High temperature characteristics of AlN film SAW sensor integrated with TC4 alloy substrate

This paper reports the high temperature characteristics of AlN film SAW sensor integrated with TC4 alloy substrate. The AlN films were directly sputtered on the TC4 metal substrate. SAW resonators were fabricated on the AlN films/TC4 structure by lift-off photolithography techniques. X-ray diffraction measurement shows that the AlN film is highly c-axis oriented. To explore the temperature behavior of the layered AlN/TC4 SAW devices, the samples with different thicknesses of AlN film were prepared and measured at different temperature. The results show that the resonance frequency of the AlN film SAW device decreases with increasing temperature. The dependence of temperature behaviors of the devices on the thickness of AlN films are also presented and discussed. The absolute value of temperature coefficient of frequency decreases from 89.4 ppm/°C to 66.2 ppm/°C, when the thickness of AlN film increases from 1.5 μm to 3.0 μm. From room temperature to 350 °C, the electromechanical coupling coefficient (K2) of the devices increases by about 30%. The thermal hysteresis errors of the SAW devices are less than 3.87%. The prepared AlN film SAW sensor integrated with TC4 alloy has great potential applications in high temperature harsh environment.