Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Jonathan Tollerud
M.S. Final
Sep 23, 2011, 4:00
ERC Electronic Classroom
Scatter loss and surface roughness in hafnium oxide thin films
Abstract: The work presented in the thesis aims to
characterize and improve the surface quality and
scatter loss of HfO2 single layer thin films. Dual
ion beam sputtered coatings of HfO2 produced at
CSU have been shown to have a high damage
threshold and low absorption. They have not been
optimized for reduced surface roughness. Both
surface quality and scattering of dual ion beam
sputtered thin films depend on the growth
conditions and substrate quality, so a study of
growth parameters and substrate choice is
conducted. The growth parameters selected in this
work are beam voltage of the main ion source and
sample thickness. Samples grown on standard
optically polished substrates are compared to
samples grown on two types of super-polished
substrates. A multilayer coating is also examined
to characterize how scatter loss scales with the
number of layers.

A device is built to measure scatter loss at
1064nm, 633nm and 405nm and an in depth analysis
is conducted of the surfaces using atomic force
microscopy and white light interferometry. The
films scatter loss at 1064nm are shown to be
sensitive to substrate choice, film thickness and
main beam voltage. Scatter loss at 1064nm
generally decreases when beam voltage is reduced.
Scatter loss at lower wavelengths decreases much
more significantly. Smoother substrates show
improved scatter performance, but it is again much
more noticeable at lower wavelengths. Thicker
samples show increased scatter, especially at
shorter wavelength. Surface scans are benchmarked
using a variety of techniques, but power spectral
density analysis is shown to be the best predictor
of scatter loss for most samples. The best growth
conditions and a super polished substrate yield a
scatter loss of 6.7ppm for a single layer and
12.3ppm for an output coupler which is comparable
to commercially available output couplers.
Adviser: Carmen Menoni
Co-Adviser: N/A
Non-ECE Member: Azer Yalin (Mechanical Engineering)
Member 3: Mario Marconi
Addional Members: N/A,N/A
Program of Study: