YX LiTaO3 Research Articles

Mass Sensitivity Evaluation of Surface Acoustic Wave Biosensor

In this paper, the mass sensitivity of a 3-Dimensional SiO2/36°YX LiTaO3 Love mode SAW biosensor is investigated by a novel approach. The normalized displacement confirms the shear horizontal nature of Love wave. The phase mass sensitivity of 76.4931 m2/kg is obtained by evaluating the phase shifts. The insertion loss of -17.2dB is achieved by impulse response analysis. This Love mode SAW biosensor has potential applications in detecting viruses, cancer markers, bacteria, etc.

Surface Acoustic Wave Resonators With Hetero Acoustic Layer (HAL) Structure Using Lithium Tantalate and Quartz.

This article reports a new concept of surface-acoustic-wave (SAW) resonator, which uses shear horizontal (SH) wave confined in a thin LiTaO3 (LT) layer supported by a quartz (Qz) substrate. The LT layer is 35-50°YX LT, and the quartz substrate is 35-60°Y90°X Qz. A negative temperature coefficient of frequency (TCF) of the SH SAW in the LT layer is compensated by the quartz substrate, which shows a wide range of positive TCF depending on the crystalline orientation. Excellent TCFs of 2 and -10 ppm/°C were measured for the series and parallel resonance frequencies, respectively. The strong confinement of the SH SAW in the LT layer results in the best level of resonance characteristics ever reported. The measured impedance ratio reached 84 dB. On the other hand, spurious waves other than the SH SAW are not confined in the LT layer due to the unique properties of quartz, which results in spurious-free characteristics throughout a wide frequency range.

A spurious-free, steep band rejection filter using a LiTaO3/quartz heteroacoustic layer surface acoustic wave resonator

We have developed prototype parallel and series types of band rejection filters at 0.9 GHz using a heteroacoustic layer (HAL) surface acoustic wave (SAW) resonator. The HAL SAW resonator is made on 0.63 μm thick 25°YX LiTaO3 supported with a 42°45′Y 90°X quartz substrate. Steep attenuation was obtained due to the large impedance ratio of the HAL SAW resonator. There is no obvious spurious response up to 6 GHz thanks to the spurious-free characteristic of the HAL SAW resonator, and temperature frequency stability is good. In addition, the attenuation at frequencies other than the rejection frequency is small. This HAL SAW band rejection filter may be useful for carrier aggregation and Internet of Things systems.

Enhanced Sensitivity of a Love Wave-Based Methane Gas Sensor Incorporating a Cryptophane-A Thin Film.

A Love wave-based sensing chip incorporating a supramolecular cryptophane A (CrypA) thin film was proposed for methane gas sensing in this work. The waveguide effect in the structure of SiO2/36° YX LiTaO3 will confine the acoustic wave energy in SiO2 thin-film, which contributes well to improvement of the mass loading sensitivity. The CrypA synthesized from vanillyl alcohol by a double trimerisation method was dropped onto the wave propagation path of the sensing device, and the adsorption to methane gas molecules by supramolecular interactions in CrypA modulates the acoustic wave propagation, and the corresponding frequency shifts were connected as the sensing signal. A theoretical analysis was performed to extract the coupling of modes for sensing devices simulation. Also, the temperature self-compensation of the Love wave devices was also achieved by using reverse polarity of the temperature coefficient in each media in the waveguide structure. The developed CrypA coated Love wave sensing device was connected into the differential oscillation loop, and the corresponding gas sensitive characterization was investigated. High sensitivity, fast response, and excellent temperature stability were successfully achieved.

Multilayered structures using thin plates of LiTaO3 for acoustic wave resonators with high quality factor

Multilayered substrates, including thin plates of LiTaO3 (LT) bonded to silicon (Si) or glass wafers either directly or via intermediate layers, were numerically investigated as potential materials for surface acoustic wave (SAW) resonators with high quality (Q)-factor required for the next generation of mobile communication systems. The propagation velocities and electromechanical coupling coefficients of shear horizontally (SH) polarized acoustic waves were estimated as functions of LT orientation and thicknesses of all layers in LT/Si, LT/SiO2/Si, LT/glass, LT/AlN/glass and structures with several pairs of SiO2/AlN layers between LT and the glass wafer. Optimal combinations of cut angle, LT and electrode thicknesses, as well as the number and thicknesses of intermediate layers, required for the construction of resonators with improved performance were observed for each analyzed structure. In the resonators employing LT/Si and LT/SiO2/Si structures with 30°YX - 48°YX LT cuts, high electromechanical coupling k2, reaching 11.6%, can be combined with high velocities up to 4000 m/s, zero TCF at the resonant frequency and Q-factors that are considerably higher than in the LSAW filters using regular LT substrates. To understand the loss mechanisms that limit resonator Q-factors in LT/glass, mechanical displacements that accompany wave propagation in multilayered structures were visualized. Investigation of the nature of acoustic modes and their transformations with number and thicknesses of the layers revealed that the low-velocity glass wafer can be used as a supporting substrate if an intermediate AlN layer or alternating pairs of low- and high-velocity layers, for example SiO2/AlN, are introduced between LT and the glass wafer.

