LiNbO3 Surface Acoustic Wave Research Articles

LiNbO3 Surface Acoustic Wave Resonators with Large Effective Electromechanical Coupling

This paper reports an LNO surface acoustic wave (SAW) resonator based on a shear horizontal mode with high operating frequency over 3 GHz, large electromechanical coupling of 33.54%, Q factor of 380, and a relatively good figure of merit (FOM) of 127. Combing crystal-ion-slicing (CIS) technology with a room temperature bonding method, a 4-inch single crystalline LNO thin film on silicon is prepared successfully. The influence of damaged LNO film on crystalline quality and SAW performance is comprehensively analyzed. After totally removing the damaged layer, the electromechanical coupling and Q factor is significantly improved. The high-performance SAW resonator possesses the potential to meet the requirements of SAW filters for the fifth-generation (5G) communication in terms of high frequency, large bandwidth, and a high-quality factor.

An Algorithm for Solving the Phase Ambiguity Problem of SAW Delay-Line Sensor Systems.

Solving the phase ambiguity problem is crucial to achieving a wide-range and high-precision measurement for the frequency-domain sampling (FDS)-based surface acoustic wave (SAW) delay-line sensor systems. This study proposes an improved phase estimation algorithm called dual-band phase estimation (DBPE) to solve the problem. By using DBPE, the SAW sensor system can obtain an extensive and alterable measuring range without further requirements for sensor design or transmitted signals. Thus, it can be widely used in various FDS-based SAW delay-line sensor systems. Monte Carlo simulations and temperature measuring experiments, based on a YZ-cut LiNbO3 SAW delay-line sensor and a switched frequency-stepped continuous wave (S-FSCW) reader, are performed to demonstrate the algorithm's validity. The Monte Carlo simulations show that DBPE can effectively solve the phase ambiguity problem and has better performance than frequency estimation in measuring precision at a low signal-to-noise ratio (SNR). The temperature-sensing experiments show that DBPE has a good performance in measuring range and precision, serving as a phase ambiguity solver in the temperature sensor system.

Enhanced Properties of SAW Device Based on Beryllium Oxide Thin Films

The present study depicts the first-ever optimized surface acoustic wave (SAW) device based on Beryllium Oxide (BeO) thin film. The feasibility of surface acoustic wave devices based on BeO/128° YX LiNbO3 layered structure has been examined theoretically. The SAW phase velocity, electromechanical coupling coefficient, and temperature coefficient of delay for BeO/128° YX LiNbO3 layered structure are calculated. The layered structure is found to exhibit optimum value of phase velocity (4476 ms−1) and coupling coefficient (~9.66%) at BeO over layer thickness of 0.08 λ. The BeO (0.08 λ)/128° YX LiNbO3 SAW device is made temperature stable, by integrating it with negative temperature coefficient of delay (TCD) TeO3 over layer of thickness 0.026λ.

A hybrid (Al)GaAs-LiNbO3 surface acoustic wave resonator for cavity quantum dot optomechanics

A hybrid device comprising a (Al)GaAs quantum dot heterostructure and a LiNbO3 surface acoustic wave resonator is fabricated by heterointegration. High acoustic quality factors Q>4000 are demonstrated for an operation frequency f≈300 MHz. The measured large quality factor-frequency products Q×f>1012 ensure the suppression of decoherence due to thermal noise for temperatures exceeding T>50 K. Frequency and position dependent optomechanical coupling of single quantum dots and resonator modes is observed.

Simulation of Nonlinear Resonance, Amplitude-Frequency, and Harmonic Generation Effects in SAW and BAW Devices.

