Filippo Bonafè

Bio: Filippo Bonafè is an academic researcher from National Research Council. The author has contributed to research in topics: Ohmic contact & Photoacoustic spectroscopy. The author has an hindex of 2, co-authored 4 publications receiving 7 citations.

Ion Implanted Lateral p+-i-n+ Diodes on HPSI 4H-SiC

Abstract: Square shaped annular lateral p+–i–n+ diodes on high purity semi-insulating (HPSI) 4H-SiC are fabricated by Al+ and P+ ion implantation to obtain anode and cathode regions, respectively. All the diodes have the same size central anode surrounded by an intrinsic region, which is surrounded by an annular cathode. Anode area and annular cathode width are fixed for all diodes, only the lateral length of the intrinsic region is varied. Post implantation annealing is performed at 1950 °C for 10 min. Static forward and reverse characteristics are measured in the temperature range of 30 - 290 °C. For all diodes, the reverse current is below the instrument detection limit of 10-14 A up to 100 °C at 200 V, the maximum reverse bias employed in this study. The reverse current increased up to low 108 A for 200 V reverse bias at 290 °C. Forward currents overlap at the low voltage region once they exceed the instrument detection limit at ~1.6 V and 30 °C. The forward currents follow almost identical exponential trend at all measured temperatures while the diode series resistance increase with increasing anode-cathode distance and decreased with increasing temperature for the given intrinsic region lateral length.

Micro-Opto-Mechanical sensors for tactile width measurements of surface opening cracks in concrete

Abstract: The fabrication and laboratory testing of Micro-Opto-Mechanical sensors for the measurements of width of surface opening cracks in concrete structures are presented. The sensors are designed to be operated on a fan-out connector containing 12 multimode optical fibers, using a microstructure that can be mounted on the connector with a self aligned procedure. Thanks to the optical alignment automatically provided by such mounting method, each fiber in the connector can be used to interrogate an individual pressure sensor within an array composed by 12 elements in total. Using a soft polymer layer between the microsensor and the crack opening, the width of the crack can be derived by means of a tactile measurement performed by interrogating the 12 elements of the array alternatively, with a space resolution of 0.25 mm. The device is designed to be operated on board of a Remotely Piloted Aerial Vehicle equipped with a vision system that will be able to locate surface cracks of the external surface of reinforced concrete bridges and perform contact measurements on cracks using a robotic arm operated from the vehicle.

1300°C Annealing of 1×1020 Al+ Ion Implanted 3C-SiC

Abstract: The results of the first experiments for achieving the thermal equilibrium during 1300 °C annealing of 1×1020 cm-3 ion implanted Al+ in 3C-SiC are shown. X-ray diffraction, through reciprocal space maps and 2Θ scans, characterizes the 3C-SiC lattice recovery. The achievement of a ohmic behavior of Ni/Al/Ti alloy indicates the onset of a measurable electrical activation of the Al implanted layer. The Al electrical activation is qualified through the implanted layer sheet resistance.

A compact cantilever-based photoacoustic sensor for trace-gas detection

Abstract: We describe the development and the first characterization of a compact trace-gas sensor based on cantilever photoacoustic spectroscopy (CEPAS). The sensor was characterized in order to find the optimal operating parameters (pressure, molecule absorption line and laser modulated frequency). N2O was selected as test molecule. A quality factor of 200 at 10 mbar of cell pressure were determined. Furthermore, the first test measurements showed a minimum detection level of hundreds of ppb with integration time of 30 ms.

Robotic System for Inspection by Contact of Bridge Beams Using UAVs

Abstract: This paper presents a robotic system using Unmanned Aerial Vehicles (UAVs) for bridge-inspection tasks that require physical contact between the aerial platform and the bridge surfaces, such as beam-deflection analysis or measuring crack depth with an ultrasonic sensor. The proposed system takes advantage of the aerodynamic ceiling effect that arises when the multirotor gets close to the bridge surface. Moreover, this paper describes how a UAV can be used as a sensor that is able to fly and touch the bridge to take measurements during an inspection by contact. A practical application of the system involving the measurement of a bridge’s beam deflection using a laser tracking station is also presented. In order to validate our system, experiments on two different bridges involving the measurement of the deflection of their beams are shown.

