Fabrication, Optimization and Testing of Photoconductively Tuned SAW Device Using CBD Method

Abstract

In this paper, we explained the fabrication process of tunable surface acoustic wave (SAW) device. We have also demonstrated the photoconductivity of the material which is deposited over piezoelectric substrate. We have used an approach which is different from the conventional approach of using aluminium interdigital transducers (IDTs) which have a fixed frequency of operation. We do this by making SAW device programmable using light pattern IDTs (LiPIDTs) which allows us to vary the frequency of operation of SAW device by changing the width of the LiPIDTs. This process of tuning have been explained using a set of schematics and by building an equivalent electrical model of SAW resonator. We have optimized this fabrication process for the targeted application. In photoconductively tuned SAW we have measured I-V characteristics for the samples prepared with 1 mm, 2 mm, 3 mm and 5 mm electrode separation width. We find that 2 mm separation sample is best suited for this application in which we need to make LiPIDTs within this area. For 2 mm sample, we obtained $I_{on} = 3.36\times 10^{-9}$ A (obtained by the light exposure) and $I_{dark} = 5.4 \times 10^{-12}$ A (in the absence of light). Thus we could achieve $I_{on}/I_{dark}>10^3$. We have also obtained the X-ray diffraction (XRD) characteristics for the deposited photoconductive layer over piezoelectric substrate and we have found the main reflections at 2$\theta$ = 26$^{\circ }$. In the study of Scanning electron microscopy (SEM), it has been observed that the clusters composed of nanoparticles have an average cluster size of 150 nm diameter.

Supported by Visvesvaraya PhD Scheme, Meity, GoI MEITY–PHD–1227.