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2019-06-24 - Colloque/Présentation - poster - Anglais - page(s)

Dupla Florian , Renoirt Marie-Sophie , Gonon Maurice , Smagin Nikolay, Duquennoy Marc, Martic Grégory, RGuiti Mohamed, "Surface acoustic wave generation and propagation on polar glass-ceramic for high temperature sensors" in Transducers 2019 - Eurosensors XXXIII, Berlin, Allemagne, 2019

  • Codes CREF : Sciences de l'ingénieur (DI2000)
  • Unités de recherche UMONS : Science des Matériaux (F502)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux)
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Abstract(s) :

(Anglais) Novelty/ Progress Claims This paper presents a surface acoustic wave (SAW) device able to operate up to 800°C, based on a piezoelectric non-ferroelectric glass-ceramic containing fresnoite crystals. This material is synthesized by a classic glassmaking technique and isothermal crystallization heat treatment. Input and output interdigital transducers (IDT) are realized on its surface to generate and receive the SAW. It creates a temperature sensor working up to 800°C, that will further be modified in pressure or humidity sensors by applying the appropriate sensitive layer between the input and the output IDT. Background/ State of the Art Surface acoustic wave devices are widely used in different fields, such as filters, sensors and actuators. They can withstand harsh environments and be used as temperature, pressure, or humidity sensors. However, most of the SAW sensors are based on ferroelectric single-crystals that cannot work at temperatures higher than 300°C. Some non-ferroelectric single crystals operate up to 1000°C but are very expensive [1]. Fresnoite glass-ceramic is a piezoelectric and non-ferroelectric polycrystalline material, making it a good candidate for high temperature applications [2][3]. Description of the New Method or System A parent glass is made by mixing reagent grade SrCO3, TiO2, SiO2, K2CO3 and Al2O3, and melting it at 1500°C. After casting the melt, a glass plate is crystallized 200°C above its glass transition temperature (figure 1). The obtained glass-ceramic contains 70 vol% of piezoelectric Sr2TiSi2O8 crystals and 30 vol% of residual glass. IDT are deposited on its surface through constantan/platinum sputtering followed by a laser ablation to shape the electrodes. Figure 2 shows IDT with a working frequency of 2 MHz. The ability of the obtained device to generate and propagate SAW at high temperature is investigated by heating the device in a tubular furnace. An alternative current is applied on the input IDT, and the output signal is monitored over temperature through an oscilloscope. The prototype of a pressure sensor is proposed in figure 3. It is realized by high temperature bonding a thin fresnoite glass-ceramic plate (1 mm thick) on a thicker block showing a hemispherical cavity. Experimental Results First step is to assess the stability of the fresnoite piezoelectric phase in temperature. Figure 4 shows no evolution of the crystallographic structure which then remains piezoelectric up to at least 1000°C. Figure 5 shows a slow decrease of the mechanical properties of the glass-ceramic above 650°C and a drastic fall above 800°C. This is explained by the viscoplastic behavior of the residual glass above its glass-transition temperature Tg at 650°C (figure 6). Figures 7a and 7b show the thickness of the sputtered layer after the deposition of a bonding layer of constantan (55 wt% Cu – 45 wt% Ni) and a conductive layer of platinum. The laser ablation parameters are then adjusted in order the remove this thickness without vaporizing the glass-ceramic during the process. Once the IDT are realized on the sample, its ability the propagate SAW in temperature is evaluated. Figure 8 shows the relative amplitude of the output SAW over temperature. There is a slow decrease from room temperature to 650°C (A), due to the thermal expansion mismatch between the fresnoite crystals and the residual glass, creating stress and microcracks. The increase above 650°C (B) is due to the progressive softening of the glassy phase that, consequently, less constrains the piezoelectric phase. The output signal remains high up to 800-850°C, before the SAW rapidly disappear because of a too high damping (C) as shown in figure 5. REFERENCES: [1] U. De et al., “Ferroelectric materials for high temperature piezoelectric applications”, Solid State Phenomena, vol. 232, no. April, pp. 235–278, 2015. [2] J. Zhang et al., “Grain oriented crystallization, piezoelectric, and pyroelectric properties of (BaxSr2-x)TiSi2O8 glass ceramics”, Journal of Applied Physics, vol. 85, no. 12, pp. 6–12, 1999. [3] A. Halliyal, A. S. Bhalla, L. E. Cross, and R. E. Newnham, “Dielectric, piezoelectric and pyroelectric properties of Sr2TiSi2O8 polar glass-ceramic: A new polar material”, Journal of Materials Science, vol. 20, no. 10, pp. 3745–3749, 1985.