Jean-Jacques Boy

A dual-mode thickness-shear quartz pressure sensor

The development of a dual-mode thickness-shear quartz pressure sensor to meet the demanding performance requirements of oil-field applications is discussed. The objective was to develop a sensor with an operating pressure range of 0-103.42 MPa (0.15 000 lb/in/sup 2/), a temperature range of -10 to +175 degrees C, a pressure calibration accuracy of 6894.8 Pa (1 lb/in/sup 2/), and resolution of 68.95 Pa (0.01 lb/in/sup 2/) with 1-s counter gate time. Doubly rotated cuts with piezoelectric coupling to both the C-modes of vibration were investigated. A theoretical study and general design considerations in the development of such sensors are described. Experimental results were obtained for two sensor designs: one uses a cylindrical design with the SBTC-cut, and the other, called SPA, is a special resonator design vibrating around 5 MHz without any activity dips. Pressure sensitivity of approximately 145 Hz/MPa (1 Hz/lb/in/sup 2/) at 175 degrees C is obtained. Laboratory evaluation of the static and dynamic performances is discussed for the prototypes based on the SPA design.<<ETX>>

Phase noise limitation due to amplitude frequency effects in state-of-the-art quartz oscillators

During the past two decades very important advances have been accomplished in reducing the phase modulation (PM) noise in state-of-the-art bulk wave quartz crystal oscillator. Various limitations have been significantly reduced, especially those related to dynamic temperature fluctuations, temperature gradients, 1/f noise in the electronic and amplitude frequency effects. Amplitude frequency effects have been studied in the past because they are so large in AT-cut resonators. The introduction of the SC-cut significantly reduced the sensitivity to amplitude fluctuations as well as the sensitivity to temperature fluctuations. The amplitude frequency effect in modern SC-cut resonators at 5 or 10 MHz is, however, far from negligible and its importance relative to temperature effects and 1/f amplifier noise must now be reexamined to chart the path to further advances in short-term stability. In this paper we show comparisons of the amplitude frequency effect in traditional 5 MHz AT-cut resonators to our results obtained with 5 MHz BVA AT-cut, 5 MHz BVA SC-cut, 10 MHz BVA AT-cut and several designs of 10 MHz BVA SC-cut resonators. We also compare these measurements with those obtained from 100 MHz resonators. A simple model in which an additional noise source arising from the amplitude frequency effect is introduced in the input of the resonator excited at a given power. This permits us to estimate the contribution of the amplitude frequency effect to /spl sigma//sub y/(/spl tau/).

Investigations on LGS and LGT crystals to realize BAW resonators

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, La3Ga5SiO14) and langatate (LGT, La3Ga5.5Ta0.5O14) 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 times 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 times f product of 1.4 times 1013 on its 5th overtone (1.7 times 1013 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.

Ultra stable oscillators dedicated for space applications: oscillator and quartz material behaviors vs radiation

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

Isochronism defect for various doubly rotated cut quartz resonators

It has been shown in earlier work, that the amplitude-frequency effect (also called isochronism defect or anisochronism) could be a limitation factor on ultra-stable oscillators. Theoretical studies based on the non-linear theory of the piezoelectricity have already been developed to explain the amplitude-frequency effect. So it is possible to estimate the dependence of the isochronism defect versus design parameters of resonators (radius of curvature, electrodes diameter, overtone rank, ...). However, due to the unknown of the fourth order elastic coefficients, it is not possible to predict isochronism defect of any resonant frequency of a given energy trapped resonator. To tentatively find the orientation of a plate which does not exhibit an isochronism defect, we have realised electroded resonators with different orientations and curvatures. We present results which verify, particularly, R/sup -1/2/ dependence of amplitude-frequency effect versus radius of curvature. Moreover, we show that the isochronism defect can be positive or negative and can vary from one orientation to other one of about two orders of magnitude.

Crystal quality of LGT samples: Influence on BAW resonators

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).

Simple energy level model for frequency degradation of USO under radiation

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.

The drive level dependence of the resonant frequency of high frequency quartz resonators

The drive level dependence of frequency, which comes from the nonlinear effects of the quartz material, is related to the amplitude of strain in the quartz resonator. High stability, and high frequency resonators are designed in such a way the vibration is trapped in the center of the vibrating plate. Therefore, the amplitude of the effect is also strongly dependent of the trapping of the vibration and the construction parameters of the resonator play a critical role. In this paper we present the basic equations when the nonlinearities are restricted to the mechanical behavior, although the nonlinearity of electrical polarization or other effects can also be introduced. As application, we restrict our attention to the most important case of contoured (plano-convex) resonator

Phase noise study of quartz crystal resonators versus the radius of curvature

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.