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ABSTRACT: Piezoelectric aluminum nitride films were deposited onto 3 in. [0001] sapphire substrates by reactive magnetron sputtering to explore the possibility of making highly (002)-textured AlN films to be used in surface acoustic wave (SAW) devices for high temperature applications. The synthesized films, typically 1 μ m thick, exhibited a columnar microstructure and a high c -axis texture. The relationship between the microstructures and process conditions was examined by x-ray diffraction (XRD), transmission electron microscopy, and atomic force microscopy analyses. The authors found that highly (002)-textured AlN films with a full width at half maximum of the rocking curve of less than 0.3° can be achieved under high nitrogen concentration and moderate growth temperature, i.e., 250 ° C . The phi-scan XRD reveals the high in-plane texture of deposited AlN films. The SAW devices, based on the optimized AlN films on sapphire substrate, were characterized before and after an air annealing process at 800 ° C for 90 min. The frequency response, recorded after the annealing process, confirmed that the thin films were still strong in a high temperature environment and that they had retained their piezoelectric properties.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 04/2011; · 1.25 Impact Factor
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Integrated Ferroelectrics 09/2010; 91(June-July 2007):119-128. · 0.30 Impact Factor
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ABSTRACT: Catalysts play a key role in the growth of carbon nanotubes. The microwave plasma-assisted chemical vapor deposition (MPACVD) method is now commonly used for directional and conformal growth of carbon nanotubes (CNTs) on substrates. In this work, we report on the effect of H(2) plasma pre-treatment on the diameter and density of iron catalyst nanoparticles for different iron layer thicknesses in order to grow isolated bundles of CNTs. Atomic force microscopy shows first that as plasma power density increases, iron nanoparticle diameters decrease, which is due to the increasing of gas dissociation giving more ion bombardment energy, and second that the diameter of nanoparticles decreases with the catalyst thickness. The growth of CNT was carried out under different CH(4) concentrations for different iron film thicknesses. Transmission electron microscopy and Raman spectroscopy show that the synthesized CNT were of good quality and had an outer diameter between 5 and 10 nm.
Nanotechnology 02/2010; 21(6):065708. · 3.98 Impact Factor
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ABSTRACT: Surface acoustic wave (SAW) devices are widely used as filter, resonator or delay line in electronic systems in a wide range of applications: mobile communication, TVs, radar, stable resonator for clock generation, etc. The resonance frequency and the delay line of SAW devices are depending on the properties of materials forming the device and could be very sensitive to the physical parameters of the environment. Since SAW devices are more and more used as sensor for a large variety of area: gas, pressure, force, temperature, strain, radiation, etc. The sensors based SAW present the advantage to be passive (batteryless) and/or wireless. These interesting properties combined with a small size, a low cost radio request system and a small antennas when operating at high frequency, offer new and exiting perspectives for wireless measurement processes and IDTAG applications. When the materials constituting the devices are properly selected, it becomes possible to use those sensors without embedded electronic in hostile environments (as high temperature, nuclear site, ...) where no solutions are currently used. General principle of the SAW sensor in wired and wireless configurations will be developed and a review of recent works concerning the field of high temperature applications will be presented with specific attention given to the choice of materials constituting the SAW device.
Electronic Measurement & Instruments, 2009. ICEMI '09. 9th International Conference on; 09/2009
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ABSTRACT: Surface acoustic wave (SAW) devices based on waveguide modes with shear-horizontal polarization (Love modes) are very promising for sensor applications, especially in liquid media. We present here the realization of a 2 GHz operating frequency sensor based on the SiO2/36YX LiTaO3 structure with an integrated PDMS micro-flow channel and using electron beam lithography to realize the submicronic interdigital transducers. Using our developed sensor operating at 2 GHz, we carried out alternate cycles of nitrogen and water circulating in the PDMS micro-flow channel. We measured an absolute sensitivity of −19 001 Hz mm2 ng−1 due to the interaction of the sensor with water. This sensitivity is higher than that of other devices operating at lower frequencies. The detection mechanism, including gravimetric and permittivity effects at high frequency, will be discussed.
