SAW-properties of langasite at high temperatures: Measurement and analysis

Abstract

The measurement range of temperature using SAW-devices is depending on the substrate material used in the measurements. This dependence is related to the temperature point, where the substrate loses its piezoelectric properties. This occurs by the SAW-materials such as quartz and lithium niobate at about 570°C or 350°C, respectively. The piezoelectric material langasite (La3Ga5SiO14) has a thermodynamically stable phase and do not lose its piezoelectric properties up to its melting point at about 1470 °C and can be used for SAW devices at high temperatures. This paper presents the measurements of acoustical parameters of langasite up to 750°C. Langasite is used as substrate in the measurements with Euler angles (0°, 138.5°, 26.6°) and two different platinum (Pt) layer heights (45 nm and 75 nm) top of a zirconium (Zr) adhesion layer (4 nm). The investigated acoustic properties of langasite are group and phase velocity, propagation loss, and electromechanical coupling coefficient as functions of temperature. The measured data is analyzed using a special signal processing algorithm to obtain these acoustic properties of the Langasite.

High Temperature SAW wireless sensors based on YCOB and Langasite

“…We can find the SAW velocity of YCOB is higher than that of LGS. These results are very close to the reported data [10,11]. 5 shows relative frequency shift in resonance frequency as a function of temperature from room temperature up to 600 °C, where f r0 is the resonance frequency at room temperature.…”

Surface Acoustic Wave Devices for Harsh Environment Wireless Sensing

“…Measurements on single crystal bulk resonators were made by Johnson et al [30] who observed increasing acoustic loss up to 700 K. Schreuer et al [31] also saw increasing loss with temperature in single-crystal langasite and examined the effect of frequency and annealing ambient. An increase in surface wave attenuation in SAW devices with temperature and frequency was subsequently observed [32–34]. Shrena et al reported lower losses for the (0°, 138°, 27°) orientation than the (0°, 30°, 27°) and also higher losses when metal was on the propagation path [33,34].…”

“…An increase in surface wave attenuation in SAW devices with temperature and frequency was subsequently observed [32–34]. Shrena et al reported lower losses for the (0°, 138°, 27°) orientation than the (0°, 30°, 27°) and also higher losses when metal was on the propagation path [33,34]. These acoustic losses represent a significant obstacle to the development of high-temperature sensors as they reduce signal strength at high temperature and limit the maximum frequency of operation.…”

“…It is well known that the electrical loss in the film peaks at the conductivity that corresponds to the largest slope in the Δ v-σ curve [45,46], and that it approaches zero for large and small conductivity. There is additional loss observed either with insulating [47,54] or conducting overlayers [33,34] (that is, layers with conductivity high enough or low enough that electrical dissipative losses are insignificant). Figure 8 compares the relative attenuation for different overlayer materials.…”

Research on the LGS SAW sensor coated with AlN film

“…Among various piezoelectric materials, langasite (LGS) has been thought as one of the most attractive material in high temperature due to its good temperature stability and large coupling constant K 2 (0.34%), which is two times larger than that of ST-quartz (0.14%) [5]. Haifeng Zhang [6] reported the force-frequency effect of LGS resonators.…”