Search

International audience; A carrier suppression system is implemented in order to measure the phase noise of acoustic resonators that have a low motional resistance. A special adapters’ system using transformers is proposed to improve the loaded quality factor of the resonators. With this developed device and described protocol, the inherent noise of resonators can be obtained without the usual electronical oscillator conditioning that could take part in the results. The loaded quality factor is improved from about 10% to 60% of the intrinsic quality factor. As an example, the system is used to study Langatate crystal resonators vibrating at 10 MHz. Langatate crystals can be an alternative to substitute for the quartz crystal resonators for frequency and time applications. Their coupling coefficient and the product quality factor-frequency are normally higher than those in quartz crystal resonators. For ultrastable resonators, the motional resistance obtained with Langatate crystals is about five times lower than that for the quartz crystal; it can reach typically few ohms. These resonators have been characterized in terms of impedance, Q-factors, turnover temperature, amplitude–frequency effect, and phase noise. The short-term stability of these resonators is given in terms of Allan standard deviation. The influence of the driving power is presented

International audience; New temperature-coefficients of quartz elasticcoefficients particularly relevant at liquid-helium temperature have been reported recently. Based on this result, frequencytemperature compensated cuts are predicted by calculation, and then demonstrated by experiment. Such compensated cuts can definitely fix the issue of remaining temperature sensitivity of crystalline quartz acoustic cavities unbeatable for their extremely low mechanical loss, as low as 10–9, when operated at liquid-He temperature.

In the time and frequency domain, we need ultrastable crystal resonators embedded in Ultra Stable Oscillators (USO), working at 10 MHz and exhibiting excellent short-term stabilities. Up to now, th...

International audience; In this paper, the intrinsic study on Langatate (LGT) crystal resonators has been carried out at 10 MHz resonant frequency. Among the crystals belonging to the Langasite family, the Langatate (La 3 Ga 5.5 Ta 0.5 O 14 ) also called LGT seems to be an alternative option to substitute the quartz crystal resonators for frequency and time applications. The intrinsic properties like electromechanical coupling coefficients, product of quality factor and frequency are normally seen higher than in quartz crystal resonators. Moreover, the amplitude-frequency effect and the force-frequency coefficient are lower. The characterization of these resonators is given in terms of impedance, Q-factors, turnover temperature, amplitude-frequency effect and phase noise. The short-term stability of some resonator pairs has been measured about 3·10 -13 in terms of Allan standard deviation.

International audience; We present the electrical conductivity measurements of La3Ga5.5Ta0.5O14 (LGT) crystals grown by Czochralski (Cz) technique in Ir crucibles and N2 atmosphere containing few percent of O2. In addition, we have studied the effect of thermal annealing on the stability and the thermal conductivity. The electrical conductivity depends on the stoichiometry, the inhomogeneous impurities levels, the growth atmosphere and the post-growth annealing conditions. Furthermore, we recorded the UV–Vis transmission spectra of the LGT samples and we note that the less resistive LGT samples have an edge of the intrinsic absorption at the highest wavelengths.

International audience; Langatate La3Ga5.5Ta0.5O14 is piezoelectric crystal from langasite family, commonly grown by Czochralski method from Ir crucible. Langatate crystals of different colors (colorless, orange, green) have been studied by optical spectroscopy in UV-Visible (200 – 800 nm) and IR (7000 – 1000 cm-1) ranges. Furthermore, the effects of irradiation by ultraviolet laser source (λ=266 nm) and post-growth annealing in N2+O2 atmosphere have been investigated. The yellow-orange is mainly due to an absorption centered in the ultraviolet that extends into the blue of the visible spectrum (250-500 nm). The IR optical absorption spectra of Langatate crystals exhibit an absorption band at 5370 cm-1. It seems linked to a point defect responsible for color. The intensity of the absorption band at 3430 cm-1 increases after annealing in oxygen containing atmosphere. We have discussed phenomenon that can occur simultaneously in langatate crystals and produce very similar colors which are related to structural defects. First, metal ions impurities (as Iron, Titanium…), whose presence is previously confirmed by femtosecond laser ablation coupled with ICP-MS spectroscopy, can contribute to langatate color. Second, ultraviolet absorption leads us to think about charge transfer phenomenon such as O2- → Fe3+ and/or Fe3+-Fe3+ pair transitions. Third, the irradiation by ultraviolet (λ=266 nm) laser source locally color the langatate sample by the creation of color centers. Origins of color centers, particularly those related to oxygen vacancies, ( , 2e′)x, are discussed. And, finally, point defects changes the band gap of langatate, leading to extend the absorption to visible light regions.