Nonlinearly coupled sets of piezoelectric field equations in the frequency domain were derived for the nonlinear propagation of finite-amplitude waves in piezoelectric bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices. To verify their accuracy, we have embedded these sets of equations in the finite-element method (FEM) of COMSOL Multiphysics software and compared the FEM results with both the analytical and experimental results found in the published literature. The nonlinear frequency responses for both plano- and contoured-plate resonators of AT-cut quartz were investigated under various voltage drives, circuit resistances, and quality factors. The proposed equations with FEM have also been employed to study 33.3-MHz very-high-frequency (VHF) quartz resonators, showing that under different conditions of how well the third overtone mode (f3) matches the third harmonic (3f) and how the fractional frequency shift of the third overtone mode (f3) occurs as a function of the fundamental mode current. Furthermore, we have studied the nonlinear harmonic generation of an 840-MHz 128° Y-cut X-propagating (128° YX) LiNbO3 SAW resonator. The second-harmonic (H2) and third-harmonic (H3) modes were observed to occur, respectively, at two-time (2f) and three-time (3f) frequencies of fundamental frequency (f) when such resonators were driven with high power. The effects of substrate thickness, bottom surface conditions of the substrate, and different circuit connections on the H2 and H3 generations were simulated and compared with available measurements. Current proposed sets of equations are general and could be used for the study of nonlinear resonance, amplitude-frequency effect, and harmonic generation in any piezoelectric devices, provided that the necessary nonlinear material constants are known.

Graphene-Based Fully Transparent Thin Film Surface Acoustic Wave Devices for Sensing and Lab-on-Chip Applications

This paper explores to use graphene as transparent interdigital transducer (IDT) electrode for a fully transparent surface acoustic wave (SAW) device due to its extraordinary electrical, physical and mechanical properties. The number of graphene atomic layers was firstly optimized for its best performance as the SAW electrode, and a 4-layered graphene IDT electrode, with aluminum doped zinc oxide, AZO, as the bus bar and wire bonding pad, was selected to fabricate fully transparent ZnO/glass SAW devices. The SAW resonators exhibited obvious resonant response at different wavelengths, and resonance signals with amplitude up to 20 dB were obtained with the transparency above 80%. The graphene-based transparent SAW sensor has been used for different sensing applications. Temperature sensing tests showed that the frequencies increase linearly with the increase of temperature, which has an opposite trend compared to that obtained from a conventional LiNbO3 SAW device. The humidity sensing and human breathing detection have been demonstrated, and discontinuous respiration measurement can be used to distinguish the human respiration at the normal state or the state after exercise. Strong acoustic streaming and particle concentration using the transparent SAW devices have been achieved, which are suitable for microfluidic and lab-on-chip applications.

SAW propagation characteristics of TeO3/3C-SiC/LiNbO3 layered structure

Surface acoustic wave (SAW) devices based on Lithium Niobate (LiNbO3) single crystal are advantageous because of its high SAW phase velocity, electromechanical coupling coefficient and cost effectiveness. In the present work a new multi-layered TeO3/3C-SiC/128° Y-X LiNbO3 SAW device has been proposed. SAW propagation properties such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of the TeO3/SiC/128° Y-X LiNbO3 multi layered structure is examined using theoretical calculations. It is found that the integration of 0.09λ thick 3C-SiC over layer on 128° Y-X LiNbO3 increases its electromechanical coupling coefficient from 5.3% to 9.77% and SAW velocity from 3800 ms−1 to 4394 ms−1. The SiC/128° Y-X LiNbO3 bilayer SAW structure exhibits a high positive TCD value. A temperature stable layered SAW device could be obtained with introduction of 0.007λ TeO3 over layer on SiC/128° Y-X LiNbO3 bilayer structure without sacrificing the efficiency of the device. The proposed TeO3/3C-SiC/128° Y-X LiNbO3 multi-layered SAW structure is found to be cost effective, efficient, temperature stable and suitable for high frequency application in harsh environment.

Zeolitic imidazolate framework-coated acoustic sensors for room temperature detection of carbon dioxide and methane.

