UNITA' DI CASSINO

UNIVERSITA’ DEGLI STUDI DI CASSINO

Dipartimento di Ingegneria Elettrica e dell'Informazione
 

Research topics 

1.      effects of Unclamped Repetitive Stress on Normally-off SiC JFETs

C. Abbate, G. Busatto, F. Iannuzzo

Collaborations: FAIRCHILD SEMICONDUCTOR

 


2.      TOPOLOGIES, DEVICES AND DRIVING STRATEGIES FOR NEXT-GENERATION HIGH-ENERGY PHYSICS POWER SUPPLIES

G. Busatto, V. De Luca, F. Iannuzzo, A. Sanseverino, F. Velardi

Collaborations: ENEA Casaccia Research Center, INFN Milan, INFN Pavia, University of Padua, University of Parma

 

 3.      DEVELOPMENT OF NEW SOFT-SWITCHING, INSULATED TOPOLOGIES FOR ABOARD INVERTERS FOR AUXILIARY SERVICES OF HEAVY TRAINS

C. Abbate, G. Busatto, F. Iannuzzo

Collaborations: Ansaldobreda Naples

 

4.      RELIABILITY OF POWER DEVICES UNDER IRRADIATION

G. Busatto, F. Iannuzzo, A. Sanseverino, F. Velardi

Collaborations: ST Microelectronics Catania

 

 1.         NEW POWER DEVICES FOR HIGH VOLTAGE APPLICATIONS

C. Abbate, G. Busatto, F. Iannuzzo, A. Sanseverino

Collaborations: ST Microelectronics Catania

 

 
effects of Unclamped Repetitive Stress on Normally-off SiC JFETs

C. Abbate, G. Busatto, F. Iannuzzo

The research activity is aimed to identify the main limits and instabilities during unclamped operation of last generation Silicon Carbide (SiC) normally off JFEts. Unclamped operations have been investigated by means of a non destructive experimental setup where the device is switched in the presence of a protection circuit capable of limiting the energy on the device during the tests. As a first result, we have demonstrated that, after a quite long avalanche phase, a failure occurs. The duration of the safe avalanche phase depends on the temperature of the device under test and the damaged area after an avalanche failure is localized at the edge termination of the device and, in particular, at the corner between source and gate metallization.

Moreover, the main parameters of SiC JFEts were monitored during Unclamped Repetitive Stress (URS), and their time evolution was recorded. As further result, we have recognized an abnormal aging in term of gate and drain leakage current, observed already at few hundred stress cycles, that lead the devices under test to fail well below their reliability expectancy, thus proposing that unclamped operations are very dangerous for the device safeness, also for SiC JFET devices. On the other hand, the commutated drain current and the energy involved during unclamped phase, plays a primary role during URS operation. Such conclusion is corroborated by a comparative analysis to short-circuit operations, where, instead, the device shows a much more larger tolerance at the same drain energy budget.
 

Pubblications 2011

1)         C. Abbate, G. Busatto, F. Iannuzzo, "Operation of SiC normally-off JFET at the edges of its safe operating area", Microelectronics Reliability, Volume 51, Issues 9-11, September-November 2011, Pages 1767-1772, ISSN 0026-2714, DOI: 10.1016/j.microrel.2011.07.055.

 

TOPOLOGIES, DEVICES AND DRIVING STRATEGIES FOR NEXT-GENERATION HIGH-ENERGY PHYSICS POWER SUPPLIES

G. Busatto, V. De Luca, F. Iannuzzo, A. Sanseverino, F. Velardi

The present activity is included in the Group V "Apollo" project of the INFN, Italian Institute for Nuclear Physics, finalized to investigate the possibility of enhance the performance of the power supplies employed in the present high-energy physics experiments, like ATLAS at the CERN laboratories, with a particular focus on the device modeling and on innovative driving strategies, aimed to the extreme target of 1Mrad.

The electronics which will instrument experiments during the high luminosity phase at the Large Hadron Collider (LHC), CERN, Geneva, Switzerland, will require new power distribution schemes compared to the ones used today. Power architecture integrating point of load converters deployed at the very heart of the experimental setup has been proposed in the literature to face these new requirements.