Measurement Science and Technology 08/2009; 20(9):095203. · 1.49 Impact Factor
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ABSTRACT: Bare cadmium sulfide (CdS) nanocrystals were successfully synthesized by the thermolysis of a single-source organometallic precursor, cadmium chloride hemipentahydrate (CdCl2⋅2.5H2O) with thiourea in ethanol. The microstructure of the CdS samples was characterized using XRD, TEM, and Raman spectroscopy. The XRD's results showed that there was a transformation from cubic to hexagonal crystalline phase when higher mass of CdCl2⋅2.5H2O was used. Further experimental with different Cd2+ source showed ion Cl− originated from CdCl2⋅2.5H2O attributed to this crystalline phase transformation. The UV-Visible analysis indicated that quantum confinement effect took place when compared to the bulk CdS. However, the photoluminescence experiments revealed that the red-light emission was observed in all samples. This finding could be ascribed to deep trap defects that were due to sulfur vacancies as suggested by XPS and also the fact that the bare CdS nanoparticles are in contact with each other as shown in the TEM images.
Journal of Nanomaterials. 01/2009;
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ABSTRACT: This paper reports on the growth and the characterization of c-axis inclined AlN thin films synthesized at low temperature. These films are of significant interest for shear wave generation in the shear mode resonators that operate as a liquid sensor. AlN films were deposited on 3 inch (1 0 0) silicon wafers using an RF-magnetron sputtering planar system. A SiO2 buffer layer was used to promote the c-axis inclination. This c-axis inclination of AlN thin films was investigated using scanning electronic microscopy and x-ray diffraction in θ/2θ, χ and rocking curve scan modes. These analyses showed up to 10° of c-axis inclination in our planar charging system at low temperature. An AlN film thickness variation of about ±5% was recorded. In this study, we only presented the effect of the pressure on the c-axis inclination of AlN films. A discussion about the effect of this parameter and the role of the SiO2 buffer layer is reported. A shear mode acoustic wave device based on the deposited c-axis inclined AlN film was constructed and showed a phase velocity of 5832 m s−1. This value of shear velocity is discussed.
Semiconductor Science and Technology 08/2008; 23(9):095013. · 1.72 Impact Factor
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ABSTRACT: In this work nanocrystalline diamond (NCD) was investigated as high velocity and low propagation loss substrate for SAW devices. The considered layered structure is AIN/NCD/Silicon. First the 16 mum of (110)-oriented NCD films were grown on <100>-oriented silicon substrates of approximately 2.5 cm2 in size. Smooth piezoelectric AIN films with columnar structure and (002) orientation were then deposited on the NCD surface. The AIN film thickness was fixed to 1 mum and the spatial periodicity of IDT to 20 mum. The operating frequency of the realized device was measured at 645 MHz. This shows that surface acoustic waves being propagated at the velocity of 13 km/s were generated in this structure. The obtained velocity value is a quite higher than the value obtained by calculation when elastic constants of polycrystalline are used.
Ultrasonics Symposium, 2007. IEEE; 11/2007
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ABSTRACT: In this work, we report about the study of electromechanical coupling coefficient (K<sup>2</sup>) and temperature coefficient of frequency (TCF) of SAW devices based on AIN/diamond layered structure intended for the X band (8 GHz). SAW devices operating in the range of 8 GHz were realized by the combination of the high velocity of the AIN/diamond layered structure and the high lateral resolution obtained using e-beam lithography (EBL). Due to high electrical resistivity of the AlN film, interdigital transducers with sub-micronic resolution were patterned by an adapted technological EBL process. The analyses of structural and morphological of the diamond and AlN layers by X-ray diffraction, atomic force microscopy (AFM) were carried out. They showed the highly (002) preferential orientation of AlN film deposited on diamond layer and a very weak surface roughness of less than 1 nm measured on the surface of AIN/diamond layered structure. The analysis of device performances in terms of K<sup>2</sup> and temperature stability were carried out and discussed. The dispersion of both parameters as a function of normalized thickness of AlN layer (kh<sub>AlN</sub>) was experimentally determined, and showed the obtaining of electromechanical coupling coefficient up to 1.4% for normalized thickness kh<sub>AlN</sub> varying between 3 and 5. Concerning the TCF, the recorder values show a quasi- parabolic behavior. This TCF behavior in such high frequencies will discussed taking into account the nature of the TCF of AlN and diamond layers separately.
