SAW temperature sensor on Quartz

Abstract

For biomedical applications, narrow temperature range and high sensor accuracy requirements define the need for high temperature sensitivity. Wireless SAW sensors connected to antennas need a reference element to account for changes in electromagnetic coupling between the transmitter and receiver antennas. A pair of sensors with different temperature sensitivities may serve as a self-referenced sensor assembly. This justifies the need for materials with useful SAW resonator properties and with the largest difference between temperature coefficients of frequency (TCF) for a resonator pair on a single substrate. We have identified several cuts of quartz having useful properties with a TCF difference up to 140 ppm/°C for a pair of resonators on a single substrate. As a rule, placing such resonators on a single substrate requires their rotation by up to 90° relative to each other. The limited range of cuts presents a unique opportunity to place both resonators along the X+90° direction with one resonator using Bleustein-Gulyaev-Shimizu (BGS) waves (with electrodes placed along the x-axis) and the other one (with electrodes inclined by about ±10° to the x-axis) using quasi-Rayleigh waves. These cuts are close to the 70°Y cut where a high TCF difference is reached together with acceptable characteristics of the resonators. Resonators were designed for all useful cuts (including the 70°Y cut) and tested. The use of different periods in reflectors and interdigital transducer (IDT) together with individual choice of gaps between reflectors and IDT meant achieving low spurious content in resonator responses. The quality factors reached values up to 3500 at central frequencies around 915 MHz for both BGS and quasi-Rayleigh types of waves. The measured difference of the TCF is about 138 ppm/°C on 70°Y cut that is close to the calculated value.

On the Performance Evaluation of Commercial SAW Resonators by Means of a Direct and Reliable Equivalent-Circuit Extraction

“…Therefore, the product f r Q r of the tested SAWs remains roughly constant (about 5-7 × 10 6 MHz), exhibiting the highest value when considering the SAW with the highest f r . The observation that the obtained values of f r Q r are reasonably similar can be linked to the fact that all of the tested SAWs have a piezoelectric crystal substrate made of quartz, which is widely used as a substrate material for commercial SAW devices because of its low cost and remarkable physical properties [33][34][35]. The input shunt static capacitance is about 2 pF and exhibits a significant increase to about 3 pF for the SAW with the highest f r , whereas the output shunt static capacitance is slightly different than the input one to model the observed differences between Y 11 and Y 22 .…”

Geometric Nonlinear Model for Prediction of Frequency–Temperature Behavior of SAW Devices for Nanosensor Applications

“…The development of SAW-based sensors on quartz substrates was partially driven by the requirement for wireless temperature measurement systems due to the availability of temperature compensated cuts and the good sensitivity to strain [ 32 , 33 ]. The fundamental material constants, the third-order material constants, and the temperature coefficients of quartz and aluminum were taken from the reference [ 24 ].…”

Instrumento de medición de temperatura con sensor piezoeléctrico

“…The processes can be monitored and optimized by thermometers and infrared cameras to ensure excellent product quality [22]. In Health Sciences there are different processes that can be monitored and optimized through non-contact temperature measurement, such as the manufacture of dental products and monitoring in cryogenics [23].…”