The electrical performance of silicon carbide metal-oxide-semiconductor field effect transistors (4H-SiC MOSFETs) are strongly related to the presence of interface states at the silicon dioxide (SiO2)/4H-SiC interface, whose density is much higher than in the Si/SiO2 system. In particular, the charged interface states determine a degradation of the carrier mobility in the channel of the MOSFET with respect to the bulk mobility. A reliable and consistent method for the evaluation of the interface state density (D (it)) and the effective channel mobility (mu (ch)) in these devices is presented in this work. The two quantities are simultaneously extracted by a combined fit of the current-voltage (I-V) and capacitance-voltage (C-V) electrical characteristics collected on a single device. The simultaneous fit of the I-V and C-V characteristics, which can be easily measured on the same device, noticeably improve the reliability of D (it) and mu (ch) estimation. The results obtained at different temperatures indicate an increase of the mu (ch) with T, in agreement with a dominance of the Coulomb scattering effect as the degradation mechanism of the carrier channel mobility induced by the presence of charged interface states.

The interfacial electrical properties of deposited oxide (SiO2) onto cubic silicon carbide (3C-SiC) were investigated after different post-oxide deposition annealing (PDA) by means of metal-oxide-semiconductor (MOS) capacitors and nanoscale capacitance mapping. The deposited oxides subjected to PDA at 450 °C in either nitrogen or forming gas showed a reduction of the interface and oxide traps, as well as an improved oxide field strength compared to the thermally grown insulating layer. Spatially resolved nanoscale capacitance mapping performed onto the oxide surface revealed that the density of the electrically active stacking faults (SFs) in 3C-SiC is diminished by appropriate PDA. The results pave the way to obtain an ideal SiO2/3C-SiC system suitable for power device applications.

The electrothermal behavior of gallium nitride (GaN) HEMTs has been simulated by using a hybrid approach in which the problem is solved by coupling together an effective model (for the electrical part) and a 3-D finite element model (for the thermal part). The effective model relies on the estimation of the channel current at different temperatures in the absence of thermal gradients. This regime occurs in real devices only during the very initial stage of bias pulses, when self-heating effects are not yet developed, for time intervals shorter than 1 ns. Virtual output electrical characteristic, in which self-heating effects are negligible, have been derived from pulsed measurements of the electrical output characteristics and electrothermal transient simulations. The maximum temperature because of self-heating evaluated by using the virtual output characteristic are substantially higher than those obtained using the short time-pulsed measurements directly. The results have been validated by a comparison with temperature measurements obtained using Raman thermography. This approach has proven to be numerically very efficient and fast, allowing the analysis of realistic complex structures and circuits.

In this work we study the electrical stability under both gate bias stress and gate and drain bias stress of short channel (L = 5 mu m) bottom contact/top gate OTFTs made on flexible substrate with solution-processed organic semiconductor and fluoropolymer gate dielectric. These devices show high field-effect mobility ( mu(FE)> 1 cm(2)V(-1)s(-1)) and excellent stability under gate bias stress (bias stress V-ds = 0V). However, after prolonged bias stress performed at high drain voltage, V-ds, the transfer characteristics show a decreased threshold voltage, degradation of the subthreshold slope and an apparent increase in the field effect mobility. Furthermore, the output characteristics show an asymmetry when measured in forward and reverse mode. These experimental results can be explained considering that the bias stress induces the damage of a small part of the device channel, localized close to the source contact. The analysis of the experimental data through 2D numerical simulations supports this explanation showing that the electrical characteristics after bias stress at high V-ds can be reproduced considering the creation of donor-like interface states and trapping of positive charge into the gate dielectric at the source end of the device channel. In order to explain this degradation mechanism, we suggest a new physical model that, assuming holes injection from the source contact into the channel in bounded polarons, envisages the defect creation at the interface near the source end of the channel induced by injection of holes that gained energy from both the high longitudinal electric fields and the polaron dissolution.

