Love mode surface acoustic wave ultraviolet sensor using ZnO films deposited on 36° Y-cut LiTaO3

Love mode surface acoustic wave (SAW) ultraviolet (UV) sensors were fabricated through sputtering ZnO films on 36° Y-cut LiTaO3 substrate. Crystalline structure, morphology and photoluminescence (PL) of the sputtered ZnO films were characterized using X-ray diffraction, atomic force microscopy and fluorescence spectrometer. The PL spectra revealed that different defects in the ZnO films were dependent on the oxygen partial pressure during deposition. UV sensing measurements showed that at a power density of 350 μW cm−2, the amplitude of the Love mode SAW UV sensor decreased up to −6.4 dB with a frequency shift of ∼150 kHz under a 254 nm illumination. When this device was illuminated with 365 nm UV light at 570 μW cm−2, the amplitude of the transmission signal decreased only −2.5 dB without any significant frequency shift. A frequency hopping effect during the downshift and recovery periods was identified due to the simultaneous interplays between the variations of the acoustic velocity and attenuation during the acoustic-electric interaction.