| Summary: | Oxygen vacancies have long been known to be the dominant intrinsic
defect in amorphous SiO2 . They exist, in concentrations dependent on
processing conditions, as neutral defects in thermal oxides without
usually causing any significant deleterious effects, with some spatial
and energy distribution. During irradiation they can capture holes and
become positively charged E´-centers, contributing to device
degradation. Over the years, a considerable database has been amassed
on the dynamics of E´-centers in bulk SiO2 films, and near the
interface under different irradiation and annealing
conditions. Theoretical calculations so far have revealed the basic
properties of prototype oxygen vacancies, primarily as they behave in
either a crystalline quartz environment, or in small clusters that
serve as a substitute for a real amorphous structure. To date at least
three categories of E´ centers, existing at or above room temperature,
have been observed in SiO2 . The unifying feature is an unpaired
electron on a threefold coordinated silicon atom, having the form O3 ?
Si*. Feigl et al. identified the E´1 center in crystalline a-quartz
as a trapped hole on an oxygen vacancy, which causes an asymmetrical
relaxation, resulting in a paramagnetic center. The unpaired electron
in the E´1 center is localized on the three-fold coordinated Si atoms,
while the hole is localized on the other Si atom.
Results from an ab initio statistical simulation examination of the
behaviors of oxygen vacancies, within amorphous structures, identify a
new form of the E´-center, the E´g5, and help in the understanding of
the underlying physical mechanisms involved in switched-bias
annealing, and electron paramagnetic resonance (EPR) studies. The
results also suggest a common border trap, induced by trapped holes in
SiO2, is a hole trapped at an O vacancy defect, which can be
compensated by an electron, as originally proposed by Lelis and
co-workers at Harry Diamond Laboratories.
This dissertation provides new insights into the basic mechanisms of
a-SiO2 defects, and provides a link between basic mechanisms and
Electronic Design Automation (EDA) tools, providing an enhanced design
flow for radiation-resistant electronics.
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