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International audience; Remote interrogation of surface acoustic wave ID-tags imposes a high signal amplitude which is related to a high coupling coefficient value (K 2) and low propagation losses (α). In this paper, we propose and discuss an alternative configuration to the standard one. Here, we replaced the conventional configuration, i.e. one interdigital transducer (IDT) and several reflectors, by a series of electrically connected IDTs. The goal is to increase the amplitude of the detected signal using direct transmission between IDTs instead of the reflection from passive reflectors. This concept can therefore increase the interrogation scope of ID-tags made on conventional substrate with high K 2 value. Moreover, it can also be extended to suitable substrates for harsh environments such as high temperature environments: the materials used exhibit limited performances (low K 2 value and relatively high propagation losses) and are therefore rarely used for identification applications. The concept was first tested and validated using the lithium niobate 128°Y-X cut substrate, which is commonly used in ID-tags. A good agreement between experimental and numerical results was obtained for the promising concept of connected IDTs. The interesting features of the structure were also validated using a langasite substrate, which is well-known to operate at very high temperatures. Performances of both substrates (lithium niobate and langasite) were tested with an in-situ RF characterization up to 600°C. Unexpected results regarding the resilience of devices based on congruent lithium niobate were obtained. Index Terms-high temperature, lithium niobate, radio frequency identification (RFID), surface acoustic wave (SAW)

Surface acoustic wave sensors are a promising solution for structural health monitoring applications. They can withstand extreme operating conditions. However, they often fail in operation due to h...

A wireless vacuum sensor based on the Pirani principle and Surface Acoustic Waves (SAW) has been designed, simulated and manufactured. The sensing unit is a heat conductivity gauge based on a passive SAW temperature sensor. The required heating energy is applied to the sensor by means of inductive coupling whereas the measurement signal is sent via a ceramic antenna. The sensor is a compact polymer cube containing all the units and operating completely wireless. Simulation was used to design and optimize the behavior of the sensor in vacuum and to predict the performances of the sensor. It was followed by the manufacturing and the assembly of a prototype. This communication presents the design, the simulation results and the manufacturing steps of the prototype.

The discovery of enhanced piezoelectricity in solid solutions of AlN and ScN is certainly one of the most important events in piezoelectric MEMS. As compared to pure AlN, it brought a crucial factor 2 to 3 improvement in a number of figures of merit governing the performance of MEMS devices. The aim of this contribution is to give a short overview on actual topics in processing, properties, and applications in RF filters and sensors.

Remote interrogation of SAW ID-tags imposes a high coupling coefficient value ($\text{K}^{\mathbf {2}}$), which many of the most promising substrates for high temperature applications do not possess. In this paper, we propose and discuss an alternative configuration to the standard one. Here, we replaced the standard configuration, i.e. one interdigital transducer (IDT) and several disconnected reflectors, by a series of electrically connected IDTs. The goal is to increase the amplitude of the reflected signals, using direct transmission between IDTs instead of the reflection on passive reflectors. Numerical simulations show promising results. A test structure was also characterized experimentally. As a first step, the test structure was based on the well-known lithium niobate $128 ^{\circ}\mathrm {Y} -\mathrm {X}-$cut substrate. This concept will be extended to other substrates with lower $\text{K}^{\mathbf {2}}$ value, which should prove especially interesting for high temperature applications.

In this abstract, a micro wireless vacuum sensor is presented to be operated between high vacuum and atmospheric pressure. The sensor combines the Pirani principle and Surface Acoustic Waves.

Surface Acoustic Wave (SAW) passive and wireless sensors are a promising solution for condition and structural health monitoring (SHM) applications. They are robust devices, which can withstand extreme operating conditions (very high temperatures, high pressure etc.). They do not require any embedded electronics and can be implanted in various kinds of (dielectric) structures. Moreover, SAW Sensors of the Reflective Delay Line (R-DL) type have built-in RFID capabilities, which can prove extremely useful for various industrial applications. Our presentation will start with an overview of CTR R&D activities. We will then present a short review of SAW RFID Sensors for industrial applications, with a focus on implantable devices like torque sensors, pressure sensors, and temperature sensors. Specific examples of applications in the chemical, automotive and steel industries will be provided. We will then discuss the potential of SAW RFID Sensors for SHM applications. Existing solutions will be described, as well as possible applications based on existing 2.45GHz R-DL devices. As SAW sensors often fail in operation, due especially to housing failure at high temperature, promising ‘package-less’ solutions will be presented. Here, guided modes that propagate in protective multilayer structures are used, instead of surface waves. Several multilayer configurations have been suggested, simulated and/or tested in the past years. Pros & cons of the different configurations will be discussed.

