Cinzia Caliendo

Sensitivity of a platinum-polyyne-based sensor to low relative humidity and chemical vapors

The sensitivity to relative humidity (RH) variations in the range 0%–90% of a platinum polyyne, namely poly-[1,4-dihexadecyloxy-2,5-diethynylbenzene-bis(triphenylphosphine) platinum(II)] (Pt-P-HDOB) membrane was investigated by means of a surface acoustic wave (SAW) based sensor. A thin film of polymeric membrane was spin deposited on the free surface of the device and the resulting acoustic velocity and attenuation perturbations allowed the acoustic characterization of the membrane by means of the perturbation theory. The SAW sensor was able to reveal even very low (<10% RH) humidity conditions at room temperature, with high reproducibility, repeatability and stability.

Advances in SAW-based gas sensors

This paper deals with some advances in surface acoustic wave (SAW) sensor research relating to the use of both a new chemically interactive material (metal porphyrin) and new amplifiers for low-noise SAW oscillators, which are illustrated and discussed in some detail. The trend toward SAW matrixes, implemented on silicon, required for more sensitive chemical image systems, has led to the observation of coupling effects between adjacent SAW oscillators, even if the electronics were not implemented on Si. This effect must be considered at design level in order to achieve a higher resolution value in detecting either single chemical species or chemical images.

Structural, optical, and acoustic characterization of high-quality AlN thick films sputtered on Al2O3(0001) at low temperature for GHz-band electroacoustic devices applications

Aluminum nitride thin and thick films were grown on Al2O3(0001) substrates by reactive radio frequency-sputtering technique at 180°C. The AlN films, 0.022–6.2μm thick, were stress-free, uniform, transparent, and extremely adhesive to the substrate. Their structural properties were investigated by x-ray diffraction measurements: the resulting films were highly c-axis oriented, with a full width at half maximum of the (0002) rocking curve in the range from 1.6° to 1.0° for AlN film thickness ranging between 0.022 and 6.2μm. The crystalline quality of AlN films was extremely good even at high thicknesses, as shown by the presence of the AlN(0004) reflection and by the narrow (0.12°–0.20°) diffraction peaks. Optical measurements of the transmission in the visual and infrared region demonstrated that the AlN films have low absorption and scattering. The extinction and the absorption coefficients, α and Ke, were estimated at λ⩾600nm(α=850±50cm−1,Ke=0.0040±0.0005). The piezoelectric strain constant d33 was measu...

Integrated optic sensor for the detection of H2 concentrations

Abstract A Mach-Zehnder interferometer has been utilized as a basic optical device for a new hydrogen sensor. The sensitivity to hydrogen is obtained through refractive index changes induced by absorption or desorption of hydrogen in a thin film of palladium deposited on one of the two branches of the interferometer. The relative phase shift of the light propagating along the two branches gives rise to a change in the output intensity, which can be correlated to the hydrogen concentration.

Structural, morphological and acoustic properties of AlN thick films sputtered on Si(001) and Si(111) substrates at low temperature

Abstract Polycrystalline AlN thick films were deposited on Si(001) and Si(111) substrates by reactive radio frequency sputtering technique at low temperature. The structure and the morphology of the films were investigated by X-ray diffraction, scanning electron microscopy and atomic force microscopy techniques. These measurements showed that the AlN films were highly c-axis oriented, with low surface roughness. The surface acoustic wave (SAW) properties of the films were investigated: a mean value of 3.8×10−12 C/N was estimated for the piezoelectric strain constant d33; the phase velocities of SAWs propagating in polycrystalline AlN/(001)[110]Si and AlN/(111)[1–10]Si structures, for different film thicknesses, were calculated and found to be in good agreement with the theoretical velocities evaluated for SAWs propagating in single crystal AlN/Si structures.

