Proton-exchanged Z-cut LiNbO/sub 3/ waveguides for surface acoustic waves

Abstract

Proton-exchanged (PE) waveguides in Z-cut LiNbO/sub 3/ have been fabricated using benzoic acid. Secondary-ion mass spectrometry (SIMS) measurements show that the distribution of hydrogen in the PE Z-cut LiNbO/sub 3/ samples exhibits a step-like profile with the diffusion constant D/sub 0/ and the activation energy Q of about 2.82/spl times/10/sup 8/ /spl mu/m/sup 2//h and 87.76 kJ/mol, respectively. On the other hand, the important parameters for the design of surface acoustic wave (SAW) devices are measured and discussed. The results show that the phase velocity and electromechanical coupling coefficient decrease with the increase of kd, where k is the wavenumber and d is the waveguide depth. The variation of insertion loss becomes saturated at about kd=0.068 with a maximum increase of about 4/spl sim/5 dB. The temperature coefficient of delay calculated from the frequency change of the output of SAW delay line shows an evident increase in the PE layer. Moreover, the effects of postannealing can result in a restoration of the decreased velocity and an improvement of the insertion loss.