Giovanni Crupi

Nonlinear Dispersive Modeling of Electron Devices Oriented to GaN Power Amplifier Design

This paper presents a new modeling approach accounting for the nonlinear description of low-frequency dispersive effects (due to thermal phenomena and traps) affecting electron devices. The theoretical formulation is quite general and includes as particular cases different models proposed in the literature. A large set of experimental results, oriented to microwave GaN power amplifier design, is provided to give an exhaustive validation under realistic device operation.

A New Millimeter-Wave Small-Signal Modeling Approach for pHEMTs Accounting for the Output Conductance Time Delay

A new technique is developed for determining analytically a millimeter-wave small-signal equivalent-circuit model of GaAs pseudomorphic HEMTs from scattering parameter measurements. In order to obtain a good agreement between model simulations and measurements up to 90 GHz, the conventional intrinsic output conductance is substituted by a voltage-controlled current source with a time delay. Consequently, a simple and accurate extraction procedure is proposed for taking into account the introduction of the output conductance time delay.

Determination and Validation of New Nonlinear FinFET Model Based on Lookup Tables

The Fin field effect transistor (FinFET) is a multiple gate structure, which is recently emerging as a leading structure to continue the scaling of CMOS technology into the nanometer regime. This promising multiple gate structure has not only the advantage of reducing short channel effects but also of being compatible with the conventional planar CMOS technology. To our knowledge, this is the first letter addressing the nonlinear FinFET model validated by large signal network analyzer measurements. Here, we present a nonlinear FinFET model which is based on lookup tables. The accuracy of the developed model is completely and successfully verified through the comparison with nonlinear FinFET measurements

Microwave characterization and modeling of packaged HEMTs by a direct extraction procedure down to 30 K

The knowledge of the small-signal equivalent circuit of microwave GaAs field effect transistors (FETs) is crucial for the design of low-noise amplifiers and is very useful to support the analysis of the transistor performance. This paper reports the results of our experimental activity concerning the application of an improved procedure for the direct extraction of the model element values from scattering (S-) parameter measurements. This analytical procedure was tested on low-noise pseudomorphic high electron mobility transistors (pHEMTs) up to 6 GHz and at cryogenic temperatures without any optimization or tuning adjustment. This paper reports the behavior of the intrinsic elements versus bias condition; the experimental results were found to match the theoretical expectations. The very good agreement between the simulated and measured S-parameters confirms the validity of the proposed method. To carry out the experimental activity, a properly designed cryogenic setup operating in our laboratory, which allows performing direct current (dc) and microwave characterization down to 30 K, was employed.

A robust and fast procedure for the determination of the small signal equivalent circuit of HEMTs

Abstract In this paper we present an analytical, fast, accurate and robust technique for the determination of the circuit model elements of HEMTs in the microwave range. By this method the values of the equivalent circuit parameters of the device under test are extracted using three measured scattering (S) parameter sets without any optimization. We also investigated the influence of the reverse transfer conductance Re(Y12) on the modelling by means of a gate drain resistance Rdg. The validity of this method was verified upon a set of pseudomorphic HEMTs having different gate widths tested on wafer at several bias and temperature conditions. Very good agreement between the simulated and measured S-parameters has been obtained. The procedure has been implemented in Agilent VEE language as a fully automated tool to allow an accurate, fast and complete device characterization requiring no operator supervision.

Temperature effects on DC and small signal RF performance of AlGaAs/GaAs HEMTs

We here report on the DC and microwave performance of HEMTs tested on wafer under different temperature conditions. The relevant experimental data show that the most important electrical parameters, such as the output current, the threshold voltage, the transconductance and the forward transmission coefficient, are sensibly affected by thermal phenomena. We focused our attention on the variations of the above parameters with the temperature because such a detailed knowledge is essential to establish the optimum bias point for a given application. Furthermore, we analyze the influence of the DC quiescent point degradations, due to thermal phenomena, on the small signal equivalent circuit. Since the thermal behavior of the circuit model is a function of the bias, we examine the behavior of the circuit elements vs. temperature over a wide range of bias conditions.

GaN HEMT Noise Model Based on Electromagnetic Simulations

This paper presents a new approach for the definition and identification of a transistor model suitable for low-noise amplifier (LNA) design. The resulting model is very robust to layout modifications (i.e., source degeneration) providing accurate predictions of device noise-performance and small-signal parameters. Moreover, the described procedure is very robust since it does not require any numerical optimization, with possibly related problems like local minima and unphysical model parameters. The adopted model topology is based on a lumped element parasitic network and a black-box intrinsic device, which are both identified on the basis of full-wave electromagnetic simulations, as well as noise and S-parameter measurements. The procedure has been applied to three GaN HEMTs having different peripheries and a Ku-band LNA has been designed, demonstrating a very good agreement between measurements and predicted results.

Technology-Independent Non-Quasi-Static Table-Based Nonlinear Model Generation

An analytical extraction of the non-quasi-static nonlinear lookup table FET model at mm-wave frequencies is demonstrated in this study. Frequency dispersion present at mm-wave frequencies is compensated for by introduction of higher order dynamics of nonlinear constituent components. Nonlinear charge- and current-sources are used as the constituent components to represent the nonlinear device where the higher order charge- and current-sources are introduced to compensate for the non-quasi-static effects. The presented approach is validated using SOI Multi-Fin MOSFET transistors, the multiple gate MOSFET structures which have been introduced as an alternative candidate for bulk planar CMOS technology in the nanometer regime. An accurate multibias linear model is employed as the keystone for building the non-quasi-static nonlinear model. Large-signal measurements are used for model validation. Significant improvements are observed over the quasi-static nonlinear model which is demonstrated by excellent agreement between measurements and nonlinear model presented here.

An Extensive Experimental Analysis of the Kink Effects in

This paper, for the first time, analyzes in detail the kink phenomenon in S22 as observed in GaN HEMT technology. To gain a comprehensive understanding, the kink effect (KE) is studied with respect to temperature and bias conditions. The achieved results clearly show that the dependence of the KE on the operating condition should be mainly ascribed to the transconductance, which plays a determinant role in the appearance of this effect. Furthermore, the analysis is extended to investigate the peak in the magnitude of h21 showing its disappearance at low drain-source voltage, due to the increase of the intrinsic output conductance. The importance of this investigation originates from the fact that an accurate and complete characterization of these anomalous phenomena enables microwave engineers to properly take them into account during the modeling and design phases.enables microwave engineers to properly take them into account during the modeling and design phases.

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A novel nonlinear de-embedding procedure based on only the use of low- and high-frequency vector large-signal measurements is proposed. The nonlinear Q-V characteristics, along with the parasitic network, are here determined by combining vector measurements with numerical optimization. Consequently, the knowledge of their contributions allows one to retrieve the actual waveform at the current generator plane starting from any high-frequency load line.