This work describes the development of a new post-implant crystal recovery technique in 4H-SiC using XeCl (?=308 nm) multiple laser pulses in the ns regime. Characterization was carried out through micro-Raman spectroscopy, Photoluminescence (PL), Transmission Electron Microscopy (TEM) and outcomes were than compared with 1h thermally annealed at 1650-1700-1750 ? P implanted samples (source implant) and P and Al implanted samples for 30 minutes at 1650 °C (source and body implants). Experimental results demonstrate that laser annealing enables crystal recovery in the energy density range between 0.50 and 0.60 J/cm. Unlike the results obtained with thermal annealing where stress up to 172 MPa and high carbon vacancies (Vc) concentration is recorded, laser annealing provides almost stress free samples and much less defective crystal avoiding intra-bandgap carrier recombination. Implant was almost preserved except for step-bouncing and surface oxidation phenomena leading to surface roughening. The results of this work gives way to laser annealing process practicability for lattice damage recovery and dopant activation.

--In this work we report on the results of DirectCurrent (DC) and Low-Frequency Noise (LFN) measurements in p-type staggered top-gate Organic Thin-Film-Transistors (OTFTs). The analysis involves the effects of Source/Drain contacts and the stability characteristics of OTFTs induced by Gate and Drain bias stress. Noise data are interpreted in the context of a multi-trap correlated-mobility-fluctuations (CMFs) model, showing that noise is dominated by acceptor-like traps. The influence of noise sources at contacts is found to be negligible. However contacts affect the measured noise by a non negligible differential resistance. The product between the scattering parameter and the effective mobility DPeff?2?107 cm2/C, which measures the strength of CMFs, is similar to what reported for a-Si:H and much higher with respect to c-Si MOSFETs revealing a strong correlation between CMFs and the state of disorder of the active layer. Instability is observed in presence of Drain bias stress and for sufficient short channel length (<10Pm). The measured shift in LFNMs appears correlated with the shift of the measured channel current. In the context of the CMF model the noise shift can be interpreted as due to the increase of DPeff caused by the increased scattering between the charged channel carriers and the charged traps at the interface.

This work describes the development of a new method for ion implantation induced crystal damage recovery using multiple XeCl (308 nm) laser pulses with a duration of 30 ns. Experimental activity was carried on single phosphorus (P) as well as double phosphorus and aluminum (Al) implanted 4H-SiC epitaxial layers. Samples were then characterized through micro-Raman spectroscopy, Photoluminescence (PL) and Transmission Electron Microscopy (TEM) and results were compared with those coming from P implanted thermally annealed samples at 1650-1700-1750 degrees C for 1 h as well as P and Al implanted samples annealed at 1650 degrees C for 30 min. The activity outcome shows that laser annealing allows to achieve full crystal recovery in the energy density range between 0.50 and 0.60 J/cm(2). Moreover, laser treated crystal shows an almost stress-free lattice with respect to thermally annealed samples that are characterized by high point and extended defects concentration. Laser annealing process, instead, allows to strongly reduce carbon vacancy (V-C) concentration in the implanted area and to avoid intra-bandgap carrier recombination centres. Implanted area was almost preserved, except for some surface oxidation processes due to oxygen leakage inside the testing chamber. However, the results of this experimental activity gives way to laser annealing process viability for damage recovery and dopant activation inside the implanted area.

