ST-cut Quartz Research Articles

Enhancing Magnetoelastic Coupling in Shear Surface Acoustic Waveguide Based on ST-Cut Quartz Substrate and Ni Thin Films With Uniaxial Magnetic Anisotropy Induced by Thermal Annealing

Enhancing Magnetoelastic Coupling in Shear Surface Acoustic Waveguide Based on ST-Cut Quartz Substrate and Ni Thin Films With Uniaxial Magnetic Anisotropy Induced by Thermal Annealing

Room temperature operating formaldehyde sensor based on n-type ZnO functionalized surface acoustic wave resonator

In this investigation, Surface Acoustic Wave (SAW) formalin gas sensor is explored for low-level formalin gas sensing applications. The formalin gas sensor consists of ST-cut quartz as a base substrate material, interdigitated transducer (IDT) electrodes, reflectors and gas sensing n-ZnO thin film coated on top of the SAW resonator. Nano-structured optimal n-ZnO thin film was deposited as a gas sensing layer. It is noted that the sensor response was not affected by relative humidity and found stable. Formalin gas concentration was established in the controlled process chamber environment. The sensor response was measured at room temperature (25 °C) and relative humidity was 50 % during the experiment. Experimental data shows that return loss peak was shifted towards down side, return loss was better when formalin content (0–8 ppm) was increased in the process chamber. In order to understand, the underlying electrical sensing mechanism, modified Butterworth-Van Dyke (mBVD) equivalent circuit model was developed using Advanced Design System (ADS) software. This model provides the insights about change in electrical behaviour of sensor when it is exposed to relative gas content. The fitted theoretical model follows the experimental data, which indicate the goodness of the mBVD model and curve fitting. The highest frequency down-shift was observed 10.5 kHz due to formalin gas content of 8.0 ppm. Motional arm is mainly influenced by the formalin gas exposure. Motional arm resistance (Rm) and inductance (Lm) was also influenced by the formalin gas content and found to increase by the formalin gas content and mainly accountable for gas sensing behaviour. It is also noted that static arm is not influenced by gas content and only motional arm is accountable for gas sensing behaviour. Highest sensitivity (S) was 1.3125 kHz/ppm and limit of detection (LOD) was 80 ppb. This new kind of formalin sensor is low cost, reliable, robust sensor and highly useful for room temperature operating formalin gas sensor applications.

Fabrication of Surface Acoustic wave resonator as Acousto-optic Modulator

Acousto-optic modulation techniques are gaining edge in diverse applications in the area of agriculture, entertainment and defense. Present work focuses on indigenously developed pump probe technique to study the acousto-optic modulation using surface acoustic wave (SAW) device. For this study, SAW device has been fabricated on ST-cut quartz that is an optically nonlinear piezoelectric material. Coupling of acoustic wave with optical wave has been monitored and a visible modulation in the intensity of probe laser beam has been obtained. A clear shift in the value of probe intensity (∼12 μW) is observed when surface acoustic waves are excited. Angular rotation of the fabricated SAW device under pump probe microscopy shows the periodicity of the nonlinearity in substrate while acoustic wave is propagating in it. The effect of variation in the intensity of pump laser beam on the acousto-optic modulation is also studied. The acousto-optic modulation behavior observed in surface acoustic devices in the present study demonstrates the possible application in telecommunication for signal modulation and in spectroscopy for frequency control.

Giant spin-vorticity coupling excited by shear-horizontal surface acoustic waves

A non-magnetic layer can inject spin-polarized currents into an adjacent ferromagnetic layer via spin vorticity coupling (SVC), inducing spin wave resonance (SWR). In this work, we present the theoretical model of SWR generated by shear-horizontal surface acoustic wave (SH-SAW) via SVC, which contains distinct vorticities from well-studied Rayleigh SAW. Both Rayleigh- and SH-SAW delay lines have been designed and fabricated with a Ni81Fe19/Cu bilayer integrated on ST-cut quartz. Given the same wavelength, the measured power absorption of SH-SAW is four orders of magnitudes higher than that of the Rayleigh SAW. In addition, a high-order frequency dependence of the SWR is observed in the SH-SAW, indicating SVC can be strong enough to compare with magnetoelastic coupling.

