sensitivity—therefore, a spatial sensitivity mapping is needed. To date, most approaches for experimental sensitivity characterization are based upon the controlled addition of small masses, e.g., the direct attachment of microbeads via atomic force microscopy or the selective microelectrodeposition of material, both of which are time consuming and require specialized equipment. This work proposes a method of experimental spatial sensitivity measurement that uses an inkjet system and standard sensor readout methodology to map the spatially dependent sensitivity of a resonant mass sensor—a significantly easier experimental approach. The methodology is described and demonstrated on a quartz resonator. In the specific case of a Kyocera CX3225 thickness-shear mode resonator, the location of the region of maximum mass sensitivity is experimentally identified.

Study of the Relation between the Resonance Behavior of Thickness Shear Mode (TSM) Sensors and the Mechanical Characteristics of Biofilms.

This work analyzes some key aspects of the behavior of sensors based on piezoelectric Thickness Shear Mode (TSM) resonators to study and monitor microbial biofilms. The operation of these sensors is based on the analysis of their resonance properties (both resonance frequency and dissipation factor) that vary in contact with the analyzed sample. This work shows that different variations during the microorganism growth can be detected by the sensors and highlights which of these changes are indicative of biofilm formation. TSM sensors have been used to monitor in real time the development of Staphylococcus epidermidis and Escherichia coli biofilms, formed on the gold electrode of the quartz crystal resonators, without any coating. Strains with different ability to produce biofilm have been tested. It was shown that, once a first homogeneous adhesion of bacteria was produced on the substrate, the biofilm can be considered as a semi-infinite layer and the quartz sensor reflects only the viscoelastic properties of the region immediately adjacent to the resonator, not being sensitive to upper layers of the biofilm. The experiments allow the microrheological evaluation of the complex shear modulus (G* = G′ + jG″) of the biofilm at 5 MHz and at 15 MHz, showing that the characteristic parameter that indicates the adhesion of a biofilm for the case of S. epidermidis and E. coli, is an increase in the resonance frequency shift of the quartz crystal sensor, which is connected with an increase of the real shear modulus, related to the elasticity or stiffness of the layer. In addition both the real and the imaginary shear modulus are frequency dependent at these high frequencies in biofilms.

Rheological monitoring of tau protein polymerisation with acoustic waves sensor

Among acoustic waves sensors, the thickness shear mode resonator presents high sensitivity for the measurement of liquid viscoelastic properties, enabling the monitoring of the shear moduli, G′ G″, by using a suitable physical model. The development of an instrumental system for detecting the tau protein involved in Alzheimer's disease is proposed which will aid in understanding the mechanisms of this disease. The tau protein is present in complex products such as blood and cerebrospinal fluid. The experimental results show that the acoustic wave system allows to differentiate between tau protein solutions with different states of polymerisation.

Evaluation of Acoustic Properties for Ca3Nb(Ga0.75Al0.25)3Si2O14 Single Crystal Using the Ultrasonic Microspectroscopy System.

Acoustically related physical constants were experimentally determined for Ca3Nb(Ga0.75Al0.25)3Si2O14 (CNGAS) single crystal for the first time. Several plate specimens of the X-, Y -, Z -, 40.24 ° Y -, and 144.98 ° Y -cut were prepared from a CNGAS single crystal ingot grown by Czochralski technique. Elastic constants, piezoelectric constants, and their temperature coefficients for CNGAS were determined from longitudinal wave and shear wave velocities at around room temperature, measured by the ultrasonic microspectroscopy system. Dielectric constants, density, and coefficients of thermal expansion were also measured. It was demonstrated that the determined constants could provide calculation accuracy within ±0.12% in leaky surface acoustic wave velocity. The piezoelectric constants for CNGAS were a 7.2% increase in e11 and a 1.7% decrease in e14 due to Al-substitution effect, compared with those of Ca3NbGa3Si2O14. The appropriate cut angle for thickness-shear mode resonator with zero temperature coefficient of velocity was estimated to be around 150 ° Y -cut from calculations using the determined constants of CNGAS exhibiting electromechanical coupling factor k2 of 3.19% and power flow angle of -1.70°.