International audience; La3Ga5,5Ta0,5O14 (LGT) langatate crystals were grown along Z-axis by Czochralski technique in argon and mixed argon with 0.1%O2 atmosphere. The coloration and the performance of langatate crystals were strongly connected to the starting chemical composition, the gas atmosphere and the growth parameters. Any deviation from the optimal LGT generate macroscopic defects such cracks and grains boundary causing a deterioration of the crystals performance.

Before using any piezoelectric crystal to realize acoustic devices (sensors, transducers, actuators or ultra-stable resonators) and beyond its mechanical properties, the crystal material itself has to be characterized. Whether the very interesting properties of the LGT crystal make it the best candidate to substitute quartz crystal for frequency output devices, we must take into account the crystal quality. Indeed, applications require homogeneous crystals with reproducible physical properties.

International audience; Glass is widely used as a structural and functional material in micro-total-analysis-systems (µTAS). Two low-cost techniques have been used to produce deep and vertical micro-structures into glass. A commercially available photosensitive glass (Foturan) is patterned by photolithography and etched in an HF solution for the construction of a microfluidic component. Channels and reservoirs were bonded to a PDMS cover. A two-level structure with various depths (reservoirs and channels) was also made by a double exposure through two different masks. The other technique uses Micro-Ultra-Sonic Machining (MUSM) to form channels by erosion into borosilicate glass (Pyrex 7740). The two structuring techniques are compared with respect to surface profiles and surface states.

Middle and near infrared (MIR/NIR) spectrometry has been used to characterize series of samples of LGx family and GaPO 4 . Since OH impurities influence the material properties, their spectroscopy is investigated in detail. The [190-3200 nm] region is measured in transmission. Furthermore, the study of spectra made at Nitrogen liquid temperature is used to follow the modification in the signature of some defects present in the lattice and induced by treatments as y irradiation or annealing. At least, we show that these new materials contain less OH-groups than quartz crystal.

cited By 2; International audience; Among the crystals belonging to the langasite family, the Langatate (La3Ga5.5Ta0.5O14 also called LGT) seems to be the best candidate to substitute quartz crystal for acoustic waves applications and frequency output devices. But, its capability to substitute quartz depends on the crystalline quality of the production of the harvested boule. Indeed, the crystal quality (its homogeneity and its atomic structure as well as the amount of chemical impurities) can be very different from one supplier to another. So, to compare and analyze the strategic interest of this crystal, we start a sufficiently researched program, supported by the French DGA, to enable us to address the parameters of the growth process, implemented on Cristal Innov platform. The Langatate is an incongruent material grown from a ternary melt of La2O3 - Ga2O3 and Ta2O5 by the Czochralski technique along or in iridium crucible and slightly oxidizing atmosphere. Furthermore, a post-growth annealing was performed in the pulling machine immediately after growth and in other oven under vacuum or in oxidizing/reducing atmosphere. Post-growth annealing is necessary to remove the thermal stress induced by the growth that are revealed by shadowscopy and it will determine the color of the boule, which varies from colorless to orange or pale-green color. We attach to analyze the stoechiometry (i.e. the amount of the majors La, Ga, Ta) by Electron Probe Micro-Analysis (EPMA) and the impurities levels by femtosecond laser ablation Inductively Coupled Plasma Mass Spectrometry (fs LA-ICP-MS) of different LGT crystals from different suppliers. The presence of point defects and inhomogeneity of the crystal composition significantly affect the optical properties and can be also revealed by optical transmission spectra in UV-VIS and IR ranges. © 2014 IEEE.

This article deals with a crystal quartz cut with virtually no amplitude-frequency effect (also called "isochronism defect" or "anisochronism"). The cut, called LD-cut (Low isochronism Defect), is set in a BVA-type structure for later use in an Ultra-Stable Oscillator (USO). Various design parameters are presented, along with the properties of the resonator. The resonance frequencies of various modes, the temperature dependence, the motional parameters and the phase noise in relation to the power supplied to the resonator are mainly studied. These properties are compared to those of the SC-cut resonators.

