A. Cetronio

High Power Microstrip GaN-HEMT Switches for Microwave Applications

In this paper the design, fabrication and test of X-band and 2-18 GHz wideband high power SPDT MMIC switches in microstrip GaN technology are presented. Such switches have demonstrated state-of-the-art performances. In particular the X-band switch exhibits 1 dB insertion loss, better than 37 dB isolation and a power handling capability at 9 GHz of better than 39 dBm at 1 dB insertion loss compression point; the wideband switch has an insertion loss lower than 2.2 dB, better than 25 dB isolation and a power handling capability of better than 38 dBm in the entire bandwidth.

Comments, with reply, on 'Impact ionization in GaAs MESFETs' by K. Hui, et al

In the above-named work (see ibid., vol.11, p.113-15, March 1990), Hui et al. proposed a method to measure impact ionization current in GaAs MESFETs and evaluated the impact ionization coefficient alpha /sub n/ in GaAs. For electric fields greater than approximately 1.5*10/sup 5/ V-cm/sup -1/, alpha /sub n/ can be fitted to the equation alpha /sub n/=4.0*10/sup 6/*exp (-2.3*10/sup 6//E). In the present work, the commenters performed careful measurements of gate current I/sub g/ in GaAs MESFET devices similar to those used by Hui et al., and they show that the ionization coefficient still fits the above equation down to alpha /sub n/=10/sup -4/ cm/sup -1/. These results extend the previous data by three orders of magnitude. In a reply, the original authors affirm that the commenters have significantly improved the accuracy of the data previously presented.<<ETX>>

A 20 Watt Micro-strip X-Band AlGaN/GaN HPA MMIC for Advanced Radar Applications

In this paper a first iteration design, fabrication and test of a two-stage X-Band MMIC HPA in micro-strip AlGaN/GaN technology is reported. With 20 V drain voltage operating bias point, at 3 dB compression point, the HPA delivers a pulsed output power ranging from 21 to 28.5 W, an associated gain from 12.9 to 16.5 dB and an associated PAE from circa 30% to 40%, over the 8-10.5 GHz frequency bandwidth. In the best performance frequency points (8.5 and 9 GHz) the HPA exhibits a saturated output power of 30 W with an associated PAE of 40%.

High power GaN-HEMT microwave switches for X-Band and wideband applications

In this article the design, fabrication and test of X-band and 2-18 GHz wideband high power SPDT MMIC switches in GaN technology are presented. Said switches have demonstrated state-of-the-art performance and RF fabrication yields better than 65%. In particular the X-band switch exhibits an on-state power handling capability of better than 37 dBm at the 1 dB insertion loss compression point and the wideband switch shows an insertion loss compression of 1 dB for input power higher than 34.3 dBm in the entire bandwidth.

Phased array systems and technologies in SELEX-Sistemi Integrati: State of art and new challenges

This paper is a follow-on of [1] and [2], presented at 1996 and 2003 IEEE Intl. Symposium on Phased Array Systems and Technology, respectively. After a brief recall of 3D Long Range phased array concepts, already presented in [2], the focus is on the G-band multifunction radar systems and on the technological capabilities that SELEX-Sistemi Integrati is developing by taking advantage of its Research and Development facilities. At the end, future trends about new challenging applications and technological issues are presented and discussed.

2-6 GHz GaN MMIC Power Amplifiers for Electronic Warfare Applications

This paper presents two MMIC broadband high power amplifiers of 4 mm of periphery at the output stage in the frequency band 2-6 GHz. The amplifiers are based on Al-GaN/GaN high electron mobility transistor (HEMT) technology on SiC substrate. They have been fabricated in two different european foundries: SELEX Sistemi Integrati and QINETIQ. SELEX has a gate process technology of 0.5 mum, and devices of 10times100 mum periphery in microstrip technology and QINETIQ has a gate-length of 0.25 mum, and devices of 8times125 mum in coplanar technology. The coplanar amplifier from QINETIQ has demonstrated an output power of 8 W in continuous wave at Vds=20 V which confirm model predictions. On the other hand, SELEX microstrip amplifier has a saturation power of 10 W CW at Vds=25 V and 4 GHz. This amplifier measured on-wafer in pulsed conditions exhibits a maximum power of 17 W at Vds=30 V.

X-Band transmit/receive module MMIC chip-set based on emerging GaN and SiGe technologies

In this paper an innovative solution leading to high performance/low-cost multi-domain T/R modules, utilizing emerging semi-conductor technologies such as GaN and SiGe, will be outlined. In particular a complete X-Band TRM MMIC chip-set based on GaN for the front-end RF functions and on SiGe multifunction chip for signal amplitude and phase control will be presented. The GaN front-end RF functions comprise state-of-the-art HPA, robust LNA and high power SPDT switch MMICs designed and fabricated by Selex Sistemi Integrati internal facilities. The SiGe multifunction Core Chip has been designed by Selex Sistemi Integrati employing a low-cost SiGe BiCMOS commercial process.

Large-Signal modeling of power GaN HEMTs including thermal effects

In this paper a procedure to extract temperature dependent equivalent circuits for modeling the small and large signal behavior of GaN HEMTs is presented. The technique explained in this work uses pulsed I-V measurements to obtain the temperature dependence of the parameters describing the nonlinear drain current source behavior. The equivalent circuits extracted are capable of correctly modeling the DC, small signal and large signal characteristics of GaN HEMTs devices. Simulations and measurements carried out on three transistors developed by SELEX-SI are compared over a wide range of frequencies, bias and load conditions.

SiC X-Ray Detectors for Spectroscopy and Imaging over a Wide Temperature Range

The advantages of using Silicon Carbide for X-ray spectroscopy and imaging has been examined over the existing semiconductor detectors. Several SiC detectors have been manufactured and tested. They are constituted by Schottky junctions on a low doped (5x10) n-4H-SiC epitaxial layer. The diodes show extremely low reverse current densities at room temperature (≤5 pA/cm) up to mean electric field of 100 kV/cm in the depleted region. These currents are two order of magnitude lower with respect to the best junctions on Silicon used for X-ray spectroscopy, so making SiC detectors extremely low noise devices. Using a pixel detector a noise of 415 eV FWHM at room temperature has been measured. Moreover for the first time an X-ray spectroscopy at high temperature has been demonstrated using a semiconductor: the SiC detector has been operated at 100°C, showing a noise of 1 keV FWHM.

Very High Performance GaN HEMT devices by Optimized Buffer and Field Plate Technology

One of the main expected benefits of AlGaN HEMT technology for microwave applications is related to the higher operating bias voltage achievable with these devices. However, various technological issues, concerning material properties and device technology must be properly tailored to fully exploit the potential of that kind of devices. In this work we report on the realization of HEMT device showing improved performance in terms of breakdown voltage, device isolation and reverse current leakage achieved by improved epilayer buffer properties and optimized field plate gate geometry. In particular the low defect density and the high resistivity obtained by using an HT-AlN crystallization layer for the growth of the GaN layer has lead to an effective 2DEG carrier concentration of 8 times 1012 cm-2 with related mobility of 1700cm2/Vs and corresponding devices with a very high voltage breakdown (VB > 200V), excellent active device isolation and limited reverse current leakage