SAW Temperature Sensor on Quartz.

Area of Science:

• Materials Science
• Acoustic Wave Devices
• Sensor Technology

Background:

• Biomedical applications demand high temperature sensitivity and accuracy in wireless sensors.
• Wireless Surface Acoustic Wave (SAW) sensors require a reference element to correct for electromagnetic coupling variations.
• A self-referenced sensor assembly using a pair of sensors with differing temperature sensitivities can address this need.

Purpose of the Study:

• To identify materials and quartz cuts enabling the largest difference in temperature coefficients of frequency (TCF) for a resonator pair on a single substrate.
• To develop a self-referenced sensor assembly for improved accuracy in wireless sensor applications.

Main Methods:

• Investigated various quartz cuts for optimal SAW resonator properties and maximum TCF difference.
• Designed and tested resonators utilizing Bleustein-Gulyaev-Shimizu (BGS) waves and quasi-Rayleigh waves on specific quartz cuts (e.g., 70°Y).
• Optimized resonator design parameters, including reflector/interdigital transducer (IDT) periods and gaps, to minimize spurious content and achieve high quality factors.

Main Results:

• Identified several quartz cuts with a TCF difference up to 140 ppm/°C for paired resonators.
• Achieved a measured TCF difference of approximately 138 ppm/°C on the 70°Y cut.
• Obtained high quality factors (up to 3500) at central frequencies around 915 MHz for both BGS and quasi-Rayleigh wave resonators.

Conclusions:

• The 70°Y cut of quartz, supporting both BGS and quasi-Rayleigh waves, is suitable for creating self-referenced sensor assemblies.
• The developed sensor design effectively leverages differing temperature sensitivities for accurate wireless sensing.
• This approach offers a promising solution for high-accuracy wireless sensors in demanding environments like biomedical applications.