D. Cannata

Microbalance chemical sensor based on thin-film bulk acoustic wave resonators

An electroacoustic chemical sensor based on thin-film bulk acoustic wave resonators (TFBAR) is presented. It operates on the same principle of the well-known quartz crystal micro-balance, at an operation frequency extended up to several GHz. The larger output signal, associated to the higher operation frequency, is a condition to improve the device sensitivity. TFBARs have been implemented on (001) Si wafers, using Si3N4∕AlN membranes, obtained by anisotropic etching of Si. Time response and calibration curves have been tested on TFBAR sensors exploiting two different chemically interactive membranes: Pd and Co-tetra-phenyl-porphyrin, both deposited in the form of thin-films by thermal evaporation. Measurements performed upon exposure to H2, CO, and ethanol have shown the ability of the device to detect low concentrations of the analyte with a fast and repeatable response.

Detection of odorant molecules via surface acoustic wave biosensor array based on odorant-binding proteins

In this paper, we present an array of biosensors for vapour phase detection of odorant molecules based on surface acoustic wave (SAW) resonators coated with odorant-binding proteins (OBPs). For the first time, the sensing capabilities of three different OBPs, as sensitive layers for SAW devices, are studied and compared. The SAW biosensor array is composed of three SAW devices coated by the droplet method with the wild-type OBP from cow (wtbOBP), a double mutant of the OBP from cow (dmbOBP) and the wild-type OBP from pig (wtpOBP). An uncoated device is used to compensate the variations of the environmental parameters. The SAW devices consist of two-port resonators fabricated on quartz (ST-cut, x propagation) with electrodes made of aluminium covered with a thin gold film (2 nm thick). The obtained surface densities of OBP layers are between 1.18×10(-6) kg/m(2) and 2.31×10(-6) kg/m(2) and were calculated measuring the resonant frequency shift of the SAW devices after the coating. The SAW biosensor array was tested in nitrogen upon exposure to vapours of R-(-)-1-octen-3-ol (octenol), in the range of concentration between 13 and 61 ppm, and R-(-)-carvone (carvone), in the range between 9 and 80 ppm. The highest sensitivity for detection of octenol (25.9 Hz/ppm) was obtained using the wtpOBP-based SAW biosensor, while the highest sensitivity for detection of carvone (9.2 Hz/ppm) was obtained using the dmbOBP-based SAW biosensor.

Thin-Film Bulk-Acoustic-Resonator Gas Sensor Functionalized With a Nanocomposite Langmuir–Blodgett Layer of Carbon Nanotubes

A thin-film bulk acoustic resonator (TFBAR) based on a vibrating membrane of AlN/Si3N4 has been fabricated onto a silicon substrate and functionally characterized as gas sensor at a resonating frequency of 1.045 GHz. This novel TFBAR-based gas sensor has been functionalized by a sensing nanocomposite layer, prepared by a Langmuir-Blodgett (LB) technique, of single-walled carbon nanotubes (SWCNTs) embedded in a host matrix of organic material of cadmium arachidate. High-performance gas detection at room temperature of a SWCNT-coated TFBAR sensor has been reported. The sensing device exhibits high sensitivity (e.g., acetone: 12 kHz/ppm; ethylacetate: 17.3 kHz/ppm), fast response (within 2-3 min), slow reversibility (within 1 h), and good repeatability (les 5% variation) of response toward tested organic vapors of acetone, ethylacetate, and toluene.

Guided lamb wave electroacoustic devices on micromachined AlN/Al plates

An electroacoustic micro-device based on the propagation of guided acoustic Lamb waves in AlN/Al plate is described. The AlN thin film is deposited by sputtering technique, optimized to achieve a high degree of orientation (rocking curve full-width at half-maximum ¿ 3.5°) of the c-axis perpendicular to the plate surface. The AlN plate is micromachined using anisotropic reactive ion etching (RIE), followed by isotropic RIE to remove the silicon underlayer. Simulation results for the dispersion phase velocity curves and the electromechanical coupling coefficient (K2) are obtained by the matrix method and by the finite element method and compared with experimental data. A delay line is implemented on the structure and tested for the propagation of the first symmetrical Lamb mode (s0) at the frequency of 1.22 GHz. Measurements have shown that the structure is suitable for implementation of arrays of electroacoustic devices on a single chip for application to both sensing devices and signal processing systems.

Gigahertz-range electro-acoustic devices based on pseudo-surface-acoustic waves in AlN∕diamond∕Si structures

Diamond and AlN are, respectively, the nonpiezoelectric and the piezoelectric materials showing the highest acoustic velocities. Consequently, pseudo-surface-acoustic waves (PSAWs) in AlN∕diamond structures exhibit the highest surface wave velocities among all known layered structures. Phase velocity dispersion curves and attenuation for PSAW propagating along this structure have been calculated for different electrical boundary conditions. An experimental delay line, designed to operate at low PSAW attenuation conditions, as predicted by theoretical results, has been implemented and tested. A good accordance between experimental results and theoretical predictions was found. It is expected that devices based on PSAW propagation in AlN∕diamond structures are suitable to operate at frequencies several times higher than those of available devices, at a given linewidth resolution limit in the transducers technology.Diamond and AlN are, respectively, the nonpiezoelectric and the piezoelectric materials showing the highest acoustic velocities. Consequently, pseudo-surface-acoustic waves (PSAWs) in AlN∕diamond structures exhibit the highest surface wave velocities among all known layered structures. Phase velocity dispersion curves and attenuation for PSAW propagating along this structure have been calculated for different electrical boundary conditions. An experimental delay line, designed to operate at low PSAW attenuation conditions, as predicted by theoretical results, has been implemented and tested. A good accordance between experimental results and theoretical predictions was found. It is expected that devices based on PSAW propagation in AlN∕diamond structures are suitable to operate at frequencies several times higher than those of available devices, at a given linewidth resolution limit in the transducers technology.