Typically, an isolated dc-dc resonant main converter (MC) supplies an intermediate medium voltage bus which distributes the voltage to the on-detector electronics. Non-isolated Point of Load (NiPoL) converters are implemented on Front-end Boards (FEBs) for precise voltage adaptation and regulation. The design of these electronics equipment, which must cope with a hostile environment in terms of high radiation, opens a severe tolerance issue for the integration technology.

On the other hand, commercially-available radiation-hard electron devices (typically MOSFET devices) are not suitable for this purpose, in general. Reasons are that a) cost per single device is very high, and b) qualification standards meet aerospace specifications that are very different from the high-energy physics ones. For these reasons, nuclear physics teams tend to perform qualifications on their own using COTS (commercial off-the-shelf) devices.

The unit of Cassino is dealing with this issue by proposing a characterization of several part numbers of state-of-the-art Silicon MOSFET devices, produced by manufacturers adopting different fabrication technologies, aimed to the main converter and to the point-of-load converter where dose targets are tenfold than the actual: 10kGy[Si] for Total Ionizing Dose, TID, and 1.6∙1013 neutrons 1MeV eq. / cm2 / 10y for displacement effects [1].

Significant results have been obtained in terms of technology: present generation trench technology MOSFET devices have resulted much more prone to the radiation effects than traditional planar MOSFETs.

 

Pubblications 2011

1)         P. Tenti, G. Spiazzi, S. Buso, M. Riva, P. Maranesi, F. Belloni, P. Cova, R. Menozzi, N. Delmonte, M. Bernardoni, F. Iannuzzo, G. Busatto, A. Porzio, F. Velardi, A. Lanza, M. Citterio, C. Meroni, “Power supply distribution system for calorimeters at the LHC beyond the nominal luminosity”,  Journal of Instrumentation, 2011, pp.1- 16, ISSN:1748-0221

 

DEVELOPMENT OF NEW SOFT-SWITCHING, INSULATED TOPOLOGIES FOR ABOARD INVERTERS FOR AUXILIARY SERVICES OF HEAVY TRAINS

C. Abbate, G. Busatto, F. Iannuzzo

Recent European rules have limited railway convoys to 200 meters in length, thus making a must to develop self motored cars, that allow to gain the locomotive length. In this scenario, each aboard service, including auxiliary power mains must be reduced in size and weight and not least, significantly improved in efficiency. This latter consequence descends from the low noise level imposed by the recent rules to the systems operating on the bottom of the car that, as a matter of fact, do not allows fan cooling.

At the present, such mains are obtained by a rough three phase inverter at the high voltage line that feeds a heavy, 50Hz transformer that lower and filters out the phase voltages.

Such a solution is unpractical in a room reduction scenario, where 1 cube meter at 1 ton weight, required for this approach, cannot be found inside the self motored car.

The solution developed by the University of Cassino together with Ansaldobreda is covered by a patent request and cannot be described in details.

Nevertheless, its basic peculiarities can be enumerated: switching operation, that allows reduced weight, room and cost of the transformer, soft switching conditions for each switch of the circuit, thus raising the overall efficiency and, not least, an advanced FPGA-based control and modulation unit that coordinates the large number of switches in an adaptive mode.

 

RELIABILITY OF POWER DEVICES UNDER IRRADIATION

G. Busatto, F. Iannuzzo, A. Sanseverino, F. Velardi


The charge generated in the active layers of a power MOSFET during an heavy ion strike plays a central role in starting the electric instability which conducts the device to fail. Specifically, the electrical instability takes place because the contemporaneous presence of a local large amount of charge and an intense electric field could trigger a Single Event Burnout - SEB or, if the electric field across the oxide surmounts a critical threshold, a latent damage or Single Event Gate Rupture - SEGR .

The amount of generated charge depends on both the transferred energy along the entire track and the area in which the ion impacts; different sensitive areas cause different parasitic BJT activation levels and different electric field growths across the oxide. Lately, backside LASER testing has been employed to only detect SEB sensitive volumes in power MOSFETs and for sketching a Save Operating Area (SOA) where the power device don’t suffer SEB. The wavelength used is not able to ionise the gate oxide for triggering a SEGR event. Similarly to backside LASER mapping, to discriminate the active areas, a microbeam facility was recently applied to the study of SEB in Power MOSFETs.

