Cadmium sulfide deposition suited for photo pattern-based SAW device

Abstract

This paper demonstrates a surface acoustic wave (SAW) device based on photopatterned interdigital transducer (IDT) created on a cadmium sulfide layer deposited over a lithium niobate substrate using two methods, viz. chemical bath deposition (CBD) and spin-coating. It allows SAW generation when the photo pattern shines on the photoconductive layer. I–V characteristics are measured for photo pattern-based SAW devices with electrode separation widths of 1 mm, 2 mm, 3 mm, and 5 mm. It is found that a 2 mm sample is best suited for this application in which we need to make photo patterns within this area. For 2 mm CBD sample, $I_{on} = 3.36\times 10^{-9}$ A (obtained by the light exposure) and $I_{dark} = 5.4 \times 10^{-12}$ A (obtained in the absence of light) with an $I_{on}/I_{dark}\approx 10^3$ is achieved. Similarly, for the spin-coated 2 mm sample, $I_{on} = 2.4\times 10^{-10}$ A and $I_{dark} = 2.9\times 10^{-13}$ A with $I_{on}/I_{dark}\approx 10^3$ is obtained. In both methods, x-ray diffraction provides the major reflections at 2$\theta$ = 26$^{\circ }$. Other important analyses such as SEM, PL, and XRD have been done to justify the results. Finally, $S_{11}$ parameters with and without photopatterned IDTs have also been measured using a vector network analyzer.