Sensitivity improvement of the surface acoustic wave ultraviolet sensor based on zinc oxide nanoparticle layer with an ultrathin gold layer

In this study, we demonstrate the improvement in the sensitivity of surface acoustic wave (SAW) ultraviolet (UV) sensor with a UV-sensitive zinc oxide nanoparticles (ZnO NPs) layer and an ultrathin gold layer. The additional gold layer plays an important role in the enhancement of photoresponse by increasing the overall sheet conductivity of the ZnO/Au layer, thereby improving the sensitivity of SAW UV sensor. The SAW sensor fabricated in this study consists of UV-sensitive ZnO NPs layer deposited onto a 41°Y-X LiNbO3 substrate that can propagate shear-horizontal (S-H) waves. The sheet conductivity of the film was calculated by transmission line method, using which the sensitivity of the sensor was estimated. The morphological and structural properties of ZnO NPs were evaluated by using scanning electron microscope (SEM) and X-ray diffraction (XRD). In addition, the effect of Au/ZnO bilayer on the UV absorption of the device was analyzed by using spectrophotometer. The device was irradiated with a commercial UV lamp, the intensity of which was assessed by a UV meter. In addition, the current-voltage characteristics and time responses of the device were determined by using a semiconductor parameter analyzer, in order to investigate the effects of annealing conditions and the additional deposition of an ultrathin gold metal layer. The improvement in the sensitivity of the SAW UV sensor with the gold layer was verified by the phase shift of S21 from 55° to 198°.