An alternative way to experimentally study the distribution of the device areas sensitive to SEB-SEGR is the use of an Ion Electron Emission Microscope (IEEM). Recently, we have presented a complete test methodology which is able to correlate the acquired current pulses related to each impacting ion, the evolution of the leakage current and the locations where the ions impact the device under test, obtained by using an IEEM. Such correlation can be a useful tool to investigate the process which causes the SEGR.

 
Pubblications 2011

1)         G.Busatto, D.Bisello, G.Currò, P.Giubilato, F.Iannuzzo, S.Mattiazzo, D.Pantano, A.Sanseverino, L.Silvestrin, M.Tessaro, F.Velardi, J.Wyss, “A new test methodology for an exhaustive study of single-event-effects on power MOSFETs”, Microelectronics and Reliability, vol.51, Issues 9-11, September-November 1011, ISSN: 0026-2714, pp. 1995-1998.

2)         G.Busatto, D.Bisello, P.Giubilato, F.Iannuzzo, S.Mattiazzo, D.Pantano, A.Sanseverino, L.Silvestrin, M.Tessaro, F.Velardi, J.Wyss, “IBICC Sensitivity Map of a Power MOSFET with the SIRAD IEEM”, INFN-LNL Report n.234 (2011), ISSN: 1828-8545, pp. 195-196.

3)         L.Silvestrin, D.Bisello, G.Busatto, P.Giubilato, F.Iannuzzo, S.Mattiazzo, D.Pantano, A.Sanseverino, M.Tessaro, F.Velardi, J.Wyss, “A time-resolved IBICC experiment using the IEEM of the SIRAD facility”, Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms, vol.273, ISSN: 0168-583X, pp 234-236.

 
 
NEW POWER DEVICES FOR HIGH VOLTAGE APPLICATIONS

C. Abbate, G. Busatto, F. Iannuzzo, A. Sanseverino

The objective of this research was to demonstrate the feasibility of a Back Side He Irradiation to improve the switching performances of power devices. He irradiation were executed on 1200V-20A MOS-GTO devices at the cyclotron facility of the LNS (Laboratori Nazionali del Sud) Catania, Italy.  This kind of device combines the advantage of a gate turn-off thyristor with an easy MOS gate control without the presence of latching parasitic devices. Since a MOS structure is present on the surface device  the back  irradiation permits to avoid damages at the gate oxide and inside the active region of the device. On the basis of SRIM and Silvaco simulations, the energy of the beam was chosen in order to obtain an expected localization of the He peak concentration at the transition between N-drift and N+ buffer layers. The wafers were irradiated at the end of all technological process, metallization included, before cut and packaging. The duration of the irradiation was changed in order to achieve tree different doses.  A thermal annealing was performed after the irradiation in order to stabilize the defects induced. The  experimental characterization performed on the irradiated devices showed that the on-state characteristics of the MOS-GTO  remains  practically unchanged, the storage time is reduced by a factor ~4 and the turn-off energy losses are reduced by about 30%.  The results obtained are less satisfactory than those ones provided by the simulations. In facts, we expected a reduction in energy loss at the turn-off by about 75%. Through spreading resistance measurements, we have checked the actual  position of the Bragg’ s peak of the implanted Helium which was found to wrongly located at about the center of the drift layer instead of the desired N/N+ transition.  A new campaign of experiments is planned in order to improve the accuracy obtained in the positioning of the Helium peak.
 

Pubblications 2011

1)         C. Ronsisvalle, V.Enea, C.Abbate, G.Busatto, F.Iannuzzo, A.Sanseverino, G.A.P.Cirrone, “Effects of back-side He irradiation on MOS-GTO performances”, IEEE 23rd International Symposium on Power Semiconductor Devices and ICs (ISPSD), 23-26 May 2011, San Diego, CA, USA, pp. 144-147.

2)         C. Abbate, G.Busatto, G.A.P.Cirrone, V.Enea, F.Iannuzzo, C.Ronsisvalle, A.Sanseverino, “Back-side He irradiation of power devices used as carriers lifetime killing technique for improving their switching characteristics”, INFN-LNS Activity Report, 2011, ISSN: 1837-1561, pp. 249-252.

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