Zinc Oxide Nanostructure-Based Langasite Crystal Microbalance Ultraviolet Sensor

An ultraviolet (UV) sensor consisting of a langasite (La3Ga5SiO14) thickness shear mode resonator and ZnO nanostructure sensing medium was fabricated. For the first time, ZnO nanostructures, including nanorods, polycrystalline film, and well-aligned nanowires, were grown directly on the active area of langasite crystal microbalance (LCM) by the thermal evaporation method without the aid of any transfer technique. As a key part of the growth process, zinc vapor trapping and two-stage temperature ramping were employed to achieve catalyst-free, self-seeding growth of ZnO nanowires at growth temperatures below 600 °C. Under illumination of 365-nm UV light, a downshift in resonant frequency was observed for the LCMs due to acousto-electric interaction between photo-induced carriers and the shear waves. ZnO nanowires showed enhanced UV photosensitivity compared with that of nanorods or polycrystalline film. LCM with nanowires exhibited maximum shift of 157.5 Hz for several ON–OFF UV cycles and generated photocurrent of 235 $\mu \text{A}$ for 5 V bias. Nanowire-based sensor also demonstrated excellent response and recovery times of 11 and 43 s, respectively. All the ZnO nanostructure-coated LCMs showed good stability and repeatability in UV sensing.

Real-Time Monitoring of Platelet Activation Using Quartz Thickness-Shear Mode Resonator Sensors

In this study, quartz thickness-shear mode (TSM) resonator sensors were adopted to monitor the process of platelet activation. Resting platelets adhering to fibrinogen-coated electrodes were activated by different concentrations of thrombin (1, 10, and 100 U/mL), and the corresponding electrical admittance spectra of TSM resonators during this process were recorded. Based on a bilayer-loading transmission line model of TSM resonators, the complex shear modulus (G′ + jG″) and the average thickness (hPL) of the platelet monolayer at a series of time points were obtained. Decrease in thrombin concentration from 100 to 1 U/mL shifted all peaks and plateaus in G′, G″, and hPL to higher time points, which could be attributed to the partial activation of platelets by low concentrations of thrombin. The peak value of hPL was acquired when platelets presented their typical spherical shape as the first transformation in activation process. The G′ peak appeared 10 ∼ 20 min after hPL peak, when some filopods were observed along the periphery of platelets but without obvious cell spreading. As platelet spreading began and continued, G′, G″, and hPL decreased, leading to a steady rise of resonance frequency shift of TSM resonator sensors. The results show high reliability and stability of TSM resonator sensors in monitoring the process of platelet activation, revealing an effective method to measure platelet activities in real-time under multiple experimental conditions. The G′, G″, and hPL values could provide useful quantitative measures on platelet structure variations in activation process, indicating potential of TSM resonators in characterization of cells during their transformation.

Modeling the response of a quartz crystal microbalance under the specific adsorption of microbubbles

Targeted microbubbles can accumulate in the targeting site via a biochemical reaction. We propose a system for evaluating the accumulation of the bubbles using a quartz crystal microbalance (QCM) as the thickness shear-mode resonator. We derive the formula of the electrical admittance of QCM for the load of bubbles by modeling the reaction force generated by the specifically adsorbed bubbles. The bubble-load model enabled the calculation of the number density of the adsorbed bubbles on the QCM surface. A comparison with experimental results showed that the proposed system yields the possibility of quantitatively estimating the number density. This system will help us to develop new targeted microbubbles.

Rapid sensing of hepatitis B virus using QCM in the thickness shear mode

It is shown that sensor for hepatitis can be manufactured using a thickness shear mode resonator. Not the added mass is measured but the moment of particle (virus) detachment from the QCM surface is detected, which explains the high sensitivity of this sensor. The sensor allows confident determination of the presence of 140–150 viruses, while a typical signal shape is an additional warranty of selectivity confirming that it is hepatitis B virus (HBV) that was fixed on the surface. This method can be the ground for a prototype of the sensor for rapid analysis based on affine interactions.

QCM-based rapid analysis of DNA

We demonstrated that it is possible to break apart double-stranded DNA using a thickness shear mode resonator. This procedure measures the force of bond rupture. The measured rupture forces were in the range of 10–40pN. The procedure was tested experimentally with model complementary and non-complementary oligonucleotides. In the case of the DNA mismatch we observed a signal at a driving voltage of 0.8V (corresponding to a shear force of 11pN), while in the case of complementarity the signal at the voltage of 3V (36pN) appeared. This procedure may be the ground for the development of new types of biosensors measuring the force of affine interactions (probe/biomolecular target) on the surface of the sensor element.