Study on Tensile and Compressive Bending Deformation Sensor Based on Surface Acoustic Wave

SAW sensors are becoming interesting in the field of strain and stress detection applications. The strain of complex structures can be divided into a combination of local surface tension and compression, hence it is pretty important that study the detection of tension and compression for the analysis of complex structures. Here, we fabricated two SAW sensors based ST-cut quartz (78.65 MHz and 157.1 MHz) through photo-lithography and wet-etching processes and focused on their comparative analysis for the bending displacement and strain testing with the performance of the sensor sensitivity studied. The SAW-IDT10 and SAW-IDT5 sensor showed the maximum bending displacement sensitivity of ∼1.9369 kHz mm−1 and ∼4.3887 kHz mm−1, respectively. Additionally, the SAW-IDT5 sensor exhibited up to 2 times higher sensitivity (1570 kHz/%) than that of SAW-IDT10 sensor (786 kHz/%) under the same bending strain conditions. And the SAW-IDT5 and the SAW-IDT10 have both 0.99 and 1 tensile and compression strain gauge factors. Thus SAW sensors with high operating frequency have a higher frequency shift response in detecting micro-strain. Meanwhile, negative frequency shift response to tension and positive frequency shift response to compression of SAW sensors can be used to classify structural deformation in a complex environment in the future.

Viscous loading effect on the transference of Love type waves In piezomagnetic layered structure

The present study outlines a theoretical model which examines the propagation of Love-type waves in a layer of piezomagnetic material (Terefnol-D) over an elastic substrate (ST-cut Quartz) immersed in a viscous liquid of finite thickness. Governing equations are framed separately for each media by using the concept of the Sturm–Liouville Problem. Frequency relations are derived in complex form for both the magnetically open and short cases and subsequently result in two nonlinear equations. Mathematica 9.0 software is used to solve the acquired equations. The objective of this study is to observe the effect of the presence of the viscous/Newtonian liquid layer on the velocity profile of the Love-type waves propagating through the PM layer. Relevant graphs are inflicted to mark the influence of viscosity and thickness of the liquid layer on the dispersive curves of the considered wave. The outcomes of this study may assist in the design and optimization of various sensors and Love-wave-based devices operating in contact with viscous/Newtonian liquid.

Hydrophobic metal organic framework for enhancing performance of acoustic wave formaldehyde sensor based on polyethyleneimine and bacterial cellulose nanofilms

A surface acoustic wave (SAW) formaldehyde gas sensor was fabricated on a 42° 75′ ST-cut quartz substrate, with a composite sensing layer of zeolitic imidazolate framework (ZIF)-8 on polyethyleneimine (PEI)/bacterial cellulose (BC) nanofilms. The addition of snowflake-like ZIF-8 structure on the PEI/BC sensitive film significantly improves the hydrophobicity of the SAW sensor and increases its sensitivity to formaldehyde gas. It also significantly increases surface roughness of the sensitive film. The hydrophobic nature of ZIF-8 prevents water molecules from entering into the internal pores of the BC film, thereby avoiding a significant mass loading caused by humidity when the sensor is used to detect low-concentration formaldehyde gas. The Zn2+ sites at the surface of ZIF-8 improves the sensor's response to formaldehyde gas through enhanced physical adsorptions of gas molecules. Experimental results show that the ZIF-8@PEI/BC SAW sensor has a response (e.g., frequency shift) of 40.3 kHz to 10 ppm formaldehyde gas at 25 °C and 30% relative humidity (RH). When the relative humidity is increased from 30 to 93%, the response of the sensor only varies ~ 5%, and the change in response is negligible at medium humidity levels (~ 50 to 60% RH).

Dynamic humidity response of surface acoustic wave sensors based on zinc oxide nanoparticles sensitive film

ZnO nanoparticles/quartz surface acoustic wave (SAW) humidity sensors were fabricated, and their sensing performance was investigated. The pristine ZnO deposited on ST-cut quartz substrates by radio frequency magnetron sputtering is nanoparticles with grain sizes of 20–50 nm. The comparative analysis for humidity sensing applications of SAW-Love devices based on ZnO sensitive layers with different deposition pressures (0.25 Pa, 0.5 Pa, 1.0 Pa) was conducted, and their properties such as sensor sensitivity, response and recovery were studied. The sensors exhibit a good sensitivity in relative humidity (RH) from ~ 1% RH to 95% RH. Rayleigh mode and Sezawa mode frequency responses of the sensors increase with increasing humidity. The Sezawa mode shows 2–3 times higher humidity sensitivity than its Rayleigh mode counterpart for different RH. Rayleigh and Sezawa mode of 0.5 Pa ZnO nanoparticles-based SAW-Love sensor obtains a higher average sensitivity of 237.4 Hz/% RH and 388.1 Hz/% RH, respectively. Furthermore, the measured response frequencies values decrease rapidly and returned to near the initial state after moisture off. This comparative study demonstrates that the SAW-Love based on Sezawa mode has a great potential for applications in chemo-sensors.