Ultrasonics Symposium, 2007. IEEE; 11/2007
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ABSTRACT: In this work, we report on the fabrication results of surface acoustic wave (SAW) devices operating at frequencies up to 8 GHz. In previous work, we have shown that high acoustic velocities (9 to 12 km/s) are obtained from the layered AIN/diamond structure. The interdigital transducers (IDT) made of aluminum with resolutions up to 250 nm were successfully patterned on AIN/diamond-layered structures with an adapted technological process. The uniformity and periodicity of IDT were confirmed by Held emission scanning electron microscopy and atomic force microscopy analyses. A highly oriented (002) piezoelectric aluminum nitride thin film was deposited on the nucleation side of the CVD diamond by magnetron sputtering technique. The X-ray diffraction effectuated on the AIN/diamond-layered structure exhibits high intensity peaks related to the (002) AlN and (111) diamond orientations. According to the calculated dispersion curves of velocity and the electromechanical coupling coefficient (K<sup>2</sup>), the AlN layer thickness was chosen in order to combine high velocity and high K<sup>2</sup>. Experimental data extracted from the fabricated SAW devices match with theoretical values quite well.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 08/2007; · 1.69 Impact Factor
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ABSTRACT: We report in this paper on the study and the realization of surface acoustic wave devices based on an AlN/diamond layered structure intended for the X band (8 GHz). Both x-ray diffraction and transmission electronic microscopy, used for characterization of the structural properties of the AlN/diamond structure, have shown (002) highly oriented sputtered AlN films on free-standing chemical vapor deposition diamond films. Surface roughness of the AlN/diamond structure was measured by atomic force microscopy and showed a very low surface roughness, less than 1 nm. Low surface roughness is very important to reduce the acoustic propagation losses. SAW devices operating in the range of 8 GHz were realized by the combination of the high velocity of the AlN/diamond layered structure and the high lateral resolution obtained using e-beam lithography (EBL). Due to high electrical resistivity of the AlN film, interdigital transducers with submicronic resolution were patterned by an adapted technological EBL process. The analysis of device performances in terms of electromechanical coupling coefficient and temperature stability was carried out and discussed. The dispersion of both parameters as a function of wavelength was experimentally determined, and showed the obtention of an electromechanical coupling coefficient up to 1.4% and a temperature coefficient of frequency varying between 9 and 20 ppm/°C. The dispersion curves of phase velocity were also analyzed and experimental results show a good agreement with theoretical calculations.
Journal of Applied Physics 06/2007; 101(11):114507-114507-5. · 2.17 Impact Factor
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Integrated Ferroelectrics 11/2006; 82(2006):45-54. · 0.30 Impact Factor
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ABSTRACT: In this work, we report on the fabrication results of SAW devices operating at frequencies up to 8GHz. In previous work, we have shown that high acoustic velocity (9 to 12 km/s) is obtained from the layered AlN/diamond structure. The interdigital transducers (IDTs) made in aluminum with resolutions down to 300nm were successfully patterned on AlN/diamond layered structures with an adapted technological process. The uniformity and periodicity of IDTs were corroborated by field emission scanning electron microscopy and atomic force microscopy analyses. Highly oriented (002) piezoelectric aluminum nitride thin film was deposited on nucleation side of CVD diamond by magnetron sputtering technique. The X-ray diffraction made on the AlN/diamond layered structure exhibits high intensity peaks related to the (002) AlN and (111) diamond orientations. According to the calculated dispersion curves of velocity and electromechanical coupling coefficient (K<sup>2 </sup>), the AlN layer thickness was chosen in order to combine high velocity and high K<sup>2</sup>. Thus, the expected values predicted by calculation match quite well the experimental data extracted from fabricated SAW device
Ultrasonics Symposium, 2006. IEEE; 11/2006
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ABSTRACT: Very high frequency surface acoustic wave (SAW) devices based on AlN/diamond layered structures were fabricated by direct writing using e-beam lithography on the nucleation side of chemical vapor deposition diamond. The interdigital transducers made in aluminum with resolutions down to 500 nm were patterned on AlN/diamond layered structure with an adapted technological process. Experimental results show that the Rayleigh wave and the higher modes are generated. The fundamental frequency around 5 GHz was obtained for this layered structure SAW device and agrees well with calculated results from dispersion curves of propagation velocity and electromechanical coupling coefficient.
Applied Physics Letters 05/2006; 88(22):223504-223504-3. · 3.84 Impact Factor
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ABSTRACT: Brillouin spectroscopy has been used to study the effect of the deposition temperature on the surface acoustic wave (SAW) propagation velocity of aluminum nitride (AlN) films. The results show a dependence of the SAW propagation velocity on the growth temperature of AlN films. The highest value of acoustic velocity was obtained for the film elaborated without heating. Structural characterization of the AlN films synthesized at various deposition temperatures was carried out by x-ray diffraction. These analyses pointed out that the deposition temperature influences the standard deviation of (002) AlN film preferred orientation. The growth temperature clearly influences the acoustical and crystalline properties of AlN thin films.