In this paper, we report on the use of Finite Elements Software to model and simulate new resonator designs, working at about 9 MHz. We aim to review the concept of BVA resonator by reducing the size. The miniaturization of the whole resonator will allow us to use collective processes and therefore reduce the cost of manufacturing. To achieve this result, we investigated to replace the radius of curvature, necessary for a good trapping of the vibrating energy at this frequency, by several mesas.

International audience; High quality resonators for spatial and military applications are only made by unitary way and high speed directional etching of piezoelectric material is yet insufficiently developed to produce high aspect ratio microstructures. So, in this paper, we report on the theoretical definition and on the realization of BAW resonators, working at 20 and 40 MHz. Part of mechanical process is made by deep Reactive Ion Etching of AT- and SC-cut quartz crystal wafers. To avoid edge effects such as mechanical stresses induced by mounting structure or leakage of the vibration mode, we have to realize a good energy trapping of the selected resonant frequency. Several trapping methods can be used depending on the frequency, thereby changing the resonator design, such as mass loading by electrodes themselves, mesa forms (i.e. 1 to 3 mu m circular or elliptical steps), or radius of curvature on one face of the resonator at least. Here, for question of manufacturing, we choose to trap the energy by a mesa form. Fabrication of complete mesa architecture with bridges aperture (like in a bva structure) requires combining high depth (about 140 mu m for a 40 MHz 3(rd) overtone resonator), high aspect ratios, good uniformity over the entire wafer (for about 40 resonators), vertical wall profiles and reasonable etching selectivity. After describing different RIE processes, we analyze the quality of the realization through the surface roughness, the geometry, the homogeneity of the mesa-step, the wall profile.

Unswept and vacuum-swept synthetic quartz crystals were investigated in order to determine the mechanisms responsible for the radiation sensitivity of this material. Results were obtained by means of infrared (IR) spectroscopy, dielectric relaxation spectroscopy (DRS), and thermoluminescence (TL). First, the effect of vacuum sweeping was clearly demonstrated in IR absorption by a significant decrease in the amount of hydroxyl ions and in DRS by the disappearance of the dielectric loss peak arising from the relaxation of alkali ions. Second, it was shown that swept quartz is less sensitive to irradiation than the unswept crystal. A sharp decrease in the TL sensitivity of the electrolyzed material was observed in the energy range corresponding to the recombination of alkaline-electronic defects. DRS results indicated that the dielectric signal is shifted toward a lower energy range for both types of crystals, suggesting that the irradiation greatly facilitates the relaxation of alkaline species by creating ...

Materials of the Langasite family are promising to design high quality bulk acoustic waves resonators. But, as for quartz crystal, LGS and LGT “boules” exist with different quality grades (not yet normalized) [1, 2]. So, to analyze the quality of a given crystal, we have used the same tools allowing the characterization of the quartz crystal: essentially the IR / visible / UV spectrometry coupled to chemical analyzes of impurities content. These experiments and analyzes are performed on LGS and LGT samples coming from different suppliers (in USA, Russia, Japan or France).

The LGS family are promising materials for the design of high quality bulk acoustic wave resonators. We have manufactured many plano-convex 10 MHz 5th overtone Y-cut resonators using langasite (LGS, La(3)Ga(5)SiO(14)) and langatate (LGT, La(3)Ga(5.5)Ta(0.5)O(14)) crystals. We observed that the quality factor strongly depends on the polishing method, the supplier of the material, and on the energy trapping. For quartz crystals, we have found that resulting IR spectra exhibit absorption peaks more or less deep, linked to defects. These predominant criteria are not surprising, but they have to be defined in manner similar to that used for quartz crystal. A satisfying machining and polishing method has been first applied to elaborate high Q resonators, and a comparison between samples of LGS and LGT materials from different suppliers is established. In addition, LGT resonators are characterized by their motional parameters and frequency-temperature curves. Nevertheless, one of the main results is that the measured Q x f product is not the expected one. We present results of Q-factor versus radius of curvature: it appears that an optimization should be performed and that this last one cannot be directly transposed from that of quartz crystal resonator. Currently, the best resonator that we have made has a Q x f product of 1.4 x 10(13) on its 5th overtone (1.7 x 10(13) on its 9th overtone). This result is slightly higher than the similar parameter obtained on a state-of-the-art SC-cut quartz crystal resonator working at the same frequency.