Aging-related viscoelasticity variation of tendon stem cells (TSCs) characterized by quartz thickness shear mode (TSM) resonators

Aging not only affects the whole body performance but also alters cellular biological properties, including cell proliferation and differentiation. This study was designed to determine the effect of aging on the mechanical properties of tendon stem cells (TSCs), a newly discovered stem cell type in tendons, using quartz thickness shear mode (TSM) resonators. TSCs were isolated from both old and young rats, and allowed to grow to confluency on the surface of TSM resonators. The admittance spectrums of TSM with TSC monolayer were acquired, and a series of complex shear modulus G′+jG″ as well as average thickness hTSC were calculated based on a two-layer-loading transmission line model (TLM) for TSM resonator sensor. The results showed an overall increase in G′, G″ and hTSC during aging process. Specifically, the storage modulus G′ of aging TSCs was over ten times than that of young, revealing an important increase in stiffness of aging TSCs. Additionally, through phase-contrast and scanning electronic microscopy, it was shown that aging TSCs were large, flat and heterogeneous in morphologies while young TSCs were uniformly elongated. Increased cell size and irregular cell shape might be associated with the dense cytoskeleton organization, which could lead to an increase in both stiffness and viscosity. These results are in agreement with previously published data using different measurement methods, indicating TSM resonator sensor as a promising tool to measure the mechanical properties of cells.

Forces affecting nanoparticles in fluid, and the shape of the acoustic signal accompanying particle detachment from QCM surface

In the present work we use a thickness shear mode resonator—QCM operating at variable amplitude. Not frequency shift is recorded during the measurement but a sharp signal generated during the rupture of nanoparticles from the surface under smoothly increasing amplitude of oscillations. We consider the process of nanoparticle rupture from the QCM surface. The nature of signal formation is described, the motion of the nanoparticle and forces affecting it are considered. A connection between the properties of the ruptured particle with signal form (shape) is revealed. A sharp single peak is observed during the rupture of a rigid spherical nanoparticle, while the separation of long nanometer-sized particles bound along their length is accompanied by peak broadening. If a nanoparticle composed of separate smaller particles is detached from the surface, the particle decomposes into fragments, and the signal appears as a set of separate peaks.

FEM Simulation of Quartz Thickness Shear Mode Resonator for Gas Sensing Applications

The objective of this paper is to present simulation results of the Thickness Shear Mode (TSM) resonator based on quartz using finite element simulation method. 3D model of quartz resonator and simulations were completed using finite element method in CoventorWare software suite for design and simulation of MEMS devices. Different techniques for simulation of adsorption effect on selective layer were studied: influence of change in mass of the sensitive layer and influence of change in density of the sensitive layer. Analyses of resonant modes were performed for both cases and displacement profiles in selected modes were determined for the resonator under study. Impedance and phase characteristics were calculated and measured for clean sample and sample with selective layer coated. The adsorption model calculates the frequency shift in basic resonant frequency with adsorbed amount of sensed gas. The simulation results were used in design of gas sensors for dangerous substances detection.

QCM-Based Measurement of Bond Rupture Forces in DNA Double Helices for Complementarity Sensing

After fixing the DNA molecule in the form of a double helix on the surface of a thickness shear mode resonator (QCM), mechanical oscillations at increasing amplitude cause detorsion of the helix. The force necessary for detorsion can be determined from the voltage applied to the QCM at the rupture moment. The high sensitivity of this method is due to the fact that measurements are carried out in the frequency region around the QCM resonance, where any (even very weak) distortions of the consistent oscillating system cause noticeable distortions of the amplitude-frequency dependence, and these distortions are used to fix the rupture moment. The measured rupture forces were within 30-40 pN, and the sensitivity was 10(8) molecules. It was demonstrated that the proposed procedure allows one to determine the factors that affect the stability of the DNA double helix. This procedure can be the basis for the development of a new method of rapid DNA analysis. Experiments performed with model DNA showed that it is possible to reveal complementarity between two DNA samples.