[Show abstract][Hide abstract] ABSTRACT: Surface acoustic wave (SAW) resonators built on Langasite (LGS) are capable to withstand temperature in excess of 900∘ C and demonstration of wireless interrogation of packaged sensors up to 700∘ C has been achieved for several tens of hours. These promising results emphasize the need for an accurate characterization of the raw material in order to design SAW resonators with a high level of confidence in the prediction, particularly concerning the temperature coefficient of frequency (TCF). Several data set have been published for LGS, offering prediction capabilities but also a significant level of data dispersion. Therefore, the evaluation of the effective thermal properties of SAW under periodic gratings turns out less robust than expected. Based also on published data and on measurements achieved within the SAWHOT project, harmonic admittance calculations have been achieved for deriving the evolution of mixed matrix parameters allowing for accurate SAW device simulation at any temperature. Adjusting the temperature coefficients then yield improved sets of material coefficients for design purpose. Using these data, we have demonstrated the possibility to develop a differential temperature sensor operating at temperature up to 600°C.
[Show abstract][Hide abstract] ABSTRACT: We fabricated a tunable surface acoustic wave resonator in the 2 GHz-frequency range by depositing and patterning 2 mu m-wide pitch inter-digitated Al electrodes on SrTiO3 (STO) paraelectric substrate. We took advantage of the electrostrictive behavior of STO, whose properties are nonlinear with respect to the applied electric field, to induce tunability of the resonance frequency. The obtained frequency tunability reaches 0.7% at 0.5 MV/cm. Besides, the main advantage of this device is its high acoustic quality factor Q reaching 2450 at 2 GHz, thanks to the single-crystal nature of STO. This is one order of magnitude larger than the typical quality factor of its tunable bulk acoustic wave resonators counterparts. (C) 2014 AIP Publishing LLC.
No preview · Article · Aug 2014 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: We report on the study of tunable surface acoustic waves (SAW) resonators fabricated on SrTiO3 (STO) substrate. Linear electromechanical coupling (induced “piezoelectric” coupling) is realized through electrostriction effect by applying a strong electric bias field in addition to the small signal electric and mechanical fields. Resonators have been fabricated at 2.2 GHz, showing an interesting tunability for variable bandwith filters or controlled sources.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate that single-piezoelectric substrate-based acoustic transducers act as ideal sensors for probing with various RADAR strategies. Because these sensors are intrinsically passive devices working in the radiofrequency range, they exhibit improved interrogation range and robustness with respect to silicon-based radio frequency identification tags. Both wideband (acoustic delay lines) and narrowband (acoustic resonators) transducers are shown to be compatible with pulse-mode and frequency-modulated continuous-wave RADAR strategies, respectively. We particularly focus on the ground-penetrating RADAR (GPR) application in which the lack of local energy source makes these sensors suitable candidates for buried applications in roads, building or civil engineering monitoring. A novel acoustic sensor concept – high-overtone bulk acoustic resonator – is especially suited as sensor interrogated by a wide range of antenna set, as demonstrated with GPR units working in the 100 and 200 MHz range.
[Show abstract][Hide abstract] ABSTRACT: Surface acoustic wave (SAW) resonators can advantageously operate as passive sensors which can be interrogated through a wireless link. Amongst the practical applications of such devices, structural health monitoring through stress measurement and more generally vibration characteristics of mechanical structures benefit from the ability to bury such sensors within the considered structure (wireless and battery-less). However, measurement bandwidth becomes a significant challenge when measuring wideband vibration characteristics of mechanical structures. A fast SAW resonator measurement scheme is demonstrated here. The measurement bandwidth is limited by the physical settling time of the resonator (Q/π periods), requiring only two probe pulses through a monostatic RADAR-like electronic setup to identify the sensor resonance frequency and hence stress on a resonator acting as a strain gauge. A measurement update rate of 4800 Hz using a high quality factor SAW resonator operating in the 434 MHz Industrial, Scientific and Medical band is experimentally demonstrated.
Full-text · Article · May 2012 · The Review of scientific instruments
[Show abstract][Hide abstract] ABSTRACT: In this work, we propose a Bragg mirror for Quartz resonator at 10MHz. Two processes based on bonding and thinning wafers is proposed. A stack of ten bonding and thinning wafers is realized. Ultrasonic characterization shows the behavior of the Bragg mirror and the evolution versus the number of layer stack. Resonators on such Bragg mirror show less spurious signal but need improvement about quality factor of resonator.