Though the use of LGS family crystals for filtering applications is now well known, we present here one of the best way to realize antimesa structures working at higher frequencies than a few tens of MHz. Generally, this kind of realizations requires dissolution depths higher than 100 mum. Consequently, the rough surface state does not remain constant: it becomes smoother or its roughness parameter can increase drastically. For that, we have compared the chemical dissolution of the crystal in four different etchants (HCl, HNO3, H3PO4 and NH4F.HF) for three crystal orientations: X-, Y-and Z-cuts (in LGS, Y-cut is similar to the AT-cut in quartz crystal). The parameters chosen to compare the efficiency of our selected solvents are the dissolution rate and the average roughness Ra. Furthermore, we have worked at 2 different temperatures: 60 and 80degC. The experiences show firstly that a X-cut plate is etched in HCl rapidly, compared to the Z-cut and so reveal the anisotropy of the material structure. Secondly, we observe that the dissolution rate of LGS in HCl solution is 8 to 10 times higher than in other solvents, at a given temperature. Unfortunately, it tends to reveal deep dissolution figures on the surface. From this set of experiments, we conclude that the best compromise is obtained with the ammonium bifluorure solvent which allows us to obtain a smoother surface state than initially.

International audience; Abstract— Materials in the LGT family are promising for designing bulk acoustic wave resonators with high quality factor. In our laboratory, we have manufactured a lot of plano-convex 10 MHz 5th overtone Y-cut resonators using LGS (langasite La3Ga5SiO14) and LGT (langatate La3Ga5.5Ta0.5O14) crystals. Our initial aim was to do noise measurements on these home-made resonators but problems occurred during manufacturing. It was the opportunity for further investigations. Indeed, we observed that the quality factor depends strongly on the energy trapping, the polishing method and the materials quality from one supplier to another. As for the quartz crystal, we have found that the material quality can be qualified by IR spectrometry whose resulting spectra exhibit absorption peaks more or less deep, linked to defects. These predominant criteria are not surprising but although they are nowadays quite well-defined in the case of quartz crystal resonators, they have to be defined again in the case of these LGS and LGT crystals. Then, a satisfying machining and polishing method has been first applied to elaborate high Q resonators. A comparison between different grades of LGS and LGT materials is established. In addition, LGT resonators are characterized by their motional parameters and frequency-temperature curves. Nevertheless, one of the main results is that the measured Q-f product is not the expected one. We present results of Q-factor versus radius of curvature and their comparison with the theoretical approach. It appears that an optimization should be performed. Right now the best resonator that we have made has got a Q-f product of 1.4 1013 on its 5th overtone (1.7 1013 on its 9th overtone). This result is slightly higher than the similar parameter obtained on a SC-cut quartz crystal resonator working at the same frequency.

The performances of quartz resonators and sensors are often limited by various defects existing in the crystal, whatever the origin of the quartz is (natural or cultured). So, before manufacturing high-quality quartz devices, it is essential to perform a systematic study of the as-grown material which will allow a prediction of the behaviour of the device. Among point defects, the most common is the OH related growth defect. It is Infrared active and it can be modified by treatments such as thermal annealing, sweeping or irradiation. Kats carried out a classical study of hydrogen in both natural and synthetic quartz. Particularly, thea author pointed out 4 stretching-mode infrared bands "growth-defects" including hydrogen, increasing with crystal growth-rate and decreasing when the sample is irradiated. After Kats, several authors (Lias, Chakraborty, Paterson, Bahadur...) worked on different methods to determine the OH content. Finally, numerous researchers (Fraser and Dodd in 1966, Rudd and Hougthon in 1966, Sawyer in 1972 and 1983, Toyo in 1976...) have shown that the electrical quality factor "Q" is closely dependant on the hydrogen content in quartz. As this Q-factor does not depend only on the material quality, it has been necessary to define the resonator as nearly as possible to an ideal device, ideally designed and manufactured. To avoid these difficulties also linked to the measurement principle of the spectrometer ("double beam" or "with Fourier transform"), we present here new measurements on SC-cut resonators working on their 10 MHz 3rd overtone. They are built in GEMMA quartz samples following a very precise manufacturing process. Furthermore, they have been extracted from various generations of cultured quartz and have also been submitted to different treatments.

