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E Wistrela, M. Schneider, A. Bittner, U. Schmid:
"Impact of the substrate dependent polarity distribution in c‑axis oriented AlN thin films on the etching behaviour and the piezoelectric properties";
Microsystem Technologies - Micro- and Nanosystems - Information Storage and Processing Systems, 22 (2016), 1691 - 1700.

In this work, the influence of substrate properties
on the polarization of highly c-axis oriented aluminium
nitride (AlN) thin films and as a consequence, on the piezoelectric
properties and the wet-chemical etching behaviour
is investigated. Therefore, 620 nm thin AlN layers are
simultaneously sputter-deposited under nominal unheated
substrate conditions on silicon (Si) substrates or on those
covered with a sputter-deposited titanium (Ti) film. After
wet-chemically etching in a phosphorous acid based solution
at 80 °C different residues of AlN remain. Wet-chemical
etching of AlN films deposited on Ti results in a high
film porosity. In contrast, AlN layers on Si are either hardly
attacked or the complete thin film is removed except some
remaining conical shaped residues. Furthermore, we demonstrate
a change in the measured electro-mechanical properties
with changing maximum deposition temperature
caused by a self-heating effect of the substrate during the
AlN deposition process. The change in piezoelectric properties
and the differing etching behaviour is caused by a
change in polarity within the AlN layer. These domains are
visualized by piezoresponse force microscopy measurements,
and are in good agreement with the observed etching
results. For layers with mixed polarization, the absolute
values of the piezoelectric constant d33 are reduced due to
the counteraction of piezoelectric domains with opposite
polarization.

In this work, the influence of substrate properties
on the polarization of highly c-axis oriented aluminium
nitride (AlN) thin films and as a consequence, on the piezoelectric
properties and the wet-chemical etching behaviour
is investigated. Therefore, 620 nm thin AlN layers are
simultaneously sputter-deposited under nominal unheated
substrate conditions on silicon (Si) substrates or on those
covered with a sputter-deposited titanium (Ti) film. After
wet-chemically etching in a phosphorous acid based solution
at 80 °C different residues of AlN remain. Wet-chemical
etching of AlN films deposited on Ti results in a high
film porosity. In contrast, AlN layers on Si are either hardly
attacked or the complete thin film is removed except some
remaining conical shaped residues. Furthermore, we demonstrate
a change in the measured electro-mechanical properties
with changing maximum deposition temperature
caused by a self-heating effect of the substrate during the
AlN deposition process. The change in piezoelectric properties
and the differing etching behaviour is caused by a
change in polarity within the AlN layer. These domains are
visualized by piezoresponse force microscopy measurements,
and are in good agreement with the observed etching
results. For layers with mixed polarization, the absolute
values of the piezoelectric constant d33 are reduced due to
the counteraction of piezoelectric domains with opposite
polarization.

http://dx.doi.org/10.1007/s00542-015-2799-6