For long-term space missions the possibility to grow vegetables and fruits inside the spacecraft or in specific living modules is pivotal. The use of indoor greenhouse is a realistic solution. However, the remote monitoring of different control functions of greenhouses remains mandatory. Indeed, this can lead to an increment of the sustainability and can increase product yield. However, a full greenhouse automation needs a continuous monitoring of different key parameters such as humidity, temperature, light intensity, CO2 concentration, etc. Low consumption wireless sensors networks represent a valuable ally to successfully define in real time how the climate inside and outside the greenhouse is changing. Among different solutions, we propose a wireless sensor network based on nodes composed by autonomous flexible patches equipped with sensors, signal processing unit, energy module and data transmission interface. In this work, we adopt both commercial and ad hoc devices such as Layered Double Hydroxides sensors to be used at low working temperature. The resulting devices exploit the porosity of disordered nanostructures and the humidity present in the air to activate the adsorption procedure, thus operating at room temperature. With this technology is possible to monitoring CO2, NOX and other gases present in the greenhouse together with humidity, temperature and light intensity.

To effectively control gaseous pollutants in air it is mandatory to fabricate reliable and non-expensive monitoring systems that can be easily deployed in urban areas. Sensing devices based on metal oxide nanostructures offer many advantages respect bulk material in detecting multiple hazardous gases such as, high stability, easy surface functionalization and potentially low operating temperature. Among diverse nanostructures, ZnO nanorods can be obtained with low cost and simple process at a low manufacturing temperature opening the possibility to integrate the material with flexible substrates. Additionally, laser annealing procedure can be exploited to improve or tune the morphology and the electrical properties of these materials. In this work, we present a comparison between the performance of as deposited and laser-annealed devices in the detection of NO and NO2. Different sensors characteristics at increasing gas concentrations and dynamic behaviors are shown and discussed evaluating the mechanisms involved in the diverse pollutant detection. As result, the laser-annealed sensor exhibits a sensitivity one-order higher respect to as-grown sample in detecting NO (3.9x10(-3) vs 2.7x10(-4) [1/ppm]) while for NO2 sensitivity is more than four times higher (3.8x10(-3) vs 8.4x10(-4) [1/ppm]).

The understanding of brain processing requires monitoring and exogenous modulation of neuronal ensembles. To this end, it is critical to implement equipment that ideally provides highly accurate, low latency recording and stimulation capabilities, that is functional for different experimental preparations and that is highly compact and mobile. To address these requirements, we designed a small ultra-flexible multielectrode array and combined it with an ultra-compact electronic system. The device consists of a polyimide microelectrode array (8 µm thick and with electrodes measuring as low as 10 µm in diameter) connected to a miniaturized electronic board capable of amplifying, filtering and digitalizing neural signals and, in addition, of stimulating brain tissue. To evaluate the system, we recorded slow oscillations generated in the cerebral cortex network both from in vitro slices and from in vivo anesthetized animals, and we modulated the oscillatory pattern by means of electrical and visual stimulation. Finally, we established a preliminary closed-loop algorithm in vitro that exploits the low latency of the electronics (<0.5 ms), thus allowing monitoring and modulating emergent cortical activity in real time to a desired target oscillatory frequency.

Organic material deposition by gravure printing is a promising pathway for the realization of large area flexible electronic devices. Nevertheless, in order to achieve high performance it is required to improve the electronic ink printability, operating on the fluid dynamic mechanisms involved during the process. In this work, this issue has been faced working on ink characteristics for a conductive and a dielectric material. The suitable ink features have been defined studying the influence on the printability of the different forces that act in the fluid during the printing process, using an experimental approach. Properly defined ink formulations have been printed, considering different shapes and dimensions of the cells on the gravure cliche to fit the ink features. The printing outcomes have been compared and analysed through the evaluation of several significant fluid dynamic parameters and the rheological characterization of the materials. Finally, exploiting the results of this study, high performance fully printed organic thin film transistors have been realized.

