Novel AlN/ScAlN composite film SAW for achieving highly sensitive temperature sensors

Traditional SAW devices, typically made from piezoelectric materials like quartz and lithium niobate (LiNbO₃), face significant challenges, such as incompatibility with CMOS processes and a decline in piezoelectric performance at high temperatures. Recently, aluminum nitride (AlN) and scandium-doped AlN (ScAlN) have gained attention as promising materials for high-performance SAW devices due to their high acoustic velocity, thermal stability, and CMOS compatibility. However, the low piezoelectric coefficient of AlN and Sc precipitation in ScAlN films limit their broader application. This study investigates the fabrication and optimization of SAW resonators using AlN/ScAlN composite films to enhance piezoelectric performance while mitigating Sc precipitation. A one-port SAW sensor device was designed based on the composite piezoelectric film, and structural optimization was performed by introducing groove structures to further reduce acoustic energy leakage and improve the quality factor (Q). Temperature sensing experiments were conducted using a peripheral oscillator circuit system. The experimental results demonstrated that the developed composite film SAW resonator exhibited excellent phase noise performance and thermal stability within the oscillator circuit, achieving a phase noise of −135.18 dBc/Hz@1 MHz and a frequency temperature coefficient of −31.07 ppm/°C. These findings confirm the potential of the AlN/ScAlN composite film as a reliable and precise temperature sensor.