[Show abstract][Hide abstract] ABSTRACT: Surface acoustic wave (SAW) devices are currently used as passive remote-controlled sensors for measuring various physical quantities through a wireless link. Among the two main classes of designs-resonator and delay line-the former has the advantage of providing narrow-band spectrum informations and hence appears compatible with an interrogation strategy complying with Industry-Scientific-Medical regulations in radio-frequency (rf) bands centered around 434, 866, or 915 MHz. Delay-line based sensors require larger bandwidths as they consists of a few interdigitated electrodes excited by short rf pulses with large instantaneous energy and short response delays but is compatible with existing equipment such as ground penetrating radar (GPR). We here demonstrate the measurement of temperature using the two configurations, particularly for long term monitoring using sensors buried in soil. Although we have demonstrated long term stability and robustness of packaged resonators and signal to noise ratio compatible with the expected application, the interrogation range (maximum 80 cm) is insufficient for most geology or geophysical purposes. We then focus on the use of delay lines, as the corresponding interrogation method is similar to the one used by GPR which allows for rf penetration distances ranging from a few meters to tens of meters and which operates in the lower rf range, depending on soil water content, permittivity, and conductivity. Assuming propagation losses in a pure dielectric medium with negligible conductivity (snow or ice), an interrogation distance of about 40 m is predicted, which overcomes the observed limits met when using interrogation methods specifically developed for wireless SAW sensors, and could partly comply with the above-mentioned applications. Although quite optimistic, this estimate is consistent with the signal to noise ratio observed during an experimental demonstration of the interrogation of a delay line buried at a depth of 5 m in snow.
Full-text · Article · Feb 2011 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: High-overtone Bulk Acoustic Resonator is an acoustic transducer based on an excitation of a bulk acoustic wave by a thin piezoelectric film bonded to a thick low acoustic loss substrate. This combination of materials aims at providing on the one hand a high frequency transducer as defined by the thickness of the thin piezoelectric layer, and on the other hand the robustness of a thick substrate while keeping the acoustic properties of single crystal piezoelectric materials. More specifically, this architecture provides high quality factors using bulk acoustic wave at frequencies only accessible to surface acoustic wave (SAW) devices with interdigitated transducer generation. The multimode spectrum is well suited for an openloop, wireless interrogation strategy in which the frequency of the incoming electromagnetic wave defines the operating point. We here demonstrate the use of a frequency sweep RADAR-like network analyzer for probing through a wireless link HBARs with different temperature coefficients in order to perform temperature measurements insensitive to other correlated noise sources (capacitive frequency pulling, electrode aging, stress).
[Show abstract][Hide abstract] ABSTRACT: This paper describes the principles of single crystal LiNb03/Quartz high overtone bulk resonators and their application to the development of compact sensors dedicated to temperature and stress measurements. Design approaches are presented and first experimental results demonstrating the operation of such sensors are reported.
[Show abstract][Hide abstract] ABSTRACT: In this work, we propose a pressure sensor fabricated on compound LiNbO<sub>3</sub>/Silicon/Silicon substrates obtained by Au/Au bonding at room temperature and double face lapping/polishing of LiNbO<sub>3</sub>/silicon stack and a final gold bonding with a structured silicon wafer. Sensitivity of the final sensor to bending moments then is tested and results show pressure sensitivity of such devices.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we present a new approach for the fabrication and use of thinned single crystal films for the development of radio-frequency temperature compensated devices. We particularly focus on High-overtone bulk acoustic resonators (HBAR) for oscillator stabilization, taking advantage of the very high quality factors achievable with such devices. We obtained a good agreement between simulation and experiments. This paper shows the possibility to obtain device which is intrinsically low sensitive to thermal effects, and even allowing a second order compensation thanks to the Quartz thermal stability.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we have proposed a new concept for pressure and more generally stress sensors exploiting single-crystal based HBAR. After describing the operation principle, the practical feasibility of the sensor has been shown, yielding electrical results allowing a first characterization of such sensor sensitivity. The process flow is generic and allows us to develop different devices such as HBAR or SAW sensors with the freedom of choosing material in function of the design requirements. Although the first reported results can not exploit the high quality resonance of such HBARs, more effort will be performed in the next future to definitely validate the approach and the corresponding stress sensitivity.
