Sergio Colangeli

GaN-Based Robust Low-Noise Amplifiers

In this paper, an overview of recently reported low-noise amplifiers (LNAs), designed, and fabricated in GaN technology is provided, highlighting their noise performance together with high-linearity and high-robustness capabilities. Several SELEX-ES GaN monolithic technologies are detailed, providing the results of the noise characterization and modeling on sample devices. An in-depth review of three LNAs based on the 0.25- μm GaN HEMT process, marginally described in previous publications, is then presented. In particular, two robust and broadband 2-18-GHz monolithic microwave integrated circuit (MMIC) LNAs are designed, fabricated, and tested, exhibiting robustness to over 40-dBm input power levels; an X-band MMIC LNA, suitable for synthetic aperture radar systems, is also designed and realized, for which measurement results show a noise figure ~ 2.2 dB with an associated gain and robustness up to 41-dBm input power level.

Gate-Source Distance Scaling Effects in H-Terminated Diamond MESFETs

In this paper, an analysis of gate-source and gate-drain scaling effects in MESFETs fabricated on hydrogen-terminated single-crystal diamond films is reported. The experimental results show that a decrease in gate-source spacing can improve the device performance by increasing the device output current density and its transconductance. On the contrary, the gate-drain distance produces less pronounced effects on device performance. Breakdown voltage, knee voltage, and threshold voltage variations due to changes in gate-source and drain-source distances have also been investigated. The obtained results can be used as a design guideline for the layout optimization of H-terminated diamond-based MESFETs.

Comparative investigation of surface transfer doping of hydrogen terminated diamond by high electron affinity insulators

We report on a comparative study of transfer doping of hydrogenated single crystal diamond surface by insulators featured by high electron affinity, such as Nb2O5, WO3, V2O5, and MoO3. The low electron affinity Al2O3 was also investigated for comparison. Hole transport properties were evaluated in the passivated hydrogenated diamond films by Hall effect measurements, and were compared to un-passivated diamond films (air-induced doping). A drastic improvement was observed in passivated samples in terms of conductivity, stability with time, and resistance to high temperatures. The efficiency of the investigated insulators, as electron accepting materials in hydrogenated diamond surface, is consistent with their electronic structure. These surface acceptor materials generate a higher hole sheet concentration, up to 6.5 × 1013 cm−2, and a lower sheet resistance, down to 2.6 kΩ/sq, in comparison to the atmosphere-induced values of about 1 × 1013 cm−2 and 10 kΩ/sq, respectively. On the other hand, hole mobiliti...

Constant Mismatch Circles and Application to Low-Noise Microwave Amplifier Design

Constant input and output mismatch circles in the output load plane are introduced as the basis for low-noise amplifier design methodology. Optimum tradeoff between input and output matching levels results as the application of a design chart providing, at the same time, the corresponding stage transducer gain. The role of degenerative series feedback is studied and systematically embedded in the design procedure, thus providing a direct way to evaluate its optimum level.

Noise measure-based design methodology for simultaneously matched multi-stage low-noise amplifiers

A novel narrow-band design methodology for multi-stage low-noise amplifiers (LNAs) is presented which is based on noise measure and on appropriately designed reactive inter-stage networks. Design formulae are given, in particular, concerning the realisation of the latter networks in T and II configurations, so as to make possible a partially automated design algorithm. As a test vehicle of the presented procedure, the design and realisation of a three-stage K-band LNA is discussed and the corresponding measured results are shown.

V 2 O 5 MISFETs on H-Terminated Diamond

We report for the first time on the dc and RF performance of novel MISFETs fabricated on hydrogen-terminated (H-terminated) single crystal diamond film using vanadium pentoxide (V2O5) as insulating material. The active devices were characterized in terms of static I-V characteristics and static transconductance as well as of S-parameters for the calculation of the maximum cutoff frequency and the maximum oscillation frequency. Time stability of the drain current was evaluated overnight observing a maximum fluctuation of 7%. Investigations on temperature dependence of diamond-based MISFET were also performed up to 130°C. The experimental results were compared with the better established diamond MESFET technology. Finally, the surface transfer doping of H-terminated diamond by very thin V2O5 insulator was also investigated in terms of conductivity, stability in air, and resistance to high temperatures.

Novel broadband nonreciprocal 180° phase-shifter

In this contribution, a novel broadband 180° phase shifter, realized in 0.5 μm GaN HEMT technology developed by SELEX Sistemi Integrati, is presented. This new topology is based on the combination of two directive three-port elements with a four-port phase-shifting network: the proposed MMIC is featured by an average zero insertion loss, 180°±2° differential phase-shift and good port matching over the 3-7GHz operating bandwidth. The MMIC size is 3.5×3.4 mm².

Characterization and modeling of low-cost, high-performance GaN-Si technology

A complete characterization of HEMT devices fabricated on a GaN-on-Silicon process developed by SELEX Sistemi Integrati is presented, together with the characterization and modeling of passive elements fabricated on the same substrate. Experimental results demonstrate that the power management capability of 1-μm GaN-Si HEMTs is suitable for most high power applications; moreover, the noise performance of such devices are in line with those of 0.5-μm GaN-SiC HEMTs fabricated by the same foundry. Finally, from the passive elements characterization the suitable operating bandwidth for the MMICs based on this technology can be assessed at least up to C-band.

GaN-on-Silicon Evaluation for High-Power MMIC Applications

Today microwave market has identified GaN-HEMT technology as a strategic enabling technology for next generation MMICs to be implemented in high performance RF sub-assemblies such as T/R Modules, Solid State Power Transmitters, Compact Receivers, High Speed Communications. To allow commercial market entry of GaN technology, a tradeoff between high RF performance and low cost is mandatory and a possible solution is represented by GaN-on-Silicon substrate. In this scenario the evaluation of FETs RF performance and losses of passive components are demanding to understand the feasibility of GaN MMIC on Si. Following such approach, in SELEX Sistemi Integrati a 4 inches GaN-on-Si wafer containing discrete active devices and passive components has been fabricated with the 50μm Si thickness. RF FETs performance demonstrates an output power of 4W/mm @ 3GHz, while passive components characterization exhibits similar behavior of GaN SiC passive elements up to C Band.

Evaluation of coaxial cable performance under thermal gradients

This paper presents a very flexible tool for numerically evaluating the small-signal and noise parameters of a transmission linesubject to an arbitrary thermal gradient. Contrary to previous methods, the proposed approach allows straightforwardly taking into account possible variations of electrical parameters along the propagation direction, such as may be expected when temperature ranges between very different values. The main application of the proposed method is cable modeling in noise-figure measurement setups under cryogenic operation: in such circumstances, indeed, the coaxial cables (or waveguide) at the interface between the outside and the inside of the cryogenic chamber are subject to remarkable temperature excursions. As a consequence, significant de-embedding errors may arise if the cables are not correctly modeled, given the very low values of noise figure which are commonly exhibited by cryo-cooled active devices.