SAW Correlators in LiNbO3 and GaN on Sapphire

Abstract

This paper describes the use of Lithium Niobate and GaN on sapphire substrates to define SAW correlators for direct sequence spread spectrum modulation. Passive correlators with maximal length sequence periods of 7 and 15 are fabricated and tested on 128° Y-cut bulk Lithium Niobate. The input transducer is modulated at carrier frequencies of 470-930 MHz with a chip duration of 100 n $s$. At the output, a maximum peak-to-sidelobe ratio of 15 dB is measured. The same design is then fabricated in GaN on sapphire in order to incorporate acoustoelectric gain sections using an AlGaN barrier engineered to ensure low sheet density. We consider a basic cell consisting of a tap followed by a gain section to support long correlator structures. This represents a first step towards mitigating acoustic propagation losses in monolithic GaN SAW correlators.