ST-cut Quartz Research Articles

SU-8 Guiding Layer for Love Wave Devices.

SU-8 is a technologically important photoresist used extensively for thefabrication of microfluidics and MEMS, allowing high aspect ratio structures to beproduced. In this work we report the use of SU-8 as a Love wave sensor guiding layerwhich allows the possibility of integrating a guiding layer with flow cell during fabrication.Devices were fabricated on ST-cut quartz substrates with a single-single finger design suchthat a surface skimming bulk wave (SSBW) at 97.4 MHz was excited. SU-8 polymer layerswere successively built up by spin coating and spectra recorded at each stage; showing afrequency decrease with increasing guiding layer thickness. The insertion loss andfrequency dependence as a function of guiding layer thickness was investigated over thefirst Love wave mode. Mass loading sensitivity of the resultant Love wave devices wasinvestigated by deposition of multiple gold layers. Liquid sensing using these devices wasalso demonstrated; water-glycerol mixtures were used to demonstrate sensing of density-viscosity and the physical adsorption and removal of protein was also assessed usingalbumin and fibrinogen as model proteins.

A micro rate gyroscope based on the SAW gyroscopic effect

We propose a micro rate gyroscope (MRG) based on the surface acoustic wave (SAW) gyroscopic effect for extremely high-shock military applications. We not only derived theoretically the SAW gyroscopic gain factor in a ST-cut quartz by introducing a wave velocity ratio and the perturbation method, but also verified this gain factor by experiment. The proposed SAWMRG, which consists of two delay-line oscillators, operates as a differential scheme. To estimate an inherent insertion loss, we adopted the equivalent circuit model in the design process of the delay line. The 9 × 9 mm2 SAWMRG was fabricated on a ST-cut quartz and loaded into a specially designed low temperature co-fired ceramic (LTCC) package to ensure good RF characteristics. The center frequency and the insertion loss of the delay line are measured at 98.6 MHz and 15.2 dB, respectively. We evaluated the performance of the SAWMRG, using a rate table and stochastic noise analysis, revealing a sensitivity of 0.431 Hz deg−1 s−1 in the angular rates up to 2000 deg s−1 and a white noise of 0.55 deg s−1 Hz−1/2, respectively. Consequently the feasibility of the proposed SAWMRG was verified through a set of performance evaluations, confirming the theoretical predictions.

Coupling coefficient determination based on simulation and experiment for ST-Cut quartz saw delay-line response

This paper used the theoretical calculation to simulate the response of surface acoustic wave (SAW) delay-line on quartz substrate and then compared to the experimental results. The coupling coefficients affected by operation frequency as well as aperture length were built up by experimental data analysis. Based on the experimental values of these two parameters, the device-coupling coefficient was defined. This method is new and we has not found in other document. In addition, it improves the simulation results and helps the analysis process more comprehensive. This study developed ST-cut quartz SAW delay-lines with gold inter-digital transducer (IDT) operating at 39.5 and 78.9 MHz corresponding to 80 and 40 μm of the wavelength. The differences of aperture length in IDT designs were investigated to help understand the effects of this parameter on SAW sensor response. The maximum error of operating frequency is 1%; of insertion loss is 4.25 and 3.13% for bandwidth. The larger of the insertion loss error is expected owing to the result of mathematical approximation and the quality of quartz substrate. The simulation results agree with the experimental results shows that the simulation method can apply to quartz-based SAW delay-line as well as for other material based SAW delay-line applications. The results help understand more about the parameters which effect the insertion loss, operating frequency and bandwidth. It should be very useful for IDT design in specific, SAW sensor and SAW filter design in general.

Numerical Development of ZnO/Quartz Love Wave Structure for Gas Contamination Detection

Love wave structures are encouraging devices for sensing applications in gaseous or liquid media because of their high sensitivity. In this paper, we first investigate basic properties of a ZnO/quartz Love wave device by the use of theoretical considerations in order to get a good gas sensor. Second, experimental results of the developed structure, ZnO(2.1 mum)/90deg ST-cut quartz, confirm the suitable characteristics, including temperature compensation, high electromechanical coupling coefficient, and good sensitivity to mass loading effect. We finally characterize the gas effect on the photoresist Shipley S1805 with the above structure, and thus we confirm our approach

Characteristics of strontium-doped ZnO films on love wave filter applications

The effect of dopant concentrations in strontium-doped ZnO films on Love wave filter characteristics was investigated. Strontium-doped ZnO films with a c-axis preferred orientation were grown on ST-cut quartz by radio frequency magnetron sputtering. The crystalline structures and surface morphology of films were studied by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The electromechanical coupling coefficient, dielectric constant, and temperature coefficient of frequency of filters were then determined using a network analyzer. A uniform crystalline structure and smooth surface of the ZnO films were obtained at the 1–2 mol% strontium dopant level. The electromechanical coupling coefficient of the 1 mol% strontium-doped ZnO film reaches a maximum of 0.61%, and the temperature coefficient of frequency declines to + 12.87 ppm/°C at a 1.5 mol% strontium dopant level.