SAW sensors are usually mounted using special types of glue. However, glue-based mounting solutions might sometimes prove inadequate, in extreme environment especially. In that case, highly reactive NanoFoils could be used, instead of glue. In this paper, we present the results of a feasibility study, aimed at testing a NanoFoil-based assembly method for wireless SAW strain sensors.

Dual mode bulk acoustic wave resonators were fabricated using tilted c-axis oriented grains. In this case, longitudinal and shear modes are excited at the same time. The stiffness matrix for the tilted geometry was derived, and served to determine c(33) and c(44) from the two basic resonance frequencies. In addition, it was possible to estimate the tilting angle from the ratio of the sound velocities.

Partial substitution of Al by Sc in AlN wurtzite films leads to a strong enhancement of the piezoelectric properties as long as the wurtzite phase is maintained. This is very promising for improving piezoelectric MEMS devices and enlarging their application range. Nucleation of (0001)-AlScN works particularly well on Pt (111) thin films. However, in some applications, the growth on insulating substrates may be required. Even though AlN can be grown well oriented on smooth amorphous surfaces of SiO 2 , it is not the case for AlScN. AlN seed layers are an evident solution when there is no vacuum break between the AlN and AlScN growth. However, when a vacuum break is unavoidable, an oxide layer is formed on AlN, which makes the “regrowth” difficult. In this contribution we show that a mild RF etch can solve the problem.

It is more difficult to nucleate AlN-ScN alloy thin films (AlScN) in pure (0001)-texture than it is with pure AlN thin films. AlN thus can serve as seed layer for AlScN. Equipment limitations may lead to the problem of a vacuum break between AlN and AlScN deposition, as it leads to oxidation of the AlN surface. This issue was studied with high resolution TEM and electron diffraction. The formed oxide layer disturbed a lot the epitaxial growth, leading to additional grain orientations. A mild RF etching step introduced before AlScN deposition was able to remove the oxide layer, and allowed for growing Al 0.84 Sc 0.16 N in local epitaxy on AlN, as shown by Hyper map EDX images. The resulting AlScN films show a pure (0001) texture. Double beam laser interferometry and finite element modeling were used to determine d 33, f of both layers together as 6.6 pm/V, and of 6.85 pm/V for AlScN alone when using the standard value of 3.9 pm/V for pure AlN. At the same time, the relative dielectric constant of Al 0.84 Sc 0.16 N was determined as 14.1.

Surface Acoustic Wave sensors are a promising enabling technology to achieve temperature monitoring in extreme conditions, and especially at very high temperature, above 900°C. Applications in the air and space, chemical, steel, and automotive industries are notably expected. Although many of the technical challenges posed by the development of these sensors have been tackled and solved over the years, there is still no SAW sensor able to withstand very high temperatures for a long time on the market (yet). A possible alternative could be to combine a SAW transponder with a thermocouple ('SAW Hybrid'). The thermocouple would be read wirelessly using a SAW transponder, itself located at a place nearby where the temperature doesn't exceed 350°C. The feasibility of this concept was recently demonstrated, using a 400MHz device. However, the obtained sensitivity was very low, and an optimized Design is needed, to increase it. It is notably expected that a higher operating frequency will significantly improve the sensitivity. In this paper, we present an optimal Design of the SAW Hybrid AlN/LN multilayered structure, for operation at 2.45GHz, with buried Pt electrodes.

Via the integration of renewable energy and storage technologies, buildings have started to change from passive (electricity) consumers to active prosumer microgrids. Along with this development come a shift from centralized to distributed production and consumption models as well as discussions about the introduction of variable demand–supply-driven grid electricity prices. Together with upcoming ICT and automation technologies, these developments open space to a wide range of novel energy management and energy trading possibilities to optimally use available energy resources. However, what is considered as an optimal energy management and trading strategy heavily depends on the individual objectives and needs of a microgrid operator. Accordingly, elaborating the most suitable strategy for each particular system configuration and operator need can become quite a complex and time-consuming task, which can massively benefit from computational support. In this article, we introduce a bio-inspired cognitive decision agent architecture for optimized, goal-specific energy management in (interconnected) microgrids, which are additionally connected to the main electricity grid. For evaluating the performance of the architecture, a number of test cases are specified targeting objectives like local photovoltaic energy consumption maximization and financial gain maximization. Obtained outcomes are compared against a modified simulating annealing optimization approach in terms of objective achievement and computational effort. Results demonstrate that the cognitive decision agent architecture yields improved optimization results in comparison to the state of the art reference method while at the same time requiring significantly less computation time.

