dc.description.abstract | Functional oxides exhibit properties that make them interesting for future
electronic devices. Thin films of functional oxides can be routinely produced, but
there lacks a standard technique for establishing nanoscale freestanding structures
on insulating substrates. The nanostructures must be well defined and maintain
bulk properties.
In this work a recipe for establishing a two layer hard mask suitable for ion beam
etching (IBE) has been developed. A chromium hard mask is patterned and
deposited using electron beam lithography (EBL) and lift off. The pattern is
transferred to an underlying carbon layer by oxygen reactive ion etching (RIE).
Hard masks with hallbar patterns have been structured on 5 × 5 mm samples
with thin films of La0.7Sr0.3MnO3 (LSMO) and BaTiO3 (BTO) on (111)-oriented
SrTiO3 (STO) substrates. The hallbars have widths from 11 µm and down to
130 nm, which are connected to 200 × 200 µm contacts pads.
A bilayer mask of PMMA and MMA with a total thickness of 240 nm is found to
work successfully for lifting off 20 nm of chromium. Samples are prone to charging
during electron beam lithography. Fine features are written using 100 pA beam
current, while large features are defined at 10 nA.
The hard mask patterned samples are prepared for IBE, which will transfer the
hard mask pattern into the oxide thin film and substrate, realizing freestanding
oxide structures. Followed by deposition of contacts and wirebonding, the devices
can be used to investigate electrical transport properties. | |