Flexible oxide electronics: getting multifunctionality, sustainability and speed altogether
P. Barquinha*, C. Fernandes, D. Lima, J. Martins, A. Rovisco, A. Kiazadeh, R. Branquinho,
E. Carlos, D. Salgueiro, P. Bahubalindruni, R. Martins, E. Fortunato
i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology,
Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516
Caparica, Portugal
*email:
Oxides are amazing materials, with a set of properties that set them apart from any other
material class. Multifunctionality is surely one of their most evident features: the range of
applications where oxides are used includes painting pigments, optical coatings, sensors,
smart windows, solid-state lighting, flexible and large-area electronics, just to name a few. In
the particular field of electronics, one can today fabricate thin-film transistors (TFTs) and
circuits entirely with oxide materials, from the substrate to the passivation/encapsulation
layer that shields oxide conductors, insulators and semiconductors. All this can be achieved
with sustainable materials and processes. In fact, even if materials as Indium-Gallium-Zinc
Oxide (IGZO) are nowadays winners in the performance/ processability compromise,
sustainable materials such as Zinc-Tin Oxide (ZTO) are quickly catching up. Moreover, there
is a growing trend to migrate the fabrication techniques for these materials from conventional
sputtering to low-cost solution processing, as spin-coating of screen-printing. Nowadays,
processing temperatures as low as 150 °C are being used in our group to create fully solution
processed oxide TFTs with field-effect mobility (µ
FE
) close to 10 cm
2
/Vs.
Then, there is speed. At this stage oxide TFTs typically offer µ
FE
≈10-30 cm
2
/Vs, which with
microscale patterning techniques takes circuit operating frequencies to 10s-100s of kHz. This,
together with design based on high-gain topologies, has been enabling us to develop
numerous digital and analog building blocks and even integrate these in smart-bottles or
flexible x-ray sensors. For this last application we recently found our oxide TFTs to have
excellent ionizing-radiation hardness, showing to be insensitive even to exposure doses of
410 krad(SiO
2
). [1]
Trying to push microscale oxide electronics to its limits, we also investigate shorter channel
devices, with L=1-3 µm. While short channel effects as channel length modulation or drain
induced barrier lowering start to be relevant, cut-off frequencies of oxide TFTs can exceed
100 MHz. [2]
Moreover, oxides are not limited to thin films: we can also synthesize oxide nanostructures,
taking advantage of the new set of properties at nanoscale. At CENIMAT we are doing this
following hydrothermal synthesis, maintaining synthesis temperature below 200 °C for a
wide range of materials, like ZnO, Cu
2
O, WO
3
or even multicomponent materials as ZTO.
Nanoparticles or nanowires with 10s-100s nm of diameter are now common with these
materials and the first steps in integrating them in devices are now being given, for an
amazing boost in device performance: in some years oxide nanotransistors can even provide
computing capabilities to your transparent and flexible foil!
This presentation will focus on the aforementioned advances on oxide electronics made at
CENIMAT, particularly on sustainable materials and processes, circuit integration of oxide
TFTs and future prospects on migration from microscale to nanoscale integration of oxides.
[1] P. G. Bahubalindruni, A. Kiazadeh, A. Sacchetti, J. Martins, A. rovisco, V. G. Tavares, R. Martins, E. M. Fortunato, and P. Barquinha,
"Influence of Channel Length Scaling on InGaZnO TFTs Characteristics: Unity Current-gain Cutoff Frequency, Intrinsic Voltage-gain and
On-resistance," Journal of Display Technology, vol. 12, pp. 515-518, 2016.
[2] T. Cramer, A. Sacchetti, M. T. Lobato, P. Barquinha, V. Fischer, M. Benwadih, J. Bablet, E. Fortunato, R. Martins, and B. Fraboni,
"Radiation-Tolerant Flexible Large-Area Electronics Based on Oxide Semiconductors," Advanced Electronic Materials, 2, 1500489, 2016.
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