This article introduces a modified simulated annealing triple-optimizer for finding the optimal energy management strategy in terms of financial gain maximization in grid-connected, storage-augmented, photovoltaics-supplied prosumer building microgrids in a variable grid price scenario. For evaluating the performance of the optimizer, a number of test cases are specified offering different trading options to the prosumers. Obtained results are compared to a total state space search reference method and demonstrate that the simulated annealing approach was for all test cases able to find a globally optimal or close to optimal solution in significantly less computation time than the total space search reference method.

Lamb wave microresonators with wavelengths, of 5-8m, vibrating in the S0 mode, and having 75 electrode pairs were fabricated and characterized. The results were compared to theoretical predictions obtained by finite element simulation. The active material was a 1m-thick Al0.85Sc0.15N thin film. Two types of acoustic isolation solutions were implemented: the first one with freestanding plates fixed by two bridges to a device frame [freestanding Lamb wave resonator (FS-LWR)] and the second one containing an acoustic W/SiO2 5-layer reflector [solidly mounted Lamb wave resonator (SM-LWR)]. All devices showed excellent agreement with FEM predictions, regarding resonance frequency and piezoelectric coupling. The quality factors of the SM-LWR devices were 5-6 times larger than the ones of the freestanding structures fabricated by the same Al0.85Sc0.15N deposition process: we achieved a figure of merit of 12-18 (Q(p) = 771, Q(s) = 507, k(2) = 2.29%) at an operation frequency of 1430MHz, which is so far the best performance realized with a MEMS Lamb wave resonator having a large number of electrode fingers. This performance opens up perspectives for filter applications.

International audience; The design of wireless SAW sensors for high-temperature applications requires accurate knowledge of the constitutive materials' physical properties in the desired temperature range. In particular, it is crucial to use reliable temperature coefficients of the stiffness, piezoelectric, dielectric, and expansion constants of the propagation medium to achieve correct simulations of the considered devices. Currently, the best-suited piezoelectric material for high-temperature SAW applications is langasite (LGS). Unfortunately, the available coefficients do not allow for precise prediction of the temperature dependence of LGS-based SAW devices above 300°C. A novel method, based on a simulated annealing algorithm cou- pled with a Rayleigh wave simulation program, was developed to find optimal LGS temperature coefficients. This approach has proven to yield accurate results up to at least 800°C.

The combination of experimental and numerical techniques previously developed for analysis of spurious BAWs in delay lines based on YX-LGS was applied to LGS cut with Euler angles (0°, 138.5°, 26.7°) used in high-temperature SAW sensors. The ratio between the amplitudes and delay times of SAW propagating at the frequency ƒ=3·ƒ 0 and the undesired BAW overlapping with this SAW was studied in order to suppress the BAW and use the SAW overtone for sensing purposes.

An inverse method based on Simulated Annealing was proposed in previous work, to help determining the first and second order temperature coefficients of the components of the LGS material tensors. The motivation and objective of this work were to improve the method, by drastically reducing the optimization time that lasted from several hours to several days. The main idea was to use the Design of Experiments approach, to reduce the slow numerical algorithm commonly used to compute the required Fractional Frequency Changes curves (FFC) to simple analytical formulas (one formula per cut). In this paper, two such formulas are derived for two distinct LGS cuts. The formulas describe the FFCs with a good enough accuracy. This validates the general feasibility of the method.

International audience; Recent studies have evidenced that Pt/AlN/Sapphire SAW devices are promising for high-temperature high-frequency applications. However, they cannot be used above 700°C in air atmosphere as the Pt interdigital transducers (IDTs) agglomerate and the AlN layer oxidizes in such conditions. In this paper, we explore the possibility to use an AlN protective overlayer to concurrently hinder these phenomena. To do so, AlN/IDT/AlN/Sapphire heterostructures undergo successive annealing steps from 800°C to 1000°C in air atmosphere. The impact of each step on the morphology, microstructure and phase composition of AlN and Pt films is evaluated by means of optical microscopy, scanning and transmission electron microscopy (SEM & TEM), X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS). Finally, acoustical performance at room temperature of both protected and unprotected SAW devices are compared, as well as the effects of annealing on these performance. These investigations show that the use of an overlayer is one possible solution to strongly hinder the Pt IDTs agglomeration up to 1000°C. Moreover, AlN/IDT/AlN/Sapphire SAW heterostructures show promising performances in terms of stability up to 800°C. At higher temperatures, the oxidation of AlN is more intense and makes it inappropriate to be used as a protective layer.