Finite element simulation of a highly sensitive SH-SAW delay line sensor with SiO $$_{2}$$ 2 micro-ridges

The paper presents 3D finite element simulation of an SH-SAW delay line sensor to investigate coupled resonance with SiO $$_{2}$$ micro-ridges designed along the wave propagation direction on a 36 $$^{\circ }$$ -YX LiTaO $$_{3}$$ substrate. Time response simulation is used to calculate the displacements and voltages at the output IDT. The device generates a shear wave with horizontal displacement component ten times greater than vertical displacement component. Mass loading is simulated by applying an equivalent surface mass density of double-stranded DNA uniformly on the SiO $$_{2}$$ ridges. At critical ridge height, both substrate and ridge vibrate in unison leading to a sharp change in the phase shift from negative to positive causing coupled resonance. In the presence of coupled resonance, the device offers high mass sensitivity of 1295 m $$^{2}$$ /kg which is about 20 times greater in comparison to the mass sensitivity of a conventional SiO $$_{2}$$ based Love wave device. The increase in mass sensitivity at coupled resonance is attributed to the increase in the area-averaged stress at the interface of micro-ridge and substrate, going above 8.5 MPa. As ridge height is varied, a transition occurs in the mode of vibration leading to a 5 dB swing in the insertion loss of the device near the coupled resonant height.

Theoretical Study of Monolayer and Double-Layer Waveguide Love Wave Sensors for Achieving High Sensitivity.

Love wave sensors have been widely used for sensing applications. In this work, we introduce the theoretical analysis of the monolayer and double-layer waveguide Love wave sensors. The velocity, particle displacement and energy distribution of Love waves were analyzed. Using the variations of the energy repartition, the sensitivity coefficients of Love wave sensors were calculated. To achieve a higher sensitivity coefficient, a thin gold layer was added as the second waveguide on top of the silicon dioxide (SiO2) waveguide–based, 36 degree–rotated, Y-cut, X-propagating lithium tantalate (36° YX LiTaO3) Love wave sensor. The Love wave velocity was significantly reduced by the added gold layer, and the flow of wave energy into the waveguide layer from the substrate was enhanced. By using the double-layer structure, almost a 72-fold enhancement in the sensitivity coefficient was achieved compared to the monolayer structure. Additionally, the thickness of the SiO2 layer was also reduced with the application of the gold layer, resulting in easier device fabrication. This study allows for the possibility of designing and realizing robust Love wave sensors with high sensitivity and a low limit of detection.

Highly Sensitive SH-SAW Resonator with SiO2 trenches for Biosensing Application

The paper presents three dimensional finite element simulation of a sensitive shear-horizontal surface acoustic wave device for biosensing application. The resonator consisting of 36°-YX LiTaO3 substrate with SiO2 trenches generates a shear-horizontal standing wave. Eigenmode study and frequency response are used to calculate displacements, admittance and electromechanical coupling coefficient of the device. For a given mode, the coupling coefficient of the device increases with trench height to a maximum of about 7% and then starts to decrease till next higher order mode becomes dominant. The trenches not only serve as guiding layer to keep the energy of the wave at the surface but also cause coupled resonance leading to increase in resonance frequency and average stress at the contact area between trench and substrate. Mass loading of resonator is simulated by applying the equivalent surface mass density of double stranded DNA of length 50 base pairs uniformly over the surface area of trenches. Close to the resonant height of trenches, mass loading causes a large frequency shift making the device a highly sensitive biosensing platform.

Temperature-compensated Love wave based gas sensor on waveguide structure of SiO2/36° YX LiTaO3

A temperature-compensated Love wave device was proposed for gas sensing utilizing a waveguide structure of SiO2/36° YX LiTaO3. Significant improvement in the temperature stability of the hybrid Love wave device was implemented by varying the guiding layer thickness. The optimal values yielding low cross-sensitivity to temperature and high mass sensitivity in gas sorption were determined theoretically by solving the coupled electromechanical field equation in layered media. The theoretical analysis was confirmed experimentally in dimethylmethylphosphonate (DMMP) detection by using a fluoroalcoholpolysiloxane (SXFA) coated Love wave sensor. The experimental results indicate that better sensitivity and excellent temperature stability were obtained from the developed Love wave gas sensor over the Rayleigh surface acoustic wave (R-SAW) sensors.