Surface Acoustic Wave DMMP Gas Sensor with a Porous Graphene/PVDF Molecularly Imprinted Sensing Membrane.

In this paper, surface acoustic wave (SAW) sensors containing porous graphene/PVDF (polyvinylidene fluoride) molecularly imprinted sensitive membrane for DMMP gas detection were investigated. A 433 MHz ST-cut quartz SAW resonator was used to convert gas concentration changes into frequency shifts by the sensors. The porous graphene/PVDF film was fabricated on the sensor’s surface by using the tape-casting method. DMMP molecules were adsorbed on the porous structure sensing film prepared by the 2-step method to achieve the specific recognition effect. The sensitivity of the sensor could reach −1.407 kHz·ppm−1. The response time and recovery time of the SAW sensor with porous graphene/PVDF sensing membrane were about 4.5 s and 5.8 s at the concentration of 10 ppm, respectively. The sensor has good anti-interference ability to most gases in the air.

Gas pressure measurement using micro-corona-discharging effect in surface acoustic wave resonators

This paper reports a gas pressure sensor using surface acoustic wave resonator (SAWR) based on both the field-induced electron emission and the micro-corona-discharging (MCD) phenomena. With the micron-scale finger-gap of electrodes covered with SiO2 passivation layer, the enhanced field-effect emission (FEE) at electrodes result in the micro-corona-discharging and thus the change in the dynamic resistance of SAWR. A high Q-factor SAWR was fabricated on ST-cut quartz substrate using microelectronics processing technology, and the gas-pressure-dependent return-loss was tested, and the MCD theory and the equivalent circuit model of SAWR were used to analyze the test results. Under argon pressure range from 0 to 601 kPa, the dynamic resistance of the SAWR varies from 24.569 to 41.589 Ω at 25 °C. The resistance rate reaches 69.3%, which is far higher than that of traditional piezoresistive pressure sensors. At the same time, the oxygen pressure was also tested by the SAWR as a comparison. The SAW-based gas pressure sensors have the potential for measurement of the super-high pressure.

One-Dimensional Bi2S3 Nanobelts-Based Surface Acoustic Wave Sensor for NO2 Detection at Room Temperature

Surface acoustic wave (SAW) devices show promising applications for highly sensitive gas sensors for continuously monitoring of hazardous and flammable gases when integrating with specifically designed sensing materials. Improving the SAW sensor's responses by using nanostructure sensing materialshas become a research hot topic in recent years. In this work, we presented a SAW room temperature NO2 gas sensor with high sensitivity using one-dimensional (1D) Bi2S3 Nanobelts as the sensing materials. SAW devices with thecentral frequency of ~200 MHz were fabricated on ST-cut quartz substrate as the sensing platform. The Bi2S3 Nanobelts were synthesized by solvothermal method and deposited onto SAW sensors using a spin-coating technology. The response of the prepared SAW gas sensors was 2 kHz when subjected to 10 ppm NO2 even at room temperature. Moreover, the sensor shows good selectivity, reversibility, and stability. The sensing mechanism of one-dimensional Bi2S3 nanobelts-based SAW sensors for NO2 detection was also be discussed.

Temperature compensated magnetic field sensor based on love waves

A temperature compensated magnetic field sensor based on the combination of CoFeB ferromagnetic thin films and Quartz/ZnO Love waveguide platform is developed and optimized. The Love wave is a shear horizontal guided wave and therefore provides an optimal interaction with magnetization in the magneto-elastic thin film resulting in higher acoustic wave magneto-elastic coupling compared to the conventional Rayleigh wave based devices. ST-cut Quartz was chosen as substrate, ZnO as insulating layer for Love wave generation and temperature coefficient of frequency (TCF) compensation and CoFeB as the magnetostrictive layer sensitive to magnetic field. Experimental results show a magneto-acoustic sensitivity of 15.53 MHz T−1 with almost zero TCF.