A new kind of surface acoustic wave (SAW) sensor has been developed to measure sub-atmospheric pressure below 100 mtorr with accuracy better than 0.1 mtorr. It provides an efficient measuring solution in the pressure range inaccessible in past by conventional diaphragm-based SAW sensors. Indeed, because of the small bending force in lower pressure and limited sensitivity, diaphragm-based SAW sensors are only suited to monitor relatively high pressure with a precision hardly better than 0.5 torr. To reach precision level better than 1 mtorr at sub-atmospheric pressure for vacuum technology applications, a radically different SAW-based solution is necessary. Our device aims to measure sub-atmospheric pressure less than 100 mtorr with a threshold resolution better than 0.1 mtorr. The concept is similar to the one used by Pirani pressure gauges. However, it is claimed that a heated and suspended SAW device should have better sensitivity. A theoretical model based on the basic concepts of gas kinetic theory and thermodynamics is presented. The validity of the model is checked by comparison between theoretical and experimental results.

The sensitivity of a ZnO/Quartz SAW (Surface Acoustic Waves) sensor has been evaluated under alcohol vapour exposure. Ethanol, isopropanol and butanol have been tested. In order to better understand the SAW frequency shifting effect due to the alcohol molecules, a Langmuir/B.E.T analysis has been carried out. Possible shifting mechanisms have been proposed and tested by numerical simulation.

The new piezoelectric crystal langasite (La 3 Ga 5 SiO 14 ; abbreviated as LGS) that presents a high chemical stability at high temperature is investigated as substrate for the new layered structure Diamond/LGS surface acoustic wave (SAW) devices. Theoretical study was performed in order to calculate the evolution, as a function of diamond film thickness, of phase velocity and electromechanical coupling coefficient (K 2 ) of the Rayleigh mode and its higher modes. The calculation results show that phase velocity up to 12 000 m/s and up to 9500 m/s are obtained respectively for the mode 2 and mode 1, while the mode 0 exhibits high K 2 values up to 2.9%. Experimental study was focused on the deposition of nanocrystalline diamond films on LGS substrate. First attempts show that good nanocrystalline properties may be obtained in Ar/H 2 /CH 4 microwave discharges.

The measured characteristics of a test SAW device built on YX cut of LGS were analyzed in the time-frequency domain, using spectrogram representation. Especially, spurious modes were detected and investigated. A combination of numerical techniques was applied to the analysis of the observed spurious modes, including simulation of the admittance of a Pt grating on an LGS plate of finite thickness and visualization of the wave structure at different frequencies. The influence of the anisotropy on the frequency-time ratio was taken into account for each of three obliquely propagating bulk waves via detailed numerical investigation of the BAW slowness surface. The main spurious BAW modes propagating parallel to the surface or at certain tilt angles and reflected from the bottom were identified. The frequency-time dependences predicted via analysis of BAW anisotropy showed good agreement with experimental results.

Aluminum nitride (AlN) is a promising material for sensor applications in harsh environments such as turbine exhausts or thermal power plants due to its piezoelectric properties, good thermal match to silicon and high temperature stability. Typically, the usage of piezoelectric materials in high temperature is limited by the Curie-temperature, the increase of the leakage current as well as by enhanced diffusion effects in the materials. In order to exploit the high temperature potential of AlN thin films, post deposition annealing experiments up to 1000°C in both oxygen and nitrogen gas atmospheres for 2 h were performed. X-ray diffraction measurements indicate that the thin films are chemically stable in a pure oxygen atmosphere for 2 h at annealing temperatures of up to 900°C. After a 2 h annealing step at 1000°C in pure oxygen. However, a 100 nm thin AlN film is completely oxidized. In contrast, the layer is stable up to 1000°C in pure nitrogen atmosphere. The surface topology changes significantly at annealing temperatures above 800°C independent of annealing atmosphere. The surface roughness is increased by about one order of magnitude compared to the "as deposited" state. This is predominantly attributed to recrystallization processes occurring during high temperature loading. Up to an annealing temperature of 700°C, a Poole-Frenkel conduction mechanism dominates the leakage current characteristics. Above, a mixture of different leakage current mechanisms is observed.