Polymer coating behavior of Rayleigh-SAW resonators with gold electrode structure for gas sensor applications

Results from systematic polymer coating experiments on surface acoustic wave (SAW) resonators and coupled resonator filters (CRF) on ST-cut quartz with a corrosion-proof electrode structure entirely made of gold (Au) are presented and compared with data from similar SAW devices using aluminium (Al) electrodes. The recently developed Au devices are intended to replace their earlier Al counterparts in sensor systems operating in highly reactive chemical gas environments. Solid parylene C and soft poly[chlorotrifluoroethylene-co-vinylidene fluoride] (PCFV) polymer films are deposited under identical conditions onto the surface of Al and Au devices. The electrical performance of the Parylene C coated devices is monitored online during film deposition. The PCVF coated devices are evaluated after film deposition. The experimental data show that the Au devices can stand up to 40% thicker solid films for the same amount of loss increase than the Al devices and retain better resonance and phase characteristics. The frequency sensitivities of Au and Al devices to parylene C deposition are nearly identical. After coating with soft PCFV sensing film, the Au devices provide up to two times higher gas sensitivity when probed with cooling agent, octane, or tetrachloroethylene.

A Study of Unknown Resonance near Upper Stop Band for 43.DEG. In-Plane Rotated ST-Cut Quartz SAW Resonator

An unknown resonance is studied, which exists near upper stop band of IDT reflection characteristics, for the 43° in-plane rotated ST-cut of quartz SAW resonator. In this study, we analyze the displacement loci of surface wave at first, and find that slight skew angles exist in them. Simple simulation model is introduced to analyze the phenomenon and anti-symmetric model of T matrix explains that phenomenon adequately.

AlN thin film as waveguide for shear acoustic waves

A set of shear acoustic waves in the 78–195MHz range composed of a surface skimming bulk wave and highly resolved shear acoustic plate modes has been simultaneously excited in a thin ST-cut quartz plate by means of transducers with a 1μm thick sputtered AlN thin film used as a waveguiding layer. The effect of coating the transducers face with AlN is shown to increase the propagation speed of the first 13 plate modes in the ST-cut quartz, but then to decreases the propagation speed of plate modes higher than the 14th.

Properties of pseudomode surface acoustic waves on ST-cut quartz substrates and the effects of the thicknesses of metallic films

The present study utilized an impedance matrix method to solve the properties of a surface acoustic wave (SAW) in a piezoelectric medium. By introducing complex wavenumbers, pseudo-SAWs (PSAWs) and high-velocity pseudo-SAW (HVPSAWs) with higher phase velocity and lower propagation loss can be achieved for certain propagation directions in ST-cut quartz. It is also found that, when a PSAW is excited on ST-cut 90°X propagation, the quartz substrate exhibits the characteristics of the existence of only the shear horizontal component, no spurious response, and zero-power flow angle (PFA). Combining a heavy-metal electrode such as gold (Au) of suitable thickness, the electromechanical coupling factor of PSAWs can be enhanced. The enhancement is about 2.5 times larger than that of conventional SAWs on an ST-X substrate with an aluminum (Al) electrode.

The influence of calcium doped ZnO films on Love wave sensor characteristics

The effects of different concentrations of Ca doped ZnO films crystalline structure on Love wave sensor characteristics were investigated in this research. Calcium doped ZnO films with c-axis preferential orientation have been grown on the ST-cut quartz substrate by RF magnetron sputtering technique. Crystalline structures and surface characteristics of films were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM); the sensitivity, electromechanical coupling coefficient, dielectric constant, and temperature coefficient of frequency of devices were measured. Sensor sensitivity increases obviously with increasing of Ca dopants but the sensitivity will be reduced when Ca over-doped.

