Source: https://www.associazione-sie.it/index.php?option=com_content&view=article&id=66&Itemid=158
Timestamp: 2019-04-22 04:55:06+00:00

Document:
G. Vannini, A. Raffo, G. Bosi.
Collaborations: HUAWEI Technologies, Milano; MEC s.r.l., Bologna; University of Leuven (Belgio); Università di Messina; Università dell’Aquila; Università di Bologna; Università di Firenze; Università di Roma Tor Vergata; Politecnico di Torino.
Collaborations: University of Leuven (Belgio); Università di Parma.
In addition, the high cell density of today large arrays is responsible also for an increase of failure mechanism interdependency and of architectural issues.
Experimental activity on large test arrays is performed through dedicated high performance instrumentation which allows gathering statistical information about memory writing/reading behaviors which are impossible to obtain in simpler test structures such as small arrays of capacitors or transistors.
In 2011, the research activity focused on different types of NVM: Phase Change Memories, Charge Trapping Memories, and also MEMs based memories.
Nonlinear modeling of active devices for microwave circuit design is quite a complex task due to the simultaneous presence of important nonlinear, reactive and parasitic effects. Conventional equivalent circuit models present some drawbacks especially in the identification procedures which are quite complex. Alternative approaches (measurement-based, technology-independent models) have been proposed which can be directly identified on the bases of conventional measurements carried out by means of automatic instrumentation.
Recently, a new “hybrid” approach to HMIC and MMIC design has been developed which effectively exploits both the direct characterization of the device I/V low-frequency load-line and a model-based description of reactive effects.
The issue of model identification on the basis of large-signal measurements as well as the problem of large-signal waveform de-embedding have been also dealt with.
1) A. Raffo, G. Avolio, D. Schreurs, S. Di Falco, V. Vadalà, F. Scappaviva, G. Crupi, B. Nauwelaers, G. Vannini, “On the Evaluation of the High-Frequency Load Line in Active Devices", International Journal of Microwave and Wireless Technologies, Jan 2011.
2) G. Crupi, A. Raffo, D. Schreurs, G. Avolio, V. Vadalà, S. Di Falco, A. Caddemi, G.V annini, “Accurate GaN HEMT non-quasi-static large-signal model including dispersive effects”, Microwave and Optical Technology Letters, Mar 2011.
3) G. Crupi, D. Schreurs, A. Caddemi, A. Raffo, F. Vanaverbeke, G. Avolio, G. Vannini, W. De Raedt, “High-Frequency Extraction of the Extrinsic Capacitances for GaN HEMT Technology”, IEEE Microwave and Wireless Components Letters, Jul 2011.
4) G. Avolio, D. Schreurs, A. Raffo, G. Crupi, I. Angelov, G. Vannini, B. Nauwelaers, “Identification technique of FET model based on vector nonlinear measurements”, Electronics Letters, Vol.47, n.24, p.1323–1324, Nov 2011.
5) A. Musio, V. Vadalà, F. Scappaviva, A. Raffo, S. Di Falco, G. Vannini, “A New Approach to Class-E Power Amplifier Design”, Proc. of INMMIC, Vienna, Austria, Apr 18-19, 2011.
6) S. Di Falco, A. Raffo, G. Vannini, V. Vadalà, “Low-Frequency Waveform Engineering Technique for Class-F Microwave Power Amplifier Design”, Proc. of EuMIC, EuMW, Manchester, UK, Oct 10-11, 2011.
7) V. Vadalà, A. Raffo, S. Di Falco, G. Vannini, “GaN HEMT Nonlinear Characterization for Wideband High-Power Amplifier Design”, Proc. of EuMIC, EuMW, Manchester, UK, Oct 10-11, 2011.
Dispersive phenomena due to surface state densities, deep-level traps and thermal effects must be accounted for in the nonlinear modeling of III-V electron devices. From a macroscopic point of view they cause important differences between the static and dynamic device current characteristics. In terms of differential parameters a frequency dependence is found in a frequency range where reactive effects due to charge storage or transit time phenomena are still negligible.
As an alternative to special purpose measurement setup's for dynamic current measurements, new characterization techniques, based on a two-source setup adopting conventional instrumentation, have been developed and applied in model identification.
New device modeling and characterization approaches oriented to GaN Power Amplifier design have been recently proposed.
1) A. Raffo, V. Vadalà, P.A. Traverso, A. Santarelli, G. Vannini, F. Filicori. “A Dual-Source Nonlinear Measurement System Oriented to the Empirical Characterization of Low-Frequency Dispersion in Microwave Electron Devices”, Computer Standards and Interfaces Journal, Special Issue of XVI IMEKO, Feb 2011.
2) G. Crupi, G. Avolio, A. Raffo, P. Barmuta, D. Schreurs, A. Caddemi, G. Vannini, “Investigation on the Thermal Behavior of Microwave GaN HEMTs”, Solid State Electronics, Elsevier, Oct 2011.
3) P. Barmuta, K. Czuba, G. Avolio, D. Schreurs, A. Raffo, G. Vannini, G. Crupi, “Temperature Dependent Vector Large-Signal Measurements”, Proc. of INMMIC, Vienna, Austria, Apr 18-19, 2011.
4) G. Crupi, A. Raffo, D. Schreurs, G. Avolio, V. Vadalà, S. Di Falco, A. Caddemi, G. Vannini, “GaN HEMT Large-Signal Model Accounting for both Low-Frequency Dispersion and High-Frequency Non-Quasi-Static Effects”, 10th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Services - TELSIKS 2011, Oct 5-8, 2011.
5) G. Avolio, D. Schreurs, B. Nauwelaers, A. Raffo, G. Vannini, G. Crupi, “Bias and Frequency Dispersion of Dynamic I-V Characteristics in Microwave Transistors”, Proc. of EuMIC, EuMW, Manchester, UK, Oct 10-11, 2011.
Electron devices may “change” their characteristics when observed at different time instants under identical forcing excitations. Two repetitions of the same measurement procedure can give significantly different results. Analogously, an electrical parameter under test (e.g., the device transconductance) can show a time-dependent behavior even in the presence of a steady-state externally-forced operation.
A significant example is the breakdown walkout, that is the time dispersion of the gate-drain and source-drain breakdown voltages, experimentally observed in field-effect microwave transistors.
Time dispersion also affects other key electrical parameters of the device such as, for instance, IDSS, or the threshold voltage, even though to a minor extent. On the contrary, important drops in rf output power have been observed after long lasting strong gain compression operation. Progressive modification (i.e., degradation) of the device electrical response is induced with respect to the one originally offered at its very first connection to the measurement system. This is clearly evident in the presence of critical operation, such as the reverse hot-electron discharge from gate in FETs, but can be also observed in correspondence with more “conventional” and nominally safe operating conditions, as when the device is employed in a class-A power amplifier and operates well inside the compliances on maximum power dissipation.
1) A. Raffo, S. Di Falco, G. Sozzi, R. Menozzi, D. Schreurs, G. Vannini, “Analysis of the Gate Current as a Suitable Indicator for FET Degradation Under Nonlinear Dynamic Regime”, Microelectronics Reliability, Feb 2011.

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