Space radiations are responsible of transient and permanent shifts of the output frequency signal of any quartz crystal oscillator. In this paper, the degradation of quartz crystals under radiation stresses is shown to be related to competition between trapping and recombination of radiation-induced carriers in quartz lattice. The presented model exhibits a good agreement with experimental data.

This paper presents the first results obtained in the R&D study initiated by the CNES at the end of 2004. Numerous French experts have been gathered to determine and to tentatively understand the mechanisms responsible for the radiation sensitivity of quartz resonators and to correlate the results of various analyses in order to reduce or to anneal their susceptibilities.

International audience; Ultrasonic machining (USM) presents a particular interest for the cutting of non-conductive, brittle materials such as ceramics, glasses or fused silica and quartz crystal. Unlike other non-traditional processes such Electrical Discharge Machining (EDM and micro-EDM, adapted to conductive materials), laser ablation or wet chemical etching, USM does not thermally damage the workpiece and does not create significant levels of stresses. Production of complex 3-D shapes with a volume of a few cubic millimeters is presented.

We report progress in modeling and measuring temperature effects in vibrating beam gallium orthophosphate (GaPO/sub 4/) resonators. In addition to the well known thickness-shear AT-cut, temperature compensated cuts exist in GaPO/sub 4/ for length extensional, flexural and torsional modes. Analytical models of temperature effects are compared with experimental measurements on devices fabricated on AT (Y-16.1/spl deg/) and Z-cut plates by ultrasonic machining. The agreement between theory and experiment is fairly good taking into account that temperature coefficients of GaPO/sub 4/ have been experimentally tested for only a few thickness-shear resonators.

The high pressure structural and elastic behaviour of LGT single crystal has been explored. The phase diagram has been investigated up to 20 GPa by x-ray diffraction and the equation of state deduced. The complete set of second order elastic constants (S.O.E.C.) and their pressure dependence have been determined by bulk acoustic wave measurements up to 8 GPa. The bulk and linear moduli and their pressure variations have been calculated and compared to values obtained by x-ray diffraction. The stability Born criteria have been deduced.

In this paper we report the method used to dissolve the Langasite and Langatate crystals. Then the characterization of chemical impurities like Al, Fe, Na, Li... incorporated in the crystal during the pooling or coming from strating oxides (La2O3, Ga2O3, Ta2O3 and SiO2) is discussed. Finally, the comparison with the quartz crystal material has been done as well in the IR range as in term of chemical impurities.

Quartz resonator quality is improved using sweeping treatment. It is well known that this operation is usually performed by applying a high electric field along the optical axis (Z) of the quartz lattice. This is due to the existence of channels formed by helicoidal structure of quartz crystal. This crystallographic structure exhibits other channels parallel to the electrical axis (X) which are larger than the previous ones. In order to compare the influence of each kind of sweeping on the quality of quartz resonator, we have performed Z- and X-sweeping on natural and cultured quartz bars used to manufacture 10 MHz SC-cut resonators. As usually, the process of qualification has been achieved by comparisons between spectrometric measurements (infrared, laser absorption, ICP) before and after treatments.

Acceleration sensitivity of a quartz resonator is usually attributed to the design of the unit. BVA technologies have largely participated to g-sensitivity reduction since 1977. At that time it was claimed that symmetry of the unit structure was fundamental. More recently it has been demonstrated by Tiersten that g-sensitivity could vanish to zero for perfect symmetry (including blank geometry, mounting, etc...). Under those conditions BVA technologies have to be considered in a general discussion on g-sensitivity reduction, because they may help to draw interesting conclusions. In this paper we show that BVA technology is adequate for very low g-sensitivity and why. By very low g-sensitivity we understand largely under 1/spl times/10/sup -10//g in industrial production. Furthermore the influence of some construction parameters and/or lack of symmetry due to manufacturing have been studied through finite element analysis. Results are shown and commented on (orientation of mounting, off centering of contour, off centering of grooves). We then compare these theoretical values to experimental ones. Experimental data are obtained by two methods: measurements under random vibrations and/or sinusoidal vibrations; measurements of frequency deviation in 2g tip over tests. Finally practical design in view of state of the art units is commented on together with production statistics.