CALCIUM AND STRONTIUM DOPED ZnO FILMS FOR LOVE WAVE SENSOR APPLICATIONS

ABSTRACT Ca and Sr doped ZnO films with c-axis prefer orientation have been grown on the ST-cut quartz substrate by RF magnetron sputtering technique. Crystalline structures and roughness characteristics of films were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effects of doping elements and concentrations on sensor's sensitivity were investigated. A suitable ZnO guiding layer for high sensitivity Love wave sensor applications could be obtained by tailoring the roughness. Smooth and over rough guiding layers decrease the sensitivity of Love wave sensor.

A study of Love wave devices in ZnO/Quartz and ZnO/LiTaO 3 structures

Love wave devices are very promising for sensing applications because of high sensitivity. In this paper, ZnO thin films doped with lithium (Li) and magnesium (Mg) were deposited on the 42°45′ ST-cut quartz and 36° YX-LiTaO 3 substrates by RF magnetron sputtering technique. XRD, SEM, and AFM measurements investigated characteristics of the films. Under different conditions such as doping content, layer thickness, and substrate temperature, the phase velocity, temperature coefficient of frequency, electromechanical coupling coefficient and sensitivity of Love wave devices in ZnO/Quartz and ZnO/LiTaO 3 structures are presented. The maximum sensitivities of ZnO/Quartz and ZnO/LiTaO 3 are much higher than the SiO 2/Quartz and SiO 2/LiTaO 3 structures reported.

Covalently anchored supramolecular monolayers on quartz surfaces for use in SAW sensors

Anchoring alkyl silane monolayers on quartz surfaces and consecutive derivatization steps, e.g. the addition of silanes and the immobilisation of calix[ n]arenes, were studied by FTIR–HATR-spectroscopy and atomic force microscopy. The entire technique of this two-dimensional chemistry was adapted to meet the favourable sensitivity of mass-sensitive SAW-devices based on ST-cut quartz substrates and gold interdigital electrodes working at 417 MHz. It leads to the successful detection of vapours, aromatic and halogenated hydrocarbons such as xylenes, toluene and tetrachloroethylene with the immobilised calix[4]- and calix[6]arenes. The sensors react to analyte changes within a few seconds and show a noise level that allows detection limits as low as a few part per million for xylenes.

A new type of acoustic modes of vibration of thin piezoelectric plates: Quasi-longitudinal normal modes

Using ST-cut quartz crystal plates as an example, a new type of normal modes of acoustic vibrations is described. The modes propagate along the x axis with a velocity close or equal to that of longitudinal bulk waves propagating in the same direction and have a longitudinal component of elastic displacement no less than two orders of magnitude greater than the two other components (the shear-horizontal and shear-vertical ones) throughout the whole plate thickness. The domain of existence of the quasi-longitudinal modes consists of a set of limited zones that contain the “allowed” values of the plate thickness H/λ (H is the plate thickness and λ is the wavelength) and are separated by “forbidden” zones corresponding to common Lamb modes. The closeness (or coincidence) of the velocities of a quasi-longitudinal mode in the plate and a longitudinal bulk wave in an unbounded crystal is a necessary but not sufficient condition for the existence of the aforementioned type of modes in ST,x quartz.

Study of structural and microstructural properties of AlN films deposited on silicon and quartz substrates for surface acoustic wave devices

Piezoelectric aluminum nitride thin films were deposited by reactive dc magnetron sputtering under various experimental conditions on a silicon (100) substrates. These films structural and microstructural properties were studied using x-ray diffraction (XRD), selected area electron diffraction (SAED), and transmission electron microscopy (TEM) in order to determine the optimum growth conditions that improve the piezoelectric coupling. A highly c-axis oriented AlN film (002) was identified from XRD and SAED. An average grain column size of about 40 nm was determined from TEM. The root-mean-square surface roughness measured using atomic-force microscopy was less than 7 nm. The optimum experimental parameters found for AlN deposition on Si(100) substrates were then extrapolated to its deposition on a ST-cut quartz substrate for the investigation of the influence of substrates on the surface acoustic wave (SAW) propagation. The AlN/Si and AlN/ST-quartz SAW devices were formed using the photolithography process. Their operating characteristics, phase velocity, temperature coefficient of frequency, and electromechanical coefficient (K2) were measured and analyzed. Experimental results show that the generalized SAW (GSAW) as well as the pseudosurface acoustic wave were excited in this structure. Their phase velocities are, respectively, 3245 m/s and 5117 m/s. The SAW device realized from the AlN/ST-cut quartz structure exhibits higher phase velocity and higher K2 compared to those formed on the ST-quartz substrate.