The integration of nanoporous materials such as metal organic frameworks (MOFs) with sensitive transducers can result in robust sensing platforms for monitoring gases and chemical vapors for a range of applications. Here, we report on an integration of the zeolitic imidazolate framework - 8 (ZIF-8) MOF with surface acoustic wave (SAW) and thickness shear mode quartz crystal microbalance (QCM) devices to monitor carbon dioxide (CO2) and methane (CH4) under ambient conditions. The MOF was directly coated on the Y-Z LiNbO3 SAW delay lines (operating frequency, f0 = 436 MHz) and AT-cut quartz TSM resonators (resonant frequency, f0 = 9 MHz) and the devices were tested for various gases in N2 under ambient conditions. The devices were able to detect the changes in CO2 or CH4 concentrations with relatively higher sensitivity to CO2, which was due to its higher adsorption potential and heavier molecular weight. The sensors showed full reversibility and repeatability which were attributed to the physisorption of the gases into the MOF and high stability of the devices. Both types of sensors showed linear responses relative to changes in the binary gas compositions thereby allowing to construct calibration curves which correlated well with the expected mass changes in the sorbent layer based on mixed-gas gravimetric adsorption isotherms measured on bulk samples. For 200 nm thick films, the SAW sensitivities to CO2 and CH4 were 1.44 × 10-6/vol% and 8 × 10-8/vol%, respectively, against the QCM sensitivities 0.24 × 10-6/vol% and 1 × 10-8/vol%, respectively, which were evaluated as the fractional change in the signal. The SAW sensors were also evaluated for 100 nm-300 nm thick films, the sensitivities of which were found to increase with the thickness due to the increased number of pores for the adsorption of a larger amount of gases. In addition, the MOF-coated SAW delay lines had a good response in wireless mode, demonstrating their potential to operate remotely for the detection of the gases at emission sites across the energy infrastructure.

A comparison of Pd and Au electrodes-based LiNbO3 surface acoustic wave devices

We report the comparison of electrode metals for LiNbO3 surface acoustic wave (SAW) devices. Palladium (Pd) was systematically studied as a SAW electrode metal for the first time, compared with gold (Au). Simulations were first conducted to gain an understanding of the differences of the materials and the metallization ratio. Two sets of identical SAW devices were then fabricated using Au and Pd as electrodes with different electrode widths and same SAW period. The insertion losses, types of resonance mode, the resonance frequencies, peak amplitudes, quality factors and trends with different metallization ratios were systematically compared and analyzed. We found that Pd electrode devices only exhibit the parallel resonance frequency and have higher resonance frequency for both the first-order and third-order harmonics. Au electrode devices tend to have a smooth response and a quality factor two times higher than Pd. Both Pd and Au electrode devices have nearly identical electromechanical coupling coefficients, and the quality factor and third-order harmonics both improve with increasing metallization ratio.

Fast-response and low-loss surface acoustic wave humidity sensor based on bovine serum albumin-gold nanoclusters film

The impact of ambient air humidity on surface acoustic wave (SAW) propagation in structures consisting of bovine serum albumin (BSA) and bovine serum albumin - gold nanoclusters (BSA-Au NCs) films deposited on YZ lithium niobate (LiNbO3) substrate has been investigated. The BSA-Au NCs film deposited on the surface of LiNbO3 significantly reduced the low-humidity value of the SAW transmission loss and considerably improved its long-term stability as compared to the BSA film. The amplitude of the output signal of the BSA-Au NCs on LiNbO3 SAW delay line was measured as a function of relative humidity (RH) at the steady-state conditions and as a function of time upon the step-like RH variation. An observed decrease in the transmitted SAW amplitude with increasing RH was explained in terms of the acoustoelectric attenuation. The response and recovery times of the structure with BSA-Au NCs on LiNbO3 SAW delay line upon abrupt humidity changes were on the order of 0.2s. No impact of RH variation on the SAW propagation was observed in the structures with BSA-Au NCs films deposited on metalized LiNbO3 substrate surface. The time-stable, fast-response and low-loss BSA-Au NCs on LiNbO3 SAW humidity sensor has been applied for monitoring the human respiration by detecting moisture contained in the exhaled air.