It has been 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 (K2). In this study, we investigate the performance of a SAW pressure sensor based on a ZnO/quartz structure. We used the quartz Y–X in this structure owing to the zero TCF value that this quartz produces when it is combined with a thin ZnO film of particular thickness. This film thickness was determined here not only to achieve such zero value, but also to increase the electromechanical coupling coefficient (K2 = 1%) to seven times higher than that of quartz Y–X. The theoretical approach to select the optimal structure is presented, which is followed by discussions on the effect of the operating frequency and on the ZnO film contribution to the pressure sensitivity.

This experimental study concerns the adsorption and absorption on surfaces submitted to oscillating mechanical strains. The influence of the amplitude of the oscillating elastic deformations is shown during exposures of FeNi alloy surfaces to very low pressures of SF 6 (5 × 10 −7 Torr). This study is carried out on a sample excited by a piezoelectric transducer observed in situ under ultra high vacuum (UHV) by Auger electron spectrometry (AES). An increase in the concentration of sulphur trapped on the surface is shown when the amplitude of oscillating elastic deformation increases. In any case, with or without mechanical strains, no traces of fluorine have been detected.

There is a need for wireless sensors able to operate in the intermediate temperature range (ITR) between 300 °C and 600 °C. Surface acoustic wave (SAW) sensors are promising candidates to solve this issue. However, existing SAW sensors most often fail in the ITR, due to the quick degradation of the sensor housing in extreme conditions. A promising way to circumvent the issue is to use “package-less” devices, where the acoustic waves are guided in a multilayered structure where they are intrinsically protected from adverse environmental effects. We present here an innovative multilayered structure that fulfills all the basic requirements, to achieve a wireless and “package-less” SAW Sensor for the ITR. The structure is made of a thin AlN layer deposited on top of a Y + 128°LN substrate and equipped with buried Pt electrodes. Numerical simulations of the acoustic waves propagating in SAW resonators built on this structure reveal the existence of a useful Rayleigh-type SAW that propagates at the AlN/LN inter...

There is a need for sensors capable operating at temperatures above 1000 degrees C. We describe an innovative sensor that might achieve this goal. The sensor comprises two main elements: a thermocouple and a surface acoustic wave (SAW) strain sensor. The cold junction of the thermocouple is electrically connected to a highly piezoelectric thin layer, deposited on top of a SAW substrate. In operation, the voltage generated by the temperature gradient between the hot (> 1000 degrees C) and cold junction (< 350 degrees C) generates a strain field in the layer, which is mechanically transmitted to the substrate. This modifies the SAW propagation conditions and therefore the sensors' radiofrequency response. The change depends on the applied voltage and thus on the hot junction temperature. As SAW devices are passive elements that can be remotely interrogated, it becomes possible to infer the hot junction temperature from the radiofrequency response, i.e., to remotely read temperatures above 1000 degrees C, without embedded electronics. In this paper, we demonstrate the feasibility of this concept, using AlN layers deposited on Y-Z Lithium Niobate (LN). The achieved sensitivity of 80 Hz/V at 400MHz is constant over a wide voltage range. Numerical simulations were performed to compute the main properties of the demonstrators and suggest optimization strategies. Improvements are expected from the use of stronger piezoelectric layers, such as AlScN or Pb(Ti, Zr)O-3 (PZT), which could increase the sensitivity by factors of 3 and 20, as estimated from their transverse piezoelectric coefficients. As a first step in this direction, thin PZT layers have been deposited on Y-Z LN.

Accurate sets of material constants and temperature coefficients are required to develop high temperature SAW sensors. It was previously shown that SAW Fractional Frequency Curve measurements combined with numerical optimization could help ease the burden of the experimental determination of some of these coefficients. To determine the other “missing” coefficients, it was suggested to use complementary BAW FFC measurements. However, to keep the global experimental effort as low as possible, a solution had to be found to avoid fabricating additional BAW devices on special LGS orientations. In this work, we describe a practical solution to simultaneously acquire BAW and SAW FFCs. Experimental results are presented then used to compute values of some of the missing coefficients. This demonstrates the whole method as being a promising way to determine accurate temperature coefficients with reduced experimental effort.

We consider a problem of waves propagation in a multi-layered piezoelectric substrate under a periodic electrode grating utilizing a full-FEM approach for a unit cell with periodic boundary conditions. The perfectly matched layer is employed in order to truncate the computational domain. The simulations are done for the structures containing one- and two-layered piezoelectric substrates. The COM parameters obtained by the proposed model are compared with those extracted using a FEM/BEM technique.