Performance requirements from pressure and temperature sensors especially for use in oil fields are very demanding. Several years of effort have been devoted to the development of a dual-mode thickness-shear quartz pressure sensor to meet such requirements. The objective of this effort was to develop a sensor with a pressure range of up to 15000 psi, a temperature range of up to 175 degrees C, a pressure calibration accuracy of 1 psi, and a resolution of 0.01 psi with 1-s counter gate time. It is demonstrated that the dual-mode thickness-shear quartz pressure sensor presented meets or exceeds these requirements. The pressure resolution is better than 0.01 psi at 1-s counter gate time. A significant advantage of the dual-mode design is its dynamic performance. An in situ measurement of the resonator temperature allows an implementation of an extremely effective dynamic compensation algorithm which yields corrected pressure readings with a response time as short as a strain-gauge-based pressure transducer while retaining the high performance of a quartz gauge under static conditions. >

The accelerometric and magnetic sensitivities of a quartz resonator are commonly attributed to the design of the resonator, for the main part. Since a few years, it is well-known that G-sensitivity can reach zero if the geometry of the structure (including blank geometry, orientation of the mounting, number of supports, ...) leads to the perfect symmetry around the three axes. In this paper, we show that the BVA resonator has been designed to exhibit a very low G-sensitivity (largely lower than 1*10/sup -10//G). By finite element analysis, we have quantified the influence of some symmetry defects due to manufacturing process (as orientation of the mounting, shift between the vibrating area center and the blank center, ...) on the accelerometric sensitivity with different boundary conditions. Furthermore, we have calculated the frequency shift due to a slight dissymmetry of the mounting structure and deduced how G-sensitivity increases when the inhomogeneity of the stress distribution in the vibrating area increases. At least, we compare these theoretical results to experimental values obtained by two methods: measurements under random vibrations in the range [20-100 Hz], measurement of the frequency shift due to a 2G-tipover test around a given axis.

Excitation, by the use of two pairs of cross-connected half electrodes, of SC-cut resonator operating on first anharmonic modes is considered. In order to obtain resonators having the best electrical response of the C-mode, it is shown that two cases can be encountered, depending on the shapes and orientation of modes, i.e. on overtone number. The computation of electrical parameters is based on Lewis formula and use of analytical expressions for the vibration and the electric field.

It is well known that, for quartz crystal, mechanical and/or thermal stress sensitivities prevent the achievement of ultimate performances of bulk acoustic wave piezoelectric resonators. It is important to check these effects in newly developed Langasite (LGS) and Langatate (LGT) resonators. A theoretical and experimental study of the force-frequency effect (denoted by the K/sub f/ coefficient) in Y-cut LGS thickness-shear resonators, working at various overtone modes, is presented. Theoretical predictions are based on Tiersten theory of wave propagation in a pre-stressed medium. For LGS crystals, 3/sup rd/ order nonlinear elastic constants have been published and used here for modeling the behavior of thickness-shear resonators submitted to diametrical compression. A comparison between theoretical predictions and experimental measurements is presented. In the case of LGT crystal, numerical data of the third order elastic coefficients are not available at this time. Only experimental measurements of Kf coefficient are presented in order to compare the behaviors of LGS and LGT Y-cut resonators.

First measurements of the phase noise versus the radius of curvature of SC-cut resonators are given. Resonators with adherent electrodes are investigated and compared with unelectroded resonators. The phase noise measurements are obtained with a crystal resonator tester specifically designed to assist in the characterization of quartz crystal resonators.

The design of a SC-cut resonator for which the C-mode has a lower resistance than the B-mode (typical ratio 1.5) is presented. This result is obtained by using an antisymmetric anharmonic mode with a particular geometry and connection of the electrodes. Experimental results (motional resistance, thermal behaviour) are given for a third overtone, 10 MHz, resonator.

