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Effets des propriétés physico-chimiques du cristal LGT (La3Ga5.5Ta0.5O14) sur les performances des résonateurs piézoélectriques.

Abstract : We have characterized Langatate piezoelectric crystals La3Ga5.5Ta0.5O14 (LGT), differently colored in order to evaluate the defects influence on the quality of Bulk Acoustic Waves resonators for the Time and Frequency domain.We have analyzed the composition of crystals whose variations around stoichiometric composition are mainly due to the evaporation of the Ga2O during growth compensated by adding an excess of Ga2O3 in the initial mixture. Among different techniques, the ICP-AES spectrometry, preceded by a dissolution by alkaline fusion seems to be the most accurate technique to determine the composition.The inevitable presence of chemical impurities, such as metallic elements, rare earth… linked to the purities of the raw materials, to the sintering of the load in an alumina crucible… is also studied. We try to explain in particular the nature of the color centers that evolve according to the growth atmosphere or during a particular annealing.So, we conclude by a list of necessary properties to obtain BAW resonators exhibiting a Q.f product higher than quartz. For this, we establish that it is necessary that:- the crystal composition is as close as possible to the stoichiometric composition,- the electrical resistivity is the highest possible,- the spectroscopic study does not reveal any absorption band in the visible domain.In these conditions, we were able to highlight that the quality factor of a 10 MHz resonance is of 1.44 million at the inversion temperature of the frequency-temperature curve (1.35 for the quartz crystal in the same conditions), but that this one decreases significantly to reach 0.35 million if we perform an annealing under air at 1000 °C during 48 hours.
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Submitted on : Wednesday, November 21, 2018 - 4:36:09 PM
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  • HAL Id : tel-01930198, version 1

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Maroua Allani. Effets des propriétés physico-chimiques du cristal LGT (La3Ga5.5Ta0.5O14) sur les performances des résonateurs piézoélectriques.. Cristallographie. Université Bourgogne Franche-Comté; Université de Carthage (Tunisie), 2017. Français. ⟨NNT : 2017UBFCD041⟩. ⟨tel-01930198⟩

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