Jacques Detaint

Crystal growth of GaPO4, a very promising material for manufacturing baw devices

GaPO4 cystals were obtained by hydrothermal solution crystal growth. The retrograd solubility of the material was investigated in different solvents. In static growth vessels, good quality crystals can be obtained only if the solute supply is higher than about 0.06M/L. Crystal characterization by infrared spectroscopy showed that dilute solvents at high temperature decrease the “-OH” group content. Seed lengthening by splicing along the Y-axis was designed. The AT cut angle and the C44 elastic constant were determined. Compared to quartz-type materials, the C0/C1 calculation shows the high ability of GaPO4 for manufacturing BAW devices.

Properties of AT cut gallium phosphate resonators

Abstract Gallium phosphate is a quartz analogue that possesses more intense piezoelectric properties. We report here a study performed to determine more accurately the properties of resonators made using crystal orientations situated near the main cut presenting a zero temperature coefficient at room temperature. Recent crystals having a much improved quality were used to cut plano-convexe resonators with five orientations situated in a range of nearly two degrees around the previously determined angular position of this cut. The temperature coefficients of the resonance frequencies of the electrically excited shear modes and the electrical properties of the resonators were determined. The vibration modes were studied using synchrotron radiation X-ray topography. For all the studied cuts, parabolic thermal variations of the resonance frequencies were observed. The temperature of the extremum varies somewhat with the rank of the mode and also, but slowly, with the cut angle. On the whole a very good thermal stability is obtained for the resonators. Q factors higher than those previously measured were obtained together with, as predicted, very interesting values of the equivalent electrical scheme. The observed vibration modes are generally close to those computed using the Tiersten theory. They present several very interesting properties but display several particularities, such as often possessing a second shear component with a noticeable amplitude, which make them somewhat different from the mode of the corresponding quartz resonators.

Crystalline quality of the trigonal piezoelectric materials and effects of the extended defects

Many frequently used or promising piezoelectric materials belong to crystal classes 32 or 3m. Among them are α quartz and its crystallographic analogs (AlPO4, GaPO4, α-GeO2, etc.), the numerous materials of the langasite (La3Ga5SiO14) family and also lithium tantalate (LiTaO3) and lithium niobate (LiNbO3). In this paper we study the present state of the art for these materials, indicate their principal point and extended defects, and present methods to reduce the dislocation density. Large concentrations of intrinsic point defects often exist in crystal grown at very high temperatures. The point defects (intrinsic or related to impurities) modify the constants and can increase the acoustic losses. This is the case for the alkali ions and the OH that induce severe losses in different temperature intervals. The extended defects also affect the performances of the piezoelectric devices. Some, such as twins, ferroelectric domains, or large solid or liquid inclusions, have very detrimental effects. Dislocations, growth bands, and planar defects are more difficult to avoid and affect the devices in a more subtle manner. In quartz and its analogs, dislocations seem to increase the nonlinear elastic effects and have a collective effect on the vibration modes, particularly in energy trapping resonators. Growth bands and stacking faults also produce similar effects.

X-ray topography studies on the influence of the mass-loading effect on resonator parameters

In this paper the results of electrical measurements of the mass-loading influence on AT-cut quartz resonator parameters are compared with those obtained by X-ray topography analysis of the same resonators. Based on the Ballatos transmission-line analogs of the trapped-energy resonators vibrating in thickness-shear mode, the mass-loading effect on resonator characteristics was studied and the effective mass-loading, motional inductance and quality factor of quartz resonators were computed. X-ray topography measurements were performed by transmission diffraction using the synchrotron radiation. Sawyer plan-parallel polished AT quartz resonators with 14 mm diameter, 5 MHz frequency, Au electrodes with various structures, diameters and thickness were used in experiments. The results of the X-ray topography investigations are in agreement with the previous ones obtained by electrical measurements.

Investigations on the langasite resonators by X-ray topography

In this paper the results of electrical measurements of the mass-loading influence on Y-cut langasite resonator parameters are compared with those obtained by X-ray topography analysis of the same resonators. Based on the Ballatos transmission-line analogs of the trapped-energy resonators vibrating in thickness-shear mode, the mass-loading effect on resonator characteristics was studied. The effective mass-loading, motional inductance and quality factor of langasite resonators were computed. Sawyer plan-parallel polished Y-cut langasite resonators with 14 mm diameter, 5 MHz resonant frequency, Au electrodes of 7 mm diameters and various thickness were used in experiments. X-ray topography measurements were performed by conventional transmission Laue setting using the white beam synchrotron radiation on fundamental, third and fifth overtones. The results are in agreement with those obtained by electrical measurements. The comparison of X-ray diffraction topography images previously performed on AT-cut quartz resonators with X-ray topographs on langasite resonators pointed out that the Y-cut langasite resonators are less influenced by the mass-loading than the AT-cut quartz resonators.

Determination of the vibration amplitude of thickness shear modes using white beam stroboscopic topography at E.S.R.F.

Abstract A new topographic method allows a direct mapping of the amplitude of the vibration modes of piezoelectric devices. With this method it is possible to measure the amplitude of the vibration of a thickness shear mode at each point of an AT cut quartz resonator. The principle of this method is based on the use of stroboscopic section topography obtained from the white beam delivered by a third generation synchrotron soure at ESRF.

Piezoelectric properties of SixGe1-xO2 crystals

We report a first measurement of several elastic, piezoelectric, and dielectric characteristics of Si0.93Ge0.07O2 crystals. This was made using the thickness modes of plates of several simple orientations, using normal and/or lateral excitation. Corrections accounting for energy trapping effect (finite electrode dimension and mass loading) or stray capacitances were made after the measurements when partially electroded plates were used. The most interesting features of SixGe1-xO2 crystals already demonstrated are mainly the extremely reduced OH concentration, the existence of compensated cuts, the larger piezoelectric constants and the increased temperature of the alpha-beta phase transition.

Vibration modes analysis by X-ray topography in quartz and langasite resonators

This paper presents the results of the vibration modes measurements by X-ray topography in SC-cut quartz and Y-cut unpolished langasite resonators. A comparison of these results with X-ray diffraction topography images on AT-cut quartz resonators and Y-cut polished langasite resonators pointed out the behavior of mass-loading effect with plate orientation angle and with the surface state of the piezoelectric substrate. The results are compared with electrical measurements performed on the same resonators. 5 MHz Sawyer, plan parallel SC-cut quartz and Y-cut unpolished langasite resonators, with 14 mm plate diameter and various electrode thickness and diameters have been investigated on fundamental, third and fifth overtones. The study on SC-cut quartz resonators and unpolished Y-cut langasite resonators pointed out a good agreement with the results obtained on the same resonators by electrical measurements. The conclusion is that the SC-cut quartz resonator characteristics present a similarly harmonic dependence with those of the Y-cut langasite resonators thus revealing the stress-compensated feature of the Y-cut in langasite crystal.