[Show abstract][Hide abstract] ABSTRACT: In our previous research we already demonstrated micro acoustic devices, such as membrane based thin film bulk acoustic shear wave resonators and surface acoustic shear wave resonators, based on metal-organic-vapour-phase-epitaxial (MOVPE) grown highly oriented a-plane piezoelectric material. Although MOVPE is a well established process for compound semiconductor layer growth especially of III-V semiconductors as InP, GaAs, and the nitrides GaN or AlN as also design and simulation of micro acoustic devices is nowadays a well established knowledge, the linkage between both is quite a technological challenge. Using an adapted MOVPE growth process for a-plane GaN on r-plane sapphire with a process linked improved surface quality; the challenge to build up high-overtone bulk acoustic wave resonators (HBAR) with a shear polarization of the acoustic wave was risen within this research. Different designs of MEMS-based prototypes of HBARs were processed on a-plane GaN after intensive simulations, their acoustic electrical behaviour analyzed and the temperature coefficient of frequency determined.
[Show abstract][Hide abstract] ABSTRACT: In this paper, electron-beam (e-beam) lithography for processing of surface acoustic wave devices is investigated, and its suitability for large-scale processing discussed. Electron-beam lithography is used for exposure of surface acoustic wave (SAW) resonator patterns on polymethyl methacrylate (PMMA) coated piezoelectric substrates. Electron-beam lithography can be used for high frequency SAW designs, due to a minimal finger width of 100 nm to 400 nm. Such SAW devices can be used for high-frequency sensor applications. This contribution will consider processing, on-wafer characterization, and characterization of sensor effects in instrumentation applications.
[Show abstract][Hide abstract] ABSTRACT: The capability to accurately handle liquids in small volumes is a key point for the development of lab-on-chip devices. In this paper, we investigate an application of surface acoustic waves (SAW) for positioning micro-droplets. A SAW device based on a 2 x 2 matrix of inter-digital transducers (IDTs) has been fabricated on a (YXI)/128 degrees LiNbO3 substrate, which implies displacement and detection in two dimensions of droplets atop a flat surface. Each IDT operates at a given frequency, allowing for an easy addressing of the active channel. Furthermore, very low cross-talk effects were observed as no frequency mixing arose in our device. Continuous as well as pulsed excitations of the IDTs have been studied, yielding, respectively, continuous and step-by-step droplet displacement modes. In addition, we also have used these two excitation types to control the velocity and the position of the droplets. We also have developed a theoretical analysis of the detection mode, which has been validated by experimental assessment.
Full-text · Article · Nov 2007 · IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control
[Show abstract][Hide abstract] ABSTRACT: Liquids handling is an important issue in biomedical analysis. Two different devices for acoustic manipulation of droplets have already been tested. The first one, more classical, uses a high frequency travelling wave and acoustic streaming. The second one uses low frequency flexural standing waves in a plate. This means of liquid handling is original and easy to implement but the physical principle is not obvious. In order to understand more precisely the phenomena involved we present new observations on droplet displacement between two planes and on the behaviour of a droplet on an inclined vibrating plane with this method. The physical principle involved is discussed. The common acoustic radiation pressure formulation is expressed via the non-linear theory of sound propagation, but in our case the acoustic wavelength is much smaller than the height of a water droplet. To get a better understanding of the phenomenon, further experiments on the internal liquid flow and behaviour of particles in the droplet have been performed. These will be compared with results obtained with particles in a thin water-filled vibrating glass tube. The general conclusion is that the phenomenon is practical to use for droplet displacement even if its complex mechanism is not completely understood.
[Show abstract][Hide abstract] ABSTRACT: Compact high stability frequency sources devoted to on-board applications may be stabilized by acousto-electric devices such as SAW and BAW resonators. Many architectures have been proposed to improve the quality factor of such devices which directly influences the phase noise figures of the oscillator. However, the quality factor-frequency products of such acousto-electric devices mainly built on quartz hardly overcome 10<sup>13</sup>, which remains rather small compared to the intrinsic mechanical quality factor of the material. In the 80's, Lakin et al. have emphasized the capability of high overtone bulk acoustic resonator (HBAR) to present high quality factors at frequencies in the GHz range. In this paper, we characterize the resonance properties of HBAR built on thick AT-cut quartz plates excited by a C-oriented aluminum nitride thin films deposited atop quartz, examining its behaviour versus temperature and its capability to stabilize a Colpitts oscillator