Bacterial cellulose coated ST-cut quartz surface acoustic wave humidity sensor with high sensitivity, fast response and recovery

A Love mode surface acoustic wave (SAW) humidity sensor based on bacterial cellulose (BC) coated ST-cut quartz was developed in this study. The BC film is composed of ultrafine interwoven fibers to form a highly porous network, and its surface contains a large amount of hydroxyl groups, which significantly improve the adsorption capability of SAW sensing layer for water molecules. This results in significant mass loading effects and enhanced responsivity of the SAW sensor. The resonant frequency of the sensor changes linearly with RH at lower relative humidity (RH) values (e.g. RH < 30%), but when RH > 80%, an exponential increase in frequency shift as a function of RH is obtained due to the enhanced mass loading effect. A frequency shift of 89.8 kHz was measured using a sensor with a BC film with a thickness of 148 nm thick when the RH was increased from 30% to 93%. The frequency of the sensor can be fully shifted back to the original reading when the RH was returned back to 30%, with the response and recovery times of 12 s and 5 s, respectively. The SAW sensor also exhibits good short-term repeatability and long-term stability for humidity sensing.

Highly selective and label-free Love-mode surface acoustic wave biosensor for carcinoembryonic antigen detection using a self-assembled monolayer bioreceptor

A Love-mode surface acoustic wave (SAW) biosensor based on ST-cut quartz was developed for highly selective and label-free detection of carcinoembryonic antigen (CEA). The delay line area of an interdigital transducer (IDT) based SAW device was coated with gold and then chemically modified through thioglycolic acid–EDC/NHS reaction mechanism. A self-assembled monolayer of anti-CEA was further immobilized on the bioreceptors through the coupling layer. The biosensing capability of the SAW device was evaluated using solutions of CEA with various concentrations and limit of detection was obtained at 0.31 ng/ml of CEA, which is better than the results reported by the literatures available for CEA detection using SAW device. The real-time detection capability of the biosensor was evaluated using clinical serum samples and selectivity was evaluated using mixed solutions of CEA with other common tumor marking proteins. Long-term stability of the biosensor was also evaluated over a period of 30 days and the immunoassay response has shown only 8% decrease in performance within the whole period. The binding of CEA onto the bioreceptor was evaluated through Langmuir and Freundlich sorption isotherm kinetic studies as well.

Magnetic anisotropy controlled FeCoSiB thin films for surface acoustic wave magnetic field sensors

Surface acoustic wave magnetic field sensors based on guided Love waves using the ΔE effect of a magnetostrictive thin film have been shown to be promising candidates for the measurement of weak fields at low frequencies as required for biomagnetic applications or as current sensors benefitting from the large dynamic range and bandwidth. The deposition of soft magnetic films with high magnetostriction is, however, more challenging on piezoelectric substrates such as quartz than on silicon. Thermally induced anisotropic expansion during the deposition process or during post-deposition magnetic field annealing leads to uniaxial stresses acting on the films, which makes the precise control of magnetic anisotropy difficult. Accordingly, this work analyzes the influence of the deposition process and heat treatment on the performance of Love wave devices. ST-cut quartz based delay line surface acoustic wave sensors with a SiO2 guiding layer are employed, and a 200 nm layer of amorphous magnetostrictive (Fe90Co10)78Si12B10 is used as the sensitive element. Magneto-optical imaging is performed for magnetic domain characterization, and the sensor performance is characterized in terms of bias field dependent phase sensitivity and frequency dependent phase noise. By performing a low temperature deposition in an external magnetic field, considerable improvement in limits of detection at biomagnetic relevant frequencies down to 70 pT/Hz at 10 Hz and 25 pT/Hz at 100 Hz is achieved.

Surface acoustic wave ammonia sensor based on ZnS mucosal-like nanostructures

Mucosal-like ZnS nanostructures were synthesized on surface of ST-cut quartz surface acoustic wave (SAW) device using a chemical bath deposition method for ammonia sensing applications. Results showed the SAW device with ZnS mucosal nanostructures achieved a good sensitivity, e.g., with a frequency shift of ~190 Hz upon exposure to 1 ppm ammonia gas. This is mainly attributed to the large specific surface areas and more active sites on the surfaces of the ZnS mucosal nanostructures. Selectivity of the SAW device with the ZnS mucosal nanostructure for ammonia sensing was excellent in comparisons with those for other types of gases such as hydrogen sulfide, hydrogen, nitrogen dioxide, carbon monoxide and ethanol.