Graphene/LiNbO3 surface acoustic wave device based relative humidity sensor

This study described relative humidity (RH) sensing using a graphene/128° YX LiNbO3 surface acoustic wave (SAW) device. The resonant frequency of the device decreased in a two-stage manner as the RH increased. For a low RH range (RH<50%), a frequency downshift of 1.38kHz per 1% RH change was observed. This was attributed to mass loading of the SAW propagation surface due to the adsorption of water molecules by the graphene surface. For a high RH range (RH>50%), a frequency downshift of 2.6kHz per 1% RH change was obtained, which was due to the change in elastic grapheme properties. The mass loading effect of the water layer was less effective at high temperature, resulting in a lower temperature coefficient of resonant frequency (TCF).

Engineering Silver Nanostructures for Surface Acoustic Wave Humidity Sensors Sensitivity Enhancement

In this paper, the sensitivity of the LiNbO3 surface acoustic wave (SAW) based humidity sensors has been enhanced with various nanostructured Ag materials, including thermally evaporated or chemically synthesized, and then thermally annealed ones. The results showed that the humidity sensitivity of the SAW devices increases with the surface roughness (porosity) of the sensing film, and can be further improved when Ag NPs are used. Smooth Ag film deposited by evaporation onto the SAW devices did not change the humidity sensitivity noticeably, but those with chemically deposited high porosity Ag films have a good sensitivity of 80 kHz/75%RH. The SAW sensors with the Ag NPs have the highest sensitivity up to about 800 kHz/75%RH, at least one order of magnitude higher than those reported before. The SAW sensors with Ag nano-particles showed a strong non-linearity, and explained by the different chemisorption capabilities of Ag and LiNbO3 surface.

Camphor Sulfonic Acid Doped Polyaniline/Diamond Nanofibers Based ZnO/64° YX LiNbO&lt;SUB&gt;3&lt;/SUB&gt; Surface Acoustic Wave H&lt;SUB&gt;2&lt;/SUB&gt; GasSensor

In this work, the novel H2 gas sensor based on polyaniline/diamond composite nanofibers thin film deposited on a ZnO/64° LiNbO3 surface acoustic wave (SAW) transducer has been developed. The film was deposited using drop-casting method. The morphology of the composite was characterised using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). It was observed that the nanofibers have average diameter of 50 nm and broad peaks were observed at 2θ ~ 16° and 44° in the X-ray diffraction pattern. The sensor dynamic and static performance were presented. A response of more than 750 kHz towards 1% of H2 gas was measured and fast response and recovery of 12 s and 180 s, respectively were observed.

Titanium Dioxide‐Based 64∘ YX LiNbO3 Surface Acoustic Wave Hydrogen Gas Sensors

Amorphous titanium dioxide (TiO2) and gold (Au) doped TiO2‐based surface acoustic wave (SAW) sensors have been investigated as hydrogen gas detectors. The nanocrystal‐doped TiO2 films were synthesized through a sol‐gel route, mixing a Ti‐butoxide‐based solution with diluted colloidal gold nanoparticles. The films were deposited via spin coating onto 64∘ YX LiNbO3 SAW transducers in a helium atmosphere. The SAW gas sensors were operated at various temperatures between 150 and 310∘C. It was found that gold doping on TiO2 increased the device sensitivity and reduced the optimum operating temperature.

Polydimethylsiloxane–LiNbO3 surface acoustic wave micropump devices for fluid control into microchannels

This paper presents prototypical microfluidic devices made by hybrid microchannels based on piezoelectric LiNbO(3) and polydimethylsiloxane. This system enables withdrawing micropumping by acoustic radiation in microchannels. The withdrawing configuration, integrated on chip, is here quantitatively investigated for the first time, and found to be related to the formation and coalescence dynamics of droplets within the microchannel, primed by surface acoustic waves. The growth dynamics of droplets is governed by the water diffusion on LiNbO(3), determining the advancement of the fluid front. Observed velocities are up to 2.6 mm s(-1) for 30 dBm signals applied to the interdigital transducer, corresponding to tens of nl s(-1), and the micropumping dynamics is described by a model taking into account an acoustic power exponentially decaying upon travelling along the microchannel. This straighforward and flexible micropumping approach is particularly promising for the withdrawing of liquids in lab-on-chip devices performing cycling transport of fluids and biochemical reactions.