Response of a Pt-polyyne membrane in surface acoustic wave sensors: Experimental and theoretical approach

A surface acoustic wave (SAW) sensor, based on a polymeric sensitive membrane, has been realized for sensor applications and materials characterization. A platinum-containing rigid-rod organometallic polymer [-Pt(PPh3)2(-C≡C-pC6H2(2,5-OC16H33)2-C≡C-)]n (Pt–P–HDOB), obtained by the reaction of cis-[Pt(PPh3)2Cl2] with 1,4-diethynyl-2,5-dihexadeciloxybenzene (HDOB) by means of the recently assessed “Extended one pot” polymerization route, was here studied. The chemical structure and chain length of Pt–P–HDOB polymer were defined by spectroscopic techniques and gel permeation chromatography measurements. The acoustic characterization of the Pt–P–HDOB film was developed with the aid of the perturbation theory applied to different polymer-coated-piezoelectric substrates and the shear modulus of Pt–P–HDOB film have been estimated. A SAW delay line has been implemented on ZnO/Si substrate and a thin polymeric film has been spin deposited on the device surface to realize a chemical sensor. The sensor has been expo...

High-frequency, high-sensitivity acoustic sensor implemented on ALN/Si substrate

AlN films, 1.6–6.3 μm thick, were sputtered at 200 °C on Si(100) and Si(111) substrates. The films were crack-free, uniform, and c-axis oriented. The experimental phase velocities of surface acoustic waves (SAW) propagating in the AlN/Si structures were estimated and showed only a small discrepancy (20–40 m/s) compared to the calculated theoretical values. A SAW resonator (SAWR)-based chemical sensor, operating at about 700 MHz, was implemented on AlN/Si. The SAWR surface was covered with a polymer film sensitive to relative humidity (RH) changes, already tested for RH sensing in previous works on SAW delay lines implemented on AlN/Si and ZnO/Si and operating at about 130 MHz. The RH mass sensitivity and the detection limit of the SAWR sensor improved by 38% and by one order of magnitude, respectively, compared to the delay line-based sensors previously tested.

Surface acoustic wave humidity sensors: a comparison between different types of sensitive membrane

Surface acoustic wave (SAW) sensors have been successfully exploited for the detection of both chemical and physical quantities. In this paper we report more recent results on SAW sensors for the detection of relative humidity (R.H.). Different chemical interactive materials (CIMs), of both organic and inorganic compounds, are tested and their performances in the R.H. range between 10 and 80% are reported and compared. All the devices analysed have been shown to operate in a reversible way, with a fairly good repeatibility and fast response times. The CIMs have been shown to produce a variety of different behaviours versus R.H. percentage, with respect to both the amplitude and linearity of the response. The response to R.H. has also been investigated for different orientations of both quartz and lithium niobate bare substrates. These data can be useful in order to investigate the effect of the R.H. of the surroundings on the performances of SAW based devices. In addition this test is of great importance in order to know how humidity influences the response of both chemical and physical sensors. The response of organic CIMs has also been tested toward hydroxylated molecules such as acetone and ethanol, and the relative calibration curves are reported.

Theoretical and experimental investigation of gigahertz-band, temperature-compensated electromechanical coupling configurations based on AlN films

Highly c-axis oriented piezoelectric AlN films were sputtered on (0001) Al2O3 substrates and four gigahertz-range surface acoustic wave (SAW) electroacoustic coupling configurations were realized by conventional photolithographic process. The thermal sensitivity of each device was experimentally estimated and found in good accordance with the theoretical predictions. Eight gigahertz-range, thermally compensated SAW devices were obtained for specific AlN thickness, SAW propagation direction, and electrical boundary conditions. A theoretical analysis of the acoustic and electrical behavior of the four coupling structures is proposed to match the achievable performances of the SAW devices with the design requirements.

An integrated optical method for measuring the thickness and refractive indexof birefringent thin films

Abstract A simple but effective method is described for the determination of the refractive indices and thickness of light guiding optically anisotropic thin films, based on measurements of the propagation modes of the guide. The accuracy of measurements of the refractive indices and the film thicknesses can be as high as 1 × 10 −3 and 1 × 10 −4 , respectively. This paperreports the computation procedure used to evaluate these parameters, together with some experimental results performed on AIN and ZnO polycrystalline oriented films and isotropic 7059 Corning glass.