Acoustic wave immunosensing of Escherichia coli in water

This paper reports an experimental study of E. coli sensing based on surface-skimming-bulk-wave delay line device fabricated on ST-cut quartz. The sensor configuration consisted of an 87.7 MHz oscillator with the delay line as control element in its feedback loop. The antigen–antibody immunochemical reaction was employed on the acoustic wave device surface to generate mass loading and frequency shift. The sensor output was monitored by an RF spectrum analyzer. Highly specific sensing is demonstrated for E. coli cells up to 0.4 cells/μl in water. The methodology offers possibility for developing highly sensitive and fast E. coli sensors for testing of water potability.

Sensing properties of normal oscillatory modes of quartz plates

The responses (relative velocity variations Δv/v of normal (symmetric or asymmetric) Lamb and shear-horizontal modes of ST-cut quartz plates, whose thickness is comparable with the wavelength, is studied. Since modes of different orders n belonging to these two families have different propagation velocities vn, polarizations ui, and displacement distributions in depth H, they exhibit different responses to variations in the parameters of the plate (density, elastic moduli, thickness, and temperature) and to the loading of its surface by thin films (i.e., to surface adsorption). Results of numerical calculation of the responses to these parameters are corroborated by experiments on the effect of the plate temperature variation and the effect of adsorption of water vapor onto the plate surface.

Experimental study of Love wave devices with thick guiding layers

An experimental study of the insertion loss changes with mass and viscous liquid loading has been carried out for the first, second and third order modes of a polymer coated Love wave acoustic sensor. Devices were fabricated on ST-cut Quartz, coated with various thickness of polymer and operated at a fundamental frequency of 110 MHz. The effect of increasing the over-layer thickness was investigated and higher order Love wave modes were observed. A systematic study of insertion loss changes as a function of deposited mass was carried out for devices incorporating guiding layers of thickness up to 12 μm by depositing thin films of gold and tin on the propagation path. In addition, sensitivity to viscous loading was investigated on the first, second and third Love modes by applying solutions of poly(ethylene glycol) with increasing densities. The change in insertion loss of the higher order modes for both experiments is shown to be of the same order of magnitude as the first Love wave mode.

Temperature Stability of Surface Acoustic Wave Resonators on In-Plane Rotated 33° Y-Cut Quartz

ST-cut quartz has been widely used in surface acoustic wave (SAW) devices due to its good temperature stability. However, ST-cut SAW devices are still not as temperature stable as AT-cut quartz. Hence new SAW resonators with better temperature stability are needed. We present surface acoustic wave resonators on the in-plane rotated 33° Y-cut quartz with improved temperature stability. We calculated the frequency temperature characteristics of Rayleigh waves using the finite element method under the condition of Euler angle (0, 123, 39-44). The second-order temperature coefficients of less than -1.5×10-8/°C2 were achieved by calculations and experiments. Compared with the second-order temperature coefficients of ST-cut quartz (-3.4×10-8/°C2), these values are more than 50% smaller. The fabricated SAW resonators have good crystal impedance (resonance impedance) and Q-value.

Real time device for biosensing: design of a bacteriophage model using love acoustic waves

Love wave sensors (ST-cut quartz substrate with interdigital transducers, SiO 2 guiding layer and sensitive coating) have been receiving a great deal of attention for a few years. Indeed, the wave coupled in a guiding layer confers a high gravimetric sensitivity and the shear horizontal (SH) polarization allows to work in liquid media. In this paper, an analytical method is proposed to calculate the Love wave phase velocity and the gravimetric sensitivity for a complete multilayer structure. This allows us to optimize the Love wave devices design in order to improve their gravimetric sensitivity in liquid media. As a model for virus or bacteria detection in liquids (drinking or bathing water, food…) we design a model using M13 bacteriophage. The first step is the anti-M13 (AM13) monoclonal antibody grafting, on the device surface (SiO 2). The second step is an immunoreaction in between the M13 bacteriophage and the AM13 antibody. The Love wave device allows to detect in real time the graft of the AM13 sensitive coating, as well as the immobilization of the M13 bacteriophages. With a pH change, the M13 bacteriophages can be removed from the sensor surface, in order to be numerated as plaque forming unit (pfu). Results on the sensitivity of Love waves are compared with similar immunological works with bulk acoustic wave devices, and demonstrate the high potentialities of Love waves sensors.