Low Insertion Loss and Highly Sensitive SH-SAW Sensors Based on 36° YX LiTaO3 Through the Incorporation of Filled Microcavities

Reduction in power consumption and improvement in mass sensitivity are important considerations for surface acoustic wave (SAW) devices used in various sensing applications. Detection of minute quantities of a particular species (clinical sensing) and power requirements (wireless sensing) are two key metrics that must be optimized. In this paper, a 3-D finite element model (FEM) was employed to compare insertion loss (IL) and mass sensitivity of SAW sensors having microcavities filled with ZnO and nanocrystalline diamond to a standard two-port SAW design. Initial simulation results show that ZnO filled cavities (depth = 5 μm) were most effective at reducing power loss ΔIL = (6.03 dB) by increasing particle displacement (acousto-electric to mechanical transduction) at the output transducer. A 100-pg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> load was applied to the sensing area of each device to evaluate mass sensitivity. Our simulations suggest that ZnO filled cavities with shallow depth (2.5 μm) have the greatest sensitivity. The FEM simulations are used to understand the acoustic wave propagation in microcavity-based SAW sensors. The observed enhancement in mass sensitivity and power transfer is attributed to waveguiding effects and constructive interference of the scattered acoustic waves from the microcavities. Devices fabricated with microcavities ~1 μm deep decreased IL by 3.306 dB compared with a standard SAW device. Additional simulations were conducted for each device configuration using the same depth in order to make a direct comparison between measured and simulated results. Our findings offer encouraging prospects for designing low IL highly sensitive microcavity-based SAW biosensors.

Surface acoustic wave electronic tongue for robust analysis of sensory components

A robust approach is presented here for the rapid identification of the different human tastes. Novel two-port resonator-based shear-horizontal surface acoustic wave (SH-SAW) sensors have been designed that operate on a purely physical detection principle. The devices were fabricated on a 3″ 36° YX LiTaO3 wafer and found to resonate at the designed wireless ISM frequency of 434MHz. They have been also designed to be low loss when operated in aqueous media and without the need for taste-specific coatings. The successful identification of six different tastes was achieved: not only the four common tastes of saltiness, sweetness, sourness, and bitterness but also solutions representing the umami and metallic tastes. 100% separation between samples of the same taste class (e.g. caffeine and quinine hydrochloride of the bitter class) was also demonstrated, as well as a detection and classification of samples of the same substance with different concentrations. Furthermore, the identification of binary taste mixtures and separating them from original component solutions was investigated and confirmed experimentally. We believe that the sensor's response to the mixtures can be described by a simple model based upon combinations of their characteristic physical properties; amongst which electrical conductivity, density and viscosity appear to have the most significant influence. Uncoated taste sensors offer the potential for robust liquid sensors that can be manufactured in volume at low unit cost.

Mass Sensitivity Evaluation and Device Design of a LOVE Wave Device for Bond Rupture Biosensors Using the Finite Element Method

The LOVE wave devices based on a number of composite structures have been designed and simulated in this paper for use as a bond-rupture biosensor. Bond-rupture biosensors use acoustic energy to probe the bond strength between the sensor substrate and the analyte. The sensitivity and displacement of LOVE wave sensors can be implemented due to energy concentration inside a guiding layer on the surface of a piezoelectric crystal. The choice of substrate and guiding layer material is the critical basic elements in the proper design of a LOVE wave biosensor applications. Finite element method (FEM) is a suitable numerical method to analyze and design the LOVE wave device. A 3-D FEM model has been created and defined to simulate the displacement response of the acoustic wave system. The LOVE wave can be clearly observed, and the total surface displacement can reach a value of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> m, which can easily induce the bond rupture between antibody and antigen. A 2-D model has been established to simulate the mass sensitivity with different composite structures of 128° YX LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , 36° YX LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , ST-quartz-PMMA and 128° YX LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and 36° YX LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and ST-quartz-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . These results indicate that the 128° YX LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> PMMA is the most suitable for bond rupture biosensors due to its high sensitivity and maximum displacement on the surface of piezoelectric crystal.

Characterization and humidity sensing of ZnO/42° YX LiTaO3 Love wave devices with ZnO nanorods

Love mode surface acoustic wave devices based on ZnO/42° YX LiTaO3 were characterized with the thickness of the sputtered ZnO guiding layer varied from 250nm to 1.18μm. Phase velocity, temperature coefficient of resonant frequency, sensitivity, electromechanical coupling coefficient and humidity sensing of the Love mode SAW devices were studied as a function of the ZnO layer thickness. With increasing ZnO thickness over the range of thickness values we have examined, the sensitivity of 42° YX LiTaO3 to liquid loading increased and the values of electromechanical coupling coefficient decreased. The device with a thickness of 250nm showed the best humidity response. ZnO nanorods were grown on this device and its humidity sensing performance has been further improved due to their large surface-to-volume ratio of the ZnO nanorods.

