F. Sarry

AlN/ZnO/diamond structure combining isolated and surface acoustic waves

In order to generate surface acoustic waves (SAW) and waveguiding layer acoustic waves (WLAW) simultaneously, a multilayer structure of AlN/ZnO/diamond has been proposed. This structure has been investigated theoretically (two-dimensional finite element method) and experimentally. The nature of the excited modes and their order were identified by modeling and confirmed experimentally by measuring the frequency response of the device in the air and in contact with the liquid. The demonstrated structure can be used to realize a packageless sensor or resonator, using the WLAW alone. A temperature compensated gas or liquid sensor can also be realized by combined usage of the SAW and the WLAW.

Innovative surface acoustic wave sensor for accurate measurement of subatmospheric pressure

An original application for surface acoustic wave (SAW) subatmospheric pressure sensor was developed to measure pressure below 100mTorr with very high precision. The basic operating principles and the most significant experimental results of the sensor are presented here. A simple theoretical model is proposed. This sensor provides an efficient measuring solution in a wide range of subatmospheric pressure, which has been inaccessible in past by conventional diaphragm-based SAW sensors.

Surface Acoustic Wave Device with Reduced Insertion Loss by Electrospinning P(VDF–TrFE)/ZnO Nanocomposites

Surface acoustic wave (SAW) devices have been utilized for the sensing of chemical and biological phenomena in microscale for the past few decades. In this study, SAW device was fabricated by electrospinning poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF−TrFE)) incorporated with zinc oxide (ZnO) nanoparticles over the delay line area of the SAW device. The morphology, composition, and crystallinity of P(VDF−TrFE)/ZnO nanocomposites were investigated. After measurement of SAW frequency response, it was found that the insertion loss of the SAW devices incorporated with ZnO nanoparticles was much less than that of the neat polymer-deposited device. The fabricated device was expected to be used in acoustic biosensors to detect and quantify the cell proliferation in cell culture systems.

Theoretical and Experimental Identification of Love Wave Frequency Peaks in Layered Structure ZnO/Quartz SAW Device

In this paper, the layered structure ZnO/Quartz (90deg rotated ST-cut) is investigated theoretically and experimentally. Both waves, Rayleigh and Love, are analyzed. Dispersion curves of phase velocities, electromechanical coupling coefficient (K 2) and temperature coefficient of frequency (TCF) were calculated as a function of normalized thickness ZnO film (kh ZnO = 2pih ZnO /lambda) and the optimum value of h ZnO was determined for experimental study. Experimental results combined with simulation lead to clearly identify the generated waves and their higher modes in this structure except the mode 0 that shows comparable velocity for both Rayleigh and Love waves. The identification of the wave type was performed by studying the frequency response of the device with or without a droplet of water in the wave path. We also demonstrate that the highest elastic velocity is obtained for the mode 1 of the Love wave. This Love wave mode exhibits very interesting electrical characteristics, good K 2, high-frequency rejection, low TCF, and very low attenuation in liquid making it very attractive for gas and liquid sensor applications.

Pressure sensitivity of Rayleigh and Sezawa wave in ZnO/Si[001] structures

In this study we investigate the pressure effect on the guided waves in ZnO/Si[001] structures. Our experimental results reveal a strong dependence of the pressure sensitivities on the depth penetration of the waves. This dependence is explained by studying the effect of layer thickness and wavelength on the pressure sensitivity of Sezawa and Rayleigh wave. The measured results shows that strain compensation can be achieved in ZnO/Si structure. A theoretical results obtained by considering strain effect in silicon substrate alone are compared with measurements and show a good agreement in the case of Sezawa wave. Concerning the Rayleigh wave, the ZnO film effect should be taken in consideration in theoretical formulation.