Journal of Applied Physics 11/2005; 98(9):096102-096102-3. · 2.17 Impact Factor
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Ultrasonics Symposium, 2005 IEEE; 10/2005
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ABSTRACT: In this study we present the first results achieved on the growth of carbon nanotubes (CNT) in both continuous mode (CM) and pulsed mode (PM) microwave plasma assisted chemical vapour deposition (MPACVD). The interest of this work is to determine the influence of the discharge parameters on the CNT properties such as diameter, length, density … etc. The experiments were carried out at a sustrate temperature around 900 °C. The catalyst used was nanostructured Fe–SiO deposited on silicide. It was found that the formation of multiwalls carbone nanotubes (MWCNTs) occurs when varying the discharge parameter from the CM to the PM and a selective growth of bundles of MWCNTs is obtained in the optimal PM plasma mode conditions. The measured diameter of isolated MWCNTs in the CM is around 20 nm. We measured a decrease of the amorphous carbon structures by a factor 7 and an increase of the CNT density by a factor 3 from the CM to the PM, confirming that the pulsed mode is more suitable for the MWCNT growth. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Physica Status Solidi (A) Applications and Materials 08/2005; 202(11):2079 - 2084. · 1.46 Impact Factor
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ABSTRACT: A new diamond based SAW device layered structure, combining high acoustic velocity (Vφ) and high electromechanical coupling coefficient (K<sup>-</sup>), is investigated for GHz-band applications. In fact, to overcome the trade-off relationship between Vφ and K<sup>2</sup>, we propose the use of a three-layer structure ZnO/AlN/diamond that combine the advantages of both piezoelectric materials: high K<sup>2</sup> 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</sup> 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</sup> larger than 4%, and of Vφ more than 15 km/s are expected on this new structure according to the theoretical results.
Ultrasonics Symposium, 2004 IEEE; 09/2004
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ABSTRACT: In this work, c-axis oriented aluminium nitride thin films on silicon substrates were deposited by reactive RF magnetron sputtering method at various substrate temperature (without heating - 400°C) with the same thickness (1.4 μm). The structural, morphological and optical properties of AlN films were investigated by X-ray diffraction, field emission scanning electron microscope, atomic force microscopy and Fourier transform infrared absorbance spectroscopy. It was found that the AlN films showed the same highly [002] preferred orientation with low full width of half maximum of rocking curve, which is about 2° for all the films elaborated in various temperatures. The optical properties of these films analysed by FTIR, exhibit absorption bands attributed to vibrational modes of Al-N bonds, in particular El(TO) at 678 cm<sup>-1</sup> and Al(TO) at 613 cm<sup>-1</sup>. The surface roughness of films determined by AFM is less than 0.5 nm for the film grown at low temperature, which is very suitable for SAW device achievement. Elastic properties of deposited AlN films were evaluated by realisation and characterisation of AlN/silicon SAW device. Experimental results show that realised structure exhibits a good frequency response and practical values of electromechanical coupling coefficient and temperature coefficient of frequency.
Applications of Ferroelectrics, 2004. ISAF-04. 2004 14th IEEE International Symposium on; 09/2004
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ABSTRACT: Piezoelectric AlN films crystallised in a hexagonal wurtzite structure with the c-axis oriented perpendicular to the surface were deposited on silicon substrates by dc reactive magnetron sputtering. The evolution of the crystallographic and electrical properties of these films with a nitrogen concentration between 10 and 100% in the Ar–N2 gas mixture was studied using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS) and four-point probe methods. It was found that the electrical properties are correlated to the film structure and to the deposition parameters. The AlN films having a high electrical resistivity (>1014 Ω cm at room temperature) also exhibit a high crystallographic orientation, as determined from the XRD peak intensity. An optimum for the nitrogen concentration is identified in the range 60–80% of N2 in the gas mixture. The Arrhenius plots of electrical resistance give an activation energy of 2.2 eV between 200 °C and 450 °C. This energy is attributed to oxygen impurities. EDXS analysis reveals that oxygen is the only element present in the deposited films, along with Al and N.
physica status solidi (a) 03/2003; 196(2):416 - 421. · 1.21 Impact Factor
