Aluminium nitride (AlN) reactively sputter deposited from an aluminium target is an interesting compound material due
to its CMOS compatible fabrication process and its piezoelectric properties. The crystal structure obtained during
sputtering is a very importance criterion to obtain a good piezoelectric performance. To demonstrate this, we focused our
investigations on two types of films. The first type shows a good c- axis orientation with round grain geometry. The
second type is (101) oriented having a triangular grain shape. For measuring the out-of-plane displacements for dij
determination, a MSV 400 Polytec scanning laser Doppler vibrometer was used. To obtain the piezoelectric constants d33
and d31 a fitting procedure between experimental and theoretical predicted results is used. Effective values for d33 and d31
in c-axis oriented films are about 3.0 pm/V and -1.0 pm/V, respectively. By contrast, films with (101) orientation show a
lower effective longitudinal piezoelectric coefficients, consistent with this different orientation.
Finally, both types of AlN layers were deposited on 640 μm long micro-cantilevers. The average displacement of the
first mode on the vertical axis was about 12 nm for the film with good c -axis orientation and 0.3 nm for that with (101)-
orientation when applying the same excitation.
Micro-cantilevers and micro-bridges actuated by sputter-deposited aluminium nitride (AlN) thin films were measured
with a scanning laser Doppler vibrometer up to 6 MHz, covering more than 10 resonance modes of different nature. A
finite element model (FEM) was used to simulate the modal response of the micromachined structures. The comparison
between experiment and simulation, regarding modal shapes and frequencies, resulted in an excellent agreement, what
confirmed the quality of the structures. Finally, we point out, and illustrate with the help of micro-bridges, the
importance for a locally tailored distribution of electrical excitation on the top surface of the device, in order to either
optimize or cancel out the displacement of a given mode.
We achieved to etch nano- and deep structures in silicon using ICP-cryogenic dry etching process. We etched nanopores
and nanocantilevers with an etch rate of 13 nm/min, nanopillars with an etch rate of 2.8 μm/min - 4.0 μm/min, membrane
and cantilever structures with an etch rate of 4 μm/min and 3 μm/min, respectively. Nanopores and nanocantilevers
are interesting structures for Bionanoelectronics. Nanopillars can be used as substrates/templates for the MOCVD
growth of GaN nanoLEDs. They are the basic constituents of a nanoparticle balance and also of a thermoelectric generator.
For the joining of the silicon wafers of the thermoelectric generator the low temperature joining technique can be
used. Cantilevers can be used for sensing, e.g. as tactile cantilevers. They can be used also as resonator for mass sensing
even in the subnanogram region. The actuation of the resonator can be done by using piezoelectric thin films on the
cantilevers. The mass detection depends on the resonance frequency shift caused by loaded mass on the cantilevers. Such
cantilevers are robust and easy to produce. The deep etching in silicon was done by using a photoresist mask and
creating perpendicular and smooth sidewalls.