Zero TCF ZnO/quartz SAW structure for gas sensing applications

A zero TCF SAW device was developed for a temperature selfcompensated gas sensor. The device is based on the combination of a ZnO film and a quartz substrate with the appropriate cut and propagation angle. The developed structure IDT/ZnO/quartz, using ST-cut 35/spl deg/ X propagation quartz, presents a zero power flow angle, a very low temperature coefficient of frequency (TCF) value, and a relatively high electromechanical coupling factor. In this structure, the ZnO film is used simultaneously as gas sensitive layer and as TCF compensation layer. As ZnO is a very promising material for the application as gas sensor, the main interaction mechanisms between the acoustic wave and gaseous species (CO/sub 2/, ethanol, butanol) are reviewed. Detailed results for the sensitivity of different acoustic modes are presented.

4E-2 Theoretical and Experimental Study of the Differential Thermal Expansion Effect on the TCD of Layered SAW Temperature Sensors Application to Aluminum Nitride Based Layered Structures

In this paper, we show that the stress and strain fields induced in a layered SAW structure by the thermal expansion of the different layers must be taken into account to compute the global structure temperature coefficient of delay (TCD). Experimental and numerical results are provided. The numerical model is described. It is based at the same time on the well- known Campbell and Jones method, the Bolotin equation and a simple way to approximate the strain field in a double layer structure. The model is then applied to test three sets of temperature coefficients for A1N thin film elastic constants. The comparison between AIN/Sapphire already published experimental data and theoretical results leads to the selection of one of the three sets. The recently released A1N 3ld order elastic constants are used here to compute the thermal strain effect. Once chosen, the set is used to compute the TCD of AIN/Diamond structures. The theoretical results are compared with new experimental data. The observed discrepancies are discussed.

Development of SAW pressure sensor using ZnO/Si structure

SAW devices have been shown to be suitable for many sensor applications. One of these applications is the pressure sensor. In this study, we present our ZnO deposition process. We also investigate the performance of SAW pressure sensors formed with a ZnO/Si(001) structure. The pressure sensitivities of the Rayleigh mode as well as the Sezawa mode are studied as a function of normalized thickness (kh=2/spl pi/h/sub ZnO///spl lambda/). The experimental results show an opposite strain effect in the ZnO layer and Si substrate. A theoretical approach was developed to show the particle displacement. For a low kh/sub ZnO/ value, the ZnO and Si medium contribute to the sensor sensitivity. For higher kh/sub ZnO/ values, the particle displacement is mainly confined in the ZnO layer. This confirmed the opposite behaviors of the sensitivity with the kh/sub ZnO/ value. Enhancement of the SAW sensitivity is also presented by the development of a pressure membrane based on the developed device.

High SAW velocity and high electromechanical coupling coefficient with the new three layered structure: ZnO/AlN/diamond

A new diamond based SAW device layered structure, combining high acoustic velocity (V/spl phi/) and high electromechanical coupling coefficient (K/sup -/), is investigated for GHz-band applications. In fact, to overcome the trade-off relationship between V/spl phi/ and K/sup 2/, we propose the use of a three-layer structure ZnO/AlN/diamond that combine the advantages of both piezoelectric materials: high K/sup 2/ of ZnO and high velocity of AlN. A theoretical study based on the Campbell and Jones model was performed to calculate the phase velocity and K/sup 2/ dispersion curves of the Rayleigh mode; its higher modes as well as the leaky waves generated in this structure. Three configurations depending on IDT position in the structure: ZnO surface, ZnO/AlN or AlN/diamond interfaces were calculated considering various thicknesses of ZnO and AlN layers. Both high values of K/sup 2/ larger than 4%, and of V/spl phi/ more than 15 km/s are expected on this new structure according to the theoretical results.

A study of surface acoustic wave pressure sensor in ZnO/quartz structure

It was previously reported that a Rayleigh wave propagating on a zinc oxide film has a relatively low temperature coefficient of frequency (TCF) and a large electromechanical coupling factor (K/sup 2/). In this study we investigate the performance of a SAW pressure sensor using ZnO/quartz structure. Y-cut is preferred in our study due to its positive TCF value permitting a zero TCF when combined with ZnO. ZnO thickness was determined to achieve a zero TCF and to improve the electromechanical coupling coefficient (K/sup 2/=1%) seven times higher than that of quartz Y-cut X propagating direction. The development of the optimal structure to be used is presented followed by the operating frequency effect and ZnO film contribution to the pressure sensitivity.