Modeling of Metal-Semiconductor Field-Effect-Transistor on H- terminated polycrystalline diamond B. Pasciuto 1 , W. Ciccognani 1 , E. Limiti 1 , P. Calvani 2 , M. C. Rossi 2 , G. Conte 2 1 University of Rome “Tor Vergata”, Electronic Eng. Dept., Via del Politecnico 1, 00133 Rome, Italy 2 University of Roma Tre, Electronic Eng. Dept., Via Vasca Navale 8, 00146 Rome, Italy Abstract — On the bases of the RF characteristics and measured small-signal parameters, an equivalent circuit model is formulated and characterized for Metal-Semiconductor Field Effect Transistors based on H-terminated polycrystalline diamond. Starting from on-wafer measurements, a bias dependent transistor behavior representation has been fully determinated. Such a equivalent circuit model is a first important step in order to realize an RF IC based on diamond. Index Terms - dc and rf performance, carbon based electronic, device technology, electrical characteristics, semiconductor devices, wide band semiconductors, device modeling, small-signal equivalent circuit I. INTRODUCTION To address the demanding requirements of the emerging wireless, mobile and wire-line applications, new semiconductor technologies are currently in development. As a result, new trends are emerging in both discrete device and IC technologies. In particular, solid state devices find increasing application in high power and high frequency electronics, where conventional technologies based on silicon and GaAs have been surpassed by wide band gap semiconductors, such as SiC, GaN and diamond. Owing to the excellent physical properties, such us high breakdown field and hole saturation velocity, giving an optimum Johnson’s figure of merit, diamond devices provide in principle the best RF power performance. Indeed, this perspective has been evaluated by several research groups [1-3] and recently also included device realization technologies of surface channel field effect transistors. In this structure, hydrogen terminated diamond behaves as a hole conductive surface channel without the addiction of extrinsic doping impurities. However a detailed analysis and modeling of passive integrated components on diamond behavior is still lacking in literature. This kind of electronic elements are essential to making MMIC and exactly for proper amplifier impedance matching and it will be one of the main goals we would like to appreciate. As a contribution to this field, an accurate bias dependent equivalent circuit model of diamond based MESFETs is formulated starting from the experimental DC and RF characteristics of MESFET based on free-standing polycrystalline diamond. II. DEVICE FABRICATION Au and Al contacts were used for the realization of source and drain ohmic contacts, while Al was employed for gate electrodes. Devices isolation was accomplished by reactive ion etching (RIE) in oxygen and argon plasma. The isolation is realized in such a way to minimize the parasitic capacitance of the gate contact. Electron beam lithography was used for gate realization. The gate electrode has been realized using an electron Beam Lithography (EBL) equipment Leica EBPG5 able to define structure down to 20 nm. III. RF MESFETS CHARACTERISTICS The application of H-terminated diamond for the realization of high frequency MESFETs to be used within a RFIC requires accurate on-wafer S parameters measurements. S-parameters were measured by a VNA calibrated with off-wafer SOLT procedure. The measurement set-up consists in: HP 8510C Vector Network Analyzer, Cascade RF1 Probe Station, Coplanar Probe GGB Picoprobe (pitch=200μm), CS5 Calibration kit. Typical S parameters of a 1 μm gate MESFET are shown in fig. 1 on a smith chart. Fig. 1 – S parameters of MESFET represented on Smith chart Due to the low dielectric constant of diamond both reactance of S 11 and S 22 are low, which is advantageous for RF applications. Due to high input and output device mismatch, S 21 parameter magnitude is less than unity but this not means that device hadn’t gain. Small signal RF gains as a function of frequency are reported in fig. 2 for a typical 1 μm gate length fabricated device, measured at V DS = -10 V and V GS = -1 V. They show a cut off frequency f T =1.5 GHz and a maximum oscillation frequency, f MAX , of typically 4.5 GHz, with a 978-1-4244-3705-4/09/$25.00 ©2009 IEEE 261