Nanoelektromechanische Siliziumaktuatoren und deren optische Charakterisierung

Nanoelectromechanics is a growing field. Nevertheless, the static
deflections of nanoelectromechanical systems are hardly
investigated. Since these are required for most nanomechanical
tools, e. g. nanotweezers, they are dealt with in the work
presented. A new fabrication scheme to build fully freely suspended
structures out of silicon-on-insulator wafers was developed to get
nanostructures with a hole-aperture right beneath them. The
expected deflections of the fabricated double cantilever system
were calculated using elasticity theory. To measure the quasistatic
deflections of these nanosystems under a bias voltage, a scanning
confocal optical microscope was used in conjunction with
demodulation of the reflected signal. This worked for freely
suspended as well as fully freely suspended structures and the
system was operated under ambient conditions. Using this technique,
signals at the first, second, and third harmonic of the excitation
frequency could be detected. These were correlated to the
deflection in horizontal and vertical direction. The vertical
deflection is a parasitic one due to the vicinity of the substrate,
since the system was designed to show a horizontal deflection,
only. The fully freely suspended structures, in contrast, do not
show deflections resulting from forces towards the substrate. To
distinguish between the two directions of motion as well as to get
a better understanding of the interference-dominated scanning
images of the structures having a substrate beneath, numerical
simulations of the imaging were performed. These reproduce the
images as well as the demodulated signals quite well. The
sensitivity of the optical demodulation measurement was shown to be
6 pm /Sqrt(Hz) (rms), a deflection of about 2 angstrom could be
proven. Using the same set-up in a non-scanning way, resonances of
the deflected structures were identified. The fabrication as well
as detection schemes are fundamental for the development of
nanotweezers capable of repositioning nano-scaled objects.
Additionally, some calculations concerning the melting that
occurred to the contacted nanostructures under investigation by a
scanning electron microscope are presented. The electroluminescence
that one of the silicon nanostructures accidentally showed is
interpreted in terms of the analogy to spark-processed silicon. In
conclusion, scanning confocal optical microscopy is shown to be a
highly sensitive as well as non-destructive technique to
investigate quasistatic deflections of nanoelectromechanical
systems in the angstrom range.