Photothermal therapy (PTT) assisted by nanomaterials is a promising minimally invasive technique for cancer treatment. Here, we explore the PTT properties of a silicon- and gold-based nanostructured platform suitable for being directly integrated in fibre laser systems rather than injected into the human body, which occurs for the most commonly unreported PTT nanoagents. In particular, the photothermal properties of an array of disordered silicon nanowires coated by a thin gold film (Au/SiNWs) were tested on a monolayer of human colon adenocarcinoma cells (Caco-2) irradiated with a 785 nm laser. Au/SiNWs allowed an efficient photothermal action and simultaneous monitoring of the process evolution through the Raman signal coming from the irradiated cellular zone. Strong near infra-red (NIR) absorption, overlapping three biological windows, cell-friendly properties and effective fabrication technology make Au/SiNWs suitable both to be integrated in surgical laser tools and as an in vitro platform to develop novel PTT protocols using different cancer types and NIR sources.

Laser annealing of semiconductor materials is a processing technique offering interesting application features when intense, transient and localized heat sources are needed for electronic device manufacturing or other nano-technological applications. The space-time localization of the induced thermal field (in the nanoseconds/nanometers scale) promotes interesting non-equilibrium phenomena in the processed material which only recently have been systematically investigated and modelled. In this review paper we discuss the current knowledge on anomalous kinetics occurring in implanted silicon and germanium (i.e. thin layers of disorder diluted alloys of Si and Ge, with variable initial disorder status according to the implantation conditions) during the pulsed laser irradiation. In particular, we focus our attention on the anomalous impurity redistribution in the transient melting stage and on the formation of non conventional and metastable extended defects.

Heavy doping of Ge is crucial for several advanced micro- and optoelectronic applications, but, at the same time, it still remains extremely challenging. Ge heavily n-type doped at a concentration of 1 × 10cm by As ion implantation and melting laser thermal annealing (LTA) is shown here to be highly metastable. Upon post-LTA conventional thermal annealing As electrically deactivates already at 350 °C reaching an active concentration of ~4 × 10cm. No significant As diffusion is detected up to 450 °C, where the As activation decreases further to ~3 × 10cm. The reason for the observed detrimental deactivation was investigated by Atom Probe Tomography and in situ High Resolution X-Ray Diffraction measurements. In general, the thermal stability of heavily doped Ge layers needs to be carefully evaluated because, as shown here, deactivation might occur at very low temperatures, close to those required for low resistivity Ohmic contacting of n-type Ge.

Electrocorticography (ECoG) is receiving growing attention for both clinical and research applications thanks to its reduced invasiveness and ability of addressing large cortical areas. These benefits come with a main drawback, i.e. a limited frequency bandwidth. However, recent studies have shown that spiking activity from cortical neurons can be recorded when the ECoG grids present the following combined properties: (I) conformable substrate, (II) small neuron-sized electrodes with (III) low-impedance interfaces. We introduce here an ad-hoc designed ECoG device for investigating how electrode size, interface material composition and electrochemical properties affect the capability to record evoked and spontaneous neural signals from the rat somatosensory cortex and influence the ability to record high frequency neural signal components. Contact diameter reduction down to 8 µm was possible thanks to a specific coating of a (3,4- ethylenedioxytiophene)-poly(styrenesulfonate)-poly-(ethyleneglycol) (PEDOT-PSS-PEG) composite that drastically reduces impedance and increases electrical and ionic conductivities. In addition, the extreme thinness of the polyimide substrate (6 - 8 µm) and the presence of multiple perforations through the device ensure an effective contact with the brain surface and the free flow of cerebrospinal fluid. In-vivo validation was performed on rat somatosensory cortex.

In this paper, a phenomenological study of Layered Double Hydroxide sensing properties respect to common pollutants is presented. Layered Double Hydroxides are a class of nanomaterials characterized by a large surface/volume ratio, able to strongly interact with a wide amount of different chemical compounds. Layered Double Hydroxides materials are also relatively easy to achieve by different synthesis methods on a multiplicity of substrates. Although their characteristics make these materials promising candidates to act as gas sensor, Layered Double Hydroxide gas sensing properties have not still been intensively investigated. To this purpose, a chlorine-intercalated Zn/Al-Layered Double Hydroxide layer is grown by hydrothermal technique on an interdigitated finger array to achieve a resistive gas sensor. The sensing layer has been characterized by Scanning Electron Microscope, X-Ray Diffraction and Energy-Dispersive X-Ray Spectroscopy and then its sensing characteristics have been successfully investigated at room temperature on five common volatile compounds (CO, CO2, NO, NO2, CH4) at six different concentrations. The results demonstrate that Layered Double Hydroxide have interesting properties as low temperature sensing tool for a large range of volatile compounds. (C) 2016 Elsevier B.V. All rights reserved.

