Temperature sensor comprising a high-overtone bulk acoustic resonator

摘要

This temperature sensor includes an HBAR resonator, a unit for determining the difference between two distinct resonance frequencies at a temperature T, measured between two electrodes of a same pair of the HBAR resonator and a unit for determining the temperature of the resonator from the difference in frequencies and from a one-to-one function providing the match between the temperature and the frequency difference. The resonator is formed by a stack of a first electrode, a transducer, a second electrode, and acoustic substrate and the cuts of the transducer and of the substrate are selected so as to obtain high electro-acoustic couplings and a difference in frequency temperature sensitivities between two distinct vibration modes co-existing within the resonator, greater than or equal to 1 ppm·K−1.

主权项

1. A temperature sensor comprising a resonator of the high overtone bulk acoustic wave HBAR type intended to operate at a predetermined operating frequency and in a range of temperatures centered around a reference temperature T0, the resonator including:
a piezoelectric transducer formed by a layer of a first thickness of a first material, cut according to a first transducer cut angle φ1 defined by the nomenclature (YXw)/φ of the IEEE Std-176 standard (revised in 1949) substantially equal to zero, and according to a second transducer cut angle θ1 defined by the nomenclature (YXl)/θ of the IEEE Std-176 standard (revised in 1949) such that the transducer has, either a first polarization direction {right arrow over (P)}Along of a first longitudinal vibration mode of the transducer, and a second polarization direction {right arrow over (P)}Acis_dual of a second shear vibration mode of the transducer, or a single polarization direction {right arrow over (P)}Acis_seul corresponding to a shear vibration mode of the transducer, and such that the electro-acoustic coupling of a shear vibration and/or of a longitudinal vibration for the material of the transducer is greater than or equal to 5%, an acoustic substrate formed by a layer of a second thickness of a second material having an acoustic quality coefficient/excitation frequency product at least equal to 5·1012, cut according to a first substrate cut angle θ2 defined by the nomenclature (YXl)/θ of the IEEE Std-176 standard (revised in 1949), cut according to a second substrate cut angle ψ2 defined by the nomenclature (YXt)/ψ of the IEEE Std-176 standard (revised in 1949), having at least two polarization directions from among a first polarization direction {right arrow over (P)}B1, a second polarization direction {right arrow over (P)}B2, a third polarization direction {right arrow over (P)}long, respectively corresponding to a shear vibration mode of the acoustic substrate with a slow phase velocity, to a shear vibration mode of the acoustic substrate with a fast phase velocity, and to a longitudinal vibration mode of the acoustic substrate, a counter-electrode formed by a metal layer adhesively bonding a first face of the transducer and a face of the acoustic substrate, and an upper electrode positioned on a second face of the transducer opposite to the first face of the transducer and to the acoustic substrate, characterized in that the ratio of the first thickness over the second thickness is less than or equal to 0.05; the cut angles φ1, θ1, ψ2, θ2, and the acoustic relative positioning of the transducer and of the acoustic substrate are configured so that there simultaneously exists at least two vibration modes of the acoustic substrate, strongly coupled to a same extent with at least one vibration mode of the transducer, and that said at least two strongly coupled vibration modes of the acoustic substrate comprise a first vibration mode having a first temperature coefficient of the substrate frequency of the first order at the reference temperature T0 and a second vibration mode of the acoustic substrate having a second temperature coefficient of the substrate frequency of the first order at the same reference temperature, and the transducer, for the first vibration mode of the acoustic substrate, has a first temperature coefficient of the transducer frequency of the first order at the reference temperature, and has for the second vibration mode of the acoustic substrate, a second temperature coefficient of the transducer frequency of the first order at the reference temperature, and the absolute value of the difference of the first and second temperature coefficients of the frequency of the resonator of the first order is greater than or equal to 1 ppm/° K, the first temperature coefficient of the frequency of the resonator of the first order being substantially equal to the sum of the first temperature coefficient of the frequency of the acoustic substrate of the first order and of the first temperature coefficient of the transducer frequency of the first order weighted by the relative thicknesses of each material relatively to the total thickness of the resonator, and the second temperature coefficient of the frequency of the resonator being substantially equal to the sum of the second temperature coefficient of the frequency of the acoustic substrate of the first order and of the second temperature coefficient of the transducer frequency of the first order weighted by the relative thicknesses of each material relatively to the total thickness of the resonator.