Applications of laser printing for organic electronics

The development of organic electronic requires a non contact digital printing process. The European funded e-LIFT project investigated the possibility of using the Laser Induced Forward Transfer (LIFT) technique to address this field of applications. This process has been optimized for the deposition of functional organic and inorganic materials in liquid and solid phase, and a set of polymer dynamic release layer (DRL) has been developed to allow a safe transfer of a large range of thin films. Then, some specific applications related to the development of heterogeneous integration in organic electronics have been addressed. We demonstrated the ability of LIFT process to print thin film of organic semiconductor and to realize Organic Thin Film Transistors (OTFT) with mobilities as high as 4 10-2 cm2.V-1.s-1 and Ion/Ioff ratio of 2.8 105. Polymer Light Emitting Diodes (PLED) have been laser printed by transferring in a single step process a stack of thin films, leading to the fabrication of red, blue green PLEDs with luminance ranging from 145 cd.m-2 to 540 cd.m-2. Then, chemical sensors and biosensors have been fabricated by printing polymers and proteins on Surface Acoustic Wave (SAW) devices. The ability of LIFT to transfer several sensing elements on a same device with high resolution allows improving the selectivity of these sensors and biosensors. Gas sensors based on the deposition of semiconducting oxide (SnO2) and biosensors for the detection of herbicides relying on the printing of proteins have also been realized and their performances overcome those of commercial devices. At last, we successfully laser-printed thermoelectric materials and realized microgenerators for energy harvesting applications.

Thin film bulk acoustic wave resonator (TFBAR) gas sensor

A novel electro-acoustic chemical sensor, based on a TFBAR, is presented. The principle of operation is the same as the well known quartz crystal micro-balance, where the frequency of operation is extended from the limit of a few tens of MHz to several GHz. The larger sensor output signals, associated with higher frequency operation, is a condition used to develop devices with improved sensitivity. TFBARs have been implemented on [001] Si wafers, using Si/sub 3/N/sub 4//AlN membranes, obtained by anisotropic chemical etching from the back side of the Si substrate. The performance of the TFBAR sensor has been tested using a thin Pd chemical interactive membrane deposited on the etched side of the membrane and exposed to different concentrations of hydrogen in nitrogen. Time response upon different cycles of H/sub 2/ adsorption and desorption are reported together with the sensor calibration curve. The operation frequency of the device, in the GHz range, allows it to obtain large responses. The device is robust in construction and miniaturized in size. Time stability, repeatability and sensitivity have been tested and reported.

Pressure sensor based on surface acoustic wave resonators

In this work we present a pressure sensor based on surface acoustic waves (SAWs) resonators and operating in the pressure range from 0 bar to 3 bar. The achieved high resolution values (3.5 Pa), are obtained making use of 2-ports SAW resonators working at approximately 393 MHz on a quartz membrane. The membrane deformations under the hydrostatic pressure, have been studied by finite element methods (FEM), using the elastic constants of the anisotropic ST-cut quartz and considering vacuum as reference pressure on the other side of the membrane. The implemented sensor is an hybrid structure where the quartz membrane is placed between two glass ceramic elements; the first to implement an hermetically closed cavity, the other to define the diaphragm. A differential configuration has been designed to reduce parasitic phenomena due to temperature variations. The response curve of the sensor is reported.

SAW sensors on Aln/diamond/Si structures

In this work we present preliminary results on surface acoustic waves (SAW) chemical sensors based on a new AlN/diamond/Si multilayered structure. The high SAW velocity in diamond allows it to operate at higher frequencies at moderate interdigital transducer (IDT) line-width resolution in order to increase the sensor output signals, with the aim to increase the sensor sensitivity. Aluminium nitride has been chosen as piezoelectric layer because of its high SAW velocity together with excellent electrical, mechanical and chemical properties. The SAW phase velocity in the experimented structure is 10716 m/s for the Sezawa mode, more than three times that in ST-cut quartz. Both SAW delay line and 1-port resonator have been implemented and tested, under the following propagation conditions: acoustic wavelength /spl lambda/=8 /spl mu/m, normalized AlN film thickness h//spl lambda/=0.225, operation frequency f/spl cong/1.35 GHz. The thickness of the diamond layer (22 /spl mu/m) is such that it can be considered as a semi-infinite substrate. The two test structures have been coated by thermal evaporation with a sensible thin (10 nm) layer of Co-tetra-phenyl-porphyrin which allowed us to detect small concentrations of ethanol and CO.

A 3-dimensional interdigitated electrode geometry for the enhancement of charge collection efficiency in diamond detectors

In this work, a single crystal CVD diamond film with a novel three-dimensional (3D) interdigitated electrode geometry has been fabricated with the reactive ion etching (RIE) technique in order to increase the charge collection efficiency (CCE) with respect to that obtained by standard superficial electrodes. The geometrical arrangement of the electric field lines due to the 3D patterning of the electrodes results in a shorter travel path for the excess charge carriers, thus contributing to a more efficient charge collection mechanism. The CCE of the device was mapped by means of the ion beam induced charge (IBIC) technique. A 1 MeV proton micro- beam was raster-scanned over the active area of the diamond detector under different bias voltage conditions, enabling to probe the charge transport properties of the detector up to a depth of 8µm below the sample surface. The experimental results, supported by the numerical simulations, show a significant improvement in the 3D detector performance (i.e. CCE, energy resolution, extension of the active area) if compared with the results obtained by standard surface metallic electrodes.