4H‐SiC surface morphology after Al ion implantation and annealing with C‐cap

Abstract: The root mean square (rms) surface roughness extracted from atomic force microscopy is widely employed to complement the characterisation of ion implantation processes in 4H-SiC. It is known that the protection of a carbon film eliminates or mitigates roughening of the SiC surface during postimplantation annealing. This study, based on a rich original data collection of Al+ ion implanted 4H-SiC samples, allows for a quantitative description of the surface morphology as a function of the annealing temperature and time and of the Al implanted concentration. With increasing thermal budget, the evolution from flat, to blurred with ripples, granular, and finally jagged surface, results in a monotonous increase in the root mean square roughness. Additional information is given by the trends of the roughness exponent and of the correlation length, extracted from the height-height correlation function, which account for the surface evolution below 1700°C and for the effect of the Al implanted concentration on the ripple size, respectively. A combination of low roughness parameter and high correlation length identify the transition from ripples to jagged morphology. LAY DESCRIPTION: Selective area doping is a key step in the fabrication of hexagonal Silicon Carbide (4H-SiC) power electronic devices. It is achieved by ion implantation followed by a high temperature postimplantation annealing to restore the lattice and electrically activate the dopants. Aluminium, the preferred p-type dopant, is electrically activated at temperature ranging between 1500°C and 2000°C. The time required to complete the activation process is longer the lower the annealing temperature, spanning between some minutes and hundreds of hours. During annealing, 4H-SiC wafers are encapsulated by a temperature-resistant carbon layer (C-cap) in order to avoid step bunching and reduce surface roughening. Nevertheless, surface modifications can occur at high temperature. For this reason, the characterisations of 4H-SiC doping processes report not only the electrical activation of the dopants, but also the root mean square surface roughness obtained at the end of the process. However, rms values can be scattered because technological parameters such as the heating system and the way to deposit and remove the C-cap can affect the final result as well as the process parameters. Furthermore, the C-cap resistance to long annealing has been proven only by electrical measurements, but the surface morphology has never been observed. This work presents a quantitative characterisation of the surface morphology of Al implanted 4H-SiC as a function of the annealing temperature, time and of the Al implanted concentration, independent of the heating system and of the C-cap technology. The produced sample collection allowed to correlate characteristic surface features with the corresponding quantities extracted from image analysis that can be more sensitive to process parameters than the sole rms. These findings can be used to enrich process optimisation tools.

SiC Complementary Junction Field-Effect Transistor Logic Gate Operation at 623 K

Abstract: Here, we show that silicon carbide (SiC) complementary logic gates composed of p- and n-channel junction field-effect transistors (JFETs) fabricated by ion implantation operate at 623 K with a supply voltage as low as 1.4 V. The logic threshold voltage shift of the complementary JFET (CJFET) inverter is only 0.2 V from 300 to 623 K. Furthermore, temperature dependencies of the static and dynamic characteristics of the CJFET inverter are well explained by a simple analytical model of SiC JFETs.

SiC Complementary Junction Field-Effect Transistor Logic Gate Operation at 623 K

Abstract: Here, we show that silicon carbide (SiC) complementary logic gates composed of p- and n-channel junction field-effect transistors (JFETs) fabricated by ion implantation operate at 623 K with a supply voltage as low as 1.4 V. The logic threshold voltage shift of the complementary JFET (CJFET) inverter is only 0.2 V from 300 to 623 K. Furthermore, temperature dependencies of the static and dynamic characteristics of the CJFET inverter are well explained by a simple analytical model of SiC JFETs.