A layered surface acoustic wave gas sensor based on apolyaniline/In2O3 nanofibre composite

A polyaniline/In2O3 nanofibre composite based layered surface acoustic wave (SAW) sensorhas been developed and investigated for different gases. Chemicaloxidative polymerization of aniline in the presence of finely dividedIn2O3 was employed to synthesize a polyanilinenanofibre/In2O3 nanoparticle composite. The nanocomposite was deposited onto a layeredZnO/64° YX LiNbO3 SAW transducer. The novel sensor was exposed toH2,NO2 and CO gases. Fast response and recovery times with good repeatability were observed atroom temperature.

Improved Temperature Stability of LiNbO3 Surface Acoustic Wave Devices with Sputtered SiO2 Over-Layers

SAW propagation characteristics, velocity and temperature coefficient of delay (TCD) of a 128° Y-X LiNbO 3 SAW device integrated with an over-layer of rf magnetron sputtered SiO2 film have been studied. A deviation in the experimental observations with respect to the theoretical calculations on the layered structure SiO 2 /LiNbO 3 are identified mainly due to the difference in the material parameters of the deposited SiO 2 film. Influence of deposition conditions on the materials parameters of SiO 2 thin film have been studied, and the representative values of density, dielectric constant, elastic constants (C 11 and C 44 and their temperature coefficients have been determined, required for the design of a temperature stable SAW device.

Temperature stable LiNbO3 surface acoustic wave device with diode sputtered amorphous TeO2 over-layer

Amorphous TeO2 thin film, sputtered in the O2+Ar(25%+75%) gas environment using a metallic tellurium target, has been identified as an attractive negative temperature coefficient of delay (TCD) material that can yield a temperature stable device when combined with a surface acoustic wave (SAW) device based on positive TCD material such as LiNbO3. The influence of amorphous TeO2 over-layer on the SAW propagation characteristics (velocity and temperature coefficient of delay) of the SAW filters (36 and 70 MHz) based on 128° rotated Y-cut X-propagating lithium niobate (128° Y-XLiNbO3) single crystal has been studied. It is found that 0.042λ thick TeO2 over-layer on a prefabricated SAW device operating at 36 MHz centre frequency, reduces the TCD of the device from 76ppm°C−1 to almost zero (∼1.4ppm°C−1) without deteriorating its efficiency and could be considered as a suitable alternative for temperature stable devices in comparison to conventional SiO2 over-layer.

Comparison of Conductometric Gas Sensitivity of Surface Acoustic Wave Modes in Layered Structures

Properties of propagation modes for a layered ZnO/XZ LiNbO3 surface acoustic wave sensor have been investigated both theoretically and experimentally. By calculating the effective permittivity function, it was shown that after the ZnO deposition two distinct propagation modes have been generated: a Rayleigh and a shear horizontal. A layer of InOx was deposited to provide a conductometric sensing mechanism to NO2. It was found that the sensor is at least one order of magnitude more sensitive when operating in Rayleigh mode than in the shear horizontal mode. This sensitivity was found to be in good agreement with calculations for low concentrations of NO2, however discrepancies were observed for higher concentrations.

Interaction of surface acoustic waves and ultraviolet light in ZnO films

The frequency response of a 37 MHz bulk LiNbO3 surface acoustic wave (SAW) filter with a 200-nm-thick ZnO overlayer exhibited a downshift in the frequency with ultraviolet (UV) light due to acoustoelectric interactions between the photo-generated carriers in the semiconducting ZnO and the surface acoustic waves. In contrast, a 36 MHz ZnO thin film SAW delay-line with insulating ZnO films exhibited an upshift in the frequency. The response was more pronounced at higher harmonics (130–315 MHz) and was attributed to changes in the elastic/dielectric properties in the upper surface layer of ZnO. A linear change in the frequency with UV intensity shows immense applicability for wireless ultraviolet sensor applications.