4 research outputs found
Solution processed pentacene thin films: new routes for building-up plastic field effect transistors
Advances in the fabrication of graphene transistors on flexible substrates
Graphene is an ideal candidate for next generation applications as a transparent electrode for electronics on plastic due to its flexibility and the conservation of electrical properties upon deformation. More importantly, its field-effect tunable carrier density, high mobility and saturation velocity make it an appealing choice as a channel material for field-effect transistors (FETs) for several potential applications. As an example, properly designed and scaled graphene FETs (Gr-FETs) can be used for flexible high frequency (RF) electronics or for high sensitivity chemical sensors. Miniaturized and flexible Gr-FET sensors would be highly advantageous for current sensors technology for in vivo and in situ applications. In this paper, we report a wafer-scale processing strategy to fabricate arrays of back-gated Gr-FETs on poly(ethylene naphthalate) (PEN) substrates. These devices present a large-area graphene channel fully exposed to the external environment, in order to be suitable for sensing applications, and the channel conductivity is efficiently modulated by a buried gate contact under a thin Al2O3 insulating film. In order to be compatible with the use of the PEN substrate, optimized deposition conditions of the Al2O3 film by plasma-enhanced atomic layer deposition (PE-ALD) at a low temperature (100 °C) have been developed without any relevant degradation of the final dielectric performance
Interface Electrical Properties of Al<sub>2</sub>O<sub>3</sub> Thin Films on Graphene Obtained by Atomic Layer Deposition with an in Situ Seedlike Layer
High-quality
thin insulating films on graphene (Gr) are essential
for field-effect transistors (FETs) and other electronics applications
of this material. Atomic layer deposition (ALD) is the method of choice
to deposit high-κ dielectrics with excellent thickness uniformity
and conformal coverage. However, to start the growth on the sp<sup>2</sup> Gr surface, a chemical prefunctionalization or the physical
deposition of a seed layer are required, which can effect, to some
extent, the electrical properties of Gr. In this paper, we report
a detailed morphological, structural, and electrical investigation
of Al<sub>2</sub>O<sub>3</sub> thin films grown by a two-steps ALD
process on a large area Gr membrane residing on an Al<sub>2</sub>O<sub>3</sub>–Si substrate. This process consists of the H<sub>2</sub>O-activated deposition of a Al<sub>2</sub>O<sub>3</sub> seed layer
a few nanometers in thickness, performed in situ at 100 °C, followed
by ALD thermal growth of Al<sub>2</sub>O<sub>3</sub> at 250 °C.
The optimization of the low-temperature seed layer allowed us to obtain
a uniform, conformal, and pinhole-free Al<sub>2</sub>O<sub>3</sub> film on Gr by the second ALD step. Nanoscale-resolution mapping
of the current through the dielectric by conductive atomic force microscopy
(CAFM) demonstrated an excellent laterally uniformity of the film.
Raman spectroscopy measurements indicated that the ALD process does
not introduce defects in Gr, whereas it produces a partial compensation
of Gr unintentional p-type doping, as confirmed by the increase of
Gr sheet resistance (from ∼300 Ω/sq in pristine Gr to
∼1100 Ω/sq after Al<sub>2</sub>O<sub>3</sub> deposition).
Analysis of the transfer characteristics of Gr field-effect transistors
(GFETs) allowed us to evaluate the relative dielectric permittivity
(ε = 7.45) and the breakdown electric field (<i>E</i><sub>BD</sub> = 7.4 MV/cm) of the Al<sub>2</sub>O<sub>3</sub> film
as well as the transconductance and the holes field-effect mobility
(∼1200 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>). A special focus has been given to the electrical characterization
of the Al<sub>2</sub>O<sub>3</sub>–Gr interface by the analysis
of high frequency capacitance–voltage measurements, which allowed
us to elucidate the charge trapping and detrapping phenomena due to
near-interface and interface oxide traps