In this paper, we report the ferrobielastic twinning in AT-cut samples issued from natural (Brazil and Madagascar) and synthetic (from Sawyer company) quartz crystals. The experiments have been carried out using an uniaxial stressing equipment for which the stress is applied in a suitable direction of the quartz sample. The stress level associated with the optical appearance of the twinned domains and coercive stress values are presented for each material. It has been observed that these stress levels are smaller for synthetic quartz than for natural one. The observations of the twin wall propagation were made by X-ray topographs obtained with synchrotron radiations. Transmission Laue patterns due to the white X-ray beam were taken at several compressive stress levels. As visualisation of a twin domain is governed by contrasts generated in topographs of chosen lattice planes, we notice that the twinned domain does not disappear after putting off the pressure. Additionally, the content of lattice impurities such as Al, Li, Na, K and broad OH band are given.

There is a growing need for ultrastable quartz oscillators operating under the special environmental conditions usually required in space program applications. This is the case for radiocommunications, navigation, precise positioning and scientific programs especially in the case of satellite applications. Under those conditions an evaluation program based on general rules ESA/SCC has been launched in 1992 for precise space evaluation of mini-BVA resonators. A special Process Identification Document (PID) has been established which includes fabrication processes and test procedures. 21 resonators have been fabricated according to the proposed PID. Then a test program has been defined and resonators have been space evaluated with interesting results which are discussed. Finally, it appeared that performances goals have been obtained. In conclusion special resonators can be fabricated by LCEP with guaranteed performance.

This work compares the dielectric relaxation properties of different crystalline quartz materials, according to their source (natural or synthetics). It is shown that these relaxation properties are due to a hopping process of alkaline (Li+, Na+ and K+) impurities, located near [Al-O4]5- tetrahedra. A detailed analysis, in terms of the distribution function of the dielectric loss peak, allowed us to perfectly distinguish the different types of as-grown quartz. We show that i) the natural quartz has less stable M+ charge carriers than the synthetic materials and that ii) the homogeneity of the M+ trapping sites, created by the [Al-O4]5- tetrahedra, strongly depends on the crystal growth conditions. These features were then studied using quartz samples with different treatment conditions: as-grown, irradiated or annealed at high temperature. We propose that the irradiation greatly facilitates the M+ relaxation, by creating additional low energy M+ hosting sites, whose number depends on the source of the quartz crystals. We also show that for 100kRad irradiation, the saturation state of the defects is already reached for all the materials under consideration. Finally, we propose that irradiation followed by annealing at 450°C improve the M+ stability and homogeneity in quartz materials, compared with the as-grown materials, this trend being much more relevant for the natural than for the synthetic quartz.

The authors have demonstrated experimental verification of the stress compensation feature for the fast thickness shear mode of vibration of stress-compensated for B-mode and temperature-compensated for C-mode (SBTC)-cut quartz resonators. For the resonator design used in the cylindrical probe structure, the motional resistance for the B-mode of vibration was approximately 12% of that of the C-mode. The relatively large motional resistance for the C-mode of vibration of the SBTC-cut was found to be largely due to the lower piezoelectric coupling for the thickness excitation of this mode. In addition the proximity of the third overtone of the A-mode to the fifth overtone of the C-mode also contributed to the increase in the motional resistance. The authors have obtained experimental data on the temperature dependence of the planar stress coefficient and pressure dependence of the frequency-temperature characteristic for both the thickness-shear modes of the SBTC-cut. It is noted that such a doubly rotated cut can have applications in the design of either stable frequency sources or sensors for pressure and temperature measurements. >

These last few years, a new doubly rotated cut of quartz crystal resonator has been thought up at the LCEP (Laboratoire de Chronometrie Electronique et Piezoelectricite). This cut, named LD-cut for "low isochronism defect" cut, exhibits an amplitude-frequency effect one hundred times lower than the SC-cut one, that is to say a relative frequency change of about 1/spl middot/10/sup -11/. This paper deals with the behavior of such a crystal cut working in an oscillator. It is based on results from a batch of 10 MHz LD-cuts recently manufactured in a BVA process. Properties, advantages and drawbacks of the LD-cut are first reviewed. They have been tested in terms of noise and then built in oscillators. Experiments with various resonator drive levels have been performed. Measurements of their power spectral density of phase fluctuations are given and discussed.