Electrospun PVP fibers and gas sensing properties of PVP/36° YX LiTaO 3 SAW device

The poly-vinyl-pyrrolidone (PVP) fibers were prepared by electrospinning of PVP aqueous solution and the PVP fibers/36° LiTaO 3 surface acoustic wave (SAW) sensor was successfully developed. The effects of the concentration of PVP solution and electrode-to-collector distance on the morphology of the electrospun PVP fibers were investigated and the H 2 sensing properties of the SAW sensor were tested. The electrode-to-collector distance significantly affected the density of PVP fibers and the smooth and uniform fibers were obtained when the concentration of PVP solution was 58%. The developed SAW sensors show large response to H 2 at room temperature.

Single-channel shear horizontal surface acoustic wave sensor for the identification of liquid-phase substances

The principal possibility of liquid-phase substances recognition with the aid of a single-channel sensor operating on a shear horizontal surface acoustic wave (SH-SAW) delay line has been experimentally demonstrated. The SH-SAW sensor was manufactured as a SAW delay line based on a layered structure on 36°YX LiTaO3 crystal substrate. The response signal is related to the analyt-induced change in a pulse characteristic obtained by the frequency-to-time domain transformation of one of the measured S-parameters.

Layered Surface Acoustic Wave Hydrogen Sensor Based on Polyethylaniline Nanofibers

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

Single Sh-Saw Sensor as a Distributed Sensor Array for Liquids Recognition

Abstract Basic possibility to use single-channel shear-horizontal surface acoustic waves sensor constructed as a delay line on multilayered structure with 36 YX LiTaO3 substrate for liquids recognition has been proposed. The changes under analytes influence of the sensor pulse responses obtained by transformation to time domain of one of the S-parameters measured in frequency domain have been used as sensor responses. Examples of responses to some liquid analytes have been demonstrated for a sensor based on LiTaO3 – SiO2 – molecularly imprinted polymer layered structure. Qualitative explanation of the result is given by treating such a sensor as a distributed sensor array.

Polypyrrole nanofiber surface acoustic wave gas sensors

Abstract We present for the first time, to the best of authors’ knowledge, surface acoustic wave (SAW) gas sensors featuring polypyrrole nanofibers as the active component for hydrogen (H2) and nitrogen dioxide (NO2) detection at room temperature. Polypyrrole nanofibers were synthesized through a template-free chemical route by introducing bipyrrole as an initiator to speed up the polymerization of pyrrole in the presence of iron (III) chloride (FeCl3) as the oxidizing agent. Polypyrrole nanofibers were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopic (FT-IR) techniques which indicated that the average diameter of the nanofibers was 18 nm with lengths in the order of several microns. The polypyrrole nanofibers were dispersed onto the surface of a ZnO/36°YX LiTaO3 SAW transducer. Gas testing towards H2 and NO2 was conducted in an enclosed environmental cell at room temperature. Measured frequency shifts due to sensor responses were 20 kHz towards 1% of H2 and 4.5 kHz towards 2.1 ppm NO2, respectively. The sensor performance was assessed during a five-day period and repeatable results were obtained.

Taste sensors utilizing high-frequency SH-SAW devices

Recent interest in the development of taste sensors has been motivated by their potential application in the food and beverage industries as well as environmental monitoring. This paper describes the development of novel high-frequency dual delay line and two-port resonator shear-horizontal surface acoustic wave (SH-SAW) microsensors for liquid analysis. The acoustic devices have been designed to function without the need for analyte-specific coatings and to operate at the wireless ISM frequency of 433 MHz; the sensors are small, robust and are built on a piezoelectric substrate (36° YX LiTaO 3). Liquid samples are introduced to the active sensing area via a microfluidic cell that has been fabricated using microstereolithography (MSL) and then attached to the SH-SAW sensor substrate. A low cost flow system has been developed and integrated with the sensor housing to create a fully automated measurement system. Tests have been performed on aqueous solutions with different tastants representing not only the four basic tastes of saltiness, sweetness, sourness, and bitterness but also of umami and metallic. Results show that good discrimination between the different taste samples is possible using both delay-line and resonator type piezoelectric devices.

SAW-based gas sensors with rf sputtered InO x and PECVD SiN x films: Response to H 2 and O 3 gases

Surface acoustic wave (SAW)-based sensors, with InO x and SiN x layers on 36° YX LiTaO 3 substrates were investigated for the detection of hydrogen (H 2) and ozone (O 3) gases at different operating temperatures. SiN x films with different thicknesses were deposited using the plasma enhanced chemical vapour deposition (PECVD) method. The InO x sensing layer was deposited using an rf magnetron sputterer. The sensors’ performance was analyzed in terms of their frequency shifts as a function of different gas concentrations. The chemical–physical characterization of the deposited films was carried out by X-ray photoelectron spectroscopy (XPS). High sensitivities and excellent repeatabilities were observed towards both gases.