Neuroprosthetic interfaces require light-weighted and power-optimized systems that combine acquisition and stimulation together with a computational unit capable to perform on-line analysis for closed-loop control. Here, we present an ultra-compact and low-power system able to acquire from 32 channels and stimulate independently using both current and voltage. The system has been validated in vivo for rats in the recording of spontaneous and evoked potentials and peripheral nerve stimulation, and it was tested to reproduce the muscular activity involved in gait. This device has potential application in long-term clinical therapies for the restoration of limb control and it can become a development platform for closed loop algorithms in neuromuscular interfaces.

Layered Double Hydroxides nanostructures and their possibility of accommodating different molecules or atoms inside their matrix bestow a large number of interesting physical and chemical properties. Indeed, these materials have been widely used for different purposes. Nevertheless, their usage in gas sensors applications is still challenging since Layered Double Hydroxides conduction mechanisms are not completely clear. To this purpose, ac impedance spectrum analysis can represent a powerful technique to investigate specific conduction mechanisms. In fact, ac characterization allows highlighting the different contributions of the conduction and it permits to find out information about the undergoing physical phenomena. In this work, a fully ac characterization of a Nitrate-intercalated Zn/Al Layered Double Hydroxides gas sensor such as is performed. In particular, the complex impedance of the sensor is measured in the range 1 Hz to 100 kHz in presence of different concentrations of three volatile compounds (CH 4 , CO 2 and NO). The Nyquist plots show an evident variation of sensor impedance when sensor is exposed to the gas. Finally, a circuital model of the sensor that takes into account the peculiar conduction processes is introduced to fit the experimental data and explain the sensor behavior.

The electro-mechanical conversion efficiency and the long-term reliability of Capacitive Micromachined Ultrasonic Transducers (CMUT) are mainly limited by the parasitic capacitance and by charge injection phenomena. In this paper, we investigated the possibility of reducing both the parasitic capacitance, by patterning the CMUT electrodes in order to avoid any superposition of the two electrodes outside the cavity area, and the charge injection phenomena, by introducing high-quality Silicon Oxide (SiO2) buffer layers between the electrodes and the cavity Silicon Nitride (SixNy) passivation layers. Test capacitors were initially fabricated with the aim of measuring the dielectric characteristics of the SixNy, and to quantitatively evaluate the effects of the SiO2 buffer layers. Successively, 256-element CMUT arrays were designed and fabricated using both the classical and the modified electrode layouts and material stacks. The electrical impedance of single array elements was measured at different increasing and successively decreasing bias voltages in the 0-260V range in order to electrically stress the in-cavity dielectrics. A 33% reduction of the parasitic capacitance was achieved with the modified electrode layout, resulting in a 40% increase of the electro-mechanical coupling coefficient. A significant reduction of charge injection and charge trapping phenomena was demonstrated by a less hysteretic behavior of the capacitance-voltage characteristic, and by a negligible residual bias of the optimized device as compared to the conventional device.

We present a compact model for the DC and small signal AC analysis of Organic Thin Film Transistors (OTFTs). The DC part of the model assumes that the electrical current injected in the OTFT is limited by the presence of a metal/organic semiconductor junction that, at source, acts as a reverse biased Schottky junction. By including this junction, modeled as a reverse biased gated diode at source, the DC model is able to reproduce the scaling of the electrical characteristics even for short channel devices.