E. Giovine

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.

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.

Surface Channel MESFETs on Hydrogenated Diamond

Metal–semiconductor field effect transistors (MESFETs) based on hydrogen terminated diamond were fabricated according to different layouts. Aluminum gates were used on single crystal and low-roughness polycrystalline diamond substrates while gold was used for ohmic contacts. Hydrogen terminated layers were deeply investigated by means of Hall bars and transfer length structures. Room temperature Hall and field effect mobility values in excess of 100 cm2 V⁻¹ s⁻¹ were measured on commercial and single crystal epitaxial growth (100) plates by using the same hydrogenation process. Hydrogen induced two-dimensional hole gas resulted in sheet resistances essentially stable and repeatable depending on the substrate quality. Self-aligned 400 nm gate length FETs on single crystal substrates showed current density and transconductance values>100 mA mm⁻¹ and >40 mS mm⁻¹, respectively. Devices with gate length LG=200 nm showed fMax=26.4 GHz and fT=13.2 GHz whereas those fabricated on polycrystalline diamond, with the same gate geometry, exceeded fMax=23 GHz and fT=7 GHz. This work focused on the optimization of a self-aligned gate structure with respect to the fixed drain-to-source structure with which we observed higher frequency values; the new structure resulted in improvement of DC characteristics, better impedance matching and a reduction in the fMax/fT ratio.

RF power performance of submicron MESFET on hydrogen terminated polycrystalline diamond

Diamond is in principle the highest performance widegap semiconductor; its outstanding electronic and thermal properties make it an attractive material for high power radiofrequency (RF) and microwave electron devices. Even though the properties of synthetic diamond have been known from many years, only recently significant technology advances in the growth of single-crystal and polycrystalline diamond have fostered the research on high-performance diamond electronics. In this framework, the use of polycrystalline diamond as a substrate offers the advantage of larger areas and lower cost with respect to single-crystal diamond. Available approaches for the control of diamond conductivity rely mainly (up to now) on p-type doping, either through extrinsic doping with boron, or exploiting hydrogen (H) surface termination, which induces a quasi-2D hole channel a few nanometers below the surface. Both approaches have been pursued to develop high speed power FETs [1], with record cut-off frequency (45 GHz) achieved by H-terminated FETs on polycrystalline diamond [2]. Despite such promising small-signal performances, only a few examples of RF power measurements have been reported so far, limited at comparatively low frequency (1 GHz), and only for single-crystal diamond FETs, with record performance of 2W/mm [3]. In this paper, we present RF power measurements of submicron H-terminated FETs on polycrystalline diamond up to 2 GHz, showing the potential of such substrate for the development of microwave power devices.

K-band diamond MESFETs for RFIC technology

Diamond is one of the suitable semi-conductor for vacuum electronics replacement in high power and high frequency applications. Sub-micron gate-length (200 nm) Metal Semiconductor Field Effect Transistor (MESFETs) have been fabricated on h-terminated polycrystalline diamond and characterized in order to investigate the possibility of RFICs integration. High power (Pout=1.5 W/mm) and high frequency (and fMAX=35 GHz) performances have been obtained.

MESFETs on H-terminated polycrystalline diamond

Metal-Semiconductor Field Effect Transistors (MESFETs) were fabricated on polycrystalline diamond. Devices were realized to be employed in Microwave Integrated Circuits for satellite communications and high frequency power amplification, areas were diamond promise the replacement of vacuum electronics. Fabricated MESFETs typically showed high drain-source current (140 ma/mm) and large transconductance values (50 ms/mm), with a cut off frequency ft=10 GHz and a maximum oscillation frequency, fmax, up to 35 GHz. These values suggest device microwave operation and are obtained through the fabrication of devices with geometry and active region dimensions (200–500 nm gate length) compatible with available microelectronic technologies.

Microwave operation of sub-micrometer gate surface channel MESFETs in polycystalline diamond

Metal-Semiconductor field effect transistor (MESFETs) were fabricated on hydrogen-terminated polycrystalline diamond. Fabricated MESFETs typically showed high drain-source current (140 mA/mm) and large transconductance values (60 mS/mm), with a cut off frequency f T =10 GHz and a maximum oscillation frequency, f MAX , up to 35 GHz. These values suggest device microwave operation in the K- band and are obtained through the fabrication of devices with geometry and active region dimensions compatible with available microelectronic technologies. Devices were realized in order to be employed in Microwave Integrated Circuits for satellite communications and high frequency power amplification, areas where diamond promises the replacement of vacuum electronics: with this perspective, our group realized a first important step formulating an equivalent circuit (EQC) model.

MESFETs on H-terminated Single Crystal Diamond

Epitaxial diamond films were deposited on polished single crystal Ib type HPHT diamond plates of (100) orientation by microwave CVD. The epilayers were used for the fabrication of surface channel MESFET structures having sub-micrometer gate length in the range 200-800 nm. Realized devices show maximum drain current and trasconductance values of about 190 mA/mm and 80 mS/mm, respectively, for MESFETs having 200 nm gate length. RF performance evaluation gave cut off frequency of about 14 GHz and maximum oscillation frequency of more than 26 GHz for the same device geometry.