Integrated sensing layer of bacterial cellulose and polyethyleneimine to achieve high sensitivity of ST-cut quartz surface acoustic wave formaldehyde gas sensor

Surface acoustic wave (SAW)-based formaldehyde gas sensor using bi-layer nanofilms of bacterial cellulose (BC) and polyethyleneimine (PEI) was developed on an ST-cut quartz substrate using sol-gel and spin coating processes. BC nanofilms significantly improve the sensitivity of PEI films to formaldehyde gas, and reduces response and recovery times. The BC films have superfine filamentary and fibrous network structures, which provide a large number of attachment sites for the PEI particles. Measurement results obtained using in situ diffuse reflectance Fourier transform infrared spectroscopy showed that the primary amino groups of PEI strongly adsorb formaldehyde molecules through nucleophilic reactions, thus resulting in a negative frequency shift of the SAW sensor due to the mass loading effect. In addition, experimental results showed that the frequency shifts of the SAW devices are determined by thickness of PEI film, concentration of formaldehyde and relative humidity. The PEI/BC sensor coated with three layers of PEI as the sensing layer showed the optimal sensing performance, which had a frequency shift of 35.6 kHz for 10 ppm formaldehyde gas, measured at room temperature and 30 % RH. The sensor also showed good selectivity and stability, with a low limit of detection down to 100 ppb.

Love-wave devices with continuous and discrete nanocrystalline diamond coating for biosensing applications

The integration of diamond layers brings biocompatibility and enhanced stability of biomolecules to Love wave devices for promising biosensor applications. Love-Wave Surface Acoustic Wave (LW-SAW) devices consisting of an ST-cut quartz substrate with a silicon oxide layer coated by a thin diamond layer have been fabricated. The effect of nucleation and growth of diamond on the properties of LW-SAW devices was studied. The Love-wave phase velocity was shown to be affected by the diamond coating and dependent on its thickness. Experimental results are in a good agreement with simulations carried out with COMSOL Multiphysics software. Deposition of isolated diamond grains results in a reduction in velocity in the Love waves, which is attributed to a mass loading effect. Conversely, coalesced diamond layers increase the stiffness of the surface, which results in faster propagation of the Love waves. Improved entrapment of the Love waves in the guiding layer was observed in the case of isolated diamond grains, which should ensure higher sensitivity for this type of coating. Diamond coated LW-SAW devices can be used for biosensing applications with appropriated functionalization of the diamond surface.

Highly sensitive and selective Love mode surface acoustic wave ammonia sensor based on graphene oxides operated at room temperature

It is crucial to develop highly sensitive and selective sensors for ammonia, one of the most common toxic gases which have been widely used in pharmaceutical, chemical, and manufacturing industries. In this study, graphene oxide (GO) film was spin-coated onto surfaces of ST-cut quartz surface acoustic wave (SAW) devices with a resonant frequency of 200 MHz for ammonia sensing. The oxygen-containing functional groups (such as hydroxyl and epoxy ones) on the surface of GO film strongly absorb ammonia molecules and thus increase the film stiffness. This is attributed to the main ammonia sensing mechanism of the Love mode SAW devices, which show not only a positive frequency shift of 620 Hz for 500 ppb ammonia gas, but also an excellent selectivity (as compared to other gases such as H2, H2S, CO, and NO2) and a good reproducibility, operated at room temperature of 22 °C.

Highly sensitive ultraviolet sensor based on ZnO nanorod film deposited on ST-cut quartz surface acoustic wave devices

A highly sensitive surface acoustic wave (SAW) ultraviolet (UV) detector operated at room temperature was developed using a sensing layer of zinc oxide (ZnO) nanorods (NRs) grown on ST-cut quartz using a hydrothermal method. Under illumination of the UV light with a wavelength of 365 nm and an intensity of 6 μW cm−2, the resonant frequency of the SAW UV sensor based on ZnO NRs/ZnO nanofilm structure was decreased by ~200 Hz, mainly due to electroacoustic effect. The estimated enhancement in the sensitivity based on the experimental results is ~3.5 folds compared to a device with only a thin nanolayer ZnO film. Meanwhile, density of ZnO NRs over the ZnO seed layer was also investigated and an optimum design was proposed.