MRS Proceedings

Table of Contents - Volume  361  - Symposium I2 – Ferroelectric Thin Films IV  

Editors : S.B. Desu, R. Ramesh, T. Shiosaki, B.A. Tuttle


Optical Losses in Ferroelectric Oxide Thin Films: Is There Light at the End of the Tunnel?

1994 MRS Fall Meeting.

D. K. Forka1, F. Armani-Leplingarda1 and J. J. Kingstona1

a1 Xerox Palo Alto Research Center, Palo Alto, CA 94304, USA


Optical losses are a barrier to use of ferroelectric waveguide thin films. Losses of about 2 dB/cm will reduce the efficiency of a frequency doubler by over 50%. Achieving losses on this order in conjunction with other essential film properties is difficult. The optical loss has several origins, including absorption, mode leakage, internal scattering and surface scattering. When the film surface morphology is accurately known, it is possible to estimate the surface scattering component of the loss. We have employed atomic force microscopy and computer modeling to compute, and correlate the optical loss as a function of film thickness and wavelength. The results suggest upper limits to the morphological roughness for various device applications. For lithium niobate films on sapphire which are intended to frequency double into the blue part of the spectrum, the optimal film thickness is about 400 nm and the RMS roughness is constrained below about 1.0 nm, with some weak dependence on grain size. Although present growth techniques do not appear to achieve this level of surface flatness intrinsically, an understanding of the morphological development of the film structure may lead to improvements.